diff --git a/.editorconfig b/.editorconfig
index 2a4ad4ec1b55..b49a2d432075 100644
--- a/.editorconfig
+++ b/.editorconfig
@@ -1,3 +1,17 @@
+root = true
+
+[*]
+charset = utf-8
+trim_trailing_whitespace = true
+insert_final_newline = true
+
+[*.bat]
+end_of_line = crlf
+
+[*.md]
+# Trailing whitespace is important in Markdown (they distinguish a new line from a new paragraph)
+trim_trailing_whitespace = false
+
 [*.{kt,kts}]
 ij_kotlin_allow_trailing_comma = false
 ij_kotlin_allow_trailing_comma_on_call_site = false
diff --git a/.github/ISSUE_TEMPLATE/bug_report.md b/.github/ISSUE_TEMPLATE/bug_report.md
index 57a6f10876d6..65eddb565fd1 100644
--- a/.github/ISSUE_TEMPLATE/bug_report.md
+++ b/.github/ISSUE_TEMPLATE/bug_report.md
@@ -5,7 +5,7 @@ type: Bug
 labels: ["type: bug"]
 ---
 
-<!-- Please provide us the version of JUnit 5 you are using and, if possible, a failing unit test with your bug report. Don't forget to describe the rationale for this issue (e.g. expected vs. actual behavior). Please also mention where it's a regression compared to a previous version. -->
+<!-- Please provide us the version of JUnit you are using and, if possible, a failing unit test with your bug report. Don't forget to describe the rationale for this issue (e.g. expected vs. actual behavior). Please also mention where it's a regression compared to a previous version. -->
 
 ## Steps to reproduce
 
diff --git a/.github/ISSUE_TEMPLATE/config.yml b/.github/ISSUE_TEMPLATE/config.yml
index 93fa0b266326..eeb371ed465e 100644
--- a/.github/ISSUE_TEMPLATE/config.yml
+++ b/.github/ISSUE_TEMPLATE/config.yml
@@ -1,7 +1,7 @@
 blank_issues_enabled: false
 contact_links:
   - name: Ask a question
-    url: https://github.com/junit-team/junit5/discussions/categories/q-a
+    url: https://github.com/junit-team/junit-framework/discussions/categories/q-a
     about: Please ask and answer questions here
   - name: Ask a question (Stack Overflow)
     url: https://stackoverflow.com/questions/tagged/junit5
diff --git a/.github/PULL_REQUEST_TEMPLATE.md b/.github/PULL_REQUEST_TEMPLATE.md
index 90d0d4bdaed2..cfeb6a90b3ee 100644
--- a/.github/PULL_REQUEST_TEMPLATE.md
+++ b/.github/PULL_REQUEST_TEMPLATE.md
@@ -4,15 +4,15 @@
 
 ---
 
-I hereby agree to the terms of the [JUnit Contributor License Agreement](https://github.com/junit-team/junit5/blob/002a0052926ddee57cf90580fa49bc37e5a72427/CONTRIBUTING.md#junit-contributor-license-agreement).
+I hereby agree to the terms of the [JUnit Contributor License Agreement](https://github.com/junit-team/junit-framework/blob/002a0052926ddee57cf90580fa49bc37e5a72427/CONTRIBUTING.md#junit-contributor-license-agreement).
 
 ---
 
 ### Definition of Done
 
 - [ ] There are no TODOs left in the code
-- [ ] Method [preconditions](https://junit.org/junit5/docs/snapshot/api/org.junit.platform.commons/org/junit/platform/commons/util/Preconditions.html) are checked and documented in the method's Javadoc
-- [ ] [Coding conventions](https://github.com/junit-team/junit5/blob/HEAD/CONTRIBUTING.md#coding-conventions) (e.g. for logging) have been followed
-- [ ] Change is covered by [automated tests](https://github.com/junit-team/junit5/blob/HEAD/CONTRIBUTING.md#tests) including corner cases, errors, and exception handling
-- [ ] Public API has [Javadoc](https://github.com/junit-team/junit5/blob/HEAD/CONTRIBUTING.md#javadoc) and [`@API` annotations](https://apiguardian-team.github.io/apiguardian/docs/current/api/org/apiguardian/api/API.html)
-- [ ] Change is documented in the [User Guide](https://junit.org/junit5/docs/snapshot/user-guide/) and [Release Notes](https://junit.org/junit5/docs/snapshot/user-guide/#release-notes)
+- [ ] Method [preconditions](https://docs.junit.org/snapshot/api/org.junit.platform.commons/org/junit/platform/commons/util/Preconditions.html) are checked and documented in the method's Javadoc
+- [ ] [Coding conventions](https://github.com/junit-team/junit-framework/blob/HEAD/CONTRIBUTING.md#coding-conventions) (e.g. for logging) have been followed
+- [ ] Change is covered by [automated tests](https://github.com/junit-team/junit-framework/blob/HEAD/CONTRIBUTING.md#tests) including corner cases, errors, and exception handling
+- [ ] Public API has [Javadoc](https://github.com/junit-team/junit-framework/blob/HEAD/CONTRIBUTING.md#javadoc) and [`@API` annotations](https://apiguardian-team.github.io/apiguardian/docs/current/api/org/apiguardian/api/API.html)
+- [ ] Change is documented in the [User Guide](https://docs.junit.org/snapshot/user-guide/) and [Release Notes](https://docs.junit.org/snapshot/user-guide/#release-notes)
diff --git a/.github/actions/run-gradle/action.yml b/.github/actions/run-gradle/action.yml
index 7506f777a7ce..06b1affcf7ff 100644
--- a/.github/actions/run-gradle/action.yml
+++ b/.github/actions/run-gradle/action.yml
@@ -15,9 +15,9 @@ runs:
       id: setup-gradle-jdk
       with:
         distribution: temurin
-        java-version: 21
+        java-version: 24
         check-latest: true
-    - uses: gradle/actions/setup-gradle@06832c7b30a0129d7fb559bcc6e43d26f6374244 # v4.3.1
+    - uses: gradle/actions/setup-gradle@ac638b010cf58a27ee6c972d7336334ccaf61c96 # v4.4.1
       with:
         cache-encryption-key: ${{ inputs.encryptionKey }}
     - shell: bash
diff --git a/.github/actions/setup-test-jdk/action.yml b/.github/actions/setup-test-jdk/action.yml
index b2d6b1dbc46b..9e650112b77b 100644
--- a/.github/actions/setup-test-jdk/action.yml
+++ b/.github/actions/setup-test-jdk/action.yml
@@ -15,3 +15,10 @@ runs:
         check-latest: true
     - shell: bash
       run: echo "JDK8=$JAVA_HOME" >> $GITHUB_ENV
+    - uses: actions/setup-java@c5195efecf7bdfc987ee8bae7a71cb8b11521c00 # v4
+      with:
+        distribution: ${{ inputs.distribution }}
+        java-version: 17
+        check-latest: true
+    - shell: bash
+      run: echo "JDK17=$JAVA_HOME" >> $GITHUB_ENV
diff --git a/.github/renovate.json5 b/.github/renovate.json5
index d256a62d0f55..ea024d3d17e6 100644
--- a/.github/renovate.json5
+++ b/.github/renovate.json5
@@ -3,7 +3,6 @@
   extends: [
     'github>junit-team/renovate-config',
   ],
-  baseBranches: ["main", "/^develop\\/.*/"],
   packageRules: [
     {
       matchCurrentValue: '/^2\\./',
diff --git a/.github/scripts/waitForMavenCentralSync.sh b/.github/scripts/waitForMavenCentralSync.sh
deleted file mode 100755
index 9a281e56d7ba..000000000000
--- a/.github/scripts/waitForMavenCentralSync.sh
+++ /dev/null
@@ -1,5 +0,0 @@
-#!/usr/bin/env bash
-
-URL_PATH=$1
-SCRIPT_DIR=$( cd -- "$( dirname -- "${BASH_SOURCE[0]}" )" &> /dev/null && pwd )
-"$SCRIPT_DIR"/waitForUrl.sh "https://repo1.maven.org/maven2/$URL_PATH"
diff --git a/.github/workflows/close-inactive-issues.yml b/.github/workflows/close-inactive-issues.yml
index 4453ca192264..2a76f9cd147d 100644
--- a/.github/workflows/close-inactive-issues.yml
+++ b/.github/workflows/close-inactive-issues.yml
@@ -3,7 +3,7 @@ on:
   schedule:
     - cron: "30 1 * * *"
   workflow_dispatch:
-permissions: read-all
+permissions: {}
 jobs:
   close-issues:
     runs-on: ubuntu-latest
diff --git a/.github/workflows/codeql-analysis.yml b/.github/workflows/codeql.yml
similarity index 60%
rename from .github/workflows/codeql-analysis.yml
rename to .github/workflows/codeql.yml
index 5664eeca4c65..817ab007f246 100644
--- a/.github/workflows/codeql-analysis.yml
+++ b/.github/workflows/codeql.yml
@@ -13,38 +13,46 @@ on:
   schedule:
     - cron: '0 19 * * 3'
 
-permissions: read-all
+permissions: {}
 
 env:
   DEVELOCITY_ACCESS_KEY: ${{ secrets.DEVELOCITY_ACCESS_KEY }}
 
 jobs:
   analyze:
-    name: Analyze
+    name: Analyze (${{ matrix.language }})
     runs-on: ubuntu-latest
     permissions:
       security-events: write
     strategy:
       fail-fast: false
       matrix:
-        language:
-          - java
-          - javascript
+        include:
+          - language: actions
+            build-mode: none
+          - language: java-kotlin
+            build-mode: manual
+          - language: javascript
+            build-mode: none
     steps:
     - name: Check out repository
       uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
     - name: Initialize CodeQL
-      uses: github/codeql-action/init@ff0a06e83cb2de871e5a09832bc6a81e7276941f # v3.28.18
+      uses: github/codeql-action/init@ce28f5bb42b7a9f2c824e633a3f6ee835bab6858 # v3.29.0
       with:
         languages: ${{ matrix.language }}
+        build-mode: ${{ matrix.build-mode }}
         tools: linked
     - name: Build
+      if: matrix.build-mode == 'manual'
       uses: ./.github/actions/run-gradle
       with:
         encryptionKey: ${{ secrets.GRADLE_ENCRYPTION_KEY }}
         arguments: |
           --no-build-cache \
           -Dscan.tag.CodeQL \
-          allMainClasses
+          classes
     - name: Perform CodeQL Analysis
-      uses: github/codeql-action/analyze@ff0a06e83cb2de871e5a09832bc6a81e7276941f # v3.28.18
+      uses: github/codeql-action/analyze@ce28f5bb42b7a9f2c824e633a3f6ee835bab6858 # v3.29.0
+      with:
+        category: "/language:${{matrix.language}}"
diff --git a/.github/workflows/cross-version.yml b/.github/workflows/cross-version.yml
index 7c51412feaaf..04f821a7f109 100644
--- a/.github/workflows/cross-version.yml
+++ b/.github/workflows/cross-version.yml
@@ -11,7 +11,7 @@ on:
     branches:
       - '**'
 
-permissions: read-all
+permissions: {}
 
 env:
   DEVELOCITY_ACCESS_KEY: ${{ secrets.DEVELOCITY_ACCESS_KEY }}
@@ -22,10 +22,10 @@ jobs:
       fail-fast: false
       matrix:
         jdk:
-        - version: 24
-          type: ga
         - version: 25
           type: ea
+        - version: 26
+          type: ea
     name: "OpenJDK ${{ matrix.jdk.version }} (${{ matrix.jdk.release || matrix.jdk.type }})"
     runs-on: ubuntu-latest
     steps:
@@ -37,7 +37,7 @@ jobs:
         uses: ./.github/actions/setup-test-jdk
       - name: "Set up JDK ${{ matrix.jdk.version }} (${{ matrix.jdk.release || 'ea' }})"
         if: matrix.jdk.type == 'ea'
-        uses: oracle-actions/setup-java@8fb9d7717810ccde9f8d4bef1e6f43d180f506b5 # v1.4.1
+        uses: oracle-actions/setup-java@b1546e588c27008e88bfcabda44d11c22316b9b8 # v1.4.2
         with:
           website: jdk.java.net
           release: ${{ matrix.jdk.release || matrix.jdk.version }}
diff --git a/.github/workflows/gradle-dependency-submission.yml b/.github/workflows/gradle-dependency-submission.yml
index d99e7d48ca52..7f3831fa0390 100644
--- a/.github/workflows/gradle-dependency-submission.yml
+++ b/.github/workflows/gradle-dependency-submission.yml
@@ -5,11 +5,14 @@ on:
     branches:
       - main
 
-permissions: read-all
+permissions: {}
+
+env:
+  DEVELOCITY_ACCESS_KEY: ${{ secrets.DEVELOCITY_ACCESS_KEY }}
 
 jobs:
   dependency-submission:
-    if: github.repository == 'junit-team/junit5'
+    if: github.repository == 'junit-team/junit-framework'
     runs-on: ubuntu-latest
     permissions:
       contents: write
@@ -22,7 +25,7 @@ jobs:
       uses: actions/setup-java@c5195efecf7bdfc987ee8bae7a71cb8b11521c00 # v4.7.1
       with:
         distribution: temurin
-        java-version: 21
+        java-version: 24
         check-latest: true
     - name: Generate and submit dependency graph
-      uses: gradle/actions/dependency-submission@06832c7b30a0129d7fb559bcc6e43d26f6374244 # v4.3.1
+      uses: gradle/actions/dependency-submission@ac638b010cf58a27ee6c972d7336334ccaf61c96 # v4.4.1
diff --git a/.github/workflows/label-opened-issues.yml b/.github/workflows/label-opened-issues.yml
index f18377bd22a1..10a5dee96dee 100644
--- a/.github/workflows/label-opened-issues.yml
+++ b/.github/workflows/label-opened-issues.yml
@@ -3,7 +3,7 @@ on:
   issues:
     types:
       - opened
-permissions: read-all
+permissions: {}
 jobs:
   label_issues:
     runs-on: ubuntu-latest
diff --git a/.github/workflows/label-pull-request.yml b/.github/workflows/label-pull-request.yml
new file mode 100644
index 000000000000..8f3807caad7f
--- /dev/null
+++ b/.github/workflows/label-pull-request.yml
@@ -0,0 +1,52 @@
+name: Copy labels from linked issues to PR
+on:
+  pull_request:
+    types: [opened, reopened, edited, synchronize]
+permissions: {}
+jobs:
+  copy_labels:
+    name: Copy labels
+    runs-on: ubuntu-latest
+    permissions:
+      pull-requests: write
+    steps:
+      - uses: actions/github-script@60a0d83039c74a4aee543508d2ffcb1c3799cdea # v7.0.1
+        with:
+          script: |
+            const query = `
+              query($owner: String!, $repo: String!, $pr: Int!) {
+                repository(owner: $owner, name: $repo) {
+                  pullRequest(number: $pr) {
+                    closingIssuesReferences(first: 10) {
+                      nodes {
+                        labels(first: 100) {
+                          nodes {
+                            name
+                          }
+                        }
+                      }
+                    }
+                  }
+                }
+              }
+            `;
+            
+            const {repository} = await github.graphql(query, {
+                owner: context.repo.owner,
+                repo: context.repo.repo,
+                pr: context.issue.number
+            });
+            
+            let labels = Array.from(new Set(repository.pullRequest.closingIssuesReferences.nodes
+                .flatMap((node) => node.labels.nodes.map((label) => label.name))))
+                .filter((label) => !label.startsWith("status:"));
+            
+            if (labels.length > 0) {
+                console.log(`Adding labels to PR: ${labels}`);
+                await github.rest.issues.addLabels({
+                    issue_number: context.issue.number,
+                    owner: context.repo.owner,
+                    repo: context.repo.repo,
+                    labels: labels
+                });
+            }
diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index aadc10b78069..097c882b871b 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -11,7 +11,7 @@ on:
     branches:
       - '**'
 
-permissions: read-all
+permissions: {}
 
 env:
   DEVELOCITY_ACCESS_KEY: ${{ secrets.DEVELOCITY_ACCESS_KEY }}
@@ -25,12 +25,11 @@ jobs:
       with:
         fetch-depth: 1
     - name: Install GraalVM
-      uses: graalvm/setup-graalvm@01ed653ac833fe80569f1ef9f25585ba2811baab # v1.3.3
+      uses: graalvm/setup-graalvm@e1df20a713a4cc6ab5b0eb03f0e0dcdc0199b805 # v1.3.4
       with:
         distribution: graalvm-community
         version: 'latest'
         java-version: '21'
-        github-token: ${{ secrets.GITHUB_TOKEN }}
     - name: Build
       uses: ./.github/actions/main-build
       with:
@@ -76,7 +75,7 @@ jobs:
     permissions:
       attestations: write # required for build provenance attestation
       id-token: write # required for build provenance attestation
-    if: github.event_name == 'push' && github.repository == 'junit-team/junit5' && (startsWith(github.ref, 'refs/heads/releases/') || github.ref == 'refs/heads/main')
+    if: github.event_name == 'push' && github.repository == 'junit-team/junit-framework' && (startsWith(github.ref, 'refs/heads/releases/') || github.ref == 'refs/heads/main')
     steps:
     - name: Check out repository
       uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
@@ -93,7 +92,7 @@ jobs:
           publish -x check \
           prepareGitHubAttestation
     - name: Generate build provenance attestations
-      uses: actions/attest-build-provenance@db473fddc028af60658334401dc6fa3ffd8669fd # v2.3.0
+      uses: actions/attest-build-provenance@e8998f949152b193b063cb0ec769d69d929409be # v2.4.0
       with:
         subject-path: documentation/build/attestation/*.jar
 
@@ -126,7 +125,7 @@ jobs:
         git config --global user.name "JUnit Team"
         git config --global user.email "team@junit.org"
     - name: Upload Documentation
-      if: github.event_name == 'push' && github.repository == 'junit-team/junit5' && github.ref == 'refs/heads/main'
+      if: github.event_name == 'push' && github.repository == 'junit-team/junit-framework' && github.ref == 'refs/heads/main'
       uses: ./.github/actions/run-gradle
       with:
         encryptionKey: ${{ secrets.GRADLE_ENCRYPTION_KEY }}
@@ -135,4 +134,4 @@ jobs:
           -Dscan.tag.Documentation
       env:
         GIT_USERNAME: git
-        GIT_PASSWORD: ${{ secrets.GH_TOKEN }}
+        GIT_PASSWORD: ${{ secrets.JUNIT_BUILDS_GITHUB_TOKEN_DOCS_REPO }}
diff --git a/.github/workflows/ossf-scorecard.yml b/.github/workflows/ossf-scorecard.yml
index c24ae2e85e54..18cacbc0cc06 100644
--- a/.github/workflows/ossf-scorecard.yml
+++ b/.github/workflows/ossf-scorecard.yml
@@ -7,7 +7,7 @@ on:
   push:
     branches: [ "main" ]
 
-permissions: read-all
+permissions: {}
 
 jobs:
   analysis:
@@ -26,7 +26,7 @@ jobs:
           persist-credentials: false
 
       - name: "Run analysis"
-        uses: ossf/scorecard-action@f49aabe0b5af0936a0987cfb85d86b75731b0186 # v2.4.1
+        uses: ossf/scorecard-action@05b42c624433fc40578a4040d5cf5e36ddca8cde # v2.4.2
         with:
           results_file: results.sarif
           results_format: sarif
@@ -57,6 +57,6 @@ jobs:
       # Upload the results to GitHub's code scanning dashboard (optional).
       # Commenting out will disable upload of results to your repo's Code Scanning dashboard
       - name: "Upload to code-scanning"
-        uses: github/codeql-action/upload-sarif@ff0a06e83cb2de871e5a09832bc6a81e7276941f # v3.28.18
+        uses: github/codeql-action/upload-sarif@ce28f5bb42b7a9f2c824e633a3f6ee835bab6858 # v3.29.0
         with:
           sarif_file: results.sarif
diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index 6988b6e873b6..0c736d216ba0 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -15,12 +15,12 @@ on:
         required: false
         default: false
 
-permissions: read-all
+permissions: {}
 
 env:
   DEVELOCITY_ACCESS_KEY: ${{ secrets.DEVELOCITY_ACCESS_KEY }}
-  STAGING_REPO_URL: https://central.sonatype.com/api/v1/publisher/deployment/${{ github.event.inputs.deploymentId }}/download
-  RELEASE_TAG: r${{ github.event.inputs.releaseVersion }}
+  STAGING_REPO_URL: https://central.sonatype.com/api/v1/publisher/deployment/${{ inputs.deploymentId }}/download
+  RELEASE_TAG: r${{ inputs.releaseVersion }}
 
 jobs:
 
@@ -46,7 +46,7 @@ jobs:
         run: |
           curl --silent --fail --location --output /tmp/reference.jar \
             --header "Authorization: Bearer $MAVEN_CENTRAL_USER_TOKEN" \
-            "${{ env.STAGING_REPO_URL }}/org/junit/jupiter/junit-jupiter-api/${{ github.event.inputs.releaseVersion }}/junit-jupiter-api-${{ github.event.inputs.releaseVersion }}.jar"
+            "${{ env.STAGING_REPO_URL }}/org/junit/jupiter/junit-jupiter-api/${{ inputs.releaseVersion }}/junit-jupiter-api-${{ inputs.releaseVersion }}.jar"
           sudo apt-get update && sudo apt-get install --yes jc
           unzip -c /tmp/reference.jar META-INF/MANIFEST.MF | jc --jar-manifest | jq '.[0]' > /tmp/manifest.json
           echo "createdBy=$(jq --raw-output .Created_By /tmp/manifest.json)" >> "$GITHUB_OUTPUT"
@@ -63,14 +63,9 @@ jobs:
             --remote-repo-url=${{ env.STAGING_REPO_URL }}
       - name: Generate build provenance attestations
         if: ${{ inputs.dryRun == false }}
-        uses: actions/attest-build-provenance@db473fddc028af60658334401dc6fa3ffd8669fd # v2.3.0
+        uses: actions/attest-build-provenance@e8998f949152b193b063cb0ec769d69d929409be # v2.4.0
         with:
           subject-path: build/repo/**/*.jar
-      - name: Upload local repository for later jobs
-        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2
-        with:
-          name: local-maven-repository
-          path: build/repo
 
   verify_consumability:
     name: Verify consumability
@@ -81,36 +76,37 @@ jobs:
         with:
           fetch-depth: 1
           ref: "refs/tags/${{ env.RELEASE_TAG }}"
-          path: junit5
-      - name: Check out samples repository
+          path: junit-framework
+      - name: Check out examples repository
         uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
-          repository: ${{ github.repository_owner }}/junit5-samples
-          token: ${{ secrets.GH_TOKEN }}
+          repository: ${{ github.repository_owner }}/junit-examples
+          token: ${{ secrets.JUNIT_BUILDS_GITHUB_TOKEN_EXAMPLES_REPO }}
           fetch-depth: 1
-          path: junit5-samples
+          path: junit-examples
+          ref: develop/6.x
       - name: Set up JDK
         uses: actions/setup-java@c5195efecf7bdfc987ee8bae7a71cb8b11521c00 # v4.7.1
         with:
-          java-version: 21
+          java-version: 24
           distribution: temurin
-      - uses: sbt/setup-sbt@26ab4b0fa1c47fa62fc1f6e51823a658fb6c760c # v1.1.7
-      - name: Update JUnit dependencies in samples
-        run: java src/Updater.java ${{ github.event.inputs.releaseVersion }}
-        working-directory: junit5-samples
+      - uses: sbt/setup-sbt@234370af1319038bf8dc432f8a7e4b83078a1781 # v1.1.11
+      - name: Update JUnit dependencies in examples
+        run: java src/Updater.java ${{ inputs.releaseVersion }}
+        working-directory: junit-examples
       - name: Prepare Maven Central user token
-        uses: ./junit5/.github/actions/maven-central-user-token
+        uses: ./junit-framework/.github/actions/maven-central-user-token
         with:
           username: ${{ secrets.MAVEN_CENTRAL_USERNAME }}
           password: ${{ secrets.MAVEN_CENTRAL_PASSWORD }}
       - name: Inject staging repository URL
         run: java src/StagingRepoInjector.java ${{ env.STAGING_REPO_URL }}
-        working-directory: junit5-samples
-      - name: Build samples
-        run: java src/Builder.java --exclude=junit5-jupiter-starter-bazel,junit5-jupiter-starter-sbt
-        working-directory: junit5-samples
+        working-directory: junit-examples
+      - name: Build examples
+        run: java src/Builder.java --exclude=junit-jupiter-starter-bazel,junit-jupiter-starter-sbt
+        working-directory: junit-examples
         env:
-          MAVEN_ARGS: --settings ${{ github.workspace }}/junit5-samples/src/central-staging-maven-settings.xml --activate-profiles central-staging
+          MAVEN_ARGS: --settings ${{ github.workspace }}/junit-examples/src/central-staging-maven-settings.xml --activate-profiles central-staging
 
   close_github_milestone:
     name: Close GitHub milestone
@@ -124,17 +120,30 @@ jobs:
         with:
           result-encoding: string
           script: |
-            const openMilestones = await github.rest.issues.listMilestones({
+            const query = `
+                query ($owner: String!, $repo: String!, $title: String!) {
+                    repository(owner: $owner, name: $repo) {
+                        milestones(first: 100, query: $title) {
+                            nodes {
+                                title
+                                number
+                                openIssueCount
+                            }
+                        }
+                    }
+                }
+            `;
+            const {repository} = await github.graphql(query, {
                 owner: context.repo.owner,
                 repo: context.repo.repo,
-                state: 'open'
+                title: "${{ inputs.releaseVersion }}"
             });
-            const [milestone] = openMilestones.data.filter(x => x.title === "${{ github.event.inputs.releaseVersion }}")
+            const [milestone] = repository.milestones.nodes.filter(it => it.title === "${{ inputs.releaseVersion }}")
             if (!milestone) {
-                throw new Error('Milestone "${{ github.event.inputs.releaseVersion }}" not found');
+                throw new Error('Milestone "${{ inputs.releaseVersion }}" not found');
             }
-            if (milestone.open_issues > 0) {
-                throw new Error(`Milestone "${{ github.event.inputs.releaseVersion }}" has ${milestone.open_issues} open issue(s)`);
+            if (milestone.openIssueCount > 0) {
+                throw new Error(`Milestone "${{ inputs.releaseVersion }}" has ${milestone.openIssueCount} open issue(s)`);
             }
             const requestBody = {
                 owner: context.repo.owner,
@@ -195,26 +204,26 @@ jobs:
             --no-configuration-cache \
             clean \
             gitPublishCopy \
-            -Pdocumentation.replaceCurrentDocs=${{ contains(github.event.inputs.releaseVersion, '-') && 'false' || 'true' }}
+            -Pdocumentation.replaceCurrentDocs=${{ contains(inputs.releaseVersion, '-') && 'false' || 'true' }}
       - name: Publish documentation
         if: ${{ inputs.dryRun == false }}
         uses: ./.github/actions/run-gradle
         env:
           GIT_USERNAME: git
-          GIT_PASSWORD: ${{ secrets.GH_TOKEN }}
+          GIT_PASSWORD: ${{ secrets.JUNIT_BUILDS_GITHUB_TOKEN_DOCS_REPO }}
         with:
           encryptionKey: ${{ secrets.GRADLE_ENCRYPTION_KEY }}
           arguments: |
             --no-build-cache \
             --no-configuration-cache \
             gitPublishPush \
-            -Pdocumentation.replaceCurrentDocs=${{ contains(github.event.inputs.releaseVersion, '-') && 'false' || 'true' }}
+            -Pdocumentation.replaceCurrentDocs=${{ contains(inputs.releaseVersion, '-') && 'false' || 'true' }}
       - name: Wait for deployment to GitHub Pages
         if: ${{ inputs.dryRun == false }}
         id: pagesDeployment
         timeout-minutes: 20
         run: |
-          URL="https://junit.org/junit5/docs/${{ github.event.inputs.releaseVersion }}/user-guide/junit-user-guide-${{ github.event.inputs.releaseVersion }}.pdf"
+          URL="https://docs.junit.org/${{ inputs.releaseVersion }}/user-guide/junit-user-guide-${{ inputs.releaseVersion }}.pdf"
           ./.github/scripts/waitForUrl.sh "$URL"
           echo "pdfUrl=$URL" >> "$GITHUB_OUTPUT"
       - name: Verify integrity of PDF version of User Guide
@@ -223,47 +232,27 @@ jobs:
           curl --silent --fail --location --output /tmp/junit-user-guide.pdf "${{ steps.pagesDeployment.outputs.pdfUrl }}"
           pdfinfo /tmp/junit-user-guide.pdf
 
-  wait_for_maven_central:
-    name: Wait for Maven Central
+  update_examples:
+    name: Update examples
     needs: publish_deployment
     runs-on: ubuntu-latest
     steps:
-      - name: Check out repository
-        uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
-        with:
-          fetch-depth: 1
-          ref: "refs/tags/${{ env.RELEASE_TAG }}"
-      - name: Download local Maven repository
-        uses: actions/download-artifact@d3f86a106a0bac45b974a628896c90dbdf5c8093 # v4.3.0
-        with:
-          name: local-maven-repository
-          path: build/repo
-      - name: Wait for sync to Maven Central
-        if: ${{ inputs.dryRun == false }}
-        timeout-minutes: 30
-        run: |
-          find build/repo -name '*.pom' -printf './.github/scripts/waitForMavenCentralSync.sh %P\n' | sh
-
-  update_samples:
-    name: Update samples
-    needs: wait_for_maven_central
-    runs-on: ubuntu-latest
-    steps:
-      - name: Check out samples repository
+      - name: Check out examples repository
         uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
-          repository: ${{ github.repository_owner }}/junit5-samples
-          token: ${{ secrets.GH_TOKEN }}
+          repository: ${{ github.repository_owner }}/junit-examples
+          token: ${{ secrets.JUNIT_BUILDS_GITHUB_TOKEN_EXAMPLES_REPO }}
           fetch-depth: 1
+          ref: develop/6.x
       - name: Set up JDK
         uses: actions/setup-java@c5195efecf7bdfc987ee8bae7a71cb8b11521c00 # v4.7.1
         with:
-          java-version: 21
+          java-version: 24
           distribution: temurin
-      - uses: sbt/setup-sbt@26ab4b0fa1c47fa62fc1f6e51823a658fb6c760c # v1.1.7
-      - name: Update JUnit dependencies in samples
-        run: java src/Updater.java ${{ github.event.inputs.releaseVersion }}
-      - name: Build samples
+      - uses: sbt/setup-sbt@234370af1319038bf8dc432f8a7e4b83078a1781 # v1.1.11
+      - name: Update JUnit dependencies in examples
+        run: java src/Updater.java ${{ inputs.releaseVersion }}
+      - name: Build examples
         if: ${{ inputs.dryRun == false }}
         run: java src/Builder.java
       - name: Create release branch
@@ -272,13 +261,13 @@ jobs:
           git config user.email "team@junit.org"
           git switch -c "${{ env.RELEASE_TAG }}"
           git status
-          git commit -a -m "Use ${{ github.event.inputs.releaseVersion }}"
+          git commit -a -m "Use ${{ inputs.releaseVersion }}"
       - name: Push release branch
         if: ${{ inputs.dryRun == false }}
         run: |
           git push origin "${{ env.RELEASE_TAG }}"
       - name: Update main branch (only for GA releases)
-        if: ${{ inputs.dryRun == false && !contains(github.event.inputs.releaseVersion, '-') }}
+        if: ${{ inputs.dryRun == false && !contains(inputs.releaseVersion, '-') }}
         run: |
           git switch main
           git merge --ff-only "${{ env.RELEASE_TAG }}"
@@ -287,7 +276,7 @@ jobs:
   create_github_release:
     name: Create GitHub release
     if: ${{ inputs.dryRun == false }}
-    needs: wait_for_maven_central
+    needs: [ publish_documentation, update_examples ]
     runs-on: ubuntu-latest
     permissions:
       contents: write
@@ -296,17 +285,14 @@ jobs:
         uses: actions/github-script@60a0d83039c74a4aee543508d2ffcb1c3799cdea # v7.0.1
         with:
           script: |
-            const releaseVersion = "${{ github.event.inputs.releaseVersion }}";
-            const jupiterVersion = releaseVersion;
-            const vintageVersion = releaseVersion;
-            const platformVersion = "1." + releaseVersion.substring(2);
+            const releaseVersion = "${{ inputs.releaseVersion }}";
             const requestBody = {
               owner: context.repo.owner,
               repo: context.repo.repo,
               tag_name: `r${releaseVersion}`,
               name: `JUnit ${releaseVersion}`,
               generate_release_notes: true,
-              body: `JUnit ${jupiterVersion} = Platform ${platformVersion} + Jupiter ${jupiterVersion} + Vintage ${vintageVersion}\n\nSee [Release Notes](https://junit.org/junit5/docs/${releaseVersion}/release-notes/).`,
+              body: `JUnit ${releaseVersion} = Platform ${releaseVersion} + Jupiter ${releaseVersion} + Vintage ${releaseVersion}\n\nSee [Release Notes](https://docs.junit.org/${releaseVersion}/release-notes/).`,
               prerelease: releaseVersion.includes("-"),
             };
             console.log(requestBody);
diff --git a/.github/workflows/reproducible-build.yml b/.github/workflows/reproducible-build.yml
index 546ff5b9cd18..9b7fa596f125 100644
--- a/.github/workflows/reproducible-build.yml
+++ b/.github/workflows/reproducible-build.yml
@@ -9,7 +9,7 @@ on:
     branches:
       - '**'
 
-permissions: read-all
+permissions: {}
 
 env:
   DEVELOCITY_ACCESS_KEY: ${{ secrets.DEVELOCITY_ACCESS_KEY }}
diff --git a/.github/workflows/sanitize-closed-issues.yml b/.github/workflows/sanitize-closed-issues.yml
index 046be82f7804..ca77b2bd4f9d 100644
--- a/.github/workflows/sanitize-closed-issues.yml
+++ b/.github/workflows/sanitize-closed-issues.yml
@@ -3,7 +3,7 @@ on:
   issues:
     types:
       - closed
-permissions: read-all
+permissions: {}
 jobs:
   label_issues:
     runs-on: ubuntu-latest
diff --git a/.idea/codeStyles/Project.xml b/.idea/codeStyles/Project.xml
index 9f10a217b5b9..da9a350c8e4c 100644
--- a/.idea/codeStyles/Project.xml
+++ b/.idea/codeStyles/Project.xml
@@ -7,6 +7,7 @@
       <option name="NAMES_COUNT_TO_USE_IMPORT_ON_DEMAND" value="99999999" />
       <option name="IMPORT_LAYOUT_TABLE">
         <value>
+          <package name="" withSubpackages="true" static="false" module="true" />
           <package name="" withSubpackages="true" static="true" />
           <emptyLine />
           <package name="java" withSubpackages="true" static="false" />
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 135a6cd3456c..9b5fd3cd1caa 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -4,7 +4,7 @@
 
 We welcome new contributors to the project!
 If you're interested, please check for [issues labeled with `up-for-grabs`
-that are not yet in progress](https://github.com/junit-team/junit5/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20label%3Aup-for-grabs%20-label%3A%22status%3A%20in%20progress%22).
+that are not yet in progress](https://github.com/junit-team/junit-framework/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20label%3Aup-for-grabs%20-label%3A%22status%3A%20in%20progress%22).
 Generally, before you work on an issue, post a comment and ask whether it can be started.
 Please wait for the core team to respond and assign the issue to you before making any code
 changes.
@@ -36,7 +36,7 @@ Issue: #999
 
 ## Pull Requests
 
-Our [Definition of Done](https://github.com/junit-team/junit5/wiki/Definition-of-Done)
+Our [Definition of Done](https://github.com/junit-team/junit-framework/wiki/Definition-of-Done)
 (DoD) offers some guidelines on what we expect from a pull request.
 Feel free to open a pull request that does not fulfill all criteria, e.g. to discuss
 a certain change before polishing it, but please be aware that we will only merge it
@@ -111,7 +111,7 @@ code -- class names, method names, variable names, etc.
 - Favor literals (e.g., `{@literal @}`) over HTML entities.
 - New classes and methods should declare a `@since ...` tag.
 - Use `@since 5.10` instead of `@since 5.10.0`.
-- Do not use `@author` tags. Instead, contributors are listed on the [GitHub](https://github.com/junit-team/junit5/graphs/contributors) page.
+- Do not use `@author` tags. Instead, contributors are listed on the [GitHub](https://github.com/junit-team/junit-framework/graphs/contributors) page.
 - Do not use verbs in third-person form in the first sentence of the Javadoc for a method -- for example, use "Discover tests..." instead of "Discovers tests...".
 
 #### Examples
@@ -120,6 +120,14 @@ See [`ExtensionContext`](junit-jupiter-api/src/main/java/org/junit/jupiter/api/e
 [`ParameterContext`](junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ParameterContext.java) for example Javadoc.
 
 
+### Nullability
+
+This project uses JSpecify's annotation to indicate nullability. In general, the approach
+is as follows:
+
+- All packages are annotated with `@NullMarked`
+- Types of fields, parameters, return types etc. may be annotated with `@Nullable`
+
 ### Tests
 
 #### Naming
@@ -140,8 +148,8 @@ See [`ExtensionContext`](junit-jupiter-api/src/main/java/org/junit/jupiter/api/e
 ### Logging
 
 - In general, logging should be used sparingly.
-- All logging must be performed via the internal `Logger` façade provided via the JUnit [LoggerFactory](https://github.com/junit-team/junit5/blob/main/junit-platform-commons/src/main/java/org/junit/platform/commons/logging/LoggerFactory.java).
-- Levels defined in JUnit's [Logger](https://github.com/junit-team/junit5/blob/main/junit-platform-commons/src/main/java/org/junit/platform/commons/logging/Logger.java) façade, which delegates to Java Util Logging (JUL) for the actual logging.
+- All logging must be performed via the internal `Logger` façade provided via the JUnit [LoggerFactory](https://github.com/junit-team/junit-framework/blob/main/junit-platform-commons/src/main/java/org/junit/platform/commons/logging/LoggerFactory.java).
+- Levels defined in JUnit's [Logger](https://github.com/junit-team/junit-framework/blob/main/junit-platform-commons/src/main/java/org/junit/platform/commons/logging/Logger.java) façade, which delegates to Java Util Logging (JUL) for the actual logging.
   - _error_ (JUL: `SEVERE`, Log4J: `ERROR`): extra information (in addition to an Exception) about errors that will halt execution
   - _warn_ (JUL: `WARNING`, Log4J: `WARN`): potential usage or configuration errors that should not halt execution
   - _info_ (JUL: `INFO`, Log4J: `INFO`): information the users might want to know but not by default
@@ -151,9 +159,9 @@ See [`ExtensionContext`](junit-jupiter-api/src/main/java/org/junit/jupiter/api/e
 
 ### Deprecation
 
-The JUnit 5 project uses the `@API` annotation from [API Guardian](https://github.com/apiguardian-team/apiguardian).
+The JUnit project uses the `@API` annotation from [API Guardian](https://github.com/apiguardian-team/apiguardian).
 Publicly available interfaces, classes, and methods have a defined lifecycle
-which is described in detail in the [User Guide](https://junit.org/junit5/docs/current/user-guide/#api-evolution).
+which is described in detail in the [User Guide](https://docs.junit.org/current/user-guide/#api-evolution).
 
 That following describes the deprecation process followed for API items.
 
diff --git a/NOTICE.md b/NOTICE.md
index 520713de1c3b..47f2ae4ed1a9 100644
--- a/NOTICE.md
+++ b/NOTICE.md
@@ -4,5 +4,5 @@ Open Source Licenses
 This product may include a number of subcomponents with separate
 copyright notices and license terms. Your use of the source code for
 these subcomponents is subject to the terms and conditions of the
-subcomponent's license, as noted in the LICENSE-<subcomponent>.md
+subcomponent's license, as noted in the `LICENSE-<subcomponent>[.md]`
 files.
diff --git a/README.md b/README.md
index 20f691ec93f5..f1be8cc97ecc 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,6 @@
-# <img src="https://junit.org/junit5/assets/img/junit5-logo.png" align="right" width="100">JUnit 5
+# <img src="https://junit.org/assets/img/junit6-logo.png" align="right" width="100">JUnit
 
-This repository is the home of _JUnit 5_.
+This repository is the home of JUnit Platform, Jupiter, and Vintage.
 
 ## Sponsors
 
@@ -12,37 +12,37 @@ This repository is the home of _JUnit 5_.
 
 ## Latest Releases
 
-- General Availability (GA): [JUnit 5.12.2](https://github.com/junit-team/junit5/releases/tag/r5.12.2) (April 11, 2025)
-- Preview (Milestone/Release Candidate): [JUnit 5.13.0-RC1](https://github.com/junit-team/junit5/releases/tag/r5.13.0-RC1) (May 16, 2025)
+- General Availability (GA): [JUnit 5.13.2](https://github.com/junit-team/junit-framework/releases/tag/r5.13.2) (June 24, 2025)
+- Preview (Milestone/Release Candidate): [JUnit 6.0.0-M1](https://github.com/junit-team/junit-framework/releases/tag/r6.0.0-M1) (June 27, 2025)
 
 ## Documentation
 
 - [User Guide]
 - [Javadoc]
 - [Release Notes]
-- [Samples]
+- [Examples]
 
 ## Contributing
 
-Contributions to JUnit 5 are both welcomed and appreciated. For specific guidelines
+Contributions to JUnit are both welcomed and appreciated. For specific guidelines
 regarding contributions, please see [CONTRIBUTING.md] in the root directory of the
 project. Those willing to use milestone or SNAPSHOT releases are encouraged
 to file feature requests and bug reports using the project's
-[issue tracker](https://github.com/junit-team/junit5/issues). Issues marked with an
-<a href="https://github.com/junit-team/junit5/issues?q=is%3Aissue+is%3Aopen+label%3Aup-for-grabs">`up-for-grabs`</a>
+[issue tracker](https://github.com/junit-team/junit-framework/issues). Issues marked with an
+<a href="https://github.com/junit-team/junit-framework/issues?q=is%3Aissue+is%3Aopen+label%3Aup-for-grabs">`up-for-grabs`</a>
 label are specifically targeted for community contributions.
 
 ## Getting Help
 
-Ask JUnit 5 related questions on [StackOverflow] or chat with the community on [Gitter].
+Ask JUnit-related questions on [StackOverflow] or use the Q&A category on [GitHub Discussions].
 
 ## Continuous Integration Builds
 
-[![CI Status](https://github.com/junit-team/junit5/workflows/CI/badge.svg)](https://github.com/junit-team/junit5/actions) [![Cross-Version Status](https://github.com/junit-team/junit5/workflows/Cross-Version/badge.svg)](https://github.com/junit-team/junit5/actions)
+[![CI](https://github.com/junit-team/junit-framework/actions/workflows/main.yml/badge.svg?branch=main)](https://github.com/junit-team/junit-framework/actions/workflows/main.yml) [![Cross-Version](https://github.com/junit-team/junit-framework/actions/workflows/cross-version.yml/badge.svg?branch=main)](https://github.com/junit-team/junit-framework/actions/workflows/cross-version.yml)
 
-Official CI build server for JUnit 5. Used to perform quick checks on submitted pull
-requests and for build matrices including the latest released OpenJDK and early access
-builds of the next OpenJDK.
+Official CI build server used to perform quick checks on submitted pull requests and for
+build matrices including the latest released OpenJDK and early access builds of the next
+OpenJDK.
 
 ## Code Coverage
 
@@ -56,7 +56,7 @@ in `build/reports/jacoco/jacocoRootReport/html/index.html`.
 
 [![Revved up by Develocity](https://img.shields.io/badge/Revved%20up%20by-Develocity-06A0CE?logo=Gradle&labelColor=02303A)](https://ge.junit.org/scans)
 
-JUnit 5 utilizes [Develocity](https://gradle.com/) for [Build Scans](https://scans.gradle.com/),
+JUnit utilizes [Develocity](https://gradle.com/) for [Build Scans](https://scans.gradle.com/),
 [Build Cache](https://docs.gradle.org/current/userguide/build_cache.html), and
 [Predictive Test Selection](https://docs.gradle.com/enterprise/predictive-test-selection/).
 
@@ -70,17 +70,15 @@ task outputs from previous CI builds.
 
 ## Building from Source
 
-You need [JDK 21] to build JUnit 5. [Gradle toolchains] are used to detect and
+You need [JDK 24] to build JUnit. [Gradle toolchains] are used to detect and
 potentially download additional JDKs for compilation and test execution.
 
-All modules can be _built_ and _tested_ with the [Gradle Wrapper] using the following command.
+All modules can be _built_ and _tested_ with the [Gradle Wrapper] using the following command:
 
 `./gradlew build`
 
-## Installing in Local Maven Repository
-
-All modules can be _installed_ with the [Gradle Wrapper] in a local Maven repository for
-consumption in other projects via the following command.
+All modules can be _installed_ in a local Maven repository for consumption in other local
+projects via the following command:
 
 `./gradlew publishToMavenLocal`
 
@@ -93,20 +91,17 @@ consumption in other projects via the following command.
 Consult the [Dependency Metadata] section of the [User Guide] for a list of all artifacts
 of the JUnit Platform, JUnit Jupiter, and JUnit Vintage.
 
-See also <https://repo1.maven.org/maven2/org/junit/> for releases and
-<https://central.sonatype.com/repository/maven-snapshots/org/junit/> for snapshots.
-
 
-[Codecov]: https://codecov.io/gh/junit-team/junit5
-[CONTRIBUTING.md]: https://github.com/junit-team/junit5/blob/HEAD/CONTRIBUTING.md
-[Dependency Metadata]: https://junit.org/junit5/docs/current/user-guide/#dependency-metadata
-[Gitter]: https://gitter.im/junit-team/junit5
+[Codecov]: https://codecov.io/gh/junit-team/junit-framework
+[CONTRIBUTING.md]: https://github.com/junit-team/junit-framework/blob/HEAD/CONTRIBUTING.md
+[Dependency Metadata]: https://docs.junit.org/current/user-guide/#dependency-metadata
+[GitHub Discussions]: https://github.com/junit-team/junit-framework/discussions/categories/q-a
 [Gradle toolchains]: https://docs.gradle.org/current/userguide/toolchains.html
 [Gradle Wrapper]: https://docs.gradle.org/current/userguide/gradle_wrapper.html#sec:using_wrapper
 [JaCoCo]: https://www.eclemma.org/jacoco/
-[Javadoc]: https://junit.org/junit5/docs/current/api/
-[JDK 21]: https://javaalmanac.io/jdk/21/
-[Release Notes]: https://junit.org/junit5/docs/current/release-notes/
-[Samples]: https://github.com/junit-team/junit5-samples
+[Javadoc]: https://docs.junit.org/current/api/
+[JDK 24]: https://javaalmanac.io/jdk/24/
+[Release Notes]: https://docs.junit.org/current/release-notes/
+[Examples]: https://github.com/junit-team/junit-examples
 [StackOverflow]: https://stackoverflow.com/questions/tagged/junit5
-[User Guide]: https://junit.org/junit5/docs/current/user-guide/
+[User Guide]: https://docs.junit.org/current/user-guide/
diff --git a/RELEASING.md b/RELEASING.md
index 4616ac429047..fc1a2d7e201f 100644
--- a/RELEASING.md
+++ b/RELEASING.md
@@ -3,15 +3,15 @@
 ## Pre-release steps
 
 - [ ] Switch or create the release branch for this feature release (e.g. `releases/5.12.x`)
-- [ ] Change `version`, `platformVersion`, and `vintageVersion` in `gradle.properties` to the versions about to be released
+- [ ] Change `version` in `gradle.properties` to the versions about to be released
 - [ ] Change release date in Release Notes
 - [ ] Change release date in `README.MD`
 - [ ] Commit with message "Release ${VERSION}"
 - [ ] Execute `./gradlew --no-build-cache --no-configuration-cache clean build jreleaserDeploy`
 - [ ] Tag current commit: `git tag -s -m ${VERSION} r${VERSION}`
-- [ ] Change `version`, `platformVersion`, and `vintageVersion` properties in `gradle.properties` on release branch to new development versions and commit with message "Back to snapshots for further development" or similar
+- [ ] Change `version` in `gradle.properties` on release branch to new development versions and commit with message "Back to snapshots for further development" or similar
 - [ ] Push release branch and tag to GitHub: `git push --set-upstream --follow-tags origin HEAD`
-- [ ] Trigger a [release build](https://github.com/junit-team/junit5/actions/workflows/release.yml): `gh workflow run --ref r${VERSION} -f releaseVersion=${VERSION} -f deploymentId=${DEPLOYMENT_ID} release.yml`
+- [ ] Trigger a [release build](https://github.com/junit-team/junit-framework/actions/workflows/release.yml): `gh workflow run --ref r${VERSION} -f releaseVersion=${VERSION} -f deploymentId=${DEPLOYMENT_ID} release.yml`
   - Select the release branch
   - Enter the version to be released
   - Enter the staging repository ID from the output of above Gradle build
@@ -30,7 +30,7 @@
 ### Feature releases (x.y.0)
 
 - [ ] Fast-forward merge the release branch to `main` and push to GitHub
-- [ ] Update the [security policy](https://github.com/junit-team/junit5/blob/main/SECURITY.md) and commit with message "Update security policy to reflect 5.x release" or similar
+- [ ] Update the [security policy](https://github.com/junit-team/junit-framework/blob/main/SECURITY.md) and commit with message "Update security policy to reflect 5.x release" or similar
 - [ ] Create release notes for the next feature release from the template
 - [ ] Update [JBang catalog](https://github.com/junit-team/jbang-catalog/blob/main/jbang-catalog.json)
 
diff --git a/SECURITY.md b/SECURITY.md
index 4d4bad5f6641..3bba42f43063 100644
--- a/SECURITY.md
+++ b/SECURITY.md
@@ -1,6 +1,6 @@
 # Security Policy
 
-[![OpenSSF Best Practices](https://www.bestpractices.dev/projects/9607/badge)](https://www.bestpractices.dev/projects/9607) [![OpenSSF Scorecard](https://api.scorecard.dev/projects/github.com/junit-team/junit5/badge)](https://scorecard.dev/viewer/?uri=github.com/junit-team/junit5)
+[![OpenSSF Best Practices](https://www.bestpractices.dev/projects/9607/badge)](https://www.bestpractices.dev/projects/9607) [![OpenSSF Scorecard](https://api.scorecard.dev/projects/github.com/junit-team/junit-framework/badge)](https://scorecard.dev/viewer/?uri=github.com/junit-team/junit-framework)
 
 ## JAR Signing
 
@@ -11,9 +11,12 @@ You'll find more information about the key here: [KEYS](./KEYS)
 
 | Version | Supported          |
 |---------| ------------------ |
-| 5.12.x  | :white_check_mark: |
-| < 5.12  | :x:                |
+| 5.13.x  | :white_check_mark: |
+| < 5.13  | :x:                |
 
 ## Reporting a Vulnerability
 
-To report a security vulnerability, please send an email to security@junit.org. You can use the [published OpenPGP key](https://keys.openpgp.org/search?q=security%40junit.org) with fingerprint `0152DA30EABC7ABADCB09D10D9A6B1329D191D25` to encrypt the message body.
+To report a security vulnerability, you have two options:
+
+- [Privately report a vulnerability](https://github.com/junit-team/junit-framework/security/advisories/new) on GitHub (see [docs](https://docs.github.com/en/code-security/security-advisories/guidance-on-reporting-and-writing-information-about-vulnerabilities/privately-reporting-a-security-vulnerability) for details)
+- Send an email to security@junit.org. You can use the [published OpenPGP key](https://keys.openpgp.org/search?q=security%40junit.org) with fingerprint `0152DA30EABC7ABADCB09D10D9A6B1329D191D25` to encrypt the message body.
diff --git a/build.gradle.kts b/build.gradle.kts
index 5f40357a56cf..21ecf2b5bc2f 100644
--- a/build.gradle.kts
+++ b/build.gradle.kts
@@ -4,13 +4,13 @@ plugins {
 	id("junitbuild.base-conventions")
 	id("junitbuild.build-metadata")
 	id("junitbuild.checkstyle-nohttp")
-	id("junitbuild.dependency-update-check")
 	id("junitbuild.jacoco-aggregation-conventions")
 	id("junitbuild.maven-central-publishing")
 	id("junitbuild.temp-maven-repo")
 }
 
-description = "JUnit 5"
+description = "JUnit"
+group = "org.junit"
 
 val license by extra(License(
 	name = "Eclipse Public License v2.0",
@@ -23,10 +23,8 @@ val platformProjects by extra(listOf(
 		projects.junitPlatformConsole,
 		projects.junitPlatformConsoleStandalone,
 		projects.junitPlatformEngine,
-		projects.junitPlatformJfr,
 		projects.junitPlatformLauncher,
 		projects.junitPlatformReporting,
-		projects.junitPlatformRunner,
 		projects.junitPlatformSuite,
 		projects.junitPlatformSuiteApi,
 		projects.junitPlatformSuiteCommons,
diff --git a/documentation/README.md b/documentation/README.md
index f06f5b2fc14b..873a2ff282f6 100644
--- a/documentation/README.md
+++ b/documentation/README.md
@@ -1,6 +1,6 @@
-# JUnit 5 User Guide
+# JUnit User Guide
 
-This subproject contains the AsciiDoc sources for the JUnit 5 User Guide.
+This subproject contains the AsciiDoc sources for the JUnit User Guide.
 
 ## Structure
 
diff --git a/documentation/documentation.gradle.kts b/documentation/documentation.gradle.kts
index a5f806e99b60..4a10e582fcd5 100644
--- a/documentation/documentation.gradle.kts
+++ b/documentation/documentation.gradle.kts
@@ -17,7 +17,7 @@ plugins {
 	alias(libs.plugins.gitPublish)
 	alias(libs.plugins.plantuml)
 	id("junitbuild.build-parameters")
-	id("junitbuild.java-multi-release-test-sources")
+	id("junitbuild.java-nullability-conventions")
 	id("junitbuild.kotlin-library-conventions")
 	id("junitbuild.testing-conventions")
 }
@@ -29,8 +29,8 @@ val modularProjects: List<Project> by rootProject
 modularProjects.forEach { evaluationDependsOn(it.path) }
 
 javaLibrary {
-	mainJavaVersion = JavaVersion.VERSION_1_8
-	testJavaVersion = JavaVersion.VERSION_1_8
+	mainJavaVersion = JavaVersion.VERSION_17
+	testJavaVersion = JavaVersion.VERSION_17
 }
 
 val apiReport = configurations.dependencyScope("apiReport")
@@ -66,11 +66,12 @@ dependencies {
 
 	testImplementation(projects.junitJupiterMigrationsupport)
 	testImplementation(projects.junitPlatformConsole)
-	testImplementation(projects.junitPlatformRunner)
 	testImplementation(projects.junitPlatformSuite)
 	testImplementation(projects.junitPlatformTestkit)
 	testImplementation(projects.junitVintageEngine)
 	testImplementation(kotlin("stdlib"))
+	testRuntimeOnly(libs.kotlinx.coroutines)
+	testRuntimeOnly(kotlin("reflect"))
 
 	toolsImplementation(projects.junitPlatformCommons)
 	toolsImplementation(libs.classgraph)
@@ -80,12 +81,6 @@ dependencies {
 		because("Jimfs is used in src/test/java")
 	}
 
-	if (java.toolchain.implementation.orNull == JvmImplementation.J9) {
-		testRuntimeOnly(libs.jfrPolyfill) {
-			because("OpenJ9 does not include JFR")
-		}
-	}
-
 	standaloneConsoleLauncher(projects.junitPlatformConsoleStandalone)
 }
 
@@ -108,10 +103,9 @@ val ota4jDocVersion = libs.versions.opentest4j.map { if (it.isSnapshot()) "snaps
 val apiGuardianDocVersion = libs.versions.apiguardian.map { if (it.isSnapshot()) "snapshot" else it }.get()
 
 gitPublish {
-	repoUri = "https://github.com/junit-team/junit5.git"
-	referenceRepoUri = rootDir.toURI().toString()
+	repoUri = "https://github.com/junit-team/docs.junit.org.git"
 
-	branch = "gh-pages"
+	branch = "main"
 	sign = false
 	fetchDepth = 1
 
@@ -120,14 +114,14 @@ gitPublish {
 
 	contents {
 		from(docsDir)
-		into("docs")
+		into(".")
 	}
 
 	preserve {
 		include("**/*")
-		exclude("docs/$docsVersion/**")
+		exclude("$docsVersion/**")
 		if (replaceCurrentDocs) {
-			exclude("docs/current/**")
+			exclude("current/**")
 		}
 	}
 }
@@ -162,9 +156,10 @@ tasks {
 		args.addAll("execute")
 		args.addAll("--scan-classpath")
 		args.addAll("--config=junit.platform.reporting.open.xml.enabled=true")
+		args.addAll("--config=junit.platform.reporting.open.xml.git.enabled=true")
 		args.addAll("--config=junit.platform.output.capture.stdout=true")
 		args.addAll("--config=junit.platform.output.capture.stderr=true")
-		args.addAll("--config=junit.platform.discovery.issue.severity.critical=info")
+		args.addAll("--config=junit.platform.discovery.issue.severity.critical=warning")
 		outputs.dir(consoleLauncherTestReportsDir)
 		argumentProviders.add(CommandLineArgumentProvider {
 			listOf(
@@ -201,13 +196,10 @@ tasks {
 		(options as JUnitPlatformOptions).apply {
 			includeEngines("junit-vintage")
 			includeTags("timeout")
+			systemProperty("junit.platform.discovery.issue.severity.critical", "warning")
 		}
 	}
 
-	testRelease21 {
-		include("**/*Demo.class")
-	}
-
 	check {
 		dependsOn(consoleLauncherTest)
 	}
@@ -300,15 +292,9 @@ tasks {
 		// Temporary workaround for https://github.com/asciidoctor/asciidoctor-gradle-plugin/issues/599
 		inputs.dir(sourceDir).withPropertyName("sourceDir").withPathSensitivity(RELATIVE)
 
-		val platformVersion: String by project
-		val vintageVersion: String by project
-
 		attributeProviders += AsciidoctorAttributeProvider {
 			mapOf(
-				"jupiter-version" to version,
-				"platform-version" to platformVersion,
-				"vintage-version" to vintageVersion,
-				"bom-version" to version,
+				"version" to version,
 				"junit4-version" to libs.versions.junit4.get(),
 				"apiguardian-version" to libs.versions.apiguardian.get(),
 				"ota4j-version" to libs.versions.opentest4j.get(),
@@ -347,13 +333,6 @@ tasks {
 			inputs.dir(kotlin.srcDirs.first())
 		}
 
-		sourceSets["testRelease21"].apply {
-			attributes(mapOf(
-				"testRelease21Dir" to java.srcDirs.first()
-			))
-			inputs.dir(java.srcDirs.first())
-		}
-
 		jvm {
 			// To avoid warning, see https://github.com/asciidoctor/asciidoctor-gradle-plugin/issues/597
 			jvmArgs(
@@ -387,7 +366,7 @@ tasks {
 			include("user-guide/index.adoc")
 		}
 		copyAllResources()
-		attributes(mapOf("releaseNotesUrl" to "https://junit.org/junit5/docs/$docsVersion/release-notes/"))
+		attributes(mapOf("releaseNotesUrl" to "https://docs.junit.org/$docsVersion/release-notes/"))
 	}
 
 	val downloadJavadocElementLists by registering {
@@ -453,19 +432,20 @@ tasks {
 			noTimestamp(true)
 
 			addStringsOption("-module", ",").value = modularProjects.map { it.javaModuleName }
-			val moduleSourcePathOption = addPathOption("-module-source-path")
-			moduleSourcePathOption.value = modularProjects.map { it.file("src/module") }
-			moduleSourcePathOption.value.forEach { inputs.dir(it) }
-			addOption(ModuleSpecificJavadocFileOption("-patch-module", modularProjects.associate { project ->
-				project.javaModuleName to files(
-					project.sourceSets.named { it.startsWith("main") }.map { it.allJava.srcDirs }
-				).asPath
+			addOption(ModuleSpecificJavadocFileOption("-module-source-path", modularProjects.associate { project ->
+				project.javaModuleName to provider {
+					files(
+						project.sourceSets.named { it.startsWith("main") }.map {
+							it.allJava.srcDirs.filter { it.exists() }
+						}
+					).asPath
+				}
 			}))
-			addStringOption("-add-modules", "info.picocli,org.opentest4j.reporting.events")
+			addStringOption("-add-modules", "info.picocli,org.opentest4j.reporting.events,de.siegmar.fastcsv")
 			addOption(ModuleSpecificJavadocFileOption("-add-reads", mapOf(
-					"org.junit.platform.console" to "info.picocli",
-					"org.junit.platform.reporting" to "org.opentest4j.reporting.events",
-					"org.junit.jupiter.params" to "univocity.parsers"
+					"org.junit.platform.console" to provider { "info.picocli" },
+					"org.junit.platform.reporting" to provider { "org.opentest4j.reporting.events" },
+					"org.junit.jupiter.params" to provider { "de.siegmar.fastcsv" }
 			)))
 		}
 
@@ -476,10 +456,6 @@ tasks {
 
 		setMaxMemory("1024m")
 		options.destinationDirectory = layout.buildDirectory.dir("docs/javadoc").get().asFile
-
-		doFirst {
-			(options as CoreJavadocOptions).modulePath = classpath.files.toList()
-		}
 	}
 
 	val fixJavadoc by registering(Copy::class) {
@@ -495,7 +471,7 @@ tasks {
 		}
 		from(inputDir) {
 			filesMatching("**/*.html") {
-				val favicon = "<link rel=\"icon\" type=\"image/png\" href=\"https://junit.org/junit5/assets/img/junit5-logo.png\">"
+				val favicon = "<link rel=\"icon\" type=\"image/png\" href=\"https://junit.org/assets/img/junit5-logo.png\">"
 				filter { line ->
 					var result = if (line.startsWith("<head>")) line.replace("<head>", "<head>$favicon") else line
 					externalModulesWithoutModularJavadoc.forEach { (moduleName, baseUrl) ->
diff --git a/documentation/src/docs/asciidoc/docinfos/docinfo.html b/documentation/src/docs/asciidoc/docinfos/docinfo.html
index 30e46e0a474e..4e2828f34013 100644
--- a/documentation/src/docs/asciidoc/docinfos/docinfo.html
+++ b/documentation/src/docs/asciidoc/docinfos/docinfo.html
@@ -1,4 +1,4 @@
-<link rel="icon" type="image/png" href="https://junit.org/junit5/assets/img/junit5-logo.png" />
+<link rel="icon" type="image/png" href="https://junit.org/assets/img/junit5-logo.png" />
 <style>
   /* Tocbot dynamic TOC, works with tocbot 3.0.2 */
   /* Source: https://github.com/asciidoctor/asciidoctor/issues/699#issuecomment-321066006 */
diff --git a/documentation/src/docs/asciidoc/link-attributes.adoc b/documentation/src/docs/asciidoc/link-attributes.adoc
index 2342763e5680..70c71f7cba49 100644
--- a/documentation/src/docs/asciidoc/link-attributes.adoc
+++ b/documentation/src/docs/asciidoc/link-attributes.adoc
@@ -1,13 +1,13 @@
 :javadoc-root:                               link:../api
 ifdef::backend-pdf[]
-:javadoc-root:                               https://junit.org/junit5/docs/{docs-version}/api
+:javadoc-root:                               https://docs.junit.org/{docs-version}/api
 endif::[]
 // Snapshot Repository
-:snapshot-repo:                              https://central.sonatype.com/repository/maven-snapshots
+:snapshot-repo:                              https://central.sonatype.com/service/rest/repository/browse/maven-snapshots
 // Base Links
 :junit-team:                                 https://github.com/junit-team
-:junit5-repo:                                {junit-team}/junit5
-:current-branch:                             {junit5-repo}/tree/{release-branch}
+:junit-framework-repo:                       {junit-team}/junit-framework
+:current-branch:                             {junit-framework-repo}/tree/{release-branch}
 // Platform Commons
 :junit-platform-support-package:             {javadoc-root}/org.junit.platform.commons/org/junit/platform/commons/support/package-summary.html[org.junit.platform.commons.support]
 :AnnotationSupport:                          {javadoc-root}/org.junit.platform.commons/org/junit/platform/commons/support/AnnotationSupport.html[AnnotationSupport]
@@ -79,8 +79,6 @@ endif::[]
 // Platform Reporting
 :LegacyXmlReportGeneratingListener:          {javadoc-root}/org.junit.platform.reporting/org/junit/platform/reporting/legacy/xml/LegacyXmlReportGeneratingListener.html[LegacyXmlReportGeneratingListener]
 :OpenTestReportGeneratingListener:           {javadoc-root}/org.junit.platform.reporting/org/junit/platform/reporting/open/xml/OpenTestReportGeneratingListener.html[OpenTestReportGeneratingListener]
-// Platform Runner
-:JUnitPlatform-Runner:                       {javadoc-root}/org.junit.platform.runnner/org/junit/platform/runner/JUnitPlatform.html[JUnitPlatform]
 // Platform Suite
 :suite-api-package:                          {javadoc-root}/org.junit.platform.suite.api/org/junit/platform/suite/api/package-summary.html[org.junit.platform.suite.api]
 :junit-platform-suite-engine:                {javadoc-root}/org.junit.platform.suite.engine/org/junit/platform/suite/engine/package-summary.html[junit-platform-suite-engine]
@@ -118,7 +116,6 @@ endif::[]
 :ClassOrderer:                               {javadoc-root}/org.junit.jupiter.api/org/junit/jupiter/api/ClassOrderer.html[ClassOrderer]
 :ClassTemplate:                              {javadoc-root}/org.junit.jupiter.api/org/junit/jupiter/api/ClassTemplate.html[@ClassTemplate]
 :Disabled:                                   {javadoc-root}/org.junit.jupiter.api/org/junit/jupiter/api/Disabled.html[@Disabled]
-:MethodOrderer_Alphanumeric:                 {javadoc-root}/org.junit.jupiter.api/org/junit/jupiter/api/MethodOrderer.Alphanumeric.html[MethodOrderer.Alphanumeric]
 :MethodOrderer_DisplayName:                  {javadoc-root}/org.junit.jupiter.api/org/junit/jupiter/api/MethodOrderer.DisplayName.html[MethodOrderer.DisplayName]
 :MethodOrderer_MethodName:                   {javadoc-root}/org.junit.jupiter.api/org/junit/jupiter/api/MethodOrderer.MethodName.html[MethodOrderer.MethodName]
 :MethodOrderer_OrderAnnotation:              {javadoc-root}/org.junit.jupiter.api/org/junit/jupiter/api/MethodOrderer.OrderAnnotation.html[MethodOrderer.OrderAnnotation]
@@ -199,7 +196,7 @@ endif::[]
 :ArgumentsAccessor:                          {javadoc-root}/org.junit.jupiter.params/org/junit/jupiter/params/aggregator/ArgumentsAccessor.html[ArgumentsAccessor]
 :ArgumentsAggregator:                        {javadoc-root}/org.junit.jupiter.params/org/junit/jupiter/params/aggregator/ArgumentsAggregator.html[ArgumentsAggregator]
 :BeforeParameterizedClassInvocation:         {javadoc-root}/org.junit.jupiter.params/org/junit/jupiter/params/BeforeParameterizedClassInvocation.html[@BeforeParameterizedClassInvocation]
-:CsvArgumentsProvider:                       {junit5-repo}/blob/main/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/CsvArgumentsProvider.java[CsvArgumentsProvider]
+:CsvArgumentsProvider:                       {junit-framework-repo}/blob/main/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/CsvArgumentsProvider.java[CsvArgumentsProvider]
 :EmptySource:                                {javadoc-root}/org.junit.jupiter.params/org/junit/jupiter/params/provider/EmptySource.html[@EmptySource]
 :FieldSource:                                {javadoc-root}/org.junit.jupiter.params/org/junit/jupiter/params/provider/FieldSource.html[@FieldSource]
 :MethodSource:                               {javadoc-root}/org.junit.jupiter.params/org/junit/jupiter/params/provider/MethodSource.html[@MethodSource]
@@ -209,7 +206,7 @@ endif::[]
 :ParameterizedClass:                         {javadoc-root}/org.junit.jupiter.params/org/junit/jupiter/params/ParameterizedClass.html[@ParameterizedClass]
 :ParameterizedTest:                          {javadoc-root}/org.junit.jupiter.params/org/junit/jupiter/params/ParameterizedTest.html[@ParameterizedTest]
 :ParameterInfo:                              {javadoc-root}/org.junit.jupiter.params/org/junit/jupiter/params/support/ParameterInfo.html[ParameterInfo]
-:ValueArgumentsProvider:                     {junit5-repo}/blob/main/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/ValueArgumentsProvider.java[ValueArgumentsProvider]
+:ValueArgumentsProvider:                     {junit-framework-repo}/blob/main/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/ValueArgumentsProvider.java[ValueArgumentsProvider]
 // Jupiter Engine
 :junit-jupiter-engine:                       {javadoc-root}/org.junit.jupiter.engine/org/junit/jupiter/engine/package-summary.html[junit-jupiter-engine]
 // Jupiter Extension Implementations
@@ -229,19 +226,19 @@ endif::[]
 :EnableRuleMigrationSupport:                 {javadoc-root}/org.junit.jupiter.migrationsupport/org/junit/jupiter/migrationsupport/rules/EnableRuleMigrationSupport.html[@EnableRuleMigrationSupport]
 // Vintage
 :junit-vintage-engine:                       {javadoc-root}/org.junit.vintage.engine/org/junit/vintage/engine/package-summary.html[junit-vintage-engine]
-// Samples Repository
-:junit5-samples-repo:                        {junit-team}/junit5-samples
-:junit5-jupiter-starter-ant:                 {junit5-samples-repo}/tree/{release-branch}/junit5-jupiter-starter-ant[junit5-jupiter-starter-ant]
-:junit5-jupiter-starter-gradle-groovy:       {junit5-samples-repo}/tree/{release-branch}/junit5-jupiter-starter-gradle-groovy[junit5-jupiter-starter-gradle-groovy]
-:junit5-jupiter-starter-gradle-kotlin:       {junit5-samples-repo}/tree/{release-branch}/junit5-jupiter-starter-gradle-kotlin[junit5-jupiter-starter-gradle-kotlin]
-:junit5-jupiter-starter-gradle:              {junit5-samples-repo}/tree/{release-branch}/junit5-jupiter-starter-gradle[junit5-jupiter-starter-gradle]
-:junit5-jupiter-starter-maven:               {junit5-samples-repo}/tree/{release-branch}/junit5-jupiter-starter-maven[junit5-jupiter-starter-maven]
-:RandomParametersExtension:                  {junit5-samples-repo}/tree/{release-branch}/junit5-jupiter-extensions/src/main/java/com/example/random/RandomParametersExtension.java[RandomParametersExtension]
+// Examples Repository
+:junit-examples-repo:                        {junit-team}/junit-examples
+:junit-jupiter-starter-ant:                  {junit-examples-repo}/tree/{release-branch}/junit-jupiter-starter-ant[junit-jupiter-starter-ant]
+:junit-jupiter-starter-gradle-groovy:        {junit-examples-repo}/tree/{release-branch}/junit-jupiter-starter-gradle-groovy[junit-jupiter-starter-gradle-groovy]
+:junit-jupiter-starter-gradle-kotlin:        {junit-examples-repo}/tree/{release-branch}/junit-jupiter-starter-gradle-kotlin[junit-jupiter-starter-gradle-kotlin]
+:junit-jupiter-starter-gradle:               {junit-examples-repo}/tree/{release-branch}/junit-jupiter-starter-gradle[junit-jupiter-starter-gradle]
+:junit-jupiter-starter-maven:                {junit-examples-repo}/tree/{release-branch}/junit-jupiter-starter-maven[junit-jupiter-starter-maven]
+:RandomParametersExtension:                  {junit-examples-repo}/tree/{release-branch}/junit-jupiter-extensions/src/main/java/com/example/random/RandomParametersExtension.java[RandomParametersExtension]
 // Third-party Links
 :API:                                        https://apiguardian-team.github.io/apiguardian/docs/current/api/[@API]
 :API_Guardian:                               https://github.com/apiguardian-team/apiguardian[@API Guardian]
 :AssertJ:                                    https://assertj.github.io/doc/[AssertJ]
-:Gitter:                                     https://gitter.im/junit-team/junit5[Gitter]
+:DiscussionsQA:                              https://github.com/junit-team/junit-framework/discussions/categories/q-a[Q&A category on GitHub Discussions]
 :Hamcrest:                                   https://hamcrest.org/JavaHamcrest/[Hamcrest]
 :Jimfs:                                      https://google.github.io/jimfs/[Jimfs]
 :Log4j:                                      https://logging.apache.org/log4j/2.x/[Log4j]
diff --git a/documentation/src/docs/asciidoc/release-notes/index.adoc b/documentation/src/docs/asciidoc/release-notes/index.adoc
index 33d93ad199b4..d3e080b7985f 100644
--- a/documentation/src/docs/asciidoc/release-notes/index.adoc
+++ b/documentation/src/docs/asciidoc/release-notes/index.adoc
@@ -1,5 +1,5 @@
 [[release-notes]]
-= JUnit 5 Release Notes
+= JUnit Release Notes
 Stefan Bechtold; Sam Brannen; Johannes Link; Matthias Merdes; Marc Philipp; Juliette de Rancourt; Christian Stein
 //
 :basedir: {includedir}/release-notes
@@ -9,7 +9,7 @@ Stefan Bechtold; Sam Brannen; Johannes Link; Matthias Merdes; Marc Philipp; Juli
 :last-update-label!:
 //
 
-This document contains the _change log_ for all JUnit 5 releases since 5.12 GA.
+This document contains the _change log_ for all JUnit releases since 5.13 GA.
 
 Please refer to the <<../user-guide/index.adoc#user-guide,User Guide>> for comprehensive
 reference documentation for programmers writing tests, extension authors, and engine
@@ -17,16 +17,12 @@ authors as well as build tool and IDE vendors.
 
 include::{includedir}/link-attributes.adoc[]
 
-include::{basedir}/release-notes-5.13.0-RC1.adoc[]
+include::{basedir}/release-notes-6.0.0-M1.adoc[]
 
-include::{basedir}/release-notes-5.13.0-M3.adoc[]
+include::{basedir}/release-notes-5.13.3.adoc[]
 
-include::{basedir}/release-notes-5.13.0-M2.adoc[]
+include::{basedir}/release-notes-5.13.2.adoc[]
 
-include::{basedir}/release-notes-5.13.0-M1.adoc[]
+include::{basedir}/release-notes-5.13.1.adoc[]
 
-include::{basedir}/release-notes-5.12.2.adoc[]
-
-include::{basedir}/release-notes-5.12.1.adoc[]
-
-include::{basedir}/release-notes-5.12.0.adoc[]
+include::{basedir}/release-notes-5.13.0.adoc[]
diff --git a/documentation/src/docs/asciidoc/release-notes/release-notes-5.12.0.adoc b/documentation/src/docs/asciidoc/release-notes/release-notes-5.12.0.adoc
deleted file mode 100644
index 75ff54748e5f..000000000000
--- a/documentation/src/docs/asciidoc/release-notes/release-notes-5.12.0.adoc
+++ /dev/null
@@ -1,24 +0,0 @@
-[[release-notes-5.12.0]]
-== 5.12.0
-
-*Date of Release:* February 21, 2025
-
-*Scope:*
-
-* Output file attachments for tests and containers
-* Improvements to the Open Test Reporting XML output
-* Resource lock definition improvements
-* Thread dumps on test timeouts
-* Parameterized test validation improvements
-* Filtering support for auto-registered extensions
-* Kotlin contracts for assertions
-* Configurable Jupiter extension context scope
-* Enhancements to the `ConsoleLauncher`
-* Better support for GraalVM native image usage
-* Improved discovery support for file-based test engines
-* Customizable classpath scanning
-* Parallel execution support in JUnit Vintage engine
-* Numerous bug fixes and other enhancements
-
-For complete details consult the
-https://junit.org/junit5/docs/5.12.0/release-notes/index.html[5.12.0 Release Notes] online.
diff --git a/documentation/src/docs/asciidoc/release-notes/release-notes-5.12.1.adoc b/documentation/src/docs/asciidoc/release-notes/release-notes-5.12.1.adoc
deleted file mode 100644
index f41490897fb5..000000000000
--- a/documentation/src/docs/asciidoc/release-notes/release-notes-5.12.1.adoc
+++ /dev/null
@@ -1,38 +0,0 @@
-[[release-notes-5.12.1]]
-== 5.12.1
-
-*Date of Release:* March 14, 2025
-
-*Scope:* Bug fixes and enhancements since 5.12.0
-
-For a complete list of all _closed_ issues and pull requests for this release, consult the
-link:{junit5-repo}+/milestone/91?closed=1+[5.12.1] milestone page in the JUnit repository
-on GitHub.
-
-
-[[release-notes-5.12.1-junit-platform]]
-=== JUnit Platform
-
-[[release-notes-5.12.1-junit-platform-deprecations-and-breaking-changes]]
-==== Deprecations and Breaking Changes
-
-* Set stable module name `org.junit.platform.console.standalone` for the
-  `junit-platform-console-standalone` artifact, superseding the unstable name generated
-  from the name of the JAR file when putting the artifact on the module path.
-
-
-[[release-notes-5.12.1-junit-jupiter]]
-=== JUnit Jupiter
-
-[[release-notes-5.12.1-junit-jupiter-new-features-and-improvements]]
-==== New Features and Improvements
-
-* New `ExtensionContext.getEnclosingTestClasses()` method to help with migration away from
-  `AnnotationSupport.findAnnotation(Class, Class, SearchOption)` (deprecated since 1.12.0)
-  to `AnnotationSupport.findAnnotation(Class, Class, List)`.
-
-
-[[release-notes-5.12.1-junit-vintage]]
-=== JUnit Vintage
-
-No changes.
diff --git a/documentation/src/docs/asciidoc/release-notes/release-notes-5.12.2.adoc b/documentation/src/docs/asciidoc/release-notes/release-notes-5.12.2.adoc
deleted file mode 100644
index 224078ba645e..000000000000
--- a/documentation/src/docs/asciidoc/release-notes/release-notes-5.12.2.adoc
+++ /dev/null
@@ -1,33 +0,0 @@
-[[release-notes-5.12.2]]
-== 5.12.2
-
-*Date of Release:* April 11, 2025
-
-*Scope:* Bug fixes and enhancements since 5.12.1
-
-For a complete list of all _closed_ issues and pull requests for this release, consult the
-link:{junit5-repo}+/milestone/95?closed=1+[5.12.2] milestone page in the JUnit repository
-on GitHub.
-
-
-[[release-notes-5.12.2-junit-platform]]
-=== JUnit Platform
-
-No changes.
-
-
-[[release-notes-5.12.2-junit-jupiter]]
-=== JUnit Jupiter
-
-[[release-notes-5.12.2-junit-jupiter-bug-fixes]]
-==== Bug Fixes
-
-* Fix handling of `CleanupMode.ON_SUCCESS` with `@TempDir` that caused no temporary
-  directories (using that mode) to be deleted after the first failure even if the
-  corresponding tests passed.
-
-
-[[release-notes-5.12.2-junit-vintage]]
-=== JUnit Vintage
-
-No changes.
diff --git a/documentation/src/docs/asciidoc/release-notes/release-notes-5.13.0-M1.adoc b/documentation/src/docs/asciidoc/release-notes/release-notes-5.13.0-M1.adoc
deleted file mode 100644
index 4fd71ff43b85..000000000000
--- a/documentation/src/docs/asciidoc/release-notes/release-notes-5.13.0-M1.adoc
+++ /dev/null
@@ -1,101 +0,0 @@
-[[release-notes-5.13.0-M1]]
-== 5.13.0-M1
-
-*Date of Release:* March 21, 2025
-
-*Scope:*
-
-* Introduce `@ClassTemplate` and `@ParameterizedClass` support in JUnit Jupiter
-* Access to `ParameterInfo` for JUnit Jupiter extensions
-* New `@SentenceFragment` annotation for use with `IndicativeSentences` display name generator
-* Add `--redirect-stdout` and `--redirect-stderr` options to `ConsoleLauncher`
-* Introduce test _discovery_ support in `EngineTestKit`
-* Bug fixes and other minor improvements
-
-For a complete list of all _closed_ issues and pull requests for this release, consult the
-link:{junit5-repo}+/milestone/85?closed=1+[5.13.0-M1] milestone page in the JUnit
-repository on GitHub.
-
-
-[[release-notes-5.13.0-M1-junit-platform]]
-=== JUnit Platform
-
-[[release-notes-5.13.0-M1-junit-platform-bug-fixes]]
-==== Bug Fixes
-
-* Notify `LauncherDiscoveryListener` implementation registered via `LaucherConfig` or on
-  the `Launcher` of `selectorProcessed` events.
-
-[[release-notes-5.13.0-M1-junit-platform-new-features-and-improvements]]
-==== New Features and Improvements
-
-* New `ConsoleLauncher` options `--redirect-stdout` and `--redirect-stderr` for
-  redirecting `stdout` and `stderr` output streams to files.
-* Add `TestDescriptor.Visitor.composite(List)` factory method for creating a composite
-  visitor that delegates to the given visitors in order.
-* Introduce test _discovery_ support in `EngineTestKit` to ease testing for discovery
-  issues produced by a `TestEngine`. Please refer to the
-  <<../user-guide/index.adoc#testkit-engine, User Guide>> for details.
-* This milestone contains preliminary APIs for reporting issues encountered by test
-  engines during test discovery. However, these are still under active development and not
-  yet ready for general use. If you're a maintainer of a test engine, please wait for the
-  next milestone before adopting these new APIs. If you're interested, you can follow
-  along our progress in link:{junit5-repo}/issues/242[#242].
-
-
-[[release-notes-5.13.0-M1-junit-jupiter]]
-=== JUnit Jupiter
-
-[[release-notes-5.13.0-M1-junit-jupiter-bug-fixes]]
-==== Bug Fixes
-
-* If the `autoCloseArguments` attribute in `@ParameterizedTest` is set to `true`, all
-  arguments returned by registered `ArgumentsProvider` implementations are now closed even
-  if the test method declares fewer parameters.
-* `AutoCloseable` arguments returned by an `ArgumentsProvider` are now closed even if they
-  are wrapped with `Named`.
-* `AutoCloseable` arguments returned by an `ArgumentsProvider` are now closed even if a
-  failure happens prior to invoking the parameterized method.
-
-[[release-notes-5.13.0-M1-junit-jupiter-new-features-and-improvements]]
-==== New Features and Improvements
-
-* New `@ClassTemplate` annotation and `ClassTemplateInvocationContextProvider` API that
-  allow declaring a top-level or `@Nested` test class as a template to be invoked multiple
-  times. This may be used, for example, to inject different parameters to be used by all
-  tests in the class template or to set up each invocation of the class template
-  differently. Please refer to the
-  <<../user-guide/index.adoc#writing-tests-class-templates, User Guide>> for details.
-* New `BeforeClassTemplateInvocationCallback` and `AfterClassTemplateInvocationCallback`
-  extension callback interfaces allow implementing extensions that are invoked before and
-  after each invocation of a class template.
-* New `@ParameterizedClass` support that builds on `@ClassTemplate` and allows declaring a
-  top-level or `@Nested` test class as a parameterized test class to be invoked multiple
-  times with different arguments. The same `@...Source` annotations supported with
-  `@ParameterizedTest` may be used to provide arguments via constructor or field
-  injection. Please refer to the
-  <<../user-guide/index.adoc#writing-tests-parameterized-tests, User Guide>> for details.
-* New `@ParameterizedClass`-specific
-  `@BeforeParameterizedClassInvocation`/`@AfterParameterizedClassInvocation` lifecycle
-  methods that are invoked once before/after each invocation of the parameterized class.
-* Provide access to the parameters and resolved arguments of a `@ParameterizedTest` or
-  `@ParameterizedClass` by storing `ParameterInfo` in the `ExtensionContext.Store` for
-  retrieval by other extensions. Please refer to the
-  link:../api/org.junit.jupiter.params/org/junit/jupiter/params/support/ParameterInfo.html[Javadoc]
-  for details.
-* New `@SentenceFragment` annotation which allows one to supply custom text for individual
-  sentence fragments when using the `IndicativeSentences` `DisplayNameGenerator`. See the
-  updated documentation in the
-  <<../user-guide/index.adoc#writing-tests-display-name-generator, User Guide>> for an
-  example.
-* New `TestTemplateInvocationContext.prepareInvocation(ExtensionContext)` callback method
-  which allows extensions to prepare the `ExtensionContext` before the test template
-  method is invoked. This may be used, for example, to store entries in the
-  `ExtensionContext.Store` to benefit from its cleanup support or for retrieval by other
-  extensions.
-
-
-[[release-notes-5.13.0-M1-junit-vintage]]
-=== JUnit Vintage
-
-No changes.
diff --git a/documentation/src/docs/asciidoc/release-notes/release-notes-5.13.0-M2.adoc b/documentation/src/docs/asciidoc/release-notes/release-notes-5.13.0-M2.adoc
deleted file mode 100644
index 725a3bba0c1a..000000000000
--- a/documentation/src/docs/asciidoc/release-notes/release-notes-5.13.0-M2.adoc
+++ /dev/null
@@ -1,33 +0,0 @@
-[[release-notes-5.13.0-M2]]
-== 5.13.0-M2
-
-*Date of Release:* March 24, 2025
-
-*Scope:* Fix regression in 5.13.0-M1
-
-For a complete list of all _closed_ issues and pull requests for this release, consult the
-link:{junit5-repo}+/milestone/92?closed=1+[5.13.0-M2] milestone page in the JUnit
-repository on GitHub.
-
-
-[[release-notes-5.13.0-M2-junit-platform]]
-=== JUnit Platform
-
-No changes.
-
-
-[[release-notes-5.13.0-M2-junit-jupiter]]
-=== JUnit Jupiter
-
-[[release-notes-5.13.0-M2-junit-jupiter-bug-fixes]]
-==== Bug Fixes
-
-* Fix regression when executing `@Nested` classes compiled without `-parameters` in
-  versions of Java prior to 21.
-
-
-[[release-notes-5.13.0-M2-junit-vintage]]
-=== JUnit Vintage
-
-
-No changes.
diff --git a/documentation/src/docs/asciidoc/release-notes/release-notes-5.13.0-M3.adoc b/documentation/src/docs/asciidoc/release-notes/release-notes-5.13.0-M3.adoc
deleted file mode 100644
index 403116a7fb51..000000000000
--- a/documentation/src/docs/asciidoc/release-notes/release-notes-5.13.0-M3.adoc
+++ /dev/null
@@ -1,115 +0,0 @@
-[[release-notes-5.13.0-M3]]
-== 5.13.0-M3
-
-*Date of Release:* May 2, 2025
-
-*Scope:*
-
-* Reporting of discovery issues for test engines
-* Resource management for launcher sessions and execution requests
-* GraalVM: removal of `native-image.properties` files from JARs
-
-For a complete list of all _closed_ issues and pull requests for this release, consult the
-link:{junit5-repo}+/milestone/93?closed=1+[5.13.0-M3] milestone page in the JUnit
-repository on GitHub.
-
-
-[[release-notes-5.13.0-M3-overall-improvements]]
-=== Overall Changes
-
-[[release-notes-5.13.0-M3-overall-new-features-and-improvements]]
-==== Deprecations and Breaking Changes
-
-* The JUnit feature in GraalVM Native Build Tools has been rewritten to no longer require
-  JUnit classes to be initialized at build time. Therefore, JUnit's JARs no longer ship
-  with `native-image.properties` files that contain `--initialize-at-build-time` options
-  (introduced in 5.12.0). Please update to the most recent version of GraalVM Native Build
-  Tools prior to upgrading to this version of JUnit.
-
-
-[[release-notes-5.13.0-M3-junit-platform]]
-=== JUnit Platform
-
-[[release-notes-5.13.0-M3-junit-platform-bug-fixes]]
-==== Bug Fixes
-
-* Reintroduce support for JVM shutdown hooks when using the `-cp`/`--classpath` option of
-  the `ConsoleLauncher`. Prior to this release, the created class loader was closed prior
-  to JVM shutdown hooks being invoked, which caused hooks to fail with a
-  `ClassNotFoundException` when loading classes during shutdown.
-
-[[release-notes-5.13.0-M3-junit-platform-new-features-and-improvements]]
-==== New Features and Improvements
-
-* Introduce resource management mechanism that allows preparing and sharing state across
-  executions or test engines via stores that are scoped to a `LauncherSession` or
-  `ExecutionRequest`. The Jupiter API uses these stores as ancestors to the `Store`
-  instances accessible via `ExtensionContext` and provides a new method to access them
-  directly. Please refer to the User Guide for examples of managing
-  <<../user-guide/index.adoc#launcher-api-launcher-session-listeners-tool-example-usage, session-scoped>>
-  and
-  <<../user-guide/index.adoc#launcher-api-managing-state-across-test-engines, request-scoped>>
-  resources.
-* Introduce a mechanism for `TestEngine` implementations to report issues encountered
-  during test discovery. If an engine reports a `DiscoveryIssue` with a `Severity` equal
-  to or higher than a configurable critical severity, its tests will not be executed.
-  Instead, the engine will be reported as failed during execution with a failure message
-  listing all critical issues. Non-critical issues will be logged but will not prevent the
-  engine from executing its tests. The critical severity can be configured via a new
-  configuration parameter and, currently, defaults to `ERROR`. Please refer to the
-  <<../user-guide/index.adoc#running-tests-discovery-issues, User Guide>> for details.
-+
-If you're a test engine maintainer, please see the
-<<../user-guide/index.adoc#test-engines-discovery-issues, User Guide>> for details on how
-to start reporting discovery issues.
-* Start reporting discovery issues for problematic `@Suite` classes:
-  - Invalid `@Suite` class declarations (for example, when `private`)
-  - Invalid `@BeforeSuite`/`@AfterSuite` method declarations (for example, when not
-    `static`)
-  - Cyclic dependencies between `@Suite` classes
-* Make validation of including `EngineFilters` more strict to avoid misconfiguration, for
-  example, due to typos. Prior to this release, an exception was only thrown when _none_
-  of a filter's included IDs matched any engine. Now, an exception is thrown if at least
-  one included ID across all filters did not match any engine.
-
-
-[[release-notes-5.13.0-M3-junit-jupiter]]
-=== JUnit Jupiter
-
-[[release-notes-5.13.0-M3-junit-jupiter-new-features-and-improvements]]
-==== New Features and Improvements
-
-* Start reporting discovery issues for potentially problematic test classes:
-    - Invalid `@Test` and `@TestTemplate` method declarations (for example, when return
-      type is not `void`)
-    - Invalid `@TestFactory` methods (for example, when return type is invalid)
-    - Multiple method-level annotations (for example, `@Test` and `@TestTemplate`)
-    - Invalid test class and `@Nested` class declarations (for example, `static` `@Nested`
-      classes)
-    - Potentially missing `@Nested` annotations (for example, non-abstract inner classes
-      that contain test methods)
-    - Invalid lifecycle method declarations (for example, when `private`)
-    - Invalid `@Tag` syntax
-    - Blank `@DisplayName` declarations
-    - Blank `@SentenceFragment` declarations
-    - `@BeforeParameterizedClassInvocation` and `@AfterParameterizedClassInvocation`
-      methods declared in non-parameterized test classes
-* By default, `AutoCloseable` objects put into `ExtensionContext.Store` are now treated
-  like instances of `CloseableResource` (which has been deprecated) and are closed
-  automatically when the store is closed at the end of the test lifecycle. It's possible
-  to <<../user-guide/index.adoc#extensions-keeping-state-autocloseable-support, revert to the old behavior>>
-  via a configuration parameter. Please also see the
-  <<../user-guide/index.adoc#extensions-keeping-state-autocloseable-migration, migration note>>
-  for third-party extensions wanting to support both JUnit 5.13 and earlier versions.
-* `java.util.Locale` arguments are now converted according to the IETF BCP 47 language tag
-  format. See the
-  <<../user-guide/index.adoc#writing-tests-parameterized-tests-argument-conversion-implicit, User Guide>>
-  for details.
-* Avoid reporting potentially misleading validation exception for `@ParameterizedClass`
-  test classes and `@ParameterizedTest` methods as suppressed exception for earlier
-  failures.
-
-[[release-notes-5.13.0-M3-junit-vintage]]
-=== JUnit Vintage
-
-No changes.
diff --git a/documentation/src/docs/asciidoc/release-notes/release-notes-5.13.0-RC1.adoc b/documentation/src/docs/asciidoc/release-notes/release-notes-5.13.0-RC1.adoc
deleted file mode 100644
index 2cac539083b9..000000000000
--- a/documentation/src/docs/asciidoc/release-notes/release-notes-5.13.0-RC1.adoc
+++ /dev/null
@@ -1,37 +0,0 @@
-[[release-notes-5.13.0-RC1]]
-== 5.13.0-RC1
-
-*Date of Release:* May 16, 2025
-
-*Scope:* Minor bug fixes and enhancements since 5.13.0-M1
-
-For a complete list of all _closed_ issues and pull requests for this release, consult the
-link:{junit5-repo}+/milestone/96?closed=1+[5.13.0-RC1] milestone page in the JUnit
-repository on GitHub.
-
-
-[[release-notes-5.13.0-RC1-junit-platform]]
-=== JUnit Platform
-
-No changes.
-
-
-[[release-notes-5.13.0-RC1-junit-jupiter]]
-=== JUnit Jupiter
-
-[[release-notes-5.13.0-RC1-junit-jupiter-bug-fixes]]
-==== Bug Fixes
-
-* Validate _all_ versions specified in `@EnabledOnJre` and `@DisabledOnJre` annotations.
-
-[[release-notes-5.13.0-RC1-junit-jupiter-new-features-and-improvements]]
-==== New Features and Improvements
-
-* Add support for Kotlin `Sequence` to `@MethodSource`, `@FieldSource`, and
-  `@TestFactory`.
-
-
-[[release-notes-5.13.0-RC1-junit-vintage]]
-=== JUnit Vintage
-
-No changes.
diff --git a/documentation/src/docs/asciidoc/release-notes/release-notes-5.13.0.adoc b/documentation/src/docs/asciidoc/release-notes/release-notes-5.13.0.adoc
new file mode 100644
index 000000000000..42c5a8614825
--- /dev/null
+++ b/documentation/src/docs/asciidoc/release-notes/release-notes-5.13.0.adoc
@@ -0,0 +1,188 @@
+[[release-notes-5.13.0]]
+== 5.13.0
+
+*Date of Release:* May 30, 2025
+
+*Scope:*
+
+* Introduce `@ClassTemplate` and `@ParameterizedClass` support in JUnit Jupiter
+* Access to `ParameterInfo` for JUnit Jupiter extensions
+* New `@SentenceFragment` annotation for use with `IndicativeSentences` display name generator
+* Add `--redirect-stdout` and `--redirect-stderr` options to `ConsoleLauncher`
+* Introduce test _discovery_ support in `EngineTestKit`
+* Reporting of discovery issues for test engines
+* Resource management for launcher sessions and execution requests
+* GraalVM: removal of `native-image.properties` files from JARs
+* Bug fixes and other minor improvements
+
+For a complete list of all _closed_ issues and pull requests for this release, consult the
+link:{junit-framework-repo}+/milestone/85?closed=1+[5.13.0-M1],
+link:{junit-framework-repo}+/milestone/92?closed=1+[5.13.0-M2],
+link:{junit-framework-repo}+/milestone/93?closed=1+[5.13.0-M3],
+link:{junit-framework-repo}+/milestone/96?closed=1+[5.13.0-RC1],
+and link:{junit-framework-repo}+/milestone/94?closed=1+[5.13.0] milestone pages in the
+JUnit repository on GitHub.
+
+
+[[release-notes-5.13.0-overall-improvements]]
+=== Overall Changes
+
+[[release-notes-5.13.0-overall-new-features-and-improvements]]
+==== Deprecations and Breaking Changes
+
+* The JUnit feature in GraalVM Native Build Tools (NBT) has been rewritten to no longer
+  require JUnit classes to be initialized at build time when running on JDK 22 and later.
+  Therefore, JUnit's JARs no longer ship with `native-image.properties` files that contain
+  `--initialize-at-build-time` options (introduced in 5.12.0). Please update to the most
+  recent version of GraalVM Native Build Tools prior to upgrading to this version of
+  JUnit. Please refer to the
+  https://github.com/junit-team/junit-framework/wiki/Upgrading-to-JUnit-5.13[Upgrade Instructions]
+  in the wiki for details if you're on NBT 0.10.x or earlier.
+
+
+[[release-notes-5.13.0-junit-platform]]
+=== JUnit Platform
+
+[[release-notes-5.13.0-junit-platform-bug-fixes]]
+==== Bug Fixes
+
+* Notify `LauncherDiscoveryListener` implementation registered via `LaucherConfig` or on
+  the `Launcher` of `selectorProcessed` events.
+* Reintroduce support for JVM shutdown hooks when using the `-cp`/`--classpath` option of
+  the `ConsoleLauncher`. Prior to this release, the created class loader was closed prior
+  to JVM shutdown hooks being invoked, which caused hooks to fail with a
+  `ClassNotFoundException` when loading classes during shutdown.
+* Fix support of `--uid` and `--select-unique-id` options in the console launcher.
+
+[[release-notes-5.13.0-junit-platform-new-features-and-improvements]]
+==== New Features and Improvements
+
+* Introduce a mechanism for `TestEngine` implementations to report issues encountered
+  during test discovery. If an engine reports a `DiscoveryIssue` with a `Severity` equal
+  to or higher than a configurable critical severity, its tests will not be executed.
+  Instead, the engine will be reported as failed during execution with a failure message
+  listing all critical issues. Non-critical issues will be logged but will not prevent the
+  engine from executing its tests. The critical severity can be configured via a new
+  configuration parameter and, currently, defaults to `ERROR`. Please refer to the
+  <<../user-guide/index.adoc#running-tests-discovery-issues, User Guide>> for details.
++
+If you're a test engine maintainer, please see the
+<<../user-guide/index.adoc#test-engines-discovery-issues, User Guide>> for details on how
+to start reporting discovery issues.
+* Start reporting discovery issues for problematic `@Suite` classes:
+  - Invalid `@Suite` class declarations (for example, when `private`)
+  - Invalid `@BeforeSuite`/`@AfterSuite` method declarations (for example, when not
+    `static`)
+  - Cyclic dependencies between `@Suite` classes
+* Introduce resource management mechanism that allows preparing and sharing state across
+  executions or test engines via stores that are scoped to a `LauncherSession` or
+  `ExecutionRequest`. The Jupiter API uses these stores as ancestors to the `Store`
+  instances accessible via `ExtensionContext` and provides a new method to access them
+  directly. Please refer to the User Guide for examples of managing
+  <<../user-guide/index.adoc#launcher-api-launcher-session-listeners-tool-example-usage, session-scoped>>
+  and
+  <<../user-guide/index.adoc#launcher-api-managing-state-across-test-engines, request-scoped>>
+  resources.
+* New `ConsoleLauncher` options `--redirect-stdout` and `--redirect-stderr` for
+  redirecting `stdout` and `stderr` output streams to files.
+* Add `TestDescriptor.Visitor.composite(List)` factory method for creating a composite
+  visitor that delegates to the given visitors in order.
+* Introduce test _discovery_ support in `EngineTestKit` to ease testing for discovery
+  issues produced by a `TestEngine`. Please refer to the
+  <<../user-guide/index.adoc#testkit-engine, User Guide>> for details.
+* Make validation of including `EngineFilters` more strict to avoid misconfiguration, for
+  example, due to typos. Prior to this release, an exception was only thrown when _none_
+  of a filter's included IDs matched any engine. Now, an exception is thrown if at least
+  one included ID across all filters did not match any engine.
+
+
+[[release-notes-5.13.0-junit-jupiter]]
+=== JUnit Jupiter
+
+[[release-notes-5.13.0-junit-jupiter-bug-fixes]]
+==== Bug Fixes
+
+* If the `autoCloseArguments` attribute in `@ParameterizedTest` is set to `true`, all
+  arguments returned by registered `ArgumentsProvider` implementations are now closed even
+  if the test method declares fewer parameters.
+* `AutoCloseable` arguments returned by an `ArgumentsProvider` are now closed even if they
+  are wrapped with `Named`.
+* `AutoCloseable` arguments returned by an `ArgumentsProvider` are now closed even if a
+  failure happens prior to invoking the parameterized method.
+* Validate _all_ versions specified in `@EnabledOnJre` and `@DisabledOnJre` annotations.
+
+[[release-notes-5.13.0-junit-jupiter-new-features-and-improvements]]
+==== New Features and Improvements
+
+* New `@ClassTemplate` annotation and `ClassTemplateInvocationContextProvider` API that
+  allow declaring a top-level or `@Nested` test class as a template to be invoked multiple
+  times. This may be used, for example, to inject different parameters to be used by all
+  tests in the class template or to set up each invocation of the class template
+  differently. Please refer to the
+  <<../user-guide/index.adoc#writing-tests-class-templates, User Guide>> for details.
+* New `BeforeClassTemplateInvocationCallback` and `AfterClassTemplateInvocationCallback`
+  extension callback interfaces allow implementing extensions that are invoked before and
+  after each invocation of a class template.
+* New `@ParameterizedClass` support that builds on `@ClassTemplate` and allows declaring a
+  top-level or `@Nested` test class as a parameterized test class to be invoked multiple
+  times with different arguments. The same `@...Source` annotations supported with
+  `@ParameterizedTest` may be used to provide arguments via constructor or field
+  injection. Please refer to the
+  <<../user-guide/index.adoc#writing-tests-parameterized-tests, User Guide>> for details.
+* New `@ParameterizedClass`-specific
+  `@BeforeParameterizedClassInvocation`/`@AfterParameterizedClassInvocation` lifecycle
+  methods that are invoked once before/after each invocation of the parameterized class.
+* Provide access to the parameters and resolved arguments of a `@ParameterizedTest` or
+  `@ParameterizedClass` by storing `ParameterInfo` in the `ExtensionContext.Store` for
+  retrieval by other extensions. Please refer to the
+  link:../api/org.junit.jupiter.params/org/junit/jupiter/params/support/ParameterInfo.html[Javadoc]
+  for details.
+* New `@SentenceFragment` annotation which allows one to supply custom text for individual
+  sentence fragments when using the `IndicativeSentences` `DisplayNameGenerator`. See the
+  updated documentation in the
+  <<../user-guide/index.adoc#writing-tests-display-name-generator, User Guide>> for an
+  example.
+* New `TestTemplateInvocationContext.prepareInvocation(ExtensionContext)` callback method
+  which allows extensions to prepare the `ExtensionContext` before the test template
+  method is invoked. This may be used, for example, to store entries in the
+  `ExtensionContext.Store` to benefit from its cleanup support or for retrieval by other
+  extensions.
+* Start reporting discovery issues for potentially problematic test classes:
+    - Invalid `@Test` and `@TestTemplate` method declarations (for example, when return
+      type is not `void`)
+    - Invalid `@TestFactory` methods (for example, when return type is invalid)
+    - Multiple method-level annotations (for example, `@Test` and `@TestTemplate`)
+    - Invalid test class and `@Nested` class declarations (for example, `static` `@Nested`
+      classes)
+    - Potentially missing `@Nested` annotations (for example, non-abstract inner classes
+      that contain test methods)
+    - Invalid lifecycle method declarations (for example, when `private`)
+    - Invalid `@Tag` syntax
+    - Blank `@DisplayName` declarations
+    - Blank `@SentenceFragment` declarations
+    - `@BeforeParameterizedClassInvocation` and `@AfterParameterizedClassInvocation`
+      methods declared in non-parameterized test classes
+* By default, `AutoCloseable` objects put into `ExtensionContext.Store` are now treated
+  like instances of `CloseableResource` (which has been deprecated) and are closed
+  automatically when the store is closed at the end of the test lifecycle. It's possible
+  to <<../user-guide/index.adoc#extensions-keeping-state-autocloseable-support, revert to the old behavior>>
+  via a configuration parameter. Please also see the
+  <<../user-guide/index.adoc#extensions-keeping-state-autocloseable-migration, migration note>>
+  for third-party extensions wanting to support both JUnit 5.13 and earlier versions.
+* `java.util.Locale` arguments are now converted according to the IETF BCP 47 language tag
+  format. See the
+  <<../user-guide/index.adoc#writing-tests-parameterized-tests-argument-conversion-implicit, User Guide>>
+  for details.
+* Avoid reporting potentially misleading validation exception for `@ParameterizedClass`
+  test classes and `@ParameterizedTest` methods as suppressed exception for earlier
+  failures.
+* Add support for Kotlin `Sequence` to `@MethodSource`, `@FieldSource`, and
+  `@TestFactory`.
+* Allow publishing files to an existing directory via `TestReporter` and
+  `ExtensionContext`, for example, when re-running a test class.
+
+
+[[release-notes-5.13.0-junit-vintage]]
+=== JUnit Vintage
+
+No changes.
diff --git a/documentation/src/docs/asciidoc/release-notes/release-notes-5.13.1.adoc b/documentation/src/docs/asciidoc/release-notes/release-notes-5.13.1.adoc
new file mode 100644
index 000000000000..92fc32281407
--- /dev/null
+++ b/documentation/src/docs/asciidoc/release-notes/release-notes-5.13.1.adoc
@@ -0,0 +1,39 @@
+[[release-notes-5.13.1]]
+== 5.13.1
+
+*Date of Release:* June 7, 2025
+
+*Scope:* Bug fixes and enhancements since 5.13.0
+
+For a complete list of all _closed_ issues and pull requests for this release, consult the
+link:{junit-framework-repo}+/milestone/97?closed=1+[5.13.1] milestone page in the JUnit
+repository on GitHub.
+
+
+[[release-notes-5.13.1-junit-platform]]
+=== JUnit Platform
+
+No changes.
+
+
+[[release-notes-5.13.1-junit-jupiter]]
+=== JUnit Jupiter
+
+[[release-notes-5.13.1-junit-jupiter-bug-fixes]]
+==== Bug Fixes
+
+* The 5.13.0 release introduced a regression regarding the execution order in test classes
+  containing both test methods and `@Nested` test classes. When classpath scanning was
+  used during test discovery -- for example, when resolving a package selector for a
+  `@Suite` class -- test methods in `@Nested` classes were executed _before_ test methods
+  in their enclosing class. This undesired change in behavior has now been reverted so
+  that tests in `@Nested` test classes are always executed _after_ tests in enclosing test
+  classes again.
+* Fix support for `AnnotationBasedArgumentsProvider` implementations that override the
+  deprecated `provideArguments(ExtensionContext, Annotation)` method.
+
+
+[[release-notes-5.13.1-junit-vintage]]
+=== JUnit Vintage
+
+No changes
diff --git a/documentation/src/docs/asciidoc/release-notes/release-notes-5.13.2.adoc b/documentation/src/docs/asciidoc/release-notes/release-notes-5.13.2.adoc
new file mode 100644
index 000000000000..ae95787331ba
--- /dev/null
+++ b/documentation/src/docs/asciidoc/release-notes/release-notes-5.13.2.adoc
@@ -0,0 +1,49 @@
+[[release-notes-5.13.2]]
+== 5.13.2
+
+*Date of Release:* June 24, 2025
+
+*Scope:* Bug fixes and enhancements since 5.13.0
+
+For a complete list of all _closed_ issues and pull requests for this release, consult the
+link:{junit-framework-repo}+/milestone/98?closed=1+[5.13.2] milestone page in the JUnit
+repository on GitHub.
+
+
+[[release-notes-5.13.2-junit-platform]]
+=== JUnit Platform
+
+[[release-notes-5.13.2-junit-platform-deprecations-and-breaking-changes]]
+==== Deprecations and Breaking Changes
+
+* Including information about the Git repository (such as the commit hash and branch name)
+  in the Open Test Reporting XML format is now an opt-in feature that can be enabled via a
+  configuration parameter. Please refer to the
+  <<../user-guide/index.adoc#junit-platform-reporting-open-test-reporting, User Guide>>
+  for details.
+
+
+[[release-notes-5.13.2-junit-jupiter]]
+=== JUnit Jupiter
+
+[[release-notes-5.13.2-junit-jupiter-bug-fixes]]
+==== Bug Fixes
+
+* Stop reporting discovery issues for cyclic inner class hierarchies not annotated with
+  `@Nested`.
+* Stop reporting discovery issues for _abstract_ inner classes that contain test methods
+  but are not annotated with `@Nested`.
+* Stop reporting discovery issues for _abstract_ test methods. While they won't be
+  executed, it's a valid pattern to annotate them with `@Test` for documentation purposes
+  and override them in subclasses while re-declaring the `@Test` annotation.
+
+[[release-notes-5.13.2-junit-jupiter-new-features-and-improvements]]
+==== New Features and Improvements
+
+* `JAVA_26` has been added to the `JRE` enum for use with JRE-based execution conditions.
+
+
+[[release-notes-5.13.2-junit-vintage]]
+=== JUnit Vintage
+
+No changes.
diff --git a/documentation/src/docs/asciidoc/release-notes/release-notes-5.13.3.adoc b/documentation/src/docs/asciidoc/release-notes/release-notes-5.13.3.adoc
new file mode 100644
index 000000000000..69472a7905df
--- /dev/null
+++ b/documentation/src/docs/asciidoc/release-notes/release-notes-5.13.3.adoc
@@ -0,0 +1,68 @@
+[[release-notes-5.13.3]]
+== 5.13.3
+
+*Date of Release:* ❓
+
+*Scope:* ❓
+
+For a complete list of all _closed_ issues and pull requests for this release, consult the
+link:{junit-framework-repo}+/milestone/100?closed=1+[5.13.3] milestone page in the JUnit
+repository on GitHub.
+
+
+[[release-notes-5.13.3-junit-platform]]
+=== JUnit Platform
+
+[[release-notes-5.13.3-junit-platform-bug-fixes]]
+==== Bug Fixes
+
+* ❓
+
+[[release-notes-5.13.3-junit-platform-deprecations-and-breaking-changes]]
+==== Deprecations and Breaking Changes
+
+* ❓
+
+[[release-notes-5.13.3-junit-platform-new-features-and-improvements]]
+==== New Features and Improvements
+
+* ❓
+
+
+[[release-notes-5.13.3-junit-jupiter]]
+=== JUnit Jupiter
+
+[[release-notes-5.13.3-junit-jupiter-bug-fixes]]
+==== Bug Fixes
+
+* Stop reporting discovery issues for composed annotation classes that are meta-annotated
+  with `@Nested`.
+
+[[release-notes-5.13.3-junit-jupiter-deprecations-and-breaking-changes]]
+==== Deprecations and Breaking Changes
+
+* ❓
+
+[[release-notes-5.13.3-junit-jupiter-new-features-and-improvements]]
+==== New Features and Improvements
+
+* ❓
+
+
+[[release-notes-5.13.3-junit-vintage]]
+=== JUnit Vintage
+
+[[release-notes-5.13.3-junit-vintage-bug-fixes]]
+==== Bug Fixes
+
+* ❓
+
+[[release-notes-5.13.3-junit-vintage-deprecations-and-breaking-changes]]
+==== Deprecations and Breaking Changes
+
+* ❓
+
+[[release-notes-5.13.3-junit-vintage-new-features-and-improvements]]
+==== New Features and Improvements
+
+* ❓
diff --git a/documentation/src/docs/asciidoc/release-notes/release-notes-6.0.0-M1.adoc b/documentation/src/docs/asciidoc/release-notes/release-notes-6.0.0-M1.adoc
new file mode 100644
index 000000000000..d43f17f1d5fd
--- /dev/null
+++ b/documentation/src/docs/asciidoc/release-notes/release-notes-6.0.0-M1.adoc
@@ -0,0 +1,154 @@
+[[release-notes-6.0.0-M1]]
+== 6.0.0-M1
+
+*Date of Release:* June 27, 2025
+
+*Scope:*
+
+* Require Java 17 and Kotlin 2.2
+* Single version number for Platform, Jupiter, and Vintage
+* Use JSpecify's annotations to document nullability
+* Remove various deprecated behaviors and APIs
+* Integrate JFR functionality into junit-platform-launcher
+* Discontinue junit-platform-runner and junit-platform-jfr
+* Switch to FastCSV library for `@Csv\{File}Source`
+* Add support for using Kotlin `suspend` functions as test methods
+
+For a complete list of all _closed_ issues and pull requests for this release, consult the
+link:{junit-framework-repo}+/milestone/87?closed=1+[6.0.0-M1] milestone page in the JUnit
+repository on GitHub.
+
+
+[[release-notes-6.0.0-M1-overall-improvements]]
+=== Overall Improvements
+
+[[release-notes-6.0.0-M1-overall-deprecations-and-breaking-changes]]
+==== Deprecations and Breaking Changes
+
+* Minimum required Java version is now 17.
+* Minimum required Kotlin version is now 2.2.
+* Platform, Jupiter, and Vintage artifacts now use the same version number.
+
+[[release-notes-6.0.0-M1-overall-new-features-and-improvements]]
+==== New Features and Improvements
+
+* All JUnit modules now use https://jspecify.dev/[JSpecify]'s nullability annotations to
+  indicate which method parameters, return types, etc. can be `null`.
+
+
+[[release-notes-6.0.0-M1-junit-platform]]
+=== JUnit Platform
+
+[[release-notes-6.0.0-M1-junit-platform-deprecations-and-breaking-changes]]
+==== Deprecations and Breaking Changes
+
+* Remove deprecated support for running the `ConsoleLauncher` without specifying a
+  subcommand.
+* Remove support for deprecated non-conventional `ConsoleLauncher` options such as
+  `--h` (rather than `-h`) or `-help` (rather than `--help`).
+* The `junit-platform-runner` module that provided the JUnit 4 based `JUnitPlatform`
+  runner has been discontinued.
+* The `junit-platform-jfr` module that provided custom Java Flight Recorder (JFR) events
+  for test discovery and execution has been discontinued. Instead, the functionality is
+  now available directly in `junit-platform-launcher` without requiring an additional
+  dependency.
+* Support for Maven Surefire/Failsafe versions less than 3.0.0 has been dropped.
+* The following deprecated APIs have been removed:
+  - `ReflectionSupport.loadClass(String)` method
+  - `ReflectionUtils.readFieldValue(...)` methods
+  - `ReflectionUtils.getMethod(...)` method
+  - `BlacklistedExceptions` class
+  - `PreconditionViolationException` class (from `org.junit.platform.commons.util`)
+  - `ClasspathScanningSupport` class
+  - `ConfigurationParameters.size()` method
+  - `MethodSelector.getMethodParameterTypes()` method
+  - `NestedMethodSelector.getMethodParameterTypes()` method
+  - `ReportEntry()` constructor
+  - `SingleTestExecutor` class
+  - `LauncherDiscoveryRequestBuilder()` constructor
+  - `LegacyReportingUtils` class
+  - `TestPlan.add(TestIdentifier)`, `TestPlan.getChildren(String)`, and
+    `TestPlan.getTestIdentifier(String)` methods
+  - `TestPlan.add(TestIdentifier)` and `TestPlan.getChildren(String)` methods
+  - `@UseTechnicalNames` annotation
+  - `EngineTestKit.execute(String, EngineDiscoveryRequest)`,
+    `EngineTestKit.execute(TestEngine, EngineDiscoveryRequest)`, and
+    `EngineTestKit.Builder.filters(...)` methods
+* Support for "legacy semantics" for field and method searches that used to be
+  configurable via the `junit.platform.reflection.search.useLegacySemantics` system
+  property has been removed. JUnit now always adheres to standard Java semantics regarding
+  whether a given field or method is visible or overridden according to the rules of the
+  Java language.
+* The type bounds of the following methods have been changed to be more flexible and allow
+  nullable and non-nullable types:
+  - `ConfigurationParameters.get(String, Function)`
+  - `NamespacedHierarchicalStore.getOrComputeIfAbsent(N, K, Function)`
+  - `NamespacedHierarchicalStore.getOrComputeIfAbsent(N, K, Function, Class)`
+
+
+[[release-notes-6.0.0-M1-junit-jupiter]]
+=== JUnit Jupiter
+
+[[release-notes-6.0.0-M1-junit-jupiter-deprecations-and-breaking-changes]]
+==== Deprecations and Breaking Changes
+
+* The following deprecated APIs have been removed:
+  - `MethodOrderer.Alphanumeric` class
+  - `InvocationInterceptor.interceptDynamicTest(Invocation, ExtensionContext)` method
+* The deprecated `junit.jupiter.tempdir.scope` configuration parameter is no longer
+  supported.
+* The `JRE` enum constants for `JAVA_8` to `JAVA_16` have been deprecated because they can
+  no longer be used at runtime since `JAVA_17` is the new baseline. Please also manually
+  update any values used with the `minVersion` and `maxVersion` attributes in
+  `@EnabledForJreRange` and `@DisabledForJreRange` or the `versions` attributes in
+  `@EnabledOnJre` and `@DisabledOnJre` to ensure that you are no longer declaring version
+  values less than 17.
+* `@EnabledForJreRange` and `@DisabledForJreRange` now use `JAVA_17` as their default
+  `min` value.
+* The contracts for the `Executable` parameters of Kotlin-specific `assertTimeout`
+  functions were changed from `callsInPlace(executable, EXACTLY_ONCE)` to
+  `callsInPlace(executable, AT_MOST_ONCE)` which might result in compilation errors.
+* As a result of migrating from
+  https://github.com/uniVocity/univocity-parsers[univocity-parsers] to
+  https://fastcsv.org/[FastCSV] for `@CsvSource` and `@CsvFileSource`, root causes and
+  messages of exceptions thrown for malformed CSV input may differ in some cases. While
+  the overall parsing behavior remains consistent, this may affect custom error handling
+  that relies on specific exception types or messages.
+* The `lineSeparator` attribute in `@CsvFileSource` has been removed. The line separator
+  is now automatically detected, meaning that any of `\r`, `\n`, or `\r\n` is treated as a
+  line separator.
+* Attributes such as `ignoreLeadingAndTrailingWhitespace`, `nullValues`, and others in
+  `@CsvSource` and `@CsvFileSource` now apply to header fields as well as to regular
+  fields.
+* The `junit-jupiter-migrationsupport` artifact and its contained classes are now
+  deprecated and will be removed in the next major version.
+* The type bounds of the following methods have been changed to be more flexible and allow
+  nullable and non-nullable types:
+  - `ExtensionContext.getConfigurationParameter(String, Function)`
+  - `ExtensionContext.getOrComputeIfAbsent(K, Function)`
+  - `ExtensionContext.getOrComputeIfAbsent(K, Function, Class)`
+
+[[release-notes-6.0.0-M1-junit-jupiter-new-features-and-improvements]]
+==== New Features and Improvements
+
+* Kotlin's `suspend` modifier may now be applied to test and lifecycle methods.
+* The `Arguments` interface for parameterized tests is now officially a
+  `@FunctionalInterface`.
+* The implementation of `@CsvSource` and `@CsvFileSource` has been migrated from the no
+  longer maintained https://github.com/uniVocity/univocity-parsers[univocity-parsers] to
+  https://fastcsv.org/[FastCSV]. This improves the consistency of CSV input handling,
+  including for malformed entries, and provides better error reporting and overall
+  performance.
+
+
+[[release-notes-6.0.0-M1-junit-vintage]]
+=== JUnit Vintage
+
+[[release-notes-6.0.0-M1-junit-vintage-deprecations-and-breaking-changes]]
+==== Deprecations and Breaking Changes
+
+* The JUnit Vintage engine is now deprecated and will report an INFO level discovery issue
+  when it finds at least one JUnit 4 test class. For now, the intent of the deprecation is
+  not to signal removal in the next major version but to clarify the intended purpose of
+  the engine. It should only be used temporarily while migrating tests to JUnit Jupiter or
+  another testing framework with native JUnit Platform support.
diff --git a/documentation/src/docs/asciidoc/release-notes/release-notes-TEMPLATE.adoc b/documentation/src/docs/asciidoc/release-notes/release-notes-TEMPLATE.adoc
index fb490f9d0da1..5bd352c3c008 100644
--- a/documentation/src/docs/asciidoc/release-notes/release-notes-TEMPLATE.adoc
+++ b/documentation/src/docs/asciidoc/release-notes/release-notes-TEMPLATE.adoc
@@ -7,9 +7,9 @@
 //    5.10.0-RC1, 5.10.0). The same version must be used in the file name and within the
 //    file.
 // 4) Replace MILESTONE_NUMBER with the appropriate milestone number. This is an integer
-//    which you can determine via https://github.com/junit-team/junit5/milestones/. If a
-//    GitHub milestone does not yet exist for the given VERSION, you will need to create
-//    a new GitHub milestone or ask a member of the JUnit team to create it for you.
+//    which you can determine via https://github.com/junit-team/junit-framework/milestones/.
+//    If a GitHub milestone does not yet exist for the given VERSION, you will need to
+//    create a new GitHub milestone or ask a member of the JUnit team to create it for you.
 // 5) 'include:' this new file in index.adoc.
 // 6) Delete this entire comment block.
 //
@@ -21,8 +21,8 @@
 *Scope:* ❓
 
 For a complete list of all _closed_ issues and pull requests for this release, consult the
-link:{junit5-repo}+/milestone/MILESTONE_NUMBER?closed=1+[VERSION] milestone page in the
-JUnit repository on GitHub.
+link:{junit-framework-repo}+/milestone/MILESTONE_NUMBER?closed=1+[VERSION] milestone page in the JUnit
+repository on GitHub.
 
 
 [[release-notes-VERSION-junit-platform]]
diff --git a/documentation/src/docs/asciidoc/user-guide/advanced-topics/engines.adoc b/documentation/src/docs/asciidoc/user-guide/advanced-topics/engines.adoc
index 89f9b127220a..c82204095cd2 100644
--- a/documentation/src/docs/asciidoc/user-guide/advanced-topics/engines.adoc
+++ b/documentation/src/docs/asciidoc/user-guide/advanced-topics/engines.adoc
@@ -60,7 +60,7 @@ configuration parameters.
 Although there is currently no official guide on how to implement a custom `TestEngine`,
 you can consult the implementation of <<test-engines-junit>> or the implementation of
 third-party test engines listed in the
-https://github.com/junit-team/junit5/wiki/Third-party-Extensions#junit-platform-test-engines[JUnit 5 wiki].
+https://github.com/junit-team/junit-framework/wiki/Third-party-Extensions#junit-platform-test-engines[JUnit wiki].
 You will also find various tutorials and blogs on the Internet that demonstrate how to
 write a custom `TestEngine`.
 
diff --git a/documentation/src/docs/asciidoc/user-guide/advanced-topics/junit-platform-reporting.adoc b/documentation/src/docs/asciidoc/user-guide/advanced-topics/junit-platform-reporting.adoc
index 79f67cc42404..036d9cf142f9 100644
--- a/documentation/src/docs/asciidoc/user-guide/advanced-topics/junit-platform-reporting.adoc
+++ b/documentation/src/docs/asciidoc/user-guide/advanced-topics/junit-platform-reporting.adoc
@@ -36,10 +36,12 @@ event-based format specified by {OpenTestReporting} which supports all features
 JUnit Platform such as hierarchical test structures, display names, tags, etc.
 
 The listener is auto-registered and can be configured via the following
-<<running-tests-config-params, configuration parameter>>:
+<<running-tests-config-params, configuration parameters>>:
 
 `junit.platform.reporting.open.xml.enabled=true|false`::
-  Enable/disable writing the report.
+  Enable/disable writing the report; defaults to `false`.
+`junit.platform.reporting.open.xml.git.enabled=true|false`::
+  Enable/disable including information about the Git repository (see https://github.com/ota4j-team/open-test-reporting#git[Git extension schema] of open-test-reporting); defaults to `false`.
 
 If enabled, the listener creates an XML report file named `open-test-report.xml` in the
 configured <<junit-platform-reporting-output-directory, output directory>>.
@@ -63,7 +65,7 @@ using Gradle's Build Cache.
 .Groovy DSL
 ----
 dependencies {
-    testRuntimeOnly("org.junit.platform:junit-platform-reporting:{platform-version}")
+    testRuntimeOnly("org.junit.platform:junit-platform-reporting:{version}")
 }
 tasks.withType(Test).configureEach {
     def outputDir = reports.junitXml.outputLocation
@@ -81,7 +83,7 @@ tasks.withType(Test).configureEach {
 .Kotlin DSL
 ----
 dependencies {
-    testRuntimeOnly("org.junit.platform:junit-platform-reporting:{platform-version}")
+    testRuntimeOnly("org.junit.platform:junit-platform-reporting:{version}")
 }
 tasks.withType<Test>().configureEach {
     val outputDir = reports.junitXml.outputLocation
@@ -109,7 +111,7 @@ XML reports as follows:
 		<dependency>
 			<groupId>org.junit.platform</groupId>
 			<artifactId>junit-platform-reporting</artifactId>
-			<version>{platform-version}</version>
+			<version>{version}</version>
 			<scope>test</scope>
 		</dependency>
 	</dependencies>
@@ -140,7 +142,7 @@ output by setting the configuration parameters via `--config`:
 
 [source,console,subs=attributes+]
 ----
-$ java -jar junit-platform-console-standalone-{platform-version}.jar <OPTIONS> \
+$ java -jar junit-platform-console-standalone-{version}.jar <OPTIONS> \
   --config=junit.platform.reporting.open.xml.enabled=true \
   --config=junit.platform.reporting.output.dir=reports
 ----
@@ -150,7 +152,7 @@ classpath resource via the `--config-resource` option:
 
 [source,console,subs=attributes+]
 ----
-$ java -jar junit-platform-console-standalone-{platform-version}.jar <OPTIONS> \
+$ java -jar junit-platform-console-standalone-{version}.jar <OPTIONS> \
   --config-resource=configuration.properties
 ----
 
diff --git a/documentation/src/docs/asciidoc/user-guide/advanced-topics/launcher-api.adoc b/documentation/src/docs/asciidoc/user-guide/advanced-topics/launcher-api.adoc
index 9f8db34b21f1..be61e66fd51d 100644
--- a/documentation/src/docs/asciidoc/user-guide/advanced-topics/launcher-api.adoc
+++ b/documentation/src/docs/asciidoc/user-guide/advanced-topics/launcher-api.adoc
@@ -4,13 +4,13 @@
 [[launcher-api]]
 === JUnit Platform Launcher API
 
-One of the prominent goals of JUnit 5 is to make the interface between JUnit and its
-programmatic clients – build tools and IDEs – more powerful and stable. The purpose is to
-decouple the internals of discovering and executing tests from all the filtering and
-configuration that's necessary from the outside.
+One of the prominent goals of the JUnit Platform is to make the interface between JUnit
+and its programmatic clients – build tools and IDEs – more powerful and stable. The
+purpose is to decouple the internals of discovering and executing tests from all the
+filtering and configuration that's necessary from the outside.
 
-JUnit 5 introduces the concept of a `Launcher` that can be used to discover, filter, and
-execute tests. Moreover, third party test libraries – like Spock, Cucumber, and FitNesse
+JUnit Platform introduces the concept of a `Launcher` that can be used to discover,
+filter, and execute tests. Moreover, third party test libraries – like Spock or Cucumber
 – can plug into the JUnit Platform's launching infrastructure by providing a custom
 <<test-engines,TestEngine>>.
 
diff --git a/documentation/src/docs/asciidoc/user-guide/advanced-topics/testkit.adoc b/documentation/src/docs/asciidoc/user-guide/advanced-topics/testkit.adoc
index 3f134f3f8ba1..7d79da360376 100644
--- a/documentation/src/docs/asciidoc/user-guide/advanced-topics/testkit.adoc
+++ b/documentation/src/docs/asciidoc/user-guide/advanced-topics/testkit.adoc
@@ -5,7 +5,7 @@
 
 The `junit-platform-testkit` artifact provides support for executing a test plan on the
 JUnit Platform and then verifying the expected results. As of JUnit Platform
-{platform-version}, this support is limited to the execution of a single `TestEngine` (see
+{version}, this support is limited to the execution of a single `TestEngine` (see
 <<testkit-engine>>).
 
 [[testkit-engine]]
diff --git a/documentation/src/docs/asciidoc/user-guide/api-evolution.adoc b/documentation/src/docs/asciidoc/user-guide/api-evolution.adoc
index bac0e8b0012c..2c7da8dae3c9 100644
--- a/documentation/src/docs/asciidoc/user-guide/api-evolution.adoc
+++ b/documentation/src/docs/asciidoc/user-guide/api-evolution.adoc
@@ -1,12 +1,13 @@
 [[api-evolution]]
 == API Evolution
 
-One of the major goals of JUnit 5 is to improve maintainers' capabilities to evolve JUnit
-despite its being used in many projects. With JUnit 4 a lot of stuff that was originally
-added as an internal construct only got used by external extension writers and tool
-builders. That made changing JUnit 4 especially difficult and sometimes impossible.
+One of the major goals of the JUnit Platform architecture is to improve maintainers'
+capabilities to evolve JUnit despite its being used in many projects. With JUnit 4 a lot
+of stuff that was originally added as an internal construct only got used by external
+extension writers and tool builders. That made changing JUnit 4 especially difficult and
+sometimes impossible.
 
-That's why JUnit 5 introduces a defined lifecycle for all publicly available interfaces,
+That's why JUnit now uses a defined lifecycle for all publicly available interfaces,
 classes, and methods.
 
 [[api-evolution-version-and-status]]
@@ -40,7 +41,7 @@ value of lower stability.
 [[api-evolution-experimental-apis]]
 === Experimental APIs
 
-The following table lists which APIs are currently designated as _experimental_ via
+The following tables list which APIs are currently designated as _experimental_ via
 `@API(status = EXPERIMENTAL)`. Caution should be taken when relying on such APIs.
 
 include::{experimentalApisTableFile}[]
@@ -48,7 +49,7 @@ include::{experimentalApisTableFile}[]
 [[api-evolution-deprecated-apis]]
 === Deprecated APIs
 
-The following table lists which APIs are currently designated as _deprecated_ via
+The following tables list which APIs are currently designated as _deprecated_ via
 `@API(status = DEPRECATED)`. You should avoid using deprecated APIs whenever possible,
 since such APIs will likely be removed in an upcoming release.
 
diff --git a/documentation/src/docs/asciidoc/user-guide/appendix.adoc b/documentation/src/docs/asciidoc/user-guide/appendix.adoc
index 9df8622629d5..567f17cdf02b 100644
--- a/documentation/src/docs/asciidoc/user-guide/appendix.adoc
+++ b/documentation/src/docs/asciidoc/user-guide/appendix.adoc
@@ -4,7 +4,7 @@
 [[reproducible-builds]]
 === Reproducible Builds
 
-Starting with version 5.7, JUnit 5 aims for its non-javadoc JARs to be
+Starting with version 5.7, JUnit aims for its non-javadoc JARs to be
 https://reproducible-builds.org/[reproducible].
 
 Under identical build conditions, such as Java version, repeated builds should provide the
@@ -17,9 +17,14 @@ artifacts in the repositories were actually generated from this source code.
 [[dependency-metadata]]
 === Dependency Metadata
 
-Artifacts for final releases and milestones are deployed to {Maven_Central}, and snapshot
-artifacts are deployed to Sonatype's {snapshot-repo}[snapshots repository] under
-{snapshot-repo}/org/junit/[/org/junit].
+Artifacts for final releases and milestones are deployed to {Maven_Central}. Consult
+https://central.sonatype.org/consume/[Sonatype's documentation] for how to consume those
+artifacts with a build tool of your choice.
+
+Snapshot artifacts are deployed to Sonatype's {snapshot-repo}[snapshots repository]
+under {snapshot-repo}/org/junit/[/org/junit]. Please refer to
+https://central.sonatype.org/publish/publish-portal-snapshots/#consuming-snapshot-releases-for-your-project[Sonatype's documentation]
+for instructions on how to consume them with a build tool of your choice.
 
 The sections below list all artifacts with their versions for the three groups:
 <<dependency-metadata-junit-platform, Platform>>,
@@ -45,7 +50,7 @@ Please refer to the corresponding sections for <<running-tests-build-maven-bom,
 ==== JUnit Platform
 
 * *Group ID*: `org.junit.platform`
-* *Version*: `{platform-version}`
+* *Version*: `{version}`
 * *Artifact IDs*:
   `junit-platform-commons`::
     Common APIs and support utilities for the JUnit Platform. Any API annotated with
@@ -60,27 +65,19 @@ Please refer to the corresponding sections for <<running-tests-build-maven-bom,
     directory. See <<running-tests-console-launcher>> for details.
   `junit-platform-engine`::
     Public API for test engines. See <<launcher-api-engines-custom>> for details.
-  `junit-platform-jfr`::
-    Provides a `LauncherDiscoveryListener` and `TestExecutionListener` for Java Flight
-	Recorder events on the JUnit Platform. See <<running-tests-listeners-flight-recorder>>
-	for details.
   `junit-platform-launcher`::
     Public API for configuring and launching test plans -- typically used by IDEs and
     build tools. See <<launcher-api>> for details.
   `junit-platform-reporting`::
     `TestExecutionListener` implementations that generate test reports -- typically used
     by IDEs and build tools. See <<junit-platform-reporting>> for details.
-  `junit-platform-runner`::
-    Runner for executing tests and test suites on the JUnit Platform in a JUnit 4
-    environment. See <<running-tests-junit-platform-runner>> for details.
   `junit-platform-suite`::
     JUnit Platform Suite artifact that transitively pulls in dependencies on
     `junit-platform-suite-api` and `junit-platform-suite-engine` for simplified dependency
 	management in build tools such as Gradle and Maven.
   `junit-platform-suite-api`::
     Annotations for configuring test suites on the JUnit Platform. Supported by the
-    <<junit-platform-suite-engine, JUnit Platform Suite Engine>> and the
-    <<running-tests-junit-platform-runner, JUnitPlatform runner>>.
+    <<junit-platform-suite-engine, JUnit Platform Suite Engine>>.
   `junit-platform-suite-commons`::
     Common support utilities for executing test suites on the JUnit Platform.
   `junit-platform-suite-engine`::
@@ -94,7 +91,7 @@ Please refer to the corresponding sections for <<running-tests-build-maven-bom,
 ==== JUnit Jupiter
 
 * *Group ID*: `org.junit.jupiter`
-* *Version*: `{jupiter-version}`
+* *Version*: `{version}`
 * *Artifact IDs*:
   `junit-jupiter`::
     JUnit Jupiter aggregator artifact that transitively pulls in dependencies on
@@ -107,14 +104,14 @@ Please refer to the corresponding sections for <<running-tests-build-maven-bom,
   `junit-jupiter-params`::
     Support for <<writing-tests-parameterized-tests>> in JUnit Jupiter.
   `junit-jupiter-migrationsupport`::
-    Support for migrating from JUnit 4 to JUnit Jupiter; only required for support for
-    JUnit 4's `@Ignore` annotation and for running selected JUnit 4 rules.
+    _Deprecated_ support for migrating from JUnit 4 to JUnit Jupiter; only required for
+    support for JUnit 4's `@Ignore` annotation and for running selected JUnit 4 rules.
 
 [[dependency-metadata-junit-vintage]]
 ==== JUnit Vintage
 
 * *Group ID*: `org.junit.vintage`
-* *Version*: `{vintage-version}`
+* *Version*: `{version}`
 * *Artifact ID*:
   `junit-vintage-engine`::
     JUnit Vintage test engine implementation that allows one to run _vintage_ JUnit tests
@@ -131,7 +128,7 @@ or https://docs.gradle.org/current/userguide/platforms.html#sub:bom_import[Gradl
 
 * *Group ID*: `org.junit`
 * *Artifact ID*: `junit-bom`
-* *Version*: `{bom-version}`
+* *Version*: `{version}`
 
 [[dependency-metadata-dependencies]]
 ==== Dependencies
diff --git a/documentation/src/docs/asciidoc/user-guide/contributors.adoc b/documentation/src/docs/asciidoc/user-guide/contributors.adoc
index c005e9e820e3..00911583c4d3 100644
--- a/documentation/src/docs/asciidoc/user-guide/contributors.adoc
+++ b/documentation/src/docs/asciidoc/user-guide/contributors.adoc
@@ -1,4 +1,4 @@
 [[contributors]]
 == Contributors
 
-Browse the {junit5-repo}/graphs/contributors[current list of contributors] directly on GitHub.
+Browse the {junit-framework-repo}/graphs/contributors[current list of contributors] directly on GitHub.
diff --git a/documentation/src/docs/asciidoc/user-guide/extensions.adoc b/documentation/src/docs/asciidoc/user-guide/extensions.adoc
index e1a3b351aedb..49ec9920176e 100644
--- a/documentation/src/docs/asciidoc/user-guide/extensions.adoc
+++ b/documentation/src/docs/asciidoc/user-guide/extensions.adoc
@@ -995,30 +995,9 @@ Various methods in `AnnotationSupport` and `ReflectionSupport` use search algori
 traverse type hierarchies to locate matching fields and methods – for example,
 `AnnotationSupport.findAnnotatedFields(...)`, `ReflectionSupport.findMethods(...)`, etc.
 
-As of JUnit 5.11 (JUnit Platform 1.11), field and method search algorithms adhere to
-standard Java semantics regarding whether a given field or method is visible or overridden
-according to the rules of the Java language.
-
-Prior to JUnit 5.11, the field and method search algorithms applied what we now refer to
-as "legacy semantics". Legacy semantics consider fields and methods to be _hidden_,
-_shadowed_, or _superseded_ by fields and methods in super types (superclasses or
-interfaces) based solely on the field's name or the method's signature, disregarding the
-actual Java language semantics for visibility and the rules that determine if one method
-overrides another method.
-
-Although the JUnit team recommends the use of the standard search semantics, developers
-may optionally revert to the legacy semantics via the
-`junit.platform.reflection.search.useLegacySemantics` JVM system property.
-
-For example, to enable legacy search semantics for fields and methods, you can start your
-JVM with the following system property.
-
-`-Djunit.platform.reflection.search.useLegacySemantics=true`
-
-NOTE: Due to the low-level nature of the feature, the
-`junit.platform.reflection.search.useLegacySemantics` flag can only be set via a JVM
-system property. It cannot be set via a <<running-tests-config-params, configuration
-parameter>>.
+The field and method search algorithms adhere to standard Java semantics regarding whether
+a given field or method is visible or overridden according to the rules of the Java
+language.
 
 [[extensions-execution-order]]
 === Relative Execution Order of User Code and Extensions
diff --git a/documentation/src/docs/asciidoc/user-guide/index.adoc b/documentation/src/docs/asciidoc/user-guide/index.adoc
index 9c34f8d33739..bbf1c670c5ad 100644
--- a/documentation/src/docs/asciidoc/user-guide/index.adoc
+++ b/documentation/src/docs/asciidoc/user-guide/index.adoc
@@ -1,5 +1,5 @@
 [[user-guide]]
-= JUnit 5 User Guide
+= JUnit User Guide
 Stefan Bechtold; Sam Brannen; Johannes Link; Matthias Merdes; Marc Philipp; Juliette de Rancourt; Christian Stein
 :basedir: {includedir}/user-guide
 :pdf-fontsdir: GEM_FONTS_DIR;{includedir}/resources/fonts
diff --git a/documentation/src/docs/asciidoc/user-guide/migration-from-junit4.adoc b/documentation/src/docs/asciidoc/user-guide/migration-from-junit4.adoc
index da24b1665ada..3d094f21d978 100644
--- a/documentation/src/docs/asciidoc/user-guide/migration-from-junit4.adoc
+++ b/documentation/src/docs/asciidoc/user-guide/migration-from-junit4.adoc
@@ -21,11 +21,15 @@ plenty of time to migrate to JUnit Jupiter on their own schedule.
 [[migrating-from-junit4-running]]
 === Running JUnit 4 Tests on the JUnit Platform
 
+WARNING: The JUnit Vintage engine is deprecated and should only be used temporarily while
+migrating tests to JUnit Jupiter or another testing framework with native JUnit Platform
+support.
+
 Make sure that the `junit-vintage-engine` artifact is in your test runtime path. In that
 case JUnit 3 and JUnit 4 tests will automatically be picked up by the JUnit Platform
 launcher.
 
-See the example projects in the {junit5-samples-repo}[`junit5-samples`] repository to
+See the example projects in the {junit-examples-repo}[`junit-examples`] repository to
 find out how this is done with Gradle and Maven.
 
 [[migrating-from-junit4-categories-support]]
@@ -256,6 +260,9 @@ include::{testDir}/example/ParameterizedMigrationDemo.java[tags=after]
 [[migrating-from-junit4-rule-support]]
 === Limited JUnit 4 Rule Support
 
+WARNING: _JUnit 4 rule support_ is deprecated for removal since version 6.0.0. Please
+migrate to the corresponding APIs and extensions provided by JUnit Jupiter.
+
 As stated above, JUnit Jupiter does not and will not support JUnit 4 rules natively. The
 JUnit team realizes, however, that many organizations, especially large ones, are likely
 to have large JUnit 4 code bases that make use of custom rules. To serve these
@@ -290,6 +297,9 @@ extension model of JUnit Jupiter instead of the rule-based model of JUnit 4.
 [[migrating-from-junit4-ignore-annotation-support]]
 === JUnit 4 @Ignore Support
 
+WARNING: _JUnit 4 `@Ignore` support_ is deprecated for removal since version 6.0.0. Please
+use JUnit Jupiter's `@Disabled` annotation instead.
+
 In order to provide a smooth migration path from JUnit 4 to JUnit Jupiter, the
 `junit-jupiter-migrationsupport` module provides support for JUnit 4's `@Ignore`
 annotation analogous to Jupiter's `{Disabled}` annotation.
diff --git a/documentation/src/docs/asciidoc/user-guide/overview.adoc b/documentation/src/docs/asciidoc/user-guide/overview.adoc
index d06a5eb53eda..c7ce5ee1bb6f 100644
--- a/documentation/src/docs/asciidoc/user-guide/overview.adoc
+++ b/documentation/src/docs/asciidoc/user-guide/overview.adoc
@@ -12,12 +12,12 @@ endif::linkToPdf[]
 endif::backend-html5[]
 
 [[overview-what-is-junit-5]]
-=== What is JUnit 5?
+=== What is JUnit?
 
-Unlike previous versions of JUnit, JUnit 5 is composed of several different modules from
-three different sub-projects.
+Unlike previous versions of JUnit, JUnit 5 and later is composed of several different
+modules from three different sub-projects.
 
-**JUnit 5 = _JUnit Platform_ + _JUnit Jupiter_ + _JUnit Vintage_**
+**JUnit {version} = _JUnit Platform_ + _JUnit Jupiter_ + _JUnit Vintage_**
 
 The **JUnit Platform** serves as a foundation for <<launcher-api,launching testing
 frameworks>> on the JVM. It also defines the `{TestEngine}` API for developing a testing
@@ -31,7 +31,7 @@ exists in popular IDEs (see <<running-tests-ide-intellij-idea>>,
 <<running-tests-build-maven>>, and <<running-tests-build-ant>>).
 
 **JUnit Jupiter** is the combination of the <<writing-tests,programming model>> and
-<<extensions,extension model>> for writing tests and extensions in JUnit 5. The Jupiter
+<<extensions,extension model>> for writing JUnit tests and extensions. The Jupiter
 sub-project provides a `TestEngine` for running Jupiter based tests on the platform.
 
 **JUnit Vintage** provides a `TestEngine` for running JUnit 3 and JUnit 4 based tests on
@@ -41,13 +41,13 @@ path.
 [[overview-java-versions]]
 === Supported Java Versions
 
-JUnit 5 requires Java 8 (or higher) at runtime. However, you can still test code that
+JUnit requires Java 17 (or higher) at runtime. However, you can still test code that
 has been compiled with previous versions of the JDK.
 
 [[overview-getting-help]]
 === Getting Help
 
-Ask JUnit 5 related questions on {StackOverflow} or chat with the community on {Gitter}.
+Ask JUnit-related questions on {StackOverflow} or use the {DiscussionsQA}.
 
 [[overview-getting-started]]
 === Getting Started
@@ -60,9 +60,9 @@ to <<dependency-metadata>>. To set up dependency management for your build, refe
 <<running-tests-build>> and the <<overview-getting-started-example-projects>>.
 
 [[overview-getting-started-features]]
-==== JUnit 5 Features
+==== JUnit Features
 
-To find out what features are available in JUnit 5 and how to use them, read the
+To find out what features are available in JUnit {version} and how to use them, read the
 corresponding sections of this User Guide, organized by topic.
 
 * <<writing-tests, Writing Tests in JUnit Jupiter>>
@@ -77,14 +77,14 @@ corresponding sections of this User Guide, organized by topic.
 ==== Example Projects
 
 To see complete, working examples of projects that you can copy and experiment with, the
-{junit5-samples-repo}[`junit5-samples`] repository is a good place to start. The
-`junit5-samples` repository hosts a collection of sample projects based on JUnit Jupiter,
+{junit-examples-repo}[`junit-examples`] repository is a good place to start. The
+`junit-examples` repository hosts a collection of example projects based on JUnit Jupiter,
 JUnit Vintage, and other testing frameworks. You'll find appropriate build scripts (e.g.,
 `build.gradle`, `pom.xml`, etc.) in the example projects. The links below highlight some
 of the combinations you can choose from.
 
-* For Gradle and Java, check out the `{junit5-jupiter-starter-gradle}` project.
-* For Gradle and Kotlin, check out the `{junit5-jupiter-starter-gradle-kotlin}` project.
-* For Gradle and Groovy, check out the `{junit5-jupiter-starter-gradle-groovy}` project.
-* For Maven, check out the `{junit5-jupiter-starter-maven}` project.
-* For Ant, check out the `{junit5-jupiter-starter-ant}` project.
+* For Gradle and Java, check out the `{junit-jupiter-starter-gradle}` project.
+* For Gradle and Kotlin, check out the `{junit-jupiter-starter-gradle-kotlin}` project.
+* For Gradle and Groovy, check out the `{junit-jupiter-starter-gradle-groovy}` project.
+* For Maven, check out the `{junit-jupiter-starter-maven}` project.
+* For Ant, check out the `{junit-jupiter-starter-ant}` project.
diff --git a/documentation/src/docs/asciidoc/user-guide/running-tests.adoc b/documentation/src/docs/asciidoc/user-guide/running-tests.adoc
index f3568ade9a31..b6533581fba2 100644
--- a/documentation/src/docs/asciidoc/user-guide/running-tests.adoc
+++ b/documentation/src/docs/asciidoc/user-guide/running-tests.adoc
@@ -13,7 +13,7 @@ however, that it is recommended to use IDEA 2017.3 or newer since more recent ve
 IDEA download the following JARs automatically based on the API version used in the
 project: `junit-platform-launcher`, `junit-jupiter-engine`, and `junit-vintage-engine`.
 
-In order to use a different JUnit 5 version (e.g., {jupiter-version}), you may need to
+In order to use a different JUnit version (e.g., {version}), you may need to
 include the corresponding versions of the `junit-platform-launcher`,
 `junit-jupiter-engine`, and `junit-vintage-engine` JARs in the classpath.
 
@@ -21,7 +21,7 @@ include the corresponding versions of the `junit-platform-launcher`,
 [source,groovy]
 [subs=attributes+]
 ----
-testImplementation(platform("org.junit:junit-bom:{bom-version}"))
+testImplementation(platform("org.junit:junit-bom:{version}"))
 testRuntimeOnly("org.junit.platform:junit-platform-launcher")
 testRuntimeOnly("org.junit.jupiter:junit-jupiter-engine")
 testRuntimeOnly("org.junit.vintage:junit-vintage-engine")
@@ -54,7 +54,7 @@ testRuntimeOnly("org.junit.vintage:junit-vintage-engine")
 		<dependency>
 			<groupId>org.junit</groupId>
 			<artifactId>junit-bom</artifactId>
-			<version>{bom-version}</version>
+			<version>{version}</version>
 			<type>pom</type>
 			<scope>import</scope>
 		</dependency>
@@ -68,8 +68,8 @@ testRuntimeOnly("org.junit.vintage:junit-vintage-engine")
 Eclipse IDE offers support for the JUnit Platform since the Eclipse Oxygen.1a (4.7.1a)
 release.
 
-For more information on using JUnit 5 in Eclipse consult the official _Eclipse support
-for JUnit 5_ section of the
+For more information on using JUnit Platform in Eclipse consult the official _Eclipse
+support for JUnit 5_ section of the
 https://www.eclipse.org/eclipse/news/4.7.1a/#junit-5-support[Eclipse Project Oxygen.1a
 (4.7.1a) - New and Noteworthy] documentation.
 
@@ -101,10 +101,8 @@ documentation.
 ==== Other IDEs
 
 If you are using an editor or IDE other than one of those listed in the previous sections,
-the JUnit team provides two alternative solutions to assist you in using JUnit 5. You can
-use the <<running-tests-console-launcher>> manually -- for example, from the command line
--- or execute tests with a <<running-tests-junit-platform-runner,JUnit 4 based Runner>> if
-your IDE has built-in support for JUnit 4.
+and it doesn't support running tests on the JUnit Platform, you can use the
+<<running-tests-console-launcher>> to run them from the command line.
 
 [[running-tests-build]]
 === Build Support
@@ -153,14 +151,14 @@ of JUnit used in your Spring Boot application.
 
 Unless you're using Spring Boot which defines its own way of managing dependencies, it is
 recommended to use the JUnit Platform <<dependency-metadata-junit-bom>> to align the
-versions of all JUnit 5 artifacts.
+versions of all JUnit artifacts.
 
 [source,groovy,indent=0]
 [subs=attributes+]
 .Explicit platform dependency on the BOM
 ----
 dependencies {
-	testImplementation(platform("org.junit:junit-bom:{bom-version}"))
+	testImplementation(platform("org.junit:junit-bom:{version}"))
 	testImplementation("org.junit.jupiter:junit-jupiter")
 	testRuntimeOnly("org.junit.platform:junit-platform-launcher")
 }
@@ -173,7 +171,7 @@ Since all JUnit artifacts declare a
 https://docs.gradle.org/current/userguide/platforms.html[platform] dependency on the BOM,
 you usually don't need to declare an explicit dependency on it yourself. Instead, it's
 sufficient to declare _one_ regular dependency that includes a version number. Gradle will
-then pull in the BOM automatically so you can omit the version for all other JUnit 5
+then pull in the BOM automatically so you can omit the version for all other JUnit
 artifacts.
 
 [source,groovy,indent=0]
@@ -181,7 +179,7 @@ artifacts.
 .Implicit platform dependency on the BOM
 ----
 dependencies {
-	testImplementation("org.junit.jupiter:junit-jupiter:{jupiter-version}") // <1>
+	testImplementation("org.junit.jupiter:junit-jupiter:{version}") // <1>
 	testRuntimeOnly("org.junit.platform:junit-platform-launcher") // <2>
 }
 ----
@@ -212,7 +210,7 @@ on the dependency-aggregating JUnit Jupiter artifact similar to the following.
 [subs=attributes+]
 ----
 dependencies {
-	testImplementation("org.junit.jupiter:junit-jupiter:{jupiter-version}")
+	testImplementation("org.junit.jupiter:junit-jupiter:{version}")
 	testRuntimeOnly("org.junit.platform:junit-platform-launcher")
 }
 ----
@@ -228,7 +226,7 @@ support.
 testing {
 	suites {
 		named<JvmTestSuite>("test") {
-			useJUnitJupiter("{jupiter-version}")
+			useJUnitJupiter("{version}")
 		}
 	}
 }
@@ -241,7 +239,7 @@ testing {
 testing {
 	suites {
 		test {
-			useJUnitJupiter("{jupiter-version}")
+			useJUnitJupiter("{version}")
 		}
 	}
 }
@@ -256,7 +254,7 @@ implementation similar to the following.
 ----
 dependencies {
 	testImplementation("junit:junit:{junit4-version}")
-	testRuntimeOnly("org.junit.vintage:junit-vintage-engine:{vintage-version}")
+	testRuntimeOnly("org.junit.vintage:junit-vintage-engine:{version}")
 	testRuntimeOnly("org.junit.platform:junit-platform-launcher")
 }
 ----
@@ -320,27 +318,9 @@ for executing tests on the JUnit Platform. The `pom.xml` file in the
 and can serve as a starting point for configuring your Maven build.
 
 [WARNING]
-.Use recent version of Maven Surefire/Failsafe to avoid interoperability issues
+.Minimum required version of Maven Surefire/Failsafe
 ====
-To avoid interoperability issues, it is recommended to use a recent version of Maven
-Surefire/Failsafe (3.0.0 or later) because it automatically aligns the version of the
-JUnit Platform Launcher that is used with the JUnit Platform version found on the test
-runtime classpath.
-
-If you are using a version older than 3.0.0-M4, you can work around the missing alignment
-by adding a test dependency on the matching version of the JUnit Platform Launcher to your
-Maven build as follows.
-
-[source,xml]
-[subs=attributes+]
-----
-<dependency>
-    <groupId>org.junit.platform</groupId>
-    <artifactId>junit-platform-launcher</artifactId>
-    <version>{platform-version}</version>
-    <scope>test</scope>
-</dependency>
-----
+As of JUnit 6.0, the minimum required version of Maven Surefire/Failsafe is 3.0.0.
 ====
 
 [[running-tests-build-maven-bom]]
@@ -348,7 +328,7 @@ Maven build as follows.
 
 Unless you're using Spring Boot which defines its own way of managing dependencies, it is
 recommended to use the JUnit Platform <<dependency-metadata-junit-bom>> to align the
-versions of all JUnit 5 artifacts.
+versions of all JUnit artifacts.
 
 [source,xml,indent=0]
 [subs=attributes+]
@@ -358,7 +338,7 @@ versions of all JUnit 5 artifacts.
 		<dependency>
 			<groupId>org.junit</groupId>
 			<artifactId>junit-bom</artifactId>
-			<version>{bom-version}</version>
+			<version>{version}</version>
 			<type>pom</type>
 			<scope>import</scope>
 		</dependency>
@@ -391,7 +371,7 @@ following.
 		<dependency>
 			<groupId>org.junit.jupiter</groupId>
 			<artifactId>junit-jupiter</artifactId>
-			<version>{jupiter-version}</version> <!-- can be omitted when using the BOM -->
+			<version>{version}</version> <!-- can be omitted when using the BOM -->
 			<scope>test</scope>
 		</dependency>
 		<!-- ... -->
@@ -430,7 +410,7 @@ long as you configure `test` scoped dependencies on JUnit 4 and the JUnit Vintag
 		<dependency>
 			<groupId>org.junit.vintage</groupId>
 			<artifactId>junit-vintage-engine</artifactId>
-			<version>{vintage-version}</version> <!-- can be omitted when using the BOM -->
+			<version>{version}</version> <!-- can be omitted when using the BOM -->
 			<scope>test</scope>
 		</dependency>
 		<!-- ... -->
@@ -659,7 +639,7 @@ With Gradle you can override the JUnit Jupiter version by including the followin
 [source,groovy,indent=0]
 [subs=attributes+]
 ----
-	ext['junit-jupiter.version'] = '{jupiter-version}'
+	ext['junit-jupiter.version'] = '{version}'
 ----
 
 With Maven you can override the JUnit Jupiter version by including the following in your
@@ -669,7 +649,7 @@ With Maven you can override the JUnit Jupiter version by including the following
 [subs=attributes+]
 ----
 	<properties>
-		<junit-jupiter.version>{jupiter-version}</junit-jupiter.version>
+		<junit-jupiter.version>{version}</junit-jupiter.version>
 	</properties>
 ----
 
@@ -680,7 +660,7 @@ The `{ConsoleLauncher}` is a command-line Java application that lets you launch
 Platform from the console. For example, it can be used to run JUnit Vintage and JUnit
 Jupiter tests and print test execution results to the console.
 
-An executable _Fat JAR_ (`junit-platform-console-standalone-{platform-version}.jar`) that
+An executable _Fat JAR_ (`junit-platform-console-standalone-{version}.jar`) that
 contains the contents of all of its dependencies is published in the {Maven_Central}
 repository under the
 https://repo1.maven.org/maven2/org/junit/platform/junit-platform-console-standalone[junit-platform-console-standalone]
@@ -711,7 +691,7 @@ standalone `ConsoleLauncher` as shown below.
 
 [source,console,subs=attributes+]
 ----
-$ java -jar junit-platform-console-standalone-{platform-version}.jar execute <OPTIONS>
+$ java -jar junit-platform-console-standalone-{version}.jar execute <OPTIONS>
 
 ├─ JUnit Vintage
 │  └─ example.JUnit4Tests
@@ -748,12 +728,6 @@ all jars in a directory):
 $ java -cp classes:testlib/* org.junit.platform.console.ConsoleLauncher <OPTIONS>
 ----
 
-.Exit Code
-NOTE: The `{ConsoleLauncher}` exits with a status code of `1` if any containers or tests
-failed. If no tests are discovered and the `--fail-if-no-tests` command-line option is
-supplied, the `ConsoleLauncher` exits with a status code of `2`. Otherwise, the exit code
-is `0`.
-
 [[running-tests-console-launcher-options]]
 ==== Subcommands and Options
 
@@ -773,6 +747,12 @@ include::{consoleLauncherDiscoverOptionsFile}[]
 [[running-tests-console-launcher-options-executing-tests]]
 ===== Executing tests
 
+.Exit Code
+NOTE: The `{ConsoleLauncher}` exits with a status code of `1` if any containers or tests
+failed. If no tests are discovered and the `--fail-if-no-tests` command-line option is
+supplied, the `ConsoleLauncher` exits with a status code of `2`. Otherwise, the exit code
+is `0`.
+
 ----
 include::{consoleLauncherExecuteOptionsFile}[]
 ----
@@ -820,7 +800,7 @@ files using the `--redirect-stdout` and `--redirect-stderr` options:
 
 [source,console,subs=attributes+]
 ----
-$ java -jar junit-platform-console-standalone-{platform-version}.jar <OPTIONS> \
+$ java -jar junit-platform-console-standalone-{version}.jar <OPTIONS> \
   --redirect-stdout=stdout.txt \
   --redirect-stderr=stderr.txt
 ----
@@ -854,122 +834,6 @@ DYNAMIC = 35
 REPORTED = 37
 ----
 
-
-[[running-tests-junit-platform-runner]]
-=== Using JUnit 4 to run the JUnit Platform
-
-[WARNING]
-.The `JUnitPlatform` runner has been deprecated
-====
-The `JUnitPlatform` runner was developed by the JUnit team as an interim solution for
-running test suites and tests on the JUnit Platform in a JUnit 4 environment.
-
-In recent years, all mainstream build tools and IDEs provide built-in support for running
-tests directly on the JUnit Platform.
-
-In addition, the introduction of `@Suite` support provided by the
-`junit-platform-suite-engine` module makes the `JUnitPlatform` runner obsolete. See
-<<junit-platform-suite-engine>> for details.
-
-The `JUnitPlatform` runner and `@UseTechnicalNames` annotation have therefore been
-deprecated in JUnit Platform 1.8 and will be removed in JUnit Platform 2.0.
-
-If you are using the `JUnitPlatform` runner, please migrate to the `@Suite` support.
-====
-
-The `JUnitPlatform` runner is a JUnit 4 based `Runner` which enables you to run any test
-whose programming model is supported on the JUnit Platform in a JUnit 4 environment --
-for example, a JUnit Jupiter test class.
-
-Annotating a class with `@RunWith(JUnitPlatform.class)` allows it to be run with IDEs and
-build systems that support JUnit 4 but do not yet support the JUnit Platform directly.
-
-NOTE: Since the JUnit Platform has features that JUnit 4 does not have, the runner is
-only able to support a subset of the JUnit Platform functionality, especially with regard
-to reporting (see <<running-tests-junit-platform-runner-technical-names>>).
-
-[[running-tests-junit-platform-runner-setup]]
-==== Setup
-
-You need the following artifacts and their dependencies on the classpath. See
-<<dependency-metadata>> for details regarding group IDs, artifact IDs, and versions.
-
-[[running-tests-junit-platform-runner-setup-explicit-dependencies]]
-===== Explicit Dependencies
-
-* `junit-platform-runner` in _test_ scope: location of the `JUnitPlatform` runner
-* `junit-{junit4-version}.jar` in _test_ scope: to run tests using JUnit 4
-* `junit-jupiter-api` in _test_ scope: API for writing tests using JUnit Jupiter,
-  including `@Test`, etc.
-* `junit-jupiter-engine` in _test runtime_ scope: implementation of the `TestEngine` API
-  for JUnit Jupiter
-
-[[running-tests-junit-platform-runner-setup-transitive-dependencies]]
-===== Transitive Dependencies
-
-* `junit-platform-suite-api` in _test_ scope
-* `junit-platform-suite-commons` in _test_ scope
-* `junit-platform-launcher` in _test_ scope
-* `junit-platform-engine` in _test_ scope
-* `junit-platform-commons` in _test_ scope
-* `opentest4j` in _test_ scope
-
-[[running-tests-junit-platform-runner-technical-names]]
-==== Display Names vs. Technical Names
-
-To define a custom _display name_ for the class run via `@RunWith(JUnitPlatform.class)`
-annotate the class with `@SuiteDisplayName` and provide a custom value.
-
-By default, _display names_ will be used for test artifacts; however, when the
-`JUnitPlatform` runner is used to execute tests with a build tool such as Gradle or
-Maven, the generated test report often needs to include the _technical names_ of test
-artifacts — for example, fully qualified class names — instead of shorter display names
-like the simple name of a test class or a custom display name containing special
-characters. To enable technical names for reporting purposes, declare the
-`@UseTechnicalNames` annotation alongside `@RunWith(JUnitPlatform.class)`.
-
-Note that the presence of `@UseTechnicalNames` overrides any custom display name
-configured via `@SuiteDisplayName`.
-
-[[running-tests-junit-platform-runner-single-test]]
-==== Single Test Class
-
-One way to use the `JUnitPlatform` runner is to annotate a test class with
-`@RunWith(JUnitPlatform.class)` directly. Please note that the test methods in the
-following example are annotated with `org.junit.jupiter.api.Test` (JUnit Jupiter), not
-`org.junit.Test` (JUnit 4). Moreover, in this case the test class must be `public`;
-otherwise, some IDEs and build tools might not recognize it as a JUnit 4 test class.
-
-[source,java,indent=0]
-----
-include::{testDir}/example/JUnitPlatformClassDemo.java[tags=user_guide]
-----
-
-[[running-tests-junit-platform-runner-test-suite]]
-==== Test Suite
-
-If you have multiple test classes you can create a test suite as can be seen in the
-following example.
-
-[source,java,indent=0]
-----
-include::{testDir}/example/JUnitPlatformSuiteDemo.java[tags=user_guide]
-----
-
-The `JUnitPlatformSuiteDemo` will discover and run all tests in the `example` package and
-its subpackages. By default, it will only include test classes whose names either begin
-with `Test` or end with `Test` or `Tests`.
-
-.Additional Configuration Options
-NOTE: There are more configuration options for discovering and filtering tests than just
-`@SelectPackages`. Please consult the Javadoc of the `{suite-api-package}` package for
-further details.
-
-WARNING: Test classes and suites annotated with `@RunWith(JUnitPlatform.class)`
-**cannot** be executed directly on the JUnit Platform (or as a "JUnit 5" test as
-documented in some IDEs). Such classes and suites can only be executed using JUnit 4
-infrastructure.
-
 [[running-tests-discovery-selectors]]
 === Discovery Selectors
 
@@ -997,7 +861,7 @@ The following discovery selectors are provided out of the box:
 | `{NestedClassSelector}`       | `{DiscoverySelectors_selectNestedClass}`       | `{Select}("<identifier>")`  | `--select <identifier>`                          | `nested-class:com.acme.Foo/Bar`
 | `{NestedMethodSelector}`      | `{DiscoverySelectors_selectNestedMethod}`      | `{Select}("<identifier>")`  | `--select <identifier>`                          | `nested-method:com.acme.Foo/Bar#m`
 | `{PackageSelector}`           | `{DiscoverySelectors_selectPackage}`           | `{SelectPackages}`          | `--select-package com.acme.foo`                  | `package:com.acme.foo`
-| `{UniqueIdSelector}`          | `{DiscoverySelectors_selectUniqueId}`          | `{Select}("<identifier>")`  | `--select <identifier>`                          | `uid:...`
+| `{UniqueIdSelector}`          | `{DiscoverySelectors_selectUniqueId}`          | `{Select}("<identifier>")`  | `--select-unique-id <identifier>`                | `uid:[engine:Foo]/[segment:Bar]`
 | `{UriSelector}`               | `{DiscoverySelectors_selectUri}`               | `{SelectUris}`              | `--select-uri \file:///foo.txt`                  | `uri:file:///foo.txt`
 |===
 
@@ -1255,9 +1119,7 @@ to a problem.
 In order to record Flight Recorder events generated while running tests, you need to:
 
 1. Ensure that you are using either Java 8 Update 262 or higher or Java 11 or later.
-2. Provide the `org.junit.platform.jfr` module (`junit-platform-jfr-{platform-version}.jar`)
-   on the class-path or module-path at test runtime.
-3. Start flight recording when launching a test run. Flight Recorder can be started via
+2. Start flight recording when launching a test run. Flight Recorder can be started via
    java command line option:
 
    -XX:StartFlightRecording:filename=...
diff --git a/documentation/src/docs/asciidoc/user-guide/writing-tests.adoc b/documentation/src/docs/asciidoc/user-guide/writing-tests.adoc
index b9c86dbb8a89..41555bc48620 100644
--- a/documentation/src/docs/asciidoc/user-guide/writing-tests.adoc
+++ b/documentation/src/docs/asciidoc/user-guide/writing-tests.adoc
@@ -1,6 +1,5 @@
 :testDir: ../../../../src/test/java
 :testResourcesDir: ../../../../src/test/resources
-:testRelease21Dir: ../../../../src/test/java21
 :kotlinTestDir: ../../../../src/test/kotlin
 
 [[writing-tests]]
@@ -271,7 +270,7 @@ lifecycle methods. For further information on runtime semantics, see
 <<extensions-execution-order-wrapping-behavior>>.
 
 [source,java,indent=0]
-.A standard test class
+.A standard Java test class
 ----
 include::{testDir}/example/StandardTests.java[tags=user_guide]
 ----
@@ -282,9 +281,25 @@ following example.
 [source,java,indent=0]
 .A test class written as a Java record
 ----
-include::{testRelease21Dir}/example/MyFirstJUnitJupiterRecordTests.java[tags=user_guide]
+include::{testDir}/example/MyFirstJUnitJupiterRecordTests.java[tags=user_guide]
 ----
 
+Test and lifecycle methods may be written in Kotlin and may optionally use the `suspend`
+keyword for testing code using coroutines.
+
+[source,kotlin]
+.A test class written in Kotlin
+----
+include::{kotlinTestDir}/example/KotlinCoroutinesDemo.kt[tags=user_guide]
+----
+
+NOTE: Using suspending functions as test or lifecycle methods requires
+https://central.sonatype.com/artifact/org.jetbrains.kotlin/kotlin-stdlib[`kotlin-stdlib`],
+https://central.sonatype.com/artifact/org.jetbrains.kotlin/kotlin-reflect[`kotlin-reflect`],
+and
+https://central.sonatype.com/artifact/org.jetbrains.kotlinx/kotlinx-coroutines-core[`kotlinx-coroutines-core`]
+to be present on the classpath or module path.
+
 [[writing-tests-display-names]]
 === Display Names
 
@@ -974,9 +989,6 @@ following built-in `MethodOrderer` implementations.
   specified via the `{Order}` annotation
 * `{MethodOrderer_Random}`: orders test methods _pseudo-randomly_ and supports
   configuration of a custom _seed_
-* `{MethodOrderer_Alphanumeric}`: sorts test methods _alphanumerically_ based on their
-  names and formal parameter lists; **deprecated in favor of `{MethodOrderer_MethodName}`,
-  to be removed in 6.0**
 
 NOTE: See also: <<extensions-execution-order-wrapping-behavior>>
 
@@ -1275,9 +1287,8 @@ include::{testDir}/example/TestInfoDemo.java[tags=user_guide]
   method, respectively. This allows them to be viewed in IDEs or included in reports.
 +
 In JUnit Jupiter you should use `TestReporter` where you used to print information to
-`stdout` or `stderr` in JUnit 4. Using `@RunWith(JUnitPlatform.class)` will output all
-reported entries to `stdout`. In addition, some IDEs print report entries to `stdout` or
-display them in the user interface for test results.
+`stdout` or `stderr` in JUnit 4. Some IDEs print report entries to `stdout` or display
+them in the user interface for test results.
 
 [source,java,indent=0]
 ----
@@ -1583,7 +1594,7 @@ _Parameterized tests_ make it possible to run a test method multiple times with
 arguments. They are declared just like regular `@Test` methods but use the
 `{ParameterizedTest}` annotation instead.
 
-_Parameterized classes_ make it possible to run _all_ tests in test class, including
+_Parameterized classes_ make it possible to run _all_ tests in a test class, including
 <<writing-tests-nested>>, multiple times with different arguments. They are declared just
 like regular test classes and may contain any supported test method type (including
 `@ParameterizedTest`) but annotated with the `{ParameterizedClass}` annotation.
@@ -1707,7 +1718,7 @@ boilerplate code of declaring a test class constructor.
 
 [source,java,indent=0]
 ----
-include::{testRelease21Dir}/example/ParameterizedRecordDemo.java[tags=example]
+include::{testDir}/example/ParameterizedRecordDemo.java[tags=example]
 ----
 
 [[writing-tests-parameterized-tests-consuming-arguments-field-injection]]
@@ -2042,7 +2053,7 @@ translates to a `Collection`, an `Iterable`, a `Supplier` of a stream (`Stream`,
 objects or primitives, or any type that provides an `iterator(): Iterator` method (such
 as, for example, a `kotlin.sequences.Sequence`). Each set of "arguments" within the
 "stream" can be supplied as an instance of `Arguments`, an array of objects (for example,
-`Object[]`, `String[]`, etc.), or a single value if the parameterized class ortest method accepts
+`Object[]`, `String[]`, etc.), or a single value if the parameterized class or test method accepts
 a single argument.
 
 [WARNING]
@@ -2819,7 +2830,7 @@ by the following example.
 [source,java,indent=0]
 .Using parameterized class lifecycle methods
 ----
-include::{testRelease21Dir}/example/ParameterizedLifecycleDemo.java[tags=example]
+include::{testDir}/example/ParameterizedLifecycleDemo.java[tags=example]
 ----
 <1> Initialization of the argument _before_ each invocation of the parameterized class
 <2> Usage of the previously initialized argument in a test method
@@ -2950,7 +2961,7 @@ interface along with `Named` via the `NamedExecutable` base class.
 
 [source,java]
 ----
-include::{testRelease21Dir}/example/DynamicTestsNamedDemo.java[tags=user_guide]
+include::{testDir}/example/DynamicTestsNamedDemo.java[tags=user_guide]
 ----
 
 [[writing-tests-dynamic-tests-uri-test-source]]
@@ -3195,6 +3206,17 @@ execution order. Thus, in both cases, test methods in such test classes are only
 concurrently if the `@Execution(CONCURRENT)` annotation is present on the test class or
 method.
 
+You can use the `@Execution` annotation to explicitly configure the execution mode for a
+test class or method:
+
+[source,java]
+----
+include::{testDir}/example/ExplicitExecutionModeDemo.java[]
+----
+
+This allows test classes or methods to opt in or out of concurrent execution regardless of
+the globally configured default.
+
 When parallel execution is enabled and a default `{ClassOrderer}` is registered (see
 <<writing-tests-test-execution-order-classes>> for details), top-level test classes will
 initially be sorted accordingly and scheduled in that order. However, they are not
@@ -3525,11 +3547,6 @@ You can inject multiple temporary directories by specifying multiple annotated p
 include::{testDir}/example/TempDirectoryDemo.java[tags=user_guide_multiple_directories]
 ----
 
-WARNING: To revert to the old behavior of using a single temporary directory for the
-entire test class or method (depending on which level the annotation is used), you can set
-the `junit.jupiter.tempdir.scope` configuration parameter to `per_context`. However,
-please note that this option is deprecated and will be removed in a future release.
-
 The following example stores a _shared_ temporary directory in a `static` field. This
 allows the same `sharedTempDir` to be used in all lifecycle methods and test methods of
 the test class. For better isolation, you should use an instance field or constructor
diff --git a/documentation/src/javadoc/junit-overview.html b/documentation/src/javadoc/junit-overview.html
index 2e79b9d5af9a..50837dbd73e6 100644
--- a/documentation/src/javadoc/junit-overview.html
+++ b/documentation/src/javadoc/junit-overview.html
@@ -7,12 +7,12 @@
     <dd>The JUnit Platform serves as a foundation for launching testing frameworks on the JVM.
         It also defines the TestEngine API for developing a testing framework that runs on the
         platform. Furthermore, the platform provides a Console Launcher to launch the platform
-        from the command line and a JUnit 4 based Runner for running any TestEngine on the
-        platform in a JUnit 4 based environment.
+        from the command line and the Suite Engine for running a custom test suite using one
+        or more test engines on the platform
     </dd>
     <dt>Jupiter</dt>
-    <dd>JUnit Jupiter is the combination of the new programming model and extension model for
-        writing tests and extensions in JUnit 5. The Jupiter sub-project provides a TestEngine
+    <dd>JUnit Jupiter is the combination of the programming model and extension model for
+        writing JUnit tests and extensions. The Jupiter sub-project provides a TestEngine
         for running Jupiter based tests on the platform.
     </dd>
     <dt>Vintage</dt>
@@ -21,6 +21,6 @@
     </dd>
 </dl>
 
-<p>Already consulted the <a href="../user-guide/index.html">JUnit 5 User Guide</a>?</p>
+<p>Already consulted the <a href="../user-guide/index.html">JUnit User Guide</a>?</p>
 
 </body>
diff --git a/documentation/src/javadoc/junit-stylesheet.css b/documentation/src/javadoc/junit-stylesheet.css
index 19fe4f0cee0a..6d5b1bb6c287 100644
--- a/documentation/src/javadoc/junit-stylesheet.css
+++ b/documentation/src/javadoc/junit-stylesheet.css
@@ -4,12 +4,44 @@
 
 @import url('https://fonts.googleapis.com/css?family=Fira+Mono:400,700|Open+Sans:300,300i,400,400i,700,700i');
 
-body, .title {
-    color:#333333;
-}
-
-body, div.block, .deprecationBlock, button {
-    font-family: 'Open Sans', Arial, Helvetica, sans-serif;
+:root {
+    /* body, block and code fonts */
+    --body-font-family: 'Open Sans', Arial, Helvetica, sans-serif;
+    --block-font-family: 'Open Sans', Arial, Helvetica, sans-serif;
+    --code-font-family: "Fira Mono", monospace;
+    /* Text colors for body and block elements */
+    --body-text-color: #333;
+    --block-text-color: #333;
+    /* Background colors for various structural elements */
+    --section-background-color: #f8f8f8;
+    /* Colors for navigation bar and table captions */
+    --navbar-background-color: #25a162;
+    /* Background color for subnavigation and various headers */
+    --subnav-background-color: #e8e8e8;
+    /* Background and text colors for selected tabs and navigation items */
+    --selected-background-color: #dc524a;
+    --selected-text-color: #fff;
+    --selected-link-color: #651410;
+    /* Background colors for generated tables */
+    --even-row-color: #fff;
+    --odd-row-color: #eee;
+    /* Text color for page title */
+    --title-color: #333;
+    /* Text colors for links */
+    --link-color: #dc524a;
+    --link-color-active: #b62b23;
+    /* Table of contents */
+    --toc-background-color: var(--section-background-color);
+    --toc-link-color: #000;
+    /* Snippet colors */
+    --snippet-background-color: #ebecee;
+    --snippet-text-color: var(--block-text-color);
+    --snippet-highlight-color: #fcdbd9;
+    /* Border colors for structural elements and user defined tables */
+    --border-color: #ddd;
+    --table-border-color: #999;
+    /* Highlight color for active search tag target */
+    --search-tag-highlight-color: #ffff00;
 }
 
 .title {
@@ -18,34 +50,8 @@ body, div.block, .deprecationBlock, button {
     margin-top: 0;
 }
 
-a:link, a:visited {
-    text-decoration:none;
-    color:#dc524a;
-}
-
-a[href]:hover, a[href]:focus {
-    text-decoration:none;
-    color:#b62b23;
-}
-
-pre, code, tt, dt code, table tr td dt code {
-    font-family: "Fira Mono", monospace;
-}
-
-.bar {
-    background-color:#25a162;
-}
-
-.top-nav {
-    background-color:#25a162;
-}
-
-.bottom-nav {
-    background-color:#25a162;
-}
-
-.sub-nav {
-    background-color:#f5f5f5;
+ul.nav-list {
+    padding-left: 10px;
 }
 
 .top-nav a:hover, .bottom-nav a:hover {
@@ -57,99 +63,14 @@ pre, code, tt, dt code, table tr td dt code {
     background-color:#fff;
     color:#dc524a;
     border-radius: 6px;
+    font-weight: bold;
 }
 
-.index-nav {
-    background-color:#eee;
-}
-
-body.class-declaration-page .summary h2,
-body.class-declaration-page .details h2,
-body.class-use-page  h2,
-body.module-declaration-page  .block-list h2 {
-    font-style: italic;
-    padding:0;
-    margin:15px 0;
-}
-body.class-declaration-page .summary h3,
-body.class-declaration-page .details h3,
-body.class-declaration-page .summary .inherited-list h2,
-div.details ul.block-list ul.block-list ul.block-list li.block-list h4,
-ul.block-list ul.block-list ul.block-list li.block-list h3 {
-    background-color:#ddd;
-    border:1px solid #ddd;
-}
-
-.constants-summary caption a:link, .constants-summary caption a:visited,
-.use-summary caption a:link, .use-summary caption a:visited {
-    color:#fff;
-}
-
-.overview-summary caption span, .member-summary caption span, .type-summary caption span,
-.use-summary caption span, .constants-summary caption span, .deprecated-summary caption span,
-.requires-summary caption span, .packages-summary caption span, .provides-summary caption span,
-.uses-summary caption span,
-.member-summary caption span.active-table-tab span, .packages-summary caption span.active-table-tab span,
-.overview-summary caption span.active-table-tab span, .type-summary caption span.active-table-tab span,
-div.table-tabs > button.active-table-tab
-{
-    background-color:#dc524a;
-    color: #fff;
-}
-
-.ui-state-active,
-.ui-widget-content .ui-state-active,
-.ui-widget-header .ui-state-active,
-a.ui-button:active,
-.ui-button:active,
-.ui-button.ui-state-active:hover {
-    /* Overrides the color of selection used in jQuery UI */
-    background: #dc524a !important;
-    color: #fff !important;
-}
-
-main a[href*="://"]::after,
-main a[href*="://"]:hover::after,
-main a[href*="://"]:focus::after {
-    background-image:url('data:image/svg+xml; utf8, \
-      <svg xmlns="http://www.w3.org/2000/svg" width="768" height="768">\
-        <path d="M584 664H104V184h216V80H0v688h688V448H584zM384 0l132 \
-        132-240 240 120 120 240-240 132 132V0z" fill="%23aaa"/>\
-      </svg>');
-}
-
-.member-summary caption span.table-tab span, .packages-summary caption span.table-tab span,
-.overview-summary caption span.table-tab span, .type-summary caption span.table-tab span,
-.ui-autocomplete-category,
-div.table-tabs > button.table-tab {
-    background-color:#aaa;
-    color: #fff;
-}
-
-th.col-first, th.col-second, th.col-last, th.col-constructor-name, th.col-deprecated-item-name, .constants-summary th,
-.packages-summary th {
-    background:#eee;
-}
-
-.table-sub-heading-color {
-    background-color:#eee;
-}
-
-.alt-color, .alt-color th {
-    background-color:#fff;
-}
-
-.row-color, .row-color th {
-    background-color:#eee;
-}
-
-.block {
-    margin:0 10px 5px 0;
+hr {
+    color: transparent;
+    border-top: 1px solid var(--border-color);
 }
 
-th.col-first, th.col-second, th.col-last, th.col-constructor-name, th.col-deprecated-item-name, .constants-summary th,
-.packages-summary th, .overview-summary td, .member-summary td, .type-summary td,
-.use-summary td, .constants-summary td, .deprecated-summary td,
-.requires-summary td, .packages-summary td, .provides-summary td, .uses-summary td {
-    padding-left:7px;
+dt {
+    font-weight: bold;
 }
diff --git a/documentation/src/main/java/example/util/StringUtils.java b/documentation/src/main/java/example/util/StringUtils.java
index a48d72e3d3ad..b0eee5e142f8 100644
--- a/documentation/src/main/java/example/util/StringUtils.java
+++ b/documentation/src/main/java/example/util/StringUtils.java
@@ -10,10 +10,14 @@
 
 package example.util;
 
+import static java.util.Objects.requireNonNull;
+
+import org.jspecify.annotations.Nullable;
+
 public class StringUtils {
 
-	public static boolean isPalindrome(String candidate) {
-		int length = candidate.length();
+	public static boolean isPalindrome(@Nullable String candidate) {
+		int length = requireNonNull(candidate).length();
 		for (int i = 0; i < length / 2; i++) {
 			if (candidate.charAt(i) != candidate.charAt(length - (i + 1))) {
 				return false;
diff --git a/documentation/src/plantuml/component-diagram.puml b/documentation/src/plantuml/component-diagram.puml
index cc06c35ccbd2..a0668125eb61 100644
--- a/documentation/src/plantuml/component-diagram.puml
+++ b/documentation/src/plantuml/component-diagram.puml
@@ -20,10 +20,8 @@ package org.junit.platform {
     [junit-platform-commons] as commons
     [junit-platform-console] as console
     [junit-platform-engine] as engine
-    [junit-platform-jfr] as jfr
     [junit-platform-launcher] as launcher
     [junit-platform-reporting] as reporting
-    [junit-platform-runner] as runner
     [junit-platform-suite] as suite
     [junit-platform-suite-api] as suite_api
     [junit-platform-suite-commons] as suite_commons
@@ -83,9 +81,6 @@ engine ..> commons
 reporting ..> launcher
 reporting ......> otr_tooling_spi
 
-runner ..> suite_commons
-runner ...> junit4
-
 suite ..> suite_api
 suite ..> suite_engine
 
diff --git a/documentation/src/test/java/example/ClassTemplateDemo.java b/documentation/src/test/java/example/ClassTemplateDemo.java
index d0291dedfbdf..93f669ab5be2 100644
--- a/documentation/src/test/java/example/ClassTemplateDemo.java
+++ b/documentation/src/test/java/example/ClassTemplateDemo.java
@@ -11,14 +11,13 @@
 package example;
 
 import static java.util.Collections.singletonList;
-import static java.util.Collections.unmodifiableList;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
-import java.util.Arrays;
 import java.util.List;
 import java.util.stream.Stream;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.ClassTemplate;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ClassTemplateInvocationContext;
@@ -35,8 +34,11 @@ class ClassTemplateDemo {
 
 	static final List<String> WELL_KNOWN_FRUITS
 	// tag::custom_line_break[]
-		= unmodifiableList(Arrays.asList("apple", "banana", "lemon"));
+		= List.of("apple", "banana", "lemon");
 
+	//end::user_guide[]
+	@Nullable
+	//tag::user_guide[]
 	private String fruit;
 
 	@Test
diff --git a/documentation/src/test/java/example/ConditionalTestExecutionDemo.java b/documentation/src/test/java/example/ConditionalTestExecutionDemo.java
index ef18bb5ddff6..0bd278ddc9c1 100644
--- a/documentation/src/test/java/example/ConditionalTestExecutionDemo.java
+++ b/documentation/src/test/java/example/ConditionalTestExecutionDemo.java
@@ -10,10 +10,11 @@
 
 package example;
 
-import static org.junit.jupiter.api.condition.JRE.JAVA_11;
 import static org.junit.jupiter.api.condition.JRE.JAVA_17;
+import static org.junit.jupiter.api.condition.JRE.JAVA_18;
+import static org.junit.jupiter.api.condition.JRE.JAVA_19;
 import static org.junit.jupiter.api.condition.JRE.JAVA_21;
-import static org.junit.jupiter.api.condition.JRE.JAVA_9;
+import static org.junit.jupiter.api.condition.JRE.JAVA_25;
 import static org.junit.jupiter.api.condition.OS.LINUX;
 import static org.junit.jupiter.api.condition.OS.MAC;
 import static org.junit.jupiter.api.condition.OS.WINDOWS;
@@ -113,44 +114,44 @@ void onJava17And21() {
 	}
 
 	@Test
-	@EnabledForJreRange(min = JAVA_9, max = JAVA_11)
-	void fromJava9To11() {
+	@EnabledForJreRange(min = JAVA_21, max = JAVA_25)
+	void fromJava21To25() {
 		// ...
 	}
 
 	@Test
-	@EnabledForJreRange(min = JAVA_9)
-	void onJava9AndHigher() {
+	@EnabledForJreRange(min = JAVA_21)
+	void onJava21ndHigher() {
 		// ...
 	}
 
 	@Test
-	@EnabledForJreRange(max = JAVA_11)
-	void fromJava8To11() {
+	@EnabledForJreRange(max = JAVA_18)
+	void fromJava17To18() {
 		// ...
 	}
 
 	@Test
-	@DisabledOnJre(JAVA_9)
-	void notOnJava9() {
+	@DisabledOnJre(JAVA_19)
+	void notOnJava19() {
 		// ...
 	}
 
 	@Test
-	@DisabledForJreRange(min = JAVA_9, max = JAVA_11)
-	void notFromJava9To11() {
+	@DisabledForJreRange(min = JAVA_17, max = JAVA_17)
+	void notFromJava17To19() {
 		// ...
 	}
 
 	@Test
-	@DisabledForJreRange(min = JAVA_9)
-	void notOnJava9AndHigher() {
+	@DisabledForJreRange(min = JAVA_19)
+	void notOnJava19AndHigher() {
 		// ...
 	}
 
 	@Test
-	@DisabledForJreRange(max = JAVA_11)
-	void notFromJava8To11() {
+	@DisabledForJreRange(max = JAVA_18)
+	void notFromJava17To18() {
 		// ...
 	}
 	// end::user_guide_jre[]
diff --git a/documentation/src/test/java/example/DynamicTestsDemo.java b/documentation/src/test/java/example/DynamicTestsDemo.java
index c5643890b2d3..547a3e122174 100644
--- a/documentation/src/test/java/example/DynamicTestsDemo.java
+++ b/documentation/src/test/java/example/DynamicTestsDemo.java
@@ -47,7 +47,7 @@ class DynamicTestsDemo {
 	@TestFactory
 	// end::user_guide[]
 	@Tag("exclude")
-	DynamicTest dummy() { return null; }
+	DynamicTest dummy() { return dynamicTest("dummy", () -> {}); }
 	// tag::user_guide[]
 	List<String> dynamicTestsWithInvalidReturnType() {
 		return Arrays.asList("Hello");
@@ -103,7 +103,7 @@ Stream<DynamicTest> generateRandomNumberOfTests() {
 
 		// Generates random positive integers between 0 and 100 until
 		// a number evenly divisible by 7 is encountered.
-		Iterator<Integer> inputGenerator = new Iterator<Integer>() {
+		Iterator<Integer> inputGenerator = new Iterator<>() {
 
 			Random random = new Random();
 			// end::user_guide[]
diff --git a/documentation/src/test/java21/example/DynamicTestsNamedDemo.java b/documentation/src/test/java/example/DynamicTestsNamedDemo.java
similarity index 97%
rename from documentation/src/test/java21/example/DynamicTestsNamedDemo.java
rename to documentation/src/test/java/example/DynamicTestsNamedDemo.java
index 0d515a8b49bc..97dfd35f5bee 100644
--- a/documentation/src/test/java21/example/DynamicTestsNamedDemo.java
+++ b/documentation/src/test/java/example/DynamicTestsNamedDemo.java
@@ -64,7 +64,7 @@ record PalindromeNamedExecutable(String text) implements NamedExecutable {
 
 		@Override
 		public String getName() {
-			return String.format("'%s' is a palindrome", text);
+			return "'%s' is a palindrome".formatted(text);
 		}
 
 		@Override
diff --git a/documentation/src/test/java/example/ExplicitExecutionModeDemo.java b/documentation/src/test/java/example/ExplicitExecutionModeDemo.java
new file mode 100644
index 000000000000..83735b7b8419
--- /dev/null
+++ b/documentation/src/test/java/example/ExplicitExecutionModeDemo.java
@@ -0,0 +1,30 @@
+/*
+ * Copyright 2015-2025 the original author or authors.
+ *
+ * All rights reserved. This program and the accompanying materials are
+ * made available under the terms of the Eclipse Public License v2.0 which
+ * accompanies this distribution and is available at
+ *
+ * https://www.eclipse.org/legal/epl-v20.html
+ */
+
+package example;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.parallel.Execution;
+import org.junit.jupiter.api.parallel.ExecutionMode;
+
+@Execution(ExecutionMode.CONCURRENT)
+class ExplicitExecutionModeDemo {
+
+	@Test
+	void testA() {
+		// concurrent
+	}
+
+	@Test
+	@Execution(ExecutionMode.SAME_THREAD)
+	void testB() {
+		// overrides to same_thread
+	}
+}
diff --git a/documentation/src/test/java/example/ExternalFieldSourceDemo.java b/documentation/src/test/java/example/ExternalFieldSourceDemo.java
index b6bdc67d5364..d981669d46dc 100644
--- a/documentation/src/test/java/example/ExternalFieldSourceDemo.java
+++ b/documentation/src/test/java/example/ExternalFieldSourceDemo.java
@@ -10,8 +10,6 @@
 
 package example;
 
-import java.util.Arrays;
-import java.util.Collections;
 import java.util.List;
 
 import org.junit.jupiter.params.ParameterizedTest;
@@ -30,6 +28,6 @@ void testWithExternalFieldSource(String tropicalFruit) {
 
 class FruitUtils {
 
-	public static final List<String> tropicalFruits = Collections.unmodifiableList(Arrays.asList("pineapple", "kiwi"));
+	public static final List<String> tropicalFruits = List.of("pineapple", "kiwi");
 
 }
diff --git a/documentation/src/test/java/example/FirstCustomEngine.java b/documentation/src/test/java/example/FirstCustomEngine.java
index efd9b14a7f0c..46c66f926540 100644
--- a/documentation/src/test/java/example/FirstCustomEngine.java
+++ b/documentation/src/test/java/example/FirstCustomEngine.java
@@ -18,6 +18,7 @@
 import java.io.UncheckedIOException;
 import java.net.ServerSocket;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.engine.EngineDiscoveryRequest;
 import org.junit.platform.engine.ExecutionRequest;
 import org.junit.platform.engine.TestDescriptor;
@@ -32,6 +33,9 @@
  */
 public class FirstCustomEngine implements TestEngine {
 
+	//end::user_guide[]
+	@Nullable
+	//tag::user_guide[]
 	public ServerSocket socket;
 
 	@Override
@@ -44,6 +48,9 @@ public TestDescriptor discover(EngineDiscoveryRequest discoveryRequest, UniqueId
 		return new EngineDescriptor(uniqueId, "First Custom Test Engine");
 	}
 
+	//end::user_guide[]
+	@SuppressWarnings("NullAway")
+	//tag::user_guide[]
 	@Override
 	public void execute(ExecutionRequest request) {
 		request.getEngineExecutionListener()
diff --git a/documentation/src/test/java/example/HttpServerDemo.java b/documentation/src/test/java/example/HttpServerDemo.java
index 6411ec5d19c4..7ef0055af765 100644
--- a/documentation/src/test/java/example/HttpServerDemo.java
+++ b/documentation/src/test/java/example/HttpServerDemo.java
@@ -37,7 +37,7 @@ public class HttpServerDemo {
 	void httpCall(HttpServer server) throws Exception {
 		String hostName = server.getAddress().getHostName();
 		int port = server.getAddress().getPort();
-		String rawUrl = String.format("http://%s:%d/example", hostName, port);
+		String rawUrl = "http://%s:%d/example".formatted(hostName, port);
 		URL requestUrl = URI.create(rawUrl).toURL();
 
 		String responseBody = sendRequest(requestUrl);
diff --git a/documentation/src/test/java/example/IgnoredTestsDemo.java b/documentation/src/test/java/example/IgnoredTestsDemo.java
index 4718c922ca9f..3daf582d6f90 100644
--- a/documentation/src/test/java/example/IgnoredTestsDemo.java
+++ b/documentation/src/test/java/example/IgnoredTestsDemo.java
@@ -16,6 +16,7 @@
 import org.junit.jupiter.migrationsupport.EnableJUnit4MigrationSupport;
 
 // @ExtendWith(IgnoreCondition.class)
+@SuppressWarnings("removal")
 @EnableJUnit4MigrationSupport
 class IgnoredTestsDemo {
 
diff --git a/documentation/src/test/java/example/JUnitPlatformClassDemo.java b/documentation/src/test/java/example/JUnitPlatformClassDemo.java
deleted file mode 100644
index bf776d627f6c..000000000000
--- a/documentation/src/test/java/example/JUnitPlatformClassDemo.java
+++ /dev/null
@@ -1,39 +0,0 @@
-/*
- * Copyright 2015-2025 the original author or authors.
- *
- * All rights reserved. This program and the accompanying materials are
- * made available under the terms of the Eclipse Public License v2.0 which
- * accompanies this distribution and is available at
- *
- * https://www.eclipse.org/legal/epl-v20.html
- */
-
-package example;
-
-// tag::user_guide[]
-import static org.junit.jupiter.api.Assertions.fail;
-
-import org.junit.jupiter.api.Test;
-import org.junit.runner.RunWith;
-
-//end::user_guide[]
-@SuppressWarnings("deprecation")
-//tag::user_guide[]
-@RunWith(org.junit.platform.runner.JUnitPlatform.class)
-public class JUnitPlatformClassDemo {
-
-	@Test
-	void succeedingTest() {
-		/* no-op */
-	}
-
-	// end::user_guide[]
-	@extensions.ExpectToFail
-	// tag::user_guide[]
-	@Test
-	void failingTest() {
-		fail("Failing for failing's sake.");
-	}
-
-}
-// end::user_guide[]
diff --git a/documentation/src/test/java/example/JUnitPlatformSuiteDemo.java b/documentation/src/test/java/example/JUnitPlatformSuiteDemo.java
deleted file mode 100644
index 259486cee3f8..000000000000
--- a/documentation/src/test/java/example/JUnitPlatformSuiteDemo.java
+++ /dev/null
@@ -1,27 +0,0 @@
-/*
- * Copyright 2015-2025 the original author or authors.
- *
- * All rights reserved. This program and the accompanying materials are
- * made available under the terms of the Eclipse Public License v2.0 which
- * accompanies this distribution and is available at
- *
- * https://www.eclipse.org/legal/epl-v20.html
- */
-
-package example;
-
-//tag::user_guide[]
-import org.junit.platform.suite.api.SelectPackages;
-import org.junit.platform.suite.api.SuiteDisplayName;
-import org.junit.runner.RunWith;
-
-@RunWith(org.junit.platform.runner.JUnitPlatform.class)
-@SuiteDisplayName("JUnit Platform Suite Demo")
-@SelectPackages("example")
-//end::user_guide[]
-@SuppressWarnings("deprecation")
-@org.junit.platform.suite.api.ExcludeTags("exclude")
-//tag::user_guide[]
-public class JUnitPlatformSuiteDemo {
-}
-//end::user_guide[]
diff --git a/documentation/src/test/java21/example/MyFirstJUnitJupiterRecordTests.java b/documentation/src/test/java/example/MyFirstJUnitJupiterRecordTests.java
similarity index 100%
rename from documentation/src/test/java21/example/MyFirstJUnitJupiterRecordTests.java
rename to documentation/src/test/java/example/MyFirstJUnitJupiterRecordTests.java
diff --git a/documentation/src/test/java21/example/ParameterizedLifecycleDemo.java b/documentation/src/test/java/example/ParameterizedLifecycleDemo.java
similarity index 90%
rename from documentation/src/test/java21/example/ParameterizedLifecycleDemo.java
rename to documentation/src/test/java/example/ParameterizedLifecycleDemo.java
index c55f121cfb3f..d06247be9518 100644
--- a/documentation/src/test/java21/example/ParameterizedLifecycleDemo.java
+++ b/documentation/src/test/java/example/ParameterizedLifecycleDemo.java
@@ -17,6 +17,7 @@
 import java.nio.file.Path;
 import java.util.List;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.io.TempDir;
@@ -53,6 +54,9 @@ static void beforeInvocation(TextFile textFile, @TempDir Path tempDir) throws Ex
 			textFile.path = Files.writeString(filePath, textFile.content);
 		}
 
+		//end::user_guide[]
+		@SuppressWarnings("DataFlowIssue")
+		//tag::user_guide[]
 		@AfterParameterizedClassInvocation
 		static void afterInvocation(TextFile textFile) throws Exception {
 			var actualContent = Files.readString(textFile.path); // <3>
@@ -61,6 +65,9 @@ static void afterInvocation(TextFile textFile) throws Exception {
 			// File will be deleted automatically by @TempDir support
 		}
 
+		//end::user_guide[]
+		@SuppressWarnings("DataFlowIssue")
+		//tag::user_guide[]
 		@Test
 		void test() {
 			assertTrue(Files.exists(textFile.path)); // <2>
@@ -75,6 +82,9 @@ static class TextFile {
 
 			final String fileName;
 			final String content;
+			// end::example[]
+			@Nullable
+			// tag::example[]
 			Path path;
 
 			TextFile(String fileName, String content) {
diff --git a/documentation/src/test/java21/example/ParameterizedRecordDemo.java b/documentation/src/test/java/example/ParameterizedRecordDemo.java
similarity index 100%
rename from documentation/src/test/java21/example/ParameterizedRecordDemo.java
rename to documentation/src/test/java/example/ParameterizedRecordDemo.java
diff --git a/documentation/src/test/java/example/ParameterizedTestDemo.java b/documentation/src/test/java/example/ParameterizedTestDemo.java
index 50bf1ff882fa..a7312f584cc5 100644
--- a/documentation/src/test/java/example/ParameterizedTestDemo.java
+++ b/documentation/src/test/java/example/ParameterizedTestDemo.java
@@ -459,14 +459,15 @@ void testWithExplicitArgumentConversion(
 
 	// end::explicit_conversion_example[]
 	static
+	@SuppressWarnings({ "NullableProblems", "NullAway" })
 	// tag::explicit_conversion_example_ToStringArgumentConverter[]
 	public class ToStringArgumentConverter extends SimpleArgumentConverter {
 
 		@Override
 		protected Object convert(Object source, Class<?> targetType) {
 			assertEquals(String.class, targetType, "Can only convert to String");
-			if (source instanceof Enum<?>) {
-				return ((Enum<?>) source).name();
+			if (source instanceof Enum<?> constant) {
+				return constant.name();
 			}
 			return String.valueOf(source);
 		}
@@ -474,6 +475,7 @@ protected Object convert(Object source, Class<?> targetType) {
 	// end::explicit_conversion_example_ToStringArgumentConverter[]
 
 	static
+	@SuppressWarnings({ "NullableProblems", "NullAway", "ConstantValue" })
 	// tag::explicit_conversion_example_TypedArgumentConverter[]
 	public class ToLengthArgumentConverter extends TypedArgumentConverter<String, Integer> {
 
diff --git a/documentation/src/test/java/example/RepeatedTestsDemo.java b/documentation/src/test/java/example/RepeatedTestsDemo.java
index dd23f1f39158..6f05dc3603c6 100644
--- a/documentation/src/test/java/example/RepeatedTestsDemo.java
+++ b/documentation/src/test/java/example/RepeatedTestsDemo.java
@@ -38,7 +38,7 @@ void beforeEach(TestInfo testInfo, RepetitionInfo repetitionInfo) {
 		int currentRepetition = repetitionInfo.getCurrentRepetition();
 		int totalRepetitions = repetitionInfo.getTotalRepetitions();
 		String methodName = testInfo.getTestMethod().get().getName();
-		logger.info(String.format("About to execute repetition %d of %d for %s", //
+		logger.info("About to execute repetition %d of %d for %s".formatted( //
 			currentRepetition, totalRepetitions, methodName));
 	}
 
diff --git a/documentation/src/test/java/example/SecondCustomEngine.java b/documentation/src/test/java/example/SecondCustomEngine.java
index 3d11c13ac18d..f41223d6dfcc 100644
--- a/documentation/src/test/java/example/SecondCustomEngine.java
+++ b/documentation/src/test/java/example/SecondCustomEngine.java
@@ -17,6 +17,7 @@
 import java.io.UncheckedIOException;
 import java.net.ServerSocket;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.engine.EngineDiscoveryRequest;
 import org.junit.platform.engine.ExecutionRequest;
 import org.junit.platform.engine.TestDescriptor;
@@ -32,6 +33,9 @@
  */
 public class SecondCustomEngine implements TestEngine {
 
+	//end::user_guide[]
+	@Nullable
+	//tag::user_guide[]
 	public ServerSocket socket;
 
 	@Override
@@ -44,6 +48,9 @@ public TestDescriptor discover(EngineDiscoveryRequest discoveryRequest, UniqueId
 		return new EngineDescriptor(uniqueId, "Second Custom Test Engine");
 	}
 
+	//end::user_guide[]
+	@SuppressWarnings("NullAway")
+	//tag::user_guide[]
 	@Override
 	public void execute(ExecutionRequest request) {
 		request.getEngineExecutionListener()
diff --git a/documentation/src/test/java/example/TestingAStackDemo.java b/documentation/src/test/java/example/TestingAStackDemo.java
index 80b1ec495d83..c4ef3a5640dc 100644
--- a/documentation/src/test/java/example/TestingAStackDemo.java
+++ b/documentation/src/test/java/example/TestingAStackDemo.java
@@ -27,8 +27,6 @@
 @DisplayName("A stack")
 class TestingAStackDemo {
 
-	Stack<Object> stack;
-
 	@Test
 	@DisplayName("is instantiated with new Stack()")
 	void isInstantiatedWithNew() {
@@ -39,6 +37,8 @@ void isInstantiatedWithNew() {
 	@DisplayName("when new")
 	class WhenNew {
 
+		Stack<Object> stack;
+
 		@BeforeEach
 		void createNewStack() {
 			stack = new Stack<>();
diff --git a/documentation/src/test/java/example/UsingTheLauncherDemo.java b/documentation/src/test/java/example/UsingTheLauncherDemo.java
index 6b0a2d508237..ee5ff525c565 100644
--- a/documentation/src/test/java/example/UsingTheLauncherDemo.java
+++ b/documentation/src/test/java/example/UsingTheLauncherDemo.java
@@ -17,7 +17,6 @@
 
 import java.io.PrintWriter;
 import java.nio.file.Path;
-import java.nio.file.Paths;
 
 import org.junit.platform.engine.FilterResult;
 import org.junit.platform.engine.TestDescriptor;
@@ -111,7 +110,7 @@ void execution() {
 
 	@org.junit.jupiter.api.Test
 	void launcherConfig() {
-		Path reportsDir = Paths.get("target", "xml-reports");
+		Path reportsDir = Path.of("target", "xml-reports");
 		PrintWriter out = new PrintWriter(System.out);
 		// @formatter:off
 		// tag::launcherConfig[]
diff --git a/documentation/src/test/java/example/callbacks/package-info.java b/documentation/src/test/java/example/callbacks/package-info.java
new file mode 100644
index 000000000000..a58f6d3a9a52
--- /dev/null
+++ b/documentation/src/test/java/example/callbacks/package-info.java
@@ -0,0 +1,5 @@
+
+@NullMarked
+package example.callbacks;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/documentation/src/test/java/example/defaultmethods/package-info.java b/documentation/src/test/java/example/defaultmethods/package-info.java
new file mode 100644
index 000000000000..851eeadc2f84
--- /dev/null
+++ b/documentation/src/test/java/example/defaultmethods/package-info.java
@@ -0,0 +1,5 @@
+
+@NullMarked
+package example.defaultmethods;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/documentation/src/test/java/example/exception/package-info.java b/documentation/src/test/java/example/exception/package-info.java
new file mode 100644
index 000000000000..5c758dfba6c9
--- /dev/null
+++ b/documentation/src/test/java/example/exception/package-info.java
@@ -0,0 +1,5 @@
+
+@NullMarked
+package example.exception;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/documentation/src/test/java/example/extensions/HttpServerExtension.java b/documentation/src/test/java/example/extensions/HttpServerExtension.java
index 5ba23509d964..33a447468790 100644
--- a/documentation/src/test/java/example/extensions/HttpServerExtension.java
+++ b/documentation/src/test/java/example/extensions/HttpServerExtension.java
@@ -28,12 +28,15 @@ public boolean supportsParameter(ParameterContext parameterContext, ExtensionCon
 		return HttpServer.class.equals(parameterContext.getParameter().getType());
 	}
 
+	//end::user_guide[]
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
+	//tag::user_guide[]
 	@Override
 	public Object resolveParameter(ParameterContext parameterContext, ExtensionContext extensionContext) {
 
 		ExtensionContext rootContext = extensionContext.getRoot();
 		ExtensionContext.Store store = rootContext.getStore(Namespace.GLOBAL);
-		String key = HttpServerResource.class.getName();
+		Class<HttpServerResource> key = HttpServerResource.class;
 		HttpServerResource resource = store.getOrComputeIfAbsent(key, __ -> {
 			try {
 				HttpServerResource serverResource = new HttpServerResource(0);
diff --git a/documentation/src/test/java/example/extensions/RandomNumberDemo.java b/documentation/src/test/java/example/extensions/RandomNumberDemo.java
index e11b87ce5b52..6cdbb7cdb87b 100644
--- a/documentation/src/test/java/example/extensions/RandomNumberDemo.java
+++ b/documentation/src/test/java/example/extensions/RandomNumberDemo.java
@@ -10,6 +10,7 @@
 
 package example.extensions;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
@@ -19,6 +20,9 @@ class RandomNumberDemo {
 	// Use static randomNumber0 field anywhere in the test class,
 	// including @BeforeAll or @AfterEach lifecycle methods.
 	@Random
+	// end::user_guide[]
+	@Nullable
+	// tag::user_guide[]
 	private static Integer randomNumber0;
 
 	// Use randomNumber1 field in test methods and @BeforeEach
diff --git a/documentation/src/test/java/example/extensions/RandomNumberExtension.java b/documentation/src/test/java/example/extensions/RandomNumberExtension.java
index 666e6ffe9ae5..c3386b0972f1 100644
--- a/documentation/src/test/java/example/extensions/RandomNumberExtension.java
+++ b/documentation/src/test/java/example/extensions/RandomNumberExtension.java
@@ -17,6 +17,7 @@
 import java.lang.reflect.Field;
 import java.util.function.Predicate;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.extension.BeforeAllCallback;
 import org.junit.jupiter.api.extension.ExtensionContext;
 import org.junit.jupiter.api.extension.ParameterContext;
@@ -69,7 +70,7 @@ public Integer resolveParameter(ParameterContext pc, ExtensionContext ec) {
 		return this.random.nextInt();
 	}
 
-	private void injectFields(Class<?> testClass, Object testInstance,
+	private void injectFields(Class<?> testClass, @Nullable Object testInstance,
 			Predicate<Field> predicate) {
 
 		predicate = predicate.and(field -> isInteger(field.getType()));
diff --git a/documentation/src/test/java/example/extensions/package-info.java b/documentation/src/test/java/example/extensions/package-info.java
new file mode 100644
index 000000000000..df450c1a5811
--- /dev/null
+++ b/documentation/src/test/java/example/extensions/package-info.java
@@ -0,0 +1,5 @@
+
+@NullMarked
+package example.extensions;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/documentation/src/test/java/example/interceptor/SwingEdtInterceptor.java b/documentation/src/test/java/example/interceptor/SwingEdtInterceptor.java
index 348fd3607c1a..657ec3ca70a4 100644
--- a/documentation/src/test/java/example/interceptor/SwingEdtInterceptor.java
+++ b/documentation/src/test/java/example/interceptor/SwingEdtInterceptor.java
@@ -23,6 +23,9 @@
 // tag::user_guide[]
 public class SwingEdtInterceptor implements InvocationInterceptor {
 
+	//end::user_guide[]
+	@SuppressWarnings("NullAway")
+	//tag::user_guide[]
 	@Override
 	public void interceptTestMethod(Invocation<Void> invocation,
 			ReflectiveInvocationContext<Method> invocationContext,
diff --git a/documentation/src/test/java/example/interceptor/package-info.java b/documentation/src/test/java/example/interceptor/package-info.java
new file mode 100644
index 000000000000..ece161c1da00
--- /dev/null
+++ b/documentation/src/test/java/example/interceptor/package-info.java
@@ -0,0 +1,5 @@
+
+@NullMarked
+package example.interceptor;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/documentation/src/test/java/example/package-info.java b/documentation/src/test/java/example/package-info.java
new file mode 100644
index 000000000000..a2bcf4a4db17
--- /dev/null
+++ b/documentation/src/test/java/example/package-info.java
@@ -0,0 +1,5 @@
+
+@NullMarked
+package example;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/documentation/src/test/java/example/registration/DocumentationDemo.java b/documentation/src/test/java/example/registration/DocumentationDemo.java
index 59571061d7de..36bc544a4e7a 100644
--- a/documentation/src/test/java/example/registration/DocumentationDemo.java
+++ b/documentation/src/test/java/example/registration/DocumentationDemo.java
@@ -12,6 +12,8 @@
 
 import java.nio.file.Path;
 
+import org.jspecify.annotations.NullMarked;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.AfterEachCallback;
 import org.junit.jupiter.api.extension.ExtensionContext;
@@ -20,6 +22,9 @@
 //tag::user_guide[]
 class DocumentationDemo {
 
+	//end::user_guide[]
+	@Nullable
+	//tag::user_guide[]
 	static Path lookUpDocsDir() {
 		// return path to docs dir
 		// end::user_guide[]
@@ -37,16 +42,17 @@ void generateDocumentation() {
 }
 //end::user_guide[]
 
+@NullMarked
 class DocumentationExtension implements AfterEachCallback {
 
 	@SuppressWarnings("unused")
-	private final Path path;
+	private final @Nullable Path path;
 
-	private DocumentationExtension(Path path) {
+	private DocumentationExtension(@Nullable Path path) {
 		this.path = path;
 	}
 
-	static DocumentationExtension forPath(Path path) {
+	static DocumentationExtension forPath(@Nullable Path path) {
 		return new DocumentationExtension(path);
 	}
 
diff --git a/documentation/src/test/java/example/session/HttpTests.java b/documentation/src/test/java/example/session/HttpTests.java
index 97a13439a3e4..ed68c283380f 100644
--- a/documentation/src/test/java/example/session/HttpTests.java
+++ b/documentation/src/test/java/example/session/HttpTests.java
@@ -49,6 +49,9 @@ public boolean supportsParameter(ParameterContext parameterContext, ExtensionCon
 		return HttpServer.class.equals(parameterContext.getParameter().getType());
 	}
 
+	//end::user_guide[]
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
+	//tag::user_guide[]
 	@Override
 	public Object resolveParameter(ParameterContext parameterContext, ExtensionContext extensionContext) {
 		return extensionContext
diff --git a/documentation/src/test/java/example/session/package-info.java b/documentation/src/test/java/example/session/package-info.java
new file mode 100644
index 000000000000..7f7249dfecf0
--- /dev/null
+++ b/documentation/src/test/java/example/session/package-info.java
@@ -0,0 +1,5 @@
+
+@NullMarked
+package example.session;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/documentation/src/test/java/example/sharedresources/SharedResourceDemo.java b/documentation/src/test/java/example/sharedresources/SharedResourceDemo.java
index 52b00c624471..4ca8e4a11efb 100644
--- a/documentation/src/test/java/example/sharedresources/SharedResourceDemo.java
+++ b/documentation/src/test/java/example/sharedresources/SharedResourceDemo.java
@@ -24,6 +24,7 @@
 
 class SharedResourceDemo {
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	//tag::user_guide[]
 	@Test
 	void runBothCustomEnginesTest() {
diff --git a/documentation/src/test/java/example/sharedresources/package-info.java b/documentation/src/test/java/example/sharedresources/package-info.java
new file mode 100644
index 000000000000..02e87d295042
--- /dev/null
+++ b/documentation/src/test/java/example/sharedresources/package-info.java
@@ -0,0 +1,5 @@
+
+@NullMarked
+package example.sharedresources;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/documentation/src/test/java/example/testinterface/TestLifecycleLogger.java b/documentation/src/test/java/example/testinterface/TestLifecycleLogger.java
index ae54cd61c3cf..0906b8674e6c 100644
--- a/documentation/src/test/java/example/testinterface/TestLifecycleLogger.java
+++ b/documentation/src/test/java/example/testinterface/TestLifecycleLogger.java
@@ -39,13 +39,13 @@ default void afterAllTests() {
 
 	@BeforeEach
 	default void beforeEachTest(TestInfo testInfo) {
-		logger.info(() -> String.format("About to execute [%s]",
+		logger.info(() -> "About to execute [%s]".formatted(
 			testInfo.getDisplayName()));
 	}
 
 	@AfterEach
 	default void afterEachTest(TestInfo testInfo) {
-		logger.info(() -> String.format("Finished executing [%s]",
+		logger.info(() -> "Finished executing [%s]".formatted(
 			testInfo.getDisplayName()));
 	}
 
diff --git a/documentation/src/test/java/example/testinterface/package-info.java b/documentation/src/test/java/example/testinterface/package-info.java
new file mode 100644
index 000000000000..3c0a7b9e0712
--- /dev/null
+++ b/documentation/src/test/java/example/testinterface/package-info.java
@@ -0,0 +1,5 @@
+
+@NullMarked
+package example.testinterface;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/documentation/src/test/java/example/testkit/package-info.java b/documentation/src/test/java/example/testkit/package-info.java
new file mode 100644
index 000000000000..bb644c62acd1
--- /dev/null
+++ b/documentation/src/test/java/example/testkit/package-info.java
@@ -0,0 +1,5 @@
+
+@NullMarked
+package example.testkit;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/documentation/src/test/java/example/timing/TimingExtension.java b/documentation/src/test/java/example/timing/TimingExtension.java
index 4d12db567543..f07abe049c3e 100644
--- a/documentation/src/test/java/example/timing/TimingExtension.java
+++ b/documentation/src/test/java/example/timing/TimingExtension.java
@@ -36,18 +36,21 @@ public class TimingExtension implements BeforeTestExecutionCallback, AfterTestEx
 	private static final String START_TIME = "start time";
 
 	@Override
-	public void beforeTestExecution(ExtensionContext context) throws Exception {
+	public void beforeTestExecution(ExtensionContext context) {
 		getStore(context).put(START_TIME, System.currentTimeMillis());
 	}
 
+	//end::user_guide[]
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
+	//tag::user_guide[]
 	@Override
-	public void afterTestExecution(ExtensionContext context) throws Exception {
+	public void afterTestExecution(ExtensionContext context) {
 		Method testMethod = context.getRequiredTestMethod();
 		long startTime = getStore(context).remove(START_TIME, long.class);
 		long duration = System.currentTimeMillis() - startTime;
 
 		logger.info(() ->
-			String.format("Method [%s] took %s ms.", testMethod.getName(), duration));
+			"Method [%s] took %s ms.".formatted(testMethod.getName(), duration));
 	}
 
 	private Store getStore(ExtensionContext context) {
diff --git a/documentation/src/test/java/example/timing/package-info.java b/documentation/src/test/java/example/timing/package-info.java
new file mode 100644
index 000000000000..545aa617da23
--- /dev/null
+++ b/documentation/src/test/java/example/timing/package-info.java
@@ -0,0 +1,5 @@
+
+@NullMarked
+package example.timing;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/documentation/src/test/java/extensions/package-info.java b/documentation/src/test/java/extensions/package-info.java
new file mode 100644
index 000000000000..edd479f63275
--- /dev/null
+++ b/documentation/src/test/java/extensions/package-info.java
@@ -0,0 +1,5 @@
+
+@NullMarked
+package extensions;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/documentation/src/test/kotlin/example/KotlinCoroutinesDemo.kt b/documentation/src/test/kotlin/example/KotlinCoroutinesDemo.kt
new file mode 100644
index 000000000000..993f75388025
--- /dev/null
+++ b/documentation/src/test/kotlin/example/KotlinCoroutinesDemo.kt
@@ -0,0 +1,36 @@
+/*
+ * Copyright 2015-2025 the original author or authors.
+ *
+ * All rights reserved. This program and the accompanying materials are
+ * made available under the terms of the Eclipse Public License v2.0 which
+ * accompanies this distribution and is available at
+ *
+ * https://www.eclipse.org/legal/epl-v20.html
+ */
+package example
+
+// tag::user_guide[]
+import org.junit.jupiter.api.BeforeEach
+import org.junit.jupiter.api.Test
+
+// end::user_guide[]
+// tag::user_guide[]
+@Suppress("JUnitMalformedDeclaration")
+class KotlinCoroutinesDemo {
+    @BeforeEach
+    fun regularSetUp() {
+    }
+
+    @BeforeEach
+    suspend fun coroutineSetUp() {
+    }
+
+    @Test
+    fun regularTest() {
+    }
+
+    @Test
+    suspend fun coroutineTest() {
+    }
+}
+// end::user_guide[]
diff --git a/documentation/src/tools/java/org/junit/api/tools/AbstractApiReportWriter.java b/documentation/src/tools/java/org/junit/api/tools/AbstractApiReportWriter.java
index a35b60211bb4..5dcc98bd6f06 100644
--- a/documentation/src/tools/java/org/junit/api/tools/AbstractApiReportWriter.java
+++ b/documentation/src/tools/java/org/junit/api/tools/AbstractApiReportWriter.java
@@ -16,6 +16,7 @@
 
 import java.io.PrintWriter;
 import java.util.List;
+import java.util.Map;
 import java.util.Set;
 import java.util.TreeMap;
 
@@ -39,7 +40,7 @@ public void printReportHeader(PrintWriter out) {
 		out.println(h1("@API Declarations"));
 		out.println();
 		out.println(paragraph(
-			format("Discovered %d types with %s declarations.", this.apiReport.types().size(), code("@API"))));
+			"Discovered %d types with %s declarations.".formatted(this.apiReport.types().size(), code("@API"))));
 		out.println();
 	}
 
@@ -52,22 +53,27 @@ public void printDeclarationInfo(PrintWriter out, Set<Status> statuses) {
 	protected void printDeclarationSection(Set<Status> statuses, Status status, List<Declaration> declarations,
 			PrintWriter out) {
 		printDeclarationSectionHeader(statuses, status, declarations, out);
-		declarations.stream() //
-				.collect(groupingBy(Declaration::moduleName, TreeMap::new, toList())) //
-				.forEach((moduleName, moduleDeclarations) -> {
-					out.println(h4("Module " + moduleName));
-					out.println();
-					moduleDeclarations.stream() //
-							.collect(groupingBy(Declaration::packageName, TreeMap::new, toList())) //
-							.forEach((packageName, packageDeclarations) -> {
-								out.println(h5("Package " + packageName));
-								out.println();
-								printDeclarationTableHeader(out);
-								packageDeclarations.forEach(it -> printDeclarationTableRow(it, out));
-								printDeclarationTableFooter(out);
-								out.println();
-							});
-				});
+		Map<String, List<Declaration>> declarationsByModule = declarations.stream() //
+				.collect(groupingBy(Declaration::moduleName, TreeMap::new, toList()));
+		if (declarationsByModule.isEmpty()) {
+			out.println(paragraph("NOTE: There are currently no APIs annotated with %s.".formatted(
+				code("@API(status = %s)".formatted(status.name())))));
+			return;
+		}
+		declarationsByModule.forEach((moduleName, moduleDeclarations) -> {
+			out.println(h4("Module " + moduleName));
+			out.println();
+			moduleDeclarations.stream() //
+					.collect(groupingBy(Declaration::packageName, TreeMap::new, toList())) //
+					.forEach((packageName, packageDeclarations) -> {
+						out.println(h5("Package " + packageName));
+						out.println();
+						printDeclarationTableHeader(out);
+						packageDeclarations.forEach(it -> printDeclarationTableRow(it, out));
+						printDeclarationTableFooter(out);
+						out.println();
+					});
+		});
 	}
 
 	protected void printDeclarationSectionHeader(Set<Status> statuses, Status status, List<Declaration> declarations,
@@ -76,7 +82,7 @@ protected void printDeclarationSectionHeader(Set<Status> statuses, Status status
 			// omit section header when only a single status is printed
 			return;
 		}
-		out.println(h2(format("@API(%s)", status)));
+		out.println(h2("@API(%s)".formatted(status)));
 		out.println();
 		out.println(
 			paragraph(format("Discovered %d " + code("@API(%s)") + " declarations.", declarations.size(), status)));
diff --git a/gradle.properties b/gradle.properties
index 6a96f24ce567..3b591bcde84e 100644
--- a/gradle.properties
+++ b/gradle.properties
@@ -1,20 +1,11 @@
-group           = org.junit
-version         = 5.13.0-RC1
-
-jupiterGroup    = org.junit.jupiter
-
-platformGroup   = org.junit.platform
-platformVersion = 1.13.0-RC1
-
-vintageGroup    = org.junit.vintage
-vintageVersion  = 5.13.0-RC1
+version = 6.0.0-M1
 
 # We need more metaspace due to apparent memory leak in Asciidoctor/JRuby
 org.gradle.jvmargs=-Xmx1g -XX:MaxMetaspaceSize=512m -XX:+HeapDumpOnOutOfMemoryError
 org.gradle.caching=true
 org.gradle.parallel=true
 org.gradle.configuration-cache.parallel=true
-org.gradle.java.installations.fromEnv=GRAALVM_HOME,JDK8,JDK18,JDK19,JDK20,JDK21,JDK22,JDK23,JDK24
+org.gradle.java.installations.fromEnv=GRAALVM_HOME,JDK17,JDK21,JDK24,JDK25
 org.gradle.kotlin.dsl.allWarningsAsErrors=true
 
 # Test Distribution
diff --git a/gradle/base/code-generator-model/.gitignore b/gradle/base/code-generator-model/.gitignore
new file mode 100644
index 000000000000..ae3c1726048c
--- /dev/null
+++ b/gradle/base/code-generator-model/.gitignore
@@ -0,0 +1 @@
+/bin/
diff --git a/gradle/base/code-generator-model/build.gradle.kts b/gradle/base/code-generator-model/build.gradle.kts
index bc0172f0f072..ca30027739e8 100644
--- a/gradle/base/code-generator-model/build.gradle.kts
+++ b/gradle/base/code-generator-model/build.gradle.kts
@@ -1,3 +1,17 @@
+import org.jetbrains.kotlin.gradle.dsl.JvmTarget.JVM_17
+
 plugins {
     `kotlin-dsl`
 }
+
+java {
+    sourceCompatibility = JavaVersion.VERSION_17
+    targetCompatibility = JavaVersion.VERSION_17
+}
+
+kotlin {
+    compilerOptions {
+        jvmTarget = JVM_17
+        freeCompilerArgs.add("-Xjdk-release=17")
+    }
+}
diff --git a/gradle/base/code-generator-model/src/main/resources/jre.yaml b/gradle/base/code-generator-model/src/main/resources/jre.yaml
index 1747ffa12dd6..90654b64919d 100644
--- a/gradle/base/code-generator-model/src/main/resources/jre.yaml
+++ b/gradle/base/code-generator-model/src/main/resources/jre.yaml
@@ -30,3 +30,5 @@
   since: '5.11'
 - version: 25
   since: '5.11.4'
+- version: 26
+  since: '6.0'
diff --git a/gradle/base/dsl-extensions/.gitignore b/gradle/base/dsl-extensions/.gitignore
new file mode 100644
index 000000000000..ae3c1726048c
--- /dev/null
+++ b/gradle/base/dsl-extensions/.gitignore
@@ -0,0 +1 @@
+/bin/
diff --git a/gradle/base/dsl-extensions/build.gradle.kts b/gradle/base/dsl-extensions/build.gradle.kts
index bc0172f0f072..a94e377f753e 100644
--- a/gradle/base/dsl-extensions/build.gradle.kts
+++ b/gradle/base/dsl-extensions/build.gradle.kts
@@ -1,3 +1,16 @@
+import org.jetbrains.kotlin.gradle.dsl.JvmTarget.JVM_21
+
 plugins {
     `kotlin-dsl`
 }
+
+tasks.compileJava {
+    options.release = 21
+}
+
+kotlin {
+    compilerOptions {
+        jvmTarget = JVM_21
+        freeCompilerArgs.add("-Xjdk-release=21")
+    }
+}
diff --git a/gradle/base/dsl-extensions/src/main/kotlin/junitbuild/extensions/TaskExtensions.kt b/gradle/base/dsl-extensions/src/main/kotlin/junitbuild/extensions/TaskExtensions.kt
index 9cd596dfbfda..ec9a6bc492c9 100644
--- a/gradle/base/dsl-extensions/src/main/kotlin/junitbuild/extensions/TaskExtensions.kt
+++ b/gradle/base/dsl-extensions/src/main/kotlin/junitbuild/extensions/TaskExtensions.kt
@@ -1,7 +1,21 @@
 package junitbuild.extensions
 
 import org.gradle.api.Task
+import org.gradle.api.file.ArchiveOperations
 import org.gradle.internal.os.OperatingSystem
+import org.gradle.kotlin.dsl.newInstance
+import javax.inject.Inject
 
 fun Task.trackOperationSystemAsInput() =
     inputs.property("os", OperatingSystem.current().familyName)
+
+fun <T> Task.withArchiveOperations(action: (ArchiveOperations) -> T): T =
+    archiveOperations.run { action(this) }
+
+private val Task.archiveOperations: ArchiveOperations
+    get() = project.objects.newInstance(DummyObject::class).archiveOperations
+
+private abstract class DummyObject {
+    @get:Inject
+    abstract val archiveOperations: ArchiveOperations
+}
diff --git a/gradle/config/checkstyle/checkstyleMain.xml b/gradle/config/checkstyle/checkstyleMain.xml
index 27ff53749020..ed8dadaaff8d 100644
--- a/gradle/config/checkstyle/checkstyleMain.xml
+++ b/gradle/config/checkstyle/checkstyleMain.xml
@@ -43,4 +43,8 @@
 		<property name="file" value="${config_loc}/suppressions.xml"/>
 	</module>
 
+	<module name="BeforeExecutionExclusionFileFilter">
+		<property name="fileNamePattern" value="module\-info\.java$"/>
+	</module>
+
 </module>
diff --git a/gradle/config/eclipse/junit-eclipse-formatter-settings.xml b/gradle/config/eclipse/junit-eclipse-formatter-settings.xml
index 34f4f9dda2b1..974eadd7caa4 100644
--- a/gradle/config/eclipse/junit-eclipse-formatter-settings.xml
+++ b/gradle/config/eclipse/junit-eclipse-formatter-settings.xml
@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8" standalone="no"?>
 <profiles version="23">
-    <profile kind="CodeFormatterProfile" name="JUnit 5" version="23">
+    <profile kind="CodeFormatterProfile" name="JUnit" version="23">
         <setting id="org.eclipse.jdt.core.formatter.insert_space_after_ellipsis" value="insert"/>
         <setting id="org.eclipse.jdt.core.formatter.insert_space_after_comma_in_enum_declarations" value="insert"/>
         <setting id="org.eclipse.jdt.core.formatter.insert_space_before_comma_in_allocation_expression" value="do not insert"/>
diff --git a/gradle/gradle-daemon-jvm.properties b/gradle/gradle-daemon-jvm.properties
index 63e5bbdf4845..9c554284ce79 100644
--- a/gradle/gradle-daemon-jvm.properties
+++ b/gradle/gradle-daemon-jvm.properties
@@ -1,2 +1,2 @@
 #This file is generated by updateDaemonJvm
-toolchainVersion=21
+toolchainVersion=24
diff --git a/gradle/libs.versions.toml b/gradle/libs.versions.toml
index 6ab7d672fb00..9390d0778395 100644
--- a/gradle/libs.versions.toml
+++ b/gradle/libs.versions.toml
@@ -5,21 +5,21 @@ asciidoctorj-pdf = "2.3.19"
 asciidoctor-plugins = "4.0.4" # Check if workaround in documentation.gradle.kts can be removed when upgrading
 assertj = "3.27.3"
 bnd = "7.1.0"
-checkstyle = "10.23.1"
-eclipse = "4.35.0"
-jackson = "2.19.0"
+checkstyle = "10.26.0"
+eclipse = "4.36.0"
+jackson = "2.19.1"
 jacoco = "0.8.13"
 jmh = "1.37"
 junit4 = "4.13.2"
 junit4Min = "4.12"
-ktlint = "1.5.0"
-log4j = "2.24.3"
+ktlint = "1.6.0"
+log4j = "2.25.0"
 logback = "1.5.18"
 opentest4j = "1.3.0"
-openTestReporting = "0.2.3"
+openTestReporting = "0.2.4"
 snapshotTests = "1.11.0"
 surefire = "3.5.3"
-xmlunit = "2.10.0"
+xmlunit = "2.10.3"
 
 [libraries]
 ant = { module = "org.apache.ant:ant", version.ref = "ant" }
@@ -33,31 +33,34 @@ archunit = { module = "com.tngtech.archunit:archunit-junit5", version = "1.4.1"
 assertj = { module = "org.assertj:assertj-core", version.ref = "assertj" }
 bndlib = { module = "biz.aQute.bnd:biz.aQute.bndlib", version.ref = "bnd" }
 checkstyle = { module = "com.puppycrawl.tools:checkstyle", version.ref = "checkstyle" }
-classgraph = { module = "io.github.classgraph:classgraph", version = "4.8.179" }
+classgraph = { module = "io.github.classgraph:classgraph", version = "4.8.180" }
 commons-io = { module = "commons-io:commons-io", version = "2.19.0" }
-groovy4 = { module = "org.apache.groovy:groovy", version = "4.0.26" }
+errorProne-core = { module = "com.google.errorprone:error_prone_core", version = "2.39.0" }
+fastcsv = { module = "de.siegmar:fastcsv", version = "4.0.0" }
+groovy4 = { module = "org.apache.groovy:groovy", version = "4.0.27" }
 groovy2-bom = { module = "org.codehaus.groovy:groovy-bom", version = "2.5.23" }
 hamcrest = { module = "org.hamcrest:hamcrest", version = "3.0" }
 jackson-dataformat-yaml = { module = "com.fasterxml.jackson.dataformat:jackson-dataformat-yaml", version.ref = "jackson" }
 jackson-module-kotlin = { module = "com.fasterxml.jackson.module:jackson-module-kotlin", version.ref = "jackson" }
-jfrPolyfill = { module = "org.gradle.jfr.polyfill:jfr-polyfill", version = "1.0.2" }
 jfrunit = { module = "org.moditect.jfrunit:jfrunit-core", version = "1.0.0.Alpha2" }
 jimfs = { module = "com.google.jimfs:jimfs", version = "1.3.0" }
 jmh-core = { module = "org.openjdk.jmh:jmh-core", version.ref = "jmh" }
 jmh-generator-annprocess = { module = "org.openjdk.jmh:jmh-generator-annprocess", version.ref = "jmh" }
 joox = { module = "org.jooq:joox", version = "2.0.1" }
+jspecify = { module = "org.jspecify:jspecify", version = "1.0.0" }
 jte = { module = "gg.jte:jte", version = "3.2.1" }
 junit4 = { module = "junit:junit", version = { require = "[4.12,)", prefer = "4.13.2" } }
 kotlinx-coroutines = { module = "org.jetbrains.kotlinx:kotlinx-coroutines-core", version = "1.10.2" }
 log4j-core = { module = "org.apache.logging.log4j:log4j-core", version.ref = "log4j" }
 log4j-jul = { module = "org.apache.logging.log4j:log4j-jul", version.ref = "log4j" }
-maven = { module = "org.apache.maven:apache-maven", version = "3.9.9" }
+maven = { module = "org.apache.maven:apache-maven", version = "3.9.10" }
 mavenSurefirePlugin = { module = "org.apache.maven.plugins:maven-surefire-plugin", version.ref = "surefire" }
 memoryfilesystem = { module = "com.github.marschall:memoryfilesystem", version = "2.8.1" }
-mockito-bom = { module = "org.mockito:mockito-bom", version = "5.17.0" }
+mockito-bom = { module = "org.mockito:mockito-bom", version = "5.18.0" }
 mockito-core = { module = "org.mockito:mockito-core" }
 mockito-junit-jupiter = { module = "org.mockito:mockito-junit-jupiter" }
 nohttp-checkstyle = { module = "io.spring.nohttp:nohttp-checkstyle", version = "0.0.11" }
+nullaway = { module = "com.uber.nullaway:nullaway", version = "0.12.7" }
 opentest4j = { module = "org.opentest4j:opentest4j", version.ref = "opentest4j" }
 openTestReporting-cli = { module = "org.opentest4j.reporting:open-test-reporting-cli", version.ref = "openTestReporting" }
 openTestReporting-events = { module = "org.opentest4j.reporting:open-test-reporting-events", version.ref = "openTestReporting" }
@@ -68,11 +71,10 @@ slf4j-julBinding = { module = "org.slf4j:slf4j-jdk14", version = "2.0.17" }
 snapshotTests-junit5 = { module = "de.skuzzle.test:snapshot-tests-junit5", version.ref = "snapshotTests" }
 snapshotTests-xml = { module = "de.skuzzle.test:snapshot-tests-xml", version.ref = "snapshotTests" }
 spock1 = { module = "org.spockframework:spock-core", version = "1.3-groovy-2.5" }
-univocity-parsers = { module = "com.sonofab1rd:univocity-parsers", version = "2.10.1" }
 xmlunit-assertj = { module = "org.xmlunit:xmlunit-assertj3", version.ref = "xmlunit" }
 xmlunit-placeholders = { module = "org.xmlunit:xmlunit-placeholders", version.ref = "xmlunit" }
 testingAnnotations = { module = "com.gradle:develocity-testing-annotations", version = "2.0.1" }
-woodstox = { module = "com.fasterxml.woodstox:woodstox-core", version = "7.1.0" }
+woodstox = { module = "com.fasterxml.woodstox:woodstox-core", version = "7.1.1" }
 
 # Only declared here so Dependabot knows when to update the referenced versions
 asciidoctorj-pdf = { module = "org.asciidoctor:asciidoctorj-pdf", version.ref = "asciidoctorj-pdf" }
@@ -93,15 +95,19 @@ asciidoctorConvert = { id = "org.asciidoctor.jvm.convert", version.ref = "asciid
 asciidoctorPdf = { id = "org.asciidoctor.jvm.pdf", version.ref = "asciidoctor-plugins" }
 bnd = { id = "biz.aQute.bnd", version.ref = "bnd" }
 buildParameters = { id = "org.gradlex.build-parameters", version = "1.4.4" }
-commonCustomUserData = { id = "com.gradle.common-custom-user-data-gradle-plugin", version = "2.2.1" }
-develocity = { id = "com.gradle.develocity", version = "4.0.1" }
-foojayResolver = { id = "org.gradle.toolchains.foojay-resolver", version = "0.10.0" }
+commonCustomUserData = { id = "com.gradle.common-custom-user-data-gradle-plugin", version = "2.3" }
+develocity = { id = "com.gradle.develocity", version = "4.0.2" }
+errorProne = { id = "net.ltgt.errorprone", version = "4.3.0" }
+foojayResolver = { id = "org.gradle.toolchains.foojay-resolver", version = "1.0.0" }
 gitPublish = { id = "org.ajoberstar.git-publish", version = "5.1.1" }
 jmh = { id = "me.champeau.jmh", version = "0.7.3" }
+# Remove `sshj` constraint in gradle/plugins/publishing/build.gradle.kts when updating
+# see https://github.com/jreleaser/jreleaser/issues/1900
 jreleaser = { id = "org.jreleaser", version = "1.18.0" }
 # check if workaround in gradle.properties can be removed when updating
-kotlin = { id = "org.jetbrains.kotlin.jvm", version = "2.1.21" }
-plantuml = { id = "io.freefair.plantuml", version = "8.13.1" }
-shadow = { id = "com.gradleup.shadow", version = "8.3.6" }
-spotless = { id = "com.diffplug.spotless", version = "7.0.3" }
-versions = { id = "com.github.ben-manes.versions", version = "0.52.0" }
+kotlin = { id = "org.jetbrains.kotlin.jvm", version = "2.2.0" }
+nullaway = { id = "net.ltgt.nullaway", version = "2.2.0" }
+openrewrite = { id = "org.openrewrite.rewrite", version = "7.9.0" }
+plantuml = { id = "io.freefair.plantuml", version = "8.14" }
+shadow = { id = "com.gradleup.shadow", version = "8.3.7" }
+spotless = { id = "com.diffplug.spotless", version = "7.0.4" }
diff --git a/gradle/plugins/build-parameters/build.gradle.kts b/gradle/plugins/build-parameters/build.gradle.kts
index 8a1276886d14..f2db3d75afaa 100644
--- a/gradle/plugins/build-parameters/build.gradle.kts
+++ b/gradle/plugins/build-parameters/build.gradle.kts
@@ -4,6 +4,10 @@ plugins {
 
 group = "junitbuild"
 
+tasks.compileJava {
+	options.release = 21
+}
+
 buildParameters {
 	pluginId("junitbuild.build-parameters")
 	bool("ci") {
diff --git a/gradle/plugins/build.gradle.kts b/gradle/plugins/build.gradle.kts
deleted file mode 100644
index f64d71d4260c..000000000000
--- a/gradle/plugins/build.gradle.kts
+++ /dev/null
@@ -1,3 +0,0 @@
-plugins {
-	alias(libs.plugins.versions)
-}
diff --git a/gradle/plugins/code-generator/build.gradle.kts b/gradle/plugins/code-generator/build.gradle.kts
index fda16a028335..4b659df799e0 100644
--- a/gradle/plugins/code-generator/build.gradle.kts
+++ b/gradle/plugins/code-generator/build.gradle.kts
@@ -1,3 +1,5 @@
+import org.jetbrains.kotlin.gradle.dsl.JvmTarget.JVM_21
+
 plugins {
 	`kotlin-dsl`
 }
@@ -10,3 +12,14 @@ dependencies {
 	implementation(libs.jackson.module.kotlin)
 	implementation(libs.jte)
 }
+
+tasks.compileJava {
+	options.release = 21
+}
+
+kotlin {
+	compilerOptions {
+		jvmTarget = JVM_21
+		freeCompilerArgs.add("-Xjdk-release=21")
+	}
+}
diff --git a/gradle/plugins/code-generator/src/main/kotlin/junitbuild.code-generator.gradle.kts b/gradle/plugins/code-generator/src/main/kotlin/junitbuild.code-generator.gradle.kts
index 1846eb6ae728..63c33d1a401f 100644
--- a/gradle/plugins/code-generator/src/main/kotlin/junitbuild.code-generator.gradle.kts
+++ b/gradle/plugins/code-generator/src/main/kotlin/junitbuild.code-generator.gradle.kts
@@ -5,10 +5,12 @@ plugins {
 	java
 }
 
-val templates by sourceSets.registering
+val templates by sourceSets.creating
+val templatesCompileOnly = configurations[templates.compileOnlyConfigurationName]
+
 dependencies {
-	add(templates.get().compileOnlyConfigurationName, dependencyFromLibs("jte"))
-	add(templates.get().compileOnlyConfigurationName, "junitbuild.base:code-generator-model")
+	templatesCompileOnly(dependencyFromLibs("jte"))
+	templatesCompileOnly("junitbuild.base:code-generator-model")
 }
 
 val license: License by rootProject.extra
@@ -18,17 +20,16 @@ val generateCode by tasks.registering
 sourceSets.named { it != templates.name }.configureEach {
 
 	val sourceSetName = name
-	val sourceSetTargetDir = rootTargetDir.map { it.dir(sourceSetName) }
 
 	val task = tasks.register(getTaskName("generateJreRelated", "SourceCode"), GenerateJreRelatedSourceCode::class) {
-		templateDir.convention(layout.dir(templates.map {
-			it.resources.srcDirs.single().resolve(sourceSetName)
+		templateDir.convention(layout.dir(provider {
+			templates.resources.srcDirs.single().resolve(sourceSetName)
 		}))
-		targetDir.convention(sourceSetTargetDir)
+		targetDir.convention(rootTargetDir.map { it.dir(sourceSetName) })
 		licenseHeaderFile.convention(license.headerFile)
 	}
 
-	java.srcDir(files(sourceSetTargetDir).builtBy(task))
+	java.srcDir(task.map { it.targetDir })
 
 	generateCode {
 		dependsOn(task)
diff --git a/gradle/plugins/code-generator/src/main/kotlin/junitbuild/generator/GenerateJreRelatedSourceCode.kt b/gradle/plugins/code-generator/src/main/kotlin/junitbuild/generator/GenerateJreRelatedSourceCode.kt
index b76ad39345d6..70f51a6d5f9f 100644
--- a/gradle/plugins/code-generator/src/main/kotlin/junitbuild/generator/GenerateJreRelatedSourceCode.kt
+++ b/gradle/plugins/code-generator/src/main/kotlin/junitbuild/generator/GenerateJreRelatedSourceCode.kt
@@ -57,9 +57,13 @@ abstract class GenerateJreRelatedSourceCode : DefaultTask() {
                 mapper.registerModule(KotlinModule.Builder().build())
                 mapper.readValue(input, object : TypeReference<List<JRE>>() {})
             }
+            val minRuntimeVersion = 17
+            val supportedJres = jres.filter { it.version >= minRuntimeVersion }
             val params = mapOf(
-                "jres" to jres,
-                "jresSortedByStringValue" to jres.sortedBy { it.version.toString() },
+                "minRuntimeVersion" to minRuntimeVersion,
+                "allJres" to jres,
+                "supportedJres" to supportedJres,
+                "supportedJresSortedByStringValue" to supportedJres.sortedBy { it.version.toString() },
                 "licenseHeader" to licenseHeaderFile.asFile.get().readText()
             )
             templates.forEach {
diff --git a/gradle/plugins/common/build.gradle.kts b/gradle/plugins/common/build.gradle.kts
index e15665d0d6e0..40df3d0c9ce4 100644
--- a/gradle/plugins/common/build.gradle.kts
+++ b/gradle/plugins/common/build.gradle.kts
@@ -1,4 +1,5 @@
 import junitbuild.extensions.markerCoordinates
+import org.jetbrains.kotlin.gradle.dsl.JvmTarget.JVM_21
 
 plugins {
 	`kotlin-dsl`
@@ -11,10 +12,22 @@ dependencies {
 	implementation(libs.plugins.bnd.markerCoordinates)
 	implementation(libs.plugins.commonCustomUserData.markerCoordinates)
 	implementation(libs.plugins.develocity.markerCoordinates)
+	implementation(libs.plugins.errorProne.markerCoordinates)
 	implementation(libs.plugins.foojayResolver.markerCoordinates)
 	implementation(libs.plugins.jmh.markerCoordinates)
-	implementation(libs.plugins.jreleaser.markerCoordinates)
+	implementation(libs.plugins.nullaway.markerCoordinates)
+	implementation(libs.plugins.openrewrite.markerCoordinates)
 	implementation(libs.plugins.shadow.markerCoordinates)
 	implementation(libs.plugins.spotless.markerCoordinates)
-	implementation(libs.plugins.versions.markerCoordinates)
+}
+
+tasks.compileJava {
+	options.release = 21
+}
+
+kotlin {
+	compilerOptions {
+		jvmTarget = JVM_21
+		freeCompilerArgs.add("-Xjdk-release=21")
+	}
 }
diff --git a/gradle/plugins/common/src/main/kotlin/JavaLibraryExtension.kt b/gradle/plugins/common/src/main/kotlin/JavaLibraryExtension.kt
index 64a61da7fb7b..122dccc585ff 100644
--- a/gradle/plugins/common/src/main/kotlin/JavaLibraryExtension.kt
+++ b/gradle/plugins/common/src/main/kotlin/JavaLibraryExtension.kt
@@ -1,7 +1,15 @@
 import org.gradle.api.JavaVersion
+import org.gradle.api.provider.Property
+
+@Suppress("LeakingThis")
+abstract class JavaLibraryExtension {
+
+    abstract val mainJavaVersion: Property<JavaVersion>
+    abstract val testJavaVersion: Property<JavaVersion>
+
+    init {
+        mainJavaVersion.convention(JavaVersion.VERSION_17)
+        testJavaVersion.convention(JavaVersion.VERSION_21)
+    }
 
-open class JavaLibraryExtension {
-    var mainJavaVersion: JavaVersion = JavaVersion.VERSION_1_8
-    var testJavaVersion: JavaVersion = JavaVersion.VERSION_21
-    var configureRelease: Boolean = true
 }
diff --git a/gradle/plugins/common/src/main/kotlin/junitbuild.checkstyle-nohttp.gradle.kts b/gradle/plugins/common/src/main/kotlin/junitbuild.checkstyle-nohttp.gradle.kts
index 0bcb0ce67641..b993fedf65fe 100644
--- a/gradle/plugins/common/src/main/kotlin/junitbuild.checkstyle-nohttp.gradle.kts
+++ b/gradle/plugins/common/src/main/kotlin/junitbuild.checkstyle-nohttp.gradle.kts
@@ -16,6 +16,10 @@ configurations.checkstyle {
 			if (requested.group == "ch.qos.logback") {
 				useVersion(requiredVersionFromLibs("logback"))
 			}
+			// Workaround for CVE-2025-48734
+			if (requested.group == "commons-beanutils") {
+				useVersion("1.11.0")
+			}
 		}
 	}
 }
diff --git a/gradle/plugins/common/src/main/kotlin/junitbuild.dependency-update-check.gradle.kts b/gradle/plugins/common/src/main/kotlin/junitbuild.dependency-update-check.gradle.kts
deleted file mode 100644
index f7bac1fb8efc..000000000000
--- a/gradle/plugins/common/src/main/kotlin/junitbuild.dependency-update-check.gradle.kts
+++ /dev/null
@@ -1,19 +0,0 @@
-plugins {
-	id("com.github.ben-manes.versions")
-}
-
-tasks.dependencyUpdates {
-	checkConstraints = true
-	resolutionStrategy {
-		componentSelection {
-			all {
-				val rejected = listOf("alpha", "beta", "rc", "cr", "m", "preview", "b", "ea")
-					.map { qualifier -> Regex("(?i).*[.-]$qualifier[.\\d-+]*") }
-					.any { it.matches(candidate.version) }
-				if (rejected) {
-					reject("Release candidate")
-				}
-			}
-		}
-	}
-}
diff --git a/gradle/plugins/common/src/main/kotlin/junitbuild.java-aggregator-conventions.gradle.kts b/gradle/plugins/common/src/main/kotlin/junitbuild.java-aggregator-conventions.gradle.kts
new file mode 100644
index 000000000000..cb169dc4d0de
--- /dev/null
+++ b/gradle/plugins/common/src/main/kotlin/junitbuild.java-aggregator-conventions.gradle.kts
@@ -0,0 +1,9 @@
+plugins {
+	id("junitbuild.java-library-conventions")
+}
+
+tasks.javadoc {
+	// Since this JAR contains no classes, running Javadoc fails with:
+	// "No public or protected classes found to document"
+	enabled = false
+}
diff --git a/gradle/plugins/common/src/main/kotlin/junitbuild.java-library-conventions.gradle.kts b/gradle/plugins/common/src/main/kotlin/junitbuild.java-library-conventions.gradle.kts
index becfe893a62a..c26214443f8a 100644
--- a/gradle/plugins/common/src/main/kotlin/junitbuild.java-library-conventions.gradle.kts
+++ b/gradle/plugins/common/src/main/kotlin/junitbuild.java-library-conventions.gradle.kts
@@ -1,12 +1,9 @@
 import com.github.jengelman.gradle.plugins.shadow.tasks.ShadowJar
-import junitbuild.extensions.javaModuleName
 import junitbuild.extensions.isSnapshot
-import junitbuild.java.ModuleCompileOptions
-import junitbuild.java.ModulePathArgumentProvider
-import junitbuild.java.PatchModuleArgumentProvider
 import org.gradle.plugins.ide.eclipse.model.Classpath
 import org.gradle.plugins.ide.eclipse.model.Library
 import org.gradle.plugins.ide.eclipse.model.ProjectDependency
+import org.gradle.plugins.ide.eclipse.model.SourceFolder
 
 plugins {
 	`java-library`
@@ -16,25 +13,34 @@ plugins {
 	id("junitbuild.build-parameters")
 	id("junitbuild.checkstyle-conventions")
 	id("junitbuild.jacoco-java-conventions")
+	id("org.openrewrite.rewrite")
+}
+
+rewrite {
+	activeRecipe("org.openrewrite.java.migrate.UpgradeToJava17")
+}
+
+dependencies {
+	rewrite(platform("org.openrewrite.recipe:rewrite-recipe-bom:latest.release"))
+	rewrite("org.openrewrite.recipe:rewrite-migrate-java")
 }
 
 val mavenizedProjects: List<Project> by rootProject.extra
-val modularProjects: List<Project> by rootProject.extra
 val buildDate: String by rootProject.extra
 val buildTime: String by rootProject.extra
 val buildRevision: Any by rootProject.extra
 
 val extension = extensions.create<JavaLibraryExtension>("javaLibrary")
 
-val moduleSourceDir = layout.projectDirectory.dir("src/module/$javaModuleName")
-val combinedModuleSourceDir = layout.buildDirectory.dir("module")
-val moduleOutputDir = layout.buildDirectory.dir("classes/java/module")
-
 eclipse {
 	jdt {
+		sourceCompatibility = JavaVersion.VERSION_21
+		targetCompatibility = JavaVersion.VERSION_21
 		file {
 			// Set properties for org.eclipse.jdt.core.prefs
 			withProperties {
+				// Configure Eclipse projects with -release compiler flag.
+				setProperty("org.eclipse.jdt.core.compiler.release", "enabled")
 				// Configure Eclipse projects with -parameters compiler flag.
 				setProperty("org.eclipse.jdt.core.compiler.codegen.methodParameters", "generate")
 			}
@@ -49,11 +55,22 @@ eclipse {
 		// Java Template Engine (JTE) which is used to generate the JRE enum and
 		// dependent tests.
 		entries.removeIf { it is ProjectDependency && it.path.equals("/code-generator-model") }
+		// Remove classpath entries for anything used by the Gradle Wrapper.
+		entries.removeIf { it is Library && it.path.contains("gradle/wrapper") }
+		entries.filterIsInstance<SourceFolder>().forEach {
+			it.excludes.add("**/module-info.java")
+		}
+		entries.filterIsInstance<ProjectDependency>().forEach {
+			it.entryAttributes.remove("module")
+		}
+		entries.filterIsInstance<Library>().forEach {
+			it.entryAttributes.remove("module")
+		}
 	}
 }
 
 java {
-	modularity.inferModulePath = false
+	modularity.inferModulePath = true
 }
 
 if (project in mavenizedProjects) {
@@ -94,9 +111,6 @@ if (project in mavenizedProjects) {
 	}
 
 	tasks.named<Jar>("sourcesJar").configure {
-		from(moduleSourceDir) {
-			include("module-info.java")
-		}
 		duplicatesStrategy = DuplicatesStrategy.EXCLUDE
 	}
 
@@ -116,7 +130,7 @@ if (project in mavenizedProjects) {
 					}
 				}
 				pom {
-					description = provider { "Module \"${project.name}\" of JUnit 5." }
+					description = provider { "Module \"${project.name}\" of JUnit" }
 				}
 			}
 		}
@@ -170,51 +184,6 @@ normalization {
 	}
 }
 
-val allMainClasses by tasks.registering {
-	dependsOn(tasks.classes)
-}
-
-val prepareModuleSourceDir by tasks.registering(Sync::class) {
-	from(moduleSourceDir)
-	from(sourceSets.named { it.startsWith("main") }.map { it.allJava })
-	into(combinedModuleSourceDir.map { it.dir(javaModuleName) })
-	duplicatesStrategy = DuplicatesStrategy.EXCLUDE
-}
-
-val compileModule by tasks.registering(JavaCompile::class) {
-	dependsOn(allMainClasses)
-	enabled = project in modularProjects
-	source = fileTree(combinedModuleSourceDir).builtBy(prepareModuleSourceDir)
-	destinationDirectory = moduleOutputDir
-	sourceCompatibility = "9"
-	targetCompatibility = "9"
-	classpath = files()
-	options.release = 9
-	options.compilerArgs.addAll(listOf(
-			// Suppress warnings for automatic modules: org.apiguardian.api, org.opentest4j
-			"-Xlint:all,-requires-automatic,-requires-transitive-automatic",
-			"-Werror", // Terminates compilation when warnings occur.
-			"--module-version", "${project.version}",
-	))
-
-	val moduleOptions = objects.newInstance(ModuleCompileOptions::class)
-	extensions.add("moduleOptions", moduleOptions)
-	moduleOptions.modulePath.from(configurations.compileClasspath)
-
-	options.compilerArgumentProviders.add(objects.newInstance(ModulePathArgumentProvider::class, project, combinedModuleSourceDir, modularProjects).apply {
-		modulePath.from(moduleOptions.modulePath)
-	})
-	options.compilerArgumentProviders.addAll(modularProjects.map { objects.newInstance(PatchModuleArgumentProvider::class, project, it) })
-
-	modularity.inferModulePath = false
-
-	doFirst {
-		options.allCompilerArgs.forEach {
-			logger.info(it)
-		}
-	}
-}
-
 tasks.withType<Jar>().configureEach {
 	from(rootDir) {
 		include("LICENSE.md")
@@ -227,13 +196,6 @@ tasks.withType<Jar>().configureEach {
 		}
 		into("META-INF")
 	}
-	val suffix = archiveClassifier.getOrElse("")
-	if (suffix.isBlank() || this is ShadowJar) {
-		dependsOn(allMainClasses, compileModule)
-		from(moduleOutputDir.map { it.dir(javaModuleName) }) {
-			include("module-info.class")
-		}
-	}
 }
 
 tasks.jar {
@@ -261,68 +223,52 @@ tasks.withType<ShadowJar>().configureEach {
 
 tasks.withType<JavaCompile>().configureEach {
 	options.encoding = "UTF-8"
-}
-
-tasks.compileJava {
-	// See: https://docs.oracle.com/en/java/javase/12/tools/javac.html
 	options.compilerArgs.addAll(listOf(
-			"-Xlint:all", // Enables all recommended warnings.
-			"-Werror", // Terminates compilation when warnings occur.
-			// Required for compatibility with Java 8's reflection APIs (see https://github.com/junit-team/junit5/issues/3797).
-			"-parameters", // Generates metadata for reflection on method parameters.
+		"-Xlint:all", // Enables all recommended warnings.
+		"-Werror", // Terminates compilation when warnings occur.
+		"-parameters", // Generates metadata for reflection on method parameters.
 	))
 }
 
-tasks.compileTestJava {
-	// See: https://docs.oracle.com/en/java/javase/12/tools/javac.html
+tasks.compileJava {
 	options.compilerArgs.addAll(listOf(
-			"-Xlint:all", // Enables all recommended warnings.
-			"-Werror", // Terminates compilation when warnings occur.
-			"-parameters" // Generates metadata for reflection on method parameters.
+		"--module-version", "${project.version}"
 	))
 }
 
-afterEvaluate {
-	configurations {
-		apiElements {
-			attributes {
-				attribute(TargetJvmVersion.TARGET_JVM_VERSION_ATTRIBUTE, extension.mainJavaVersion.majorVersion.toInt())
-			}
-		}
-		runtimeElements {
-			attributes {
-				attribute(TargetJvmVersion.TARGET_JVM_VERSION_ATTRIBUTE, extension.mainJavaVersion.majorVersion.toInt())
-			}
+configurations {
+	apiElements {
+		attributes {
+			attributeProvider(TargetJvmVersion.TARGET_JVM_VERSION_ATTRIBUTE, extension.mainJavaVersion.map { it.majorVersion.toInt() })
 		}
 	}
-	tasks {
-		compileJava {
-			if (extension.configureRelease) {
-				options.release = extension.mainJavaVersion.majorVersion.toInt()
-			} else {
-				sourceCompatibility = extension.mainJavaVersion.majorVersion
-				targetCompatibility = extension.mainJavaVersion.majorVersion
-			}
-		}
-		compileTestJava {
-			if (extension.configureRelease) {
-				options.release = extension.testJavaVersion.majorVersion.toInt()
-			} else {
-				sourceCompatibility = extension.testJavaVersion.majorVersion
-				targetCompatibility = extension.testJavaVersion.majorVersion
-			}
+	runtimeElements {
+		attributes {
+			attributeProvider(TargetJvmVersion.TARGET_JVM_VERSION_ATTRIBUTE, extension.mainJavaVersion.map { it.majorVersion.toInt() })
 		}
 	}
+}
+
+tasks {
+	compileJava {
+		options.release = extension.mainJavaVersion.map { it.majorVersion.toInt() }
+	}
+	compileTestJava {
+		options.release = extension.testJavaVersion.map { it.majorVersion.toInt() }
+	}
+}
+
+afterEvaluate {
 	pluginManager.withPlugin("groovy") {
 		tasks.named<GroovyCompile>("compileGroovy").configure {
 			// Groovy compiler does not support the --release flag.
-			sourceCompatibility = extension.mainJavaVersion.majorVersion
-			targetCompatibility = extension.mainJavaVersion.majorVersion
+			sourceCompatibility = extension.mainJavaVersion.get().majorVersion
+			targetCompatibility = extension.mainJavaVersion.get().majorVersion
 		}
-		tasks.named<GroovyCompile>("compileTestGroovy").configure {
+		tasks.withType<GroovyCompile>().named { it.startsWith("compileTest") }.configureEach {
 			// Groovy compiler does not support the --release flag.
-			sourceCompatibility = extension.testJavaVersion.majorVersion
-			targetCompatibility = extension.testJavaVersion.majorVersion
+			sourceCompatibility = extension.testJavaVersion.get().majorVersion
+			targetCompatibility = extension.testJavaVersion.get().majorVersion
 		}
 	}
 }
@@ -341,6 +287,6 @@ pluginManager.withPlugin("java-test-fixtures") {
 		config = resources.text.fromFile(checkstyle.configDirectory.file("checkstyleTest.xml"))
 	}
 	tasks.named<JavaCompile>("compileTestFixturesJava") {
-		options.release = extension.testJavaVersion.majorVersion.toInt()
+		options.release = extension.testJavaVersion.map { it.majorVersion.toInt() }
 	}
 }
diff --git a/gradle/plugins/common/src/main/kotlin/junitbuild.java-multi-release-sources.gradle.kts b/gradle/plugins/common/src/main/kotlin/junitbuild.java-multi-release-sources.gradle.kts
deleted file mode 100644
index 83b2a8e8e273..000000000000
--- a/gradle/plugins/common/src/main/kotlin/junitbuild.java-multi-release-sources.gradle.kts
+++ /dev/null
@@ -1,45 +0,0 @@
-import junitbuild.extensions.capitalized
-
-plugins {
-	id("junitbuild.java-library-conventions")
-}
-
-val mavenizedProjects: List<Project> by rootProject.extra
-
-listOf(9, 17).forEach { javaVersion ->
-	val sourceSet = sourceSets.register("mainRelease${javaVersion}") {
-		compileClasspath += sourceSets.main.get().output
-		runtimeClasspath += sourceSets.main.get().output
-		java {
-			setSrcDirs(setOf("src/main/java${javaVersion}"))
-		}
-	}
-
-	configurations.named(sourceSet.get().compileClasspathConfigurationName).configure {
-		extendsFrom(configurations.compileClasspath.get())
-	}
-
-	tasks {
-
-		named("allMainClasses").configure {
-			dependsOn(sourceSet.get().classesTaskName)
-		}
-
-		named<JavaCompile>(sourceSet.get().compileJavaTaskName).configure {
-			options.release = javaVersion
-		}
-
-		named<Checkstyle>("checkstyle${sourceSet.name.capitalized()}").configure {
-			config = resources.text.fromFile(checkstyle.configDirectory.file("checkstyleMain.xml"))
-		}
-
-		if (project in mavenizedProjects) {
-			javadoc {
-				source(sourceSet.get().allJava)
-			}
-			named<Jar>("sourcesJar").configure {
-				from(sourceSet.get().allSource)
-			}
-		}
-	}
-}
diff --git a/gradle/plugins/common/src/main/kotlin/junitbuild.java-multi-release-test-sources.gradle.kts b/gradle/plugins/common/src/main/kotlin/junitbuild.java-multi-release-test-sources.gradle.kts
deleted file mode 100644
index 4dd191dbe0b0..000000000000
--- a/gradle/plugins/common/src/main/kotlin/junitbuild.java-multi-release-test-sources.gradle.kts
+++ /dev/null
@@ -1,42 +0,0 @@
-import junitbuild.extensions.capitalized
-
-plugins {
-	id("junitbuild.java-library-conventions")
-}
-
-listOf(21).forEach { javaVersion ->
-	val sourceSet = sourceSets.register("testRelease${javaVersion}") {
-		compileClasspath += sourceSets.main.get().output
-		runtimeClasspath += sourceSets.main.get().output
-		java {
-			setSrcDirs(setOf("src/test/java${javaVersion}"))
-		}
-	}
-
-	configurations {
-		named(sourceSet.get().compileClasspathConfigurationName).configure {
-			extendsFrom(configurations.testCompileClasspath.get())
-		}
-		named(sourceSet.get().runtimeClasspathConfigurationName).configure {
-			extendsFrom(configurations.testRuntimeClasspath.get())
-		}
-	}
-
-	tasks {
-		val testTask = register<Test>("testRelease${javaVersion}") {
-			group = "verification"
-			description = "Runs the tests for Java ${javaVersion}"
-			testClassesDirs = sourceSet.get().output.classesDirs
-			classpath = sourceSet.get().runtimeClasspath
-		}
-		check {
-			dependsOn(testTask)
-		}
-		named<JavaCompile>(sourceSet.get().compileJavaTaskName).configure {
-			options.release = javaVersion
-		}
-		named<Checkstyle>("checkstyle${sourceSet.name.capitalized()}").configure {
-			config = resources.text.fromFile(checkstyle.configDirectory.file("checkstyleTest.xml"))
-		}
-	}
-}
diff --git a/gradle/plugins/common/src/main/kotlin/junitbuild.java-nullability-conventions.gradle.kts b/gradle/plugins/common/src/main/kotlin/junitbuild.java-nullability-conventions.gradle.kts
new file mode 100644
index 000000000000..a06ab1becca9
--- /dev/null
+++ b/gradle/plugins/common/src/main/kotlin/junitbuild.java-nullability-conventions.gradle.kts
@@ -0,0 +1,47 @@
+import junitbuild.extensions.dependencyFromLibs
+import net.ltgt.gradle.errorprone.errorprone
+import net.ltgt.gradle.nullaway.nullaway
+
+plugins {
+	`java-library`
+	id("net.ltgt.errorprone")
+	id("net.ltgt.nullaway")
+}
+
+dependencies {
+	errorprone(dependencyFromLibs("errorProne-core"))
+	errorprone(dependencyFromLibs("nullaway"))
+}
+
+nullaway {
+	onlyNullMarked = true
+}
+
+tasks.withType<JavaCompile>().configureEach {
+	options.errorprone {
+		disableAllChecks = true
+		nullaway {
+			if (java.toolchain.implementation.orNull == JvmImplementation.J9) {
+				disable()
+			} else {
+				enable()
+			}
+			isJSpecifyMode = true
+		}
+	}
+}
+
+tasks.withType<JavaCompile>().named { it.startsWith("compileTest") }.configureEach {
+	options.errorprone.nullaway {
+		handleTestAssertionLibraries = true
+		excludedFieldAnnotations.addAll(
+			"org.junit.jupiter.api.io.TempDir",
+			"org.junit.jupiter.params.Parameter",
+			"org.junit.runners.Parameterized.Parameter",
+			"org.mockito.Captor",
+			"org.mockito.InjectMocks",
+			"org.mockito.Mock",
+			"org.mockito.Spy",
+		)
+	}
+}
diff --git a/gradle/plugins/common/src/main/kotlin/junitbuild.java-toolchain-conventions.gradle.kts b/gradle/plugins/common/src/main/kotlin/junitbuild.java-toolchain-conventions.gradle.kts
index 873ff64cfb1e..159068f4be39 100644
--- a/gradle/plugins/common/src/main/kotlin/junitbuild.java-toolchain-conventions.gradle.kts
+++ b/gradle/plugins/common/src/main/kotlin/junitbuild.java-toolchain-conventions.gradle.kts
@@ -5,7 +5,7 @@ plugins {
 }
 
 project.pluginManager.withPlugin("java") {
-	val defaultLanguageVersion = JavaLanguageVersion.of(21)
+	val defaultLanguageVersion = JavaLanguageVersion.of(24)
 	val javaLanguageVersion = buildParameters.javaToolchain.version.map { JavaLanguageVersion.of(it) }.getOrElse(defaultLanguageVersion)
 	val jvmImplementation = buildParameters.javaToolchain.implementation.map {
 		when(it) {
@@ -50,7 +50,7 @@ project.pluginManager.withPlugin("java") {
 		doFirst {
 			if (options.release.orNull == 8 && javaLanguageVersion.asInt() >= 20) {
 				options.compilerArgs.add(
-					"-Xlint:-options" // see https://github.com/junit-team/junit5/issues/3029
+					"-Xlint:-options" // see https://github.com/junit-team/junit-framework/issues/3029
 				)
 			}
 		}
diff --git a/gradle/plugins/common/src/main/kotlin/junitbuild.kotlin-library-conventions.gradle.kts b/gradle/plugins/common/src/main/kotlin/junitbuild.kotlin-library-conventions.gradle.kts
index 73680fcf6e6d..907b672a734a 100644
--- a/gradle/plugins/common/src/main/kotlin/junitbuild.kotlin-library-conventions.gradle.kts
+++ b/gradle/plugins/common/src/main/kotlin/junitbuild.kotlin-library-conventions.gradle.kts
@@ -1,5 +1,6 @@
+
 import org.jetbrains.kotlin.gradle.dsl.JvmTarget
-import org.jetbrains.kotlin.gradle.dsl.KotlinVersion
+import org.jetbrains.kotlin.gradle.dsl.KotlinVersion.KOTLIN_2_1
 import org.jetbrains.kotlin.gradle.tasks.KotlinCompile
 
 plugins {
@@ -11,26 +12,20 @@ tasks.named("kotlinSourcesJar") {
 	enabled = false
 }
 
+val javaLibraryExtension = project.the<JavaLibraryExtension>()
+
 tasks.withType<KotlinCompile>().configureEach {
 	compilerOptions {
-		apiVersion = KotlinVersion.fromVersion("1.6")
+		jvmTarget = javaLibraryExtension.mainJavaVersion.map { JvmTarget.fromTarget(it.toString()) }
+		apiVersion = KOTLIN_2_1
 		languageVersion = apiVersion
-		allWarningsAsErrors = false
-		// Compiler arg is required for Kotlin 1.6 and below
-		// see https://kotlinlang.org/docs/whatsnew17.html#stable-opt-in-requirements
+		allWarningsAsErrors.convention(true)
+		javaParameters = true
 		freeCompilerArgs.add("-opt-in=kotlin.RequiresOptIn")
+		freeCompilerArgs.add(jvmTarget.map { "-Xjdk-release=${JavaVersion.toVersion(it.target).majorVersion}" })
 	}
 }
 
-afterEvaluate {
-	val extension = project.the<JavaLibraryExtension>()
-	tasks {
-		withType<KotlinCompile>().configureEach {
-			compilerOptions.jvmTarget = JvmTarget.fromTarget(extension.mainJavaVersion.toString())
-			compilerOptions.javaParameters = true
-		}
-		named<KotlinCompile>("compileTestKotlin") {
-			compilerOptions.jvmTarget = JvmTarget.fromTarget(extension.testJavaVersion.toString())
-		}
-	}
+tasks.named<KotlinCompile>("compileTestKotlin") {
+	compilerOptions.jvmTarget = javaLibraryExtension.testJavaVersion.map { JvmTarget.fromTarget(it.toString()) }
 }
diff --git a/gradle/plugins/common/src/main/kotlin/junitbuild.osgi-conventions.gradle.kts b/gradle/plugins/common/src/main/kotlin/junitbuild.osgi-conventions.gradle.kts
index d1adaa09ff68..d5f47a50e2e8 100644
--- a/gradle/plugins/common/src/main/kotlin/junitbuild.osgi-conventions.gradle.kts
+++ b/gradle/plugins/common/src/main/kotlin/junitbuild.osgi-conventions.gradle.kts
@@ -5,8 +5,6 @@ plugins {
 	`java-library`
 }
 
-val importAPIGuardian = "org.apiguardian.*;resolution:=\"optional\""
-
 val projectDescription = objects.property<String>().convention(provider { project.description })
 
 // This task enhances `jar` and `shadowJar` tasks with the bnd
@@ -15,7 +13,9 @@ val projectDescription = objects.property<String>().convention(provider { projec
 tasks.withType<Jar>().named {
 	it == "jar" || it == "shadowJar"
 }.all { // configure tasks eagerly as workaround for https://github.com/bndtools/bnd/issues/5695
-	extra["importAPIGuardian"] = importAPIGuardian
+
+	val importAPIGuardian by extra { "org.apiguardian.*;resolution:=\"optional\"" }
+	val importJSpecify by extra { "org.jspecify.*;resolution:=\"optional\"" }
 
 	extensions.create<BundleTaskExtension>(BundleTaskExtension.NAME, this).apply {
 		properties.set(projectDescription.map {
@@ -37,6 +37,7 @@ tasks.withType<Jar>().named {
 				# These are the general rules for package imports.
 				Import-Package: \
 					${importAPIGuardian},\
+					${importJSpecify},\
 					org.junit.platform.commons.logging;status=INTERNAL,\
 					kotlin.*;resolution:="optional",\
 					*
@@ -45,6 +46,7 @@ tasks.withType<Jar>().named {
 				# the kotlin and apiguardian packages, but enough modules do to make it a default.
 				-fixupmessages.kotlin.import: "Unused Import-Package instructions: \\[kotlin.*\\]";is:=ignore
 				-fixupmessages.apiguardian.import: "Unused Import-Package instructions: \\[org.apiguardian.*\\]";is:=ignore
+				-fixupmessages.jspecify.import: "Unused Import-Package instructions: \\[org.jspecify.*\\]";is:=ignore
 
 				# This tells bnd to ignore classes it finds in `META-INF/versions/`
 				# because bnd doesn't yet support multi-release jars.
@@ -79,8 +81,8 @@ tasks.withType<Jar>().named {
 val osgiProperties by tasks.registering(WriteProperties::class) {
 	destinationFile = layout.buildDirectory.file("verifyOSGiProperties.bndrun")
 	property("-standalone", true)
-	project.extensions.getByType(JavaLibraryExtension::class.java).let { javaLibrary ->
-		property("-runee", "JavaSE-${javaLibrary.mainJavaVersion}")
+	project.extensions.getByType(JavaLibraryExtension::class).let { javaLibrary ->
+		property("-runee", Callable { "JavaSE-${javaLibrary.mainJavaVersion.get()}" })
 	}
 	property("-runrequires", "osgi.identity;filter:='(osgi.identity=${project.name})'")
 	property("-runsystempackages", "jdk.internal.misc,jdk.jfr,sun.misc")
diff --git a/gradle/plugins/common/src/main/kotlin/junitbuild.publishing-conventions.gradle.kts b/gradle/plugins/common/src/main/kotlin/junitbuild.publishing-conventions.gradle.kts
index 08664ee9a0d0..30fedc5c2fc2 100644
--- a/gradle/plugins/common/src/main/kotlin/junitbuild.publishing-conventions.gradle.kts
+++ b/gradle/plugins/common/src/main/kotlin/junitbuild.publishing-conventions.gradle.kts
@@ -11,18 +11,11 @@ val jupiterProjects: List<Project> by rootProject
 val platformProjects: List<Project> by rootProject
 val vintageProjects: List<Project> by rootProject
 
-when (project) {
-	in jupiterProjects -> {
-		group = property("jupiterGroup")!!
-	}
-	in platformProjects -> {
-		group = property("platformGroup")!!
-		version = property("platformVersion")!!
-	}
-	in vintageProjects -> {
-		group = property("vintageGroup")!!
-		version = property("vintageVersion")!!
-	}
+group = when (project) {
+	in jupiterProjects -> "org.junit.jupiter"
+	in platformProjects -> "org.junit.platform"
+	in vintageProjects -> "org.junit.vintage"
+	else -> "org.junit"
 }
 
 // ensure project is built successfully before publishing it
@@ -59,11 +52,11 @@ publishing {
 				name.set(provider {
 					project.description ?: "${project.group}:${project.name}"
 				})
-				url = "https://junit.org/junit5/"
+				url = "https://junit.org/"
 				scm {
-					connection = "scm:git:git://github.com/junit-team/junit5.git"
-					developerConnection = "scm:git:git://github.com/junit-team/junit5.git"
-					url = "https://github.com/junit-team/junit5"
+					connection = "scm:git:git://github.com/junit-team/junit-framework.git"
+					developerConnection = "scm:git:git://github.com/junit-team/junit-framework.git"
+					url = "https://github.com/junit-team/junit-framework"
 				}
 				licenses {
 					license {
diff --git a/gradle/plugins/common/src/main/kotlin/junitbuild.shadow-conventions.gradle.kts b/gradle/plugins/common/src/main/kotlin/junitbuild.shadow-conventions.gradle.kts
index ed1732e00e78..6962f80c3ca3 100644
--- a/gradle/plugins/common/src/main/kotlin/junitbuild.shadow-conventions.gradle.kts
+++ b/gradle/plugins/common/src/main/kotlin/junitbuild.shadow-conventions.gradle.kts
@@ -1,5 +1,3 @@
-import junitbuild.java.ModuleCompileOptions
-
 plugins {
 	id("junitbuild.java-library-conventions")
 	id("com.gradleup.shadow")
@@ -21,28 +19,13 @@ configurations {
 			}
 		}
 	}
-}
-
-sourceSets {
-	main {
-		compileClasspath += shadowedClasspath.get()
-	}
-	test {
-		runtimeClasspath += shadowedClasspath.get()
-	}
-}
-
-eclipse {
-	classpath {
-		plusConfigurations.add(shadowedClasspath.get())
+	compileClasspath {
+		extendsFrom(shadowed.get())
 	}
 }
 
-idea {
-	module {
-		scopes["PROVIDED"]!!["plus"]!!.add(shadowedClasspath.get())
-	}
-}
+val javaComponent = components["java"] as AdhocComponentWithVariants
+javaComponent.withVariantsFromConfiguration(configurations.shadowRuntimeElements.get()) { skip() }
 
 tasks {
 	javadoc {
@@ -65,13 +48,4 @@ tasks {
 		from(shadowJar.map { zipTree(it.archiveFile) })
 		exclude("**/shadow/**")
 	}
-	test {
-		dependsOn(shadowJar)
-		// in order to run the test against the shadowJar
-		classpath -= sourceSets.main.get().output
-		classpath += files(shadowJar.map { it.archiveFile })
-	}
-	named<JavaCompile>("compileModule") {
-		the<ModuleCompileOptions>().modulePath.from(shadowedClasspath.get())
-	}
 }
diff --git a/gradle/plugins/common/src/main/kotlin/junitbuild.spotless-conventions.gradle.kts b/gradle/plugins/common/src/main/kotlin/junitbuild.spotless-conventions.gradle.kts
index ee94535fab22..af3d6818a029 100644
--- a/gradle/plugins/common/src/main/kotlin/junitbuild.spotless-conventions.gradle.kts
+++ b/gradle/plugins/common/src/main/kotlin/junitbuild.spotless-conventions.gradle.kts
@@ -29,6 +29,7 @@ spotless {
 		val javaFormatterConfigFile = configDir.file("junit-eclipse-formatter-settings.xml")
 
 		java {
+			targetExclude("**/module-info.java")
 			licenseHeaderFile(license.headerFile, "(package|import) ")
 			importOrderFile(importOrderConfigFile)
 			val fullVersion = requiredVersionFromLibs("eclipse")
@@ -40,8 +41,8 @@ spotless {
 		}
 
 		format("moduleDescriptor") {
-			target(fileTree(layout.projectDirectory.dir("src/module")) {
-				include("**/module-info.java")
+			target(fileTree(layout.projectDirectory.dir("src/main/java")) {
+				include("module-info.java")
 			})
 			licenseHeaderFile(license.headerFile, "^$")
 			trimTrailingWhitespace()
diff --git a/gradle/plugins/common/src/main/kotlin/junitbuild.testing-conventions.gradle.kts b/gradle/plugins/common/src/main/kotlin/junitbuild.testing-conventions.gradle.kts
index b79be1dbbeed..2ba0f59d1152 100644
--- a/gradle/plugins/common/src/main/kotlin/junitbuild.testing-conventions.gradle.kts
+++ b/gradle/plugins/common/src/main/kotlin/junitbuild.testing-conventions.gradle.kts
@@ -1,13 +1,20 @@
 import com.gradle.develocity.agent.gradle.internal.test.PredictiveTestSelectionConfigurationInternal
 import com.gradle.develocity.agent.gradle.test.PredictiveTestSelectionMode
-import junitbuild.extensions.trackOperationSystemAsInput
-import junitbuild.extensions.dependencyFromLibs
 import junitbuild.extensions.bundleFromLibs
+import junitbuild.extensions.dependencyFromLibs
+import junitbuild.extensions.trackOperationSystemAsInput
 import org.gradle.api.tasks.PathSensitivity.RELATIVE
 import org.gradle.api.tasks.testing.logging.TestExceptionFormat.FULL
 import org.gradle.api.tasks.testing.logging.TestLogEvent.FAILED
 import org.gradle.internal.os.OperatingSystem
+import java.io.IOException
 import java.io.OutputStream
+import java.nio.file.FileVisitResult
+import java.nio.file.Files
+import java.nio.file.NoSuchFileException
+import java.nio.file.Path
+import java.nio.file.SimpleFileVisitor
+import java.nio.file.attribute.BasicFileAttributes
 
 plugins {
 	`java-library`
@@ -22,6 +29,10 @@ var javaAgentClasspath = configurations.resolvable("javaAgentClasspath") {
 var openTestReportingCli = configurations.dependencyScope("openTestReportingCli")
 var openTestReportingCliClasspath = configurations.resolvable("openTestReportingCliClasspath") {
 	extendsFrom(openTestReportingCli.get())
+	attributes {
+		// Avoid using the shadowed variant of junit-platform-reporting
+		attribute(Bundling.BUNDLING_ATTRIBUTE, objects.named(Bundling::class, Bundling.EXTERNAL))
+	}
 }
 
 val generateOpenTestHtmlReport by tasks.registering(JavaExec::class) {
@@ -106,6 +117,8 @@ tasks.withType<Test>().configureEach {
 	systemProperty("log4j2.julLoggerAdapter", "org.apache.logging.log4j.jul.CoreLoggerAdapter")
 	// Avoid overhead (see https://logging.apache.org/log4j/2.x/manual/jmx.html#enabling-jmx)
 	systemProperty("log4j2.disableJmx", "true")
+	// https://github.com/raphw/byte-buddy/issues/1803
+	systemProperty("net.bytebuddy.safe", true)
 	// Required until ASM officially supports the JDK 14
 	systemProperty("net.bytebuddy.experimental", true)
 	if (buildParameters.testing.enableJFR) {
@@ -130,6 +143,7 @@ tasks.withType<Test>().configureEach {
 	jvmArgumentProviders += CommandLineArgumentProvider {
 		listOf(
 			"-Djunit.platform.reporting.open.xml.enabled=true",
+			"-Djunit.platform.reporting.open.xml.git.enabled=true",
 			"-Djunit.platform.reporting.output.dir=${reports.junitXml.outputLocation.get().asFile.absolutePath}/junit-{uniqueNumber}",
 		)
 	}
@@ -142,13 +156,38 @@ tasks.withType<Test>().configureEach {
 	}
 	jvmArgs("-Xshare:off") // https://github.com/mockito/mockito/issues/3111
 
-	val reportDirTree = objects.fileTree().from(reports.junitXml.outputLocation)
 	doFirst {
-		reportDirTree.visit {
-			if (name.startsWith("junit-")) {
-				file.deleteRecursively()
+		reports.junitXml.outputLocation.asFile.get()
+			.listFiles { _, name -> name.startsWith("junit-") }
+			?.forEach { dir ->
+				Files.walkFileTree(dir.toPath(), object : SimpleFileVisitor<Path>() {
+					override fun visitFile(file: Path, attrs: BasicFileAttributes): FileVisitResult {
+						return deleteIfExistsAndContinue(file)
+					}
+
+					override fun postVisitDirectory(dir: Path, ex: IOException?): FileVisitResult {
+						if (ex is NoSuchFileException) {
+							return FileVisitResult.CONTINUE
+						}
+						if (ex != null) {
+							throw ex
+						}
+						return deleteIfExistsAndContinue(dir)
+					}
+
+					private fun deleteIfExistsAndContinue(dir: Path): FileVisitResult {
+						Files.deleteIfExists(dir)
+						return FileVisitResult.CONTINUE
+					}
+
+					override fun visitFileFailed(file: Path, ex: IOException): FileVisitResult {
+						if (ex is NoSuchFileException) {
+							return FileVisitResult.CONTINUE
+						}
+						throw ex
+					}
+				})
 			}
-		}
 	}
 
 	finalizedBy(generateOpenTestHtmlReport)
@@ -162,13 +201,9 @@ dependencies {
 	testImplementation(project(":junit-jupiter"))
 
 	testRuntimeOnly(project(":junit-platform-engine"))
-	testRuntimeOnly(project(":junit-platform-jfr"))
 	testRuntimeOnly(project(":junit-platform-reporting"))
 
 	testRuntimeOnly(bundleFromLibs("log4j"))
-	testRuntimeOnly(dependencyFromLibs("jfrPolyfill")) {
-		because("OpenJ9 does not include JFR")
-	}
 	testRuntimeOnly(dependencyFromLibs("openTestReporting-events")) {
 		because("it's required to run tests via IntelliJ which does not consumed the shadowed jar of junit-platform-reporting")
 	}
diff --git a/gradle/plugins/common/src/main/kotlin/junitbuild/java/ModuleCompileOptions.kt b/gradle/plugins/common/src/main/kotlin/junitbuild/java/ModuleCompileOptions.kt
deleted file mode 100644
index 13c6fde1c09d..000000000000
--- a/gradle/plugins/common/src/main/kotlin/junitbuild/java/ModuleCompileOptions.kt
+++ /dev/null
@@ -1,7 +0,0 @@
-package junitbuild.java
-
-import org.gradle.api.file.ConfigurableFileCollection
-
-abstract class ModuleCompileOptions {
-    abstract val modulePath: ConfigurableFileCollection
-}
diff --git a/gradle/plugins/common/src/main/kotlin/junitbuild/java/ModulePathArgumentProvider.kt b/gradle/plugins/common/src/main/kotlin/junitbuild/java/ModulePathArgumentProvider.kt
deleted file mode 100644
index 9d05430ad810..000000000000
--- a/gradle/plugins/common/src/main/kotlin/junitbuild/java/ModulePathArgumentProvider.kt
+++ /dev/null
@@ -1,40 +0,0 @@
-package junitbuild.java
-
-import org.gradle.api.Named
-import org.gradle.api.Project
-import org.gradle.api.file.ConfigurableFileCollection
-import org.gradle.api.file.Directory
-import org.gradle.api.provider.Provider
-import org.gradle.api.tasks.*
-import org.gradle.process.CommandLineArgumentProvider
-import javax.inject.Inject
-
-abstract class ModulePathArgumentProvider @Inject constructor(project: Project, combinedModuleSourceDir: Provider<Directory>, modularProjects: List<Project>) :
-    CommandLineArgumentProvider, Named {
-
-    @get:CompileClasspath
-    abstract val modulePath: ConfigurableFileCollection
-
-    @get:InputFiles
-    @get:PathSensitive(PathSensitivity.RELATIVE)
-    abstract val moduleSourceDirs: ConfigurableFileCollection
-
-    init {
-        modularProjects.forEach {
-            if (it == project)
-                moduleSourceDirs.from(combinedModuleSourceDir)
-            else
-                moduleSourceDirs.from(project.files("${it.projectDir}/src/module"))
-        }
-    }
-
-    override fun asArguments() = listOf(
-        "--module-path",
-        modulePath.asPath,
-        "--module-source-path",
-        moduleSourceDirs.asPath
-    )
-
-    @Internal
-    override fun getName() = "module-path"
-}
diff --git a/gradle/plugins/common/src/main/kotlin/junitbuild/java/PatchModuleArgumentProvider.kt b/gradle/plugins/common/src/main/kotlin/junitbuild/java/PatchModuleArgumentProvider.kt
deleted file mode 100644
index 6b21c5a1bb7b..000000000000
--- a/gradle/plugins/common/src/main/kotlin/junitbuild/java/PatchModuleArgumentProvider.kt
+++ /dev/null
@@ -1,50 +0,0 @@
-package junitbuild.java
-
-import junitbuild.extensions.javaModuleName
-import org.gradle.api.Named
-import org.gradle.api.Project
-import org.gradle.api.file.ConfigurableFileCollection
-import org.gradle.api.provider.Property
-import org.gradle.api.tasks.Input
-import org.gradle.api.tasks.InputFiles
-import org.gradle.api.tasks.Internal
-import org.gradle.api.tasks.PathSensitive
-import org.gradle.api.tasks.PathSensitivity
-import org.gradle.api.tasks.SourceSetContainer
-import org.gradle.kotlin.dsl.get
-import org.gradle.kotlin.dsl.the
-import org.gradle.process.CommandLineArgumentProvider
-import javax.inject.Inject
-
-abstract class PatchModuleArgumentProvider @Inject constructor(compiledProject: Project, patchModuleProject: Project) :
-    CommandLineArgumentProvider, Named {
-
-    @get:Input
-    abstract val module: Property<String>
-
-    @get:InputFiles
-    @get:PathSensitive(PathSensitivity.RELATIVE)
-    abstract val patch: ConfigurableFileCollection
-
-    init {
-        module.convention(patchModuleProject.javaModuleName)
-        patch.from(compiledProject.provider {
-            if (patchModuleProject == compiledProject)
-                compiledProject.files(compiledProject.the<SourceSetContainer>().matching { it.name.startsWith("main") }
-                    .map { it.output })
-            else
-                patchModuleProject.files(patchModuleProject.the<SourceSetContainer>()["main"].java.sourceDirectories)
-        })
-    }
-
-    override fun asArguments(): List<String> {
-        val path = patch.filter { it.exists() }.asPath
-        if (path.isEmpty()) {
-            return emptyList()
-        }
-        return listOf("--patch-module", "${module.get()}=$path")
-    }
-
-    @Internal
-    override fun getName() = "patch-module(${module.get()})"
-}
diff --git a/gradle/plugins/common/src/main/kotlin/junitbuild/javadoc/ModuleSpecificJavadocFileOption.kt b/gradle/plugins/common/src/main/kotlin/junitbuild/javadoc/ModuleSpecificJavadocFileOption.kt
index f4c6f124b65e..d5ce178a4b14 100644
--- a/gradle/plugins/common/src/main/kotlin/junitbuild/javadoc/ModuleSpecificJavadocFileOption.kt
+++ b/gradle/plugins/common/src/main/kotlin/junitbuild/javadoc/ModuleSpecificJavadocFileOption.kt
@@ -1,15 +1,16 @@
 package junitbuild.javadoc
 
+import org.gradle.api.provider.Provider
 import org.gradle.external.javadoc.JavadocOptionFileOption
 import org.gradle.external.javadoc.internal.JavadocOptionFileWriterContext
 
-class ModuleSpecificJavadocFileOption(private val option: String, private var valuePerModule: Map<String, String>) : JavadocOptionFileOption<Map<String, String>> {
+class ModuleSpecificJavadocFileOption(private val option: String, private var valuePerModule: Map<String, Provider<String>>) : JavadocOptionFileOption<Map<String, Provider<String>>> {
 
     override fun getOption() = option
 
     override fun getValue() = valuePerModule
 
-    override fun setValue(value: Map<String, String>) {
+    override fun setValue(value: Map<String, Provider<String>>) {
         this.valuePerModule = value
     }
 
@@ -19,7 +20,7 @@ class ModuleSpecificJavadocFileOption(private val option: String, private var va
                     .writeOptionHeader(option)
                     .write(moduleName)
                     .write("=")
-                    .write(value)
+                    .write(value.get())
                     .newLine()
         }
     }
diff --git a/gradle/plugins/publishing/build.gradle.kts b/gradle/plugins/publishing/build.gradle.kts
index e010a00708d4..a52228904a92 100644
--- a/gradle/plugins/publishing/build.gradle.kts
+++ b/gradle/plugins/publishing/build.gradle.kts
@@ -1,4 +1,5 @@
 import junitbuild.extensions.markerCoordinates
+import org.jetbrains.kotlin.gradle.dsl.JvmTarget.JVM_21
 
 plugins {
 	`kotlin-dsl`
@@ -7,4 +8,29 @@ plugins {
 dependencies {
 	implementation("junitbuild.base:dsl-extensions")
 	implementation(libs.plugins.jreleaser.markerCoordinates)
+	constraints {
+		implementation("com.hierynomus:sshj") {
+			version {
+				require("0.40.0")
+			}
+			because("Workaround for CVE-2020-36843")
+		}
+		implementation("org.eclipse.jgit:org.eclipse.jgit") {
+			version {
+				require("6.10.1.202505221210-r")
+			}
+			because("Workaround for CVE-2025-4949")
+		}
+	}
+}
+
+tasks.compileJava {
+	options.release = 21
+}
+
+kotlin {
+	compilerOptions {
+		jvmTarget = JVM_21
+		freeCompilerArgs.add("-Xjdk-release=21")
+	}
 }
diff --git a/gradle/wrapper/gradle-wrapper.properties b/gradle/wrapper/gradle-wrapper.properties
index 247cf2a9f5ce..3735f265b953 100644
--- a/gradle/wrapper/gradle-wrapper.properties
+++ b/gradle/wrapper/gradle-wrapper.properties
@@ -1,7 +1,7 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionSha256Sum=61ad310d3c7d3e5da131b76bbf22b5a4c0786e9d892dae8c1658d4b484de3caa
-distributionUrl=https\://services.gradle.org/distributions/gradle-8.14-bin.zip
+distributionSha256Sum=7197a12f450794931532469d4ff21a59ea2c1cd59a3ec3f89c035c3c420a6999
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.14.2-bin.zip
 networkTimeout=10000
 validateDistributionUrl=true
 zipStoreBase=GRADLE_USER_HOME
diff --git a/junit-bom/README.md b/junit-bom/README.md
index e3c52f7f76d1..0f27a6f9ab89 100644
--- a/junit-bom/README.md
+++ b/junit-bom/README.md
@@ -5,4 +5,4 @@ or [Gradle]. Please refer to the [User Guide] for details.
 
 [Maven]:      https://maven.apache.org/guides/introduction/introduction-to-dependency-mechanism.html#Importing_Dependencies
 [Gradle]:     https://docs.gradle.org/current/userguide/platforms.html#sub:bom_import
-[User Guide]: https://junit.org/junit5/docs/current/user-guide/#dependency-metadata-junit-bom
+[User Guide]: https://docs.junit.org/current/user-guide/#dependency-metadata-junit-bom
diff --git a/junit-jupiter-api/junit-jupiter-api.gradle.kts b/junit-jupiter-api/junit-jupiter-api.gradle.kts
index 402b5323eb57..f2592212772c 100644
--- a/junit-jupiter-api/junit-jupiter-api.gradle.kts
+++ b/junit-jupiter-api/junit-jupiter-api.gradle.kts
@@ -1,5 +1,6 @@
 plugins {
 	id("junitbuild.kotlin-library-conventions")
+	id("junitbuild.java-nullability-conventions")
 	id("junitbuild.code-generator")
 	`java-test-fixtures`
 }
@@ -12,6 +13,7 @@ dependencies {
 	api(projects.junitPlatformCommons)
 
 	compileOnlyApi(libs.apiguardian)
+	compileOnly(libs.jspecify)
 
 	compileOnly(kotlin("stdlib"))
 
diff --git a/junit-jupiter-api/src/module/org.junit.jupiter.api/module-info.java b/junit-jupiter-api/src/main/java/module-info.java
similarity index 93%
rename from junit-jupiter-api/src/module/org.junit.jupiter.api/module-info.java
rename to junit-jupiter-api/src/main/java/module-info.java
index a9d9249f0eb1..2660f24f0d87 100644
--- a/junit-jupiter-api/src/module/org.junit.jupiter.api/module-info.java
+++ b/junit-jupiter-api/src/main/java/module-info.java
@@ -14,10 +14,15 @@
  * @since 5.0
  */
 module org.junit.jupiter.api {
+
 	requires static transitive org.apiguardian.api;
+	requires static org.jspecify;
+
 	requires transitive org.junit.platform.commons;
 	requires transitive org.opentest4j;
 
+	requires static kotlin.stdlib;
+
 	exports org.junit.jupiter.api;
 	exports org.junit.jupiter.api.condition;
 	exports org.junit.jupiter.api.extension;
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertAll.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertAll.java
index ae5f2828c795..14cc239ce08d 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertAll.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertAll.java
@@ -14,9 +14,9 @@
 import java.util.Collection;
 import java.util.List;
 import java.util.Objects;
-import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.function.Executable;
 import org.junit.platform.commons.util.Preconditions;
 import org.junit.platform.commons.util.UnrecoverableExceptions;
@@ -38,7 +38,7 @@ static void assertAll(Executable... executables) {
 		assertAll(null, executables);
 	}
 
-	static void assertAll(String heading, Executable... executables) {
+	static void assertAll(@Nullable String heading, Executable... executables) {
 		Preconditions.notEmpty(executables, "executables array must not be null or empty");
 		Preconditions.containsNoNullElements(executables, "individual executables must not be null");
 		assertAll(heading, Arrays.stream(executables));
@@ -48,7 +48,7 @@ static void assertAll(Collection<Executable> executables) {
 		assertAll(null, executables);
 	}
 
-	static void assertAll(String heading, Collection<Executable> executables) {
+	static void assertAll(@Nullable String heading, Collection<Executable> executables) {
 		Preconditions.notNull(executables, "executables collection must not be null");
 		Preconditions.containsNoNullElements(executables, "individual executables must not be null");
 		assertAll(heading, executables.stream());
@@ -58,7 +58,7 @@ static void assertAll(Stream<Executable> executables) {
 		assertAll(null, executables);
 	}
 
-	static void assertAll(String heading, Stream<Executable> executables) {
+	static void assertAll(@Nullable String heading, Stream<Executable> executables) {
 		Preconditions.notNull(executables, "executables stream must not be null");
 
 		List<Throwable> failures = executables //
@@ -74,7 +74,7 @@ static void assertAll(String heading, Stream<Executable> executables) {
 					}
 				}) //
 				.filter(Objects::nonNull) //
-				.collect(Collectors.toList());
+				.toList();
 
 		if (!failures.isEmpty()) {
 			MultipleFailuresError multipleFailuresError = new MultipleFailuresError(heading, failures);
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertArrayEquals.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertArrayEquals.java
index 06be401319d6..35bc69437fae 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertArrayEquals.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertArrayEquals.java
@@ -19,6 +19,9 @@
 import java.util.Objects;
 import java.util.function.Supplier;
 
+import org.jspecify.annotations.Nullable;
+import org.opentest4j.AssertionFailedError;
+
 /**
  * {@code AssertArrayEquals} is a collection of utility methods that support asserting
  * array equality in tests.
@@ -31,145 +34,165 @@ private AssertArrayEquals() {
 		/* no-op */
 	}
 
-	static void assertArrayEquals(boolean[] expected, boolean[] actual) {
+	static void assertArrayEquals(boolean @Nullable [] expected, boolean @Nullable [] actual) {
 		assertArrayEquals(expected, actual, (String) null);
 	}
 
-	static void assertArrayEquals(boolean[] expected, boolean[] actual, String message) {
+	static void assertArrayEquals(boolean @Nullable [] expected, boolean @Nullable [] actual,
+			@Nullable String message) {
 		assertArrayEquals(expected, actual, null, message);
 	}
 
-	static void assertArrayEquals(boolean[] expected, boolean[] actual, Supplier<String> messageSupplier) {
+	static void assertArrayEquals(boolean @Nullable [] expected, boolean @Nullable [] actual,
+			Supplier<@Nullable String> messageSupplier) {
 		assertArrayEquals(expected, actual, null, messageSupplier);
 	}
 
-	static void assertArrayEquals(char[] expected, char[] actual, String message) {
+	static void assertArrayEquals(char @Nullable [] expected, char @Nullable [] actual, @Nullable String message) {
 		assertArrayEquals(expected, actual, null, message);
 	}
 
-	static void assertArrayEquals(char[] expected, char[] actual) {
+	static void assertArrayEquals(char @Nullable [] expected, char @Nullable [] actual) {
 		assertArrayEquals(expected, actual, (String) null);
 	}
 
-	static void assertArrayEquals(char[] expected, char[] actual, Supplier<String> messageSupplier) {
+	static void assertArrayEquals(char @Nullable [] expected, char @Nullable [] actual,
+			@Nullable Supplier<@Nullable String> messageSupplier) {
 		assertArrayEquals(expected, actual, null, messageSupplier);
 	}
 
-	static void assertArrayEquals(byte[] expected, byte[] actual) {
+	static void assertArrayEquals(byte @Nullable [] expected, byte @Nullable [] actual) {
 		assertArrayEquals(expected, actual, (String) null);
 	}
 
-	static void assertArrayEquals(byte[] expected, byte[] actual, String message) {
+	static void assertArrayEquals(byte @Nullable [] expected, byte @Nullable [] actual, @Nullable String message) {
 		assertArrayEquals(expected, actual, null, message);
 	}
 
-	static void assertArrayEquals(byte[] expected, byte[] actual, Supplier<String> messageSupplier) {
+	static void assertArrayEquals(byte @Nullable [] expected, byte @Nullable [] actual,
+			Supplier<@Nullable String> messageSupplier) {
 		assertArrayEquals(expected, actual, null, messageSupplier);
 	}
 
-	static void assertArrayEquals(short[] expected, short[] actual) {
+	static void assertArrayEquals(short @Nullable [] expected, short @Nullable [] actual) {
 		assertArrayEquals(expected, actual, (String) null);
 	}
 
-	static void assertArrayEquals(short[] expected, short[] actual, String message) {
+	static void assertArrayEquals(short @Nullable [] expected, short @Nullable [] actual, @Nullable String message) {
 		assertArrayEquals(expected, actual, null, message);
 	}
 
-	static void assertArrayEquals(short[] expected, short[] actual, Supplier<String> messageSupplier) {
+	static void assertArrayEquals(short @Nullable [] expected, short @Nullable [] actual,
+			Supplier<@Nullable String> messageSupplier) {
 		assertArrayEquals(expected, actual, null, messageSupplier);
 	}
 
-	static void assertArrayEquals(int[] expected, int[] actual) {
+	static void assertArrayEquals(int @Nullable [] expected, int @Nullable [] actual) {
 		assertArrayEquals(expected, actual, (String) null);
 	}
 
-	static void assertArrayEquals(int[] expected, int[] actual, String message) {
+	static void assertArrayEquals(int @Nullable [] expected, int @Nullable [] actual, @Nullable String message) {
 		assertArrayEquals(expected, actual, null, message);
 	}
 
-	static void assertArrayEquals(int[] expected, int[] actual, Supplier<String> messageSupplier) {
+	static void assertArrayEquals(int @Nullable [] expected, int @Nullable [] actual,
+			Supplier<@Nullable String> messageSupplier) {
 		assertArrayEquals(expected, actual, null, messageSupplier);
 	}
 
-	static void assertArrayEquals(long[] expected, long[] actual) {
+	static void assertArrayEquals(long @Nullable [] expected, long @Nullable [] actual) {
 		assertArrayEquals(expected, actual, (String) null);
 	}
 
-	static void assertArrayEquals(long[] expected, long[] actual, String message) {
+	static void assertArrayEquals(long @Nullable [] expected, long @Nullable [] actual, @Nullable String message) {
 		assertArrayEquals(expected, actual, null, message);
 	}
 
-	static void assertArrayEquals(long[] expected, long[] actual, Supplier<String> messageSupplier) {
+	static void assertArrayEquals(long @Nullable [] expected, long @Nullable [] actual,
+			Supplier<@Nullable String> messageSupplier) {
 		assertArrayEquals(expected, actual, null, messageSupplier);
 	}
 
-	static void assertArrayEquals(float[] expected, float[] actual) {
+	static void assertArrayEquals(float @Nullable [] expected, float @Nullable [] actual) {
 		assertArrayEquals(expected, actual, (String) null);
 	}
 
-	static void assertArrayEquals(float[] expected, float[] actual, String message) {
+	static void assertArrayEquals(float @Nullable [] expected, float @Nullable [] actual, @Nullable String message) {
 		assertArrayEquals(expected, actual, null, message);
 	}
 
-	static void assertArrayEquals(float[] expected, float[] actual, Supplier<String> messageSupplier) {
+	static void assertArrayEquals(float @Nullable [] expected, float @Nullable [] actual,
+			Supplier<@Nullable String> messageSupplier) {
 		assertArrayEquals(expected, actual, null, messageSupplier);
 	}
 
-	static void assertArrayEquals(float[] expected, float[] actual, float delta) {
+	static void assertArrayEquals(float @Nullable [] expected, float @Nullable [] actual, float delta) {
 		assertArrayEquals(expected, actual, delta, (String) null);
 	}
 
-	static void assertArrayEquals(float[] expected, float[] actual, float delta, String message) {
+	static void assertArrayEquals(float @Nullable [] expected, float @Nullable [] actual, float delta,
+			@Nullable String message) {
 		assertArrayEquals(expected, actual, delta, null, message);
 	}
 
-	static void assertArrayEquals(float[] expected, float[] actual, float delta, Supplier<String> messageSupplier) {
+	static void assertArrayEquals(float @Nullable [] expected, float @Nullable [] actual, float delta,
+			Supplier<@Nullable String> messageSupplier) {
 		assertArrayEquals(expected, actual, delta, null, messageSupplier);
 	}
 
-	static void assertArrayEquals(double[] expected, double[] actual) {
+	static void assertArrayEquals(double @Nullable [] expected, double @Nullable [] actual) {
 		assertArrayEquals(expected, actual, (String) null);
 	}
 
-	static void assertArrayEquals(double[] expected, double[] actual, String message) {
+	static void assertArrayEquals(double @Nullable [] expected, double @Nullable [] actual, @Nullable String message) {
 		assertArrayEquals(expected, actual, null, message);
 	}
 
-	static void assertArrayEquals(double[] expected, double[] actual, Supplier<String> messageSupplier) {
+	static void assertArrayEquals(double @Nullable [] expected, double @Nullable [] actual,
+			Supplier<@Nullable String> messageSupplier) {
 		assertArrayEquals(expected, actual, null, messageSupplier);
 	}
 
-	static void assertArrayEquals(double[] expected, double[] actual, double delta) {
+	static void assertArrayEquals(double @Nullable [] expected, double @Nullable [] actual, double delta) {
 		assertArrayEquals(expected, actual, delta, (String) null);
 	}
 
-	static void assertArrayEquals(double[] expected, double[] actual, double delta, String message) {
+	static void assertArrayEquals(double @Nullable [] expected, double @Nullable [] actual, double delta,
+			@Nullable String message) {
 		assertArrayEquals(expected, actual, delta, null, message);
 	}
 
-	static void assertArrayEquals(double[] expected, double[] actual, double delta, Supplier<String> messageSupplier) {
+	static void assertArrayEquals(double @Nullable [] expected, double @Nullable [] actual, double delta,
+			Supplier<@Nullable String> messageSupplier) {
 		assertArrayEquals(expected, actual, delta, null, messageSupplier);
 	}
 
-	static void assertArrayEquals(Object[] expected, Object[] actual) {
+	static void assertArrayEquals(@Nullable Object @Nullable [] expected, @Nullable Object @Nullable [] actual) {
 		assertArrayEquals(expected, actual, (String) null);
 	}
 
-	static void assertArrayEquals(Object[] expected, Object[] actual, String message) {
+	static void assertArrayEquals(@Nullable Object @Nullable [] expected, @Nullable Object @Nullable [] actual,
+			@Nullable String message) {
 		assertArrayEquals(expected, actual, new ArrayDeque<>(), message);
 	}
 
-	static void assertArrayEquals(Object[] expected, Object[] actual, Supplier<String> messageSupplier) {
+	static void assertArrayEquals(@Nullable Object @Nullable [] expected, @Nullable Object @Nullable [] actual,
+			Supplier<@Nullable String> messageSupplier) {
 		assertArrayEquals(expected, actual, new ArrayDeque<>(), messageSupplier);
 	}
 
-	private static void assertArrayEquals(boolean[] expected, boolean[] actual, Deque<Integer> indexes,
-			Object messageOrSupplier) {
+	private static void assertArrayEquals(boolean @Nullable [] expected, boolean @Nullable [] actual,
+			@Nullable Deque<Integer> indexes, @Nullable Object messageOrSupplier) {
 
 		if (expected == actual) {
 			return;
 		}
-		assertArraysNotNull(expected, actual, indexes, messageOrSupplier);
+		if (expected == null) {
+			throw expectedArrayIsNullFailure(indexes, messageOrSupplier);
+		}
+		if (actual == null) {
+			throw actualArrayIsNullFailure(indexes, messageOrSupplier);
+		}
 		assertArraysHaveSameLength(expected.length, actual.length, indexes, messageOrSupplier);
 
 		for (int i = 0; i < expected.length; i++) {
@@ -179,13 +202,19 @@ private static void assertArrayEquals(boolean[] expected, boolean[] actual, Dequ
 		}
 	}
 
-	private static void assertArrayEquals(char[] expected, char[] actual, Deque<Integer> indexes,
-			Object messageOrSupplier) {
+	private static void assertArrayEquals(char @Nullable [] expected, char @Nullable [] actual,
+			@Nullable Deque<Integer> indexes, @Nullable Object messageOrSupplier) {
 
 		if (expected == actual) {
 			return;
 		}
-		assertArraysNotNull(expected, actual, indexes, messageOrSupplier);
+
+		if (expected == null) {
+			throw expectedArrayIsNullFailure(indexes, messageOrSupplier);
+		}
+		if (actual == null) {
+			throw actualArrayIsNullFailure(indexes, messageOrSupplier);
+		}
 		assertArraysHaveSameLength(expected.length, actual.length, indexes, messageOrSupplier);
 
 		for (int i = 0; i < expected.length; i++) {
@@ -195,13 +224,19 @@ private static void assertArrayEquals(char[] expected, char[] actual, Deque<Inte
 		}
 	}
 
-	private static void assertArrayEquals(byte[] expected, byte[] actual, Deque<Integer> indexes,
-			Object messageOrSupplier) {
+	private static void assertArrayEquals(byte @Nullable [] expected, byte @Nullable [] actual,
+			@Nullable Deque<Integer> indexes, @Nullable Object messageOrSupplier) {
 
 		if (expected == actual) {
 			return;
 		}
-		assertArraysNotNull(expected, actual, indexes, messageOrSupplier);
+
+		if (expected == null) {
+			throw expectedArrayIsNullFailure(indexes, messageOrSupplier);
+		}
+		if (actual == null) {
+			throw actualArrayIsNullFailure(indexes, messageOrSupplier);
+		}
 		assertArraysHaveSameLength(expected.length, actual.length, indexes, messageOrSupplier);
 
 		for (int i = 0; i < expected.length; i++) {
@@ -211,13 +246,19 @@ private static void assertArrayEquals(byte[] expected, byte[] actual, Deque<Inte
 		}
 	}
 
-	private static void assertArrayEquals(short[] expected, short[] actual, Deque<Integer> indexes,
-			Object messageOrSupplier) {
+	private static void assertArrayEquals(short @Nullable [] expected, short @Nullable [] actual,
+			@Nullable Deque<Integer> indexes, @Nullable Object messageOrSupplier) {
 
 		if (expected == actual) {
 			return;
 		}
-		assertArraysNotNull(expected, actual, indexes, messageOrSupplier);
+
+		if (expected == null) {
+			throw expectedArrayIsNullFailure(indexes, messageOrSupplier);
+		}
+		if (actual == null) {
+			throw actualArrayIsNullFailure(indexes, messageOrSupplier);
+		}
 		assertArraysHaveSameLength(expected.length, actual.length, indexes, messageOrSupplier);
 
 		for (int i = 0; i < expected.length; i++) {
@@ -227,13 +268,19 @@ private static void assertArrayEquals(short[] expected, short[] actual, Deque<In
 		}
 	}
 
-	private static void assertArrayEquals(int[] expected, int[] actual, Deque<Integer> indexes,
-			Object messageOrSupplier) {
+	private static void assertArrayEquals(int @Nullable [] expected, int @Nullable [] actual,
+			@Nullable Deque<Integer> indexes, @Nullable Object messageOrSupplier) {
 
 		if (expected == actual) {
 			return;
 		}
-		assertArraysNotNull(expected, actual, indexes, messageOrSupplier);
+
+		if (expected == null) {
+			throw expectedArrayIsNullFailure(indexes, messageOrSupplier);
+		}
+		if (actual == null) {
+			throw actualArrayIsNullFailure(indexes, messageOrSupplier);
+		}
 		assertArraysHaveSameLength(expected.length, actual.length, indexes, messageOrSupplier);
 
 		for (int i = 0; i < expected.length; i++) {
@@ -243,13 +290,19 @@ private static void assertArrayEquals(int[] expected, int[] actual, Deque<Intege
 		}
 	}
 
-	private static void assertArrayEquals(long[] expected, long[] actual, Deque<Integer> indexes,
-			Object messageOrSupplier) {
+	private static void assertArrayEquals(long @Nullable [] expected, long @Nullable [] actual,
+			@Nullable Deque<Integer> indexes, @Nullable Object messageOrSupplier) {
 
 		if (expected == actual) {
 			return;
 		}
-		assertArraysNotNull(expected, actual, indexes, messageOrSupplier);
+
+		if (expected == null) {
+			throw expectedArrayIsNullFailure(indexes, messageOrSupplier);
+		}
+		if (actual == null) {
+			throw actualArrayIsNullFailure(indexes, messageOrSupplier);
+		}
 		assertArraysHaveSameLength(expected.length, actual.length, indexes, messageOrSupplier);
 
 		for (int i = 0; i < expected.length; i++) {
@@ -259,13 +312,19 @@ private static void assertArrayEquals(long[] expected, long[] actual, Deque<Inte
 		}
 	}
 
-	private static void assertArrayEquals(float[] expected, float[] actual, Deque<Integer> indexes,
-			Object messageOrSupplier) {
+	private static void assertArrayEquals(float @Nullable [] expected, float @Nullable [] actual,
+			@Nullable Deque<Integer> indexes, @Nullable Object messageOrSupplier) {
 
 		if (expected == actual) {
 			return;
 		}
-		assertArraysNotNull(expected, actual, indexes, messageOrSupplier);
+
+		if (expected == null) {
+			throw expectedArrayIsNullFailure(indexes, messageOrSupplier);
+		}
+		if (actual == null) {
+			throw actualArrayIsNullFailure(indexes, messageOrSupplier);
+		}
 		assertArraysHaveSameLength(expected.length, actual.length, indexes, messageOrSupplier);
 
 		for (int i = 0; i < expected.length; i++) {
@@ -275,14 +334,20 @@ private static void assertArrayEquals(float[] expected, float[] actual, Deque<In
 		}
 	}
 
-	private static void assertArrayEquals(float[] expected, float[] actual, float delta, Deque<Integer> indexes,
-			Object messageOrSupplier) {
+	private static void assertArrayEquals(float @Nullable [] expected, float @Nullable [] actual, float delta,
+			@Nullable Deque<Integer> indexes, @Nullable Object messageOrSupplier) {
 
 		AssertionUtils.assertValidDelta(delta);
 		if (expected == actual) {
 			return;
 		}
-		assertArraysNotNull(expected, actual, indexes, messageOrSupplier);
+
+		if (expected == null) {
+			throw expectedArrayIsNullFailure(indexes, messageOrSupplier);
+		}
+		if (actual == null) {
+			throw actualArrayIsNullFailure(indexes, messageOrSupplier);
+		}
 		assertArraysHaveSameLength(expected.length, actual.length, indexes, messageOrSupplier);
 
 		for (int i = 0; i < expected.length; i++) {
@@ -292,13 +357,19 @@ private static void assertArrayEquals(float[] expected, float[] actual, float de
 		}
 	}
 
-	private static void assertArrayEquals(double[] expected, double[] actual, Deque<Integer> indexes,
-			Object messageOrSupplier) {
+	private static void assertArrayEquals(double @Nullable [] expected, double @Nullable [] actual,
+			@Nullable Deque<Integer> indexes, @Nullable Object messageOrSupplier) {
 
 		if (expected == actual) {
 			return;
 		}
-		assertArraysNotNull(expected, actual, indexes, messageOrSupplier);
+
+		if (expected == null) {
+			throw expectedArrayIsNullFailure(indexes, messageOrSupplier);
+		}
+		if (actual == null) {
+			throw actualArrayIsNullFailure(indexes, messageOrSupplier);
+		}
 		assertArraysHaveSameLength(expected.length, actual.length, indexes, messageOrSupplier);
 
 		for (int i = 0; i < expected.length; i++) {
@@ -308,14 +379,20 @@ private static void assertArrayEquals(double[] expected, double[] actual, Deque<
 		}
 	}
 
-	private static void assertArrayEquals(double[] expected, double[] actual, double delta, Deque<Integer> indexes,
-			Object messageOrSupplier) {
+	private static void assertArrayEquals(double @Nullable [] expected, double @Nullable [] actual, double delta,
+			@Nullable Deque<Integer> indexes, @Nullable Object messageOrSupplier) {
 
 		AssertionUtils.assertValidDelta(delta);
 		if (expected == actual) {
 			return;
 		}
-		assertArraysNotNull(expected, actual, indexes, messageOrSupplier);
+
+		if (expected == null) {
+			throw expectedArrayIsNullFailure(indexes, messageOrSupplier);
+		}
+		if (actual == null) {
+			throw actualArrayIsNullFailure(indexes, messageOrSupplier);
+		}
 		assertArraysHaveSameLength(expected.length, actual.length, indexes, messageOrSupplier);
 
 		for (int i = 0; i < expected.length; i++) {
@@ -325,13 +402,19 @@ private static void assertArrayEquals(double[] expected, double[] actual, double
 		}
 	}
 
-	private static void assertArrayEquals(Object[] expected, Object[] actual, Deque<Integer> indexes,
-			Object messageOrSupplier) {
+	private static void assertArrayEquals(@Nullable Object @Nullable [] expected, @Nullable Object @Nullable [] actual,
+			Deque<Integer> indexes, @Nullable Object messageOrSupplier) {
 
 		if (expected == actual) {
 			return;
 		}
-		assertArraysNotNull(expected, actual, indexes, messageOrSupplier);
+
+		if (expected == null) {
+			throw expectedArrayIsNullFailure(indexes, messageOrSupplier);
+		}
+		if (actual == null) {
+			throw actualArrayIsNullFailure(indexes, messageOrSupplier);
+		}
 		assertArraysHaveSameLength(expected.length, actual.length, indexes, messageOrSupplier);
 
 		for (int i = 0; i < expected.length; i++) {
@@ -348,35 +431,35 @@ private static void assertArrayEquals(Object[] expected, Object[] actual, Deque<
 		}
 	}
 
-	private static void assertArrayElementsEqual(Object expected, Object actual, Deque<Integer> indexes,
-			Object messageOrSupplier) {
+	private static void assertArrayElementsEqual(@Nullable Object expected, @Nullable Object actual,
+			Deque<Integer> indexes, @Nullable Object messageOrSupplier) {
 
-		if (expected instanceof Object[] && actual instanceof Object[]) {
-			assertArrayEquals((Object[]) expected, (Object[]) actual, indexes, messageOrSupplier);
+		if (expected instanceof Object[] expectedArray && actual instanceof Object[] actualArray) {
+			assertArrayEquals(expectedArray, actualArray, indexes, messageOrSupplier);
 		}
-		else if (expected instanceof byte[] && actual instanceof byte[]) {
-			assertArrayEquals((byte[]) expected, (byte[]) actual, indexes, messageOrSupplier);
+		else if (expected instanceof byte[] expectedArray && actual instanceof byte[] actualArray) {
+			assertArrayEquals(expectedArray, actualArray, indexes, messageOrSupplier);
 		}
-		else if (expected instanceof short[] && actual instanceof short[]) {
-			assertArrayEquals((short[]) expected, (short[]) actual, indexes, messageOrSupplier);
+		else if (expected instanceof short[] expectedArray && actual instanceof short[] actualArray) {
+			assertArrayEquals(expectedArray, actualArray, indexes, messageOrSupplier);
 		}
-		else if (expected instanceof int[] && actual instanceof int[]) {
-			assertArrayEquals((int[]) expected, (int[]) actual, indexes, messageOrSupplier);
+		else if (expected instanceof int[] expectedArray && actual instanceof int[] actualArray) {
+			assertArrayEquals(expectedArray, actualArray, indexes, messageOrSupplier);
 		}
-		else if (expected instanceof long[] && actual instanceof long[]) {
-			assertArrayEquals((long[]) expected, (long[]) actual, indexes, messageOrSupplier);
+		else if (expected instanceof long[] expectedArray && actual instanceof long[] actualArray) {
+			assertArrayEquals(expectedArray, actualArray, indexes, messageOrSupplier);
 		}
-		else if (expected instanceof char[] && actual instanceof char[]) {
-			assertArrayEquals((char[]) expected, (char[]) actual, indexes, messageOrSupplier);
+		else if (expected instanceof char[] expectedArray && actual instanceof char[] actualArray) {
+			assertArrayEquals(expectedArray, actualArray, indexes, messageOrSupplier);
 		}
-		else if (expected instanceof float[] && actual instanceof float[]) {
-			assertArrayEquals((float[]) expected, (float[]) actual, indexes, messageOrSupplier);
+		else if (expected instanceof float[] expectedArray && actual instanceof float[] actualArray) {
+			assertArrayEquals(expectedArray, actualArray, indexes, messageOrSupplier);
 		}
-		else if (expected instanceof double[] && actual instanceof double[]) {
-			assertArrayEquals((double[]) expected, (double[]) actual, indexes, messageOrSupplier);
+		else if (expected instanceof double[] expectedArray && actual instanceof double[] actualArray) {
+			assertArrayEquals(expectedArray, actualArray, indexes, messageOrSupplier);
 		}
-		else if (expected instanceof boolean[] && actual instanceof boolean[]) {
-			assertArrayEquals((boolean[]) expected, (boolean[]) actual, indexes, messageOrSupplier);
+		else if (expected instanceof boolean[] expectedArray && actual instanceof boolean[] actualArray) {
+			assertArrayEquals(expectedArray, actualArray, indexes, messageOrSupplier);
 		}
 		else if (!Objects.equals(expected, actual)) {
 			if (expected == null && isArray(actual)) {
@@ -391,33 +474,32 @@ else if (isArray(expected) && actual == null) {
 		}
 	}
 
-	private static void assertArraysNotNull(Object expected, Object actual, Deque<Integer> indexes,
-			Object messageOrSupplier) {
-
-		if (expected == null) {
-			failExpectedArrayIsNull(indexes, messageOrSupplier);
-		}
-		if (actual == null) {
-			failActualArrayIsNull(indexes, messageOrSupplier);
-		}
+	private static void failExpectedArrayIsNull(@Nullable Deque<Integer> indexes, @Nullable Object messageOrSupplier) {
+		throw expectedArrayIsNullFailure(indexes, messageOrSupplier);
 	}
 
-	private static void failExpectedArrayIsNull(Deque<Integer> indexes, Object messageOrSupplier) {
-		assertionFailure() //
+	private static AssertionFailedError expectedArrayIsNullFailure(@Nullable Deque<Integer> indexes,
+			@Nullable Object messageOrSupplier) {
+		return assertionFailure() //
 				.message(messageOrSupplier) //
 				.reason("expected array was <null>" + formatIndexes(indexes)) //
-				.buildAndThrow();
+				.build();
 	}
 
-	private static void failActualArrayIsNull(Deque<Integer> indexes, Object messageOrSupplier) {
-		assertionFailure() //
+	private static void failActualArrayIsNull(@Nullable Deque<Integer> indexes, @Nullable Object messageOrSupplier) {
+		throw actualArrayIsNullFailure(indexes, messageOrSupplier);
+	}
+
+	private static AssertionFailedError actualArrayIsNullFailure(@Nullable Deque<Integer> indexes,
+			@Nullable Object messageOrSupplier) {
+		return assertionFailure() //
 				.message(messageOrSupplier) //
 				.reason("actual array was <null>" + formatIndexes(indexes)) //
-				.buildAndThrow();
+				.build();
 	}
 
-	private static void assertArraysHaveSameLength(int expected, int actual, Deque<Integer> indexes,
-			Object messageOrSupplier) {
+	private static void assertArraysHaveSameLength(int expected, int actual, @Nullable Deque<Integer> indexes,
+			@Nullable Object messageOrSupplier) {
 
 		if (expected != actual) {
 			assertionFailure() //
@@ -429,8 +511,8 @@ private static void assertArraysHaveSameLength(int expected, int actual, Deque<I
 		}
 	}
 
-	private static void failArraysNotEqual(Object expected, Object actual, Deque<Integer> indexes,
-			Object messageOrSupplier) {
+	private static void failArraysNotEqual(@Nullable Object expected, @Nullable Object actual,
+			@Nullable Deque<Integer> indexes, @Nullable Object messageOrSupplier) {
 
 		assertionFailure() //
 				.message(messageOrSupplier) //
@@ -440,7 +522,7 @@ private static void failArraysNotEqual(Object expected, Object actual, Deque<Int
 				.buildAndThrow();
 	}
 
-	private static Deque<Integer> nullSafeIndexes(Deque<Integer> indexes, int newIndex) {
+	private static Deque<Integer> nullSafeIndexes(@Nullable Deque<Integer> indexes, int newIndex) {
 		Deque<Integer> result = (indexes != null ? indexes : new ArrayDeque<>());
 		result.addLast(newIndex);
 		return result;
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertDoesNotThrow.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertDoesNotThrow.java
index e2b9135dbd88..82e15c85a41a 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertDoesNotThrow.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertDoesNotThrow.java
@@ -10,10 +10,13 @@
 
 package org.junit.jupiter.api;
 
+import static org.apiguardian.api.API.Status.INTERNAL;
 import static org.junit.jupiter.api.AssertionFailureBuilder.assertionFailure;
 
 import java.util.function.Supplier;
 
+import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.function.Executable;
 import org.junit.jupiter.api.function.ThrowingSupplier;
 import org.junit.platform.commons.util.StringUtils;
@@ -36,15 +39,15 @@ static void assertDoesNotThrow(Executable executable) {
 		assertDoesNotThrow(executable, (Object) null);
 	}
 
-	static void assertDoesNotThrow(Executable executable, String message) {
+	static void assertDoesNotThrow(Executable executable, @Nullable String message) {
 		assertDoesNotThrow(executable, (Object) message);
 	}
 
-	static void assertDoesNotThrow(Executable executable, Supplier<String> messageSupplier) {
+	static void assertDoesNotThrow(Executable executable, Supplier<@Nullable String> messageSupplier) {
 		assertDoesNotThrow(executable, (Object) messageSupplier);
 	}
 
-	private static void assertDoesNotThrow(Executable executable, Object messageOrSupplier) {
+	private static void assertDoesNotThrow(Executable executable, @Nullable Object messageOrSupplier) {
 		try {
 			executable.execute();
 		}
@@ -54,19 +57,21 @@ private static void assertDoesNotThrow(Executable executable, Object messageOrSu
 		}
 	}
 
-	static <T> T assertDoesNotThrow(ThrowingSupplier<T> supplier) {
+	static <T extends @Nullable Object> T assertDoesNotThrow(ThrowingSupplier<T> supplier) {
 		return assertDoesNotThrow(supplier, (Object) null);
 	}
 
-	static <T> T assertDoesNotThrow(ThrowingSupplier<T> supplier, String message) {
+	static <T extends @Nullable Object> T assertDoesNotThrow(ThrowingSupplier<T> supplier, @Nullable String message) {
 		return assertDoesNotThrow(supplier, (Object) message);
 	}
 
-	static <T> T assertDoesNotThrow(ThrowingSupplier<T> supplier, Supplier<String> messageSupplier) {
+	static <T extends @Nullable Object> T assertDoesNotThrow(ThrowingSupplier<T> supplier,
+			Supplier<@Nullable String> messageSupplier) {
 		return assertDoesNotThrow(supplier, (Object) messageSupplier);
 	}
 
-	private static <T> T assertDoesNotThrow(ThrowingSupplier<T> supplier, Object messageOrSupplier) {
+	private static <T extends @Nullable Object> T assertDoesNotThrow(ThrowingSupplier<T> supplier,
+			@Nullable Object messageOrSupplier) {
 		try {
 			return supplier.get();
 		}
@@ -76,7 +81,8 @@ private static <T> T assertDoesNotThrow(ThrowingSupplier<T> supplier, Object mes
 		}
 	}
 
-	private static AssertionFailedError createAssertionFailedError(Object messageOrSupplier, Throwable t) {
+	@API(status = INTERNAL, since = "6.0")
+	public static AssertionFailedError createAssertionFailedError(@Nullable Object messageOrSupplier, Throwable t) {
 		return assertionFailure() //
 				.message(messageOrSupplier) //
 				.reason("Unexpected exception thrown: " + t.getClass().getName() + buildSuffix(t.getMessage())) //
@@ -84,7 +90,7 @@ private static AssertionFailedError createAssertionFailedError(Object messageOrS
 				.build();
 	}
 
-	private static String buildSuffix(String message) {
+	private static String buildSuffix(@Nullable String message) {
 		return StringUtils.isNotBlank(message) ? ": " + message : "";
 	}
 
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertEquals.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertEquals.java
index 94afc3fe49c7..2e38bdb6f1c6 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertEquals.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertEquals.java
@@ -17,6 +17,8 @@
 
 import java.util.function.Supplier;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * {@code AssertEquals} is a collection of utility methods that support asserting
  * equality on objects and primitives in tests.
@@ -33,13 +35,13 @@ static void assertEquals(byte expected, byte actual) {
 		assertEquals(expected, actual, (String) null);
 	}
 
-	static void assertEquals(byte expected, byte actual, String message) {
+	static void assertEquals(byte expected, byte actual, @Nullable String message) {
 		if (expected != actual) {
 			failNotEqual(expected, actual, message);
 		}
 	}
 
-	static void assertEquals(byte expected, byte actual, Supplier<String> messageSupplier) {
+	static void assertEquals(byte expected, byte actual, Supplier<@Nullable String> messageSupplier) {
 		if (expected != actual) {
 			failNotEqual(expected, actual, messageSupplier);
 		}
@@ -49,13 +51,13 @@ static void assertEquals(char expected, char actual) {
 		assertEquals(expected, actual, (String) null);
 	}
 
-	static void assertEquals(char expected, char actual, String message) {
+	static void assertEquals(char expected, char actual, @Nullable String message) {
 		if (expected != actual) {
 			failNotEqual(expected, actual, message);
 		}
 	}
 
-	static void assertEquals(char expected, char actual, Supplier<String> messageSupplier) {
+	static void assertEquals(char expected, char actual, Supplier<@Nullable String> messageSupplier) {
 		if (expected != actual) {
 			failNotEqual(expected, actual, messageSupplier);
 		}
@@ -65,13 +67,13 @@ static void assertEquals(double expected, double actual) {
 		assertEquals(expected, actual, (String) null);
 	}
 
-	static void assertEquals(double expected, double actual, String message) {
+	static void assertEquals(double expected, double actual, @Nullable String message) {
 		if (!doublesAreEqual(expected, actual)) {
 			failNotEqual(expected, actual, message);
 		}
 	}
 
-	static void assertEquals(double expected, double actual, Supplier<String> messageSupplier) {
+	static void assertEquals(double expected, double actual, Supplier<@Nullable String> messageSupplier) {
 		if (!doublesAreEqual(expected, actual)) {
 			failNotEqual(expected, actual, messageSupplier);
 		}
@@ -81,13 +83,13 @@ static void assertEquals(double expected, double actual, double delta) {
 		assertEquals(expected, actual, delta, (String) null);
 	}
 
-	static void assertEquals(double expected, double actual, double delta, String message) {
+	static void assertEquals(double expected, double actual, double delta, @Nullable String message) {
 		if (!doublesAreEqual(expected, actual, delta)) {
 			failNotEqual(expected, actual, message);
 		}
 	}
 
-	static void assertEquals(double expected, double actual, double delta, Supplier<String> messageSupplier) {
+	static void assertEquals(double expected, double actual, double delta, Supplier<@Nullable String> messageSupplier) {
 		if (!doublesAreEqual(expected, actual, delta)) {
 			failNotEqual(expected, actual, messageSupplier);
 		}
@@ -97,13 +99,13 @@ static void assertEquals(float expected, float actual) {
 		assertEquals(expected, actual, (String) null);
 	}
 
-	static void assertEquals(float expected, float actual, String message) {
+	static void assertEquals(float expected, float actual, @Nullable String message) {
 		if (!floatsAreEqual(expected, actual)) {
 			failNotEqual(expected, actual, message);
 		}
 	}
 
-	static void assertEquals(float expected, float actual, Supplier<String> messageSupplier) {
+	static void assertEquals(float expected, float actual, Supplier<@Nullable String> messageSupplier) {
 		if (!floatsAreEqual(expected, actual)) {
 			failNotEqual(expected, actual, messageSupplier);
 		}
@@ -113,13 +115,13 @@ static void assertEquals(float expected, float actual, float delta) {
 		assertEquals(expected, actual, delta, (String) null);
 	}
 
-	static void assertEquals(float expected, float actual, float delta, String message) {
+	static void assertEquals(float expected, float actual, float delta, @Nullable String message) {
 		if (!floatsAreEqual(expected, actual, delta)) {
 			failNotEqual(expected, actual, message);
 		}
 	}
 
-	static void assertEquals(float expected, float actual, float delta, Supplier<String> messageSupplier) {
+	static void assertEquals(float expected, float actual, float delta, Supplier<@Nullable String> messageSupplier) {
 		if (!floatsAreEqual(expected, actual, delta)) {
 			failNotEqual(expected, actual, messageSupplier);
 		}
@@ -129,13 +131,13 @@ static void assertEquals(short expected, short actual) {
 		assertEquals(expected, actual, (String) null);
 	}
 
-	static void assertEquals(short expected, short actual, String message) {
+	static void assertEquals(short expected, short actual, @Nullable String message) {
 		if (expected != actual) {
 			failNotEqual(expected, actual, message);
 		}
 	}
 
-	static void assertEquals(short expected, short actual, Supplier<String> messageSupplier) {
+	static void assertEquals(short expected, short actual, Supplier<@Nullable String> messageSupplier) {
 		if (expected != actual) {
 			failNotEqual(expected, actual, messageSupplier);
 		}
@@ -145,13 +147,13 @@ static void assertEquals(int expected, int actual) {
 		assertEquals(expected, actual, (String) null);
 	}
 
-	static void assertEquals(int expected, int actual, String message) {
+	static void assertEquals(int expected, int actual, @Nullable String message) {
 		if (expected != actual) {
 			failNotEqual(expected, actual, message);
 		}
 	}
 
-	static void assertEquals(int expected, int actual, Supplier<String> messageSupplier) {
+	static void assertEquals(int expected, int actual, Supplier<@Nullable String> messageSupplier) {
 		if (expected != actual) {
 			failNotEqual(expected, actual, messageSupplier);
 		}
@@ -161,35 +163,37 @@ static void assertEquals(long expected, long actual) {
 		assertEquals(expected, actual, (String) null);
 	}
 
-	static void assertEquals(long expected, long actual, String message) {
+	static void assertEquals(long expected, long actual, @Nullable String message) {
 		if (expected != actual) {
 			failNotEqual(expected, actual, message);
 		}
 	}
 
-	static void assertEquals(long expected, long actual, Supplier<String> messageSupplier) {
+	static void assertEquals(long expected, long actual, Supplier<@Nullable String> messageSupplier) {
 		if (expected != actual) {
 			failNotEqual(expected, actual, messageSupplier);
 		}
 	}
 
-	static void assertEquals(Object expected, Object actual) {
+	static void assertEquals(@Nullable Object expected, @Nullable Object actual) {
 		assertEquals(expected, actual, (String) null);
 	}
 
-	static void assertEquals(Object expected, Object actual, String message) {
+	static void assertEquals(@Nullable Object expected, @Nullable Object actual, @Nullable String message) {
 		if (!objectsAreEqual(expected, actual)) {
 			failNotEqual(expected, actual, message);
 		}
 	}
 
-	static void assertEquals(Object expected, Object actual, Supplier<String> messageSupplier) {
+	static void assertEquals(@Nullable Object expected, @Nullable Object actual,
+			Supplier<@Nullable String> messageSupplier) {
 		if (!objectsAreEqual(expected, actual)) {
 			failNotEqual(expected, actual, messageSupplier);
 		}
 	}
 
-	private static void failNotEqual(Object expected, Object actual, Object messageOrSupplier) {
+	private static void failNotEqual(@Nullable Object expected, @Nullable Object actual,
+			@Nullable Object messageOrSupplier) {
 		assertionFailure() //
 				.message(messageOrSupplier) //
 				.expected(expected) //
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertFalse.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertFalse.java
index f7582574166d..ea248480a299 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertFalse.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertFalse.java
@@ -15,6 +15,8 @@
 import java.util.function.BooleanSupplier;
 import java.util.function.Supplier;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * {@code AssertFalse} is a collection of utility methods that support asserting
  * {@code false} in tests.
@@ -31,13 +33,13 @@ static void assertFalse(boolean condition) {
 		assertFalse(condition, (String) null);
 	}
 
-	static void assertFalse(boolean condition, String message) {
+	static void assertFalse(boolean condition, @Nullable String message) {
 		if (condition) {
 			failNotFalse(message);
 		}
 	}
 
-	static void assertFalse(boolean condition, Supplier<String> messageSupplier) {
+	static void assertFalse(boolean condition, Supplier<@Nullable String> messageSupplier) {
 		if (condition) {
 			failNotFalse(messageSupplier);
 		}
@@ -47,15 +49,15 @@ static void assertFalse(BooleanSupplier booleanSupplier) {
 		assertFalse(booleanSupplier.getAsBoolean(), (String) null);
 	}
 
-	static void assertFalse(BooleanSupplier booleanSupplier, String message) {
+	static void assertFalse(BooleanSupplier booleanSupplier, @Nullable String message) {
 		assertFalse(booleanSupplier.getAsBoolean(), message);
 	}
 
-	static void assertFalse(BooleanSupplier booleanSupplier, Supplier<String> messageSupplier) {
+	static void assertFalse(BooleanSupplier booleanSupplier, Supplier<@Nullable String> messageSupplier) {
 		assertFalse(booleanSupplier.getAsBoolean(), messageSupplier);
 	}
 
-	private static void failNotFalse(Object messageOrSupplier) {
+	private static void failNotFalse(@Nullable Object messageOrSupplier) {
 		assertionFailure() //
 				.message(messageOrSupplier) //
 				.expected(false) //
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertInstanceOf.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertInstanceOf.java
index 4d3197ba46fe..02f72aeffdc3 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertInstanceOf.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertInstanceOf.java
@@ -14,6 +14,8 @@
 
 import java.util.function.Supplier;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * {@code AssertInstanceOf} is a collection of utility methods that support
  * asserting that an object is of an expected type &mdash; in other words, if it
@@ -27,19 +29,22 @@ private AssertInstanceOf() {
 		/* no-op */
 	}
 
-	static <T> T assertInstanceOf(Class<T> expectedType, Object actualValue) {
+	static <T> T assertInstanceOf(Class<T> expectedType, @Nullable Object actualValue) {
 		return assertInstanceOf(expectedType, actualValue, (Object) null);
 	}
 
-	static <T> T assertInstanceOf(Class<T> expectedType, Object actualValue, String message) {
+	static <T> T assertInstanceOf(Class<T> expectedType, @Nullable Object actualValue, @Nullable String message) {
 		return assertInstanceOf(expectedType, actualValue, (Object) message);
 	}
 
-	static <T> T assertInstanceOf(Class<T> expectedType, Object actualValue, Supplier<String> messageSupplier) {
+	static <T> T assertInstanceOf(Class<T> expectedType, @Nullable Object actualValue,
+			Supplier<@Nullable String> messageSupplier) {
 		return assertInstanceOf(expectedType, actualValue, (Object) messageSupplier);
 	}
 
-	private static <T> T assertInstanceOf(Class<T> expectedType, Object actualValue, Object messageOrSupplier) {
+	@SuppressWarnings("NullAway")
+	private static <T> T assertInstanceOf(Class<T> expectedType, @Nullable Object actualValue,
+			@Nullable Object messageOrSupplier) {
 		if (!expectedType.isInstance(actualValue)) {
 			assertionFailure() //
 					.message(messageOrSupplier) //
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertIterableEquals.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertIterableEquals.java
index c0dcf1dd5875..b9e70a58844d 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertIterableEquals.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertIterableEquals.java
@@ -22,6 +22,9 @@
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.function.Supplier;
 
+import org.jspecify.annotations.Nullable;
+import org.opentest4j.AssertionFailedError;
+
 /**
  * {@code AssertIterable} is a collection of utility methods that support asserting
  * Iterable equality in tests.
@@ -34,30 +37,37 @@ private AssertIterableEquals() {
 		/* no-op */
 	}
 
-	static void assertIterableEquals(Iterable<?> expected, Iterable<?> actual) {
+	static void assertIterableEquals(@Nullable Iterable<?> expected, @Nullable Iterable<?> actual) {
 		assertIterableEquals(expected, actual, (String) null);
 	}
 
-	static void assertIterableEquals(Iterable<?> expected, Iterable<?> actual, String message) {
+	static void assertIterableEquals(@Nullable Iterable<?> expected, @Nullable Iterable<?> actual,
+			@Nullable String message) {
 		assertIterableEquals(expected, actual, new ArrayDeque<>(), message);
 	}
 
-	static void assertIterableEquals(Iterable<?> expected, Iterable<?> actual, Supplier<String> messageSupplier) {
+	static void assertIterableEquals(@Nullable Iterable<?> expected, @Nullable Iterable<?> actual,
+			Supplier<@Nullable String> messageSupplier) {
 		assertIterableEquals(expected, actual, new ArrayDeque<>(), messageSupplier);
 	}
 
-	private static void assertIterableEquals(Iterable<?> expected, Iterable<?> actual, Deque<Integer> indexes,
-			Object messageOrSupplier) {
+	private static void assertIterableEquals(@Nullable Iterable<?> expected, @Nullable Iterable<?> actual,
+			Deque<Integer> indexes, @Nullable Object messageOrSupplier) {
 		assertIterableEquals(expected, actual, indexes, messageOrSupplier, new LinkedHashMap<>());
 	}
 
-	private static void assertIterableEquals(Iterable<?> expected, Iterable<?> actual, Deque<Integer> indexes,
-			Object messageOrSupplier, Map<Pair, Status> investigatedElements) {
+	private static void assertIterableEquals(@Nullable Iterable<?> expected, @Nullable Iterable<?> actual,
+			Deque<Integer> indexes, @Nullable Object messageOrSupplier, Map<Pair, Status> investigatedElements) {
 
 		if (expected == actual) {
 			return;
 		}
-		assertIterablesNotNull(expected, actual, indexes, messageOrSupplier);
+		if (expected == null) {
+			throw expectedIterableIsNullFailure(indexes, messageOrSupplier);
+		}
+		if (actual == null) {
+			throw actualIterableIsNullFailure(indexes, messageOrSupplier);
+		}
 
 		Iterator<?> expectedIterator = expected.iterator();
 		Iterator<?> actualIterator = actual.iterator();
@@ -80,7 +90,7 @@ private static void assertIterableEquals(Iterable<?> expected, Iterable<?> actua
 	}
 
 	private static void assertIterableElementsEqual(Object expected, Object actual, Deque<Integer> indexes,
-			Object messageOrSupplier, Map<Pair, Status> investigatedElements) {
+			@Nullable Object messageOrSupplier, Map<Pair, Status> investigatedElements) {
 
 		// If both are equal, we don't need to check recursively.
 		if (Objects.equals(expected, actual)) {
@@ -88,7 +98,7 @@ private static void assertIterableElementsEqual(Object expected, Object actual,
 		}
 
 		// If both are iterables, we need to check whether they contain the same elements.
-		if (expected instanceof Iterable && actual instanceof Iterable) {
+		if (expected instanceof Iterable<?> expectedIterable && actual instanceof Iterable<?> actualIterable) {
 
 			Pair pair = new Pair(expected, actual);
 
@@ -109,8 +119,7 @@ private static void assertIterableElementsEqual(Object expected, Object actual,
 			// Otherwise, we put the pair under investigation and recurse.
 			investigatedElements.put(pair, Status.UNDER_INVESTIGATION);
 
-			assertIterableEquals((Iterable<?>) expected, (Iterable<?>) actual, indexes, messageOrSupplier,
-				investigatedElements);
+			assertIterableEquals(expectedIterable, actualIterable, indexes, messageOrSupplier, investigatedElements);
 
 			// If we reach this point, we've checked that the two iterables contain the same elements so we store this information
 			// in case we come across the same pair again.
@@ -124,8 +133,8 @@ private static void assertIterableElementsEqual(Object expected, Object actual,
 		}
 	}
 
-	private static void assertIterablesNotNull(Object expected, Object actual, Deque<Integer> indexes,
-			Object messageOrSupplier) {
+	private static void assertIterablesNotNull(@Nullable Object expected, @Nullable Object actual,
+			Deque<Integer> indexes, @Nullable Object messageOrSupplier) {
 
 		if (expected == null) {
 			failExpectedIterableIsNull(indexes, messageOrSupplier);
@@ -135,22 +144,32 @@ private static void assertIterablesNotNull(Object expected, Object actual, Deque
 		}
 	}
 
-	private static void failExpectedIterableIsNull(Deque<Integer> indexes, Object messageOrSupplier) {
-		assertionFailure() //
+	private static void failExpectedIterableIsNull(Deque<Integer> indexes, @Nullable Object messageOrSupplier) {
+		throw expectedIterableIsNullFailure(indexes, messageOrSupplier);
+	}
+
+	private static AssertionFailedError expectedIterableIsNullFailure(Deque<Integer> indexes,
+			@Nullable Object messageOrSupplier) {
+		return assertionFailure() //
 				.message(messageOrSupplier) //
 				.reason("expected iterable was <null>" + formatIndexes(indexes)) //
-				.buildAndThrow();
+				.build();
 	}
 
-	private static void failActualIterableIsNull(Deque<Integer> indexes, Object messageOrSupplier) {
-		assertionFailure() //
+	private static void failActualIterableIsNull(Deque<Integer> indexes, @Nullable Object messageOrSupplier) {
+		throw actualIterableIsNullFailure(indexes, messageOrSupplier);
+	}
+
+	private static AssertionFailedError actualIterableIsNullFailure(Deque<Integer> indexes,
+			@Nullable Object messageOrSupplier) {
+		return assertionFailure() //
 				.message(messageOrSupplier) //
 				.reason("actual iterable was <null>" + formatIndexes(indexes)) //
-				.buildAndThrow();
+				.build();
 	}
 
 	private static void assertIteratorsAreEmpty(Iterator<?> expected, Iterator<?> actual, int processed,
-			Deque<Integer> indexes, Object messageOrSupplier) {
+			Deque<Integer> indexes, @Nullable Object messageOrSupplier) {
 
 		if (expected.hasNext() || actual.hasNext()) {
 			AtomicInteger expectedCount = new AtomicInteger(processed);
@@ -169,7 +188,7 @@ private static void assertIteratorsAreEmpty(Iterator<?> expected, Iterator<?> ac
 	}
 
 	private static void failIterablesNotEqual(Object expected, Object actual, Deque<Integer> indexes,
-			Object messageOrSupplier) {
+			@Nullable Object messageOrSupplier) {
 
 		assertionFailure() //
 				.message(messageOrSupplier) //
@@ -179,30 +198,7 @@ private static void failIterablesNotEqual(Object expected, Object actual, Deque<
 				.buildAndThrow();
 	}
 
-	private final static class Pair {
-		private final Object left;
-		private final Object right;
-
-		public Pair(Object left, Object right) {
-			this.left = left;
-			this.right = right;
-		}
-
-		@Override
-		public boolean equals(Object o) {
-			if (this == o)
-				return true;
-			if (o == null || getClass() != o.getClass())
-				return false;
-			Pair that = (Pair) o;
-			return Objects.equals(this.left, that.left) //
-					&& Objects.equals(this.right, that.right);
-		}
-
-		@Override
-		public int hashCode() {
-			return Objects.hash(left, right);
-		}
+	private record Pair(Object left, Object right) {
 	}
 
 	private enum Status {
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertLinesMatch.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertLinesMatch.java
index 7596aed881f0..16921e088eff 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertLinesMatch.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertLinesMatch.java
@@ -10,7 +10,6 @@
 
 package org.junit.jupiter.api;
 
-import static java.lang.String.format;
 import static java.lang.String.join;
 import static org.junit.jupiter.api.AssertionFailureBuilder.assertionFailure;
 import static org.junit.platform.commons.util.Preconditions.condition;
@@ -20,10 +19,11 @@
 import java.util.Deque;
 import java.util.List;
 import java.util.regex.PatternSyntaxException;
-import java.util.stream.Collectors;
 import java.util.stream.IntStream;
 import java.util.stream.Stream;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * {@code AssertLinesMatch} is a collection of utility methods that support asserting
  * lines of {@link String} equality or {@link java.util.regex.Pattern}-match in tests.
@@ -42,7 +42,7 @@ static void assertLinesMatch(List<String> expectedLines, List<String> actualLine
 		assertLinesMatch(expectedLines, actualLines, (Object) null);
 	}
 
-	static void assertLinesMatch(List<String> expectedLines, List<String> actualLines, String message) {
+	static void assertLinesMatch(List<String> expectedLines, List<String> actualLines, @Nullable String message) {
 		assertLinesMatch(expectedLines, actualLines, (Object) message);
 	}
 
@@ -50,11 +50,12 @@ static void assertLinesMatch(Stream<String> expectedLines, Stream<String> actual
 		assertLinesMatch(expectedLines, actualLines, (Object) null);
 	}
 
-	static void assertLinesMatch(Stream<String> expectedLines, Stream<String> actualLines, String message) {
+	static void assertLinesMatch(Stream<String> expectedLines, Stream<String> actualLines, @Nullable String message) {
 		assertLinesMatch(expectedLines, actualLines, (Object) message);
 	}
 
-	static void assertLinesMatch(Stream<String> expectedLines, Stream<String> actualLines, Object messageOrSupplier) {
+	static void assertLinesMatch(Stream<String> expectedLines, Stream<String> actualLines,
+			@Nullable Object messageOrSupplier) {
 		notNull(expectedLines, "expectedLines must not be null");
 		notNull(actualLines, "actualLines must not be null");
 
@@ -63,12 +64,13 @@ static void assertLinesMatch(Stream<String> expectedLines, Stream<String> actual
 			return;
 		}
 
-		List<String> expectedListOfStrings = expectedLines.collect(Collectors.toList());
-		List<String> actualListOfStrings = actualLines.collect(Collectors.toList());
+		List<String> expectedListOfStrings = expectedLines.toList();
+		List<String> actualListOfStrings = actualLines.toList();
 		assertLinesMatch(expectedListOfStrings, actualListOfStrings, messageOrSupplier);
 	}
 
-	static void assertLinesMatch(List<String> expectedLines, List<String> actualLines, Object messageOrSupplier) {
+	static void assertLinesMatch(List<String> expectedLines, List<String> actualLines,
+			@Nullable Object messageOrSupplier) {
 		notNull(expectedLines, "expectedLines must not be null");
 		notNull(actualLines, "actualLines must not be null");
 
@@ -80,17 +82,8 @@ static void assertLinesMatch(List<String> expectedLines, List<String> actualLine
 		new LinesMatcher(expectedLines, actualLines, messageOrSupplier).assertLinesMatch();
 	}
 
-	private static class LinesMatcher {
-
-		private final List<String> expectedLines;
-		private final List<String> actualLines;
-		private final Object messageOrSupplier;
-
-		LinesMatcher(List<String> expectedLines, List<String> actualLines, Object messageOrSupplier) {
-			this.expectedLines = expectedLines;
-			this.actualLines = actualLines;
-			this.messageOrSupplier = messageOrSupplier;
-		}
+	private record LinesMatcher(List<String> expectedLines, List<String> actualLines,
+			@Nullable Object messageOrSupplier) {
 
 		void assertLinesMatch() {
 			int expectedSize = expectedLines.size();
@@ -196,7 +189,7 @@ void fail(String format, Object... args) {
 			String newLine = System.lineSeparator();
 			assertionFailure() //
 					.message(messageOrSupplier) //
-					.reason(format(format, args)) //
+					.reason(format.formatted(args)) //
 					.expected(join(newLine, expectedLines)) //
 					.actual(join(newLine, actualLines)) //
 					.includeValuesInMessage(false) //
@@ -214,7 +207,7 @@ static int parseFastForwardLimit(String fastForwardLine) {
 		String text = fastForwardLine.substring(2, fastForwardLine.length() - 2).trim();
 		try {
 			int limit = Integer.parseInt(text);
-			condition(limit > 0, () -> format("fast-forward(%d) limit must be greater than zero", limit));
+			condition(limit > 0, () -> "fast-forward(%d) limit must be greater than zero".formatted(limit));
 			return limit;
 		}
 		catch (NumberFormatException e) {
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertNotEquals.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertNotEquals.java
index 1ccc41b7bb13..e78a32eb4aa8 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertNotEquals.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertNotEquals.java
@@ -17,6 +17,8 @@
 
 import java.util.function.Supplier;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * {@code AssertNotEquals} is a collection of utility methods that support asserting
  * inequality in objects and primitive values in tests.
@@ -39,7 +41,7 @@ static void assertNotEquals(byte unexpected, byte actual) {
 	/**
 	 * @since 5.4
 	 */
-	static void assertNotEquals(byte unexpected, byte actual, String message) {
+	static void assertNotEquals(byte unexpected, byte actual, @Nullable String message) {
 		if (unexpected == actual) {
 			failEqual(actual, message);
 		}
@@ -48,7 +50,7 @@ static void assertNotEquals(byte unexpected, byte actual, String message) {
 	/**
 	 * @since 5.4
 	 */
-	static void assertNotEquals(byte unexpected, byte actual, Supplier<String> messageSupplier) {
+	static void assertNotEquals(byte unexpected, byte actual, Supplier<@Nullable String> messageSupplier) {
 		if (unexpected == actual) {
 			failEqual(actual, messageSupplier);
 		}
@@ -64,7 +66,7 @@ static void assertNotEquals(short unexpected, short actual) {
 	/**
 	 * @since 5.4
 	 */
-	static void assertNotEquals(short unexpected, short actual, String message) {
+	static void assertNotEquals(short unexpected, short actual, @Nullable String message) {
 		if (unexpected == actual) {
 			failEqual(actual, message);
 		}
@@ -73,7 +75,7 @@ static void assertNotEquals(short unexpected, short actual, String message) {
 	/**
 	 * @since 5.4
 	 */
-	static void assertNotEquals(short unexpected, short actual, Supplier<String> messageSupplier) {
+	static void assertNotEquals(short unexpected, short actual, Supplier<@Nullable String> messageSupplier) {
 		if (unexpected == actual) {
 			failEqual(actual, messageSupplier);
 		}
@@ -89,7 +91,7 @@ static void assertNotEquals(int unexpected, int actual) {
 	/**
 	 * @since 5.4
 	 */
-	static void assertNotEquals(int unexpected, int actual, String message) {
+	static void assertNotEquals(int unexpected, int actual, @Nullable String message) {
 		if (unexpected == actual) {
 			failEqual(actual, message);
 		}
@@ -98,7 +100,7 @@ static void assertNotEquals(int unexpected, int actual, String message) {
 	/**
 	 * @since 5.4
 	 */
-	static void assertNotEquals(int unexpected, int actual, Supplier<String> messageSupplier) {
+	static void assertNotEquals(int unexpected, int actual, Supplier<@Nullable String> messageSupplier) {
 		if (unexpected == actual) {
 			failEqual(actual, messageSupplier);
 		}
@@ -114,7 +116,7 @@ static void assertNotEquals(long unexpected, long actual) {
 	/**
 	 * @since 5.4
 	 */
-	static void assertNotEquals(long unexpected, long actual, String message) {
+	static void assertNotEquals(long unexpected, long actual, @Nullable String message) {
 		if (unexpected == actual) {
 			failEqual(actual, message);
 		}
@@ -123,7 +125,7 @@ static void assertNotEquals(long unexpected, long actual, String message) {
 	/**
 	 * @since 5.4
 	 */
-	static void assertNotEquals(long unexpected, long actual, Supplier<String> messageSupplier) {
+	static void assertNotEquals(long unexpected, long actual, Supplier<@Nullable String> messageSupplier) {
 		if (unexpected == actual) {
 			failEqual(actual, messageSupplier);
 		}
@@ -139,7 +141,7 @@ static void assertNotEquals(float unexpected, float actual) {
 	/**
 	 * @since 5.4
 	 */
-	static void assertNotEquals(float unexpected, float actual, String message) {
+	static void assertNotEquals(float unexpected, float actual, @Nullable String message) {
 		if (floatsAreEqual(unexpected, actual)) {
 			failEqual(actual, message);
 		}
@@ -148,7 +150,7 @@ static void assertNotEquals(float unexpected, float actual, String message) {
 	/**
 	 * @since 5.4
 	 */
-	static void assertNotEquals(float unexpected, float actual, Supplier<String> messageSupplier) {
+	static void assertNotEquals(float unexpected, float actual, Supplier<@Nullable String> messageSupplier) {
 		if (floatsAreEqual(unexpected, actual)) {
 			failEqual(actual, messageSupplier);
 		}
@@ -164,7 +166,7 @@ static void assertNotEquals(float unexpected, float actual, float delta) {
 	/**
 	 * @since 5.4
 	 */
-	static void assertNotEquals(float unexpected, float actual, float delta, String message) {
+	static void assertNotEquals(float unexpected, float actual, float delta, @Nullable String message) {
 		if (floatsAreEqual(unexpected, actual, delta)) {
 			failEqual(actual, message);
 		}
@@ -173,7 +175,8 @@ static void assertNotEquals(float unexpected, float actual, float delta, String
 	/**
 	 * @since 5.4
 	 */
-	static void assertNotEquals(float unexpected, float actual, float delta, Supplier<String> messageSupplier) {
+	static void assertNotEquals(float unexpected, float actual, float delta,
+			Supplier<@Nullable String> messageSupplier) {
 		if (floatsAreEqual(unexpected, actual, delta)) {
 			failEqual(actual, messageSupplier);
 		}
@@ -189,7 +192,7 @@ static void assertNotEquals(double unexpected, double actual) {
 	/**
 	 * @since 5.4
 	 */
-	static void assertNotEquals(double unexpected, double actual, String message) {
+	static void assertNotEquals(double unexpected, double actual, @Nullable String message) {
 		if (doublesAreEqual(unexpected, actual)) {
 			failEqual(actual, message);
 		}
@@ -198,7 +201,7 @@ static void assertNotEquals(double unexpected, double actual, String message) {
 	/**
 	 * @since 5.4
 	 */
-	static void assertNotEquals(double unexpected, double actual, Supplier<String> messageSupplier) {
+	static void assertNotEquals(double unexpected, double actual, Supplier<@Nullable String> messageSupplier) {
 		if (doublesAreEqual(unexpected, actual)) {
 			failEqual(actual, messageSupplier);
 		}
@@ -214,7 +217,7 @@ static void assertNotEquals(double unexpected, double actual, double delta) {
 	/**
 	 * @since 5.4
 	 */
-	static void assertNotEquals(double unexpected, double actual, double delta, String message) {
+	static void assertNotEquals(double unexpected, double actual, double delta, @Nullable String message) {
 		if (doublesAreEqual(unexpected, actual, delta)) {
 			failEqual(actual, message);
 		}
@@ -223,7 +226,8 @@ static void assertNotEquals(double unexpected, double actual, double delta, Stri
 	/**
 	 * @since 5.4
 	 */
-	static void assertNotEquals(double unexpected, double actual, double delta, Supplier<String> messageSupplier) {
+	static void assertNotEquals(double unexpected, double actual, double delta,
+			Supplier<@Nullable String> messageSupplier) {
 		if (doublesAreEqual(unexpected, actual, delta)) {
 			failEqual(actual, messageSupplier);
 		}
@@ -239,7 +243,7 @@ static void assertNotEquals(char unexpected, char actual) {
 	/**
 	 * @since 5.4
 	 */
-	static void assertNotEquals(char unexpected, char actual, String message) {
+	static void assertNotEquals(char unexpected, char actual, @Nullable String message) {
 		if (unexpected == actual) {
 			failEqual(actual, message);
 		}
@@ -248,29 +252,30 @@ static void assertNotEquals(char unexpected, char actual, String message) {
 	/**
 	 * @since 5.4
 	 */
-	static void assertNotEquals(char unexpected, char actual, Supplier<String> messageSupplier) {
+	static void assertNotEquals(char unexpected, char actual, Supplier<@Nullable String> messageSupplier) {
 		if (unexpected == actual) {
 			failEqual(actual, messageSupplier);
 		}
 	}
 
-	static void assertNotEquals(Object unexpected, Object actual) {
+	static void assertNotEquals(@Nullable Object unexpected, @Nullable Object actual) {
 		assertNotEquals(unexpected, actual, (String) null);
 	}
 
-	static void assertNotEquals(Object unexpected, Object actual, String message) {
+	static void assertNotEquals(@Nullable Object unexpected, @Nullable Object actual, @Nullable String message) {
 		if (objectsAreEqual(unexpected, actual)) {
 			failEqual(actual, message);
 		}
 	}
 
-	static void assertNotEquals(Object unexpected, Object actual, Supplier<String> messageSupplier) {
+	static void assertNotEquals(@Nullable Object unexpected, @Nullable Object actual,
+			Supplier<@Nullable String> messageSupplier) {
 		if (objectsAreEqual(unexpected, actual)) {
 			failEqual(actual, messageSupplier);
 		}
 	}
 
-	private static void failEqual(Object actual, Object messageOrSupplier) {
+	private static void failEqual(@Nullable Object actual, @Nullable Object messageOrSupplier) {
 		assertionFailure() //
 				.message(messageOrSupplier) //
 				.reason("expected: not equal but was: <" + actual + ">") //
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertNotNull.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertNotNull.java
index f5fb9b849230..1f1208f297dc 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertNotNull.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertNotNull.java
@@ -14,6 +14,8 @@
 
 import java.util.function.Supplier;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * {@code AssertNotNull} is a collection of utility methods that support asserting
  * that there is an object.
@@ -26,23 +28,23 @@ private AssertNotNull() {
 		/* no-op */
 	}
 
-	static void assertNotNull(Object actual) {
+	static void assertNotNull(@Nullable Object actual) {
 		assertNotNull(actual, (String) null);
 	}
 
-	static void assertNotNull(Object actual, String message) {
+	static void assertNotNull(@Nullable Object actual, @Nullable String message) {
 		if (actual == null) {
 			failNull(message);
 		}
 	}
 
-	static void assertNotNull(Object actual, Supplier<String> messageSupplier) {
+	static void assertNotNull(@Nullable Object actual, Supplier<@Nullable String> messageSupplier) {
 		if (actual == null) {
 			failNull(messageSupplier);
 		}
 	}
 
-	private static void failNull(Object messageOrSupplier) {
+	private static void failNull(@Nullable Object messageOrSupplier) {
 		assertionFailure() //
 				.message(messageOrSupplier) //
 				.reason("expected: not <null>") //
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertNotSame.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertNotSame.java
index 860371937076..d46c8f711fe1 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertNotSame.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertNotSame.java
@@ -14,6 +14,8 @@
 
 import java.util.function.Supplier;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * {@code AssertNotSame} is a collection of utility methods that support asserting
  * two objects are not the same.
@@ -26,23 +28,24 @@ private AssertNotSame() {
 		/* no-op */
 	}
 
-	static void assertNotSame(Object unexpected, Object actual) {
+	static void assertNotSame(@Nullable Object unexpected, @Nullable Object actual) {
 		assertNotSame(unexpected, actual, (String) null);
 	}
 
-	static void assertNotSame(Object unexpected, Object actual, String message) {
+	static void assertNotSame(@Nullable Object unexpected, @Nullable Object actual, @Nullable String message) {
 		if (unexpected == actual) {
 			failSame(actual, message);
 		}
 	}
 
-	static void assertNotSame(Object unexpected, Object actual, Supplier<String> messageSupplier) {
+	static void assertNotSame(@Nullable Object unexpected, @Nullable Object actual,
+			Supplier<@Nullable String> messageSupplier) {
 		if (unexpected == actual) {
 			failSame(actual, messageSupplier);
 		}
 	}
 
-	private static void failSame(Object actual, Object messageOrSupplier) {
+	private static void failSame(@Nullable Object actual, @Nullable Object messageOrSupplier) {
 		assertionFailure() //
 				.message(messageOrSupplier) //
 				.reason("expected: not same but was: <" + actual + ">") //
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertNull.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertNull.java
index a81e7925415f..1acf4c1e6154 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertNull.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertNull.java
@@ -14,6 +14,8 @@
 
 import java.util.function.Supplier;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * {@code AssertNull} is a collection of utility methods that support asserting
  * there is no object.
@@ -26,23 +28,23 @@ private AssertNull() {
 		/* no-op */
 	}
 
-	static void assertNull(Object actual) {
+	static void assertNull(@Nullable Object actual) {
 		assertNull(actual, (String) null);
 	}
 
-	static void assertNull(Object actual, String message) {
+	static void assertNull(@Nullable Object actual, @Nullable String message) {
 		if (actual != null) {
 			failNotNull(actual, message);
 		}
 	}
 
-	static void assertNull(Object actual, Supplier<String> messageSupplier) {
+	static void assertNull(@Nullable Object actual, Supplier<@Nullable String> messageSupplier) {
 		if (actual != null) {
 			failNotNull(actual, messageSupplier);
 		}
 	}
 
-	private static void failNotNull(Object actual, Object messageOrSupplier) {
+	private static void failNotNull(@Nullable Object actual, @Nullable Object messageOrSupplier) {
 		assertionFailure() //
 				.message(messageOrSupplier) //
 				.expected(null) //
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertSame.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertSame.java
index f006dab823ff..2cf1476f3742 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertSame.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertSame.java
@@ -14,6 +14,8 @@
 
 import java.util.function.Supplier;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * {@code AssertSame} is a collection of utility methods that support asserting
  * two objects are the same.
@@ -26,23 +28,25 @@ private AssertSame() {
 		/* no-op */
 	}
 
-	static void assertSame(Object expected, Object actual) {
+	static void assertSame(@Nullable Object expected, @Nullable Object actual) {
 		assertSame(expected, actual, (String) null);
 	}
 
-	static void assertSame(Object expected, Object actual, String message) {
+	static void assertSame(@Nullable Object expected, @Nullable Object actual, @Nullable String message) {
 		if (expected != actual) {
 			failNotSame(expected, actual, message);
 		}
 	}
 
-	static void assertSame(Object expected, Object actual, Supplier<String> messageSupplier) {
+	static void assertSame(@Nullable Object expected, @Nullable Object actual,
+			Supplier<@Nullable String> messageSupplier) {
 		if (expected != actual) {
 			failNotSame(expected, actual, messageSupplier);
 		}
 	}
 
-	private static void failNotSame(Object expected, Object actual, Object messageOrSupplier) {
+	private static void failNotSame(@Nullable Object expected, @Nullable Object actual,
+			@Nullable Object messageOrSupplier) {
 		assertionFailure() //
 				.message(messageOrSupplier) //
 				.expected(expected) //
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertThrows.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertThrows.java
index 70ee8b02fe4f..d198486087a4 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertThrows.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertThrows.java
@@ -10,12 +10,12 @@
 
 package org.junit.jupiter.api;
 
-import static java.lang.String.format;
 import static org.junit.jupiter.api.AssertionFailureBuilder.assertionFailure;
 import static org.junit.jupiter.api.AssertionUtils.getCanonicalName;
 
 import java.util.function.Supplier;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.function.Executable;
 import org.junit.platform.commons.util.UnrecoverableExceptions;
 
@@ -35,19 +35,20 @@ static <T extends Throwable> T assertThrows(Class<T> expectedType, Executable ex
 		return assertThrows(expectedType, executable, (Object) null);
 	}
 
-	static <T extends Throwable> T assertThrows(Class<T> expectedType, Executable executable, String message) {
+	static <T extends Throwable> T assertThrows(Class<T> expectedType, Executable executable,
+			@Nullable String message) {
 		return assertThrows(expectedType, executable, (Object) message);
 	}
 
 	static <T extends Throwable> T assertThrows(Class<T> expectedType, Executable executable,
-			Supplier<String> messageSupplier) {
+			Supplier<@Nullable String> messageSupplier) {
 
 		return assertThrows(expectedType, executable, (Object) messageSupplier);
 	}
 
 	@SuppressWarnings("unchecked")
 	private static <T extends Throwable> T assertThrows(Class<T> expectedType, Executable executable,
-			Object messageOrSupplier) {
+			@Nullable Object messageOrSupplier) {
 
 		try {
 			executable.execute();
@@ -69,7 +70,7 @@ private static <T extends Throwable> T assertThrows(Class<T> expectedType, Execu
 		}
 		throw assertionFailure() //
 				.message(messageOrSupplier) //
-				.reason(format("Expected %s to be thrown, but nothing was thrown.", getCanonicalName(expectedType))) //
+				.reason("Expected %s to be thrown, but nothing was thrown.".formatted(getCanonicalName(expectedType))) //
 				.build();
 	}
 
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertThrowsExactly.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertThrowsExactly.java
index 4fa017318589..59e72305be9e 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertThrowsExactly.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertThrowsExactly.java
@@ -10,12 +10,12 @@
 
 package org.junit.jupiter.api;
 
-import static java.lang.String.format;
 import static org.junit.jupiter.api.AssertionFailureBuilder.assertionFailure;
 import static org.junit.jupiter.api.AssertionUtils.getCanonicalName;
 
 import java.util.function.Supplier;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.function.Executable;
 import org.junit.platform.commons.util.UnrecoverableExceptions;
 
@@ -35,19 +35,20 @@ static <T extends Throwable> T assertThrowsExactly(Class<T> expectedType, Execut
 		return assertThrowsExactly(expectedType, executable, (Object) null);
 	}
 
-	static <T extends Throwable> T assertThrowsExactly(Class<T> expectedType, Executable executable, String message) {
+	static <T extends Throwable> T assertThrowsExactly(Class<T> expectedType, Executable executable,
+			@Nullable String message) {
 		return assertThrowsExactly(expectedType, executable, (Object) message);
 	}
 
 	static <T extends Throwable> T assertThrowsExactly(Class<T> expectedType, Executable executable,
-			Supplier<String> messageSupplier) {
+			Supplier<@Nullable String> messageSupplier) {
 
 		return assertThrowsExactly(expectedType, executable, (Object) messageSupplier);
 	}
 
 	@SuppressWarnings("unchecked")
 	private static <T extends Throwable> T assertThrowsExactly(Class<T> expectedType, Executable executable,
-			Object messageOrSupplier) {
+			@Nullable Object messageOrSupplier) {
 
 		try {
 			executable.execute();
@@ -70,7 +71,7 @@ private static <T extends Throwable> T assertThrowsExactly(Class<T> expectedType
 
 		throw assertionFailure() //
 				.message(messageOrSupplier) //
-				.reason(format("Expected %s to be thrown, but nothing was thrown.", getCanonicalName(expectedType))) //
+				.reason("Expected %s to be thrown, but nothing was thrown.".formatted(getCanonicalName(expectedType))) //
 				.build();
 	}
 
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertTimeout.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertTimeout.java
index 3aadf60f88af..d60b065be1bb 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertTimeout.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertTimeout.java
@@ -16,6 +16,7 @@
 import java.time.Duration;
 import java.util.function.Supplier;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.function.Executable;
 import org.junit.jupiter.api.function.ThrowingSupplier;
 
@@ -35,36 +36,39 @@ static void assertTimeout(Duration timeout, Executable executable) {
 		assertTimeout(timeout, executable, (String) null);
 	}
 
-	static void assertTimeout(Duration timeout, Executable executable, String message) {
-		assertTimeout(timeout, () -> {
+	static void assertTimeout(Duration timeout, Executable executable, @Nullable String message) {
+		AssertTimeout.<@Nullable Object> assertTimeout(timeout, () -> {
 			executable.execute();
 			return null;
 		}, message);
 	}
 
-	static void assertTimeout(Duration timeout, Executable executable, Supplier<String> messageSupplier) {
-		assertTimeout(timeout, () -> {
+	static void assertTimeout(Duration timeout, Executable executable, Supplier<@Nullable String> messageSupplier) {
+		AssertTimeout.<@Nullable Object> assertTimeout(timeout, () -> {
 			executable.execute();
 			return null;
 		}, messageSupplier);
 	}
 
-	static <T> T assertTimeout(Duration timeout, ThrowingSupplier<T> supplier) {
+	static <T extends @Nullable Object> T assertTimeout(Duration timeout, ThrowingSupplier<T> supplier) {
 		return assertTimeout(timeout, supplier, (Object) null);
 	}
 
-	static <T> T assertTimeout(Duration timeout, ThrowingSupplier<T> supplier, String message) {
+	static <T extends @Nullable Object> T assertTimeout(Duration timeout, ThrowingSupplier<T> supplier,
+			@Nullable String message) {
 		return assertTimeout(timeout, supplier, (Object) message);
 	}
 
-	static <T> T assertTimeout(Duration timeout, ThrowingSupplier<T> supplier, Supplier<String> messageSupplier) {
+	static <T extends @Nullable Object> T assertTimeout(Duration timeout, ThrowingSupplier<T> supplier,
+			Supplier<@Nullable String> messageSupplier) {
 		return assertTimeout(timeout, supplier, (Object) messageSupplier);
 	}
 
-	private static <T> T assertTimeout(Duration timeout, ThrowingSupplier<T> supplier, Object messageOrSupplier) {
+	private static <T extends @Nullable Object> T assertTimeout(Duration timeout, ThrowingSupplier<T> supplier,
+			@Nullable Object messageOrSupplier) {
 		long timeoutInMillis = timeout.toMillis();
 		long start = System.currentTimeMillis();
-		T result = null;
+		T result;
 		try {
 			result = supplier.get();
 		}
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertTimeoutPreemptively.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertTimeoutPreemptively.java
index 1eaea9ce4f3e..a2d277de1932 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertTimeoutPreemptively.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertTimeoutPreemptively.java
@@ -10,9 +10,11 @@
 
 package org.junit.jupiter.api;
 
+import static java.util.Objects.requireNonNullElse;
 import static org.junit.jupiter.api.AssertionFailureBuilder.assertionFailure;
 import static org.junit.platform.commons.util.ExceptionUtils.throwAsUncheckedException;
 
+import java.io.Serial;
 import java.time.Duration;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.ExecutorService;
@@ -25,6 +27,7 @@
 import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.Supplier;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.function.Executable;
 import org.junit.jupiter.api.function.ThrowingSupplier;
 import org.junit.platform.commons.JUnitException;
@@ -43,37 +46,42 @@ static void assertTimeoutPreemptively(Duration timeout, Executable executable) {
 		assertTimeoutPreemptively(timeout, executable, (String) null);
 	}
 
-	static void assertTimeoutPreemptively(Duration timeout, Executable executable, String message) {
+	@SuppressWarnings("NullAway")
+	static void assertTimeoutPreemptively(Duration timeout, Executable executable, @Nullable String message) {
 		assertTimeoutPreemptively(timeout, () -> {
 			executable.execute();
 			return null;
 		}, message);
 	}
 
-	static void assertTimeoutPreemptively(Duration timeout, Executable executable, Supplier<String> messageSupplier) {
+	@SuppressWarnings("NullAway")
+	static void assertTimeoutPreemptively(Duration timeout, Executable executable,
+			Supplier<@Nullable String> messageSupplier) {
 		assertTimeoutPreemptively(timeout, () -> {
 			executable.execute();
 			return null;
 		}, messageSupplier);
 	}
 
-	static <T> T assertTimeoutPreemptively(Duration timeout, ThrowingSupplier<T> supplier) {
+	static <T extends @Nullable Object> T assertTimeoutPreemptively(Duration timeout, ThrowingSupplier<T> supplier) {
 		return assertTimeoutPreemptively(timeout, supplier, null, AssertTimeoutPreemptively::createAssertionFailure);
 	}
 
-	static <T> T assertTimeoutPreemptively(Duration timeout, ThrowingSupplier<T> supplier, String message) {
+	static <T extends @Nullable Object> T assertTimeoutPreemptively(Duration timeout, ThrowingSupplier<T> supplier,
+			@Nullable String message) {
 		return assertTimeoutPreemptively(timeout, supplier, message == null ? null : () -> message,
 			AssertTimeoutPreemptively::createAssertionFailure);
 	}
 
-	static <T> T assertTimeoutPreemptively(Duration timeout, ThrowingSupplier<T> supplier,
-			Supplier<String> messageSupplier) {
+	static <T extends @Nullable Object> T assertTimeoutPreemptively(Duration timeout, ThrowingSupplier<T> supplier,
+			Supplier<@Nullable String> messageSupplier) {
 		return assertTimeoutPreemptively(timeout, supplier, messageSupplier,
 			AssertTimeoutPreemptively::createAssertionFailure);
 	}
 
-	static <T, E extends Throwable> T assertTimeoutPreemptively(Duration timeout, ThrowingSupplier<T> supplier,
-			Supplier<String> messageSupplier, Assertions.TimeoutFailureFactory<E> failureFactory) throws E {
+	static <T extends @Nullable Object, E extends Throwable> T assertTimeoutPreemptively(Duration timeout,
+			ThrowingSupplier<T> supplier, @Nullable Supplier<@Nullable String> messageSupplier,
+			Assertions.TimeoutFailureFactory<E> failureFactory) throws E {
 		AtomicReference<Thread> threadReference = new AtomicReference<>();
 		ExecutorService executorService = Executors.newSingleThreadExecutor(new TimeoutThreadFactory());
 
@@ -87,8 +95,8 @@ static <T, E extends Throwable> T assertTimeoutPreemptively(Duration timeout, Th
 		}
 	}
 
-	private static <T> Future<T> submitTask(ThrowingSupplier<T> supplier, AtomicReference<Thread> threadReference,
-			ExecutorService executorService) {
+	private static <T extends @Nullable Object> Future<T> submitTask(ThrowingSupplier<T> supplier,
+			AtomicReference<Thread> threadReference, ExecutorService executorService) {
 		return executorService.submit(() -> {
 			try {
 				threadReference.set(Thread.currentThread());
@@ -100,9 +108,10 @@ private static <T> Future<T> submitTask(ThrowingSupplier<T> supplier, AtomicRefe
 		});
 	}
 
-	private static <T, E extends Throwable> T resolveFutureAndHandleException(Future<T> future, Duration timeout,
-			Supplier<String> messageSupplier, Supplier<Thread> threadSupplier,
-			Assertions.TimeoutFailureFactory<E> failureFactory) throws E {
+	private static <T extends @Nullable Object, E extends Throwable> T resolveFutureAndHandleException(Future<T> future,
+			Duration timeout, @Nullable Supplier<@Nullable String> messageSupplier,
+			Supplier<@Nullable Thread> threadSupplier, Assertions.TimeoutFailureFactory<E> failureFactory)
+			throws E, RuntimeException {
 		try {
 			return future.get(timeout.toMillis(), TimeUnit.MILLISECONDS);
 		}
@@ -116,15 +125,15 @@ private static <T, E extends Throwable> T resolveFutureAndHandleException(Future
 			throw failureFactory.createTimeoutFailure(timeout, messageSupplier, cause, thread);
 		}
 		catch (ExecutionException ex) {
-			throw throwAsUncheckedException(ex.getCause());
+			throw throwAsUncheckedException(requireNonNullElse(ex.getCause(), ex));
 		}
 		catch (Throwable ex) {
 			throw throwAsUncheckedException(ex);
 		}
 	}
 
-	private static AssertionFailedError createAssertionFailure(Duration timeout, Supplier<String> messageSupplier,
-			Throwable cause, Thread thread) {
+	private static AssertionFailedError createAssertionFailure(Duration timeout,
+			@Nullable Supplier<@Nullable String> messageSupplier, @Nullable Throwable cause, @Nullable Thread thread) {
 		return assertionFailure() //
 				.message(messageSupplier) //
 				.reason("execution timed out after " + timeout.toMillis() + " ms") //
@@ -134,6 +143,7 @@ private static AssertionFailedError createAssertionFailure(Duration timeout, Sup
 
 	private static class ExecutionTimeoutException extends JUnitException {
 
+		@Serial
 		private static final long serialVersionUID = 1L;
 
 		ExecutionTimeoutException(String message) {
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertTrue.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertTrue.java
index af43e0613263..c106e08995e5 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertTrue.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertTrue.java
@@ -15,6 +15,8 @@
 import java.util.function.BooleanSupplier;
 import java.util.function.Supplier;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * {@code AssertTrue} is a collection of utility methods that support asserting
  * {@code true} in tests.
@@ -31,13 +33,13 @@ static void assertTrue(boolean condition) {
 		assertTrue(condition, (String) null);
 	}
 
-	static void assertTrue(boolean condition, String message) {
+	static void assertTrue(boolean condition, @Nullable String message) {
 		if (!condition) {
 			failNotTrue(message);
 		}
 	}
 
-	static void assertTrue(boolean condition, Supplier<String> messageSupplier) {
+	static void assertTrue(boolean condition, Supplier<@Nullable String> messageSupplier) {
 		if (!condition) {
 			failNotTrue(messageSupplier);
 		}
@@ -47,15 +49,15 @@ static void assertTrue(BooleanSupplier booleanSupplier) {
 		assertTrue(booleanSupplier.getAsBoolean(), (String) null);
 	}
 
-	static void assertTrue(BooleanSupplier booleanSupplier, String message) {
+	static void assertTrue(BooleanSupplier booleanSupplier, @Nullable String message) {
 		assertTrue(booleanSupplier.getAsBoolean(), message);
 	}
 
-	static void assertTrue(BooleanSupplier booleanSupplier, Supplier<String> messageSupplier) {
+	static void assertTrue(BooleanSupplier booleanSupplier, Supplier<@Nullable String> messageSupplier) {
 		assertTrue(booleanSupplier.getAsBoolean(), messageSupplier);
 	}
 
-	private static void failNotTrue(Object messageOrSupplier) {
+	private static void failNotTrue(@Nullable Object messageOrSupplier) {
 		assertionFailure() //
 				.message(messageOrSupplier) //
 				.expected(true) //
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertionFailureBuilder.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertionFailureBuilder.java
index 9e98fb06f3a9..a8fd354ce2a4 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertionFailureBuilder.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertionFailureBuilder.java
@@ -16,6 +16,7 @@
 import java.util.function.Supplier;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.util.StringUtils;
 import org.opentest4j.AssertionFailedError;
 
@@ -31,12 +32,18 @@
 @API(status = STABLE, since = "5.9")
 public class AssertionFailureBuilder {
 
-	private Object message;
-	private Throwable cause;
+	private @Nullable Object message;
+
+	private @Nullable Throwable cause;
+
 	private boolean mismatch;
-	private Object expected;
-	private Object actual;
-	private String reason;
+
+	private @Nullable Object expected;
+
+	private @Nullable Object actual;
+
+	private @Nullable String reason;
+
 	private boolean includeValuesInMessage = true;
 
 	/**
@@ -59,7 +66,7 @@ private AssertionFailureBuilder() {
 	 * @param message the user-defined failure message; may be {@code null}
 	 * @return this builder for method chaining
 	 */
-	public AssertionFailureBuilder message(Object message) {
+	public AssertionFailureBuilder message(@Nullable Object message) {
 		this.message = message;
 		return this;
 	}
@@ -70,7 +77,7 @@ public AssertionFailureBuilder message(Object message) {
 	 * @param reason the failure reason; may be {@code null}
 	 * @return this builder for method chaining
 	 */
-	public AssertionFailureBuilder reason(String reason) {
+	public AssertionFailureBuilder reason(@Nullable String reason) {
 		this.reason = reason;
 		return this;
 	}
@@ -81,7 +88,7 @@ public AssertionFailureBuilder reason(String reason) {
 	 * @param cause the failure cause; may be {@code null}
 	 * @return this builder for method chaining
 	 */
-	public AssertionFailureBuilder cause(Throwable cause) {
+	public AssertionFailureBuilder cause(@Nullable Throwable cause) {
 		this.cause = cause;
 		return this;
 	}
@@ -92,7 +99,7 @@ public AssertionFailureBuilder cause(Throwable cause) {
 	 * @param expected the expected value; may be {@code null}
 	 * @return this builder for method chaining
 	 */
-	public AssertionFailureBuilder expected(Object expected) {
+	public AssertionFailureBuilder expected(@Nullable Object expected) {
 		this.mismatch = true;
 		this.expected = expected;
 		return this;
@@ -104,7 +111,7 @@ public AssertionFailureBuilder expected(Object expected) {
 	 * @param actual the actual value; may be {@code null}
 	 * @return this builder for method chaining
 	 */
-	public AssertionFailureBuilder actual(Object actual) {
+	public AssertionFailureBuilder actual(@Nullable Object actual) {
 		this.mismatch = true;
 		this.actual = actual;
 		return this;
@@ -152,32 +159,32 @@ public AssertionFailedError build() {
 				: new AssertionFailedError(message, cause);
 	}
 
-	private static String nullSafeGet(Object messageOrSupplier) {
+	private static @Nullable String nullSafeGet(@Nullable Object messageOrSupplier) {
 		if (messageOrSupplier == null) {
 			return null;
 		}
-		if (messageOrSupplier instanceof Supplier) {
-			Object message = ((Supplier<?>) messageOrSupplier).get();
+		if (messageOrSupplier instanceof Supplier<?> supplier) {
+			Object message = supplier.get();
 			return StringUtils.nullSafeToString(message);
 		}
 		return StringUtils.nullSafeToString(messageOrSupplier);
 	}
 
-	private static String buildPrefix(String message) {
+	private static String buildPrefix(@Nullable String message) {
 		return (StringUtils.isNotBlank(message) ? message + " ==> " : "");
 	}
 
-	private static String formatValues(Object expected, Object actual) {
+	private static String formatValues(@Nullable Object expected, @Nullable Object actual) {
 		String expectedString = toString(expected);
 		String actualString = toString(actual);
 		if (expectedString.equals(actualString)) {
-			return String.format("expected: %s but was: %s", formatClassAndValue(expected, expectedString),
+			return "expected: %s but was: %s".formatted(formatClassAndValue(expected, expectedString),
 				formatClassAndValue(actual, actualString));
 		}
-		return String.format("expected: <%s> but was: <%s>", expectedString, actualString);
+		return "expected: <%s> but was: <%s>".formatted(expectedString, actualString);
 	}
 
-	private static String formatClassAndValue(Object value, String valueString) {
+	private static String formatClassAndValue(@Nullable Object value, String valueString) {
 		// If the value is null, return <null> instead of null<null>.
 		if (value == null) {
 			return "<null>";
@@ -187,20 +194,20 @@ private static String formatClassAndValue(Object value, String valueString) {
 		return (value instanceof Class ? "<" + classAndHash + ">" : classAndHash + "<" + valueString + ">");
 	}
 
-	private static String toString(Object obj) {
-		if (obj instanceof Class) {
-			return getCanonicalName((Class<?>) obj);
+	private static String toString(@Nullable Object obj) {
+		if (obj instanceof Class<?> clazz) {
+			return getCanonicalName(clazz);
 		}
 		return StringUtils.nullSafeToString(obj);
 	}
 
-	private static String toHash(Object obj) {
+	private static String toHash(@Nullable Object obj) {
 		return (obj == null ? "" : "@" + Integer.toHexString(System.identityHashCode(obj)));
 	}
 
-	private static String getClassName(Object obj) {
+	private static String getClassName(@Nullable Object obj) {
 		return (obj == null ? "null"
-				: obj instanceof Class ? getCanonicalName((Class<?>) obj) : obj.getClass().getName());
+				: obj instanceof Class<?> clazz ? getCanonicalName(clazz) : obj.getClass().getName());
 	}
 
 }
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertionUtils.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertionUtils.java
index 9431e30b3940..1d18b446f2f9 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertionUtils.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertionUtils.java
@@ -15,6 +15,7 @@
 import java.util.Deque;
 import java.util.function.Supplier;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.util.UnrecoverableExceptions;
 import org.opentest4j.AssertionFailedError;
 
@@ -34,23 +35,23 @@ static void fail() {
 		throw new AssertionFailedError();
 	}
 
-	static void fail(String message) {
+	static void fail(@Nullable String message) {
 		throw new AssertionFailedError(message);
 	}
 
-	static void fail(String message, Throwable cause) {
+	static void fail(@Nullable String message, @Nullable Throwable cause) {
 		throw new AssertionFailedError(message, cause);
 	}
 
-	static void fail(Throwable cause) {
+	static void fail(@Nullable Throwable cause) {
 		throw new AssertionFailedError(null, cause);
 	}
 
-	static void fail(Supplier<String> messageSupplier) {
+	static void fail(Supplier<@Nullable String> messageSupplier) {
 		throw new AssertionFailedError(nullSafeGet(messageSupplier));
 	}
 
-	static String nullSafeGet(Supplier<String> messageSupplier) {
+	static @Nullable String nullSafeGet(@Nullable Supplier<@Nullable String> messageSupplier) {
 		return (messageSupplier != null ? messageSupplier.get() : null);
 	}
 
@@ -65,7 +66,7 @@ static String getCanonicalName(Class<?> clazz) {
 		}
 	}
 
-	static String formatIndexes(Deque<Integer> indexes) {
+	static String formatIndexes(@Nullable Deque<Integer> indexes) {
 		if (indexes == null || indexes.isEmpty()) {
 			return "";
 		}
@@ -103,7 +104,7 @@ static boolean doublesAreEqual(double value1, double value2) {
 		return Double.doubleToLongBits(value1) == Double.doubleToLongBits(value2);
 	}
 
-	static boolean objectsAreEqual(Object obj1, Object obj2) {
+	static boolean objectsAreEqual(@Nullable Object obj1, @Nullable Object obj2) {
 		if (obj1 == null) {
 			return (obj2 == null);
 		}
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/Assertions.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/Assertions.java
index cd037a416914..90f5837520af 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/Assertions.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/Assertions.java
@@ -23,6 +23,7 @@
 import java.util.stream.Stream;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.function.Executable;
 import org.junit.jupiter.api.function.ThrowingSupplier;
 import org.opentest4j.MultipleFailuresError;
@@ -115,6 +116,7 @@ protected Assertions() {
 	 * <p>See Javadoc for {@link #fail(String)} for an explanation of this method's
 	 * generic return type {@code V}.
 	 */
+	@SuppressWarnings("NullAway")
 	public static <V> V fail() {
 		AssertionUtils.fail();
 		return null; // appeasing the compiler: this line will never be executed.
@@ -134,7 +136,8 @@ public static <V> V fail() {
 	 * Stream.of().map(entry -> fail("should not be called"));
 	 * }</pre>
 	 */
-	public static <V> V fail(String message) {
+	@SuppressWarnings("NullAway")
+	public static <V> V fail(@Nullable String message) {
 		AssertionUtils.fail(message);
 		return null; // appeasing the compiler: this line will never be executed.
 	}
@@ -146,7 +149,8 @@ public static <V> V fail(String message) {
 	 * <p>See Javadoc for {@link #fail(String)} for an explanation of this method's
 	 * generic return type {@code V}.
 	 */
-	public static <V> V fail(String message, Throwable cause) {
+	@SuppressWarnings("NullAway")
+	public static <V> V fail(@Nullable String message, @Nullable Throwable cause) {
 		AssertionUtils.fail(message, cause);
 		return null; // appeasing the compiler: this line will never be executed.
 	}
@@ -157,7 +161,8 @@ public static <V> V fail(String message, Throwable cause) {
 	 * <p>See Javadoc for {@link #fail(String)} for an explanation of this method's
 	 * generic return type {@code V}.
 	 */
-	public static <V> V fail(Throwable cause) {
+	@SuppressWarnings("NullAway")
+	public static <V> V fail(@Nullable Throwable cause) {
 		AssertionUtils.fail(cause);
 		return null; // appeasing the compiler: this line will never be executed.
 	}
@@ -169,7 +174,8 @@ public static <V> V fail(Throwable cause) {
 	 * <p>See Javadoc for {@link #fail(String)} for an explanation of this method's
 	 * generic return type {@code V}.
 	 */
-	public static <V> V fail(Supplier<String> messageSupplier) {
+	@SuppressWarnings("NullAway")
+	public static <V> V fail(Supplier<@Nullable String> messageSupplier) {
 		AssertionUtils.fail(messageSupplier);
 		return null; // appeasing the compiler: this line will never be executed.
 	}
@@ -187,7 +193,7 @@ public static void assertTrue(boolean condition) {
 	 * <em>Assert</em> that the supplied {@code condition} is {@code true}.
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied {@code messageSupplier}.
 	 */
-	public static void assertTrue(boolean condition, Supplier<String> messageSupplier) {
+	public static void assertTrue(boolean condition, Supplier<@Nullable String> messageSupplier) {
 		AssertTrue.assertTrue(condition, messageSupplier);
 	}
 
@@ -202,7 +208,7 @@ public static void assertTrue(BooleanSupplier booleanSupplier) {
 	 * <em>Assert</em> that the boolean condition supplied by {@code booleanSupplier} is {@code true}.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertTrue(BooleanSupplier booleanSupplier, String message) {
+	public static void assertTrue(BooleanSupplier booleanSupplier, @Nullable String message) {
 		AssertTrue.assertTrue(booleanSupplier, message);
 	}
 
@@ -210,7 +216,7 @@ public static void assertTrue(BooleanSupplier booleanSupplier, String message) {
 	 * <em>Assert</em> that the supplied {@code condition} is {@code true}.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertTrue(boolean condition, String message) {
+	public static void assertTrue(boolean condition, @Nullable String message) {
 		AssertTrue.assertTrue(condition, message);
 	}
 
@@ -218,7 +224,7 @@ public static void assertTrue(boolean condition, String message) {
 	 * <em>Assert</em> that the boolean condition supplied by {@code booleanSupplier} is {@code true}.
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied {@code messageSupplier}.
 	 */
-	public static void assertTrue(BooleanSupplier booleanSupplier, Supplier<String> messageSupplier) {
+	public static void assertTrue(BooleanSupplier booleanSupplier, Supplier<@Nullable String> messageSupplier) {
 		AssertTrue.assertTrue(booleanSupplier, messageSupplier);
 	}
 
@@ -235,7 +241,7 @@ public static void assertFalse(boolean condition) {
 	 * <em>Assert</em> that the supplied {@code condition} is {@code false}.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertFalse(boolean condition, String message) {
+	public static void assertFalse(boolean condition, @Nullable String message) {
 		AssertFalse.assertFalse(condition, message);
 	}
 
@@ -243,7 +249,7 @@ public static void assertFalse(boolean condition, String message) {
 	 * <em>Assert</em> that the supplied {@code condition} is {@code false}.
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied {@code messageSupplier}.
 	 */
-	public static void assertFalse(boolean condition, Supplier<String> messageSupplier) {
+	public static void assertFalse(boolean condition, Supplier<@Nullable String> messageSupplier) {
 		AssertFalse.assertFalse(condition, messageSupplier);
 	}
 
@@ -258,7 +264,7 @@ public static void assertFalse(BooleanSupplier booleanSupplier) {
 	 * <em>Assert</em> that the boolean condition supplied by {@code booleanSupplier} is {@code false}.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertFalse(BooleanSupplier booleanSupplier, String message) {
+	public static void assertFalse(BooleanSupplier booleanSupplier, @Nullable String message) {
 		AssertFalse.assertFalse(booleanSupplier, message);
 	}
 
@@ -266,7 +272,7 @@ public static void assertFalse(BooleanSupplier booleanSupplier, String message)
 	 * <em>Assert</em> that the boolean condition supplied by {@code booleanSupplier} is {@code false}.
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied {@code messageSupplier}.
 	 */
-	public static void assertFalse(BooleanSupplier booleanSupplier, Supplier<String> messageSupplier) {
+	public static void assertFalse(BooleanSupplier booleanSupplier, Supplier<@Nullable String> messageSupplier) {
 		AssertFalse.assertFalse(booleanSupplier, messageSupplier);
 	}
 
@@ -275,7 +281,7 @@ public static void assertFalse(BooleanSupplier booleanSupplier, Supplier<String>
 	/**
 	 * <em>Assert</em> that {@code actual} is {@code null}.
 	 */
-	public static void assertNull(Object actual) {
+	public static void assertNull(@Nullable Object actual) {
 		AssertNull.assertNull(actual);
 	}
 
@@ -283,7 +289,7 @@ public static void assertNull(Object actual) {
 	 * <em>Assert</em> that {@code actual} is {@code null}.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertNull(Object actual, String message) {
+	public static void assertNull(@Nullable Object actual, @Nullable String message) {
 		AssertNull.assertNull(actual, message);
 	}
 
@@ -291,7 +297,7 @@ public static void assertNull(Object actual, String message) {
 	 * <em>Assert</em> that {@code actual} is {@code null}.
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied {@code messageSupplier}.
 	 */
-	public static void assertNull(Object actual, Supplier<String> messageSupplier) {
+	public static void assertNull(@Nullable Object actual, Supplier<@Nullable String> messageSupplier) {
 		AssertNull.assertNull(actual, messageSupplier);
 	}
 
@@ -300,7 +306,7 @@ public static void assertNull(Object actual, Supplier<String> messageSupplier) {
 	/**
 	 * <em>Assert</em> that {@code actual} is not {@code null}.
 	 */
-	public static void assertNotNull(Object actual) {
+	public static void assertNotNull(@Nullable Object actual) {
 		AssertNotNull.assertNotNull(actual);
 	}
 
@@ -308,7 +314,7 @@ public static void assertNotNull(Object actual) {
 	 * <em>Assert</em> that {@code actual} is not {@code null}.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertNotNull(Object actual, String message) {
+	public static void assertNotNull(@Nullable Object actual, @Nullable String message) {
 		AssertNotNull.assertNotNull(actual, message);
 	}
 
@@ -316,7 +322,7 @@ public static void assertNotNull(Object actual, String message) {
 	 * <em>Assert</em> that {@code actual} is not {@code null}.
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied {@code messageSupplier}.
 	 */
-	public static void assertNotNull(Object actual, Supplier<String> messageSupplier) {
+	public static void assertNotNull(@Nullable Object actual, Supplier<@Nullable String> messageSupplier) {
 		AssertNotNull.assertNotNull(actual, messageSupplier);
 	}
 
@@ -332,14 +338,14 @@ public static void assertEquals(short expected, short actual) {
 	/**
 	 * <em>Assert</em> that {@code expected} and {@code actual} are equal.
 	 */
-	public static void assertEquals(short expected, Short actual) {
+	public static void assertEquals(short expected, @Nullable Short actual) {
 		AssertEquals.assertEquals((Short) expected, actual);
 	}
 
 	/**
 	 * <em>Assert</em> that {@code expected} and {@code actual} are equal.
 	 */
-	public static void assertEquals(Short expected, short actual) {
+	public static void assertEquals(@Nullable Short expected, short actual) {
 		AssertEquals.assertEquals(expected, (Short) actual);
 	}
 
@@ -349,7 +355,7 @@ public static void assertEquals(Short expected, short actual) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertEquals(Short expected, Short actual) {
+	public static void assertEquals(@Nullable Short expected, @Nullable Short actual) {
 		AssertEquals.assertEquals(expected, actual);
 	}
 
@@ -357,7 +363,7 @@ public static void assertEquals(Short expected, Short actual) {
 	 * <em>Assert</em> that {@code expected} and {@code actual} are equal.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertEquals(short expected, short actual, String message) {
+	public static void assertEquals(short expected, short actual, @Nullable String message) {
 		AssertEquals.assertEquals(expected, actual, message);
 	}
 
@@ -365,7 +371,7 @@ public static void assertEquals(short expected, short actual, String message) {
 	 * <em>Assert</em> that {@code expected} and {@code actual} are equal.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertEquals(short expected, Short actual, String message) {
+	public static void assertEquals(short expected, @Nullable Short actual, @Nullable String message) {
 		AssertEquals.assertEquals((Short) expected, actual, message);
 	}
 
@@ -373,7 +379,7 @@ public static void assertEquals(short expected, Short actual, String message) {
 	 * <em>Assert</em> that {@code expected} and {@code actual} are equal.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertEquals(Short expected, short actual, String message) {
+	public static void assertEquals(@Nullable Short expected, short actual, @Nullable String message) {
 		AssertEquals.assertEquals(expected, (Short) actual, message);
 	}
 
@@ -384,7 +390,7 @@ public static void assertEquals(Short expected, short actual, String message) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertEquals(Short expected, Short actual, String message) {
+	public static void assertEquals(@Nullable Short expected, @Nullable Short actual, @Nullable String message) {
 		AssertEquals.assertEquals(expected, actual, message);
 	}
 
@@ -392,7 +398,7 @@ public static void assertEquals(Short expected, Short actual, String message) {
 	 * <em>Assert</em> that {@code expected} and {@code actual} are equal.
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied {@code messageSupplier}.
 	 */
-	public static void assertEquals(short expected, short actual, Supplier<String> messageSupplier) {
+	public static void assertEquals(short expected, short actual, Supplier<@Nullable String> messageSupplier) {
 		AssertEquals.assertEquals(expected, actual, messageSupplier);
 	}
 
@@ -400,7 +406,8 @@ public static void assertEquals(short expected, short actual, Supplier<String> m
 	 * <em>Assert</em> that {@code expected} and {@code actual} are equal.
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied {@code messageSupplier}.
 	 */
-	public static void assertEquals(short expected, Short actual, Supplier<String> messageSupplier) {
+	public static void assertEquals(short expected, @Nullable Short actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertEquals.assertEquals((Short) expected, actual, messageSupplier);
 	}
 
@@ -408,7 +415,8 @@ public static void assertEquals(short expected, Short actual, Supplier<String> m
 	 * <em>Assert</em> that {@code expected} and {@code actual} are equal.
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied {@code messageSupplier}.
 	 */
-	public static void assertEquals(Short expected, short actual, Supplier<String> messageSupplier) {
+	public static void assertEquals(@Nullable Short expected, short actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertEquals.assertEquals(expected, (Short) actual, messageSupplier);
 	}
 
@@ -419,7 +427,8 @@ public static void assertEquals(Short expected, short actual, Supplier<String> m
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertEquals(Short expected, Short actual, Supplier<String> messageSupplier) {
+	public static void assertEquals(@Nullable Short expected, @Nullable Short actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertEquals.assertEquals(expected, actual, messageSupplier);
 	}
 
@@ -433,14 +442,14 @@ public static void assertEquals(byte expected, byte actual) {
 	/**
 	 * <em>Assert</em> that {@code expected} and {@code actual} are equal.
 	 */
-	public static void assertEquals(byte expected, Byte actual) {
+	public static void assertEquals(byte expected, @Nullable Byte actual) {
 		AssertEquals.assertEquals((Byte) expected, actual);
 	}
 
 	/**
 	 * <em>Assert</em> that {@code expected} and {@code actual} are equal.
 	 */
-	public static void assertEquals(Byte expected, byte actual) {
+	public static void assertEquals(@Nullable Byte expected, byte actual) {
 		AssertEquals.assertEquals(expected, (Byte) actual);
 	}
 
@@ -450,7 +459,7 @@ public static void assertEquals(Byte expected, byte actual) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertEquals(Byte expected, Byte actual) {
+	public static void assertEquals(@Nullable Byte expected, @Nullable Byte actual) {
 		AssertEquals.assertEquals(expected, actual);
 	}
 
@@ -458,7 +467,7 @@ public static void assertEquals(Byte expected, Byte actual) {
 	 * <em>Assert</em> that {@code expected} and {@code actual} are equal.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertEquals(byte expected, byte actual, String message) {
+	public static void assertEquals(byte expected, byte actual, @Nullable String message) {
 		AssertEquals.assertEquals(expected, actual, message);
 	}
 
@@ -466,7 +475,7 @@ public static void assertEquals(byte expected, byte actual, String message) {
 	 * <em>Assert</em> that {@code expected} and {@code actual} are equal.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertEquals(byte expected, Byte actual, String message) {
+	public static void assertEquals(byte expected, @Nullable Byte actual, @Nullable String message) {
 		AssertEquals.assertEquals((Byte) expected, actual, message);
 	}
 
@@ -474,7 +483,7 @@ public static void assertEquals(byte expected, Byte actual, String message) {
 	 * <em>Assert</em> that {@code expected} and {@code actual} are equal.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertEquals(Byte expected, byte actual, String message) {
+	public static void assertEquals(@Nullable Byte expected, byte actual, @Nullable String message) {
 		AssertEquals.assertEquals(expected, (Byte) actual, message);
 	}
 
@@ -485,7 +494,7 @@ public static void assertEquals(Byte expected, byte actual, String message) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertEquals(Byte expected, Byte actual, String message) {
+	public static void assertEquals(@Nullable Byte expected, @Nullable Byte actual, @Nullable String message) {
 		AssertEquals.assertEquals(expected, actual, message);
 	}
 
@@ -493,7 +502,7 @@ public static void assertEquals(Byte expected, Byte actual, String message) {
 	 * <em>Assert</em> that {@code expected} and {@code actual} are equal.
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied {@code messageSupplier}.
 	 */
-	public static void assertEquals(byte expected, byte actual, Supplier<String> messageSupplier) {
+	public static void assertEquals(byte expected, byte actual, Supplier<@Nullable String> messageSupplier) {
 		AssertEquals.assertEquals(expected, actual, messageSupplier);
 	}
 
@@ -501,7 +510,7 @@ public static void assertEquals(byte expected, byte actual, Supplier<String> mes
 	 * <em>Assert</em> that {@code expected} and {@code actual} are equal.
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied {@code messageSupplier}.
 	 */
-	public static void assertEquals(byte expected, Byte actual, Supplier<String> messageSupplier) {
+	public static void assertEquals(byte expected, @Nullable Byte actual, Supplier<@Nullable String> messageSupplier) {
 		AssertEquals.assertEquals((Byte) expected, actual, messageSupplier);
 	}
 
@@ -509,7 +518,7 @@ public static void assertEquals(byte expected, Byte actual, Supplier<String> mes
 	 * <em>Assert</em> that {@code expected} and {@code actual} are equal.
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied {@code messageSupplier}.
 	 */
-	public static void assertEquals(Byte expected, byte actual, Supplier<String> messageSupplier) {
+	public static void assertEquals(@Nullable Byte expected, byte actual, Supplier<@Nullable String> messageSupplier) {
 		AssertEquals.assertEquals(expected, (Byte) actual, messageSupplier);
 	}
 
@@ -520,7 +529,8 @@ public static void assertEquals(Byte expected, byte actual, Supplier<String> mes
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertEquals(Byte expected, Byte actual, Supplier<String> messageSupplier) {
+	public static void assertEquals(@Nullable Byte expected, @Nullable Byte actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertEquals.assertEquals(expected, actual, messageSupplier);
 	}
 
@@ -534,14 +544,14 @@ public static void assertEquals(int expected, int actual) {
 	/**
 	 * <em>Assert</em> that {@code expected} and {@code actual} are equal.
 	 */
-	public static void assertEquals(int expected, Integer actual) {
+	public static void assertEquals(int expected, @Nullable Integer actual) {
 		AssertEquals.assertEquals((Integer) expected, actual);
 	}
 
 	/**
 	 * <em>Assert</em> that {@code expected} and {@code actual} are equal.
 	 */
-	public static void assertEquals(Integer expected, int actual) {
+	public static void assertEquals(@Nullable Integer expected, int actual) {
 		AssertEquals.assertEquals(expected, (Integer) actual);
 	}
 
@@ -551,7 +561,7 @@ public static void assertEquals(Integer expected, int actual) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertEquals(Integer expected, Integer actual) {
+	public static void assertEquals(@Nullable Integer expected, @Nullable Integer actual) {
 		AssertEquals.assertEquals(expected, actual);
 	}
 
@@ -559,7 +569,7 @@ public static void assertEquals(Integer expected, Integer actual) {
 	 * <em>Assert</em> that {@code expected} and {@code actual} are equal.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertEquals(int expected, int actual, String message) {
+	public static void assertEquals(int expected, int actual, @Nullable String message) {
 		AssertEquals.assertEquals(expected, actual, message);
 	}
 
@@ -567,7 +577,7 @@ public static void assertEquals(int expected, int actual, String message) {
 	 * <em>Assert</em> that {@code expected} and {@code actual} are equal.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertEquals(int expected, Integer actual, String message) {
+	public static void assertEquals(int expected, @Nullable Integer actual, @Nullable String message) {
 		AssertEquals.assertEquals((Integer) expected, actual, message);
 	}
 
@@ -575,7 +585,7 @@ public static void assertEquals(int expected, Integer actual, String message) {
 	 * <em>Assert</em> that {@code expected} and {@code actual} are equal.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertEquals(Integer expected, int actual, String message) {
+	public static void assertEquals(@Nullable Integer expected, int actual, @Nullable String message) {
 		AssertEquals.assertEquals(expected, (Integer) actual, message);
 	}
 
@@ -586,7 +596,7 @@ public static void assertEquals(Integer expected, int actual, String message) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertEquals(Integer expected, Integer actual, String message) {
+	public static void assertEquals(@Nullable Integer expected, @Nullable Integer actual, @Nullable String message) {
 		AssertEquals.assertEquals(expected, actual, message);
 	}
 
@@ -594,7 +604,7 @@ public static void assertEquals(Integer expected, Integer actual, String message
 	 * <em>Assert</em> that {@code expected} and {@code actual} are equal.
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied {@code messageSupplier}.
 	 */
-	public static void assertEquals(int expected, int actual, Supplier<String> messageSupplier) {
+	public static void assertEquals(int expected, int actual, Supplier<@Nullable String> messageSupplier) {
 		AssertEquals.assertEquals(expected, actual, messageSupplier);
 	}
 
@@ -602,7 +612,8 @@ public static void assertEquals(int expected, int actual, Supplier<String> messa
 	 * <em>Assert</em> that {@code expected} and {@code actual} are equal.
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied {@code messageSupplier}.
 	 */
-	public static void assertEquals(int expected, Integer actual, Supplier<String> messageSupplier) {
+	public static void assertEquals(int expected, @Nullable Integer actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertEquals.assertEquals((Integer) expected, actual, messageSupplier);
 	}
 
@@ -610,7 +621,8 @@ public static void assertEquals(int expected, Integer actual, Supplier<String> m
 	 * <em>Assert</em> that {@code expected} and {@code actual} are equal.
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied {@code messageSupplier}.
 	 */
-	public static void assertEquals(Integer expected, int actual, Supplier<String> messageSupplier) {
+	public static void assertEquals(@Nullable Integer expected, int actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertEquals.assertEquals(expected, (Integer) actual, messageSupplier);
 	}
 
@@ -621,7 +633,8 @@ public static void assertEquals(Integer expected, int actual, Supplier<String> m
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertEquals(Integer expected, Integer actual, Supplier<String> messageSupplier) {
+	public static void assertEquals(@Nullable Integer expected, @Nullable Integer actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertEquals.assertEquals(expected, actual, messageSupplier);
 	}
 
@@ -635,14 +648,14 @@ public static void assertEquals(long expected, long actual) {
 	/**
 	 * <em>Assert</em> that {@code expected} and {@code actual} are equal.
 	 */
-	public static void assertEquals(long expected, Long actual) {
+	public static void assertEquals(long expected, @Nullable Long actual) {
 		AssertEquals.assertEquals((Long) expected, actual);
 	}
 
 	/**
 	 * <em>Assert</em> that {@code expected} and {@code actual} are equal.
 	 */
-	public static void assertEquals(Long expected, long actual) {
+	public static void assertEquals(@Nullable Long expected, long actual) {
 		AssertEquals.assertEquals(expected, (Long) actual);
 	}
 
@@ -652,7 +665,7 @@ public static void assertEquals(Long expected, long actual) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertEquals(Long expected, Long actual) {
+	public static void assertEquals(@Nullable Long expected, @Nullable Long actual) {
 		AssertEquals.assertEquals(expected, actual);
 	}
 
@@ -660,7 +673,7 @@ public static void assertEquals(Long expected, Long actual) {
 	 * <em>Assert</em> that {@code expected} and {@code actual} are equal.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertEquals(long expected, long actual, String message) {
+	public static void assertEquals(long expected, long actual, @Nullable String message) {
 		AssertEquals.assertEquals(expected, actual, message);
 	}
 
@@ -668,7 +681,7 @@ public static void assertEquals(long expected, long actual, String message) {
 	 * <em>Assert</em> that {@code expected} and {@code actual} are equal.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertEquals(long expected, Long actual, String message) {
+	public static void assertEquals(long expected, @Nullable Long actual, @Nullable String message) {
 		AssertEquals.assertEquals((Long) expected, actual, message);
 	}
 
@@ -676,7 +689,7 @@ public static void assertEquals(long expected, Long actual, String message) {
 	 * <em>Assert</em> that {@code expected} and {@code actual} are equal.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertEquals(Long expected, long actual, String message) {
+	public static void assertEquals(@Nullable Long expected, long actual, @Nullable String message) {
 		AssertEquals.assertEquals(expected, (Long) actual, message);
 	}
 
@@ -687,7 +700,7 @@ public static void assertEquals(Long expected, long actual, String message) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertEquals(Long expected, Long actual, String message) {
+	public static void assertEquals(@Nullable Long expected, @Nullable Long actual, @Nullable String message) {
 		AssertEquals.assertEquals(expected, actual, message);
 	}
 
@@ -695,7 +708,7 @@ public static void assertEquals(Long expected, Long actual, String message) {
 	 * <em>Assert</em> that {@code expected} and {@code actual} are equal.
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied {@code messageSupplier}.
 	 */
-	public static void assertEquals(long expected, long actual, Supplier<String> messageSupplier) {
+	public static void assertEquals(long expected, long actual, Supplier<@Nullable String> messageSupplier) {
 		AssertEquals.assertEquals(expected, actual, messageSupplier);
 	}
 
@@ -703,7 +716,7 @@ public static void assertEquals(long expected, long actual, Supplier<String> mes
 	 * <em>Assert</em> that {@code expected} and {@code actual} are equal.
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied {@code messageSupplier}.
 	 */
-	public static void assertEquals(long expected, Long actual, Supplier<String> messageSupplier) {
+	public static void assertEquals(long expected, @Nullable Long actual, Supplier<@Nullable String> messageSupplier) {
 		AssertEquals.assertEquals((Long) expected, actual, messageSupplier);
 	}
 
@@ -711,7 +724,7 @@ public static void assertEquals(long expected, Long actual, Supplier<String> mes
 	 * <em>Assert</em> that {@code expected} and {@code actual} are equal.
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied {@code messageSupplier}.
 	 */
-	public static void assertEquals(Long expected, long actual, Supplier<String> messageSupplier) {
+	public static void assertEquals(@Nullable Long expected, long actual, Supplier<@Nullable String> messageSupplier) {
 		AssertEquals.assertEquals(expected, (Long) actual, messageSupplier);
 	}
 
@@ -722,7 +735,8 @@ public static void assertEquals(Long expected, long actual, Supplier<String> mes
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertEquals(Long expected, Long actual, Supplier<String> messageSupplier) {
+	public static void assertEquals(@Nullable Long expected, @Nullable Long actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertEquals.assertEquals(expected, actual, messageSupplier);
 	}
 
@@ -740,7 +754,7 @@ public static void assertEquals(float expected, float actual) {
 	 * <p>Equality imposed by this method is consistent with {@link Float#equals(Object)} and
 	 * {@link Float#compare(float, float)}.
 	 */
-	public static void assertEquals(float expected, Float actual) {
+	public static void assertEquals(float expected, @Nullable Float actual) {
 		AssertEquals.assertEquals((Float) expected, actual);
 	}
 
@@ -749,7 +763,7 @@ public static void assertEquals(float expected, Float actual) {
 	 * <p>Equality imposed by this method is consistent with {@link Float#equals(Object)} and
 	 * {@link Float#compare(float, float)}.
 	 */
-	public static void assertEquals(Float expected, float actual) {
+	public static void assertEquals(@Nullable Float expected, float actual) {
 		AssertEquals.assertEquals(expected, (Float) actual);
 	}
 
@@ -761,7 +775,7 @@ public static void assertEquals(Float expected, float actual) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertEquals(Float expected, Float actual) {
+	public static void assertEquals(@Nullable Float expected, @Nullable Float actual) {
 		AssertEquals.assertEquals(expected, actual);
 	}
 
@@ -771,7 +785,7 @@ public static void assertEquals(Float expected, Float actual) {
 	 * {@link Float#compare(float, float)}.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertEquals(float expected, float actual, String message) {
+	public static void assertEquals(float expected, float actual, @Nullable String message) {
 		AssertEquals.assertEquals(expected, actual, message);
 	}
 
@@ -781,7 +795,7 @@ public static void assertEquals(float expected, float actual, String message) {
 	 * {@link Float#compare(float, float)}.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertEquals(float expected, Float actual, String message) {
+	public static void assertEquals(float expected, @Nullable Float actual, @Nullable String message) {
 		AssertEquals.assertEquals((Float) expected, actual, message);
 	}
 
@@ -791,7 +805,7 @@ public static void assertEquals(float expected, Float actual, String message) {
 	 * {@link Float#compare(float, float)}.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertEquals(Float expected, float actual, String message) {
+	public static void assertEquals(@Nullable Float expected, float actual, @Nullable String message) {
 		AssertEquals.assertEquals(expected, (Float) actual, message);
 	}
 
@@ -804,7 +818,7 @@ public static void assertEquals(Float expected, float actual, String message) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertEquals(Float expected, Float actual, String message) {
+	public static void assertEquals(@Nullable Float expected, @Nullable Float actual, @Nullable String message) {
 		AssertEquals.assertEquals(expected, actual, message);
 	}
 
@@ -814,7 +828,7 @@ public static void assertEquals(Float expected, Float actual, String message) {
 	 * {@link Float#compare(float, float)}.
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied {@code messageSupplier}.
 	 */
-	public static void assertEquals(float expected, float actual, Supplier<String> messageSupplier) {
+	public static void assertEquals(float expected, float actual, Supplier<@Nullable String> messageSupplier) {
 		AssertEquals.assertEquals(expected, actual, messageSupplier);
 	}
 
@@ -824,7 +838,8 @@ public static void assertEquals(float expected, float actual, Supplier<String> m
 	 * {@link Float#compare(float, float)}.
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied {@code messageSupplier}.
 	 */
-	public static void assertEquals(float expected, Float actual, Supplier<String> messageSupplier) {
+	public static void assertEquals(float expected, @Nullable Float actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertEquals.assertEquals((Float) expected, actual, messageSupplier);
 	}
 
@@ -834,7 +849,8 @@ public static void assertEquals(float expected, Float actual, Supplier<String> m
 	 * {@link Float#compare(float, float)}.
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied {@code messageSupplier}.
 	 */
-	public static void assertEquals(Float expected, float actual, Supplier<String> messageSupplier) {
+	public static void assertEquals(@Nullable Float expected, float actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertEquals.assertEquals(expected, (Float) actual, messageSupplier);
 	}
 
@@ -847,7 +863,8 @@ public static void assertEquals(Float expected, float actual, Supplier<String> m
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertEquals(Float expected, Float actual, Supplier<String> messageSupplier) {
+	public static void assertEquals(@Nullable Float expected, @Nullable Float actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertEquals.assertEquals(expected, actual, messageSupplier);
 	}
 
@@ -866,7 +883,7 @@ public static void assertEquals(float expected, float actual, float delta) {
 	 * {@link Float#compare(float, float)}.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertEquals(float expected, float actual, float delta, String message) {
+	public static void assertEquals(float expected, float actual, float delta, @Nullable String message) {
 		AssertEquals.assertEquals(expected, actual, delta, message);
 	}
 
@@ -876,7 +893,8 @@ public static void assertEquals(float expected, float actual, float delta, Strin
 	 * {@link Float#compare(float, float)}.
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied {@code messageSupplier}.
 	 */
-	public static void assertEquals(float expected, float actual, float delta, Supplier<String> messageSupplier) {
+	public static void assertEquals(float expected, float actual, float delta,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertEquals.assertEquals(expected, actual, delta, messageSupplier);
 	}
 
@@ -894,7 +912,7 @@ public static void assertEquals(double expected, double actual) {
 	 * <p>Equality imposed by this method is consistent with {@link Double#equals(Object)} and
 	 * {@link Double#compare(double, double)}.
 	 */
-	public static void assertEquals(double expected, Double actual) {
+	public static void assertEquals(double expected, @Nullable Double actual) {
 		AssertEquals.assertEquals((Double) expected, actual);
 	}
 
@@ -903,7 +921,7 @@ public static void assertEquals(double expected, Double actual) {
 	 * <p>Equality imposed by this method is consistent with {@link Double#equals(Object)} and
 	 * {@link Double#compare(double, double)}.
 	 */
-	public static void assertEquals(Double expected, double actual) {
+	public static void assertEquals(@Nullable Double expected, double actual) {
 		AssertEquals.assertEquals(expected, (Double) actual);
 	}
 
@@ -915,7 +933,7 @@ public static void assertEquals(Double expected, double actual) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertEquals(Double expected, Double actual) {
+	public static void assertEquals(@Nullable Double expected, @Nullable Double actual) {
 		AssertEquals.assertEquals(expected, actual);
 	}
 
@@ -925,7 +943,7 @@ public static void assertEquals(Double expected, Double actual) {
 	 * {@link Double#compare(double, double)}.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertEquals(double expected, double actual, String message) {
+	public static void assertEquals(double expected, double actual, @Nullable String message) {
 		AssertEquals.assertEquals(expected, actual, message);
 	}
 
@@ -935,7 +953,7 @@ public static void assertEquals(double expected, double actual, String message)
 	 * {@link Double#compare(double, double)}.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertEquals(double expected, Double actual, String message) {
+	public static void assertEquals(double expected, @Nullable Double actual, @Nullable String message) {
 		AssertEquals.assertEquals((Double) expected, actual, message);
 	}
 
@@ -945,7 +963,7 @@ public static void assertEquals(double expected, Double actual, String message)
 	 * {@link Double#compare(double, double)}.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertEquals(Double expected, double actual, String message) {
+	public static void assertEquals(@Nullable Double expected, double actual, @Nullable String message) {
 		AssertEquals.assertEquals(expected, (Double) actual, message);
 	}
 
@@ -958,7 +976,7 @@ public static void assertEquals(Double expected, double actual, String message)
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertEquals(Double expected, Double actual, String message) {
+	public static void assertEquals(@Nullable Double expected, @Nullable Double actual, @Nullable String message) {
 		AssertEquals.assertEquals(expected, actual, message);
 	}
 
@@ -968,7 +986,7 @@ public static void assertEquals(Double expected, Double actual, String message)
 	 * {@link Double#compare(double, double)}.
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied {@code messageSupplier}.
 	 */
-	public static void assertEquals(double expected, double actual, Supplier<String> messageSupplier) {
+	public static void assertEquals(double expected, double actual, Supplier<@Nullable String> messageSupplier) {
 		AssertEquals.assertEquals(expected, actual, messageSupplier);
 	}
 
@@ -978,7 +996,8 @@ public static void assertEquals(double expected, double actual, Supplier<String>
 	 * {@link Double#compare(double, double)}.
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied {@code messageSupplier}.
 	 */
-	public static void assertEquals(double expected, Double actual, Supplier<String> messageSupplier) {
+	public static void assertEquals(double expected, @Nullable Double actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertEquals.assertEquals((Double) expected, actual, messageSupplier);
 	}
 
@@ -988,7 +1007,8 @@ public static void assertEquals(double expected, Double actual, Supplier<String>
 	 * {@link Double#compare(double, double)}.
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied {@code messageSupplier}.
 	 */
-	public static void assertEquals(Double expected, double actual, Supplier<String> messageSupplier) {
+	public static void assertEquals(@Nullable Double expected, double actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertEquals.assertEquals(expected, (Double) actual, messageSupplier);
 	}
 
@@ -1001,7 +1021,8 @@ public static void assertEquals(Double expected, double actual, Supplier<String>
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertEquals(Double expected, Double actual, Supplier<String> messageSupplier) {
+	public static void assertEquals(@Nullable Double expected, @Nullable Double actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertEquals.assertEquals(expected, actual, messageSupplier);
 	}
 
@@ -1020,7 +1041,7 @@ public static void assertEquals(double expected, double actual, double delta) {
 	 * {@link Double#compare(double, double)}.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertEquals(double expected, double actual, double delta, String message) {
+	public static void assertEquals(double expected, double actual, double delta, @Nullable String message) {
 		AssertEquals.assertEquals(expected, actual, delta, message);
 	}
 
@@ -1030,7 +1051,8 @@ public static void assertEquals(double expected, double actual, double delta, St
 	 * {@link Double#compare(double, double)}.
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied {@code messageSupplier}.
 	 */
-	public static void assertEquals(double expected, double actual, double delta, Supplier<String> messageSupplier) {
+	public static void assertEquals(double expected, double actual, double delta,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertEquals.assertEquals(expected, actual, delta, messageSupplier);
 	}
 
@@ -1044,14 +1066,14 @@ public static void assertEquals(char expected, char actual) {
 	/**
 	 * <em>Assert</em> that {@code expected} and {@code actual} are equal.
 	 */
-	public static void assertEquals(char expected, Character actual) {
+	public static void assertEquals(char expected, @Nullable Character actual) {
 		AssertEquals.assertEquals((Character) expected, actual);
 	}
 
 	/**
 	 * <em>Assert</em> that {@code expected} and {@code actual} are equal.
 	 */
-	public static void assertEquals(Character expected, char actual) {
+	public static void assertEquals(@Nullable Character expected, char actual) {
 		AssertEquals.assertEquals(expected, (Character) actual);
 	}
 
@@ -1061,7 +1083,7 @@ public static void assertEquals(Character expected, char actual) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertEquals(Character expected, Character actual) {
+	public static void assertEquals(@Nullable Character expected, @Nullable Character actual) {
 		AssertEquals.assertEquals(expected, actual);
 	}
 
@@ -1069,7 +1091,7 @@ public static void assertEquals(Character expected, Character actual) {
 	 * <em>Assert</em> that {@code expected} and {@code actual} are equal.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertEquals(char expected, char actual, String message) {
+	public static void assertEquals(char expected, char actual, @Nullable String message) {
 		AssertEquals.assertEquals(expected, actual, message);
 	}
 
@@ -1077,7 +1099,7 @@ public static void assertEquals(char expected, char actual, String message) {
 	 * <em>Assert</em> that {@code expected} and {@code actual} are equal.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertEquals(char expected, Character actual, String message) {
+	public static void assertEquals(char expected, @Nullable Character actual, @Nullable String message) {
 		AssertEquals.assertEquals((Character) expected, actual, message);
 	}
 
@@ -1085,7 +1107,7 @@ public static void assertEquals(char expected, Character actual, String message)
 	 * <em>Assert</em> that {@code expected} and {@code actual} are equal.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertEquals(Character expected, char actual, String message) {
+	public static void assertEquals(@Nullable Character expected, char actual, @Nullable String message) {
 		AssertEquals.assertEquals(expected, (Character) actual, message);
 	}
 
@@ -1096,7 +1118,8 @@ public static void assertEquals(Character expected, char actual, String message)
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertEquals(Character expected, Character actual, String message) {
+	public static void assertEquals(@Nullable Character expected, @Nullable Character actual,
+			@Nullable String message) {
 		AssertEquals.assertEquals(expected, actual, message);
 	}
 
@@ -1104,7 +1127,7 @@ public static void assertEquals(Character expected, Character actual, String mes
 	 * <em>Assert</em> that {@code expected} and {@code actual} are equal.
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied {@code messageSupplier}.
 	 */
-	public static void assertEquals(char expected, char actual, Supplier<String> messageSupplier) {
+	public static void assertEquals(char expected, char actual, Supplier<@Nullable String> messageSupplier) {
 		AssertEquals.assertEquals(expected, actual, messageSupplier);
 	}
 
@@ -1112,7 +1135,8 @@ public static void assertEquals(char expected, char actual, Supplier<String> mes
 	 * <em>Assert</em> that {@code expected} and {@code actual} are equal.
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied {@code messageSupplier}.
 	 */
-	public static void assertEquals(char expected, Character actual, Supplier<String> messageSupplier) {
+	public static void assertEquals(char expected, @Nullable Character actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertEquals.assertEquals((Character) expected, actual, messageSupplier);
 	}
 
@@ -1120,7 +1144,8 @@ public static void assertEquals(char expected, Character actual, Supplier<String
 	 * <em>Assert</em> that {@code expected} and {@code actual} are equal.
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied {@code messageSupplier}.
 	 */
-	public static void assertEquals(Character expected, char actual, Supplier<String> messageSupplier) {
+	public static void assertEquals(@Nullable Character expected, char actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertEquals.assertEquals(expected, (Character) actual, messageSupplier);
 	}
 
@@ -1131,7 +1156,8 @@ public static void assertEquals(Character expected, char actual, Supplier<String
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertEquals(Character expected, Character actual, Supplier<String> messageSupplier) {
+	public static void assertEquals(@Nullable Character expected, @Nullable Character actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertEquals.assertEquals(expected, actual, messageSupplier);
 	}
 
@@ -1141,7 +1167,7 @@ public static void assertEquals(Character expected, Character actual, Supplier<S
 	 *
 	 * @see Object#equals(Object)
 	 */
-	public static void assertEquals(Object expected, Object actual) {
+	public static void assertEquals(@Nullable Object expected, @Nullable Object actual) {
 		AssertEquals.assertEquals(expected, actual);
 	}
 
@@ -1152,7 +1178,7 @@ public static void assertEquals(Object expected, Object actual) {
 	 *
 	 * @see Object#equals(Object)
 	 */
-	public static void assertEquals(Object expected, Object actual, String message) {
+	public static void assertEquals(@Nullable Object expected, @Nullable Object actual, @Nullable String message) {
 		AssertEquals.assertEquals(expected, actual, message);
 	}
 
@@ -1163,7 +1189,8 @@ public static void assertEquals(Object expected, Object actual, String message)
 	 *
 	 * @see Object#equals(Object)
 	 */
-	public static void assertEquals(Object expected, Object actual, Supplier<String> messageSupplier) {
+	public static void assertEquals(@Nullable Object expected, @Nullable Object actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertEquals.assertEquals(expected, actual, messageSupplier);
 	}
 
@@ -1173,7 +1200,7 @@ public static void assertEquals(Object expected, Object actual, Supplier<String>
 	 * <em>Assert</em> that {@code expected} and {@code actual} boolean arrays are equal.
 	 * <p>If both are {@code null}, they are considered equal.
 	 */
-	public static void assertArrayEquals(boolean[] expected, boolean[] actual) {
+	public static void assertArrayEquals(boolean @Nullable [] expected, boolean @Nullable [] actual) {
 		AssertArrayEquals.assertArrayEquals(expected, actual);
 	}
 
@@ -1182,7 +1209,8 @@ public static void assertArrayEquals(boolean[] expected, boolean[] actual) {
 	 * <p>If both are {@code null}, they are considered equal.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertArrayEquals(boolean[] expected, boolean[] actual, String message) {
+	public static void assertArrayEquals(boolean @Nullable [] expected, boolean @Nullable [] actual,
+			@Nullable String message) {
 		AssertArrayEquals.assertArrayEquals(expected, actual, message);
 	}
 
@@ -1191,7 +1219,8 @@ public static void assertArrayEquals(boolean[] expected, boolean[] actual, Strin
 	 * <p>If both are {@code null}, they are considered equal.
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied {@code messageSupplier}.
 	 */
-	public static void assertArrayEquals(boolean[] expected, boolean[] actual, Supplier<String> messageSupplier) {
+	public static void assertArrayEquals(boolean @Nullable [] expected, boolean @Nullable [] actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertArrayEquals.assertArrayEquals(expected, actual, messageSupplier);
 	}
 
@@ -1199,7 +1228,7 @@ public static void assertArrayEquals(boolean[] expected, boolean[] actual, Suppl
 	 * <em>Assert</em> that {@code expected} and {@code actual} char arrays are equal.
 	 * <p>If both are {@code null}, they are considered equal.
 	 */
-	public static void assertArrayEquals(char[] expected, char[] actual) {
+	public static void assertArrayEquals(char @Nullable [] expected, char @Nullable [] actual) {
 		AssertArrayEquals.assertArrayEquals(expected, actual);
 	}
 
@@ -1208,7 +1237,8 @@ public static void assertArrayEquals(char[] expected, char[] actual) {
 	 * <p>If both are {@code null}, they are considered equal.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertArrayEquals(char[] expected, char[] actual, String message) {
+	public static void assertArrayEquals(char @Nullable [] expected, char @Nullable [] actual,
+			@Nullable String message) {
 		AssertArrayEquals.assertArrayEquals(expected, actual, message);
 	}
 
@@ -1217,7 +1247,8 @@ public static void assertArrayEquals(char[] expected, char[] actual, String mess
 	 * <p>If both are {@code null}, they are considered equal.
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied {@code messageSupplier}.
 	 */
-	public static void assertArrayEquals(char[] expected, char[] actual, Supplier<String> messageSupplier) {
+	public static void assertArrayEquals(char @Nullable [] expected, char @Nullable [] actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertArrayEquals.assertArrayEquals(expected, actual, messageSupplier);
 	}
 
@@ -1225,7 +1256,7 @@ public static void assertArrayEquals(char[] expected, char[] actual, Supplier<St
 	 * <em>Assert</em> that {@code expected} and {@code actual} byte arrays are equal.
 	 * <p>If both are {@code null}, they are considered equal.
 	 */
-	public static void assertArrayEquals(byte[] expected, byte[] actual) {
+	public static void assertArrayEquals(byte @Nullable [] expected, byte @Nullable [] actual) {
 		AssertArrayEquals.assertArrayEquals(expected, actual);
 	}
 
@@ -1234,7 +1265,8 @@ public static void assertArrayEquals(byte[] expected, byte[] actual) {
 	 * <p>If both are {@code null}, they are considered equal.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertArrayEquals(byte[] expected, byte[] actual, String message) {
+	public static void assertArrayEquals(byte @Nullable [] expected, byte @Nullable [] actual,
+			@Nullable String message) {
 		AssertArrayEquals.assertArrayEquals(expected, actual, message);
 	}
 
@@ -1243,7 +1275,8 @@ public static void assertArrayEquals(byte[] expected, byte[] actual, String mess
 	 * <p>If both are {@code null}, they are considered equal.
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied {@code messageSupplier}.
 	 */
-	public static void assertArrayEquals(byte[] expected, byte[] actual, Supplier<String> messageSupplier) {
+	public static void assertArrayEquals(byte @Nullable [] expected, byte @Nullable [] actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertArrayEquals.assertArrayEquals(expected, actual, messageSupplier);
 	}
 
@@ -1251,7 +1284,7 @@ public static void assertArrayEquals(byte[] expected, byte[] actual, Supplier<St
 	 * <em>Assert</em> that {@code expected} and {@code actual} short arrays are equal.
 	 * <p>If both are {@code null}, they are considered equal.
 	 */
-	public static void assertArrayEquals(short[] expected, short[] actual) {
+	public static void assertArrayEquals(short @Nullable [] expected, short @Nullable [] actual) {
 		AssertArrayEquals.assertArrayEquals(expected, actual);
 	}
 
@@ -1260,7 +1293,8 @@ public static void assertArrayEquals(short[] expected, short[] actual) {
 	 * <p>If both are {@code null}, they are considered equal.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertArrayEquals(short[] expected, short[] actual, String message) {
+	public static void assertArrayEquals(short @Nullable [] expected, short @Nullable [] actual,
+			@Nullable String message) {
 		AssertArrayEquals.assertArrayEquals(expected, actual, message);
 	}
 
@@ -1269,7 +1303,8 @@ public static void assertArrayEquals(short[] expected, short[] actual, String me
 	 * <p>If both are {@code null}, they are considered equal.
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied {@code messageSupplier}.
 	 */
-	public static void assertArrayEquals(short[] expected, short[] actual, Supplier<String> messageSupplier) {
+	public static void assertArrayEquals(short @Nullable [] expected, short @Nullable [] actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertArrayEquals.assertArrayEquals(expected, actual, messageSupplier);
 	}
 
@@ -1277,7 +1312,7 @@ public static void assertArrayEquals(short[] expected, short[] actual, Supplier<
 	 * <em>Assert</em> that {@code expected} and {@code actual} int arrays are equal.
 	 * <p>If both are {@code null}, they are considered equal.
 	 */
-	public static void assertArrayEquals(int[] expected, int[] actual) {
+	public static void assertArrayEquals(int @Nullable [] expected, int @Nullable [] actual) {
 		AssertArrayEquals.assertArrayEquals(expected, actual);
 	}
 
@@ -1286,7 +1321,7 @@ public static void assertArrayEquals(int[] expected, int[] actual) {
 	 * <p>If both are {@code null}, they are considered equal.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertArrayEquals(int[] expected, int[] actual, String message) {
+	public static void assertArrayEquals(int @Nullable [] expected, int @Nullable [] actual, @Nullable String message) {
 		AssertArrayEquals.assertArrayEquals(expected, actual, message);
 	}
 
@@ -1295,7 +1330,8 @@ public static void assertArrayEquals(int[] expected, int[] actual, String messag
 	 * <p>If both are {@code null}, they are considered equal.
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied {@code messageSupplier}.
 	 */
-	public static void assertArrayEquals(int[] expected, int[] actual, Supplier<String> messageSupplier) {
+	public static void assertArrayEquals(int @Nullable [] expected, int @Nullable [] actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertArrayEquals.assertArrayEquals(expected, actual, messageSupplier);
 	}
 
@@ -1303,7 +1339,7 @@ public static void assertArrayEquals(int[] expected, int[] actual, Supplier<Stri
 	 * <em>Assert</em> that {@code expected} and {@code actual} long arrays are equal.
 	 * <p>If both are {@code null}, they are considered equal.
 	 */
-	public static void assertArrayEquals(long[] expected, long[] actual) {
+	public static void assertArrayEquals(long @Nullable [] expected, long @Nullable [] actual) {
 		AssertArrayEquals.assertArrayEquals(expected, actual);
 	}
 
@@ -1312,7 +1348,8 @@ public static void assertArrayEquals(long[] expected, long[] actual) {
 	 * <p>If both are {@code null}, they are considered equal.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertArrayEquals(long[] expected, long[] actual, String message) {
+	public static void assertArrayEquals(long @Nullable [] expected, long @Nullable [] actual,
+			@Nullable String message) {
 		AssertArrayEquals.assertArrayEquals(expected, actual, message);
 	}
 
@@ -1321,7 +1358,8 @@ public static void assertArrayEquals(long[] expected, long[] actual, String mess
 	 * <p>If both are {@code null}, they are considered equal.
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied {@code messageSupplier}.
 	 */
-	public static void assertArrayEquals(long[] expected, long[] actual, Supplier<String> messageSupplier) {
+	public static void assertArrayEquals(long @Nullable [] expected, long @Nullable [] actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertArrayEquals.assertArrayEquals(expected, actual, messageSupplier);
 	}
 
@@ -1330,7 +1368,7 @@ public static void assertArrayEquals(long[] expected, long[] actual, Supplier<St
 	 * <p>Equality imposed by this method is consistent with {@link Float#equals(Object)} and
 	 * {@link Float#compare(float, float)}.
 	 */
-	public static void assertArrayEquals(float[] expected, float[] actual) {
+	public static void assertArrayEquals(float @Nullable [] expected, float @Nullable [] actual) {
 		AssertArrayEquals.assertArrayEquals(expected, actual);
 	}
 
@@ -1340,7 +1378,8 @@ public static void assertArrayEquals(float[] expected, float[] actual) {
 	 * {@link Float#compare(float, float)}.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertArrayEquals(float[] expected, float[] actual, String message) {
+	public static void assertArrayEquals(float @Nullable [] expected, float @Nullable [] actual,
+			@Nullable String message) {
 		AssertArrayEquals.assertArrayEquals(expected, actual, message);
 	}
 
@@ -1350,7 +1389,8 @@ public static void assertArrayEquals(float[] expected, float[] actual, String me
 	 * {@link Float#compare(float, float)}.
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied {@code messageSupplier}.
 	 */
-	public static void assertArrayEquals(float[] expected, float[] actual, Supplier<String> messageSupplier) {
+	public static void assertArrayEquals(float @Nullable [] expected, float @Nullable [] actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertArrayEquals.assertArrayEquals(expected, actual, messageSupplier);
 	}
 
@@ -1359,7 +1399,7 @@ public static void assertArrayEquals(float[] expected, float[] actual, Supplier<
 	 * <p>Equality imposed by this method is consistent with {@link Float#equals(Object)} and
 	 * {@link Float#compare(float, float)}.
 	 */
-	public static void assertArrayEquals(float[] expected, float[] actual, float delta) {
+	public static void assertArrayEquals(float @Nullable [] expected, float @Nullable [] actual, float delta) {
 		AssertArrayEquals.assertArrayEquals(expected, actual, delta);
 	}
 
@@ -1369,7 +1409,8 @@ public static void assertArrayEquals(float[] expected, float[] actual, float del
 	 * {@link Float#compare(float, float)}.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertArrayEquals(float[] expected, float[] actual, float delta, String message) {
+	public static void assertArrayEquals(float @Nullable [] expected, float @Nullable [] actual, float delta,
+			@Nullable String message) {
 		AssertArrayEquals.assertArrayEquals(expected, actual, delta, message);
 	}
 
@@ -1379,8 +1420,8 @@ public static void assertArrayEquals(float[] expected, float[] actual, float del
 	 * {@link Float#compare(float, float)}.
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied {@code messageSupplier}.
 	 */
-	public static void assertArrayEquals(float[] expected, float[] actual, float delta,
-			Supplier<String> messageSupplier) {
+	public static void assertArrayEquals(float @Nullable [] expected, float @Nullable [] actual, float delta,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertArrayEquals.assertArrayEquals(expected, actual, delta, messageSupplier);
 	}
 
@@ -1389,7 +1430,7 @@ public static void assertArrayEquals(float[] expected, float[] actual, float del
 	 * <p>Equality imposed by this method is consistent with {@link Double#equals(Object)} and
 	 * {@link Double#compare(double, double)}.
 	 */
-	public static void assertArrayEquals(double[] expected, double[] actual) {
+	public static void assertArrayEquals(double @Nullable [] expected, double @Nullable [] actual) {
 		AssertArrayEquals.assertArrayEquals(expected, actual);
 	}
 
@@ -1399,7 +1440,8 @@ public static void assertArrayEquals(double[] expected, double[] actual) {
 	 * {@link Double#compare(double, double)}.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertArrayEquals(double[] expected, double[] actual, String message) {
+	public static void assertArrayEquals(double @Nullable [] expected, double @Nullable [] actual,
+			@Nullable String message) {
 		AssertArrayEquals.assertArrayEquals(expected, actual, message);
 	}
 
@@ -1409,7 +1451,8 @@ public static void assertArrayEquals(double[] expected, double[] actual, String
 	 * {@link Double#compare(double, double)}.
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied {@code messageSupplier}.
 	 */
-	public static void assertArrayEquals(double[] expected, double[] actual, Supplier<String> messageSupplier) {
+	public static void assertArrayEquals(double @Nullable [] expected, double @Nullable [] actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertArrayEquals.assertArrayEquals(expected, actual, messageSupplier);
 	}
 
@@ -1418,7 +1461,7 @@ public static void assertArrayEquals(double[] expected, double[] actual, Supplie
 	 * <p>Equality imposed by this method is consistent with {@link Double#equals(Object)} and
 	 * {@link Double#compare(double, double)}.
 	 */
-	public static void assertArrayEquals(double[] expected, double[] actual, double delta) {
+	public static void assertArrayEquals(double @Nullable [] expected, double @Nullable [] actual, double delta) {
 		AssertArrayEquals.assertArrayEquals(expected, actual, delta);
 	}
 
@@ -1428,7 +1471,8 @@ public static void assertArrayEquals(double[] expected, double[] actual, double
 	 * {@link Double#compare(double, double)}.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertArrayEquals(double[] expected, double[] actual, double delta, String message) {
+	public static void assertArrayEquals(double @Nullable [] expected, double @Nullable [] actual, double delta,
+			@Nullable String message) {
 		AssertArrayEquals.assertArrayEquals(expected, actual, delta, message);
 	}
 
@@ -1438,8 +1482,8 @@ public static void assertArrayEquals(double[] expected, double[] actual, double
 	 * {@link Double#compare(double, double)}.
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied {@code messageSupplier}.
 	 */
-	public static void assertArrayEquals(double[] expected, double[] actual, double delta,
-			Supplier<String> messageSupplier) {
+	public static void assertArrayEquals(double @Nullable [] expected, double @Nullable [] actual, double delta,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertArrayEquals.assertArrayEquals(expected, actual, delta, messageSupplier);
 	}
 
@@ -1452,7 +1496,7 @@ public static void assertArrayEquals(double[] expected, double[] actual, double
 	 * @see Objects#equals(Object, Object)
 	 * @see Arrays#deepEquals(Object[], Object[])
 	 */
-	public static void assertArrayEquals(Object[] expected, Object[] actual) {
+	public static void assertArrayEquals(@Nullable Object @Nullable [] expected, @Nullable Object @Nullable [] actual) {
 		AssertArrayEquals.assertArrayEquals(expected, actual);
 	}
 
@@ -1466,7 +1510,8 @@ public static void assertArrayEquals(Object[] expected, Object[] actual) {
 	 * @see Objects#equals(Object, Object)
 	 * @see Arrays#deepEquals(Object[], Object[])
 	 */
-	public static void assertArrayEquals(Object[] expected, Object[] actual, String message) {
+	public static void assertArrayEquals(@Nullable Object @Nullable [] expected, @Nullable Object @Nullable [] actual,
+			@Nullable String message) {
 		AssertArrayEquals.assertArrayEquals(expected, actual, message);
 	}
 
@@ -1480,7 +1525,8 @@ public static void assertArrayEquals(Object[] expected, Object[] actual, String
 	 * @see Objects#equals(Object, Object)
 	 * @see Arrays#deepEquals(Object[], Object[])
 	 */
-	public static void assertArrayEquals(Object[] expected, Object[] actual, Supplier<String> messageSupplier) {
+	public static void assertArrayEquals(@Nullable Object @Nullable [] expected, @Nullable Object @Nullable [] actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertArrayEquals.assertArrayEquals(expected, actual, messageSupplier);
 	}
 
@@ -1504,7 +1550,7 @@ public static void assertArrayEquals(Object[] expected, Object[] actual, Supplie
 	 * @see Arrays#deepEquals(Object[], Object[])
 	 * @see #assertArrayEquals(Object[], Object[])
 	 */
-	public static void assertIterableEquals(Iterable<?> expected, Iterable<?> actual) {
+	public static void assertIterableEquals(@Nullable Iterable<?> expected, @Nullable Iterable<?> actual) {
 		AssertIterableEquals.assertIterableEquals(expected, actual);
 	}
 
@@ -1528,7 +1574,8 @@ public static void assertIterableEquals(Iterable<?> expected, Iterable<?> actual
 	 * @see Arrays#deepEquals(Object[], Object[])
 	 * @see #assertArrayEquals(Object[], Object[], String)
 	 */
-	public static void assertIterableEquals(Iterable<?> expected, Iterable<?> actual, String message) {
+	public static void assertIterableEquals(@Nullable Iterable<?> expected, @Nullable Iterable<?> actual,
+			@Nullable String message) {
 		AssertIterableEquals.assertIterableEquals(expected, actual, message);
 	}
 
@@ -1552,8 +1599,8 @@ public static void assertIterableEquals(Iterable<?> expected, Iterable<?> actual
 	 * @see Arrays#deepEquals(Object[], Object[])
 	 * @see #assertArrayEquals(Object[], Object[], Supplier)
 	 */
-	public static void assertIterableEquals(Iterable<?> expected, Iterable<?> actual,
-			Supplier<String> messageSupplier) {
+	public static void assertIterableEquals(@Nullable Iterable<?> expected, @Nullable Iterable<?> actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertIterableEquals.assertIterableEquals(expected, actual, messageSupplier);
 	}
 
@@ -1613,7 +1660,8 @@ public static void assertLinesMatch(List<String> expectedLines, List<String> act
 	 *
 	 * @see #assertLinesMatch(List, List)
 	 */
-	public static void assertLinesMatch(List<String> expectedLines, List<String> actualLines, String message) {
+	public static void assertLinesMatch(List<String> expectedLines, List<String> actualLines,
+			@Nullable String message) {
 		AssertLinesMatch.assertLinesMatch(expectedLines, actualLines, message);
 	}
 
@@ -1630,7 +1678,7 @@ public static void assertLinesMatch(List<String> expectedLines, List<String> act
 	 * @see #assertLinesMatch(List, List)
 	 */
 	public static void assertLinesMatch(List<String> expectedLines, List<String> actualLines,
-			Supplier<String> messageSupplier) {
+			Supplier<@Nullable String> messageSupplier) {
 		AssertLinesMatch.assertLinesMatch(expectedLines, actualLines, messageSupplier);
 	}
 
@@ -1664,7 +1712,8 @@ public static void assertLinesMatch(Stream<String> expectedLines, Stream<String>
 	 * @since 5.7
 	 * @see #assertLinesMatch(List, List)
 	 */
-	public static void assertLinesMatch(Stream<String> expectedLines, Stream<String> actualLines, String message) {
+	public static void assertLinesMatch(Stream<String> expectedLines, Stream<String> actualLines,
+			@Nullable String message) {
 		AssertLinesMatch.assertLinesMatch(expectedLines, actualLines, message);
 	}
 
@@ -1685,7 +1734,7 @@ public static void assertLinesMatch(Stream<String> expectedLines, Stream<String>
 	 * @see #assertLinesMatch(List, List)
 	 */
 	public static void assertLinesMatch(Stream<String> expectedLines, Stream<String> actualLines,
-			Supplier<String> messageSupplier) {
+			Supplier<@Nullable String> messageSupplier) {
 		AssertLinesMatch.assertLinesMatch(expectedLines, actualLines, messageSupplier);
 	}
 
@@ -1707,7 +1756,7 @@ public static void assertNotEquals(byte unexpected, byte actual) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(byte unexpected, Byte actual) {
+	public static void assertNotEquals(byte unexpected, @Nullable Byte actual) {
 		AssertNotEquals.assertNotEquals((Byte) unexpected, actual);
 	}
 
@@ -1717,7 +1766,7 @@ public static void assertNotEquals(byte unexpected, Byte actual) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Byte unexpected, byte actual) {
+	public static void assertNotEquals(@Nullable Byte unexpected, byte actual) {
 		AssertNotEquals.assertNotEquals(unexpected, (Byte) actual);
 	}
 
@@ -1727,7 +1776,7 @@ public static void assertNotEquals(Byte unexpected, byte actual) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Byte unexpected, Byte actual) {
+	public static void assertNotEquals(@Nullable Byte unexpected, @Nullable Byte actual) {
 		AssertNotEquals.assertNotEquals(unexpected, actual);
 	}
 
@@ -1739,7 +1788,7 @@ public static void assertNotEquals(Byte unexpected, Byte actual) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(byte unexpected, byte actual, String message) {
+	public static void assertNotEquals(byte unexpected, byte actual, @Nullable String message) {
 		AssertNotEquals.assertNotEquals(unexpected, actual, message);
 	}
 
@@ -1751,7 +1800,7 @@ public static void assertNotEquals(byte unexpected, byte actual, String message)
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(byte unexpected, Byte actual, String message) {
+	public static void assertNotEquals(byte unexpected, @Nullable Byte actual, @Nullable String message) {
 		AssertNotEquals.assertNotEquals((Byte) unexpected, actual, message);
 	}
 
@@ -1763,7 +1812,7 @@ public static void assertNotEquals(byte unexpected, Byte actual, String message)
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Byte unexpected, byte actual, String message) {
+	public static void assertNotEquals(@Nullable Byte unexpected, byte actual, @Nullable String message) {
 		AssertNotEquals.assertNotEquals(unexpected, (Byte) actual, message);
 	}
 
@@ -1775,7 +1824,7 @@ public static void assertNotEquals(Byte unexpected, byte actual, String message)
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Byte unexpected, Byte actual, String message) {
+	public static void assertNotEquals(@Nullable Byte unexpected, @Nullable Byte actual, @Nullable String message) {
 		AssertNotEquals.assertNotEquals(unexpected, actual, message);
 	}
 
@@ -1788,7 +1837,7 @@ public static void assertNotEquals(Byte unexpected, Byte actual, String message)
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(byte unexpected, byte actual, Supplier<String> messageSupplier) {
+	public static void assertNotEquals(byte unexpected, byte actual, Supplier<@Nullable String> messageSupplier) {
 		AssertNotEquals.assertNotEquals(unexpected, actual, messageSupplier);
 	}
 
@@ -1801,7 +1850,8 @@ public static void assertNotEquals(byte unexpected, byte actual, Supplier<String
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(byte unexpected, Byte actual, Supplier<String> messageSupplier) {
+	public static void assertNotEquals(byte unexpected, @Nullable Byte actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertNotEquals.assertNotEquals((Byte) unexpected, actual, messageSupplier);
 	}
 
@@ -1814,7 +1864,8 @@ public static void assertNotEquals(byte unexpected, Byte actual, Supplier<String
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Byte unexpected, byte actual, Supplier<String> messageSupplier) {
+	public static void assertNotEquals(@Nullable Byte unexpected, byte actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertNotEquals.assertNotEquals(unexpected, (Byte) actual, messageSupplier);
 	}
 
@@ -1827,7 +1878,8 @@ public static void assertNotEquals(Byte unexpected, byte actual, Supplier<String
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Byte unexpected, Byte actual, Supplier<String> messageSupplier) {
+	public static void assertNotEquals(@Nullable Byte unexpected, @Nullable Byte actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertNotEquals.assertNotEquals(unexpected, actual, messageSupplier);
 	}
 
@@ -1847,7 +1899,7 @@ public static void assertNotEquals(short unexpected, short actual) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(short unexpected, Short actual) {
+	public static void assertNotEquals(short unexpected, @Nullable Short actual) {
 		AssertNotEquals.assertNotEquals((Short) unexpected, actual);
 	}
 
@@ -1857,7 +1909,7 @@ public static void assertNotEquals(short unexpected, Short actual) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Short unexpected, short actual) {
+	public static void assertNotEquals(@Nullable Short unexpected, short actual) {
 		AssertNotEquals.assertNotEquals(unexpected, (Short) actual);
 	}
 
@@ -1867,7 +1919,7 @@ public static void assertNotEquals(Short unexpected, short actual) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Short unexpected, Short actual) {
+	public static void assertNotEquals(@Nullable Short unexpected, @Nullable Short actual) {
 		AssertNotEquals.assertNotEquals(unexpected, actual);
 	}
 
@@ -1879,7 +1931,7 @@ public static void assertNotEquals(Short unexpected, Short actual) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(short unexpected, short actual, String message) {
+	public static void assertNotEquals(short unexpected, short actual, @Nullable String message) {
 		AssertNotEquals.assertNotEquals(unexpected, actual, message);
 	}
 
@@ -1891,7 +1943,7 @@ public static void assertNotEquals(short unexpected, short actual, String messag
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(short unexpected, Short actual, String message) {
+	public static void assertNotEquals(short unexpected, @Nullable Short actual, @Nullable String message) {
 		AssertNotEquals.assertNotEquals((Short) unexpected, actual, message);
 	}
 
@@ -1903,7 +1955,7 @@ public static void assertNotEquals(short unexpected, Short actual, String messag
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Short unexpected, short actual, String message) {
+	public static void assertNotEquals(@Nullable Short unexpected, short actual, @Nullable String message) {
 		AssertNotEquals.assertNotEquals(unexpected, (Short) actual, message);
 	}
 
@@ -1915,7 +1967,7 @@ public static void assertNotEquals(Short unexpected, short actual, String messag
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Short unexpected, Short actual, String message) {
+	public static void assertNotEquals(@Nullable Short unexpected, @Nullable Short actual, @Nullable String message) {
 		AssertNotEquals.assertNotEquals(unexpected, actual, message);
 	}
 
@@ -1928,7 +1980,7 @@ public static void assertNotEquals(Short unexpected, Short actual, String messag
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(short unexpected, short actual, Supplier<String> messageSupplier) {
+	public static void assertNotEquals(short unexpected, short actual, Supplier<@Nullable String> messageSupplier) {
 		AssertNotEquals.assertNotEquals(unexpected, actual, messageSupplier);
 	}
 
@@ -1941,7 +1993,8 @@ public static void assertNotEquals(short unexpected, short actual, Supplier<Stri
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(short unexpected, Short actual, Supplier<String> messageSupplier) {
+	public static void assertNotEquals(short unexpected, @Nullable Short actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertNotEquals.assertNotEquals((Short) unexpected, actual, messageSupplier);
 	}
 
@@ -1954,7 +2007,8 @@ public static void assertNotEquals(short unexpected, Short actual, Supplier<Stri
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Short unexpected, short actual, Supplier<String> messageSupplier) {
+	public static void assertNotEquals(@Nullable Short unexpected, short actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertNotEquals.assertNotEquals(unexpected, (Short) actual, messageSupplier);
 	}
 
@@ -1967,7 +2021,8 @@ public static void assertNotEquals(Short unexpected, short actual, Supplier<Stri
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Short unexpected, Short actual, Supplier<String> messageSupplier) {
+	public static void assertNotEquals(@Nullable Short unexpected, @Nullable Short actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertNotEquals.assertNotEquals(unexpected, actual, messageSupplier);
 	}
 
@@ -1987,7 +2042,7 @@ public static void assertNotEquals(int unexpected, int actual) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(int unexpected, Integer actual) {
+	public static void assertNotEquals(int unexpected, @Nullable Integer actual) {
 		AssertNotEquals.assertNotEquals((Integer) unexpected, actual);
 	}
 
@@ -1997,7 +2052,7 @@ public static void assertNotEquals(int unexpected, Integer actual) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Integer unexpected, int actual) {
+	public static void assertNotEquals(@Nullable Integer unexpected, int actual) {
 		AssertNotEquals.assertNotEquals(unexpected, (Integer) actual);
 	}
 
@@ -2007,7 +2062,7 @@ public static void assertNotEquals(Integer unexpected, int actual) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Integer unexpected, Integer actual) {
+	public static void assertNotEquals(@Nullable Integer unexpected, @Nullable Integer actual) {
 		AssertNotEquals.assertNotEquals(unexpected, actual);
 	}
 
@@ -2019,7 +2074,7 @@ public static void assertNotEquals(Integer unexpected, Integer actual) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(int unexpected, int actual, String message) {
+	public static void assertNotEquals(int unexpected, int actual, @Nullable String message) {
 		AssertNotEquals.assertNotEquals(unexpected, actual, message);
 	}
 
@@ -2031,7 +2086,7 @@ public static void assertNotEquals(int unexpected, int actual, String message) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(int unexpected, Integer actual, String message) {
+	public static void assertNotEquals(int unexpected, @Nullable Integer actual, @Nullable String message) {
 		AssertNotEquals.assertNotEquals((Integer) unexpected, actual, message);
 	}
 
@@ -2043,7 +2098,7 @@ public static void assertNotEquals(int unexpected, Integer actual, String messag
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Integer unexpected, int actual, String message) {
+	public static void assertNotEquals(@Nullable Integer unexpected, int actual, @Nullable String message) {
 		AssertNotEquals.assertNotEquals(unexpected, (Integer) actual, message);
 	}
 
@@ -2055,7 +2110,8 @@ public static void assertNotEquals(Integer unexpected, int actual, String messag
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Integer unexpected, Integer actual, String message) {
+	public static void assertNotEquals(@Nullable Integer unexpected, @Nullable Integer actual,
+			@Nullable String message) {
 		AssertNotEquals.assertNotEquals(unexpected, actual, message);
 	}
 
@@ -2068,7 +2124,7 @@ public static void assertNotEquals(Integer unexpected, Integer actual, String me
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(int unexpected, int actual, Supplier<String> messageSupplier) {
+	public static void assertNotEquals(int unexpected, int actual, Supplier<@Nullable String> messageSupplier) {
 		AssertNotEquals.assertNotEquals(unexpected, actual, messageSupplier);
 	}
 
@@ -2081,7 +2137,8 @@ public static void assertNotEquals(int unexpected, int actual, Supplier<String>
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(int unexpected, Integer actual, Supplier<String> messageSupplier) {
+	public static void assertNotEquals(int unexpected, @Nullable Integer actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertNotEquals.assertNotEquals((Integer) unexpected, actual, messageSupplier);
 	}
 
@@ -2094,7 +2151,8 @@ public static void assertNotEquals(int unexpected, Integer actual, Supplier<Stri
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Integer unexpected, int actual, Supplier<String> messageSupplier) {
+	public static void assertNotEquals(@Nullable Integer unexpected, int actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertNotEquals.assertNotEquals(unexpected, (Integer) actual, messageSupplier);
 	}
 
@@ -2107,7 +2165,8 @@ public static void assertNotEquals(Integer unexpected, int actual, Supplier<Stri
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Integer unexpected, Integer actual, Supplier<String> messageSupplier) {
+	public static void assertNotEquals(@Nullable Integer unexpected, @Nullable Integer actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertNotEquals.assertNotEquals(unexpected, actual, messageSupplier);
 	}
 
@@ -2127,7 +2186,7 @@ public static void assertNotEquals(long unexpected, long actual) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(long unexpected, Long actual) {
+	public static void assertNotEquals(long unexpected, @Nullable Long actual) {
 		AssertNotEquals.assertNotEquals((Long) unexpected, actual);
 	}
 
@@ -2137,7 +2196,7 @@ public static void assertNotEquals(long unexpected, Long actual) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Long unexpected, long actual) {
+	public static void assertNotEquals(@Nullable Long unexpected, long actual) {
 		AssertNotEquals.assertNotEquals(unexpected, (Long) actual);
 	}
 
@@ -2147,7 +2206,7 @@ public static void assertNotEquals(Long unexpected, long actual) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Long unexpected, Long actual) {
+	public static void assertNotEquals(@Nullable Long unexpected, @Nullable Long actual) {
 		AssertNotEquals.assertNotEquals(unexpected, actual);
 	}
 
@@ -2159,7 +2218,7 @@ public static void assertNotEquals(Long unexpected, Long actual) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(long unexpected, long actual, String message) {
+	public static void assertNotEquals(long unexpected, long actual, @Nullable String message) {
 		AssertNotEquals.assertNotEquals(unexpected, actual, message);
 	}
 
@@ -2171,7 +2230,7 @@ public static void assertNotEquals(long unexpected, long actual, String message)
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(long unexpected, Long actual, String message) {
+	public static void assertNotEquals(long unexpected, @Nullable Long actual, @Nullable String message) {
 		AssertNotEquals.assertNotEquals((Long) unexpected, actual, message);
 	}
 
@@ -2183,7 +2242,7 @@ public static void assertNotEquals(long unexpected, Long actual, String message)
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Long unexpected, long actual, String message) {
+	public static void assertNotEquals(@Nullable Long unexpected, long actual, @Nullable String message) {
 		AssertNotEquals.assertNotEquals(unexpected, (Long) actual, message);
 	}
 
@@ -2195,7 +2254,7 @@ public static void assertNotEquals(Long unexpected, long actual, String message)
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Long unexpected, Long actual, String message) {
+	public static void assertNotEquals(@Nullable Long unexpected, @Nullable Long actual, @Nullable String message) {
 		AssertNotEquals.assertNotEquals(unexpected, actual, message);
 	}
 
@@ -2208,7 +2267,7 @@ public static void assertNotEquals(Long unexpected, Long actual, String message)
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(long unexpected, long actual, Supplier<String> messageSupplier) {
+	public static void assertNotEquals(long unexpected, long actual, Supplier<@Nullable String> messageSupplier) {
 		AssertNotEquals.assertNotEquals(unexpected, actual, messageSupplier);
 	}
 
@@ -2221,7 +2280,8 @@ public static void assertNotEquals(long unexpected, long actual, Supplier<String
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(long unexpected, Long actual, Supplier<String> messageSupplier) {
+	public static void assertNotEquals(long unexpected, @Nullable Long actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertNotEquals.assertNotEquals((Long) unexpected, actual, messageSupplier);
 	}
 
@@ -2234,7 +2294,8 @@ public static void assertNotEquals(long unexpected, Long actual, Supplier<String
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Long unexpected, long actual, Supplier<String> messageSupplier) {
+	public static void assertNotEquals(@Nullable Long unexpected, long actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertNotEquals.assertNotEquals(unexpected, (Long) actual, messageSupplier);
 	}
 
@@ -2247,7 +2308,8 @@ public static void assertNotEquals(Long unexpected, long actual, Supplier<String
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Long unexpected, Long actual, Supplier<String> messageSupplier) {
+	public static void assertNotEquals(@Nullable Long unexpected, @Nullable Long actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertNotEquals.assertNotEquals(unexpected, actual, messageSupplier);
 	}
 
@@ -2273,7 +2335,7 @@ public static void assertNotEquals(float unexpected, float actual) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(float unexpected, Float actual) {
+	public static void assertNotEquals(float unexpected, @Nullable Float actual) {
 		AssertNotEquals.assertNotEquals((Float) unexpected, actual);
 	}
 
@@ -2286,7 +2348,7 @@ public static void assertNotEquals(float unexpected, Float actual) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Float unexpected, float actual) {
+	public static void assertNotEquals(@Nullable Float unexpected, float actual) {
 		AssertNotEquals.assertNotEquals(unexpected, (Float) actual);
 	}
 
@@ -2299,7 +2361,7 @@ public static void assertNotEquals(Float unexpected, float actual) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Float unexpected, Float actual) {
+	public static void assertNotEquals(@Nullable Float unexpected, @Nullable Float actual) {
 		AssertNotEquals.assertNotEquals(unexpected, actual);
 	}
 
@@ -2314,7 +2376,7 @@ public static void assertNotEquals(Float unexpected, Float actual) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(float unexpected, float actual, String message) {
+	public static void assertNotEquals(float unexpected, float actual, @Nullable String message) {
 		AssertNotEquals.assertNotEquals(unexpected, actual, message);
 	}
 
@@ -2329,7 +2391,7 @@ public static void assertNotEquals(float unexpected, float actual, String messag
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(float unexpected, Float actual, String message) {
+	public static void assertNotEquals(float unexpected, @Nullable Float actual, @Nullable String message) {
 		AssertNotEquals.assertNotEquals((Float) unexpected, actual, message);
 	}
 
@@ -2344,7 +2406,7 @@ public static void assertNotEquals(float unexpected, Float actual, String messag
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Float unexpected, float actual, String message) {
+	public static void assertNotEquals(@Nullable Float unexpected, float actual, @Nullable String message) {
 		AssertNotEquals.assertNotEquals(unexpected, (Float) actual, message);
 	}
 
@@ -2359,7 +2421,7 @@ public static void assertNotEquals(Float unexpected, float actual, String messag
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Float unexpected, Float actual, String message) {
+	public static void assertNotEquals(@Nullable Float unexpected, @Nullable Float actual, @Nullable String message) {
 		AssertNotEquals.assertNotEquals(unexpected, actual, message);
 	}
 
@@ -2372,7 +2434,7 @@ public static void assertNotEquals(Float unexpected, Float actual, String messag
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(float unexpected, float actual, Supplier<String> messageSupplier) {
+	public static void assertNotEquals(float unexpected, float actual, Supplier<@Nullable String> messageSupplier) {
 		AssertNotEquals.assertNotEquals(unexpected, actual, messageSupplier);
 	}
 
@@ -2385,7 +2447,8 @@ public static void assertNotEquals(float unexpected, float actual, Supplier<Stri
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(float unexpected, Float actual, Supplier<String> messageSupplier) {
+	public static void assertNotEquals(float unexpected, @Nullable Float actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertNotEquals.assertNotEquals((Float) unexpected, actual, messageSupplier);
 	}
 
@@ -2398,7 +2461,8 @@ public static void assertNotEquals(float unexpected, Float actual, Supplier<Stri
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Float unexpected, float actual, Supplier<String> messageSupplier) {
+	public static void assertNotEquals(@Nullable Float unexpected, float actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertNotEquals.assertNotEquals(unexpected, (Float) actual, messageSupplier);
 	}
 
@@ -2411,7 +2475,8 @@ public static void assertNotEquals(Float unexpected, float actual, Supplier<Stri
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Float unexpected, Float actual, Supplier<String> messageSupplier) {
+	public static void assertNotEquals(@Nullable Float unexpected, @Nullable Float actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertNotEquals.assertNotEquals(unexpected, actual, messageSupplier);
 	}
 
@@ -2441,7 +2506,7 @@ public static void assertNotEquals(float unexpected, float actual, float delta)
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(float unexpected, float actual, float delta, String message) {
+	public static void assertNotEquals(float unexpected, float actual, float delta, @Nullable String message) {
 		AssertNotEquals.assertNotEquals(unexpected, actual, delta, message);
 	}
 
@@ -2455,7 +2520,8 @@ public static void assertNotEquals(float unexpected, float actual, float delta,
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(float unexpected, float actual, float delta, Supplier<String> messageSupplier) {
+	public static void assertNotEquals(float unexpected, float actual, float delta,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertNotEquals.assertNotEquals(unexpected, actual, delta, messageSupplier);
 	}
 
@@ -2481,7 +2547,7 @@ public static void assertNotEquals(double unexpected, double actual) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(double unexpected, Double actual) {
+	public static void assertNotEquals(double unexpected, @Nullable Double actual) {
 		AssertNotEquals.assertNotEquals((Double) unexpected, actual);
 	}
 
@@ -2494,7 +2560,7 @@ public static void assertNotEquals(double unexpected, Double actual) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Double unexpected, double actual) {
+	public static void assertNotEquals(@Nullable Double unexpected, double actual) {
 		AssertNotEquals.assertNotEquals(unexpected, (Double) actual);
 	}
 
@@ -2507,7 +2573,7 @@ public static void assertNotEquals(Double unexpected, double actual) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Double unexpected, Double actual) {
+	public static void assertNotEquals(@Nullable Double unexpected, @Nullable Double actual) {
 		AssertNotEquals.assertNotEquals(unexpected, actual);
 	}
 
@@ -2522,7 +2588,7 @@ public static void assertNotEquals(Double unexpected, Double actual) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(double unexpected, double actual, String message) {
+	public static void assertNotEquals(double unexpected, double actual, @Nullable String message) {
 		AssertNotEquals.assertNotEquals(unexpected, actual, message);
 	}
 
@@ -2537,7 +2603,7 @@ public static void assertNotEquals(double unexpected, double actual, String mess
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(double unexpected, Double actual, String message) {
+	public static void assertNotEquals(double unexpected, @Nullable Double actual, @Nullable String message) {
 		AssertNotEquals.assertNotEquals((Double) unexpected, actual, message);
 	}
 
@@ -2552,7 +2618,7 @@ public static void assertNotEquals(double unexpected, Double actual, String mess
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Double unexpected, double actual, String message) {
+	public static void assertNotEquals(@Nullable Double unexpected, double actual, @Nullable String message) {
 		AssertNotEquals.assertNotEquals(unexpected, (Double) actual, message);
 	}
 
@@ -2567,7 +2633,7 @@ public static void assertNotEquals(Double unexpected, double actual, String mess
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Double unexpected, Double actual, String message) {
+	public static void assertNotEquals(@Nullable Double unexpected, @Nullable Double actual, @Nullable String message) {
 		AssertNotEquals.assertNotEquals(unexpected, actual, message);
 	}
 
@@ -2580,7 +2646,7 @@ public static void assertNotEquals(Double unexpected, Double actual, String mess
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(double unexpected, double actual, Supplier<String> messageSupplier) {
+	public static void assertNotEquals(double unexpected, double actual, Supplier<@Nullable String> messageSupplier) {
 		AssertNotEquals.assertNotEquals(unexpected, actual, messageSupplier);
 	}
 
@@ -2593,7 +2659,8 @@ public static void assertNotEquals(double unexpected, double actual, Supplier<St
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(double unexpected, Double actual, Supplier<String> messageSupplier) {
+	public static void assertNotEquals(double unexpected, @Nullable Double actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertNotEquals.assertNotEquals((Double) unexpected, actual, messageSupplier);
 	}
 
@@ -2606,7 +2673,8 @@ public static void assertNotEquals(double unexpected, Double actual, Supplier<St
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Double unexpected, double actual, Supplier<String> messageSupplier) {
+	public static void assertNotEquals(@Nullable Double unexpected, double actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertNotEquals.assertNotEquals(unexpected, (Double) actual, messageSupplier);
 	}
 
@@ -2619,7 +2687,8 @@ public static void assertNotEquals(Double unexpected, double actual, Supplier<St
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Double unexpected, Double actual, Supplier<String> messageSupplier) {
+	public static void assertNotEquals(@Nullable Double unexpected, @Nullable Double actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertNotEquals.assertNotEquals(unexpected, actual, messageSupplier);
 	}
 
@@ -2649,7 +2718,7 @@ public static void assertNotEquals(double unexpected, double actual, double delt
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(double unexpected, double actual, double delta, String message) {
+	public static void assertNotEquals(double unexpected, double actual, double delta, @Nullable String message) {
 		AssertNotEquals.assertNotEquals(unexpected, actual, delta, message);
 	}
 
@@ -2664,7 +2733,7 @@ public static void assertNotEquals(double unexpected, double actual, double delt
 	 */
 	@API(status = STABLE, since = "5.4")
 	public static void assertNotEquals(double unexpected, double actual, double delta,
-			Supplier<String> messageSupplier) {
+			Supplier<@Nullable String> messageSupplier) {
 		AssertNotEquals.assertNotEquals(unexpected, actual, delta, messageSupplier);
 	}
 
@@ -2684,7 +2753,7 @@ public static void assertNotEquals(char unexpected, char actual) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(char unexpected, Character actual) {
+	public static void assertNotEquals(char unexpected, @Nullable Character actual) {
 		AssertNotEquals.assertNotEquals((Character) unexpected, actual);
 	}
 
@@ -2694,7 +2763,7 @@ public static void assertNotEquals(char unexpected, Character actual) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Character unexpected, char actual) {
+	public static void assertNotEquals(@Nullable Character unexpected, char actual) {
 		AssertNotEquals.assertNotEquals(unexpected, (Character) actual);
 	}
 
@@ -2704,7 +2773,7 @@ public static void assertNotEquals(Character unexpected, char actual) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Character unexpected, Character actual) {
+	public static void assertNotEquals(@Nullable Character unexpected, @Nullable Character actual) {
 		AssertNotEquals.assertNotEquals(unexpected, actual);
 	}
 
@@ -2716,7 +2785,7 @@ public static void assertNotEquals(Character unexpected, Character actual) {
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(char unexpected, char actual, String message) {
+	public static void assertNotEquals(char unexpected, char actual, @Nullable String message) {
 		AssertNotEquals.assertNotEquals(unexpected, actual, message);
 	}
 
@@ -2728,7 +2797,7 @@ public static void assertNotEquals(char unexpected, char actual, String message)
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(char unexpected, Character actual, String message) {
+	public static void assertNotEquals(char unexpected, @Nullable Character actual, @Nullable String message) {
 		AssertNotEquals.assertNotEquals((Character) unexpected, actual, message);
 	}
 
@@ -2740,7 +2809,7 @@ public static void assertNotEquals(char unexpected, Character actual, String mes
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Character unexpected, char actual, String message) {
+	public static void assertNotEquals(@Nullable Character unexpected, char actual, @Nullable String message) {
 		AssertNotEquals.assertNotEquals(unexpected, (Character) actual, message);
 	}
 
@@ -2752,7 +2821,8 @@ public static void assertNotEquals(Character unexpected, char actual, String mes
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Character unexpected, Character actual, String message) {
+	public static void assertNotEquals(@Nullable Character unexpected, @Nullable Character actual,
+			@Nullable String message) {
 		AssertNotEquals.assertNotEquals(unexpected, actual, message);
 	}
 
@@ -2765,7 +2835,7 @@ public static void assertNotEquals(Character unexpected, Character actual, Strin
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(char unexpected, char actual, Supplier<String> messageSupplier) {
+	public static void assertNotEquals(char unexpected, char actual, Supplier<@Nullable String> messageSupplier) {
 		AssertNotEquals.assertNotEquals(unexpected, actual, messageSupplier);
 	}
 
@@ -2778,7 +2848,8 @@ public static void assertNotEquals(char unexpected, char actual, Supplier<String
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(char unexpected, Character actual, Supplier<String> messageSupplier) {
+	public static void assertNotEquals(char unexpected, @Nullable Character actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertNotEquals.assertNotEquals((Character) unexpected, actual, messageSupplier);
 	}
 
@@ -2791,7 +2862,8 @@ public static void assertNotEquals(char unexpected, Character actual, Supplier<S
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Character unexpected, char actual, Supplier<String> messageSupplier) {
+	public static void assertNotEquals(@Nullable Character unexpected, char actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertNotEquals.assertNotEquals(unexpected, (Character) actual, messageSupplier);
 	}
 
@@ -2804,7 +2876,8 @@ public static void assertNotEquals(Character unexpected, char actual, Supplier<S
 	 * @since 5.4
 	 */
 	@API(status = STABLE, since = "5.4")
-	public static void assertNotEquals(Character unexpected, Character actual, Supplier<String> messageSupplier) {
+	public static void assertNotEquals(@Nullable Character unexpected, @Nullable Character actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertNotEquals.assertNotEquals(unexpected, actual, messageSupplier);
 	}
 
@@ -2815,7 +2888,7 @@ public static void assertNotEquals(Character unexpected, Character actual, Suppl
 	 *
 	 * @see Object#equals(Object)
 	 */
-	public static void assertNotEquals(Object unexpected, Object actual) {
+	public static void assertNotEquals(@Nullable Object unexpected, @Nullable Object actual) {
 		AssertNotEquals.assertNotEquals(unexpected, actual);
 	}
 
@@ -2828,7 +2901,7 @@ public static void assertNotEquals(Object unexpected, Object actual) {
 	 *
 	 * @see Object#equals(Object)
 	 */
-	public static void assertNotEquals(Object unexpected, Object actual, String message) {
+	public static void assertNotEquals(@Nullable Object unexpected, @Nullable Object actual, @Nullable String message) {
 		AssertNotEquals.assertNotEquals(unexpected, actual, message);
 	}
 
@@ -2842,7 +2915,8 @@ public static void assertNotEquals(Object unexpected, Object actual, String mess
 	 *
 	 * @see Object#equals(Object)
 	 */
-	public static void assertNotEquals(Object unexpected, Object actual, Supplier<String> messageSupplier) {
+	public static void assertNotEquals(@Nullable Object unexpected, @Nullable Object actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertNotEquals.assertNotEquals(unexpected, actual, messageSupplier);
 	}
 
@@ -2856,7 +2930,7 @@ public static void assertNotEquals(Object unexpected, Object actual, Supplier<St
 	 * use one of the {@code assertEquals(...)} methods instead &mdash; for example,
 	 * use {@code assertEquals(999, 999)} instead of {@code assertSame(999, 999)}.
 	 */
-	public static void assertSame(Object expected, Object actual) {
+	public static void assertSame(@Nullable Object expected, @Nullable Object actual) {
 		AssertSame.assertSame(expected, actual);
 	}
 
@@ -2869,7 +2943,7 @@ public static void assertSame(Object expected, Object actual) {
 	 * use {@code assertEquals(999, 999)} instead of {@code assertSame(999, 999)}.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertSame(Object expected, Object actual, String message) {
+	public static void assertSame(@Nullable Object expected, @Nullable Object actual, @Nullable String message) {
 		AssertSame.assertSame(expected, actual, message);
 	}
 
@@ -2883,7 +2957,8 @@ public static void assertSame(Object expected, Object actual, String message) {
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied
 	 * {@code messageSupplier}.
 	 */
-	public static void assertSame(Object expected, Object actual, Supplier<String> messageSupplier) {
+	public static void assertSame(@Nullable Object expected, @Nullable Object actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertSame.assertSame(expected, actual, messageSupplier);
 	}
 
@@ -2896,7 +2971,7 @@ public static void assertSame(Object expected, Object actual, Supplier<String> m
 	 * objects. To assert that two objects or two primitive values are not
 	 * <em>equal</em>, use one of the {@code assertNotEquals(...)} methods instead.
 	 */
-	public static void assertNotSame(Object unexpected, Object actual) {
+	public static void assertNotSame(@Nullable Object unexpected, @Nullable Object actual) {
 		AssertNotSame.assertNotSame(unexpected, actual);
 	}
 
@@ -2908,7 +2983,7 @@ public static void assertNotSame(Object unexpected, Object actual) {
 	 * <em>equal</em>, use one of the {@code assertNotEquals(...)} methods instead.
 	 * <p>Fails with the supplied failure {@code message}.
 	 */
-	public static void assertNotSame(Object unexpected, Object actual, String message) {
+	public static void assertNotSame(@Nullable Object unexpected, @Nullable Object actual, @Nullable String message) {
 		AssertNotSame.assertNotSame(unexpected, actual, message);
 	}
 
@@ -2921,7 +2996,8 @@ public static void assertNotSame(Object unexpected, Object actual, String messag
 	 * <p>If necessary, the failure message will be retrieved lazily from the supplied
 	 * {@code messageSupplier}.
 	 */
-	public static void assertNotSame(Object unexpected, Object actual, Supplier<String> messageSupplier) {
+	public static void assertNotSame(@Nullable Object unexpected, @Nullable Object actual,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertNotSame.assertNotSame(unexpected, actual, messageSupplier);
 	}
 
@@ -2957,7 +3033,7 @@ public static void assertAll(Executable... executables) throws MultipleFailuresE
 	 * @see #assertAll(String, Collection)
 	 * @see #assertAll(String, Stream)
 	 */
-	public static void assertAll(String heading, Executable... executables) throws MultipleFailuresError {
+	public static void assertAll(@Nullable String heading, Executable... executables) throws MultipleFailuresError {
 		AssertAll.assertAll(heading, executables);
 	}
 
@@ -2991,7 +3067,8 @@ public static void assertAll(Collection<Executable> executables) throws Multiple
 	 * @see #assertAll(Stream)
 	 * @see #assertAll(String, Stream)
 	 */
-	public static void assertAll(String heading, Collection<Executable> executables) throws MultipleFailuresError {
+	public static void assertAll(@Nullable String heading, Collection<Executable> executables)
+			throws MultipleFailuresError {
 		AssertAll.assertAll(heading, executables);
 	}
 
@@ -3035,7 +3112,8 @@ public static void assertAll(Stream<Executable> executables) throws MultipleFail
 	 * @see #assertAll(String, Collection)
 	 * @see #assertAll(Stream)
 	 */
-	public static void assertAll(String heading, Stream<Executable> executables) throws MultipleFailuresError {
+	public static void assertAll(@Nullable String heading, Stream<Executable> executables)
+			throws MultipleFailuresError {
 		AssertAll.assertAll(heading, executables);
 	}
 
@@ -3080,7 +3158,7 @@ public static <T extends Throwable> T assertThrowsExactly(Class<T> expectedType,
 	 */
 	@API(status = STABLE, since = "5.10")
 	public static <T extends Throwable> T assertThrowsExactly(Class<T> expectedType, Executable executable,
-			String message) {
+			@Nullable String message) {
 		return AssertThrowsExactly.assertThrowsExactly(expectedType, executable, message);
 	}
 
@@ -3105,7 +3183,7 @@ public static <T extends Throwable> T assertThrowsExactly(Class<T> expectedType,
 	 */
 	@API(status = STABLE, since = "5.10")
 	public static <T extends Throwable> T assertThrowsExactly(Class<T> expectedType, Executable executable,
-			Supplier<String> messageSupplier) {
+			Supplier<@Nullable String> messageSupplier) {
 		return AssertThrowsExactly.assertThrowsExactly(expectedType, executable, messageSupplier);
 	}
 
@@ -3149,7 +3227,8 @@ public static <T extends Throwable> T assertThrows(Class<T> expectedType, Execut
 	 *
 	 * @see #assertThrowsExactly(Class, Executable, String)
 	 */
-	public static <T extends Throwable> T assertThrows(Class<T> expectedType, Executable executable, String message) {
+	public static <T extends Throwable> T assertThrows(Class<T> expectedType, Executable executable,
+			@Nullable String message) {
 		return AssertThrows.assertThrows(expectedType, executable, message);
 	}
 
@@ -3176,7 +3255,7 @@ public static <T extends Throwable> T assertThrows(Class<T> expectedType, Execut
 	 * @see #assertThrowsExactly(Class, Executable, Supplier)
 	 */
 	public static <T extends Throwable> T assertThrows(Class<T> expectedType, Executable executable,
-			Supplier<String> messageSupplier) {
+			Supplier<@Nullable String> messageSupplier) {
 		return AssertThrows.assertThrows(expectedType, executable, messageSupplier);
 	}
 
@@ -3214,7 +3293,7 @@ public static void assertDoesNotThrow(Executable executable) {
 	 * @since 5.2
 	 */
 	@API(status = STABLE, since = "5.2")
-	public static void assertDoesNotThrow(Executable executable, String message) {
+	public static void assertDoesNotThrow(Executable executable, @Nullable String message) {
 		AssertDoesNotThrow.assertDoesNotThrow(executable, message);
 	}
 
@@ -3234,7 +3313,7 @@ public static void assertDoesNotThrow(Executable executable, String message) {
 	 * @since 5.2
 	 */
 	@API(status = STABLE, since = "5.2")
-	public static void assertDoesNotThrow(Executable executable, Supplier<String> messageSupplier) {
+	public static void assertDoesNotThrow(Executable executable, Supplier<@Nullable String> messageSupplier) {
 		AssertDoesNotThrow.assertDoesNotThrow(executable, messageSupplier);
 	}
 
@@ -3255,7 +3334,7 @@ public static void assertDoesNotThrow(Executable executable, Supplier<String> me
 	 * @since 5.2
 	 */
 	@API(status = STABLE, since = "5.2")
-	public static <T> T assertDoesNotThrow(ThrowingSupplier<T> supplier) {
+	public static <T extends @Nullable Object> T assertDoesNotThrow(ThrowingSupplier<T> supplier) {
 		return AssertDoesNotThrow.assertDoesNotThrow(supplier);
 	}
 
@@ -3276,7 +3355,8 @@ public static <T> T assertDoesNotThrow(ThrowingSupplier<T> supplier) {
 	 * @since 5.2
 	 */
 	@API(status = STABLE, since = "5.2")
-	public static <T> T assertDoesNotThrow(ThrowingSupplier<T> supplier, String message) {
+	public static <T extends @Nullable Object> T assertDoesNotThrow(ThrowingSupplier<T> supplier,
+			@Nullable String message) {
 		return AssertDoesNotThrow.assertDoesNotThrow(supplier, message);
 	}
 
@@ -3298,7 +3378,8 @@ public static <T> T assertDoesNotThrow(ThrowingSupplier<T> supplier, String mess
 	 * @since 5.2
 	 */
 	@API(status = STABLE, since = "5.2")
-	public static <T> T assertDoesNotThrow(ThrowingSupplier<T> supplier, Supplier<String> messageSupplier) {
+	public static <T extends @Nullable Object> T assertDoesNotThrow(ThrowingSupplier<T> supplier,
+			Supplier<@Nullable String> messageSupplier) {
 		return AssertDoesNotThrow.assertDoesNotThrow(supplier, messageSupplier);
 	}
 
@@ -3342,7 +3423,7 @@ public static void assertTimeout(Duration timeout, Executable executable) {
 	 * @see #assertTimeout(Duration, ThrowingSupplier, Supplier)
 	 * @see #assertTimeoutPreemptively(Duration, Executable, String)
 	 */
-	public static void assertTimeout(Duration timeout, Executable executable, String message) {
+	public static void assertTimeout(Duration timeout, Executable executable, @Nullable String message) {
 		AssertTimeout.assertTimeout(timeout, executable, message);
 	}
 
@@ -3364,7 +3445,8 @@ public static void assertTimeout(Duration timeout, Executable executable, String
 	 * @see #assertTimeout(Duration, ThrowingSupplier, Supplier)
 	 * @see #assertTimeoutPreemptively(Duration, Executable, Supplier)
 	 */
-	public static void assertTimeout(Duration timeout, Executable executable, Supplier<String> messageSupplier) {
+	public static void assertTimeout(Duration timeout, Executable executable,
+			Supplier<@Nullable String> messageSupplier) {
 		AssertTimeout.assertTimeout(timeout, executable, messageSupplier);
 	}
 
@@ -3387,7 +3469,7 @@ public static void assertTimeout(Duration timeout, Executable executable, Suppli
 	 * @see #assertTimeout(Duration, ThrowingSupplier, Supplier)
 	 * @see #assertTimeoutPreemptively(Duration, Executable)
 	 */
-	public static <T> T assertTimeout(Duration timeout, ThrowingSupplier<T> supplier) {
+	public static <T extends @Nullable Object> T assertTimeout(Duration timeout, ThrowingSupplier<T> supplier) {
 		return AssertTimeout.assertTimeout(timeout, supplier);
 	}
 
@@ -3410,7 +3492,8 @@ public static <T> T assertTimeout(Duration timeout, ThrowingSupplier<T> supplier
 	 * @see #assertTimeout(Duration, ThrowingSupplier, Supplier)
 	 * @see #assertTimeoutPreemptively(Duration, Executable, String)
 	 */
-	public static <T> T assertTimeout(Duration timeout, ThrowingSupplier<T> supplier, String message) {
+	public static <T extends @Nullable Object> T assertTimeout(Duration timeout, ThrowingSupplier<T> supplier,
+			@Nullable String message) {
 		return AssertTimeout.assertTimeout(timeout, supplier, message);
 	}
 
@@ -3434,8 +3517,8 @@ public static <T> T assertTimeout(Duration timeout, ThrowingSupplier<T> supplier
 	 * @see #assertTimeout(Duration, ThrowingSupplier, String)
 	 * @see #assertTimeoutPreemptively(Duration, Executable, Supplier)
 	 */
-	public static <T> T assertTimeout(Duration timeout, ThrowingSupplier<T> supplier,
-			Supplier<String> messageSupplier) {
+	public static <T extends @Nullable Object> T assertTimeout(Duration timeout, ThrowingSupplier<T> supplier,
+			Supplier<@Nullable String> messageSupplier) {
 		return AssertTimeout.assertTimeout(timeout, supplier, messageSupplier);
 	}
 
@@ -3475,7 +3558,7 @@ public static void assertTimeoutPreemptively(Duration timeout, Executable execut
 	 * @see #assertTimeoutPreemptively(Duration, ThrowingSupplier, Supplier)
 	 * @see #assertTimeout(Duration, Executable, String)
 	 */
-	public static void assertTimeoutPreemptively(Duration timeout, Executable executable, String message) {
+	public static void assertTimeoutPreemptively(Duration timeout, Executable executable, @Nullable String message) {
 		AssertTimeoutPreemptively.assertTimeoutPreemptively(timeout, executable, message);
 	}
 
@@ -3497,7 +3580,7 @@ public static void assertTimeoutPreemptively(Duration timeout, Executable execut
 	 * @see #assertTimeout(Duration, Executable, Supplier)
 	 */
 	public static void assertTimeoutPreemptively(Duration timeout, Executable executable,
-			Supplier<String> messageSupplier) {
+			Supplier<@Nullable String> messageSupplier) {
 		AssertTimeoutPreemptively.assertTimeoutPreemptively(timeout, executable, messageSupplier);
 	}
 
@@ -3519,7 +3602,8 @@ public static void assertTimeoutPreemptively(Duration timeout, Executable execut
 	 * @see #assertTimeoutPreemptively(Duration, ThrowingSupplier, Supplier)
 	 * @see #assertTimeout(Duration, Executable)
 	 */
-	public static <T> T assertTimeoutPreemptively(Duration timeout, ThrowingSupplier<T> supplier) {
+	public static <T extends @Nullable Object> T assertTimeoutPreemptively(Duration timeout,
+			ThrowingSupplier<T> supplier) {
 		return AssertTimeoutPreemptively.assertTimeoutPreemptively(timeout, supplier);
 	}
 
@@ -3541,7 +3625,8 @@ public static <T> T assertTimeoutPreemptively(Duration timeout, ThrowingSupplier
 	 * @see #assertTimeoutPreemptively(Duration, ThrowingSupplier, Supplier)
 	 * @see #assertTimeout(Duration, Executable, String)
 	 */
-	public static <T> T assertTimeoutPreemptively(Duration timeout, ThrowingSupplier<T> supplier, String message) {
+	public static <T extends @Nullable Object> T assertTimeoutPreemptively(Duration timeout,
+			ThrowingSupplier<T> supplier, @Nullable String message) {
 		return AssertTimeoutPreemptively.assertTimeoutPreemptively(timeout, supplier, message);
 	}
 
@@ -3564,8 +3649,8 @@ public static <T> T assertTimeoutPreemptively(Duration timeout, ThrowingSupplier
 	 * @see #assertTimeoutPreemptively(Duration, ThrowingSupplier, String)
 	 * @see #assertTimeout(Duration, Executable, Supplier)
 	 */
-	public static <T> T assertTimeoutPreemptively(Duration timeout, ThrowingSupplier<T> supplier,
-			Supplier<String> messageSupplier) {
+	public static <T extends @Nullable Object> T assertTimeoutPreemptively(Duration timeout,
+			ThrowingSupplier<T> supplier, Supplier<@Nullable String> messageSupplier) {
 		return AssertTimeoutPreemptively.assertTimeoutPreemptively(timeout, supplier, messageSupplier);
 	}
 
@@ -3593,8 +3678,9 @@ public static <T> T assertTimeoutPreemptively(Duration timeout, ThrowingSupplier
 	 * @see #assertTimeout(Duration, Executable, Supplier)
 	 */
 	@API(status = INTERNAL, since = "5.9.1")
-	public static <T, E extends Throwable> T assertTimeoutPreemptively(Duration timeout, ThrowingSupplier<T> supplier,
-			Supplier<String> messageSupplier, TimeoutFailureFactory<E> failureFactory) throws E {
+	public static <T extends @Nullable Object, E extends Throwable> T assertTimeoutPreemptively(Duration timeout,
+			ThrowingSupplier<T> supplier, Supplier<@Nullable String> messageSupplier,
+			TimeoutFailureFactory<E> failureFactory) throws E {
 		return AssertTimeoutPreemptively.assertTimeoutPreemptively(timeout, supplier, messageSupplier, failureFactory);
 	}
 
@@ -3610,7 +3696,7 @@ public static <T, E extends Throwable> T assertTimeoutPreemptively(Duration time
 	 * @since 5.8
 	 */
 	@API(status = STABLE, since = "5.10")
-	public static <T> T assertInstanceOf(Class<T> expectedType, Object actualValue) {
+	public static <T> T assertInstanceOf(Class<T> expectedType, @Nullable Object actualValue) {
 		return AssertInstanceOf.assertInstanceOf(expectedType, actualValue);
 	}
 
@@ -3626,7 +3712,8 @@ public static <T> T assertInstanceOf(Class<T> expectedType, Object actualValue)
 	 * @since 5.8
 	 */
 	@API(status = STABLE, since = "5.10")
-	public static <T> T assertInstanceOf(Class<T> expectedType, Object actualValue, String message) {
+	public static <T> T assertInstanceOf(Class<T> expectedType, @Nullable Object actualValue,
+			@Nullable String message) {
 		return AssertInstanceOf.assertInstanceOf(expectedType, actualValue, message);
 	}
 
@@ -3643,7 +3730,8 @@ public static <T> T assertInstanceOf(Class<T> expectedType, Object actualValue,
 	 * @since 5.8
 	 */
 	@API(status = STABLE, since = "5.10")
-	public static <T> T assertInstanceOf(Class<T> expectedType, Object actualValue, Supplier<String> messageSupplier) {
+	public static <T> T assertInstanceOf(Class<T> expectedType, @Nullable Object actualValue,
+			Supplier<@Nullable String> messageSupplier) {
 		return AssertInstanceOf.assertInstanceOf(expectedType, actualValue, messageSupplier);
 	}
 
@@ -3662,6 +3750,7 @@ public interface TimeoutFailureFactory<T extends Throwable> {
 		 *
 		 * @return timeout failure; never {@code null}
 		 */
-		T createTimeoutFailure(Duration timeout, Supplier<String> messageSupplier, Throwable cause, Thread testThread);
+		T createTimeoutFailure(Duration timeout, @Nullable Supplier<@Nullable String> messageSupplier,
+				@Nullable Throwable cause, @Nullable Thread testThread);
 	}
 }
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/Assumptions.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/Assumptions.java
index 6545518b4d3e..b0619ad3cc32 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/Assumptions.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/Assumptions.java
@@ -16,6 +16,7 @@
 import java.util.function.Supplier;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.function.Executable;
 import org.junit.platform.commons.util.ExceptionUtils;
 import org.junit.platform.commons.util.StringUtils;
@@ -89,7 +90,8 @@ public static void assumeTrue(BooleanSupplier assumptionSupplier) throws TestAbo
 	 * if the assumption is invalid
 	 * @throws TestAbortedException if the assumption is not {@code true}
 	 */
-	public static void assumeTrue(BooleanSupplier assumptionSupplier, String message) throws TestAbortedException {
+	public static void assumeTrue(BooleanSupplier assumptionSupplier, @Nullable String message)
+			throws TestAbortedException {
 		assumeTrue(assumptionSupplier.getAsBoolean(), message);
 	}
 
@@ -101,7 +103,8 @@ public static void assumeTrue(BooleanSupplier assumptionSupplier, String message
 	 * the {@code TestAbortedException} if the assumption is invalid
 	 * @throws TestAbortedException if the assumption is not {@code true}
 	 */
-	public static void assumeTrue(boolean assumption, Supplier<String> messageSupplier) throws TestAbortedException {
+	public static void assumeTrue(boolean assumption, Supplier<@Nullable String> messageSupplier)
+			throws TestAbortedException {
 		if (!assumption) {
 			throwAssumptionFailed(messageSupplier.get());
 		}
@@ -115,7 +118,7 @@ public static void assumeTrue(boolean assumption, Supplier<String> messageSuppli
 	 * if the assumption is invalid
 	 * @throws TestAbortedException if the assumption is not {@code true}
 	 */
-	public static void assumeTrue(boolean assumption, String message) throws TestAbortedException {
+	public static void assumeTrue(boolean assumption, @Nullable String message) throws TestAbortedException {
 		if (!assumption) {
 			throwAssumptionFailed(message);
 		}
@@ -129,7 +132,7 @@ public static void assumeTrue(boolean assumption, String message) throws TestAbo
 	 * the {@code TestAbortedException} if the assumption is invalid
 	 * @throws TestAbortedException if the assumption is not {@code true}
 	 */
-	public static void assumeTrue(BooleanSupplier assumptionSupplier, Supplier<String> messageSupplier)
+	public static void assumeTrue(BooleanSupplier assumptionSupplier, Supplier<@Nullable String> messageSupplier)
 			throws TestAbortedException {
 
 		assumeTrue(assumptionSupplier.getAsBoolean(), messageSupplier);
@@ -165,7 +168,8 @@ public static void assumeFalse(BooleanSupplier assumptionSupplier) throws TestAb
 	 * if the assumption is invalid
 	 * @throws TestAbortedException if the assumption is not {@code false}
 	 */
-	public static void assumeFalse(BooleanSupplier assumptionSupplier, String message) throws TestAbortedException {
+	public static void assumeFalse(BooleanSupplier assumptionSupplier, @Nullable String message)
+			throws TestAbortedException {
 		assumeFalse(assumptionSupplier.getAsBoolean(), message);
 	}
 
@@ -177,7 +181,8 @@ public static void assumeFalse(BooleanSupplier assumptionSupplier, String messag
 	 * the {@code TestAbortedException} if the assumption is invalid
 	 * @throws TestAbortedException if the assumption is not {@code false}
 	 */
-	public static void assumeFalse(boolean assumption, Supplier<String> messageSupplier) throws TestAbortedException {
+	public static void assumeFalse(boolean assumption, Supplier<@Nullable String> messageSupplier)
+			throws TestAbortedException {
 		if (assumption) {
 			throwAssumptionFailed(messageSupplier.get());
 		}
@@ -191,7 +196,7 @@ public static void assumeFalse(boolean assumption, Supplier<String> messageSuppl
 	 * if the assumption is invalid
 	 * @throws TestAbortedException if the assumption is not {@code false}
 	 */
-	public static void assumeFalse(boolean assumption, String message) throws TestAbortedException {
+	public static void assumeFalse(boolean assumption, @Nullable String message) throws TestAbortedException {
 		if (assumption) {
 			throwAssumptionFailed(message);
 		}
@@ -205,7 +210,7 @@ public static void assumeFalse(boolean assumption, String message) throws TestAb
 	 * the {@code TestAbortedException} if the assumption is invalid
 	 * @throws TestAbortedException if the assumption is not {@code false}
 	 */
-	public static void assumeFalse(BooleanSupplier assumptionSupplier, Supplier<String> messageSupplier)
+	public static void assumeFalse(BooleanSupplier assumptionSupplier, Supplier<@Nullable String> messageSupplier)
 			throws TestAbortedException {
 
 		assumeFalse(assumptionSupplier.getAsBoolean(), messageSupplier);
@@ -316,7 +321,7 @@ public static <V> V abort(Supplier<String> messageSupplier) {
 		throw new TestAbortedException(messageSupplier.get());
 	}
 
-	private static void throwAssumptionFailed(String message) {
+	private static void throwAssumptionFailed(@Nullable String message) {
 		throw new TestAbortedException(
 			StringUtils.isNotBlank(message) ? "Assumption failed: " + message : "Assumption failed");
 	}
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AutoClose.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AutoClose.java
index f0bbc4646cc7..8288be1e8416 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AutoClose.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/AutoClose.java
@@ -10,7 +10,7 @@
 
 package org.junit.jupiter.api;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import java.lang.annotation.Documented;
 import java.lang.annotation.ElementType;
@@ -78,7 +78,7 @@
 @Target({ ElementType.ANNOTATION_TYPE, ElementType.FIELD })
 @Retention(RetentionPolicy.RUNTIME)
 @Documented
-@API(status = EXPERIMENTAL, since = "5.11")
+@API(status = MAINTAINED, since = "5.13.3")
 public @interface AutoClose {
 
 	/**
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/ClassTemplate.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/ClassTemplate.java
index 95cf2ba436d7..03d40e9dbd11 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/ClassTemplate.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/ClassTemplate.java
@@ -66,7 +66,7 @@
 @Retention(RetentionPolicy.RUNTIME)
 @Documented
 @Inherited
-@API(status = EXPERIMENTAL, since = "5.13")
+@API(status = EXPERIMENTAL, since = "6.0")
 @Testable
 public @interface ClassTemplate {
 }
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/DisplayNameGenerator.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/DisplayNameGenerator.java
index d7714236f56e..7e4fc350c915 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/DisplayNameGenerator.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/DisplayNameGenerator.java
@@ -14,9 +14,12 @@
 import static org.apiguardian.api.API.Status.DEPRECATED;
 import static org.apiguardian.api.API.Status.EXPERIMENTAL;
 import static org.apiguardian.api.API.Status.INTERNAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
 import static org.junit.platform.commons.support.AnnotationSupport.findAnnotation;
 import static org.junit.platform.commons.support.ModifierSupport.isStatic;
+import static org.junit.platform.commons.util.KotlinReflectionUtils.getKotlinSuspendingFunctionParameterTypes;
+import static org.junit.platform.commons.util.KotlinReflectionUtils.isKotlinSuspendingFunction;
 
 import java.lang.annotation.ElementType;
 import java.lang.annotation.Retention;
@@ -29,6 +32,7 @@
 import java.util.function.Predicate;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.support.ReflectionSupport;
 import org.junit.platform.commons.util.ClassUtils;
 import org.junit.platform.commons.util.Preconditions;
@@ -128,7 +132,7 @@ default String generateDisplayNameForNestedClass(Class<?> nestedClass) {
 	 * @return the display name for the nested class; never blank
 	 * @since 5.12
 	 */
-	@API(status = EXPERIMENTAL, since = "5.12")
+	@API(status = MAINTAINED, since = "5.13.3")
 	default String generateDisplayNameForNestedClass(List<Class<?>> enclosingInstanceTypes, Class<?> nestedClass) {
 		return generateDisplayNameForNestedClass(nestedClass);
 	}
@@ -177,7 +181,7 @@ default String generateDisplayNameForMethod(Class<?> testClass, Method testMetho
 	 * @return the display name for the test; never blank
 	 * @since 5.12
 	 */
-	@API(status = EXPERIMENTAL, since = "5.12")
+	@API(status = MAINTAINED, since = "5.13.3")
 	default String generateDisplayNameForMethod(List<Class<?>> enclosingInstanceTypes, Class<?> testClass,
 			Method testMethod) {
 		return generateDisplayNameForMethod(testClass, testMethod);
@@ -195,7 +199,10 @@ default String generateDisplayNameForMethod(List<Class<?>> enclosingInstanceType
 	 */
 	static String parameterTypesAsString(Method method) {
 		Preconditions.notNull(method, "Method must not be null");
-		return '(' + ClassUtils.nullSafeToString(Class::getSimpleName, method.getParameterTypes()) + ')';
+		var parameterTypes = isKotlinSuspendingFunction(method) //
+				? getKotlinSuspendingFunctionParameterTypes(method) //
+				: method.getParameterTypes();
+		return '(' + ClassUtils.nullSafeToString(Class::getSimpleName, parameterTypes) + ')';
 	}
 
 	/**
@@ -332,7 +339,7 @@ class IndicativeSentences implements DisplayNameGenerator {
 		 */
 		@Target({ ElementType.TYPE, ElementType.METHOD })
 		@Retention(RetentionPolicy.RUNTIME)
-		@API(status = EXPERIMENTAL, since = "5.13")
+		@API(status = EXPERIMENTAL, since = "6.0")
 		public @interface SentenceFragment {
 
 			/**
@@ -381,14 +388,13 @@ public String generateDisplayNameForMethod(List<Class<?>> enclosingInstanceTypes
 		private String getSentenceBeginning(Class<?> testClass, List<Class<?>> enclosingInstanceTypes) {
 			Class<?> enclosingClass = enclosingInstanceTypes.isEmpty() ? null
 					: enclosingInstanceTypes.get(enclosingInstanceTypes.size() - 1);
-			boolean topLevelTestClass = (enclosingClass == null || isStatic(testClass));
 
 			String sentenceFragment = findAnnotation(testClass, DisplayName.class)//
 					.map(DisplayName::value)//
 					.map(String::trim)//
 					.orElseGet(() -> getSentenceFragment(testClass));
 
-			if (topLevelTestClass) {
+			if (enclosingClass == null || isStatic(testClass)) { // top-level class
 				if (sentenceFragment != null) {
 					return sentenceFragment;
 				}
@@ -496,12 +502,12 @@ private static Optional<IndicativeSentencesGeneration> findIndicativeSentencesGe
 			return findAnnotation(testClass, IndicativeSentencesGeneration.class, enclosingInstanceTypes);
 		}
 
-		private static String getSentenceFragment(AnnotatedElement element) {
+		private static @Nullable String getSentenceFragment(AnnotatedElement element) {
 			return findAnnotation(element, SentenceFragment.class) //
 					.map(SentenceFragment::value) //
 					.map(sentenceFragment -> {
-						Preconditions.notBlank(sentenceFragment, String.format(
-							"@SentenceFragment on [%s] must be declared with a non-blank value.", element));
+						Preconditions.notBlank(sentenceFragment,
+							"@SentenceFragment on [%s] must be declared with a non-blank value.".formatted(element));
 						return sentenceFragment.trim();
 					}) //
 					.orElse(null);
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/DynamicContainer.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/DynamicContainer.java
index da947b68c778..2bdf44fda25d 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/DynamicContainer.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/DynamicContainer.java
@@ -17,6 +17,7 @@
 import java.util.stream.StreamSupport;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.util.Preconditions;
 
 /**
@@ -84,7 +85,7 @@ public static DynamicContainer dynamicContainer(String displayName, Stream<? ext
 	 * @since 5.3
 	 * @see #dynamicContainer(String, Iterable)
 	 */
-	public static DynamicContainer dynamicContainer(String displayName, URI testSourceUri,
+	public static DynamicContainer dynamicContainer(String displayName, @Nullable URI testSourceUri,
 			Stream<? extends DynamicNode> dynamicNodes) {
 
 		return new DynamicContainer(displayName, testSourceUri, dynamicNodes);
@@ -92,7 +93,7 @@ public static DynamicContainer dynamicContainer(String displayName, URI testSour
 
 	private final Stream<? extends DynamicNode> children;
 
-	private DynamicContainer(String displayName, URI testSourceUri, Stream<? extends DynamicNode> children) {
+	private DynamicContainer(String displayName, @Nullable URI testSourceUri, Stream<? extends DynamicNode> children) {
 		super(displayName, testSourceUri);
 		Preconditions.notNull(children, "children must not be null");
 		this.children = children;
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/DynamicNode.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/DynamicNode.java
index 43574ee853a7..0f4d66c5b652 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/DynamicNode.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/DynamicNode.java
@@ -16,6 +16,7 @@
 import java.util.Optional;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.util.Preconditions;
 import org.junit.platform.commons.util.ToStringBuilder;
 
@@ -33,9 +34,9 @@ public abstract class DynamicNode {
 	private final String displayName;
 
 	/** Custom test source {@link URI} associated with this node; potentially {@code null}. */
-	private final URI testSourceUri;
+	private final @Nullable URI testSourceUri;
 
-	DynamicNode(String displayName, URI testSourceUri) {
+	DynamicNode(String displayName, @Nullable URI testSourceUri) {
 		this.displayName = Preconditions.notBlank(displayName, "displayName must not be null or blank");
 		this.testSourceUri = testSourceUri;
 	}
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/DynamicTest.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/DynamicTest.java
index d87ae1ab4f71..54b8fdc3a925 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/DynamicTest.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/DynamicTest.java
@@ -12,7 +12,6 @@
 
 import static java.util.Spliterator.ORDERED;
 import static java.util.Spliterators.spliteratorUnknownSize;
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
 import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import java.net.URI;
@@ -22,6 +21,7 @@
 import java.util.stream.StreamSupport;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.function.Executable;
 import org.junit.jupiter.api.function.ThrowingConsumer;
 import org.junit.platform.commons.util.Preconditions;
@@ -78,7 +78,7 @@ public static DynamicTest dynamicTest(String displayName, Executable executable)
 	 * @since 5.3
 	 * @see #stream(Iterator, Function, ThrowingConsumer)
 	 */
-	public static DynamicTest dynamicTest(String displayName, URI testSourceUri, Executable executable) {
+	public static DynamicTest dynamicTest(String displayName, @Nullable URI testSourceUri, Executable executable) {
 		return new DynamicTest(displayName, testSourceUri, executable);
 	}
 
@@ -249,7 +249,7 @@ public static <T> Stream<DynamicTest> stream(Stream<? extends Named<T>> inputStr
 	 * @see #stream(Stream)
 	 * @see NamedExecutable
 	 */
-	@API(status = EXPERIMENTAL, since = "5.11")
+	@API(status = MAINTAINED, since = "5.13.3")
 	public static <T extends Named<E>, E extends Executable> Stream<DynamicTest> stream(
 			Iterator<? extends T> iterator) {
 		Preconditions.notNull(iterator, "iterator must not be null");
@@ -279,7 +279,7 @@ public static <T extends Named<E>, E extends Executable> Stream<DynamicTest> str
 	 * @see #stream(Iterator)
 	 * @see NamedExecutable
 	 */
-	@API(status = EXPERIMENTAL, since = "5.11")
+	@API(status = MAINTAINED, since = "5.13.3")
 	public static <T extends Named<E>, E extends Executable> Stream<DynamicTest> stream(
 			Stream<? extends T> inputStream) {
 		Preconditions.notNull(inputStream, "inputStream must not be null");
@@ -290,7 +290,7 @@ public static <T extends Named<E>, E extends Executable> Stream<DynamicTest> str
 
 	private final Executable executable;
 
-	private DynamicTest(String displayName, URI testSourceUri, Executable executable) {
+	private DynamicTest(String displayName, @Nullable URI testSourceUri, Executable executable) {
 		super(displayName, testSourceUri);
 		this.executable = Preconditions.notNull(executable, "executable must not be null");
 	}
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/MethodOrderer.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/MethodOrderer.java
index e853106480f6..f1b60a0f4adf 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/MethodOrderer.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/MethodOrderer.java
@@ -11,7 +11,6 @@
 package org.junit.jupiter.api;
 
 import static java.util.Comparator.comparingInt;
-import static org.apiguardian.api.API.Status.DEPRECATED;
 import static org.apiguardian.api.API.Status.STABLE;
 
 import java.lang.reflect.Method;
@@ -126,26 +125,6 @@ default Optional<ExecutionMode> getDefaultExecutionMode() {
 		return Optional.of(ExecutionMode.SAME_THREAD);
 	}
 
-	/**
-	 * {@code MethodOrderer} that sorts methods alphanumerically based on their
-	 * names using {@link String#compareTo(String)}.
-	 *
-	 * <p>If two methods have the same name, {@code String} representations of
-	 * their formal parameter lists will be used as a fallback for comparing the
-	 * methods.
-	 *
-	 * @since 5.4
-	 * @deprecated as of JUnit Jupiter 5.7 in favor of {@link MethodOrderer.MethodName};
-	 * to be removed in 6.0
-	 */
-	@API(status = DEPRECATED, since = "5.7")
-	@Deprecated
-	class Alphanumeric extends MethodName {
-
-		public Alphanumeric() {
-		}
-	}
-
 	/**
 	 * {@code MethodOrderer} that sorts methods alphanumerically based on their
 	 * names using {@link String#compareTo(String)}.
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/Named.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/Named.java
index dfeff26354e4..2e3edf94164f 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/Named.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/Named.java
@@ -13,6 +13,7 @@
 import static org.apiguardian.api.API.Status.STABLE;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.util.Preconditions;
 
 /**
@@ -23,7 +24,7 @@
  * @since 5.8
  */
 @API(status = STABLE, since = "5.8")
-public interface Named<T> {
+public interface Named<T extends @Nullable Object> {
 
 	/**
 	 * Factory method for creating an instance of {@code Named} based on a
@@ -37,10 +38,10 @@ public interface Named<T> {
 	 * @return an instance of {@code Named}; never {@code null}
 	 * @see #named(String, java.lang.Object)
 	 */
-	static <T> Named<T> of(String name, T payload) {
+	static <T extends @Nullable Object> Named<T> of(String name, T payload) {
 		Preconditions.notBlank(name, "name must not be null or blank");
 
-		return new Named<T>() {
+		return new Named<>() {
 			@Override
 			public String getName() {
 				return name;
@@ -73,7 +74,7 @@ public String toString() {
 	 * @param <T> the type of the payload
 	 * @return an instance of {@code Named}; never {@code null}
 	 */
-	static <T> Named<T> named(String name, T payload) {
+	static <T extends @Nullable Object> Named<T> named(String name, T payload) {
 		return of(name, payload);
 	}
 
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/NamedExecutable.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/NamedExecutable.java
index c11a631885f3..1014960d4cf9 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/NamedExecutable.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/NamedExecutable.java
@@ -10,7 +10,7 @@
 
 package org.junit.jupiter.api;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import java.util.Iterator;
 import java.util.stream.Stream;
@@ -34,7 +34,7 @@
  * @see DynamicTest#stream(Iterator)
  */
 @FunctionalInterface
-@API(status = EXPERIMENTAL, since = "5.11")
+@API(status = MAINTAINED, since = "5.13.3")
 public interface NamedExecutable extends Named<Executable>, Executable {
 	@Override
 	default String getName() {
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/RandomOrdererUtils.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/RandomOrdererUtils.java
index de221d3d5d61..16ca5250e539 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/RandomOrdererUtils.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/RandomOrdererUtils.java
@@ -36,7 +36,7 @@ private static Optional<Long> getCustomSeed(Function<String, Optional<String>> c
 			Logger logger) {
 		return configurationParameterLookup.apply(RANDOM_SEED_PROPERTY_NAME).map(configurationParameter -> {
 			try {
-				logger.config(() -> String.format("Using custom seed for configuration parameter [%s] with value [%s].",
+				logger.config(() -> "Using custom seed for configuration parameter [%s] with value [%s].".formatted(
 					RANDOM_SEED_PROPERTY_NAME, configurationParameter));
 				return Long.valueOf(configurationParameter);
 			}
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/RepeatedTest.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/RepeatedTest.java
index 15c991357c4e..aa04813cab97 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/RepeatedTest.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/RepeatedTest.java
@@ -10,7 +10,7 @@
 
 package org.junit.jupiter.api;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
 
 import java.lang.annotation.Documented;
@@ -191,7 +191,7 @@
 	 * @return the failure threshold; must be greater than zero and less than the
 	 * total number of repetitions
 	 */
-	@API(status = EXPERIMENTAL, since = "5.10")
+	@API(status = MAINTAINED, since = "5.13.3")
 	int failureThreshold() default Integer.MAX_VALUE;
 
 }
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/RepetitionInfo.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/RepetitionInfo.java
index a24dce3e3d6c..87a383f31ce5 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/RepetitionInfo.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/RepetitionInfo.java
@@ -10,7 +10,7 @@
 
 package org.junit.jupiter.api;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
 
 import org.apiguardian.api.API;
@@ -58,7 +58,7 @@ public interface RepetitionInfo {
 	 * @since 5.10
 	 * @see #getFailureThreshold()
 	 */
-	@API(status = EXPERIMENTAL, since = "5.10")
+	@API(status = MAINTAINED, since = "5.13.3")
 	int getFailureCount();
 
 	/**
@@ -68,7 +68,7 @@ public interface RepetitionInfo {
 	 * @since 5.10
 	 * @see RepeatedTest#failureThreshold()
 	 */
-	@API(status = EXPERIMENTAL, since = "5.10")
+	@API(status = MAINTAINED, since = "5.13.3")
 	int getFailureThreshold();
 
 }
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/TestReporter.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/TestReporter.java
index 7805ab93ab29..99f7a7537065 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/TestReporter.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/TestReporter.java
@@ -11,7 +11,7 @@
 package org.junit.jupiter.api;
 
 import static java.nio.file.StandardCopyOption.REPLACE_EXISTING;
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
 
 import java.io.IOException;
@@ -98,7 +98,7 @@ default void publishEntry(String value) {
 	 * {@link MediaType#APPLICATION_OCTET_STREAM} if unknown
 	 * @since 5.12
 	 */
-	@API(status = EXPERIMENTAL, since = "5.12")
+	@API(status = MAINTAINED, since = "5.13.3")
 	default void publishFile(Path file, MediaType mediaType) {
 		Preconditions.condition(Files.exists(file), () -> "file must exist: " + file);
 		Preconditions.condition(Files.isRegularFile(file), () -> "file must be a regular file: " + file);
@@ -115,7 +115,7 @@ default void publishFile(Path file, MediaType mediaType) {
 	 * @param directory the file to be attached; never {@code null} or blank
 	 * @since 5.12
 	 */
-	@API(status = EXPERIMENTAL, since = "5.12")
+	@API(status = MAINTAINED, since = "5.13.3")
 	default void publishDirectory(Path directory) {
 		Preconditions.condition(Files.exists(directory), () -> "directory must exist: " + directory);
 		Preconditions.condition(Files.isDirectory(directory), () -> "directory must be a directory: " + directory);
@@ -153,7 +153,7 @@ default void publishDirectory(Path directory) {
 	 * @param action the action to be executed to write the file; never {@code null}
 	 * @since 5.12
 	 */
-	@API(status = EXPERIMENTAL, since = "5.12")
+	@API(status = MAINTAINED, since = "5.13.3")
 	default void publishFile(String name, MediaType mediaType, ThrowingConsumer<Path> action) {
 		throw new UnsupportedOperationException();
 	}
@@ -171,7 +171,7 @@ default void publishFile(String name, MediaType mediaType, ThrowingConsumer<Path
 	 * @param action the action to be executed to write the file; never {@code null}
 	 * @since 5.12
 	 */
-	@API(status = EXPERIMENTAL, since = "5.12")
+	@API(status = MAINTAINED, since = "5.13.3")
 	default void publishDirectory(String name, ThrowingConsumer<Path> action) {
 		throw new UnsupportedOperationException();
 	}
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/Timeout.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/Timeout.java
index f7081d629cda..f8338fe9a26e 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/Timeout.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/Timeout.java
@@ -10,7 +10,7 @@
 
 package org.junit.jupiter.api;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
 
 import java.lang.annotation.Documented;
@@ -329,7 +329,7 @@
 	 *
 	 * @since 5.9
 	 */
-	@API(status = EXPERIMENTAL, since = "5.9")
+	@API(status = MAINTAINED, since = "5.13.3")
 	String DEFAULT_TIMEOUT_THREAD_MODE_PROPERTY_NAME = "junit.jupiter.execution.timeout.thread.mode.default";
 
 	/**
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/AbstractJreCondition.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/AbstractJreCondition.java
index 1eb301b2d894..84811acee7d3 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/AbstractJreCondition.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/AbstractJreCondition.java
@@ -33,21 +33,20 @@ abstract class AbstractJreCondition<A extends Annotation> extends BooleanExecuti
 	static final String DISABLED_ON_CURRENT_JRE = //
 		"Disabled on JRE version: " + System.getProperty("java.version");
 
-	private final String annotationName;
-
 	AbstractJreCondition(Class<A> annotationType, Function<A, String> customDisabledReason) {
 		super(annotationType, ENABLED_ON_CURRENT_JRE, DISABLED_ON_CURRENT_JRE, customDisabledReason);
-		this.annotationName = annotationType.getSimpleName();
 	}
 
 	protected final IntStream validatedVersions(JRE[] jres, int[] versions) {
+		String annotationName = super.annotationType.getSimpleName();
+
 		Preconditions.condition(jres.length > 0 || versions.length > 0,
-			() -> "You must declare at least one JRE or version in @" + this.annotationName);
+			() -> "You must declare at least one JRE or version in @" + annotationName);
 
 		Preconditions.condition(Arrays.stream(jres).noneMatch(isEqual(JRE.UNDEFINED)),
-			() -> "JRE.UNDEFINED is not supported in @" + this.annotationName);
+			() -> "JRE.UNDEFINED is not supported in @" + annotationName);
 		Arrays.stream(versions).min().ifPresent(version -> Preconditions.condition(version >= JRE.MINIMUM_VERSION,
-			() -> String.format("Version [%d] in @%s must be greater than or equal to %d", version, this.annotationName,
+			() -> "Version [%d] in @%s must be greater than or equal to %d".formatted(version, annotationName,
 				JRE.MINIMUM_VERSION)));
 
 		return IntStream.concat(//
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/AbstractJreRangeCondition.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/AbstractJreRangeCondition.java
index 7bc7d8a0b117..342d25e9a266 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/AbstractJreRangeCondition.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/AbstractJreRangeCondition.java
@@ -26,53 +26,55 @@
  */
 abstract class AbstractJreRangeCondition<A extends Annotation> extends BooleanExecutionCondition<A> {
 
-	private final String annotationName;
+	private static final JRE DEFAULT_MINIMUM_JRE = JRE.JAVA_17;
+	private static final JRE DEFAULT_MAXIMUM_JRE = JRE.OTHER;
 
 	AbstractJreRangeCondition(Class<A> annotationType, Function<A, String> customDisabledReason) {
 		super(annotationType, ENABLED_ON_CURRENT_JRE, DISABLED_ON_CURRENT_JRE, customDisabledReason);
-		this.annotationName = annotationType.getSimpleName();
 	}
 
 	protected final boolean isCurrentVersionWithinRange(JRE minJre, JRE maxJre, int minVersion, int maxVersion) {
+		String annotationName = super.annotationType.getSimpleName();
+
 		boolean minJreSet = minJre != JRE.UNDEFINED;
 		boolean maxJreSet = maxJre != JRE.UNDEFINED;
 		boolean minVersionSet = minVersion != JRE.UNDEFINED_VERSION;
 		boolean maxVersionSet = maxVersion != JRE.UNDEFINED_VERSION;
 
 		// Users must choose between JRE enum constants and version numbers.
-		Preconditions.condition(!minJreSet || !minVersionSet, () -> String.format(
-			"@%s's minimum value must be configured with either a JRE enum constant or numeric version, but not both",
-			this.annotationName));
-		Preconditions.condition(!maxJreSet || !maxVersionSet, () -> String.format(
-			"@%s's maximum value must be configured with either a JRE enum constant or numeric version, but not both",
-			this.annotationName));
+		Preconditions.condition(!minJreSet || !minVersionSet,
+			() -> "@%s's minimum value must be configured with either a JRE enum constant or numeric version, but not both".formatted(
+				annotationName));
+		Preconditions.condition(!maxJreSet || !maxVersionSet,
+			() -> "@%s's maximum value must be configured with either a JRE enum constant or numeric version, but not both".formatted(
+				annotationName));
 
 		// Users must supply valid values for minVersion and maxVersion.
 		Preconditions.condition(!minVersionSet || (minVersion >= JRE.MINIMUM_VERSION),
-			() -> String.format("@%s's minVersion [%d] must be greater than or equal to %d", this.annotationName,
-				minVersion, JRE.MINIMUM_VERSION));
+			() -> "@%s's minVersion [%d] must be greater than or equal to %d".formatted(annotationName, minVersion,
+				JRE.MINIMUM_VERSION));
 		Preconditions.condition(!maxVersionSet || (maxVersion >= JRE.MINIMUM_VERSION),
-			() -> String.format("@%s's maxVersion [%d] must be greater than or equal to %d", this.annotationName,
-				maxVersion, JRE.MINIMUM_VERSION));
+			() -> "@%s's maxVersion [%d] must be greater than or equal to %d".formatted(annotationName, maxVersion,
+				JRE.MINIMUM_VERSION));
 
 		// Now that we have checked the basic preconditions, we need to ensure that we are
 		// using valid JRE enum constants.
 		if (!minJreSet) {
-			minJre = JRE.JAVA_8;
+			minJre = DEFAULT_MINIMUM_JRE;
 		}
 		if (!maxJreSet) {
-			maxJre = JRE.OTHER;
+			maxJre = DEFAULT_MAXIMUM_JRE;
 		}
 
 		int min = (minVersionSet ? minVersion : minJre.version());
 		int max = (maxVersionSet ? maxVersion : maxJre.version());
 
 		// Finally, we need to validate the effective minimum and maximum values.
-		Preconditions.condition((min != JRE.MINIMUM_VERSION || max != Integer.MAX_VALUE),
-			() -> "You must declare a non-default value for the minimum or maximum value in @" + this.annotationName);
+		Preconditions.condition((min != DEFAULT_MINIMUM_JRE.version() || max != DEFAULT_MAXIMUM_JRE.version()),
+			() -> "You must declare a non-default value for the minimum or maximum value in @" + annotationName);
 		Preconditions.condition(min <= max,
-			() -> String.format("@%s's minimum value [%d] must be less than or equal to its maximum value [%d]",
-				this.annotationName, min, max));
+			() -> "@%s's minimum value [%d] must be less than or equal to its maximum value [%d]".formatted(
+				annotationName, min, max));
 
 		return JRE.isCurrentVersionWithinRange(min, max);
 	}
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/AbstractOsBasedExecutionCondition.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/AbstractOsBasedExecutionCondition.java
index c4ae691aee63..f581052c56ff 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/AbstractOsBasedExecutionCondition.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/AbstractOsBasedExecutionCondition.java
@@ -50,7 +50,7 @@ String createReason(boolean enabled, boolean osSpecified, boolean archSpecified)
 				.append(osSpecified ? " on operating system: " : " on architecture: ");
 
 		if (osSpecified && archSpecified) {
-			reason.append(String.format("%s (%s)", CURRENT_OS, CURRENT_ARCHITECTURE));
+			reason.append("%s (%s)".formatted(CURRENT_OS, CURRENT_ARCHITECTURE));
 		}
 		else if (osSpecified) {
 			reason.append(CURRENT_OS);
@@ -63,7 +63,7 @@ else if (osSpecified) {
 	}
 
 	private ConditionEvaluationResult enabledByDefault() {
-		String reason = String.format("@%s is not present", this.annotationType.getSimpleName());
+		String reason = "@%s is not present".formatted(this.annotationType.getSimpleName());
 		return enabled(reason);
 	}
 
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/AbstractRepeatableAnnotationCondition.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/AbstractRepeatableAnnotationCondition.java
index 66cc3d2e61c6..feb94e25f4b6 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/AbstractRepeatableAnnotationCondition.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/AbstractRepeatableAnnotationCondition.java
@@ -10,7 +10,6 @@
 
 package org.junit.jupiter.api.condition;
 
-import static java.lang.String.format;
 import static org.junit.platform.commons.support.AnnotationSupport.findRepeatableAnnotations;
 
 import java.lang.annotation.Annotation;
@@ -66,7 +65,7 @@ public final ConditionEvaluationResult evaluateExecutionCondition(ExtensionConte
 	protected abstract ConditionEvaluationResult getNoDisabledConditionsEncounteredResult();
 
 	private void logResult(A annotation, AnnotatedElement annotatedElement, ConditionEvaluationResult result) {
-		logger.trace(() -> format("Evaluation of %s on [%s] resulted in: %s", annotation, annotatedElement, result));
+		logger.trace(() -> "Evaluation of %s on [%s] resulted in: %s".formatted(annotation, annotatedElement, result));
 	}
 
 }
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/BooleanExecutionCondition.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/BooleanExecutionCondition.java
index 0bc4281b9618..ffb9a9d03636 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/BooleanExecutionCondition.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/BooleanExecutionCondition.java
@@ -48,7 +48,7 @@ public ConditionEvaluationResult evaluateExecutionCondition(ExtensionContext con
 	abstract boolean isEnabled(A annotation);
 
 	private ConditionEvaluationResult enabledByDefault() {
-		String reason = String.format("@%s is not present", this.annotationType.getSimpleName());
+		String reason = "@%s is not present".formatted(this.annotationType.getSimpleName());
 		return enabled(reason);
 	}
 
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/DisabledForJreRange.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/DisabledForJreRange.java
index f2b077a0b2f3..7feffabff6fa 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/DisabledForJreRange.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/DisabledForJreRange.java
@@ -10,7 +10,7 @@
 
 package org.junit.jupiter.api.condition;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
 
 import java.lang.annotation.Documented;
@@ -96,7 +96,7 @@
 	 * {@link #minVersion() minVersion} instead.
 	 *
 	 * <p>Defaults to {@link JRE#UNDEFINED UNDEFINED}, which will be interpreted
-	 * as {@link JRE#JAVA_8 JAVA_8} if the {@link #minVersion() minVersion} is
+	 * as {@link JRE#JAVA_17 JAVA_17} if the {@link #minVersion() minVersion} is
 	 * not set.
 	 *
 	 * @see JRE
@@ -138,7 +138,7 @@
 	 * @see JRE#version()
 	 * @see Runtime.Version#feature()
 	 */
-	@API(status = EXPERIMENTAL, since = "5.12")
+	@API(status = MAINTAINED, since = "5.13.3")
 	int minVersion() default -1;
 
 	/**
@@ -157,7 +157,7 @@
 	 * @see JRE#version()
 	 * @see Runtime.Version#feature()
 	 */
-	@API(status = EXPERIMENTAL, since = "5.12")
+	@API(status = MAINTAINED, since = "5.13.3")
 	int maxVersion() default -1;
 
 	/**
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/DisabledIfEnvironmentVariableCondition.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/DisabledIfEnvironmentVariableCondition.java
index cac8fe5300c4..968eca1a4e28 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/DisabledIfEnvironmentVariableCondition.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/DisabledIfEnvironmentVariableCondition.java
@@ -10,10 +10,10 @@
 
 package org.junit.jupiter.api.condition;
 
-import static java.lang.String.format;
 import static org.junit.jupiter.api.extension.ConditionEvaluationResult.disabled;
 import static org.junit.jupiter.api.extension.ConditionEvaluationResult.enabled;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.extension.ConditionEvaluationResult;
 import org.junit.jupiter.api.extension.ExecutionCondition;
 import org.junit.platform.commons.util.Preconditions;
@@ -49,16 +49,16 @@ protected ConditionEvaluationResult evaluate(DisabledIfEnvironmentVariable annot
 
 		// Nothing to match against?
 		if (actual == null) {
-			return enabled(format("Environment variable [%s] does not exist", name));
+			return enabled("Environment variable [%s] does not exist".formatted(name));
 		}
 
 		if (actual.matches(regex)) {
-			return disabled(format("Environment variable [%s] with value [%s] matches regular expression [%s]", name,
+			return disabled("Environment variable [%s] with value [%s] matches regular expression [%s]".formatted(name,
 				actual, regex), annotation.disabledReason());
 		}
 		// else
-		return enabled(format("Environment variable [%s] with value [%s] does not match regular expression [%s]", name,
-			actual, regex));
+		return enabled("Environment variable [%s] with value [%s] does not match regular expression [%s]".formatted(
+			name, actual, regex));
 	}
 
 	/**
@@ -68,7 +68,7 @@ protected ConditionEvaluationResult evaluate(DisabledIfEnvironmentVariable annot
 	 * {@link System#getenv(String)}. Can be overridden in a subclass for
 	 * testing purposes.
 	 */
-	protected String getEnvironmentVariable(String name) {
+	protected @Nullable String getEnvironmentVariable(String name) {
 		return System.getenv(name);
 	}
 
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/DisabledIfSystemPropertyCondition.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/DisabledIfSystemPropertyCondition.java
index 45abb83f8cea..3c260a47c778 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/DisabledIfSystemPropertyCondition.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/DisabledIfSystemPropertyCondition.java
@@ -10,7 +10,6 @@
 
 package org.junit.jupiter.api.condition;
 
-import static java.lang.String.format;
 import static org.junit.jupiter.api.extension.ConditionEvaluationResult.disabled;
 import static org.junit.jupiter.api.extension.ConditionEvaluationResult.enabled;
 
@@ -48,17 +47,17 @@ protected ConditionEvaluationResult evaluate(DisabledIfSystemProperty annotation
 
 		// Nothing to match against?
 		if (actual == null) {
-			return enabled(format("System property [%s] does not exist", name));
+			return enabled("System property [%s] does not exist".formatted(name));
 		}
 
 		if (actual.matches(regex)) {
 			return disabled(
-				format("System property [%s] with value [%s] matches regular expression [%s]", name, actual, regex),
+				"System property [%s] with value [%s] matches regular expression [%s]".formatted(name, actual, regex),
 				annotation.disabledReason());
 		}
 		// else
-		return enabled(
-			format("System property [%s] with value [%s] does not match regular expression [%s]", name, actual, regex));
+		return enabled("System property [%s] with value [%s] does not match regular expression [%s]".formatted(name,
+			actual, regex));
 	}
 
 }
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/DisabledOnJre.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/DisabledOnJre.java
index 28281d086430..358c2e33c9b7 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/DisabledOnJre.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/DisabledOnJre.java
@@ -10,7 +10,7 @@
 
 package org.junit.jupiter.api.condition;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
 
 import java.lang.annotation.Documented;
@@ -110,7 +110,7 @@
 	 * @see JRE#version()
 	 * @see Runtime.Version#feature()
 	 */
-	@API(status = EXPERIMENTAL, since = "5.12")
+	@API(status = MAINTAINED, since = "5.13.3")
 	int[] versions() default {};
 
 	/**
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/EnabledForJreRange.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/EnabledForJreRange.java
index d60bae33d75d..a161df108e84 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/EnabledForJreRange.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/EnabledForJreRange.java
@@ -10,7 +10,7 @@
 
 package org.junit.jupiter.api.condition;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
 
 import java.lang.annotation.Documented;
@@ -96,7 +96,7 @@
 	 * {@link #minVersion() minVersion} instead.
 	 *
 	 * <p>Defaults to {@link JRE#UNDEFINED UNDEFINED}, which will be interpreted
-	 * as {@link JRE#JAVA_8 JAVA_8} if the {@link #minVersion() minVersion} is
+	 * as {@link JRE#JAVA_17 JAVA_17} if the {@link #minVersion() minVersion} is
 	 * not set.
 	 *
 	 * @see JRE
@@ -138,7 +138,7 @@
 	 * @see JRE#version()
 	 * @see Runtime.Version#feature()
 	 */
-	@API(status = EXPERIMENTAL, since = "5.12")
+	@API(status = MAINTAINED, since = "5.13.3")
 	int minVersion() default -1;
 
 	/**
@@ -157,7 +157,7 @@
 	 * @see JRE#version()
 	 * @see Runtime.Version#feature()
 	 */
-	@API(status = EXPERIMENTAL, since = "5.12")
+	@API(status = MAINTAINED, since = "5.13.3")
 	int maxVersion() default -1;
 
 	/**
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/EnabledIfEnvironmentVariableCondition.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/EnabledIfEnvironmentVariableCondition.java
index 050206f5559f..1885aa9c8a39 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/EnabledIfEnvironmentVariableCondition.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/EnabledIfEnvironmentVariableCondition.java
@@ -10,10 +10,10 @@
 
 package org.junit.jupiter.api.condition;
 
-import static java.lang.String.format;
 import static org.junit.jupiter.api.extension.ConditionEvaluationResult.disabled;
 import static org.junit.jupiter.api.extension.ConditionEvaluationResult.enabled;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.extension.ConditionEvaluationResult;
 import org.junit.jupiter.api.extension.ExecutionCondition;
 import org.junit.platform.commons.util.Preconditions;
@@ -50,14 +50,14 @@ protected ConditionEvaluationResult evaluate(EnabledIfEnvironmentVariable annota
 
 		// Nothing to match against?
 		if (actual == null) {
-			return disabled(format("Environment variable [%s] does not exist", name), annotation.disabledReason());
+			return disabled("Environment variable [%s] does not exist".formatted(name), annotation.disabledReason());
 		}
 		if (actual.matches(regex)) {
-			return enabled(format("Environment variable [%s] with value [%s] matches regular expression [%s]", name,
+			return enabled("Environment variable [%s] with value [%s] matches regular expression [%s]".formatted(name,
 				actual, regex));
 		}
-		return disabled(format("Environment variable [%s] with value [%s] does not match regular expression [%s]", name,
-			actual, regex), annotation.disabledReason());
+		return disabled("Environment variable [%s] with value [%s] does not match regular expression [%s]".formatted(
+			name, actual, regex), annotation.disabledReason());
 	}
 
 	/**
@@ -67,7 +67,7 @@ protected ConditionEvaluationResult evaluate(EnabledIfEnvironmentVariable annota
 	 * {@link System#getenv(String)}. Can be overridden in a subclass for
 	 * testing purposes.
 	 */
-	protected String getEnvironmentVariable(String name) {
+	protected @Nullable String getEnvironmentVariable(String name) {
 		return System.getenv(name);
 	}
 
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/EnabledIfSystemPropertyCondition.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/EnabledIfSystemPropertyCondition.java
index 00ce9a4c4c1f..c3baab3768f5 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/EnabledIfSystemPropertyCondition.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/EnabledIfSystemPropertyCondition.java
@@ -10,7 +10,6 @@
 
 package org.junit.jupiter.api.condition;
 
-import static java.lang.String.format;
 import static org.junit.jupiter.api.extension.ConditionEvaluationResult.disabled;
 import static org.junit.jupiter.api.extension.ConditionEvaluationResult.enabled;
 
@@ -49,15 +48,14 @@ protected ConditionEvaluationResult evaluate(EnabledIfSystemProperty annotation)
 
 		// Nothing to match against?
 		if (actual == null) {
-			return disabled(format("System property [%s] does not exist", name), annotation.disabledReason());
+			return disabled("System property [%s] does not exist".formatted(name), annotation.disabledReason());
 		}
 		if (actual.matches(regex)) {
 			return enabled(
-				format("System property [%s] with value [%s] matches regular expression [%s]", name, actual, regex));
+				"System property [%s] with value [%s] matches regular expression [%s]".formatted(name, actual, regex));
 		}
-		return disabled(
-			format("System property [%s] with value [%s] does not match regular expression [%s]", name, actual, regex),
-			annotation.disabledReason());
+		return disabled("System property [%s] with value [%s] does not match regular expression [%s]".formatted(name,
+			actual, regex), annotation.disabledReason());
 	}
 
 }
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/EnabledOnJre.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/EnabledOnJre.java
index 5671e8c2bc51..c92938fcbd57 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/EnabledOnJre.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/EnabledOnJre.java
@@ -10,7 +10,7 @@
 
 package org.junit.jupiter.api.condition;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
 
 import java.lang.annotation.Documented;
@@ -110,7 +110,7 @@
 	 * @see JRE#version()
 	 * @see Runtime.Version#feature()
 	 */
-	@API(status = EXPERIMENTAL, since = "5.12")
+	@API(status = MAINTAINED, since = "5.13.3")
 	int[] versions() default {};
 
 	/**
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/MethodBasedCondition.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/MethodBasedCondition.java
index 48088225cf01..157a75dadd57 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/MethodBasedCondition.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/MethodBasedCondition.java
@@ -10,7 +10,6 @@
 
 package org.junit.jupiter.api.condition;
 
-import static java.lang.String.format;
 import static org.junit.jupiter.api.extension.ConditionEvaluationResult.disabled;
 import static org.junit.jupiter.api.extension.ConditionEvaluationResult.enabled;
 import static org.junit.platform.commons.support.AnnotationSupport.findAnnotation;
@@ -21,6 +20,7 @@
 import java.util.function.Function;
 import java.util.function.Supplier;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.extension.ConditionEvaluationResult;
 import org.junit.jupiter.api.extension.ExecutionCondition;
 import org.junit.jupiter.api.extension.ExtensionContext;
@@ -68,8 +68,8 @@ Method getConditionMethod(String fullyQualifiedMethodName, ExtensionContext cont
 		String className = methodParts[0];
 		String methodName = methodParts[1];
 		ClassLoader classLoader = ClassLoaderUtils.getClassLoader(testClass);
-		Class<?> clazz = ReflectionSupport.tryToLoadClass(className, classLoader).getOrThrow(
-			cause -> new JUnitException(format("Could not load class [%s]", className), cause));
+		Class<?> clazz = ReflectionSupport.tryToLoadClass(className, classLoader).getNonNullOrThrow(
+			cause -> new JUnitException("Could not load class [%s]".formatted(className), cause));
 		return findMethod(clazz, methodName);
 	}
 
@@ -80,11 +80,16 @@ private Method findMethod(Class<?> clazz, String methodName) {
 
 	private boolean invokeConditionMethod(Method method, ExtensionContext context) {
 		Preconditions.condition(method.getReturnType() == boolean.class,
-			() -> format("Method [%s] must return a boolean", method));
+			() -> "Method [%s] must return a boolean".formatted(method));
 		Preconditions.condition(acceptsExtensionContextOrNoArguments(method),
-			() -> format("Method [%s] must accept either an ExtensionContext or no arguments", method));
+			() -> "Method [%s] must accept either an ExtensionContext or no arguments".formatted(method));
 
 		Object testInstance = context.getTestInstance().orElse(null);
+		return invokeMethod(method, context, testInstance);
+	}
+
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
+	private static boolean invokeMethod(Method method, ExtensionContext context, @Nullable Object testInstance) {
 		if (method.getParameterCount() == 0) {
 			return (boolean) ReflectionSupport.invokeMethod(method, testInstance);
 		}
@@ -97,7 +102,7 @@ private boolean acceptsExtensionContextOrNoArguments(Method method) {
 	}
 
 	private ConditionEvaluationResult buildConditionEvaluationResult(boolean methodResult, A annotation) {
-		Supplier<String> defaultReason = () -> format("@%s(\"%s\") evaluated to %s",
+		Supplier<String> defaultReason = () -> "@%s(\"%s\") evaluated to %s".formatted(
 			this.annotationType.getSimpleName(), this.methodName.apply(annotation), methodResult);
 		if (isEnabled(methodResult)) {
 			return enabled(defaultReason.get());
@@ -109,7 +114,7 @@ private ConditionEvaluationResult buildConditionEvaluationResult(boolean methodR
 	protected abstract boolean isEnabled(boolean methodResult);
 
 	private ConditionEvaluationResult enabledByDefault() {
-		return enabled(format("@%s is not present", this.annotationType.getSimpleName()));
+		return enabled("@%s is not present".formatted(this.annotationType.getSimpleName()));
 	}
 
 }
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/OS.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/OS.java
index 49878580bd66..0c7ab8be1bc6 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/OS.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/OS.java
@@ -15,6 +15,7 @@
 import java.util.Locale;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.logging.Logger;
 import org.junit.platform.commons.logging.LoggerFactory;
 import org.junit.platform.commons.util.StringUtils;
@@ -94,23 +95,23 @@ public enum OS {
 
 	private static final Logger logger = LoggerFactory.getLogger(OS.class);
 
-	private static final OS CURRENT_OS = determineCurrentOs();
+	private static final @Nullable OS CURRENT_OS = determineCurrentOs();
 
 	/**
-	 * Get the current operating system.
+	 * {@return the current operating system, if known; otherwise, {@code null}}
 	 *
 	 * @since 5.9
 	 */
 	@API(status = STABLE, since = "5.10")
-	public static OS current() {
+	public static @Nullable OS current() {
 		return CURRENT_OS;
 	}
 
-	private static OS determineCurrentOs() {
+	private static @Nullable OS determineCurrentOs() {
 		return parse(System.getProperty("os.name"));
 	}
 
-	static OS parse(String osName) {
+	static @Nullable OS parse(String osName) {
 		if (StringUtils.isBlank(osName)) {
 			logger.debug(
 				() -> "JVM system property 'os.name' is undefined. It is therefore not possible to detect the current OS.");
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/package-info.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/package-info.java
index 14d1f7fb2a80..77ddff4c5100 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/package-info.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/package-info.java
@@ -2,4 +2,7 @@
  * Annotation-based conditions for enabling or disabling tests in JUnit Jupiter.
  */
 
+@NullMarked
 package org.junit.jupiter.api.condition;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/AfterClassTemplateInvocationCallback.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/AfterClassTemplateInvocationCallback.java
index 1a278418b2ef..103e33b51a20 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/AfterClassTemplateInvocationCallback.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/AfterClassTemplateInvocationCallback.java
@@ -60,7 +60,7 @@
  * @see AfterTestExecutionCallback
  */
 @FunctionalInterface
-@API(status = EXPERIMENTAL, since = "5.13")
+@API(status = EXPERIMENTAL, since = "6.0")
 public interface AfterClassTemplateInvocationCallback extends Extension {
 
 	/**
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/AnnotatedElementContext.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/AnnotatedElementContext.java
index 19ad328fb7a4..27d8a48146b9 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/AnnotatedElementContext.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/AnnotatedElementContext.java
@@ -10,7 +10,7 @@
 
 package org.junit.jupiter.api.extension;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import java.lang.annotation.Annotation;
 import java.lang.reflect.AnnotatedElement;
@@ -33,7 +33,7 @@
  *
  * @since 5.10
  */
-@API(status = EXPERIMENTAL, since = "5.10")
+@API(status = MAINTAINED, since = "5.13.3")
 public interface AnnotatedElementContext {
 
 	/**
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/BeforeClassTemplateInvocationCallback.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/BeforeClassTemplateInvocationCallback.java
index e5c3b97bea72..f4e4eeb31c1d 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/BeforeClassTemplateInvocationCallback.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/BeforeClassTemplateInvocationCallback.java
@@ -60,7 +60,7 @@
  * @see AfterTestExecutionCallback
  */
 @FunctionalInterface
-@API(status = EXPERIMENTAL, since = "5.13")
+@API(status = EXPERIMENTAL, since = "6.0")
 public interface BeforeClassTemplateInvocationCallback extends Extension {
 
 	/**
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ClassTemplateInvocationContext.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ClassTemplateInvocationContext.java
index 00bb30b2ed61..39ef4268fede 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ClassTemplateInvocationContext.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ClassTemplateInvocationContext.java
@@ -29,7 +29,7 @@
  * @see ClassTemplate
  * @see ClassTemplateInvocationContextProvider
  */
-@API(status = EXPERIMENTAL, since = "5.13")
+@API(status = EXPERIMENTAL, since = "6.0")
 public interface ClassTemplateInvocationContext {
 
 	/**
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ClassTemplateInvocationContextProvider.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ClassTemplateInvocationContextProvider.java
index 0af499b57f14..eb1578289457 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ClassTemplateInvocationContextProvider.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ClassTemplateInvocationContextProvider.java
@@ -58,7 +58,7 @@
  * @see ClassTemplate
  * @see ClassTemplateInvocationContext
  */
-@API(status = EXPERIMENTAL, since = "5.13")
+@API(status = EXPERIMENTAL, since = "6.0")
 public interface ClassTemplateInvocationContextProvider extends Extension {
 
 	/**
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ConditionEvaluationResult.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ConditionEvaluationResult.java
index 316d5961813c..5b683e43f32b 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ConditionEvaluationResult.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ConditionEvaluationResult.java
@@ -60,7 +60,7 @@ public static ConditionEvaluationResult disabled(String reason, String customRea
 		if (StringUtils.isBlank(customReason)) {
 			return disabled(reason);
 		}
-		return disabled(String.format("%s ==> %s", reason, customReason));
+		return disabled("%s ==> %s".formatted(reason, customReason));
 	}
 
 	private final boolean enabled;
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ExecutableInvoker.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ExecutableInvoker.java
index 37645f08e1ee..6defd08748ac 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ExecutableInvoker.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ExecutableInvoker.java
@@ -16,6 +16,7 @@
 import java.lang.reflect.Method;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 
 /**
  * {@code ExecutableInvoker} allows invoking methods and constructors
@@ -33,7 +34,7 @@ public interface ExecutableInvoker {
 	 * @param method the method to invoke and resolve parameters for
 	 * @see #invoke(Method, Object)
 	 */
-	default Object invoke(Method method) {
+	default @Nullable Object invoke(Method method) {
 		return invoke(method, null);
 	}
 
@@ -44,7 +45,8 @@ default Object invoke(Method method) {
 	 * @param target the target on which the executable will be invoked;
 	 * can be {@code null} for {@code static} methods
 	 */
-	Object invoke(Method method, Object target);
+	@Nullable
+	Object invoke(Method method, @Nullable Object target);
 
 	/**
 	 * Invoke the supplied top-level constructor with dynamic parameter resolution.
@@ -67,6 +69,6 @@ default <T> T invoke(Constructor<T> constructor) {
 	 * to the constructor; must be {@code null} for top-level classes
 	 * or {@code static} nested classes
 	 */
-	<T> T invoke(Constructor<T> constructor, Object outerInstance);
+	<T> T invoke(Constructor<T> constructor, @Nullable Object outerInstance);
 
 }
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ExtensionConfigurationException.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ExtensionConfigurationException.java
index 91e5c7ee997d..eedd682c7992 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ExtensionConfigurationException.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ExtensionConfigurationException.java
@@ -12,7 +12,10 @@
 
 import static org.apiguardian.api.API.Status.STABLE;
 
+import java.io.Serial;
+
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.JUnitException;
 
 /**
@@ -24,13 +27,14 @@
 @API(status = STABLE, since = "5.0")
 public class ExtensionConfigurationException extends JUnitException {
 
+	@Serial
 	private static final long serialVersionUID = 1L;
 
 	public ExtensionConfigurationException(String message) {
 		super(message);
 	}
 
-	public ExtensionConfigurationException(String message, Throwable cause) {
+	public ExtensionConfigurationException(String message, @Nullable Throwable cause) {
 		super(message, cause);
 	}
 
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ExtensionContext.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ExtensionContext.java
index 1f1eeda903f4..ce7523be8980 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ExtensionContext.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ExtensionContext.java
@@ -10,17 +10,16 @@
 
 package org.junit.jupiter.api.extension;
 
-import static java.util.Collections.unmodifiableList;
 import static org.apiguardian.api.API.Status.DEPRECATED;
 import static org.apiguardian.api.API.Status.EXPERIMENTAL;
 import static org.apiguardian.api.API.Status.INTERNAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
 
 import java.lang.reflect.AnnotatedElement;
 import java.lang.reflect.Method;
 import java.nio.file.Path;
 import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
 import java.util.Map;
@@ -29,6 +28,7 @@
 import java.util.function.Function;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.TestInstance.Lifecycle;
 import org.junit.jupiter.api.function.ThrowingConsumer;
 import org.junit.jupiter.api.parallel.ExecutionMode;
@@ -156,7 +156,7 @@ public interface ExtensionContext {
 	 * @since 5.12.1
 	 * @see org.junit.platform.commons.support.AnnotationSupport#findAnnotation(Class, Class, List)
 	 */
-	@API(status = EXPERIMENTAL, since = "5.12.1")
+	@API(status = MAINTAINED, since = "5.13.3")
 	List<Class<?>> getEnclosingTestClasses();
 
 	/**
@@ -346,7 +346,7 @@ default Method getRequiredTestMethod() {
 	 * @see org.junit.platform.engine.ConfigurationParameters
 	 */
 	@API(status = STABLE, since = "5.10")
-	<T> Optional<T> getConfigurationParameter(String key, Function<String, T> transformer);
+	<T> Optional<T> getConfigurationParameter(String key, Function<? super String, ? extends @Nullable T> transformer);
 
 	/**
 	 * Publish a map of key-value pairs to be consumed by an
@@ -412,7 +412,7 @@ default void publishReportEntry(String value) {
 	 * @since 5.12
 	 * @see org.junit.platform.engine.EngineExecutionListener#fileEntryPublished
 	 */
-	@API(status = EXPERIMENTAL, since = "5.12")
+	@API(status = MAINTAINED, since = "5.13.3")
 	void publishFile(String name, MediaType mediaType, ThrowingConsumer<Path> action);
 
 	/**
@@ -420,7 +420,7 @@ default void publishReportEntry(String value) {
 	 * and attach it to the current test or container.
 	 *
 	 * <p>The directory will be resolved and created in the report output directory
-	 * prior to invoking the supplied action.
+	 * prior to invoking the supplied action, if it doesn't already exist.
 	 *
 	 * @param name the name of the directory to be attached; never {@code null}
 	 * or blank and must not contain any path separators
@@ -428,7 +428,7 @@ default void publishReportEntry(String value) {
 	 * @since 5.12
 	 * @see org.junit.platform.engine.EngineExecutionListener#fileEntryPublished
 	 */
-	@API(status = EXPERIMENTAL, since = "5.12")
+	@API(status = MAINTAINED, since = "5.13.3")
 	void publishDirectory(String name, ThrowingConsumer<Path> action);
 
 	/**
@@ -464,7 +464,7 @@ default void publishReportEntry(String value) {
 	 * @see StoreScope
 	 * @see #getStore(Namespace)
 	 */
-	@API(status = EXPERIMENTAL, since = "5.13")
+	@API(status = EXPERIMENTAL, since = "6.0")
 	Store getStore(StoreScope scope, Namespace namespace);
 
 	/**
@@ -535,6 +535,7 @@ interface CloseableResource {
 		 * @see #get(Object, Class)
 		 * @see #getOrDefault(Object, Class, Object)
 		 */
+		@Nullable
 		Object get(Object key);
 
 		/**
@@ -553,7 +554,7 @@ interface CloseableResource {
 		 * @see #get(Object)
 		 * @see #getOrDefault(Object, Class, Object)
 		 */
-		<V> V get(Object key, Class<V> requiredType);
+		<V> @Nullable V get(Object key, Class<V> requiredType);
 
 		/**
 		 * Get the value of the specified required type that is stored under
@@ -570,7 +571,8 @@ interface CloseableResource {
 		 * @param requiredType the required type of the value; never {@code null}
 		 * @param defaultValue the default value
 		 * @param <V> the value type
-		 * @return the value; potentially {@code null}
+		 * @return the value; potentially {@code null} if {@code defaultValue}
+		 * is {@code null}
 		 * @since 5.5
 		 * @see #get(Object, Class)
 		 */
@@ -614,7 +616,7 @@ default <V> V getOrDefault(Object key, Class<V> requiredType, V defaultValue) {
 		 * @see AutoCloseable
 		 */
 		@API(status = STABLE, since = "5.1")
-		default <V> V getOrComputeIfAbsent(Class<V> type) {
+		default <V> @Nullable V getOrComputeIfAbsent(Class<V> type) {
 			return getOrComputeIfAbsent(type, ReflectionSupport::newInstance, type);
 		}
 
@@ -648,7 +650,8 @@ default <V> V getOrComputeIfAbsent(Class<V> type) {
 		 * @see CloseableResource
 		 * @see AutoCloseable
 		 */
-		<K, V> Object getOrComputeIfAbsent(K key, Function<K, V> defaultCreator);
+		<K, V extends @Nullable Object> @Nullable Object getOrComputeIfAbsent(K key,
+				Function<? super K, ? extends V> defaultCreator);
 
 		/**
 		 * Get the value of the specified required type that is stored under the
@@ -679,7 +682,8 @@ default <V> V getOrComputeIfAbsent(Class<V> type) {
 		 * @see CloseableResource
 		 * @see AutoCloseable
 		 */
-		<K, V> V getOrComputeIfAbsent(K key, Function<K, V> defaultCreator, Class<V> requiredType);
+		<K, V extends @Nullable Object> @Nullable V getOrComputeIfAbsent(K key,
+				Function<? super K, ? extends V> defaultCreator, Class<V> requiredType);
 
 		/**
 		 * Store a {@code value} for later retrieval under the supplied {@code key}.
@@ -700,7 +704,7 @@ default <V> V getOrComputeIfAbsent(Class<V> type) {
 		 * @see CloseableResource
 		 * @see AutoCloseable
 		 */
-		void put(Object key, Object value);
+		void put(Object key, @Nullable Object value);
 
 		/**
 		 * Remove the value that was previously stored under the supplied {@code key}.
@@ -717,6 +721,7 @@ default <V> V getOrComputeIfAbsent(Class<V> type) {
 		 * for the specified key
 		 * @see #remove(Object, Class)
 		 */
+		@Nullable
 		Object remove(Object key);
 
 		/**
@@ -734,7 +739,7 @@ default <V> V getOrComputeIfAbsent(Class<V> type) {
 		 * for the specified key
 		 * @see #remove(Object)
 		 */
-		<V> V remove(Object key, Class<V> requiredType);
+		<V> @Nullable V remove(Object key, Class<V> requiredType);
 
 	}
 
@@ -765,13 +770,13 @@ class Namespace {
 		public static Namespace create(Object... parts) {
 			Preconditions.notEmpty(parts, "parts array must not be null or empty");
 			Preconditions.containsNoNullElements(parts, "individual parts must not be null");
-			return new Namespace(new ArrayList<>(Arrays.asList(parts)));
+			return new Namespace(List.of(parts));
 		}
 
 		private final List<Object> parts;
 
 		private Namespace(List<Object> parts) {
-			this.parts = parts;
+			this.parts = List.copyOf(parts);
 		}
 
 		@Override
@@ -810,7 +815,7 @@ public Namespace append(Object... parts) {
 
 		@API(status = INTERNAL, since = "5.13")
 		public List<Object> getParts() {
-			return unmodifiableList(parts);
+			return parts;
 		}
 	}
 
@@ -821,7 +826,7 @@ public List<Object> getParts() {
 	 * @since 5.13
 	 * @see #getStore(StoreScope, Namespace)
 	 */
-	@API(status = EXPERIMENTAL, since = "5.13")
+	@API(status = EXPERIMENTAL, since = "6.0")
 	enum StoreScope {
 
 		/**
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ExtensionContextException.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ExtensionContextException.java
index c31797d17362..51144ffd78fc 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ExtensionContextException.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ExtensionContextException.java
@@ -10,10 +10,13 @@
 
 package org.junit.jupiter.api.extension;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
 
+import java.io.Serial;
+
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.extension.ExtensionContext.Store;
 import org.junit.platform.commons.JUnitException;
 
@@ -26,15 +29,16 @@
 @API(status = STABLE, since = "5.0")
 public class ExtensionContextException extends JUnitException {
 
+	@Serial
 	private static final long serialVersionUID = 1L;
 
 	@SuppressWarnings("unused")
-	public ExtensionContextException(String message) {
+	public ExtensionContextException(@Nullable String message) {
 		super(message);
 	}
 
-	@API(status = EXPERIMENTAL, since = "5.10")
-	public ExtensionContextException(String message, Throwable cause) {
+	@API(status = MAINTAINED, since = "5.13.3")
+	public ExtensionContextException(@Nullable String message, Throwable cause) {
 		super(message, cause);
 	}
 
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/InvocationInterceptor.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/InvocationInterceptor.java
index dc02002508d0..89ee85a7735d 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/InvocationInterceptor.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/InvocationInterceptor.java
@@ -10,13 +10,13 @@
 
 package org.junit.jupiter.api.extension;
 
-import static org.apiguardian.api.API.Status.DEPRECATED;
 import static org.apiguardian.api.API.Status.STABLE;
 
 import java.lang.reflect.Constructor;
 import java.lang.reflect.Method;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.AfterAll;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeAll;
@@ -94,7 +94,7 @@ default <T> T interceptTestClassConstructor(Invocation<T> invocation,
 	 * @param extensionContext the current extension context; never {@code null}
 	 * @throws Throwable in case of failures
 	 */
-	default void interceptBeforeAllMethod(Invocation<Void> invocation,
+	default void interceptBeforeAllMethod(Invocation<@Nullable Void> invocation,
 			ReflectiveInvocationContext<Method> invocationContext, ExtensionContext extensionContext) throws Throwable {
 		invocation.proceed();
 	}
@@ -109,7 +109,7 @@ default void interceptBeforeAllMethod(Invocation<Void> invocation,
 	 * @param extensionContext the current extension context; never {@code null}
 	 * @throws Throwable in case of failures
 	 */
-	default void interceptBeforeEachMethod(Invocation<Void> invocation,
+	default void interceptBeforeEachMethod(Invocation<@Nullable Void> invocation,
 			ReflectiveInvocationContext<Method> invocationContext, ExtensionContext extensionContext) throws Throwable {
 		invocation.proceed();
 	}
@@ -124,8 +124,8 @@ default void interceptBeforeEachMethod(Invocation<Void> invocation,
 	 * @param extensionContext the current extension context; never {@code null}
 	 * @throws Throwable in case of failures
 	 */
-	default void interceptTestMethod(Invocation<Void> invocation, ReflectiveInvocationContext<Method> invocationContext,
-			ExtensionContext extensionContext) throws Throwable {
+	default void interceptTestMethod(Invocation<@Nullable Void> invocation,
+			ReflectiveInvocationContext<Method> invocationContext, ExtensionContext extensionContext) throws Throwable {
 		invocation.proceed();
 	}
 
@@ -143,7 +143,7 @@ default void interceptTestMethod(Invocation<Void> invocation, ReflectiveInvocati
 	 * @return the result of the invocation; potentially {@code null}
 	 * @throws Throwable in case of failures
 	 */
-	default <T> T interceptTestFactoryMethod(Invocation<T> invocation,
+	default <T extends @Nullable Object> T interceptTestFactoryMethod(Invocation<T> invocation,
 			ReflectiveInvocationContext<Method> invocationContext, ExtensionContext extensionContext) throws Throwable {
 		return invocation.proceed();
 	}
@@ -158,26 +158,11 @@ default <T> T interceptTestFactoryMethod(Invocation<T> invocation,
 	 * @param extensionContext the current extension context; never {@code null}
 	 * @throws Throwable in case of failures
 	 */
-	default void interceptTestTemplateMethod(Invocation<Void> invocation,
+	default void interceptTestTemplateMethod(Invocation<@Nullable Void> invocation,
 			ReflectiveInvocationContext<Method> invocationContext, ExtensionContext extensionContext) throws Throwable {
 		invocation.proceed();
 	}
 
-	/**
-	 * Intercept the invocation of a {@link DynamicTest}.
-	 *
-	 * @param invocation the invocation that is being intercepted; never
-	 * {@code null}
-	 * @param extensionContext the current extension context; never {@code null}
-	 * @throws Throwable in case of failures
-	 * @deprecated use {@link #interceptDynamicTest(Invocation, DynamicTestInvocationContext, ExtensionContext)} instead
-	 */
-	@Deprecated
-	@API(status = DEPRECATED, since = "5.8")
-	default void interceptDynamicTest(Invocation<Void> invocation, ExtensionContext extensionContext) throws Throwable {
-		invocation.proceed();
-	}
-
 	/**
 	 * Intercept the invocation of a {@link DynamicTest}.
 	 *
@@ -189,10 +174,9 @@ default void interceptDynamicTest(Invocation<Void> invocation, ExtensionContext
 	 * @throws Throwable in case of failures
 	 */
 	@API(status = STABLE, since = "5.11")
-	default void interceptDynamicTest(Invocation<Void> invocation, DynamicTestInvocationContext invocationContext,
-			ExtensionContext extensionContext) throws Throwable {
-		// by default call the old interceptDynamicTest(Invocation, ExtensionContext) method so that existing extensions still work
-		interceptDynamicTest(invocation, extensionContext);
+	default void interceptDynamicTest(Invocation<@Nullable Void> invocation,
+			DynamicTestInvocationContext invocationContext, ExtensionContext extensionContext) throws Throwable {
+		invocation.proceed();
 	}
 
 	/**
@@ -205,7 +189,7 @@ default void interceptDynamicTest(Invocation<Void> invocation, DynamicTestInvoca
 	 * @param extensionContext the current extension context; never {@code null}
 	 * @throws Throwable in case of failures
 	 */
-	default void interceptAfterEachMethod(Invocation<Void> invocation,
+	default void interceptAfterEachMethod(Invocation<@Nullable Void> invocation,
 			ReflectiveInvocationContext<Method> invocationContext, ExtensionContext extensionContext) throws Throwable {
 		invocation.proceed();
 	}
@@ -220,7 +204,7 @@ default void interceptAfterEachMethod(Invocation<Void> invocation,
 	 * @param extensionContext the current extension context; never {@code null}
 	 * @throws Throwable in case of failures
 	 */
-	default void interceptAfterAllMethod(Invocation<Void> invocation,
+	default void interceptAfterAllMethod(Invocation<@Nullable Void> invocation,
 			ReflectiveInvocationContext<Method> invocationContext, ExtensionContext extensionContext) throws Throwable {
 		invocation.proceed();
 	}
@@ -234,7 +218,7 @@ default void interceptAfterAllMethod(Invocation<Void> invocation,
 	 * @since 5.5
 	 */
 	@API(status = STABLE, since = "5.10")
-	interface Invocation<T> {
+	interface Invocation<T extends @Nullable Object> {
 
 		/**
 		 * Proceed with this invocation.
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/MediaType.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/MediaType.java
index 82513d94bcc2..2a8458e61a4e 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/MediaType.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/MediaType.java
@@ -11,7 +11,7 @@
 package org.junit.jupiter.api.extension;
 
 import static java.nio.charset.StandardCharsets.UTF_8;
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import java.nio.charset.Charset;
 import java.nio.file.Path;
@@ -34,7 +34,7 @@
  * @see TestReporter#publishFile(String, MediaType, ThrowingConsumer)
  * @see ExtensionContext#publishFile(String, MediaType, ThrowingConsumer)
  */
-@API(status = EXPERIMENTAL, since = "5.12")
+@API(status = MAINTAINED, since = "5.13.3")
 public class MediaType {
 
 	private static final Pattern PATTERN;
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ParameterContext.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ParameterContext.java
index 844b7aed9592..5ddec73b55a0 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ParameterContext.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ParameterContext.java
@@ -10,7 +10,7 @@
 
 package org.junit.jupiter.api.extension;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
 
 import java.lang.annotation.Annotation;
@@ -94,7 +94,7 @@ default Executable getDeclaringExecutable() {
 	 * {@inheritDoc}
 	 * @since 5.10
 	 */
-	@API(status = EXPERIMENTAL, since = "5.10")
+	@API(status = MAINTAINED, since = "5.13.3")
 	@Override
 	default AnnotatedElement getAnnotatedElement() {
 		return getParameter();
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ParameterResolutionException.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ParameterResolutionException.java
index 31c9730b6222..3c5d87458904 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ParameterResolutionException.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ParameterResolutionException.java
@@ -12,6 +12,8 @@
 
 import static org.apiguardian.api.API.Status.STABLE;
 
+import java.io.Serial;
+
 import org.apiguardian.api.API;
 import org.junit.platform.commons.JUnitException;
 
@@ -25,6 +27,7 @@
 @API(status = STABLE, since = "5.0")
 public class ParameterResolutionException extends JUnitException {
 
+	@Serial
 	private static final long serialVersionUID = 1L;
 
 	public ParameterResolutionException(String message) {
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ParameterResolver.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ParameterResolver.java
index 093fe276bcf5..898f73a94760 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ParameterResolver.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/ParameterResolver.java
@@ -15,6 +15,7 @@
 import java.lang.reflect.Parameter;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.TestInstance;
 
 /**
@@ -99,6 +100,7 @@ boolean supportsParameter(ParameterContext parameterContext, ExtensionContext ex
 	 * @see #supportsParameter
 	 * @see ParameterContext
 	 */
+	@Nullable
 	Object resolveParameter(ParameterContext parameterContext, ExtensionContext extensionContext)
 			throws ParameterResolutionException;
 
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/PreInterruptCallback.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/PreInterruptCallback.java
index 03fd96f03800..f4c23529a61f 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/PreInterruptCallback.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/PreInterruptCallback.java
@@ -10,7 +10,7 @@
 
 package org.junit.jupiter.api.extension;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import org.apiguardian.api.API;
 
@@ -28,7 +28,7 @@
  * @since 5.12
  * @see org.junit.jupiter.api.Timeout
  */
-@API(status = EXPERIMENTAL, since = "5.12")
+@API(status = MAINTAINED, since = "5.13.3")
 public interface PreInterruptCallback extends Extension {
 
 	/**
@@ -39,7 +39,7 @@ public interface PreInterruptCallback extends Extension {
 	 *
 	 * @since 5.12
 	 */
-	@API(status = EXPERIMENTAL, since = "5.12")
+	@API(status = MAINTAINED, since = "5.13.3")
 	String THREAD_DUMP_ENABLED_PROPERTY_NAME = "junit.jupiter.execution.timeout.threaddump.enabled";
 
 	/**
@@ -54,7 +54,7 @@ public interface PreInterruptCallback extends Extension {
 	 * @since 5.12
 	 * @see PreInterruptContext
 	 */
-	@API(status = EXPERIMENTAL, since = "5.12")
+	@API(status = MAINTAINED, since = "5.13.3")
 	void beforeThreadInterrupt(PreInterruptContext preInterruptContext, ExtensionContext extensionContext)
 			throws Exception;
 }
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/PreInterruptContext.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/PreInterruptContext.java
index 77bb98e728ff..f67df1450777 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/PreInterruptContext.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/PreInterruptContext.java
@@ -10,7 +10,7 @@
 
 package org.junit.jupiter.api.extension;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import org.apiguardian.api.API;
 
@@ -21,7 +21,7 @@
  * @since 5.12
  * @see PreInterruptCallback
  */
-@API(status = EXPERIMENTAL, since = "5.12")
+@API(status = MAINTAINED, since = "5.13.3")
 public interface PreInterruptContext {
 
 	/**
@@ -30,6 +30,6 @@ public interface PreInterruptContext {
 	 * @return the Thread; never {@code null}
 	 * @since 5.12
 	 */
-	@API(status = EXPERIMENTAL, since = "5.12")
+	@API(status = MAINTAINED, since = "5.13.3")
 	Thread getThreadToInterrupt();
 }
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/TemplateInvocationValidationException.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/TemplateInvocationValidationException.java
index 94cad7ab8677..e38bad363c29 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/TemplateInvocationValidationException.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/TemplateInvocationValidationException.java
@@ -12,6 +12,8 @@
 
 import static org.apiguardian.api.API.Status.EXPERIMENTAL;
 
+import java.io.Serial;
+
 import org.apiguardian.api.API;
 import org.junit.platform.commons.JUnitException;
 
@@ -24,9 +26,10 @@
  *
  * @since 5.13
  */
-@API(status = EXPERIMENTAL, since = "5.13")
+@API(status = EXPERIMENTAL, since = "6.0")
 public class TemplateInvocationValidationException extends JUnitException {
 
+	@Serial
 	private static final long serialVersionUID = 1L;
 
 	public TemplateInvocationValidationException(String message) {
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/TestInstantiationAwareExtension.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/TestInstantiationAwareExtension.java
index 7f4847304c06..2045d264080f 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/TestInstantiationAwareExtension.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/TestInstantiationAwareExtension.java
@@ -11,7 +11,7 @@
 package org.junit.jupiter.api.extension;
 
 import static org.apiguardian.api.API.Status.DEPRECATED;
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import org.apiguardian.api.API;
 import org.junit.jupiter.api.TestInstance;
@@ -31,7 +31,7 @@
  * @see TestInstancePostProcessor
  * @see TestInstanceFactory
  */
-@API(status = EXPERIMENTAL, since = "5.12")
+@API(status = MAINTAINED, since = "5.13.3")
 public interface TestInstantiationAwareExtension extends Extension {
 
 	/**
@@ -89,7 +89,7 @@ public interface TestInstantiationAwareExtension extends Extension {
 	 *                    configuration parameters; never {@code null}
 	 * @since 5.12
 	 */
-	@API(status = EXPERIMENTAL, since = "5.12")
+	@API(status = MAINTAINED, since = "5.13.3")
 	default ExtensionContextScope getTestInstantiationExtensionContextScope(ExtensionContext rootContext) {
 		return ExtensionContextScope.DEFAULT;
 	}
@@ -102,7 +102,7 @@ default ExtensionContextScope getTestInstantiationExtensionContextScope(Extensio
 	 * @since 5.12
 	 * @see TestInstantiationAwareExtension#getTestInstantiationExtensionContextScope
 	 */
-	@API(status = EXPERIMENTAL, since = "5.12")
+	@API(status = MAINTAINED, since = "5.13.3")
 	enum ExtensionContextScope {
 
 		/**
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/TestInstantiationException.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/TestInstantiationException.java
index 66884bdba9db..4ec882a2ea5d 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/TestInstantiationException.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/TestInstantiationException.java
@@ -12,6 +12,8 @@
 
 import static org.apiguardian.api.API.Status.STABLE;
 
+import java.io.Serial;
+
 import org.apiguardian.api.API;
 import org.junit.platform.commons.JUnitException;
 
@@ -24,6 +26,7 @@
 @API(status = STABLE, since = "5.10")
 public class TestInstantiationException extends JUnitException {
 
+	@Serial
 	private static final long serialVersionUID = 1L;
 
 	public TestInstantiationException(String message) {
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/TestTemplateInvocationContext.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/TestTemplateInvocationContext.java
index 1d74bed2dd7d..122caf3650a6 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/TestTemplateInvocationContext.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/TestTemplateInvocationContext.java
@@ -77,7 +77,7 @@ default List<Extension> getAdditionalExtensions() {
 	 * @param context The invocation-level extension context.
 	 * @since 5.13
 	 */
-	@API(status = EXPERIMENTAL, since = "5.13")
+	@API(status = EXPERIMENTAL, since = "6.0")
 	default void prepareInvocation(ExtensionContext context) {
 	}
 
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/TestTemplateInvocationContextProvider.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/TestTemplateInvocationContextProvider.java
index f4a64479cde9..90cb4b79f033 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/TestTemplateInvocationContextProvider.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/TestTemplateInvocationContextProvider.java
@@ -10,7 +10,7 @@
 
 package org.junit.jupiter.api.extension;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
 
 import java.util.stream.Stream;
@@ -111,7 +111,7 @@ public interface TestTemplateInvocationContextProvider extends Extension {
 	 *
 	 * @since 5.12
 	 */
-	@API(status = EXPERIMENTAL, since = "5.12")
+	@API(status = MAINTAINED, since = "5.13.3")
 	default boolean mayReturnZeroTestTemplateInvocationContexts(ExtensionContext context) {
 		return false;
 	}
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/TestWatcher.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/TestWatcher.java
index 54c7c24da942..4c4c129e320b 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/TestWatcher.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/TestWatcher.java
@@ -15,6 +15,7 @@
 import java.util.Optional;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 
 /**
  * {@code TestWatcher} defines the API for {@link Extension Extensions} that
@@ -103,7 +104,7 @@ default void testSuccessful(ExtensionContext context) {
 	 * @param context the current extension context; never {@code null}
 	 * @param cause the throwable responsible for the test being aborted; may be {@code null}
 	 */
-	default void testAborted(ExtensionContext context, Throwable cause) {
+	default void testAborted(ExtensionContext context, @Nullable Throwable cause) {
 		/* no-op */
 	}
 
@@ -116,7 +117,7 @@ default void testAborted(ExtensionContext context, Throwable cause) {
 	 * @param context the current extension context; never {@code null}
 	 * @param cause the throwable that caused test failure; may be {@code null}
 	 */
-	default void testFailed(ExtensionContext context, Throwable cause) {
+	default void testFailed(ExtensionContext context, @Nullable Throwable cause) {
 		/* no-op */
 	}
 
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/package-info.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/package-info.java
index 68f070a2fb4d..940def614dd4 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/package-info.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/package-info.java
@@ -2,4 +2,7 @@
  * JUnit Jupiter API for writing extensions.
  */
 
+@NullMarked
 package org.junit.jupiter.api.extension;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/support/TypeBasedParameterResolver.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/support/TypeBasedParameterResolver.java
index 25608a4a1ae8..be80ed5c3a0a 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/support/TypeBasedParameterResolver.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/support/TypeBasedParameterResolver.java
@@ -16,6 +16,7 @@
 import java.lang.reflect.Type;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.extension.ExtensionContext;
 import org.junit.jupiter.api.extension.ParameterContext;
 import org.junit.jupiter.api.extension.ParameterResolutionException;
@@ -29,7 +30,7 @@
  * @since 5.6
  */
 @API(status = STABLE, since = "5.10")
-public abstract class TypeBasedParameterResolver<T> implements ParameterResolver {
+public abstract class TypeBasedParameterResolver<T extends @Nullable Object> implements ParameterResolver {
 
 	private final Type supportedParameterType;
 
@@ -51,8 +52,8 @@ private Type getParameterType(ParameterContext parameterContext) {
 	}
 
 	private Type enclosedTypeOfParameterResolver() {
-		ParameterizedType typeBasedParameterResolverSuperclass = findTypeBasedParameterResolverSuperclass(getClass());
-		Preconditions.notNull(typeBasedParameterResolverSuperclass,
+		ParameterizedType typeBasedParameterResolverSuperclass = Preconditions.notNull(
+			findTypeBasedParameterResolverSuperclass(getClass()),
 			() -> String.format(
 				"Failed to discover parameter type supported by %s; "
 						+ "potentially caused by lacking parameterized type in class declaration.",
@@ -60,7 +61,7 @@ private Type enclosedTypeOfParameterResolver() {
 		return typeBasedParameterResolverSuperclass.getActualTypeArguments()[0];
 	}
 
-	private ParameterizedType findTypeBasedParameterResolverSuperclass(Class<?> clazz) {
+	private @Nullable ParameterizedType findTypeBasedParameterResolverSuperclass(Class<?> clazz) {
 		Class<?> superclass = clazz.getSuperclass();
 
 		// Abort?
@@ -69,10 +70,10 @@ private ParameterizedType findTypeBasedParameterResolverSuperclass(Class<?> claz
 		}
 
 		Type genericSuperclass = clazz.getGenericSuperclass();
-		if (genericSuperclass instanceof ParameterizedType) {
-			Type rawType = ((ParameterizedType) genericSuperclass).getRawType();
+		if (genericSuperclass instanceof ParameterizedType type) {
+			Type rawType = type.getRawType();
 			if (rawType == TypeBasedParameterResolver.class) {
-				return (ParameterizedType) genericSuperclass;
+				return type;
 			}
 		}
 		return findTypeBasedParameterResolverSuperclass(superclass);
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/support/package-info.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/support/package-info.java
index 3d4156a34d6b..897de7983f57 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/support/package-info.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/extension/support/package-info.java
@@ -2,4 +2,7 @@
  * JUnit Jupiter API support for writing extensions.
  */
 
+@NullMarked
 package org.junit.jupiter.api.extension.support;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/function/ThrowingConsumer.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/function/ThrowingConsumer.java
index ca32cf145b02..f9a897126f2d 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/function/ThrowingConsumer.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/function/ThrowingConsumer.java
@@ -13,6 +13,7 @@
 import static org.apiguardian.api.API.Status.STABLE;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 
 /**
  * {@code ThrowingConsumer} is a functional interface that can be used to
@@ -41,7 +42,7 @@
  */
 @FunctionalInterface
 @API(status = STABLE, since = "5.0")
-public interface ThrowingConsumer<T> {
+public interface ThrowingConsumer<T extends @Nullable Object> {
 
 	/**
 	 * Consume the supplied argument, potentially throwing an exception.
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/function/ThrowingSupplier.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/function/ThrowingSupplier.java
index 42212221844a..bfa2c4d87b55 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/function/ThrowingSupplier.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/function/ThrowingSupplier.java
@@ -13,6 +13,7 @@
 import static org.apiguardian.api.API.Status.STABLE;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 
 /**
  * {@code ThrowingSupplier} is a functional interface that can be used to
@@ -42,7 +43,7 @@
  */
 @FunctionalInterface
 @API(status = STABLE, since = "5.0")
-public interface ThrowingSupplier<T> {
+public interface ThrowingSupplier<T extends @Nullable Object> {
 
 	/**
 	 * Get a result, potentially throwing an exception.
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/function/package-info.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/function/package-info.java
index aaebdbdb3aab..b70c3db4db85 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/function/package-info.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/function/package-info.java
@@ -2,4 +2,7 @@
  * Functional interfaces used within JUnit Jupiter.
  */
 
+@NullMarked
 package org.junit.jupiter.api.function;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/io/TempDir.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/io/TempDir.java
index 4b9053ba237d..7d5191bedeb2 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/io/TempDir.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/io/TempDir.java
@@ -10,8 +10,7 @@
 
 package org.junit.jupiter.api.io;
 
-import static org.apiguardian.api.API.Status.DEPRECATED;
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
 
 import java.io.File;
@@ -63,21 +62,6 @@
  * {@code static} field or on a parameter of a
  * {@link org.junit.jupiter.api.BeforeAll @BeforeAll} method.
  *
- * <h3>Old behavior</h3>
- *
- * <p>You can revert to the old behavior of using a single temporary directory
- * by setting the {@value #SCOPE_PROPERTY_NAME} configuration parameter to
- * {@code per_context}. In that case, the scope of the temporary directory
- * depends on where the first {@code @TempDir} annotation is encountered when
- * executing a test class. The temporary directory will be shared by all tests
- * in a class when the annotation is present on a {@code static} field or on a
- * parameter of a {@link org.junit.jupiter.api.BeforeAll @BeforeAll} method.
- * Otherwise &mdash; for example, when {@code @TempDir} is only used on instance
- * fields or on parameters in test,
- * {@link org.junit.jupiter.api.BeforeEach @BeforeEach}, or
- * {@link org.junit.jupiter.api.AfterEach @AfterEach} methods &mdash; each test
- * will use its own temporary directory.
- *
  * <h2>Clean Up</h2>
  *
  * <p>By default, when the end of the scope of a temporary directory is reached,
@@ -120,15 +104,12 @@
 	 *
 	 * @since 5.10
 	 */
-	@API(status = EXPERIMENTAL, since = "5.10")
+	@API(status = MAINTAINED, since = "5.13.3")
 	String DEFAULT_FACTORY_PROPERTY_NAME = "junit.jupiter.tempdir.factory.default";
 
 	/**
 	 * Factory for the temporary directory.
 	 *
-	 * <p>If the {@value #SCOPE_PROPERTY_NAME} configuration parameter is set to
-	 * {@code per_context}, no custom factory is allowed.
-	 *
 	 * <p>Defaults to {@link TempDirFactory.Standard}.
 	 *
 	 * <p>As an alternative to setting this attribute, a global
@@ -142,31 +123,9 @@
 	 * @since 5.10
 	 * @see TempDirFactory
 	 */
-	@API(status = EXPERIMENTAL, since = "5.10")
+	@API(status = MAINTAINED, since = "5.13.3")
 	Class<? extends TempDirFactory> factory() default TempDirFactory.class;
 
-	/**
-	 * Property name used to set the scope of temporary directories created via
-	 * the {@link TempDir @TempDir} annotation: {@value}
-	 *
-	 * <h4>Supported Values</h4>
-	 * <ul>
-	 * <li>{@code per_context}: creates a single temporary directory for the
-	 * entire test class or method, depending on where {@code @TempDir} is first
-	 * declared</li>
-	 * <li>{@code per_declaration}: creates separate temporary directories for
-	 * each declaration site of the {@code @TempDir} annotation</li>
-	 * </ul>
-	 *
-	 * <p>If not specified, the default is {@code per_declaration}.
-	 *
-	 * @since 5.8
-	 */
-	@SuppressWarnings("DeprecatedIsStillUsed")
-	@Deprecated
-	@API(status = DEPRECATED, since = "5.9")
-	String SCOPE_PROPERTY_NAME = "junit.jupiter.tempdir.scope";
-
 	/**
 	 * The name of the configuration parameter that is used to configure the
 	 * default {@link CleanupMode}.
@@ -176,7 +135,7 @@
 	 *
 	 * @since 5.9
 	 */
-	@API(status = EXPERIMENTAL, since = "5.9")
+	@API(status = MAINTAINED, since = "5.13.3")
 	String DEFAULT_CLEANUP_MODE_PROPERTY_NAME = "junit.jupiter.tempdir.cleanup.mode.default";
 
 	/**
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/io/TempDirFactory.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/io/TempDirFactory.java
index d5bbce4a4e2f..52b6713fa4a7 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/io/TempDirFactory.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/io/TempDirFactory.java
@@ -10,7 +10,7 @@
 
 package org.junit.jupiter.api.io;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import java.io.Closeable;
 import java.io.IOException;
@@ -45,7 +45,7 @@
  * @see TempDir @TempDir
  */
 @FunctionalInterface
-@API(status = EXPERIMENTAL, since = "5.10")
+@API(status = MAINTAINED, since = "5.13.3")
 public interface TempDirFactory extends Closeable {
 
 	/**
@@ -73,7 +73,7 @@ default void close() throws IOException {
 
 	/**
 	 * Standard {@link TempDirFactory} implementation which delegates to
-	 * {@link Files#createTempDirectory} using {@code "junit-,"} as prefix.
+	 * {@link Files#createTempDirectory} using {@code "junit-"} as prefix.
 	 *
 	 * <p>The created temporary directory is always created in the default
 	 * file system with the system's default temporary directory as its parent.
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/io/package-info.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/io/package-info.java
index 7e8938932e9b..34a9dc7ef6bf 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/io/package-info.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/io/package-info.java
@@ -2,4 +2,7 @@
  * IO-related support in JUnit Jupiter.
  */
 
+@NullMarked
 package org.junit.jupiter.api.io;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/package-info.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/package-info.java
index 38e623dde4aa..7b3888e95e0b 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/package-info.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/package-info.java
@@ -2,4 +2,7 @@
  * JUnit Jupiter API for writing tests.
  */
 
+@NullMarked
 package org.junit.jupiter.api;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/parallel/Execution.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/parallel/Execution.java
index d1c53ca87d96..f46680ca5b00 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/parallel/Execution.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/parallel/Execution.java
@@ -10,7 +10,7 @@
 
 package org.junit.jupiter.api.parallel;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
 
 import java.lang.annotation.ElementType;
@@ -77,7 +77,7 @@
 	 *
 	 * @since 5.4
 	 */
-	@API(status = EXPERIMENTAL, since = "5.9")
+	@API(status = MAINTAINED, since = "5.13.3")
 	String DEFAULT_EXECUTION_MODE_PROPERTY_NAME = "junit.jupiter.execution.parallel.mode.default";
 
 	/**
@@ -96,7 +96,7 @@
 	 *
 	 * @since 5.4
 	 */
-	@API(status = EXPERIMENTAL, since = "5.9")
+	@API(status = MAINTAINED, since = "5.13.3")
 	String DEFAULT_CLASSES_EXECUTION_MODE_PROPERTY_NAME = "junit.jupiter.execution.parallel.mode.classes.default";
 
 	/**
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/parallel/ResourceLock.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/parallel/ResourceLock.java
index 370e0c679a4f..19ef61206ca4 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/parallel/ResourceLock.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/parallel/ResourceLock.java
@@ -10,7 +10,7 @@
 
 package org.junit.jupiter.api.parallel;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
 
 import java.lang.annotation.ElementType;
@@ -118,7 +118,7 @@
 	 * @see ResourceLocksProvider.Lock
 	 * @since 5.12
 	 */
-	@API(status = EXPERIMENTAL, since = "5.12")
+	@API(status = MAINTAINED, since = "5.13.3")
 	Class<? extends ResourceLocksProvider>[] providers() default {};
 
 	/**
@@ -132,7 +132,7 @@
 	 * @see ResourceLockTarget
 	 * @since 5.12
 	 */
-	@API(status = EXPERIMENTAL, since = "5.12")
+	@API(status = MAINTAINED, since = "5.13.3")
 	ResourceLockTarget target() default ResourceLockTarget.SELF;
 
 }
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/parallel/ResourceLockTarget.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/parallel/ResourceLockTarget.java
index 94a7a0bf7d68..69a7d7d2e7ed 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/parallel/ResourceLockTarget.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/parallel/ResourceLockTarget.java
@@ -10,7 +10,7 @@
 
 package org.junit.jupiter.api.parallel;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import org.apiguardian.api.API;
 
@@ -20,7 +20,7 @@
  * @since 5.12
  * @see ResourceLock#target()
  */
-@API(status = EXPERIMENTAL, since = "5.12")
+@API(status = MAINTAINED, since = "5.13.3")
 public enum ResourceLockTarget {
 
 	/**
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/parallel/ResourceLocksProvider.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/parallel/ResourceLocksProvider.java
index 2cffc5d6101f..7708b8b5b9e3 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/parallel/ResourceLocksProvider.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/parallel/ResourceLocksProvider.java
@@ -11,7 +11,7 @@
 package org.junit.jupiter.api.parallel;
 
 import static java.util.Collections.emptySet;
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import java.lang.reflect.Method;
 import java.util.List;
@@ -40,7 +40,7 @@
  * @see ResourceAccessMode
  * @see Lock
  */
-@API(status = EXPERIMENTAL, since = "5.12")
+@API(status = MAINTAINED, since = "5.13.3")
 public interface ResourceLocksProvider {
 
 	/**
diff --git a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/parallel/package-info.java b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/parallel/package-info.java
index 16b34edfb116..3969d01029d5 100644
--- a/junit-jupiter-api/src/main/java/org/junit/jupiter/api/parallel/package-info.java
+++ b/junit-jupiter-api/src/main/java/org/junit/jupiter/api/parallel/package-info.java
@@ -2,4 +2,7 @@
  * JUnit Jupiter API for influencing parallel test execution.
  */
 
+@NullMarked
 package org.junit.jupiter.api.parallel;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-jupiter-api/src/main/kotlin/org/junit/jupiter/api/Assertions.kt b/junit-jupiter-api/src/main/kotlin/org/junit/jupiter/api/Assertions.kt
index ce93a2fdd56b..f65ff26c7551 100644
--- a/junit-jupiter-api/src/main/kotlin/org/junit/jupiter/api/Assertions.kt
+++ b/junit-jupiter-api/src/main/kotlin/org/junit/jupiter/api/Assertions.kt
@@ -12,12 +12,11 @@
 package org.junit.jupiter.api
 
 import org.apiguardian.api.API
-import org.apiguardian.api.API.Status.EXPERIMENTAL
+import org.apiguardian.api.API.Status.MAINTAINED
 import org.apiguardian.api.API.Status.STABLE
 import org.junit.jupiter.api.function.Executable
-import org.junit.jupiter.api.function.ThrowingSupplier
+import org.junit.platform.commons.util.UnrecoverableExceptions.rethrowIfUnrecoverable
 import java.time.Duration
-import java.util.function.Supplier
 import java.util.stream.Stream
 import kotlin.contracts.ExperimentalContracts
 import kotlin.contracts.InvocationKind.AT_MOST_ONCE
@@ -36,14 +35,14 @@ fun fail(
  * @see Assertions.fail
  */
 @OptIn(ExperimentalContracts::class)
-@API(since = "5.12", status = EXPERIMENTAL)
+@API(status = MAINTAINED, since = "5.13.3")
 @JvmName("fail_nonNullableLambda")
 fun fail(message: () -> String): Nothing {
     contract {
         callsInPlace(message, EXACTLY_ONCE)
     }
 
-    return Assertions.fail(message)
+    return Assertions.fail(message())
 }
 
 /**
@@ -122,7 +121,7 @@ fun assertAll(
  * @see Assertions.assertNull
  */
 @OptIn(ExperimentalContracts::class)
-@API(since = "5.12", status = EXPERIMENTAL)
+@API(status = MAINTAINED, since = "5.13.3")
 fun assertNull(actual: Any?) {
     contract {
         returns() implies (actual == null)
@@ -144,7 +143,7 @@ fun assertNull(actual: Any?) {
  * @see Assertions.assertNull
  */
 @OptIn(ExperimentalContracts::class)
-@API(since = "5.12", status = EXPERIMENTAL)
+@API(status = MAINTAINED, since = "5.13.3")
 fun assertNull(
     actual: Any?,
     message: String
@@ -169,7 +168,7 @@ fun assertNull(
  * @see Assertions.assertNull
  */
 @OptIn(ExperimentalContracts::class)
-@API(since = "5.12", status = EXPERIMENTAL)
+@API(status = MAINTAINED, since = "5.13.3")
 fun assertNull(
     actual: Any?,
     messageSupplier: () -> String
@@ -196,7 +195,7 @@ fun assertNull(
  * @see Assertions.assertNotNull
  */
 @OptIn(ExperimentalContracts::class)
-@API(since = "5.12", status = EXPERIMENTAL)
+@API(status = MAINTAINED, since = "5.13.3")
 fun assertNotNull(actual: Any?) {
     contract {
         returns() implies (actual != null)
@@ -218,7 +217,7 @@ fun assertNotNull(actual: Any?) {
  * @see Assertions.assertNotNull
  */
 @OptIn(ExperimentalContracts::class)
-@API(since = "5.12", status = EXPERIMENTAL)
+@API(status = MAINTAINED, since = "5.13.3")
 fun assertNotNull(
     actual: Any?,
     message: String
@@ -243,7 +242,7 @@ fun assertNotNull(
  * @see Assertions.assertNotNull
  */
 @OptIn(ExperimentalContracts::class)
-@API(since = "5.12", status = EXPERIMENTAL)
+@API(status = MAINTAINED, since = "5.13.3")
 fun assertNotNull(
     actual: Any?,
     messageSupplier: () -> String
@@ -334,7 +333,7 @@ inline fun <reified T : Throwable> assertThrows(
                 throw throwable
             }
         },
-        Supplier(message)
+        message
     )
 }
 
@@ -355,7 +354,12 @@ inline fun <R> assertDoesNotThrow(executable: () -> R): R {
         callsInPlace(executable, EXACTLY_ONCE)
     }
 
-    return Assertions.assertDoesNotThrow(evaluateAndWrap(executable))
+    try {
+        return executable()
+    } catch (t: Throwable) {
+        rethrowIfUnrecoverable(t)
+        throw AssertDoesNotThrow.createAssertionFailedError(null, t)
+    }
 }
 
 /**
@@ -402,20 +406,13 @@ inline fun <R> assertDoesNotThrow(
         callsInPlace(message, AT_MOST_ONCE)
     }
 
-    return Assertions.assertDoesNotThrow(
-        evaluateAndWrap(executable),
-        Supplier(message)
-    )
-}
-
-@PublishedApi
-internal inline fun <R> evaluateAndWrap(executable: () -> R): ThrowingSupplier<R> =
     try {
-        val result = executable()
-        ThrowingSupplier { result }
-    } catch (throwable: Throwable) {
-        ThrowingSupplier { throw throwable }
+        return executable()
+    } catch (t: Throwable) {
+        rethrowIfUnrecoverable(t)
+        throw AssertDoesNotThrow.createAssertionFailedError(message(), t)
     }
+}
 
 /**
  * Example usage:
@@ -434,7 +431,7 @@ fun <R> assertTimeout(
     executable: () -> R
 ): R {
     contract {
-        callsInPlace(executable, EXACTLY_ONCE)
+        callsInPlace(executable, AT_MOST_ONCE)
     }
 
     return Assertions.assertTimeout(timeout, executable)
@@ -458,7 +455,7 @@ fun <R> assertTimeout(
     executable: () -> R
 ): R {
     contract {
-        callsInPlace(executable, EXACTLY_ONCE)
+        callsInPlace(executable, AT_MOST_ONCE)
     }
 
     return Assertions.assertTimeout(timeout, executable, message)
@@ -482,7 +479,7 @@ fun <R> assertTimeout(
     executable: () -> R
 ): R {
     contract {
-        callsInPlace(executable, EXACTLY_ONCE)
+        callsInPlace(executable, AT_MOST_ONCE)
         callsInPlace(message, AT_MOST_ONCE)
     }
 
@@ -568,7 +565,7 @@ fun <R> assertTimeoutPreemptively(
  * @since 5.11
  */
 @OptIn(ExperimentalContracts::class)
-@API(status = EXPERIMENTAL, since = "5.11")
+@API(status = MAINTAINED, since = "5.13.3")
 inline fun <reified T : Any> assertInstanceOf(
     actualValue: Any?,
     message: String? = null
@@ -593,7 +590,7 @@ inline fun <reified T : Any> assertInstanceOf(
  * @since 5.11
  */
 @OptIn(ExperimentalContracts::class)
-@API(status = EXPERIMENTAL, since = "5.11")
+@API(status = MAINTAINED, since = "5.13.3")
 inline fun <reified T : Any> assertInstanceOf(
     actualValue: Any?,
     noinline message: () -> String
diff --git a/junit-jupiter-api/src/templates/resources/main/org/junit/jupiter/api/condition/JRE.java.jte b/junit-jupiter-api/src/templates/resources/main/org/junit/jupiter/api/condition/JRE.java.jte
index f664e0df2e74..4d7d64286bd8 100644
--- a/junit-jupiter-api/src/templates/resources/main/org/junit/jupiter/api/condition/JRE.java.jte
+++ b/junit-jupiter-api/src/templates/resources/main/org/junit/jupiter/api/condition/JRE.java.jte
@@ -2,35 +2,27 @@
 @import gg.jte.support.ForSupport
 @import junitbuild.generator.model.JRE
 
-@param List<JRE> jres
+@param int minRuntimeVersion
+@param List<JRE> allJres
 @param String licenseHeader
 ${licenseHeader}
 package org.junit.jupiter.api.condition;
 
 import static org.apiguardian.api.API.Status.DEPRECATED;
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
 
-import java.lang.reflect.Method;
-
 import org.apiguardian.api.API;
-import org.junit.platform.commons.logging.Logger;
-import org.junit.platform.commons.logging.LoggerFactory;
-import org.junit.platform.commons.support.ReflectionSupport;
-import org.junit.platform.commons.util.StringUtils;
 
 /**
  * Enumeration of Java Runtime Environment (JRE) versions.
  *
  * <p>If the current JRE version can be detected but is not one of the predefined
  * constants in this enum, {@link #OTHER} will be considered to be the
- * {@linkplain #isCurrentVersion current JRE version}. If the current JRE version
- * cannot be detected &mdash; for example, if the {@code java.version} JVM system
- * property is undefined &mdash; {@link #UNDEFINED} will be considered to be the
- * current JRE version.
+ * {@linkplain #isCurrentVersion current JRE version}.
  *
  * @since 5.1
-@for(JRE jre : jres)<%--
+@for(JRE jre : allJres)<%--
 --%> * @see #JAVA_${jre.getVersion()}
 @endfor<%--
 --%> * @see #OTHER
@@ -52,24 +44,32 @@ public enum JRE {
 	 *
 	 * @since 5.12
 	 */
-	@API(status = EXPERIMENTAL, since = "5.12")
+	@API(status = MAINTAINED, since = "5.13.3")
 	UNDEFINED(-1),
-@for(var jre : jres)
+@for(var jre : allJres)
 	/**
 	 * Java ${jre.getVersion()}.
-	@if(jre.getSince() != null)<%--
+	@if(jre.getSince() != null || jre.getVersion() < minRuntimeVersion)<%--
 --%> *
-	 * @since ${jre.getSince()}
+	@endif<%--
+--%>@if(jre.getSince() != null)<%--
+--%> * @since ${jre.getSince()}
+	@endif<%--
+--%>@if(jre.getVersion() < minRuntimeVersion)<%--
+--%> * @deprecated No longer supported at runtime; please use {@link #JAVA_17} or later
 	@endif<%--
 --%> */
-	@if(jre.getSince() != null)<%--
+	@if(jre.getVersion() < minRuntimeVersion)<%--
+--%>@API(status = DEPRECATED, since = "6.0") //
+	@Deprecated(since = "6.0", forRemoval = true)
+	@elseif(jre.getSince() != null)<%--
 --%>@API(status = STABLE, since = "${jre.getSince()}")
 	@endif<%--
 --%>JAVA_${jre.getVersion()}(${jre.getVersion()}),
 @endfor
 	/**
 	 * A JRE version other than <%--
---%>@for(var jre : ForSupport.of(jres))<%--
+--%>@for(var jre : ForSupport.of(allJres))<%--
 	--%>@if(jre.isLast())or @endif<%--
 	--%>{@link #JAVA_${jre.get().getVersion()}}<%--
 	--%>@if(jre.isLast()).@else,@endif<%--
@@ -85,59 +85,13 @@ public enum JRE {
 
 	static final int UNDEFINED_VERSION = -1;
 
-	static final int MINIMUM_VERSION = 8;
-
-	private static final Logger logger = LoggerFactory.getLogger(JRE.class);
-
-	private static final int CURRENT_VERSION = determineCurrentVersion();
-
-	private static final JRE CURRENT_JRE = determineCurrentJre(CURRENT_VERSION);
-
-	private static int determineCurrentVersion() {
-		String javaVersion = System.getProperty("java.version");
-		boolean javaVersionIsBlank = StringUtils.isBlank(javaVersion);
+	static final int MINIMUM_VERSION = ${allJres.getFirst().getVersion()};
 
-		if (javaVersionIsBlank) {
-			logger.debug(
-				() -> "JVM system property 'java.version' is undefined. It is therefore not possible to detect Java 8.");
-		}
-
-		if (!javaVersionIsBlank && javaVersion.startsWith("1.8")) {
-			return 8;
-		}
-
-		try {
-			// java.lang.Runtime.version() is a static method available on Java 9+
-			// that returns an instance of java.lang.Runtime.Version which has the
-			// following method: public int major()
-			Method versionMethod = Runtime.class.getMethod("version");
-			Object version = ReflectionSupport.invokeMethod(versionMethod, null);
-			Method majorMethod = version.getClass().getMethod("major");
-			return (int) ReflectionSupport.invokeMethod(majorMethod, version);
-		}
-		catch (Exception ex) {
-			logger.debug(ex, () -> "Failed to determine the current JRE version via java.lang.Runtime.Version.");
-		}
-
-		return UNDEFINED_VERSION;
-	}
-
-	private static JRE determineCurrentJre(int currentVersion) {
-		switch (currentVersion) {
-			case UNDEFINED_VERSION:
-				return UNDEFINED;<%--
-			--%>@for(var jre : jres)
-			case ${jre.getVersion()}:
-				return JAVA_${jre.getVersion()};<%--
-			--%>@endfor
-			default:
-				return OTHER;
-		}
-	}
+	private static final int CURRENT_VERSION = Runtime.version().feature();
 
 	private final int version;
 
-	private JRE(int version) {
+	JRE(int version) {
 		this.version = version;
 	}
 
@@ -153,7 +107,7 @@ public enum JRE {
 	 * @see Runtime.Version#feature()
 	 * @see #currentVersionNumber()
 	 */
-	@API(status = EXPERIMENTAL, since = "5.12")
+	@API(status = MAINTAINED, since = "5.13.3")
 	public int version() {
 		return this.version;
 	}
@@ -161,18 +115,18 @@ public enum JRE {
 	/**
 	 * @return {@code true} if <em>this</em> {@code JRE} is known to be the
 	 * Java Runtime Environment version for the currently executing JVM or if
-	 * the version is {@link #OTHER} or {@link #UNDEFINED}
+	 * the version is {@link #OTHER}
 	 *
 	 * @see #currentJre()
 	 * @see #currentVersionNumber()
 	 */
 	public boolean isCurrentVersion() {
-		return this == CURRENT_JRE;
+		return this == currentJre();
 	}
 
 	/**
 	 * @return the {@link JRE} for the currently executing JVM, potentially
-	 * {@link #OTHER} or {@link #UNDEFINED}
+	 * {@link #OTHER}
 	 *
 	 * @since 5.7
 	 * @see #currentVersionNumber()
@@ -186,14 +140,19 @@ public enum JRE {
 
 	/**
 	 * @return the {@link JRE} for the currently executing JVM, potentially
-	 * {@link #OTHER} or {@link #UNDEFINED}
+	 * {@link #OTHER}
 	 *
 	 * @since 5.12
 	 * @see #currentVersionNumber()
 	 */
 	@API(status = STABLE, since = "5.12")
 	public static JRE currentJre() {
-		return CURRENT_JRE;
+		return switch (CURRENT_VERSION) {<%--
+				--%>@for(var jre : allJres)
+			case ${jre.getVersion()} -> JAVA_${jre.getVersion()};<%--
+				--%>@endfor
+			default -> OTHER;
+		};
 	}
 
 	/**
@@ -204,7 +163,7 @@ public enum JRE {
 	 * @see Runtime.Version#feature()
 	 * @see #currentJre()
 	 */
-	@API(status = EXPERIMENTAL, since = "5.12")
+	@API(status = MAINTAINED, since = "5.13.3")
 	public static int currentVersionNumber() {
 		return CURRENT_VERSION;
 	}
@@ -218,7 +177,7 @@ public enum JRE {
 	 * @since 5.12
 	 * @see Runtime.Version#feature()
 	 */
-	@API(status = EXPERIMENTAL, since = "5.12")
+	@API(status = MAINTAINED, since = "5.13.3")
 	public static boolean isCurrentVersion(int version) {
 		return version == CURRENT_VERSION;
 	}
diff --git a/junit-jupiter-api/src/templates/resources/testFixtures/org/junit/jupiter/api/condition/JavaVersionPredicates.java.jte b/junit-jupiter-api/src/templates/resources/testFixtures/org/junit/jupiter/api/condition/JavaVersionPredicates.java.jte
index 41db82bc794e..bf4929f61752 100644
--- a/junit-jupiter-api/src/templates/resources/testFixtures/org/junit/jupiter/api/condition/JavaVersionPredicates.java.jte
+++ b/junit-jupiter-api/src/templates/resources/testFixtures/org/junit/jupiter/api/condition/JavaVersionPredicates.java.jte
@@ -2,7 +2,7 @@
 @import gg.jte.support.ForSupport
 @import junitbuild.generator.model.JRE
 
-@param List<JRE> jres
+@param List<JRE> supportedJres
 @param String licenseHeader
 ${licenseHeader}
 package org.junit.jupiter.api.condition;
@@ -10,13 +10,13 @@ package org.junit.jupiter.api.condition;
 public class JavaVersionPredicates {
 
 	private static final int JAVA_VERSION = Runtime.version().feature();
-@for(JRE jre : jres)
+@for(JRE jre : supportedJres)
 	static boolean onJava${jre.getVersion()}() {
 		return JAVA_VERSION == ${jre.getVersion()};
 	}
 @endfor
 	static boolean onKnownVersion() {
-		return @for(var jre : ForSupport.of(jres))onJava${jre.get().getVersion()}()@if(!jre.isLast()) //
+		return @for(var jre : ForSupport.of(supportedJres))onJava${jre.get().getVersion()}()@if(!jre.isLast()) //
 				|| @endif@endfor;
 	}
 }
diff --git a/junit-jupiter-api/src/testFixtures/java/org/junit/jupiter/api/TemporaryClasspathExecutor.java b/junit-jupiter-api/src/testFixtures/java/org/junit/jupiter/api/TemporaryClasspathExecutor.java
new file mode 100644
index 000000000000..82f822da9e20
--- /dev/null
+++ b/junit-jupiter-api/src/testFixtures/java/org/junit/jupiter/api/TemporaryClasspathExecutor.java
@@ -0,0 +1,54 @@
+/*
+ * Copyright 2015-2025 the original author or authors.
+ *
+ * All rights reserved. This program and the accompanying materials are
+ * made available under the terms of the Eclipse Public License v2.0 which
+ * accompanies this distribution and is available at
+ *
+ * https://www.eclipse.org/legal/epl-v20.html
+ */
+
+package org.junit.jupiter.api;
+
+import java.io.IOException;
+import java.io.UncheckedIOException;
+import java.net.URL;
+import java.net.URLClassLoader;
+
+/**
+ * Utility class for executing code with a temporary classpath.
+ *
+ * @since 5.13
+ */
+public class TemporaryClasspathExecutor {
+
+	private TemporaryClasspathExecutor() {
+	}
+
+	/**
+	 * Execute the {@link Runnable} within a custom classpath, temporarily modifying the
+	 * thread's {@link Thread#getContextClassLoader() context class loader} to include
+	 * the provided {@code classpathRoot}.
+	 *
+	 * <p>After the given {@code Runnable} completes, the original context class loader is
+	 * restored.
+	 *
+	 * @param classpathRoot the root path to be added to the classpath, resolved relative
+	 * to the current thread's context class loader.
+	 * @param runnable the {@code Runnable} to execute with the temporary classpath.
+	 */
+	public static void withAdditionalClasspathRoot(String classpathRoot, Runnable runnable) {
+		var current = Thread.currentThread().getContextClassLoader();
+		try (var classLoader = new URLClassLoader(new URL[] { current.getResource(classpathRoot) }, current)) {
+			Thread.currentThread().setContextClassLoader(classLoader);
+			runnable.run();
+		}
+		catch (IOException e) {
+			throw new UncheckedIOException(e);
+		}
+		finally {
+			Thread.currentThread().setContextClassLoader(current);
+		}
+	}
+
+}
diff --git a/junit-jupiter-engine/junit-jupiter-engine.gradle.kts b/junit-jupiter-engine/junit-jupiter-engine.gradle.kts
index 04d86e5f0da7..7b3e9afcd3e7 100644
--- a/junit-jupiter-engine/junit-jupiter-engine.gradle.kts
+++ b/junit-jupiter-engine/junit-jupiter-engine.gradle.kts
@@ -1,5 +1,6 @@
 plugins {
-	id("junitbuild.kotlin-library-conventions")
+	id("junitbuild.java-library-conventions")
+	id("junitbuild.java-nullability-conventions")
 	`java-test-fixtures`
 }
 
@@ -11,6 +12,7 @@ dependencies {
 	api(projects.junitJupiterApi)
 
 	compileOnlyApi(libs.apiguardian)
+	compileOnly(libs.jspecify)
 
 	osgiVerification(projects.junitPlatformLauncher)
 }
@@ -18,7 +20,6 @@ dependencies {
 tasks {
 	jar {
 		bundle {
-			val platformVersion: String by rootProject.extra
 			bnd("""
 				Provide-Capability:\
 					org.junit.platform.engine;\
@@ -26,7 +27,7 @@ tasks {
 						version:Version="${'$'}{version_cleanup;${project.version}}"
 				Require-Capability:\
 					org.junit.platform.launcher;\
-						filter:='(&(org.junit.platform.launcher=junit-platform-launcher)(version>=${'$'}{version_cleanup;${platformVersion}})(!(version>=${'$'}{versionmask;+;${'$'}{version_cleanup;${platformVersion}}})))';\
+						filter:='(&(org.junit.platform.launcher=junit-platform-launcher)(version>=${'$'}{version_cleanup;${project.version}})(!(version>=${'$'}{versionmask;+;${'$'}{version_cleanup;${project.version}}})))';\
 						effective:=active
 			""")
 		}
diff --git a/junit-jupiter-engine/src/module/org.junit.jupiter.engine/module-info.java b/junit-jupiter-engine/src/main/java/module-info.java
similarity index 97%
rename from junit-jupiter-engine/src/module/org.junit.jupiter.engine/module-info.java
rename to junit-jupiter-engine/src/main/java/module-info.java
index e8e188aad477..ac95e98aeb2f 100644
--- a/junit-jupiter-engine/src/module/org.junit.jupiter.engine/module-info.java
+++ b/junit-jupiter-engine/src/main/java/module-info.java
@@ -18,7 +18,10 @@
  * runs Jupiter based tests on the platform.
  */
 module org.junit.jupiter.engine {
+
 	requires static org.apiguardian.api;
+	requires static org.jspecify;
+
 	requires org.junit.jupiter.api;
 	requires org.junit.platform.commons;
 	requires org.junit.platform.engine;
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/Constants.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/Constants.java
index 321a707be394..d395dc71fdc6 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/Constants.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/Constants.java
@@ -10,8 +10,8 @@
 
 package org.junit.jupiter.engine;
 
-import static org.apiguardian.api.API.Status.DEPRECATED;
 import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
 import static org.junit.platform.engine.support.hierarchical.DefaultParallelExecutionConfigurationStrategy.CONFIG_CUSTOM_CLASS_PROPERTY_NAME;
 import static org.junit.platform.engine.support.hierarchical.DefaultParallelExecutionConfigurationStrategy.CONFIG_DYNAMIC_FACTOR_PROPERTY_NAME;
@@ -190,7 +190,7 @@ public final class Constants {
 	 *
 	 * @since 5.12
 	 */
-	@API(status = EXPERIMENTAL, since = "5.12")
+	@API(status = MAINTAINED, since = "5.13.3")
 	public static final String EXTENSIONS_TIMEOUT_THREAD_DUMP_ENABLED_PROPERTY_NAME = JupiterConfiguration.EXTENSIONS_TIMEOUT_THREAD_DUMP_ENABLED_PROPERTY_NAME;
 
 	/**
@@ -217,7 +217,7 @@ public final class Constants {
 	 *
 	 * @since 5.13
 	 */
-	@API(status = EXPERIMENTAL, since = "5.13")
+	@API(status = EXPERIMENTAL, since = "6.0")
 	public static final String CLOSING_STORED_AUTO_CLOSEABLE_ENABLED_PROPERTY_NAME = JupiterConfiguration.CLOSING_STORED_AUTO_CLOSEABLE_ENABLED_PROPERTY_NAME;
 
 	/**
@@ -276,7 +276,7 @@ public final class Constants {
 	 *
 	 * @since 5.10
 	 */
-	@API(status = EXPERIMENTAL, since = "5.10")
+	@API(status = MAINTAINED, since = "5.13.3")
 	public static final String PARALLEL_CONFIG_FIXED_MAX_POOL_SIZE_PROPERTY_NAME = PARALLEL_CONFIG_PREFIX
 			+ CONFIG_FIXED_MAX_POOL_SIZE_PROPERTY_NAME;
 
@@ -294,7 +294,7 @@ public final class Constants {
 	 *
 	 * @since 5.10
 	 */
-	@API(status = EXPERIMENTAL, since = "5.10")
+	@API(status = MAINTAINED, since = "5.13.3")
 	public static final String PARALLEL_CONFIG_FIXED_SATURATE_PROPERTY_NAME = PARALLEL_CONFIG_PREFIX
 			+ CONFIG_FIXED_SATURATE_PROPERTY_NAME;
 
@@ -434,17 +434,6 @@ public final class Constants {
 	@API(status = STABLE, since = "5.9")
 	public static final String DEFAULT_TEST_CLASS_ORDER_PROPERTY_NAME = ClassOrderer.DEFAULT_ORDER_PROPERTY_NAME;
 
-	/**
-	 * Property name used to set the scope of temporary directories created via
-	 * the {@link TempDir @TempDir} annotation: {@value}
-	 *
-	 * @see TempDir#SCOPE_PROPERTY_NAME
-	 */
-	@Deprecated
-	@API(status = DEPRECATED, since = "5.8")
-	@SuppressWarnings("deprecation")
-	public static final String TEMP_DIR_SCOPE_PROPERTY_NAME = TempDir.SCOPE_PROPERTY_NAME;
-
 	/**
 	 * Property name used to set the default timeout thread mode.
 	 *
@@ -452,7 +441,7 @@ public final class Constants {
 	 * @see Timeout
 	 * @see Timeout.ThreadMode
 	 */
-	@API(status = EXPERIMENTAL, since = "5.9")
+	@API(status = MAINTAINED, since = "5.13.3")
 	public static final String DEFAULT_TIMEOUT_THREAD_MODE_PROPERTY_NAME = Timeout.DEFAULT_TIMEOUT_THREAD_MODE_PROPERTY_NAME;
 
 	/**
@@ -462,7 +451,7 @@ public final class Constants {
 	 * @since 5.10
 	 * @see TempDir#DEFAULT_FACTORY_PROPERTY_NAME
 	 */
-	@API(status = EXPERIMENTAL, since = "5.10")
+	@API(status = MAINTAINED, since = "5.13.3")
 	public static final String DEFAULT_TEMP_DIR_FACTORY_PROPERTY_NAME = TempDir.DEFAULT_FACTORY_PROPERTY_NAME;
 
 	/**
@@ -472,7 +461,7 @@ public final class Constants {
 	 * @since 5.12
 	 * @see org.junit.jupiter.api.extension.TestInstantiationAwareExtension
 	 */
-	@API(status = EXPERIMENTAL, since = "5.12")
+	@API(status = MAINTAINED, since = "5.13.3")
 	public static final String DEFAULT_TEST_CLASS_INSTANCE_CONSTRUCTION_EXTENSION_CONTEXT_SCOPE_PROPERTY_NAME = ExtensionContextScope.DEFAULT_SCOPE_PROPERTY_NAME;
 
 	private Constants() {
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/JupiterTestEngine.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/JupiterTestEngine.java
index c3878b9c84b7..59f2bc794c92 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/JupiterTestEngine.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/JupiterTestEngine.java
@@ -28,6 +28,7 @@
 import org.junit.platform.engine.TestDescriptor;
 import org.junit.platform.engine.UniqueId;
 import org.junit.platform.engine.support.config.PrefixedConfigurationParameters;
+import org.junit.platform.engine.support.discovery.DiscoveryIssueReporter;
 import org.junit.platform.engine.support.hierarchical.ForkJoinPoolHierarchicalTestExecutorService;
 import org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine;
 import org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutorService;
@@ -64,10 +65,13 @@ public Optional<String> getArtifactId() {
 
 	@Override
 	public TestDescriptor discover(EngineDiscoveryRequest discoveryRequest, UniqueId uniqueId) {
-		JupiterConfiguration configuration = new CachingJupiterConfiguration(new DefaultJupiterConfiguration(
-			discoveryRequest.getConfigurationParameters(), discoveryRequest.getOutputDirectoryProvider()));
+		DiscoveryIssueReporter issueReporter = DiscoveryIssueReporter.deduplicating(
+			DiscoveryIssueReporter.forwarding(discoveryRequest.getDiscoveryListener(), uniqueId));
+		JupiterConfiguration configuration = new CachingJupiterConfiguration(
+			new DefaultJupiterConfiguration(discoveryRequest.getConfigurationParameters(),
+				discoveryRequest.getOutputDirectoryProvider(), issueReporter));
 		JupiterEngineDescriptor engineDescriptor = new JupiterEngineDescriptor(uniqueId, configuration);
-		new DiscoverySelectorResolver().resolveSelectors(discoveryRequest, engineDescriptor);
+		DiscoverySelectorResolver.resolveSelectors(discoveryRequest, engineDescriptor, issueReporter);
 		return engineDescriptor;
 	}
 
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/config/CachingJupiterConfiguration.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/config/CachingJupiterConfiguration.java
index ecab219838f3..33c927038ec3 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/config/CachingJupiterConfiguration.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/config/CachingJupiterConfiguration.java
@@ -59,7 +59,7 @@ public Optional<String> getRawConfigurationParameter(String key) {
 	}
 
 	@Override
-	public <T> Optional<T> getRawConfigurationParameter(String key, Function<String, T> transformer) {
+	public <T> Optional<T> getRawConfigurationParameter(String key, Function<? super String, ? extends T> transformer) {
 		return delegate.getRawConfigurationParameter(key, transformer);
 	}
 
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/config/DefaultJupiterConfiguration.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/config/DefaultJupiterConfiguration.java
index c6ab8b0d5508..99f08e00ee4a 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/config/DefaultJupiterConfiguration.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/config/DefaultJupiterConfiguration.java
@@ -15,6 +15,7 @@
 import static org.junit.jupiter.api.io.TempDir.DEFAULT_CLEANUP_MODE_PROPERTY_NAME;
 import static org.junit.jupiter.api.io.TempDir.DEFAULT_FACTORY_PROPERTY_NAME;
 
+import java.util.List;
 import java.util.Optional;
 import java.util.function.Function;
 import java.util.function.Predicate;
@@ -34,7 +35,10 @@
 import org.junit.platform.commons.util.ClassNamePatternFilterUtils;
 import org.junit.platform.commons.util.Preconditions;
 import org.junit.platform.engine.ConfigurationParameters;
+import org.junit.platform.engine.DiscoveryIssue;
+import org.junit.platform.engine.DiscoveryIssue.Severity;
 import org.junit.platform.engine.reporting.OutputDirectoryProvider;
+import org.junit.platform.engine.support.discovery.DiscoveryIssueReporter;
 
 /**
  * Default implementation of the {@link JupiterConfiguration} API.
@@ -44,6 +48,8 @@
 @API(status = INTERNAL, since = "5.4")
 public class DefaultJupiterConfiguration implements JupiterConfiguration {
 
+	private final List<String> UNSUPPORTED_CONFIGURATION_PARAMETERS = List.of("junit.jupiter.tempdir.scope");
+
 	private static final EnumConfigurationParameterConverter<ExecutionMode> executionModeConverter = //
 		new EnumConfigurationParameterConverter<>(ExecutionMode.class, "parallel execution mode");
 
@@ -72,10 +78,21 @@ public class DefaultJupiterConfiguration implements JupiterConfiguration {
 	private final OutputDirectoryProvider outputDirectoryProvider;
 
 	public DefaultJupiterConfiguration(ConfigurationParameters configurationParameters,
-			OutputDirectoryProvider outputDirectoryProvider) {
+			OutputDirectoryProvider outputDirectoryProvider, DiscoveryIssueReporter issueReporter) {
 		this.configurationParameters = Preconditions.notNull(configurationParameters,
 			"ConfigurationParameters must not be null");
 		this.outputDirectoryProvider = outputDirectoryProvider;
+		validateConfigurationParameters(issueReporter);
+	}
+
+	private void validateConfigurationParameters(DiscoveryIssueReporter issueReporter) {
+		UNSUPPORTED_CONFIGURATION_PARAMETERS.forEach(key -> configurationParameters.get(key) //
+				.ifPresent(value -> {
+					var warning = DiscoveryIssue.create(Severity.WARNING,
+						"The '%s' configuration parameter is no longer supported: %s. Please remove it from your configuration.".formatted(
+							key, value));
+					issueReporter.reportIssue(warning);
+				}));
 	}
 
 	@Override
@@ -103,7 +120,7 @@ public Optional<String> getRawConfigurationParameter(String key) {
 	}
 
 	@Override
-	public <T> Optional<T> getRawConfigurationParameter(String key, Function<String, T> transformer) {
+	public <T> Optional<T> getRawConfigurationParameter(String key, Function<? super String, ? extends T> transformer) {
 		return configurationParameters.get(key, transformer);
 	}
 
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/config/EnumConfigurationParameterConverter.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/config/EnumConfigurationParameterConverter.java
index 19c8222c76ad..d0a470aed8ec 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/config/EnumConfigurationParameterConverter.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/config/EnumConfigurationParameterConverter.java
@@ -53,8 +53,8 @@ public E get(String key, Function<String, Optional<String>> lookup, E defaultVal
 			try {
 				constantName = value.get().trim().toUpperCase(Locale.ROOT);
 				E result = Enum.valueOf(enumType, constantName);
-				logger.config(() -> String.format("Using %s '%s' set via the '%s' configuration parameter.",
-					enumDisplayName, result, key));
+				logger.config(() -> "Using %s '%s' set via the '%s' configuration parameter.".formatted(enumDisplayName,
+					result, key));
 				return result;
 			}
 			catch (Exception ex) {
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/config/InstantiatingConfigurationParameterConverter.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/config/InstantiatingConfigurationParameterConverter.java
index c0df1064f0c3..5f2eaf34745b 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/config/InstantiatingConfigurationParameterConverter.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/config/InstantiatingConfigurationParameterConverter.java
@@ -67,7 +67,7 @@ private void logFailureMessage(String className, String key, Exception cause) {
 	}
 
 	private void logSuccessMessage(String className, String key) {
-		logger.config(() -> String.format("Using default %s '%s' set via the '%s' configuration parameter.", this.name,
+		logger.config(() -> "Using default %s '%s' set via the '%s' configuration parameter.".formatted(this.name,
 			className, key));
 	}
 
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/config/JupiterConfiguration.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/config/JupiterConfiguration.java
index ca4f8ff76a7d..92607e4614c3 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/config/JupiterConfiguration.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/config/JupiterConfiguration.java
@@ -57,7 +57,7 @@ public interface JupiterConfiguration {
 
 	Optional<String> getRawConfigurationParameter(String key);
 
-	<T> Optional<T> getRawConfigurationParameter(String key, Function<String, T> transformer);
+	<T> Optional<T> getRawConfigurationParameter(String key, Function<? super String, ? extends T> transformer);
 
 	boolean isParallelExecutionEnabled();
 
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/config/package-info.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/config/package-info.java
index ede680886ac3..1ce02462c321 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/config/package-info.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/config/package-info.java
@@ -2,4 +2,7 @@
  * Configuration specific to the JUnit Jupiter test engine.
  */
 
+@NullMarked
 package org.junit.jupiter.engine.config;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/AbstractExtensionContext.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/AbstractExtensionContext.java
index 219acbb474c7..d19c71845461 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/AbstractExtensionContext.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/AbstractExtensionContext.java
@@ -24,6 +24,7 @@
 import java.util.Set;
 import java.util.function.Function;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.extension.ExecutableInvoker;
 import org.junit.jupiter.api.extension.Extension;
 import org.junit.jupiter.api.extension.ExtensionContext;
@@ -54,7 +55,7 @@ abstract class AbstractExtensionContext<T extends TestDescriptor> implements Ext
 
 	private static final Logger LOGGER = LoggerFactory.getLogger(AbstractExtensionContext.class);
 
-	private final ExtensionContext parent;
+	private final @Nullable ExtensionContext parent;
 	private final EngineExecutionListener engineExecutionListener;
 	private final T testDescriptor;
 	private final Set<String> tags;
@@ -64,8 +65,8 @@ abstract class AbstractExtensionContext<T extends TestDescriptor> implements Ext
 	private final LauncherStoreFacade launcherStoreFacade;
 	private final NamespacedHierarchicalStore<org.junit.platform.engine.support.store.Namespace> valuesStore;
 
-	AbstractExtensionContext(ExtensionContext parent, EngineExecutionListener engineExecutionListener, T testDescriptor,
-			JupiterConfiguration configuration, ExtensionRegistry extensionRegistry,
+	AbstractExtensionContext(@Nullable ExtensionContext parent, EngineExecutionListener engineExecutionListener,
+			T testDescriptor, JupiterConfiguration configuration, ExtensionRegistry extensionRegistry,
 			LauncherStoreFacade launcherStoreFacade) {
 
 		Preconditions.notNull(testDescriptor, "TestDescriptor must not be null");
@@ -93,23 +94,23 @@ private NamespacedHierarchicalStore.CloseAction<org.junit.platform.engine.suppor
 		return (__, ___, value) -> {
 			boolean isAutoCloseEnabled = this.configuration.isClosingStoredAutoCloseablesEnabled();
 
-			if (value instanceof AutoCloseable && isAutoCloseEnabled) {
-				((AutoCloseable) value).close();
+			if (value instanceof @SuppressWarnings("resource") AutoCloseable closeable && isAutoCloseEnabled) {
+				closeable.close();
 				return;
 			}
 
-			if (value instanceof Store.CloseableResource) {
+			if (value instanceof Store.CloseableResource resource) {
 				if (isAutoCloseEnabled) {
 					LOGGER.warn(
 						() -> "Type implements CloseableResource but not AutoCloseable: " + value.getClass().getName());
 				}
-				((Store.CloseableResource) value).close();
+				resource.close();
 			}
 		};
 	}
 
 	private static NamespacedHierarchicalStore<org.junit.platform.engine.support.store.Namespace> createStore(
-			ExtensionContext parent, LauncherStoreFacade launcherStoreFacade,
+			@Nullable ExtensionContext parent, LauncherStoreFacade launcherStoreFacade,
 			NamespacedHierarchicalStore.CloseAction<org.junit.platform.engine.support.store.Namespace> closeAction) {
 		NamespacedHierarchicalStore<org.junit.platform.engine.support.store.Namespace> parentStore;
 		if (parent == null) {
@@ -159,7 +160,9 @@ public void publishDirectory(String name, ThrowingConsumer<Path> action) {
 		Preconditions.notNull(action, "action must not be null");
 
 		ThrowingConsumer<Path> enhancedAction = path -> {
-			Files.createDirectory(path);
+			if (!Files.isDirectory(path)) {
+				Files.createDirectory(path);
+			}
 			action.accept(path);
 		};
 		publishFileEntry(name, enhancedAction, file -> {
@@ -172,7 +175,8 @@ private void publishFileEntry(String name, ThrowingConsumer<Path> action,
 			Function<Path, FileEntry> fileEntryCreator) {
 		Path dir = createOutputDirectory();
 		Path path = dir.resolve(name);
-		Preconditions.condition(path.getParent().equals(dir), () -> "name must not contain path separators: " + name);
+		Preconditions.condition(path.getParent() != null && path.getParent().equals(dir),
+			() -> "name must not contain path separators: " + name);
 		try {
 			action.accept(path);
 		}
@@ -218,16 +222,11 @@ public Store getStore(Namespace namespace) {
 
 	@Override
 	public Store getStore(StoreScope scope, Namespace namespace) {
-		// TODO [#4246] Use switch expression
-		switch (scope) {
-			case LAUNCHER_SESSION:
-				return launcherStoreFacade.getSessionLevelStore(namespace);
-			case EXECUTION_REQUEST:
-				return launcherStoreFacade.getRequestLevelStore(namespace);
-			case EXTENSION_CONTEXT:
-				return getStore(namespace);
-		}
-		throw new JUnitException("Unknown StoreScope: " + scope);
+		return switch (scope) {
+			case LAUNCHER_SESSION -> launcherStoreFacade.getSessionLevelStore(namespace);
+			case EXECUTION_REQUEST -> launcherStoreFacade.getRequestLevelStore(namespace);
+			case EXTENSION_CONTEXT -> getStore(namespace);
+		};
 	}
 
 	@Override
@@ -242,7 +241,8 @@ public Optional<String> getConfigurationParameter(String key) {
 	}
 
 	@Override
-	public <V> Optional<V> getConfigurationParameter(String key, Function<String, V> transformer) {
+	public <V> Optional<V> getConfigurationParameter(String key,
+			Function<? super String, ? extends @Nullable V> transformer) {
 		return this.configuration.getRawConfigurationParameter(key, transformer);
 	}
 
@@ -264,12 +264,9 @@ public <E extends Extension> List<E> getExtensions(Class<E> extensionType) {
 	protected abstract Node.ExecutionMode getPlatformExecutionMode();
 
 	private ExecutionMode toJupiterExecutionMode(Node.ExecutionMode mode) {
-		switch (mode) {
-			case CONCURRENT:
-				return ExecutionMode.CONCURRENT;
-			case SAME_THREAD:
-				return ExecutionMode.SAME_THREAD;
-		}
-		throw new JUnitException("Unknown ExecutionMode: " + mode);
+		return switch (mode) {
+			case CONCURRENT -> ExecutionMode.CONCURRENT;
+			case SAME_THREAD -> ExecutionMode.SAME_THREAD;
+		};
 	}
 }
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/ClassBasedTestDescriptor.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/ClassBasedTestDescriptor.java
index d6837494403e..5aacb02d1af2 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/ClassBasedTestDescriptor.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/ClassBasedTestDescriptor.java
@@ -10,6 +10,7 @@
 
 package org.junit.jupiter.engine.descriptor;
 
+import static java.util.Objects.requireNonNull;
 import static java.util.stream.Collectors.joining;
 import static org.apiguardian.api.API.Status.INTERNAL;
 import static org.junit.jupiter.engine.descriptor.CallbackSupport.invokeAfterCallbacks;
@@ -37,6 +38,7 @@
 import java.util.function.Supplier;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.TestInstance.Lifecycle;
 import org.junit.jupiter.api.extension.AfterAllCallback;
 import org.junit.jupiter.api.extension.BeforeAllCallback;
@@ -59,7 +61,6 @@
 import org.junit.jupiter.engine.execution.DefaultTestInstances;
 import org.junit.jupiter.engine.execution.ExtensionContextSupplier;
 import org.junit.jupiter.engine.execution.InterceptingExecutableInvoker;
-import org.junit.jupiter.engine.execution.InterceptingExecutableInvoker.ReflectiveInterceptorCall;
 import org.junit.jupiter.engine.execution.InterceptingExecutableInvoker.ReflectiveInterceptorCall.VoidMethodInterceptorCall;
 import org.junit.jupiter.engine.execution.JupiterEngineExecutionContext;
 import org.junit.jupiter.engine.execution.TestInstancesProvider;
@@ -92,8 +93,9 @@ public abstract class ClassBasedTestDescriptor extends JupiterTestDescriptor
 
 	protected final ClassInfo classInfo;
 
-	private LifecycleMethods lifecycleMethods;
-	private TestInstanceFactory testInstanceFactory;
+	private @Nullable LifecycleMethods lifecycleMethods;
+
+	private @Nullable TestInstanceFactory testInstanceFactory;
 
 	ClassBasedTestDescriptor(UniqueId uniqueId, Class<?> testClass, Supplier<String> displayNameSupplier,
 			JupiterConfiguration configuration) {
@@ -142,13 +144,13 @@ public final void validate(DiscoveryIssueReporter reporter) {
 
 	private void validateDisplayNameAnnotation(DiscoveryIssueReporter reporter) {
 		DisplayNameUtils.validateAnnotation(getTestClass(), //
-			() -> String.format("class '%s'", getTestClass().getName()), //
+			() -> "class '%s'".formatted(getTestClass().getName()), //
 			() -> getSource().orElse(null), //
 			reporter);
 	}
 
 	protected void validateCoreLifecycleMethods(DiscoveryIssueReporter reporter) {
-		Validatable.reportAndClear(this.lifecycleMethods.discoveryIssues, reporter);
+		Validatable.reportAndClear(requireLifecycleMethods().discoveryIssues, reporter);
 	}
 
 	protected void validateClassTemplateInvocationLifecycleMethods(DiscoveryIssueReporter reporter) {
@@ -198,7 +200,8 @@ public final JupiterEngineExecutionContext prepare(JupiterEngineExecutionContext
 			registerExtensionsFromConstructorParameters(registry, getTestClass());
 		}
 
-		this.lifecycleMethods.beforeAll.forEach(method -> registerExtensionsFromExecutableParameters(registry, method));
+		requireLifecycleMethods().beforeAll.forEach(
+			method -> registerExtensionsFromExecutableParameters(registry, method));
 		// Since registerBeforeEachMethodAdapters() and registerAfterEachMethodAdapters() also
 		// invoke registerExtensionsFromExecutableParameters(), we invoke those methods before
 		// invoking registerExtensionsFromExecutableParameters() for @AfterAll methods,
@@ -206,7 +209,8 @@ public final JupiterEngineExecutionContext prepare(JupiterEngineExecutionContext
 		// on parameters in lifecycle methods.
 		registerBeforeEachMethodAdapters(registry);
 		registerAfterEachMethodAdapters(registry);
-		this.lifecycleMethods.afterAll.forEach(method -> registerExtensionsFromExecutableParameters(registry, method));
+		requireLifecycleMethods().afterAll.forEach(
+			method -> registerExtensionsFromExecutableParameters(registry, method));
 		registerExtensionsFromInstanceFields(registry, getTestClass());
 
 		ThrowableCollector throwableCollector = createThrowableCollector();
@@ -288,7 +292,7 @@ public void cleanUp(JupiterEngineExecutionContext context) throws Exception {
 		this.testInstanceFactory = null;
 	}
 
-	private TestInstanceFactory resolveTestInstanceFactory(ExtensionRegistry registry) {
+	private @Nullable TestInstanceFactory resolveTestInstanceFactory(ExtensionRegistry registry) {
 		List<TestInstanceFactory> factories = registry.getExtensions(TestInstanceFactory.class);
 
 		if (factories.size() == 1) {
@@ -300,8 +304,7 @@ private TestInstanceFactory resolveTestInstanceFactory(ExtensionRegistry registr
 					.map(factory -> factory.getClass().getName())//
 					.collect(joining(", "));
 
-			String errorMessage = String.format(
-				"The following TestInstanceFactory extensions were registered for test class [%s], but only one is permitted: %s",
+			String errorMessage = "The following TestInstanceFactory extensions were registered for test class [%s], but only one is permitted: %s".formatted(
 				getTestClass().getName(), factoryNames);
 
 			throw new ExtensionConfigurationException(errorMessage);
@@ -348,30 +351,30 @@ protected final TestInstances instantiateTestClass(Optional<TestInstances> outer
 		invokeTestInstancePreConstructCallbacks(new DefaultTestInstanceFactoryContext(getTestClass(), outerInstance),
 			registry, extensionContext);
 		Object instance = this.testInstanceFactory != null //
-				? invokeTestInstanceFactory(outerInstance, extensionContext) //
+				? invokeTestInstanceFactory(this.testInstanceFactory, outerInstance, extensionContext) //
 				: invokeTestClassConstructor(outerInstance, registry, extensionContext);
 		return outerInstances.map(instances -> DefaultTestInstances.of(instances, instance)) //
 				.orElse(DefaultTestInstances.of(instance));
 	}
 
-	private Object invokeTestInstanceFactory(Optional<Object> outerInstance,
+	private Object invokeTestInstanceFactory(TestInstanceFactory testInstanceFactory, Optional<Object> outerInstance,
 			ExtensionContextSupplier extensionContext) {
 		Object instance;
 
 		try {
-			ExtensionContext actualExtensionContext = extensionContext.get(this.testInstanceFactory);
-			instance = this.testInstanceFactory.createTestInstance(
+			ExtensionContext actualExtensionContext = extensionContext.get(testInstanceFactory);
+			instance = testInstanceFactory.createTestInstance(
 				new DefaultTestInstanceFactoryContext(getTestClass(), outerInstance), actualExtensionContext);
 		}
 		catch (Throwable throwable) {
 			UnrecoverableExceptions.rethrowIfUnrecoverable(throwable);
 
-			if (throwable instanceof TestInstantiationException) {
-				throw (TestInstantiationException) throwable;
+			if (throwable instanceof TestInstantiationException exception) {
+				throw exception;
 			}
 
-			String message = String.format("TestInstanceFactory [%s] failed to instantiate test class [%s]",
-				this.testInstanceFactory.getClass().getName(), getTestClass().getName());
+			String message = "TestInstanceFactory [%s] failed to instantiate test class [%s]".formatted(
+				testInstanceFactory.getClass().getName(), getTestClass().getName());
 			if (StringUtils.isNotBlank(throwable.getMessage())) {
 				message += ": " + throwable.getMessage();
 			}
@@ -390,9 +393,8 @@ private Object invokeTestInstanceFactory(Optional<Object> outerInstance,
 				testClassName += "@" + Integer.toHexString(System.identityHashCode(getTestClass()));
 				instanceClassName += "@" + Integer.toHexString(System.identityHashCode(instanceClass));
 			}
-			String message = String.format(
-				"TestInstanceFactory [%s] failed to return an instance of [%s] and instead returned an instance of [%s].",
-				this.testInstanceFactory.getClass().getName(), testClassName, instanceClassName);
+			String message = "TestInstanceFactory [%s] failed to return an instance of [%s] and instead returned an instance of [%s].".formatted(
+				testInstanceFactory.getClass().getName(), testClassName, instanceClassName);
 
 			throw new TestInstantiationException(message);
 		}
@@ -440,11 +442,11 @@ private void invokeBeforeAllMethods(JupiterEngineExecutionContext context) {
 		ThrowableCollector throwableCollector = context.getThrowableCollector();
 		Object testInstance = extensionContext.getTestInstance().orElse(null);
 
-		for (Method method : this.lifecycleMethods.beforeAll) {
+		for (Method method : requireLifecycleMethods().beforeAll) {
 			throwableCollector.execute(() -> {
 				try {
-					executableInvoker.invoke(method, testInstance, extensionContext, registry,
-						ReflectiveInterceptorCall.ofVoidMethod(InvocationInterceptor::interceptBeforeAllMethod));
+					executableInvoker.invokeVoid(method, testInstance, extensionContext, registry,
+						InvocationInterceptor::interceptBeforeAllMethod);
 				}
 				catch (Throwable throwable) {
 					invokeBeforeAllMethodExecutionExceptionHandlers(registry, extensionContext, throwable);
@@ -469,10 +471,10 @@ private void invokeAfterAllMethods(JupiterEngineExecutionContext context) {
 		ThrowableCollector throwableCollector = context.getThrowableCollector();
 		Object testInstance = extensionContext.getTestInstance().orElse(null);
 
-		this.lifecycleMethods.afterAll.forEach(method -> throwableCollector.execute(() -> {
+		requireLifecycleMethods().afterAll.forEach(method -> throwableCollector.execute(() -> {
 			try {
-				executableInvoker.invoke(method, testInstance, extensionContext, registry,
-					ReflectiveInterceptorCall.ofVoidMethod(InvocationInterceptor::interceptAfterAllMethod));
+				executableInvoker.invokeVoid(method, testInstance, extensionContext, registry,
+					InvocationInterceptor::interceptAfterAllMethod);
 			}
 			catch (Throwable throwable) {
 				invokeAfterAllMethodExecutionExceptionHandlers(registry, extensionContext, throwable);
@@ -502,13 +504,13 @@ private boolean isPerClassLifecycle(JupiterEngineExecutionContext context) {
 	}
 
 	private void registerBeforeEachMethodAdapters(ExtensionRegistrar registrar) {
-		registerMethodsAsExtensions(this.lifecycleMethods.beforeEach, registrar,
+		registerMethodsAsExtensions(requireLifecycleMethods().beforeEach, registrar,
 			this::synthesizeBeforeEachMethodAdapter);
 	}
 
 	private void registerAfterEachMethodAdapters(ExtensionRegistrar registrar) {
 		// Make a local copy since findAfterEachMethods() returns an immutable list.
-		List<Method> afterEachMethods = new ArrayList<>(this.lifecycleMethods.afterEach);
+		List<Method> afterEachMethods = new ArrayList<>(requireLifecycleMethods().afterEach);
 
 		// Since the bottom-up ordering of afterEachMethods will later be reversed when the
 		// synthesized AfterEachMethodAdapters are executed within TestMethodTestDescriptor,
@@ -544,8 +546,11 @@ private void invokeMethodInExtensionContext(Method method, ExtensionContext cont
 		Object target = testInstances.findInstance(getTestClass()).orElseThrow(
 			() -> new JUnitException("Failed to find instance for method: " + method.toGenericString()));
 
-		executableInvoker.invoke(method, target, context, registry,
-			ReflectiveInterceptorCall.ofVoidMethod(interceptorCall));
+		executableInvoker.invokeVoid(method, target, context, registry, interceptorCall);
+	}
+
+	private LifecycleMethods requireLifecycleMethods() {
+		return requireNonNull(this.lifecycleMethods);
 	}
 
 	protected static class ClassInfo {
@@ -555,13 +560,16 @@ protected static class ClassInfo {
 		final Class<?> testClass;
 		final Set<TestTag> tags;
 		final Lifecycle lifecycle;
+
+		@Nullable
 		ExecutionMode defaultChildExecutionMode;
+
 		final ExclusiveResourceCollector exclusiveResourceCollector;
 
 		ClassInfo(Class<?> testClass, JupiterConfiguration configuration) {
 			this.testClass = testClass;
 			this.tags = getTags(testClass, //
-				() -> String.format("class '%s'", testClass.getName()), //
+				() -> "class '%s'".formatted(testClass.getName()), //
 				() -> ClassSource.from(testClass), //
 				discoveryIssues::add);
 			this.lifecycle = getTestInstanceLifecycle(testClass, configuration);
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/ClassExtensionContext.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/ClassExtensionContext.java
index cc052d0a60f5..10e987049260 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/ClassExtensionContext.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/ClassExtensionContext.java
@@ -15,6 +15,7 @@
 import java.util.List;
 import java.util.Optional;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.TestInstance.Lifecycle;
 import org.junit.jupiter.api.extension.ExtensionContext;
 import org.junit.jupiter.api.extension.TestInstances;
@@ -33,7 +34,7 @@ final class ClassExtensionContext extends AbstractExtensionContext<ClassBasedTes
 
 	private final ThrowableCollector throwableCollector;
 
-	private TestInstances testInstances;
+	private @Nullable TestInstances testInstances;
 
 	ClassExtensionContext(ExtensionContext parent, EngineExecutionListener engineExecutionListener,
 			ClassBasedTestDescriptor testDescriptor, Lifecycle lifecycle, JupiterConfiguration configuration,
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/ClassTemplateInvocationTestDescriptor.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/ClassTemplateInvocationTestDescriptor.java
index c6774c9689d0..9d3037b6059b 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/ClassTemplateInvocationTestDescriptor.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/ClassTemplateInvocationTestDescriptor.java
@@ -10,6 +10,7 @@
 
 package org.junit.jupiter.engine.descriptor;
 
+import static java.util.Objects.requireNonNull;
 import static org.apiguardian.api.API.Status.INTERNAL;
 import static org.junit.jupiter.engine.descriptor.CallbackSupport.invokeAfterCallbacks;
 import static org.junit.jupiter.engine.descriptor.CallbackSupport.invokeBeforeCallbacks;
@@ -23,6 +24,7 @@
 import java.util.stream.Stream;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.extension.AfterClassTemplateInvocationCallback;
 import org.junit.jupiter.api.extension.BeforeClassTemplateInvocationCallback;
 import org.junit.jupiter.api.extension.ClassTemplateInvocationContext;
@@ -46,11 +48,13 @@ public class ClassTemplateInvocationTestDescriptor extends JupiterTestDescriptor
 	public static final String SEGMENT_TYPE = "class-template-invocation";
 
 	private final ClassTemplateTestDescriptor parent;
-	private ClassTemplateInvocationContext invocationContext;
+
+	private @Nullable ClassTemplateInvocationContext invocationContext;
+
 	private final int index;
 
 	public ClassTemplateInvocationTestDescriptor(UniqueId uniqueId, ClassTemplateTestDescriptor parent,
-			ClassTemplateInvocationContext invocationContext, int index, TestSource source,
+			ClassTemplateInvocationContext invocationContext, int index, @Nullable TestSource source,
 			JupiterConfiguration configuration) {
 		super(uniqueId, invocationContext.getDisplayName(index), source, configuration);
 		this.parent = parent;
@@ -67,7 +71,7 @@ public int getIndex() {
 	@Override
 	protected ClassTemplateInvocationTestDescriptor withUniqueId(UnaryOperator<UniqueId> uniqueIdTransformer) {
 		return new ClassTemplateInvocationTestDescriptor(uniqueIdTransformer.apply(getUniqueId()), parent,
-			this.invocationContext, this.index, getSource().orElse(null), this.configuration);
+			requiredInvocationContext(), this.index, getSource().orElse(null), this.configuration);
 	}
 
 	// --- TestDescriptor ------------------------------------------------------
@@ -111,18 +115,18 @@ public Function<ResourceLocksProvider, Set<ResourceLocksProvider.Lock>> getResou
 	@Override
 	public JupiterEngineExecutionContext prepare(JupiterEngineExecutionContext context) {
 		MutableExtensionRegistry registry = context.getExtensionRegistry();
-		List<Extension> additionalExtensions = this.invocationContext.getAdditionalExtensions();
+		List<Extension> additionalExtensions = requiredInvocationContext().getAdditionalExtensions();
 		if (!additionalExtensions.isEmpty()) {
 			MutableExtensionRegistry childRegistry = createRegistryFrom(registry, Stream.empty());
 			additionalExtensions.forEach(
-				extension -> childRegistry.registerExtension(extension, this.invocationContext));
+				extension -> childRegistry.registerExtension(extension, requiredInvocationContext()));
 			registry = childRegistry;
 		}
 		ExtensionContext extensionContext = new ClassTemplateInvocationExtensionContext(context.getExtensionContext(),
 			context.getExecutionListener(), this, context.getConfiguration(), registry,
 			context.getLauncherStoreFacade());
 		ThrowableCollector throwableCollector = createThrowableCollector();
-		throwableCollector.execute(() -> this.invocationContext.prepareInvocation(extensionContext));
+		throwableCollector.execute(() -> requiredInvocationContext().prepareInvocation(extensionContext));
 		return context.extend() //
 				.withExtensionRegistry(registry) //
 				.withExtensionContext(extensionContext) //
@@ -177,4 +181,8 @@ public void cleanUp(JupiterEngineExecutionContext context) throws Exception {
 		this.invocationContext = null;
 		super.cleanUp(context);
 	}
+
+	private ClassTemplateInvocationContext requiredInvocationContext() {
+		return requireNonNull(this.invocationContext);
+	}
 }
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/ClassTemplateTestDescriptor.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/ClassTemplateTestDescriptor.java
index 77b540c6e2bb..29fb3c54652d 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/ClassTemplateTestDescriptor.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/ClassTemplateTestDescriptor.java
@@ -11,7 +11,6 @@
 package org.junit.jupiter.engine.descriptor;
 
 import static java.util.stream.Collectors.toCollection;
-import static java.util.stream.Collectors.toList;
 import static org.apiguardian.api.API.Status.INTERNAL;
 import static org.junit.jupiter.api.TestInstance.Lifecycle.PER_METHOD;
 import static org.junit.jupiter.engine.descriptor.LifecycleMethodUtils.validateClassTemplateInvocationLifecycleMethodsAreDeclaredCorrectly;
@@ -108,9 +107,9 @@ protected JupiterTestDescriptor copyIncludingDescendants(UnaryOperator<UniqueId>
 			copy.childrenPrototypes.add(newChild);
 		});
 		this.childrenPrototypesByIndex.forEach((index, oldChildren) -> {
-			List<TestDescriptor> newChildren = oldChildren.stream() //
+			List<? extends TestDescriptor> newChildren = oldChildren.stream() //
 					.map(oldChild -> ((JupiterTestDescriptor) oldChild).copyIncludingDescendants(uniqueIdTransformer)) //
-					.collect(toList());
+					.toList();
 			copy.childrenPrototypesByIndex.put(index, newChildren);
 		});
 		return copy;
@@ -134,8 +133,8 @@ public void prune() {
 		new LinkedHashSet<>(this.children).forEach(child -> child.accept(TestDescriptor::prune));
 		// Second iteration to avoid processing children that were pruned in the first iteration
 		this.children.forEach(child -> {
-			if (child instanceof ClassTemplateInvocationTestDescriptor) {
-				int index = ((ClassTemplateInvocationTestDescriptor) child).getIndex();
+			if (child instanceof ClassTemplateInvocationTestDescriptor descriptor) {
+				int index = descriptor.getIndex();
 				this.dynamicDescendantFilter.allowIndex(index - 1);
 				this.childrenPrototypesByIndex.put(index, child.getChildren());
 			}
@@ -180,8 +179,8 @@ public Function<ResourceLocksProvider, Set<ResourceLocksProvider.Lock>> getResou
 	public Set<ExclusiveResource> getExclusiveResources() {
 		Set<ExclusiveResource> result = determineExclusiveResources().collect(toCollection(HashSet::new));
 		Visitor visitor = testDescriptor -> {
-			if (testDescriptor instanceof Node) {
-				result.addAll(((Node<?>) testDescriptor).getExclusiveResources());
+			if (testDescriptor instanceof Node<?> node) {
+				result.addAll(node.getExclusiveResources());
 			}
 		};
 		this.childrenPrototypes.forEach(child -> child.accept(visitor));
@@ -221,7 +220,7 @@ boolean supports(ClassTemplateInvocationContextProvider provider, ExtensionConte
 
 		@Override
 		protected String getNoRegisteredProviderErrorMessage() {
-			return String.format("You must register at least one %s that supports @%s class [%s]",
+			return "You must register at least one %s that supports @%s class [%s]".formatted(
 				ClassTemplateInvocationContextProvider.class.getSimpleName(), ClassTemplate.class.getSimpleName(),
 				getTestClass().getName());
 		}
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/DefaultDynamicTestInvocationContext.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/DefaultDynamicTestInvocationContext.java
index 72ef0981b728..402b6478bbed 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/DefaultDynamicTestInvocationContext.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/DefaultDynamicTestInvocationContext.java
@@ -18,13 +18,7 @@
  *
  * @since 5.8
  */
-class DefaultDynamicTestInvocationContext implements DynamicTestInvocationContext {
-
-	private final Executable executable;
-
-	DefaultDynamicTestInvocationContext(Executable executable) {
-		this.executable = executable;
-	}
+record DefaultDynamicTestInvocationContext(Executable executable) implements DynamicTestInvocationContext {
 
 	@Override
 	public Executable getExecutable() {
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/DefaultTestInstanceFactoryContext.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/DefaultTestInstanceFactoryContext.java
index 8414ab8c834a..096b6b4c60dc 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/DefaultTestInstanceFactoryContext.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/DefaultTestInstanceFactoryContext.java
@@ -20,15 +20,8 @@
  *
  * @since 5.3
  */
-class DefaultTestInstanceFactoryContext implements TestInstanceFactoryContext {
-
-	private final Class<?> testClass;
-	private final Optional<Object> outerInstance;
-
-	DefaultTestInstanceFactoryContext(Class<?> testClass, Optional<Object> outerInstance) {
-		this.testClass = testClass;
-		this.outerInstance = outerInstance;
-	}
+record DefaultTestInstanceFactoryContext(Class<?> testClass, Optional<Object> outerInstance)
+		implements TestInstanceFactoryContext {
 
 	@Override
 	public Class<?> getTestClass() {
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/DisplayNameUtils.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/DisplayNameUtils.java
index 619bbf81a60c..bb8d5e5427b2 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/DisplayNameUtils.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/DisplayNameUtils.java
@@ -10,8 +10,6 @@
 
 package org.junit.jupiter.engine.descriptor;
 
-import static java.util.Collections.emptyList;
-import static java.util.Collections.unmodifiableList;
 import static org.junit.platform.commons.support.AnnotationSupport.findAnnotation;
 
 import java.lang.reflect.AnnotatedElement;
@@ -22,6 +20,7 @@
 import java.util.function.BiFunction;
 import java.util.function.Supplier;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.DisplayName;
 import org.junit.jupiter.api.DisplayNameGeneration;
 import org.junit.jupiter.api.DisplayNameGenerator;
@@ -82,12 +81,12 @@ static String determineDisplayName(AnnotatedElement element, Supplier<String> di
 	}
 
 	static void validateAnnotation(AnnotatedElement element, Supplier<String> elementDescription,
-			Supplier<TestSource> sourceProvider, DiscoveryIssueReporter reporter) {
+			Supplier<@Nullable TestSource> sourceProvider, DiscoveryIssueReporter reporter) {
 		findAnnotation(element, DisplayName.class) //
 				.map(DisplayName::value) //
 				.filter(StringUtils::isBlank) //
 				.ifPresent(__ -> {
-					String message = String.format("@DisplayName on %s must be declared with a non-blank value.",
+					String message = "@DisplayName on %s must be declared with a non-blank value.".formatted(
 						elementDescription.get());
 					reporter.reportIssue(
 						DiscoveryIssue.builder(Severity.WARNING, message).source(sourceProvider.get()).build());
@@ -125,7 +124,7 @@ private static Supplier<String> createDisplayNameSupplier(Supplier<List<Class<?>
 			Class<?> testClass, JupiterConfiguration configuration,
 			BiFunction<DisplayNameGenerator, List<Class<?>>, String> generatorFunction) {
 		return () -> {
-			List<Class<?>> enclosingInstanceTypes = makeUnmodifiable(enclosingInstanceTypesSupplier.get());
+			List<Class<?>> enclosingInstanceTypes = List.copyOf(enclosingInstanceTypesSupplier.get());
 			return findDisplayNameGenerator(enclosingInstanceTypes, testClass) //
 					.map(it -> generatorFunction.apply(it, enclosingInstanceTypes)) //
 					.orElseGet(() -> generatorFunction.apply(configuration.getDefaultDisplayNameGenerator(),
@@ -133,10 +132,6 @@ private static Supplier<String> createDisplayNameSupplier(Supplier<List<Class<?>
 		};
 	}
 
-	private static <T> List<T> makeUnmodifiable(List<T> list) {
-		return list.isEmpty() ? emptyList() : unmodifiableList(list);
-	}
-
 	private static Optional<DisplayNameGenerator> findDisplayNameGenerator(List<Class<?>> enclosingInstanceTypes,
 			Class<?> testClass) {
 		Preconditions.notNull(testClass, "Test class must not be null");
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/DynamicContainerTestDescriptor.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/DynamicContainerTestDescriptor.java
index 8f157b9f8726..c5ade66011e3 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/DynamicContainerTestDescriptor.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/DynamicContainerTestDescriptor.java
@@ -69,8 +69,7 @@ public JupiterEngineExecutionContext execute(JupiterEngineExecutionContext conte
 						Preconditions.notNull(child, "individual dynamic node must not be null");
 						return toDynamicDescriptor(index.getAndIncrement(), child);
 					})
-					.filter(Optional::isPresent)
-					.map(Optional::get)
+					.flatMap(Optional::stream)
 					.forEachOrdered(dynamicTestExecutor::execute);
 			// @formatter:on
 		}
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/DynamicNodeTestDescriptor.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/DynamicNodeTestDescriptor.java
index 865e4044f52b..f68c98b480bf 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/DynamicNodeTestDescriptor.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/DynamicNodeTestDescriptor.java
@@ -10,6 +10,7 @@
 
 package org.junit.jupiter.engine.descriptor;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.DynamicNode;
 import org.junit.jupiter.api.extension.ExtensionContext;
 import org.junit.jupiter.engine.config.JupiterConfiguration;
@@ -27,7 +28,7 @@ abstract class DynamicNodeTestDescriptor extends JupiterTestDescriptor {
 
 	protected final int index;
 
-	DynamicNodeTestDescriptor(UniqueId uniqueId, int index, DynamicNode dynamicNode, TestSource testSource,
+	DynamicNodeTestDescriptor(UniqueId uniqueId, int index, DynamicNode dynamicNode, @Nullable TestSource testSource,
 			JupiterConfiguration configuration) {
 		super(uniqueId, dynamicNode.getDisplayName(), testSource, configuration);
 		this.index = index;
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/DynamicTestTestDescriptor.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/DynamicTestTestDescriptor.java
index 9209b8c1f3d6..bde06de8f93b 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/DynamicTestTestDescriptor.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/DynamicTestTestDescriptor.java
@@ -10,8 +10,11 @@
 
 package org.junit.jupiter.engine.descriptor;
 
+import static java.util.Objects.requireNonNull;
+
 import java.util.function.UnaryOperator;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.DynamicTest;
 import org.junit.jupiter.api.extension.DynamicTestInvocationContext;
 import org.junit.jupiter.api.extension.ExtensionContext;
@@ -35,9 +38,9 @@ class DynamicTestTestDescriptor extends DynamicNodeTestDescriptor {
 
 	private static final InvocationInterceptorChain interceptorChain = new InvocationInterceptorChain();
 
-	private DynamicTest dynamicTest;
+	private @Nullable DynamicTest dynamicTest;
 
-	DynamicTestTestDescriptor(UniqueId uniqueId, int index, DynamicTest dynamicTest, TestSource source,
+	DynamicTestTestDescriptor(UniqueId uniqueId, int index, DynamicTest dynamicTest, @Nullable TestSource source,
 			JupiterConfiguration configuration) {
 		super(uniqueId, index, dynamicTest, source, configuration);
 		this.dynamicTest = dynamicTest;
@@ -45,8 +48,8 @@ class DynamicTestTestDescriptor extends DynamicNodeTestDescriptor {
 
 	@Override
 	protected DynamicTestTestDescriptor withUniqueId(UnaryOperator<UniqueId> uniqueIdTransformer) {
-		return new DynamicTestTestDescriptor(uniqueIdTransformer.apply(getUniqueId()), this.index, this.dynamicTest,
-			this.getSource().orElse(null), this.configuration);
+		return new DynamicTestTestDescriptor(uniqueIdTransformer.apply(getUniqueId()), this.index,
+			requireNonNull(this.dynamicTest), this.getSource().orElse(null), this.configuration);
 	}
 
 	@Override
@@ -57,20 +60,24 @@ public Type getType() {
 	@Override
 	public JupiterEngineExecutionContext execute(JupiterEngineExecutionContext context,
 			DynamicTestExecutor dynamicTestExecutor) {
-		InvocationInterceptor.Invocation<Void> invocation = () -> {
-			dynamicTest.getExecutable().execute();
-			return null;
-		};
 		DynamicTestInvocationContext dynamicTestInvocationContext = new DefaultDynamicTestInvocationContext(
-			dynamicTest.getExecutable());
+			requiredDynamicTest().getExecutable());
 		ExtensionContext extensionContext = context.getExtensionContext();
 		ExtensionRegistry extensionRegistry = context.getExtensionRegistry();
-		interceptorChain.invoke(invocation, extensionRegistry, InterceptorCall.ofVoid(
-			(interceptor, wrappedInvocation) -> interceptor.interceptDynamicTest(wrappedInvocation,
-				dynamicTestInvocationContext, extensionContext)));
+		interceptorChain.<@Nullable Void> invoke(toInvocation(), extensionRegistry, InterceptorCall.ofVoid((
+				InvocationInterceptor interceptor,
+				InvocationInterceptor.Invocation<@Nullable Void> wrappedInvocation) -> interceptor.interceptDynamicTest(
+					wrappedInvocation, dynamicTestInvocationContext, extensionContext)));
 		return context;
 	}
 
+	private InvocationInterceptor.Invocation<@Nullable Void> toInvocation() {
+		return () -> {
+			requiredDynamicTest().getExecutable().execute();
+			return null;
+		};
+	}
+
 	/**
 	 * Avoid an {@link OutOfMemoryError} by releasing the reference to this
 	 * descriptor's {@link DynamicTest} which holds a reference to the user-supplied
@@ -78,7 +85,7 @@ public JupiterEngineExecutionContext execute(JupiterEngineExecutionContext conte
 	 * on the heap.
 	 *
 	 * @since 5.5
-	 * @see <a href="https://github.com/junit-team/junit5/issues/1865">Issue 1865</a>
+	 * @see <a href="https://github.com/junit-team/junit-framework/issues/1865">Issue 1865</a>
 	 */
 	@Override
 	public void after(JupiterEngineExecutionContext context) throws Exception {
@@ -86,4 +93,8 @@ public void after(JupiterEngineExecutionContext context) throws Exception {
 		this.dynamicTest = null;
 	}
 
+	private DynamicTest requiredDynamicTest() {
+		return requireNonNull(dynamicTest);
+	}
+
 }
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/ExclusiveResourceCollector.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/ExclusiveResourceCollector.java
index 15e7d26b6db5..6c08e136720c 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/ExclusiveResourceCollector.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/ExclusiveResourceCollector.java
@@ -12,7 +12,6 @@
 
 import static org.junit.jupiter.api.parallel.ResourceLockTarget.SELF;
 import static org.junit.platform.commons.support.AnnotationSupport.findRepeatableAnnotations;
-import static org.junit.platform.commons.util.CollectionUtils.toUnmodifiableList;
 
 import java.lang.reflect.AnnotatedElement;
 import java.util.Collection;
@@ -21,11 +20,11 @@
 import java.util.function.Function;
 import java.util.stream.Stream;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.parallel.ResourceAccessMode;
 import org.junit.jupiter.api.parallel.ResourceLock;
 import org.junit.jupiter.api.parallel.ResourceLockTarget;
 import org.junit.jupiter.api.parallel.ResourceLocksProvider;
-import org.junit.platform.commons.JUnitException;
 import org.junit.platform.commons.util.ReflectionUtils;
 import org.junit.platform.commons.util.StringUtils;
 import org.junit.platform.engine.support.hierarchical.ExclusiveResource;
@@ -73,6 +72,8 @@ static ExclusiveResourceCollector from(AnnotatedElement element) {
 	private static class DefaultExclusiveResourceCollector extends ExclusiveResourceCollector {
 
 		private final List<ResourceLock> annotations;
+
+		@Nullable
 		private List<ResourceLocksProvider> providers;
 
 		DefaultExclusiveResourceCollector(List<ResourceLock> annotations) {
@@ -103,20 +104,21 @@ Stream<ExclusiveResource> getDynamicResources(
 		private List<ResourceLocksProvider> getProviders() {
 			if (this.providers == null) {
 				this.providers = annotations.stream() //
-						.flatMap(annotation -> Stream.of(annotation.providers()).map(ReflectionUtils::newInstance)) //
-						.collect(toUnmodifiableList());
+						.flatMap(annotation -> instantiate(annotation.providers())) //
+						.toList();
 			}
 			return providers;
 		}
 
+		private static Stream<ResourceLocksProvider> instantiate(Class<? extends ResourceLocksProvider>[] providers) {
+			return Stream.of(providers).map(ReflectionUtils::newInstance);
+		}
+
 		private static ExclusiveResource.LockMode toLockMode(ResourceAccessMode mode) {
-			switch (mode) {
-				case READ:
-					return ExclusiveResource.LockMode.READ;
-				case READ_WRITE:
-					return ExclusiveResource.LockMode.READ_WRITE;
-			}
-			throw new JUnitException("Unknown ResourceAccessMode: " + mode);
+			return switch (mode) {
+				case READ -> ExclusiveResource.LockMode.READ;
+				case READ_WRITE -> ExclusiveResource.LockMode.READ_WRITE;
+			};
 		}
 	}
 }
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/ExtensionUtils.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/ExtensionUtils.java
index 976e7df23790..08fcb599dde0 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/ExtensionUtils.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/ExtensionUtils.java
@@ -29,6 +29,7 @@
 import java.util.function.Predicate;
 import java.util.stream.Stream;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Order;
 import org.junit.jupiter.api.extension.ExtendWith;
 import org.junit.jupiter.api.extension.Extension;
@@ -138,15 +139,16 @@ static void registerExtensionsFromInstanceFields(ExtensionRegistrar registrar, C
 	/**
 	 * @since 5.11
 	 */
-	private static Extension readAndValidateExtensionFromField(Field field, Object instance,
+	@SuppressWarnings("NullAway")
+	private static Extension readAndValidateExtensionFromField(Field field, @Nullable Object instance,
 			List<Class<? extends Extension>> declarativeExtensionTypes) {
 		Object value = tryToReadFieldValue(field, instance) //
 				.getOrThrow(e -> new PreconditionViolationException(
-					String.format("Failed to read @RegisterExtension field [%s]", field), e));
+					"Failed to read @RegisterExtension field [%s]".formatted(field), e));
 
-		Preconditions.condition(value instanceof Extension, () -> String.format(
-			"Failed to register extension via @RegisterExtension field [%s]: field value's type [%s] must implement an [%s] API.",
-			field, (value != null ? value.getClass().getName() : null), Extension.class.getName()));
+		Preconditions.condition(value instanceof Extension,
+			() -> "Failed to register extension via @RegisterExtension field [%s]: field value's type [%s] must implement an [%s] API.".formatted(
+				field, (value != null ? value.getClass().getName() : null), Extension.class.getName()));
 
 		declarativeExtensionTypes.forEach(extensionType -> {
 			Class<?> valueType = value.getClass();
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/JupiterTestDescriptor.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/JupiterTestDescriptor.java
index b9e737463d32..8bd1c7941b5a 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/JupiterTestDescriptor.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/JupiterTestDescriptor.java
@@ -31,6 +31,7 @@
 import java.util.function.UnaryOperator;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Tag;
 import org.junit.jupiter.api.extension.ConditionEvaluationResult;
 import org.junit.jupiter.api.extension.Extension;
@@ -40,7 +41,6 @@
 import org.junit.jupiter.engine.execution.ConditionEvaluator;
 import org.junit.jupiter.engine.execution.JupiterEngineExecutionContext;
 import org.junit.jupiter.engine.extension.ExtensionRegistry;
-import org.junit.platform.commons.JUnitException;
 import org.junit.platform.commons.util.ExceptionUtils;
 import org.junit.platform.commons.util.UnrecoverableExceptions;
 import org.junit.platform.engine.DiscoveryIssue;
@@ -65,11 +65,11 @@ public abstract class JupiterTestDescriptor extends AbstractTestDescriptor
 	final JupiterConfiguration configuration;
 
 	JupiterTestDescriptor(UniqueId uniqueId, AnnotatedElement element, Supplier<String> displayNameSupplier,
-			TestSource source, JupiterConfiguration configuration) {
+			@Nullable TestSource source, JupiterConfiguration configuration) {
 		this(uniqueId, determineDisplayName(element, displayNameSupplier), source, configuration);
 	}
 
-	JupiterTestDescriptor(UniqueId uniqueId, String displayName, TestSource source,
+	JupiterTestDescriptor(UniqueId uniqueId, String displayName, @Nullable TestSource source,
 			JupiterConfiguration configuration) {
 		super(uniqueId, displayName, source);
 		this.configuration = configuration;
@@ -79,15 +79,14 @@ public abstract class JupiterTestDescriptor extends AbstractTestDescriptor
 
 	static Set<TestTag> getTags(AnnotatedElement element, Supplier<String> elementDescription,
 			Supplier<TestSource> sourceProvider, Consumer<DiscoveryIssue> issueCollector) {
-		AtomicReference<TestSource> source = new AtomicReference<>();
+		AtomicReference<@Nullable TestSource> source = new AtomicReference<>();
 		return findRepeatableAnnotations(element, Tag.class).stream() //
 				.map(Tag::value) //
 				.filter(tag -> {
 					boolean isValid = TestTag.isValid(tag);
 					if (!isValid) {
-						String message = String.format(
-							"Invalid tag syntax in @Tag(\"%s\") declaration on %s. Tag will be ignored.", tag,
-							elementDescription.get());
+						String message = "Invalid tag syntax in @Tag(\"%s\") declaration on %s. Tag will be ignored.".formatted(
+							tag, elementDescription.get());
 						if (source.get() == null) {
 							source.set(sourceProvider.get());
 						}
@@ -139,8 +138,7 @@ public ExecutionMode getExecutionMode() {
 			return executionMode.get();
 		}
 		Optional<TestDescriptor> parent = getParent();
-		while (parent.isPresent() && parent.get() instanceof JupiterTestDescriptor) {
-			JupiterTestDescriptor jupiterParent = (JupiterTestDescriptor) parent.get();
+		while (parent.isPresent() && parent.get() instanceof JupiterTestDescriptor jupiterParent) {
 			executionMode = jupiterParent.getExplicitExecutionMode();
 			if (executionMode.isPresent()) {
 				return executionMode.get();
@@ -171,19 +169,16 @@ Optional<ExecutionMode> getExecutionModeFromAnnotation(AnnotatedElement element)
 	}
 
 	public static ExecutionMode toExecutionMode(org.junit.jupiter.api.parallel.ExecutionMode mode) {
-		switch (mode) {
-			case CONCURRENT:
-				return ExecutionMode.CONCURRENT;
-			case SAME_THREAD:
-				return ExecutionMode.SAME_THREAD;
-		}
-		throw new JUnitException("Unknown ExecutionMode: " + mode);
+		return switch (mode) {
+			case CONCURRENT -> ExecutionMode.CONCURRENT;
+			case SAME_THREAD -> ExecutionMode.SAME_THREAD;
+		};
 	}
 
 	@Override
 	public Set<ExclusiveResource> getExclusiveResources() {
-		if (this instanceof ResourceLockAware) {
-			return ((ResourceLockAware) this).determineExclusiveResources().collect(toSet());
+		if (this instanceof ResourceLockAware resourceLockAware) {
+			return resourceLockAware.determineExclusiveResources().collect(toSet());
 		}
 		return emptySet();
 	}
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/LifecycleMethodUtils.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/LifecycleMethodUtils.java
index 8d629e82fbf4..954074408e1c 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/LifecycleMethodUtils.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/LifecycleMethodUtils.java
@@ -10,9 +10,9 @@
 
 package org.junit.jupiter.engine.descriptor;
 
+import static org.junit.jupiter.engine.support.MethodReflectionUtils.getReturnType;
 import static org.junit.platform.commons.support.AnnotationSupport.findAnnotatedMethods;
 import static org.junit.platform.commons.support.AnnotationSupport.findAnnotation;
-import static org.junit.platform.commons.util.CollectionUtils.toUnmodifiableList;
 import static org.junit.platform.engine.support.discovery.DiscoveryIssueReporter.Condition.alwaysSatisfied;
 
 import java.lang.annotation.Annotation;
@@ -30,7 +30,6 @@
 import org.junit.jupiter.api.extension.ClassTemplateInvocationLifecycleMethod;
 import org.junit.platform.commons.support.HierarchyTraversalMode;
 import org.junit.platform.commons.support.ModifierSupport;
-import org.junit.platform.commons.util.ReflectionUtils;
 import org.junit.platform.engine.DiscoveryIssue;
 import org.junit.platform.engine.DiscoveryIssue.Severity;
 import org.junit.platform.engine.support.descriptor.MethodSource;
@@ -76,8 +75,7 @@ static void validateNoClassTemplateInvocationLifecycleMethodsAreDeclared(Class<?
 		findAllClassTemplateInvocationLifecycleMethods(testClass) //
 				.forEach(method -> findClassTemplateInvocationLifecycleMethodAnnotation(method) //
 						.ifPresent(annotation -> {
-							String message = String.format(
-								"@%s method '%s' must not be declared in test class '%s' because it is not annotated with @%s.",
+							String message = "@%s method '%s' must not be declared in test class '%s' because it is not annotated with @%s.".formatted(
 								annotation.lifecycleMethodAnnotation().getSimpleName(), method.toGenericString(),
 								testClass.getName(), annotation.classTemplateAnnotation().getSimpleName());
 							issueReporter.reportIssue(createIssue(Severity.ERROR, message, method));
@@ -135,14 +133,13 @@ private static List<Method> findMethodsAndCheckVoidReturnType(Class<?> testClass
 				.peek(isNotPrivateWarning(issueReporter, annotationType::getSimpleName).toConsumer()) //
 				.filter(returnsPrimitiveVoid(issueReporter, __ -> annotationType.getSimpleName()).and(
 					additionalCondition).toPredicate()) //
-				.collect(toUnmodifiableList());
+				.toList();
 	}
 
 	private static Condition<Method> isStatic(DiscoveryIssueReporter issueReporter,
 			Function<Method, String> annotationNameProvider) {
 		return issueReporter.createReportingCondition(ModifierSupport::isStatic, method -> {
-			String message = String.format(
-				"@%s method '%s' must be static unless the test class is annotated with @TestInstance(Lifecycle.PER_CLASS).",
+			String message = "@%s method '%s' must be static unless the test class is annotated with @TestInstance(Lifecycle.PER_CLASS).".formatted(
 				annotationNameProvider.apply(method), method.toGenericString());
 			return createIssue(Severity.ERROR, message, method);
 		});
@@ -151,7 +148,7 @@ private static Condition<Method> isStatic(DiscoveryIssueReporter issueReporter,
 	private static Condition<Method> isNotStatic(DiscoveryIssueReporter issueReporter,
 			Function<Method, String> annotationNameProvider) {
 		return issueReporter.createReportingCondition(ModifierSupport::isNotStatic, method -> {
-			String message = String.format("@%s method '%s' must not be static.", annotationNameProvider.apply(method),
+			String message = "@%s method '%s' must not be static.".formatted(annotationNameProvider.apply(method),
 				method.toGenericString());
 			return createIssue(Severity.ERROR, message, method);
 		});
@@ -159,7 +156,7 @@ private static Condition<Method> isNotStatic(DiscoveryIssueReporter issueReporte
 
 	private static Condition<Method> isNotPrivateError(DiscoveryIssueReporter issueReporter) {
 		return issueReporter.createReportingCondition(ModifierSupport::isNotPrivate, method -> {
-			String message = String.format("@%s method '%s' must not be private.",
+			String message = "@%s method '%s' must not be private.".formatted(
 				classTemplateInvocationLifecycleMethodAnnotationName(method), method.toGenericString());
 			return createIssue(Severity.ERROR, message, method);
 		});
@@ -168,8 +165,7 @@ private static Condition<Method> isNotPrivateError(DiscoveryIssueReporter issueR
 	private static Condition<Method> isNotPrivateWarning(DiscoveryIssueReporter issueReporter,
 			Supplier<String> annotationNameProvider) {
 		return issueReporter.createReportingCondition(ModifierSupport::isNotPrivate, method -> {
-			String message = String.format(
-				"@%s method '%s' should not be private. This will be disallowed in a future release.",
+			String message = "@%s method '%s' should not be private. This will be disallowed in a future release.".formatted(
 				annotationNameProvider.get(), method.toGenericString());
 			return createIssue(Severity.WARNING, message, method);
 		});
@@ -177,9 +173,9 @@ private static Condition<Method> isNotPrivateWarning(DiscoveryIssueReporter issu
 
 	private static Condition<Method> returnsPrimitiveVoid(DiscoveryIssueReporter issueReporter,
 			Function<Method, String> annotationNameProvider) {
-		return issueReporter.createReportingCondition(ReflectionUtils::returnsPrimitiveVoid, method -> {
-			String message = String.format("@%s method '%s' must not return a value.",
-				annotationNameProvider.apply(method), method.toGenericString());
+		return issueReporter.createReportingCondition(method -> getReturnType(method) == void.class, method -> {
+			String message = "@%s method '%s' must not return a value.".formatted(annotationNameProvider.apply(method),
+				method.toGenericString());
 			return createIssue(Severity.ERROR, message, method);
 		});
 	}
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/MethodBasedTestDescriptor.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/MethodBasedTestDescriptor.java
index 4af8de8080e7..ae07732fdf70 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/MethodBasedTestDescriptor.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/MethodBasedTestDescriptor.java
@@ -88,7 +88,7 @@ public final Set<TestTag> getTags() {
 
 	@Override
 	public String getLegacyReportingName() {
-		return String.format("%s(%s)", getTestMethod().getName(),
+		return "%s(%s)".formatted(getTestMethod().getName(),
 			ClassUtils.nullSafeToString(Class::getSimpleName, getTestMethod().getParameterTypes()));
 	}
 
@@ -114,7 +114,7 @@ public List<Class<?>> getEnclosingTestClasses() {
 	public void validate(DiscoveryIssueReporter reporter) {
 		Validatable.reportAndClear(this.methodInfo.discoveryIssues, reporter);
 		DisplayNameUtils.validateAnnotation(getTestMethod(), //
-			() -> String.format("method '%s'", getTestMethod().toGenericString()), //
+			() -> "method '%s'".formatted(getTestMethod().toGenericString()), //
 			// Use _declaring_ class here because that's where the `@DisplayName` annotation is declared
 			() -> MethodSource.from(getTestMethod()), //
 			reporter);
@@ -156,10 +156,8 @@ protected Optional<ExecutionMode> getExplicitExecutionMode() {
 	 */
 	@Override
 	public void nodeSkipped(JupiterEngineExecutionContext context, TestDescriptor descriptor, SkipResult result) {
-		if (context != null) {
-			invokeTestWatchers(context, false,
-				watcher -> watcher.testDisabled(context.getExtensionContext(), result.getReason()));
-		}
+		invokeTestWatchers(context, false,
+			watcher -> watcher.testDisabled(context.getExtensionContext(), result.getReason()));
 	}
 
 	/**
@@ -178,7 +176,7 @@ protected void invokeTestWatchers(JupiterEngineExecutionContext context, boolean
 				UnrecoverableExceptions.rethrowIfUnrecoverable(throwable);
 				ExtensionContext extensionContext = context.getExtensionContext();
 				logger.warn(throwable,
-					() -> String.format("Failed to invoke TestWatcher [%s] for method [%s] with display name [%s]",
+					() -> "Failed to invoke TestWatcher [%s] for method [%s] with display name [%s]".formatted(
 						watcher.getClass().getName(),
 						ReflectionUtils.getFullyQualifiedMethodName(extensionContext.getRequiredTestClass(),
 							extensionContext.getRequiredTestMethod()),
@@ -209,7 +207,7 @@ private static class MethodInfo {
 			this.testClass = Preconditions.notNull(testClass, "Class must not be null");
 			this.testMethod = testMethod;
 			this.tags = getTags(testMethod, //
-				() -> String.format("method '%s'", testMethod.toGenericString()), //
+				() -> "method '%s'".formatted(testMethod.toGenericString()), //
 				// Use _declaring_ class here because that's where the `@Tag` annotation is declared
 				() -> MethodSource.from(testMethod.getDeclaringClass(), testMethod), //
 				discoveryIssues::add);
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/MethodExtensionContext.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/MethodExtensionContext.java
index eaed0fe9418a..5ffeb5b22988 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/MethodExtensionContext.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/MethodExtensionContext.java
@@ -15,6 +15,7 @@
 import java.util.List;
 import java.util.Optional;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.TestInstance.Lifecycle;
 import org.junit.jupiter.api.extension.ExtensionContext;
 import org.junit.jupiter.api.extension.TestInstances;
@@ -31,7 +32,7 @@ final class MethodExtensionContext extends AbstractExtensionContext<TestMethodTe
 
 	private final ThrowableCollector throwableCollector;
 
-	private TestInstances testInstances;
+	private @Nullable TestInstances testInstances;
 
 	MethodExtensionContext(ExtensionContext parent, EngineExecutionListener engineExecutionListener,
 			TestMethodTestDescriptor testDescriptor, JupiterConfiguration configuration,
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/NestedClassTestDescriptor.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/NestedClassTestDescriptor.java
index deb609ef8814..d4b354b09d0e 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/NestedClassTestDescriptor.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/NestedClassTestDescriptor.java
@@ -25,6 +25,7 @@
 import java.util.function.UnaryOperator;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.extension.TestInstances;
 import org.junit.jupiter.api.parallel.ResourceLocksProvider;
 import org.junit.jupiter.engine.config.JupiterConfiguration;
@@ -87,11 +88,10 @@ public List<Class<?>> getEnclosingTestClasses() {
 	}
 
 	@API(status = INTERNAL, since = "5.12")
-	public static List<Class<?>> getEnclosingTestClasses(TestDescriptor parent) {
-		if (parent instanceof TestClassAware) {
-			TestClassAware parentClassDescriptor = (TestClassAware) parent;
-			List<Class<?>> result = new ArrayList<>(parentClassDescriptor.getEnclosingTestClasses());
-			result.add(parentClassDescriptor.getTestClass());
+	public static List<Class<?>> getEnclosingTestClasses(@Nullable TestDescriptor parent) {
+		if (parent instanceof TestClassAware testClassAwareParent) {
+			List<Class<?>> result = new ArrayList<>(testClassAwareParent.getEnclosingTestClasses());
+			result.add(testClassAwareParent.getTestClass());
 			return result;
 		}
 		return emptyList();
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/ResourceLockAware.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/ResourceLockAware.java
index c66398105f4b..d7d5a85e6cbf 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/ResourceLockAware.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/ResourceLockAware.java
@@ -10,8 +10,6 @@
 
 package org.junit.jupiter.engine.descriptor;
 
-import static java.util.Collections.emptyList;
-import static java.util.Collections.unmodifiableList;
 import static org.junit.jupiter.api.parallel.ResourceLockTarget.CHILDREN;
 
 import java.util.ArrayDeque;
@@ -23,6 +21,7 @@
 import java.util.function.Supplier;
 import java.util.stream.Stream;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.parallel.ResourceLocksProvider;
 import org.junit.platform.engine.TestDescriptor;
 import org.junit.platform.engine.support.hierarchical.ExclusiveResource;
@@ -36,8 +35,8 @@ default Stream<ExclusiveResource> determineExclusiveResources() {
 
 		Deque<ResourceLockAware> ancestors = new ArrayDeque<>();
 		TestDescriptor parent = this.getParent().orElse(null);
-		while (parent instanceof ResourceLockAware) {
-			ancestors.addFirst((ResourceLockAware) parent);
+		while (parent instanceof ResourceLockAware resourceLockAwareParent) {
+			ancestors.addFirst(resourceLockAwareParent);
 			parent = parent.getParent().orElse(null);
 		}
 
@@ -71,21 +70,19 @@ default Stream<ExclusiveResource> determineOwnExclusiveResources(
 	static Function<ResourceLocksProvider, Set<ResourceLocksProvider.Lock>> enclosingInstanceTypesDependentResourceLocksProviderEvaluator(
 			Supplier<List<Class<?>>> enclosingInstanceTypesSupplier,
 			BiFunction<ResourceLocksProvider, List<Class<?>>, Set<ResourceLocksProvider.Lock>> evaluator) {
-		return new Function<ResourceLocksProvider, Set<ResourceLocksProvider.Lock>>() {
+		return new Function<>() {
 
+			@Nullable
 			private List<Class<?>> enclosingInstanceTypes;
 
 			@Override
 			public Set<ResourceLocksProvider.Lock> apply(ResourceLocksProvider provider) {
 				if (this.enclosingInstanceTypes == null) {
-					this.enclosingInstanceTypes = makeUnmodifiable(enclosingInstanceTypesSupplier.get());
+					this.enclosingInstanceTypes = List.copyOf(enclosingInstanceTypesSupplier.get());
 				}
 				return evaluator.apply(provider, this.enclosingInstanceTypes);
 			}
 
-			private <T> List<T> makeUnmodifiable(List<T> list) {
-				return list.isEmpty() ? emptyList() : unmodifiableList(list);
-			}
 		};
 	}
 
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/TemplateExecutor.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/TemplateExecutor.java
index b2537fb226c9..acb006eb0370 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/TemplateExecutor.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/TemplateExecutor.java
@@ -10,8 +10,6 @@
 
 package org.junit.jupiter.engine.descriptor;
 
-import static java.util.stream.Collectors.toList;
-
 import java.util.List;
 import java.util.Optional;
 import java.util.concurrent.atomic.AtomicInteger;
@@ -81,7 +79,7 @@ private void executeForProvider(P provider, AtomicInteger invocationIndex,
 	private List<P> validateProviders(ExtensionContext extensionContext, ExtensionRegistry extensionRegistry) {
 		List<P> providers = extensionRegistry.stream(providerType) //
 				.filter(provider -> supports(provider, extensionContext)) //
-				.collect(toList());
+				.toList();
 		return Preconditions.notEmpty(providers, this::getNoRegisteredProviderErrorMessage);
 	}
 
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/TestFactoryTestDescriptor.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/TestFactoryTestDescriptor.java
index 5b8183513ed1..5ad248efa279 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/TestFactoryTestDescriptor.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/TestFactoryTestDescriptor.java
@@ -25,6 +25,7 @@
 import java.util.stream.Stream;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.DynamicContainer;
 import org.junit.jupiter.api.DynamicNode;
 import org.junit.jupiter.api.DynamicTest;
@@ -58,7 +59,7 @@ public class TestFactoryTestDescriptor extends TestMethodTestDescriptor implemen
 	public static final String DYNAMIC_CONTAINER_SEGMENT_TYPE = "dynamic-container";
 	public static final String DYNAMIC_TEST_SEGMENT_TYPE = "dynamic-test";
 
-	private static final ReflectiveInterceptorCall<Method, Object> interceptorCall = InvocationInterceptor::interceptTestFactoryMethod;
+	private static final ReflectiveInterceptorCall<Method, @Nullable Object> interceptorCall = InvocationInterceptor::interceptTestFactoryMethod;
 	private static final InterceptingExecutableInvoker executableInvoker = new InterceptingExecutableInvoker();
 
 	private final DynamicDescendantFilter dynamicDescendantFilter;
@@ -110,8 +111,8 @@ protected void invokeTestMethod(JupiterEngineExecutionContext context, DynamicTe
 
 		context.getThrowableCollector().execute(() -> {
 			Object instance = extensionContext.getRequiredTestInstance();
-			Object testFactoryMethodResult = executableInvoker.invoke(getTestMethod(), instance, extensionContext,
-				context.getExtensionRegistry(), interceptorCall);
+			Object testFactoryMethodResult = executableInvoker.<@Nullable Object> invoke(getTestMethod(), instance,
+				extensionContext, context.getExtensionRegistry(), interceptorCall);
 			TestSource defaultTestSource = getSource().orElseThrow(
 				() -> new JUnitException("Illegal state: TestSource must be present"));
 			try (Stream<DynamicNode> dynamicNodeStream = toDynamicNodeStream(testFactoryMethodResult)) {
@@ -133,15 +134,18 @@ protected void invokeTestMethod(JupiterEngineExecutionContext context, DynamicTe
 	}
 
 	@SuppressWarnings("unchecked")
-	private Stream<DynamicNode> toDynamicNodeStream(Object testFactoryMethodResult) {
-		if (testFactoryMethodResult instanceof DynamicNode) {
-			return Stream.of((DynamicNode) testFactoryMethodResult);
+	private Stream<DynamicNode> toDynamicNodeStream(@Nullable Object testFactoryMethodResult) {
+		if (testFactoryMethodResult == null) {
+			throw new JUnitException("@TestFactory method must not return null");
+		}
+		if (testFactoryMethodResult instanceof DynamicNode node) {
+			return Stream.of(node);
 		}
 		return (Stream<DynamicNode>) CollectionUtils.toStream(testFactoryMethodResult);
 	}
 
 	private JUnitException invalidReturnTypeException(Throwable cause) {
-		String message = String.format("Objects produced by @TestFactory method '%s' must be of type %s.",
+		String message = "Objects produced by @TestFactory method '%s' must be of type %s.".formatted(
 			getTestMethod().toGenericString(), DynamicNode.class.getName());
 		return new JUnitException(message, cause);
 	}
@@ -155,8 +159,7 @@ static Optional<JupiterTestDescriptor> createDynamicDescriptor(JupiterTestDescri
 		Optional<TestSource> customTestSource = node.getTestSourceUri().map(TestFactoryTestDescriptor::fromUri);
 		TestSource source = customTestSource.orElse(defaultTestSource);
 
-		if (node instanceof DynamicTest) {
-			DynamicTest test = (DynamicTest) node;
+		if (node instanceof DynamicTest test) {
 			uniqueId = parent.getUniqueId().append(DYNAMIC_TEST_SEGMENT_TYPE, "#" + index);
 			descriptorCreator = () -> new DynamicTestTestDescriptor(uniqueId, index, test, source, configuration);
 		}
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/TestMethodTestDescriptor.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/TestMethodTestDescriptor.java
index c6a416bd443a..885ae6d54cdd 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/TestMethodTestDescriptor.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/TestMethodTestDescriptor.java
@@ -39,7 +39,7 @@
 import org.junit.jupiter.engine.execution.AfterEachMethodAdapter;
 import org.junit.jupiter.engine.execution.BeforeEachMethodAdapter;
 import org.junit.jupiter.engine.execution.InterceptingExecutableInvoker;
-import org.junit.jupiter.engine.execution.InterceptingExecutableInvoker.ReflectiveInterceptorCall;
+import org.junit.jupiter.engine.execution.InterceptingExecutableInvoker.ReflectiveInterceptorCall.VoidMethodInterceptorCall;
 import org.junit.jupiter.engine.execution.JupiterEngineExecutionContext;
 import org.junit.jupiter.engine.extension.ExtensionRegistry;
 import org.junit.jupiter.engine.extension.MutableExtensionRegistry;
@@ -72,10 +72,8 @@ public class TestMethodTestDescriptor extends MethodBasedTestDescriptor {
 
 	public static final String SEGMENT_TYPE = "method";
 	private static final InterceptingExecutableInvoker executableInvoker = new InterceptingExecutableInvoker();
-	private static final ReflectiveInterceptorCall<Method, Void> defaultInterceptorCall = ReflectiveInterceptorCall.ofVoidMethod(
-		InvocationInterceptor::interceptTestMethod);
-
-	private final ReflectiveInterceptorCall<Method, Void> interceptorCall;
+	private static final VoidMethodInterceptorCall defaultInterceptorCall = InvocationInterceptor::interceptTestMethod;
+	private final VoidMethodInterceptorCall interceptorCall;
 
 	public TestMethodTestDescriptor(UniqueId uniqueId, Class<?> testClass, Method testMethod,
 			Supplier<List<Class<?>>> enclosingInstanceTypes, JupiterConfiguration configuration) {
@@ -89,7 +87,7 @@ public TestMethodTestDescriptor(UniqueId uniqueId, Class<?> testClass, Method te
 	}
 
 	TestMethodTestDescriptor(UniqueId uniqueId, String displayName, Class<?> testClass, Method testMethod,
-			JupiterConfiguration configuration, ReflectiveInterceptorCall<Method, Void> interceptorCall) {
+			JupiterConfiguration configuration, VoidMethodInterceptorCall interceptorCall) {
 		super(uniqueId, displayName, testClass, testMethod, configuration);
 		this.interceptorCall = interceptorCall;
 	}
@@ -218,7 +216,7 @@ protected void invokeTestMethod(JupiterEngineExecutionContext context, DynamicTe
 			try {
 				Method testMethod = getTestMethod();
 				Object instance = extensionContext.getRequiredTestInstance();
-				executableInvoker.invoke(testMethod, instance, extensionContext, context.getExtensionRegistry(),
+				executableInvoker.invokeVoid(testMethod, instance, extensionContext, context.getExtensionRegistry(),
 					interceptorCall);
 			}
 			catch (Throwable throwable) {
@@ -280,24 +278,16 @@ private void invokeTestInstancePreDestroyCallbacks(JupiterEngineExecutionContext
 	public void nodeFinished(JupiterEngineExecutionContext context, TestDescriptor descriptor,
 			TestExecutionResult result) {
 
-		if (context != null) {
-			ExtensionContext extensionContext = context.getExtensionContext();
-			TestExecutionResult.Status status = result.getStatus();
-
-			invokeTestWatchers(context, true, watcher -> {
-				switch (status) {
-					case SUCCESSFUL:
-						watcher.testSuccessful(extensionContext);
-						break;
-					case ABORTED:
-						watcher.testAborted(extensionContext, result.getThrowable().orElse(null));
-						break;
-					case FAILED:
-						watcher.testFailed(extensionContext, result.getThrowable().orElse(null));
-						break;
-				}
-			});
-		}
+		ExtensionContext extensionContext = context.getExtensionContext();
+		TestExecutionResult.Status status = result.getStatus();
+
+		invokeTestWatchers(context, true, watcher -> {
+			switch (status) {
+				case SUCCESSFUL -> watcher.testSuccessful(extensionContext);
+				case ABORTED -> watcher.testAborted(extensionContext, result.getThrowable().orElse(null));
+				case FAILED -> watcher.testFailed(extensionContext, result.getThrowable().orElse(null));
+			}
+		});
 	}
 
 }
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/TestTemplateExtensionContext.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/TestTemplateExtensionContext.java
index 9a30e567ba2b..4074a8788de0 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/TestTemplateExtensionContext.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/TestTemplateExtensionContext.java
@@ -15,6 +15,7 @@
 import java.util.List;
 import java.util.Optional;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.TestInstance.Lifecycle;
 import org.junit.jupiter.api.extension.ExtensionContext;
 import org.junit.jupiter.api.extension.TestInstances;
@@ -28,11 +29,12 @@
  */
 final class TestTemplateExtensionContext extends AbstractExtensionContext<TestTemplateTestDescriptor> {
 
-	private final TestInstances testInstances;
+	private final @Nullable TestInstances testInstances;
 
 	TestTemplateExtensionContext(ExtensionContext parent, EngineExecutionListener engineExecutionListener,
 			TestTemplateTestDescriptor testDescriptor, JupiterConfiguration configuration,
-			ExtensionRegistry extensionRegistry, LauncherStoreFacade launcherStoreFacade, TestInstances testInstances) {
+			ExtensionRegistry extensionRegistry, LauncherStoreFacade launcherStoreFacade,
+			@Nullable TestInstances testInstances) {
 
 		super(parent, engineExecutionListener, testDescriptor, configuration, extensionRegistry, launcherStoreFacade);
 		this.testInstances = testInstances;
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/TestTemplateInvocationTestDescriptor.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/TestTemplateInvocationTestDescriptor.java
index 88d494a9731d..f33a4a035f82 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/TestTemplateInvocationTestDescriptor.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/TestTemplateInvocationTestDescriptor.java
@@ -11,6 +11,7 @@
 package org.junit.jupiter.engine.descriptor;
 
 import static java.util.Collections.emptySet;
+import static java.util.Objects.requireNonNull;
 import static org.apiguardian.api.API.Status.INTERNAL;
 
 import java.lang.reflect.Method;
@@ -18,11 +19,12 @@
 import java.util.function.UnaryOperator;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.extension.ExtensionContext;
 import org.junit.jupiter.api.extension.InvocationInterceptor;
 import org.junit.jupiter.api.extension.TestTemplateInvocationContext;
 import org.junit.jupiter.engine.config.JupiterConfiguration;
-import org.junit.jupiter.engine.execution.InterceptingExecutableInvoker.ReflectiveInterceptorCall;
+import org.junit.jupiter.engine.execution.InterceptingExecutableInvoker.ReflectiveInterceptorCall.VoidMethodInterceptorCall;
 import org.junit.jupiter.engine.execution.JupiterEngineExecutionContext;
 import org.junit.jupiter.engine.extension.MutableExtensionRegistry;
 import org.junit.platform.engine.TestDescriptor;
@@ -39,10 +41,10 @@
 public class TestTemplateInvocationTestDescriptor extends TestMethodTestDescriptor {
 
 	public static final String SEGMENT_TYPE = "test-template-invocation";
-	private static final ReflectiveInterceptorCall<Method, Void> interceptorCall = ReflectiveInterceptorCall.ofVoidMethod(
-		InvocationInterceptor::interceptTestTemplateMethod);
+	private static final VoidMethodInterceptorCall interceptorCall = InvocationInterceptor::interceptTestTemplateMethod;
+
+	private @Nullable TestTemplateInvocationContext invocationContext;
 
-	private TestTemplateInvocationContext invocationContext;
 	private final int index;
 
 	TestTemplateInvocationTestDescriptor(UniqueId uniqueId, Class<?> testClass, Method templateMethod,
@@ -58,7 +60,7 @@ public class TestTemplateInvocationTestDescriptor extends TestMethodTestDescript
 	@Override
 	protected TestTemplateInvocationTestDescriptor withUniqueId(UnaryOperator<UniqueId> uniqueIdTransformer) {
 		return new TestTemplateInvocationTestDescriptor(uniqueIdTransformer.apply(getUniqueId()), getTestClass(),
-			getTestMethod(), this.invocationContext, this.index, this.configuration);
+			getTestMethod(), requiredInvocationContext(), this.index, this.configuration);
 	}
 
 	// --- TestDescriptor ------------------------------------------------------
@@ -77,14 +79,15 @@ public String getLegacyReportingName() {
 	@Override
 	protected MutableExtensionRegistry populateNewExtensionRegistry(JupiterEngineExecutionContext context) {
 		MutableExtensionRegistry registry = super.populateNewExtensionRegistry(context);
-		this.invocationContext.getAdditionalExtensions().forEach(
+		var invocationContext = requiredInvocationContext();
+		invocationContext.getAdditionalExtensions().forEach(
 			extension -> registry.registerExtension(extension, invocationContext));
 		return registry;
 	}
 
 	@Override
 	protected void prepareExtensionContext(ExtensionContext extensionContext) {
-		this.invocationContext.prepareInvocation(extensionContext);
+		requiredInvocationContext().prepareInvocation(extensionContext);
 	}
 
 	@Override
@@ -93,4 +96,8 @@ public void after(JupiterEngineExecutionContext context) {
 		this.invocationContext = null;
 	}
 
+	private TestTemplateInvocationContext requiredInvocationContext() {
+		return requireNonNull(this.invocationContext);
+	}
+
 }
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/TestTemplateTestDescriptor.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/TestTemplateTestDescriptor.java
index 90a0515e1e00..32cbbcc8a4a2 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/TestTemplateTestDescriptor.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/TestTemplateTestDescriptor.java
@@ -127,7 +127,7 @@ boolean supports(TestTemplateInvocationContextProvider provider, ExtensionContex
 
 		@Override
 		protected String getNoRegisteredProviderErrorMessage() {
-			return String.format("You must register at least one %s that supports @%s method [%s]",
+			return "You must register at least one %s that supports @%s method [%s]".formatted(
 				TestTemplateInvocationContextProvider.class.getSimpleName(), TestTemplate.class.getSimpleName(),
 				getTestMethod());
 		}
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/UniqueIdPrefixTransformer.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/UniqueIdPrefixTransformer.java
index 20a85ba1382b..7389c307b905 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/UniqueIdPrefixTransformer.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/UniqueIdPrefixTransformer.java
@@ -34,7 +34,7 @@ class UniqueIdPrefixTransformer implements UnaryOperator<UniqueId> {
 	@Override
 	public UniqueId apply(UniqueId uniqueId) {
 		Preconditions.condition(uniqueId.hasPrefix(oldPrefix),
-			() -> String.format("Unique ID %s does not have the expected prefix %s", uniqueId, oldPrefix));
+			() -> "Unique ID %s does not have the expected prefix %s".formatted(uniqueId, oldPrefix));
 		List<UniqueId.Segment> oldSegments = uniqueId.getSegments();
 		List<UniqueId.Segment> suffix = oldSegments.subList(oldPrefixLength, oldSegments.size());
 		UniqueId newValue = newPrefix;
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/package-info.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/package-info.java
index e3e0028ce4fb..62b21c2e4993 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/package-info.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/descriptor/package-info.java
@@ -2,4 +2,7 @@
  * Test descriptors used within the JUnit Jupiter test engine.
  */
 
+@NullMarked
 package org.junit.jupiter.engine.descriptor;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/AbstractOrderingVisitor.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/AbstractOrderingVisitor.java
index 8f104923bf5c..5dfedbc48ee3 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/AbstractOrderingVisitor.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/AbstractOrderingVisitor.java
@@ -11,8 +11,8 @@
 package org.junit.jupiter.engine.discovery;
 
 import static java.util.Comparator.comparing;
+import static java.util.Objects.requireNonNull;
 import static java.util.stream.Collectors.toCollection;
-import static java.util.stream.Collectors.toList;
 
 import java.util.ArrayList;
 import java.util.HashMap;
@@ -23,6 +23,7 @@
 import java.util.function.Function;
 import java.util.stream.Stream;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.util.UnrecoverableExceptions;
 import org.junit.platform.engine.DiscoveryIssue;
 import org.junit.platform.engine.DiscoveryIssue.Severity;
@@ -108,11 +109,11 @@ protected <CHILD extends TestDescriptor, WRAPPER extends AbstractAnnotatedDescri
 
 			if (shouldNonMatchingDescriptorsComeBeforeOrderedOnes()) {
 				return Stream.concat(nonMatchingTestDescriptors, orderedTestDescriptors)//
-						.collect(toList());
+						.toList();
 			}
 			else {
 				return Stream.concat(orderedTestDescriptors, nonMatchingTestDescriptors)//
-						.collect(toList());
+						.toList();
 			}
 		});
 	}
@@ -137,12 +138,15 @@ protected static <ORDERER, WRAPPER> DescriptorWrapperOrderer<ORDERER, WRAPPER> n
 			return (DescriptorWrapperOrderer<ORDERER, WRAPPER>) NOOP;
 		}
 
+		@Nullable
 		private final ORDERER orderer;
+		@Nullable
 		private final Consumer<List<WRAPPER>> orderingAction;
+
 		private final MessageGenerator descriptorsAddedMessageGenerator;
 		private final MessageGenerator descriptorsRemovedMessageGenerator;
 
-		DescriptorWrapperOrderer(ORDERER orderer, Consumer<List<WRAPPER>> orderingAction,
+		DescriptorWrapperOrderer(@Nullable ORDERER orderer, @Nullable Consumer<List<WRAPPER>> orderingAction,
 				MessageGenerator descriptorsAddedMessageGenerator,
 				MessageGenerator descriptorsRemovedMessageGenerator) {
 
@@ -152,6 +156,7 @@ protected static <ORDERER, WRAPPER> DescriptorWrapperOrderer<ORDERER, WRAPPER> n
 			this.descriptorsRemovedMessageGenerator = descriptorsRemovedMessageGenerator;
 		}
 
+		@Nullable
 		ORDERER getOrderer() {
 			return orderer;
 		}
@@ -162,7 +167,7 @@ private boolean canOrderWrappers() {
 
 		private void orderWrappers(List<WRAPPER> wrappers, Consumer<String> errorHandler) {
 			List<WRAPPER> orderedWrappers = new ArrayList<>(wrappers);
-			this.orderingAction.accept(orderedWrappers);
+			requireNonNull(this.orderingAction).accept(orderedWrappers);
 			Map<Object, Integer> distinctWrappersToIndex = distinctWrappersToIndex(orderedWrappers);
 
 			int difference = orderedWrappers.size() - wrappers.size();
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/ClassOrderingVisitor.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/ClassOrderingVisitor.java
index e64063088600..2d6502f6c898 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/ClassOrderingVisitor.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/ClassOrderingVisitor.java
@@ -49,8 +49,7 @@ class ClassOrderingVisitor extends AbstractOrderingVisitor {
 		this.globalOrderer = createGlobalOrderer(configuration);
 		this.noOrderAnnotation = issueReporter.createReportingCondition(
 			testDescriptor -> !isAnnotated(testDescriptor.getTestClass(), Order.class), testDescriptor -> {
-				String message = String.format(
-					"Ineffective @Order annotation on class '%s'. It will not be applied because ClassOrderer.OrderAnnotation is not in use.",
+				String message = "Ineffective @Order annotation on class '%s'. It will not be applied because ClassOrderer.OrderAnnotation is not in use.".formatted(
 					testDescriptor.getTestClass().getName());
 				return DiscoveryIssue.builder(Severity.INFO, message) //
 						.source(ClassSource.from(testDescriptor.getTestClass())) //
@@ -117,8 +116,7 @@ private DescriptorWrapperOrderer<ClassOrderer, DefaultClassDescriptor> createCla
 				.map(this::createDescriptorWrapperOrderer)//
 				.orElseGet(() -> {
 					Object parent = classBasedTestDescriptor.getParent().orElse(null);
-					if (parent instanceof ClassBasedTestDescriptor) {
-						ClassBasedTestDescriptor parentClassTestDescriptor = (ClassBasedTestDescriptor) parent;
+					if (parent instanceof ClassBasedTestDescriptor parentClassTestDescriptor) {
 						DescriptorWrapperOrderer<ClassOrderer, DefaultClassDescriptor> cacheEntry = ordererCache.get(
 							parentClassTestDescriptor);
 						return cacheEntry != null ? cacheEntry : createClassLevelOrderer(parentClassTestDescriptor);
@@ -132,11 +130,9 @@ private DescriptorWrapperOrderer<ClassOrderer, DefaultClassDescriptor> createDes
 		Consumer<List<DefaultClassDescriptor>> orderingAction = classDescriptors -> classOrderer.orderClasses(
 			new DefaultClassOrdererContext(classDescriptors, this.configuration));
 
-		MessageGenerator descriptorsAddedMessageGenerator = number -> String.format(
-			"ClassOrderer [%s] added %s ClassDescriptor(s) which will be ignored.", classOrderer.getClass().getName(),
-			number);
-		MessageGenerator descriptorsRemovedMessageGenerator = number -> String.format(
-			"ClassOrderer [%s] removed %s ClassDescriptor(s) which will be retained with arbitrary ordering.",
+		MessageGenerator descriptorsAddedMessageGenerator = number -> "ClassOrderer [%s] added %s ClassDescriptor(s) which will be ignored.".formatted(
+			classOrderer.getClass().getName(), number);
+		MessageGenerator descriptorsRemovedMessageGenerator = number -> "ClassOrderer [%s] removed %s ClassDescriptor(s) which will be retained with arbitrary ordering.".formatted(
 			classOrderer.getClass().getName(), number);
 
 		return new DescriptorWrapperOrderer<>(classOrderer, orderingAction, descriptorsAddedMessageGenerator,
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/ClassSelectorResolver.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/ClassSelectorResolver.java
index 19480129303e..3294a1757a05 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/ClassSelectorResolver.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/ClassSelectorResolver.java
@@ -17,9 +17,10 @@
 import static org.junit.jupiter.engine.descriptor.NestedClassTestDescriptor.getEnclosingTestClasses;
 import static org.junit.platform.commons.support.HierarchyTraversalMode.TOP_DOWN;
 import static org.junit.platform.commons.support.ReflectionSupport.findMethods;
-import static org.junit.platform.commons.support.ReflectionSupport.streamNestedClasses;
 import static org.junit.platform.commons.util.FunctionUtils.where;
 import static org.junit.platform.commons.util.ReflectionUtils.isInnerClass;
+import static org.junit.platform.commons.util.ReflectionUtils.isNotAbstract;
+import static org.junit.platform.commons.util.ReflectionUtils.streamNestedClasses;
 import static org.junit.platform.engine.discovery.DiscoverySelectors.selectUniqueId;
 import static org.junit.platform.engine.support.discovery.SelectorResolver.Resolution.unresolved;
 
@@ -46,6 +47,7 @@
 import org.junit.jupiter.engine.discovery.predicates.TestClassPredicates;
 import org.junit.platform.commons.support.ReflectionSupport;
 import org.junit.platform.commons.util.ReflectionUtils;
+import org.junit.platform.commons.util.ReflectionUtils.CycleErrorHandling;
 import org.junit.platform.engine.DiscoveryIssue;
 import org.junit.platform.engine.DiscoveryIssue.Severity;
 import org.junit.platform.engine.DiscoverySelector;
@@ -112,9 +114,9 @@ public Resolution resolve(NestedClassSelector selector, Context context) {
 					parent -> Optional.of(newMemberClassTestDescriptor(parent, nestedClass))));
 			}
 		}
-		else if (isInnerClass(nestedClass) && predicates.looksLikeIntendedTestClass(nestedClass)) {
-			String message = String.format(
-				"Inner class '%s' looks like it was intended to be a test class but will not be executed. It must be static or annotated with @Nested.",
+		else if (isInnerClass(nestedClass) && isNotAbstract(nestedClass)
+				&& predicates.looksLikeIntendedTestClass(nestedClass)) {
+			String message = "Inner class '%s' looks like it was intended to be a test class but will not be executed. It must be static or annotated with @Nested.".formatted(
 				nestedClass.getName());
 			issueReporter.reportIssue(DiscoveryIssue.builder(Severity.WARNING, message) //
 					.source(ClassSource.from(nestedClass)));
@@ -126,42 +128,40 @@ else if (isInnerClass(nestedClass) && predicates.looksLikeIntendedTestClass(nest
 	public Resolution resolve(UniqueIdSelector selector, Context context) {
 		UniqueId uniqueId = selector.getUniqueId();
 		UniqueId.Segment lastSegment = uniqueId.getLastSegment();
-		if (ClassTestDescriptor.SEGMENT_TYPE.equals(lastSegment.getType())) {
-			return resolveStandaloneClassUniqueId(context, lastSegment, __ -> true, this::newClassTestDescriptor);
-		}
-		if (ClassTemplateTestDescriptor.STANDALONE_CLASS_SEGMENT_TYPE.equals(lastSegment.getType())) {
-			return resolveStandaloneClassUniqueId(context, lastSegment, this.predicates.isAnnotatedWithClassTemplate,
-				this::newClassTemplateTestDescriptor);
-		}
-		if (NestedClassTestDescriptor.SEGMENT_TYPE.equals(lastSegment.getType())) {
-			return resolveNestedClassUniqueId(context, uniqueId, __ -> true, this::newNestedClassTestDescriptor);
-		}
-		if (ClassTemplateTestDescriptor.NESTED_CLASS_SEGMENT_TYPE.equals(lastSegment.getType())) {
-			return resolveNestedClassUniqueId(context, uniqueId, this.predicates.isAnnotatedWithClassTemplate,
-				this::newNestedClassTemplateTestDescriptor);
-		}
-		if (ClassTemplateInvocationTestDescriptor.SEGMENT_TYPE.equals(lastSegment.getType())) {
-			Optional<ClassTemplateInvocationTestDescriptor> testDescriptor = context.addToParent(
-				() -> selectUniqueId(uniqueId.removeLastSegment()), parent -> {
-					int index = Integer.parseInt(lastSegment.getValue().substring(1));
-					return Optional.of(newDummyClassTemplateInvocationTestDescriptor(parent, index));
-				});
-			return toInvocationMatch(testDescriptor) //
-					.map(Resolution::match) //
-					.orElse(unresolved());
-		}
-		return unresolved();
+		return switch (lastSegment.getType()) {
+			case ClassTestDescriptor.SEGMENT_TYPE -> //
+					resolveStandaloneClassUniqueId(context, lastSegment, __ -> true, this::newClassTestDescriptor);
+			case ClassTemplateTestDescriptor.STANDALONE_CLASS_SEGMENT_TYPE -> //
+					resolveStandaloneClassUniqueId(context, lastSegment, this.predicates.isAnnotatedWithClassTemplate,
+						this::newClassTemplateTestDescriptor);
+			case NestedClassTestDescriptor.SEGMENT_TYPE -> //
+					resolveNestedClassUniqueId(context, uniqueId, __ -> true, this::newNestedClassTestDescriptor);
+			case ClassTemplateTestDescriptor.NESTED_CLASS_SEGMENT_TYPE -> //
+					resolveNestedClassUniqueId(context, uniqueId, this.predicates.isAnnotatedWithClassTemplate,
+						this::newNestedClassTemplateTestDescriptor);
+			case ClassTemplateInvocationTestDescriptor.SEGMENT_TYPE -> {
+				Optional<ClassTemplateInvocationTestDescriptor> testDescriptor = context.addToParent(
+					() -> selectUniqueId(uniqueId.removeLastSegment()), parent -> {
+						int index = Integer.parseInt(lastSegment.getValue().substring(1));
+						return Optional.of(newDummyClassTemplateInvocationTestDescriptor(parent, index));
+					});
+				yield toInvocationMatch(testDescriptor) //
+						.map(Resolution::match) //
+						.orElse(unresolved());
+			}
+			default -> unresolved();
+		};
 	}
 
 	@Override
 	public Resolution resolve(IterationSelector selector, Context context) {
 		DiscoverySelector parentSelector = selector.getParentSelector();
-		if (parentSelector instanceof ClassSelector
-				&& this.predicates.isAnnotatedWithClassTemplate.test(((ClassSelector) parentSelector).getJavaClass())) {
+		if (parentSelector instanceof ClassSelector classSelector
+				&& this.predicates.isAnnotatedWithClassTemplate.test(classSelector.getJavaClass())) {
 			return resolveIterations(selector, context);
 		}
-		if (parentSelector instanceof NestedClassSelector && this.predicates.isAnnotatedWithClassTemplate.test(
-			((NestedClassSelector) parentSelector).getNestedClass())) {
+		if (parentSelector instanceof NestedClassSelector nestedClassSelector
+				&& this.predicates.isAnnotatedWithClassTemplate.test(nestedClassSelector.getNestedClass())) {
 			return resolveIterations(selector, context);
 		}
 		return unresolved();
@@ -173,8 +173,7 @@ private Resolution resolveIterations(IterationSelector selector, Context context
 				.map(index -> context.addToParent(() -> parentSelector,
 					parent -> Optional.of(newDummyClassTemplateInvocationTestDescriptor(parent, index + 1)))) //
 				.map(this::toInvocationMatch) //
-				.filter(Optional::isPresent) //
-				.map(Optional::get) //
+				.flatMap(Optional::stream) //
 				.collect(toSet());
 		return matches.isEmpty() ? unresolved() : Resolution.matches(matches);
 	}
@@ -285,8 +284,7 @@ private static List<Class<?>> getTestClasses(TestClassAware testDescriptor) {
 	private Supplier<Set<? extends DiscoverySelector>> expansionCallback(TestDescriptor testDescriptor,
 			Supplier<List<Class<?>>> testClassesSupplier) {
 		return () -> {
-			if (testDescriptor instanceof Filterable) {
-				Filterable filterable = (Filterable) testDescriptor;
+			if (testDescriptor instanceof Filterable filterable) {
 				filterable.getDynamicDescendantFilter().allowAll();
 			}
 			List<Class<?>> testClasses = testClassesSupplier.get();
@@ -294,9 +292,13 @@ private Supplier<Set<? extends DiscoverySelector>> expansionCallback(TestDescrip
 			Stream<DiscoverySelector> methods = findMethods(testClass,
 				this.predicates.isTestOrTestFactoryOrTestTemplateMethod, TOP_DOWN).stream() //
 						.map(method -> selectMethod(testClasses, method));
-			Stream<NestedClassSelector> nestedClasses = streamNestedClasses(testClass,
-				this.predicates.isAnnotatedWithNested.or(ReflectionUtils::isInnerClass)) //
-						.map(nestedClass -> DiscoverySelectors.selectNestedClass(testClasses, nestedClass));
+			Stream<Class<?>> annotatedNestedClasses = streamNestedClasses(testClass,
+				this.predicates.isAnnotatedWithNested);
+			Stream<Class<?>> notAnnotatedInnerClasses = streamNestedClasses(testClass,
+				this.predicates.isAnnotatedWithNested.negate().and(ReflectionUtils::isInnerClass),
+				CycleErrorHandling.ABORT_VISIT);
+			var nestedClasses = Stream.concat(annotatedNestedClasses, notAnnotatedInnerClasses) //
+					.map(nestedClass -> DiscoverySelectors.selectNestedClass(testClasses, nestedClass));
 			return Stream.concat(methods, nestedClasses).collect(
 				toCollection((Supplier<Set<DiscoverySelector>>) LinkedHashSet::new));
 		};
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/DiscoverySelectorResolver.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/DiscoverySelectorResolver.java
index 6fabb7546b73..dbe6c9a92a2b 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/DiscoverySelectorResolver.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/DiscoverySelectorResolver.java
@@ -47,8 +47,8 @@ public class DiscoverySelectorResolver {
 				new ClassOrderingVisitor(getConfiguration(ctx), ctx.getIssueReporter()), //
 				new MethodOrderingVisitor(getConfiguration(ctx), ctx.getIssueReporter()), //
 				descriptor -> {
-					if (descriptor instanceof Validatable) {
-						((Validatable) descriptor).validate(ctx.getIssueReporter());
+					if (descriptor instanceof Validatable validatable) {
+						validatable.validate(ctx.getIssueReporter());
 					}
 				})) //
 			.build();
@@ -57,9 +57,8 @@ private static JupiterConfiguration getConfiguration(InitializationContext<Jupit
 		return context.getEngineDescriptor().getConfiguration();
 	}
 
-	public void resolveSelectors(EngineDiscoveryRequest request, JupiterEngineDescriptor engineDescriptor) {
-		DiscoveryIssueReporter issueReporter = DiscoveryIssueReporter.deduplicating(
-			DiscoveryIssueReporter.forwarding(request.getDiscoveryListener(), engineDescriptor.getUniqueId()));
+	public static void resolveSelectors(EngineDiscoveryRequest request, JupiterEngineDescriptor engineDescriptor,
+			DiscoveryIssueReporter issueReporter) {
 		resolver.resolve(request, engineDescriptor, issueReporter);
 	}
 
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/MethodFinder.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/MethodFinder.java
index 59fc6e356012..10bb24ab5139 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/MethodFinder.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/MethodFinder.java
@@ -30,7 +30,7 @@ Optional<Method> findMethod(String methodSpecPart, Class<?> clazz) {
 		Matcher matcher = METHOD_PATTERN.matcher(methodSpecPart);
 
 		Preconditions.condition(matcher.matches(),
-			() -> String.format("Method [%s] does not match pattern [%s]", methodSpecPart, METHOD_PATTERN));
+			() -> "Method [%s] does not match pattern [%s]".formatted(methodSpecPart, METHOD_PATTERN));
 
 		String methodName = matcher.group(1);
 		String parameterTypeNames = matcher.group(2);
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/MethodOrderingVisitor.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/MethodOrderingVisitor.java
index 471b9ecf8368..de4646820d37 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/MethodOrderingVisitor.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/MethodOrderingVisitor.java
@@ -10,12 +10,14 @@
 
 package org.junit.jupiter.engine.discovery;
 
+import static java.util.Comparator.comparing;
 import static org.junit.platform.commons.support.AnnotationSupport.findAnnotation;
 import static org.junit.platform.commons.support.AnnotationSupport.isAnnotated;
 
 import java.util.List;
 import java.util.Optional;
 import java.util.function.Consumer;
+import java.util.function.UnaryOperator;
 
 import org.junit.jupiter.api.MethodOrderer;
 import org.junit.jupiter.api.Order;
@@ -40,18 +42,21 @@ class MethodOrderingVisitor extends AbstractOrderingVisitor {
 	private final JupiterConfiguration configuration;
 	private final Condition<MethodBasedTestDescriptor> noOrderAnnotation;
 
+	// Not a static field to avoid initialization at build time for GraalVM
+	private final UnaryOperator<List<TestDescriptor>> methodsBeforeNestedClassesOrderer;
+
 	MethodOrderingVisitor(JupiterConfiguration configuration, DiscoveryIssueReporter issueReporter) {
 		super(issueReporter);
 		this.configuration = configuration;
 		this.noOrderAnnotation = issueReporter.createReportingCondition(
 			testDescriptor -> !isAnnotated(testDescriptor.getTestMethod(), Order.class), testDescriptor -> {
-				String message = String.format(
-					"Ineffective @Order annotation on method '%s'. It will not be applied because MethodOrderer.OrderAnnotation is not in use.",
+				String message = "Ineffective @Order annotation on method '%s'. It will not be applied because MethodOrderer.OrderAnnotation is not in use.".formatted(
 					testDescriptor.getTestMethod().toGenericString());
 				return DiscoveryIssue.builder(Severity.INFO, message) //
 						.source(MethodSource.from(testDescriptor.getTestMethod())) //
 						.build();
 			});
+		this.methodsBeforeNestedClassesOrderer = createMethodsBeforeNestedClassesOrderer();
 	}
 
 	@Override
@@ -74,14 +79,14 @@ protected boolean shouldNonMatchingDescriptorsComeBeforeOrderedOnes() {
 	private void orderContainedMethods(ClassBasedTestDescriptor classBasedTestDescriptor, Class<?> testClass) {
 		Optional<MethodOrderer> methodOrderer = findAnnotation(testClass, TestMethodOrder.class)//
 				.map(TestMethodOrder::value)//
-				.<MethodOrderer> map(ReflectionSupport::newInstance)//
-				.map(Optional::of)//
-				.orElseGet(configuration::getDefaultTestMethodOrderer);
+				.<MethodOrderer> map(ReflectionSupport::newInstance) //
+				.or(configuration::getDefaultTestMethodOrderer);
 		orderContainedMethods(classBasedTestDescriptor, testClass, methodOrderer);
 	}
 
 	private void orderContainedMethods(ClassBasedTestDescriptor classBasedTestDescriptor, Class<?> testClass,
 			Optional<MethodOrderer> methodOrderer) {
+
 		DescriptorWrapperOrderer<?, DefaultMethodDescriptor> descriptorWrapperOrderer = createDescriptorWrapperOrderer(
 			testClass, methodOrderer);
 
@@ -91,6 +96,11 @@ private void orderContainedMethods(ClassBasedTestDescriptor classBasedTestDescri
 			DefaultMethodDescriptor::new, //
 			descriptorWrapperOrderer);
 
+		if (methodOrderer.isEmpty()) {
+			// If there is an orderer, this is ensured by the call above
+			classBasedTestDescriptor.orderChildren(methodsBeforeNestedClassesOrderer);
+		}
+
 		// Note: MethodOrderer#getDefaultExecutionMode() is guaranteed
 		// to be invoked after MethodOrderer#orderMethods().
 		methodOrderer //
@@ -112,11 +122,9 @@ private DescriptorWrapperOrderer<?, DefaultMethodDescriptor> createDescriptorWra
 		Consumer<List<DefaultMethodDescriptor>> orderingAction = methodDescriptors -> methodOrderer.orderMethods(
 			new DefaultMethodOrdererContext(testClass, methodDescriptors, this.configuration));
 
-		MessageGenerator descriptorsAddedMessageGenerator = number -> String.format(
-			"MethodOrderer [%s] added %s MethodDescriptor(s) for test class [%s] which will be ignored.",
+		MessageGenerator descriptorsAddedMessageGenerator = number -> "MethodOrderer [%s] added %s MethodDescriptor(s) for test class [%s] which will be ignored.".formatted(
 			methodOrderer.getClass().getName(), number, testClass.getName());
-		MessageGenerator descriptorsRemovedMessageGenerator = number -> String.format(
-			"MethodOrderer [%s] removed %s MethodDescriptor(s) for test class [%s] which will be retained with arbitrary ordering.",
+		MessageGenerator descriptorsRemovedMessageGenerator = number -> "MethodOrderer [%s] removed %s MethodDescriptor(s) for test class [%s] which will be retained with arbitrary ordering.".formatted(
 			methodOrderer.getClass().getName(), number, testClass.getName());
 
 		return new DescriptorWrapperOrderer<>(methodOrderer, orderingAction, descriptorsAddedMessageGenerator,
@@ -130,4 +138,12 @@ private Optional<Consumer<MethodBasedTestDescriptor>> toValidationAction(Optiona
 		return Optional.of(noOrderAnnotation::check);
 	}
 
+	private static UnaryOperator<List<TestDescriptor>> createMethodsBeforeNestedClassesOrderer() {
+		var methodsFirst = comparing(MethodBasedTestDescriptor.class::isInstance).reversed();
+		return children -> {
+			children.sort(methodsFirst);
+			return children;
+		};
+	}
+
 }
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/MethodSelectorResolver.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/MethodSelectorResolver.java
index 09b021766f72..bc69f0a0ce15 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/MethodSelectorResolver.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/MethodSelectorResolver.java
@@ -12,7 +12,6 @@
 
 import static java.util.Collections.emptyList;
 import static java.util.Collections.emptySet;
-import static java.util.stream.Collectors.toList;
 import static java.util.stream.Collectors.toSet;
 import static org.junit.platform.engine.discovery.DiscoverySelectors.selectUniqueId;
 import static org.junit.platform.engine.support.discovery.SelectorResolver.Resolution.matches;
@@ -95,8 +94,7 @@ private Resolution resolve(Context context, List<Class<?>> enclosingClasses, Cla
 		// @formatter:off
 		Set<Match> matches = methodTypes.stream()
 				.map(methodType -> methodType.resolve(enclosingClasses, testClass, method, context, configuration))
-				.filter(Optional::isPresent)
-				.map(Optional::get)
+				.flatMap(Optional::stream)
 				.map(testDescriptor -> matchFactory.apply(testDescriptor, expansionCallback(testDescriptor)))
 				.collect(toSet());
 		// @formatter:on
@@ -106,7 +104,7 @@ private Resolution resolve(Context context, List<Class<?>> enclosingClasses, Cla
 				"Possible configuration error: method [%s] resulted in multiple TestDescriptors %s. "
 						+ "This is typically the result of annotating a method with multiple competing annotations "
 						+ "such as @Test, @RepeatedTest, @ParameterizedTest, @TestFactory, etc.",
-				method.toGenericString(), testDescriptors.map(d -> d.getClass().getName()).collect(toList()));
+				method.toGenericString(), testDescriptors.map(d -> d.getClass().getName()).toList());
 			issueReporter.reportIssue(
 				DiscoveryIssue.builder(Severity.WARNING, message).source(MethodSource.from(method)));
 		}
@@ -119,12 +117,10 @@ public Resolution resolve(UniqueIdSelector selector, Context context) {
 		// @formatter:off
 		return methodTypes.stream()
 				.map(methodType -> methodType.resolveUniqueIdIntoTestDescriptor(uniqueId, context, configuration))
-				.filter(Optional::isPresent)
-				.map(Optional::get)
+				.flatMap(Optional::stream)
 				.map(testDescriptor -> {
 					boolean exactMatch = uniqueId.equals(testDescriptor.getUniqueId());
-					if (testDescriptor instanceof Filterable) {
-						Filterable filterable = (Filterable) testDescriptor;
+					if (testDescriptor instanceof Filterable filterable) {
 						if (exactMatch) {
 							filterable.getDynamicDescendantFilter().allowAll();
 						}
@@ -141,12 +137,10 @@ public Resolution resolve(UniqueIdSelector selector, Context context) {
 
 	@Override
 	public Resolution resolve(IterationSelector selector, Context context) {
-		if (selector.getParentSelector() instanceof MethodSelector) {
-			MethodSelector methodSelector = (MethodSelector) selector.getParentSelector();
+		if (selector.getParentSelector() instanceof MethodSelector methodSelector) {
 			return resolve(context, emptyList(), methodSelector.getJavaClass(), methodSelector::getJavaMethod,
 				(testDescriptor, childSelectorsSupplier) -> {
-					if (testDescriptor instanceof Filterable) {
-						Filterable filterable = (Filterable) testDescriptor;
+					if (testDescriptor instanceof Filterable filterable) {
 						filterable.getDynamicDescendantFilter().allowIndex(selector.getIterationIndices());
 					}
 					return Match.partial(testDescriptor, childSelectorsSupplier);
@@ -157,8 +151,7 @@ public Resolution resolve(IterationSelector selector, Context context) {
 
 	private Supplier<Set<? extends DiscoverySelector>> expansionCallback(TestDescriptor testDescriptor) {
 		return () -> {
-			if (testDescriptor instanceof Filterable) {
-				Filterable filterable = (Filterable) testDescriptor;
+			if (testDescriptor instanceof Filterable filterable) {
 				filterable.getDynamicDescendantFilter().allowAll();
 			}
 			return emptySet();
@@ -236,7 +229,7 @@ private TestDescriptor createTestDescriptor(TestDescriptor parent, Class<?> test
 		}
 
 		private UniqueId createUniqueId(Method method, TestDescriptor parent) {
-			String methodId = String.format("%s(%s)", method.getName(),
+			String methodId = "%s(%s)".formatted(method.getName(),
 				ClassUtils.nullSafeToString(method.getParameterTypes()));
 			return parent.getUniqueId().append(segmentType, methodId);
 		}
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/package-info.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/package-info.java
index 0426627d49ba..d9a5e573aafc 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/package-info.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/package-info.java
@@ -3,4 +3,7 @@
  * Contains resolvers for Java elements.
  */
 
+@NullMarked
 package org.junit.jupiter.engine.discovery;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/predicates/IsTestFactoryMethod.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/predicates/IsTestFactoryMethod.java
index 144ec6db621c..7b3e27d6abc7 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/predicates/IsTestFactoryMethod.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/predicates/IsTestFactoryMethod.java
@@ -11,6 +11,8 @@
 package org.junit.jupiter.engine.discovery.predicates;
 
 import static org.apiguardian.api.API.Status.INTERNAL;
+import static org.junit.jupiter.engine.support.MethodReflectionUtils.getGenericReturnType;
+import static org.junit.jupiter.engine.support.MethodReflectionUtils.getReturnType;
 import static org.junit.platform.commons.util.CollectionUtils.isConvertibleToStream;
 
 import java.lang.annotation.Annotation;
@@ -38,8 +40,7 @@
 @API(status = INTERNAL, since = "5.0")
 public class IsTestFactoryMethod extends IsTestableMethod {
 
-	private static final String EXPECTED_RETURN_TYPE_MESSAGE = String.format(
-		"must return a single %1$s or a Stream, Collection, Iterable, Iterator, Iterator provider, or array of %1$s",
+	private static final String EXPECTED_RETURN_TYPE_MESSAGE = "must return a single %1$s or a Stream, Collection, Iterable, Iterator, Iterator provider, or array of %1$s".formatted(
 		DynamicNode.class.getName());
 
 	public IsTestFactoryMethod(DiscoveryIssueReporter issueReporter) {
@@ -53,7 +54,7 @@ private static DiscoveryIssueReporter.Condition<Method> hasCompatibleReturnType(
 	}
 
 	private static boolean isCompatible(Method method, DiscoveryIssueReporter issueReporter) {
-		Class<?> returnType = method.getReturnType();
+		Class<?> returnType = getReturnType(method);
 		if (DynamicNode.class.isAssignableFrom(returnType) || DynamicNode[].class.isAssignableFrom(returnType)) {
 			return true;
 		}
@@ -66,22 +67,21 @@ private static boolean isCompatible(Method method, DiscoveryIssueReporter issueR
 	}
 
 	private static boolean isCompatibleContainerType(Method method, DiscoveryIssueReporter issueReporter) {
-		Type genericReturnType = method.getGenericReturnType();
+		Type genericReturnType = getGenericReturnType(method);
 
-		if (genericReturnType instanceof ParameterizedType) {
-			Type[] typeArguments = ((ParameterizedType) genericReturnType).getActualTypeArguments();
+		if (genericReturnType instanceof ParameterizedType type) {
+			Type[] typeArguments = type.getActualTypeArguments();
 			if (typeArguments.length == 1) {
 				Type typeArgument = typeArguments[0];
-				if (typeArgument instanceof Class) {
+				if (typeArgument instanceof Class<?> clazz) {
 					// Stream<DynamicNode> etc.
-					return DynamicNode.class.isAssignableFrom((Class<?>) typeArgument);
+					return DynamicNode.class.isAssignableFrom(clazz);
 				}
-				if (typeArgument instanceof WildcardType) {
-					WildcardType wildcardType = (WildcardType) typeArgument;
+				if (typeArgument instanceof WildcardType wildcardType) {
 					Type[] upperBounds = wildcardType.getUpperBounds();
 					Type[] lowerBounds = wildcardType.getLowerBounds();
-					if (upperBounds.length == 1 && lowerBounds.length == 0 && upperBounds[0] instanceof Class) {
-						Class<?> upperBound = (Class<?>) upperBounds[0];
+					if (upperBounds.length == 1 && lowerBounds.length == 0
+							&& upperBounds[0] instanceof Class<?> upperBound) {
 						if (Object.class.equals(upperBound)) { // Stream<?> etc.
 							issueReporter.reportIssue(createTooGenericReturnTypeIssue(method));
 							return true;
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/predicates/IsTestableMethod.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/predicates/IsTestableMethod.java
index 498d04e62992..7e95f77f8307 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/predicates/IsTestableMethod.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/predicates/IsTestableMethod.java
@@ -10,7 +10,9 @@
 
 package org.junit.jupiter.engine.discovery.predicates;
 
+import static org.junit.jupiter.engine.support.MethodReflectionUtils.getReturnType;
 import static org.junit.platform.commons.support.AnnotationSupport.isAnnotated;
+import static org.junit.platform.commons.support.ModifierSupport.isNotAbstract;
 
 import java.lang.annotation.Annotation;
 import java.lang.reflect.Method;
@@ -18,7 +20,6 @@
 import java.util.function.Predicate;
 
 import org.junit.platform.commons.support.ModifierSupport;
-import org.junit.platform.commons.util.ReflectionUtils;
 import org.junit.platform.engine.DiscoveryIssue;
 import org.junit.platform.engine.DiscoveryIssue.Severity;
 import org.junit.platform.engine.support.descriptor.MethodSource;
@@ -39,14 +40,13 @@ abstract class IsTestableMethod implements Predicate<Method> {
 		this.annotationType = annotationType;
 		this.condition = isNotStatic(annotationType, issueReporter) //
 				.and(isNotPrivate(annotationType, issueReporter)) //
-				.and(isNotAbstract(annotationType, issueReporter)) //
 				.and(returnTypeConditionFactory.apply(annotationType, issueReporter));
 	}
 
 	@Override
 	public boolean test(Method candidate) {
 		if (isAnnotated(candidate, this.annotationType)) {
-			return condition.check(candidate);
+			return condition.check(candidate) && isNotAbstract(candidate);
 		}
 		return false;
 	}
@@ -63,21 +63,15 @@ private static Condition<Method> isNotPrivate(Class<? extends Annotation> annota
 			method -> createIssue(annotationType, method, "must not be private"));
 	}
 
-	private static Condition<Method> isNotAbstract(Class<? extends Annotation> annotationType,
-			DiscoveryIssueReporter issueReporter) {
-		return issueReporter.createReportingCondition(ModifierSupport::isNotAbstract,
-			method -> createIssue(annotationType, method, "must not be abstract"));
-	}
-
 	protected static Condition<Method> hasVoidReturnType(Class<? extends Annotation> annotationType,
 			DiscoveryIssueReporter issueReporter) {
-		return issueReporter.createReportingCondition(ReflectionUtils::returnsPrimitiveVoid,
+		return issueReporter.createReportingCondition(method -> getReturnType(method) == void.class,
 			method -> createIssue(annotationType, method, "must not return a value"));
 	}
 
 	protected static DiscoveryIssue createIssue(Class<? extends Annotation> annotationType, Method method,
 			String condition) {
-		String message = String.format("@%s method '%s' %s. It will not be executed.", annotationType.getSimpleName(),
+		String message = "@%s method '%s' %s. It will not be executed.".formatted(annotationType.getSimpleName(),
 			method.toGenericString(), condition);
 		return DiscoveryIssue.builder(Severity.WARNING, message) //
 				.source(MethodSource.from(method)) //
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/predicates/TestClassPredicates.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/predicates/TestClassPredicates.java
index 6dceea4dfb98..d34f8a885d68 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/predicates/TestClassPredicates.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/predicates/TestClassPredicates.java
@@ -19,13 +19,17 @@
 import static org.junit.platform.commons.util.ReflectionUtils.isMethodPresent;
 import static org.junit.platform.commons.util.ReflectionUtils.isNestedClassPresent;
 
+import java.lang.annotation.Annotation;
 import java.lang.reflect.Method;
+import java.util.HashSet;
+import java.util.Set;
 import java.util.function.Predicate;
 
 import org.apiguardian.api.API;
 import org.junit.jupiter.api.ClassTemplate;
 import org.junit.jupiter.api.Nested;
 import org.junit.platform.commons.util.ReflectionUtils;
+import org.junit.platform.commons.util.ReflectionUtils.CycleErrorHandling;
 import org.junit.platform.engine.DiscoveryIssue;
 import org.junit.platform.engine.support.descriptor.ClassSource;
 import org.junit.platform.engine.support.discovery.DiscoveryIssueReporter;
@@ -39,8 +43,9 @@
 @API(status = INTERNAL, since = "5.13")
 public class TestClassPredicates {
 
-	public final Predicate<Class<?>> isAnnotatedWithNested = testClass -> isAnnotated(testClass, Nested.class);
-	public final Predicate<Class<?>> isAnnotatedWithClassTemplate = testClass -> isAnnotated(testClass,
+	public final Predicate<Class<?>> isAnnotatedWithNested = candidate -> isAnnotatedButNotComposed(candidate,
+		Nested.class);
+	public final Predicate<Class<?>> isAnnotatedWithClassTemplate = candidate -> isAnnotatedButNotComposed(candidate,
 		ClassTemplate.class);
 
 	public final Predicate<Class<?>> isAnnotatedWithNestedAndValid = candidate -> this.isAnnotatedWithNested.test(
@@ -60,14 +65,21 @@ public TestClassPredicates(DiscoveryIssueReporter issueReporter) {
 				.and(isInner(issueReporter));
 		this.isValidStandaloneTestClass = isNotPrivateUnlessAbstract("Test", issueReporter) //
 				.and(isNotLocal(issueReporter)) //
-				.and(isNotInner(issueReporter)) // or should be annotated with @Nested!
+				.and(isNotInnerUnlessAbstract(issueReporter)) //
 				.and(isNotAnonymous(issueReporter));
 	}
 
 	public boolean looksLikeIntendedTestClass(Class<?> candidate) {
-		return this.isAnnotatedWithClassTemplate.test(candidate) //
-				|| hasTestOrTestFactoryOrTestTemplateMethods(candidate) //
-				|| hasNestedTests(candidate);
+		return looksLikeIntendedTestClass(candidate, new HashSet<>());
+	}
+
+	private boolean looksLikeIntendedTestClass(Class<?> candidate, Set<Class<?>> seen) {
+		if (seen.add(candidate)) {
+			return this.isAnnotatedWithClassTemplate.test(candidate) //
+					|| hasTestOrTestFactoryOrTestTemplateMethods(candidate) //
+					|| hasNestedTests(candidate, seen);
+		}
+		return false;
 	}
 
 	public boolean isValidNestedTestClass(Class<?> candidate) {
@@ -84,15 +96,17 @@ private boolean hasTestOrTestFactoryOrTestTemplateMethods(Class<?> candidate) {
 		return isMethodPresent(candidate, this.isTestOrTestFactoryOrTestTemplateMethod);
 	}
 
-	private boolean hasNestedTests(Class<?> candidate) {
+	private boolean hasNestedTests(Class<?> candidate, Set<Class<?>> seen) {
+		var hasAnnotatedClass = isNestedClassPresent(candidate, this.isAnnotatedWithNested,
+			CycleErrorHandling.THROW_EXCEPTION);
+		if (hasAnnotatedClass) {
+			return true;
+		}
 		return isNestedClassPresent( //
 			candidate, //
-			isNotSame(candidate).and(
-				this.isAnnotatedWithNested.or(it -> isInnerClass(it) && looksLikeIntendedTestClass(it))));
-	}
-
-	private static Predicate<Class<?>> isNotSame(Class<?> candidate) {
-		return clazz -> candidate != clazz;
+			it -> isInnerClass(it) && looksLikeIntendedTestClass(it, seen), //
+			CycleErrorHandling.ABORT_VISIT //
+		);
 	}
 
 	private static Condition<Class<?>> isNotPrivateUnlessAbstract(String prefix, DiscoveryIssueReporter issueReporter) {
@@ -115,8 +129,8 @@ private static Condition<Class<?>> isInner(DiscoveryIssueReporter issueReporter)
 		});
 	}
 
-	private static Condition<Class<?>> isNotInner(DiscoveryIssueReporter issueReporter) {
-		return issueReporter.createReportingCondition(testClass -> !isInnerClass(testClass),
+	private static Condition<Class<?>> isNotInnerUnlessAbstract(DiscoveryIssueReporter issueReporter) {
+		return issueReporter.createReportingCondition(testClass -> !isInnerClass(testClass) || isAbstract(testClass),
 			testClass -> createIssue("Test", testClass, "must not be an inner class unless annotated with @Nested"));
 	}
 
@@ -126,10 +140,14 @@ private static Condition<Class<?>> isNotAnonymous(DiscoveryIssueReporter issueRe
 	}
 
 	private static DiscoveryIssue createIssue(String prefix, Class<?> testClass, String detailMessage) {
-		String message = String.format("%s class '%s' %s. It will not be executed.", prefix, testClass.getName(),
+		String message = "%s class '%s' %s. It will not be executed.".formatted(prefix, testClass.getName(),
 			detailMessage);
 		return DiscoveryIssue.builder(DiscoveryIssue.Severity.WARNING, message) //
 				.source(ClassSource.from(testClass)) //
 				.build();
 	}
+
+	private static boolean isAnnotatedButNotComposed(Class<?> candidate, Class<? extends Annotation> annotationType) {
+		return !candidate.isAnnotation() && isAnnotated(candidate, annotationType);
+	}
 }
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/predicates/package-info.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/predicates/package-info.java
index 579eb486e17d..028f0bbbf8c0 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/predicates/package-info.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/discovery/predicates/package-info.java
@@ -2,4 +2,7 @@
  * Internal predicate classes used by test discovery within the JUnit Jupiter test engine.
  */
 
+@NullMarked
 package org.junit.jupiter.engine.discovery.predicates;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/ConditionEvaluationException.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/ConditionEvaluationException.java
index 7b9a948205c2..35f7b29f79dd 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/ConditionEvaluationException.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/ConditionEvaluationException.java
@@ -10,6 +10,8 @@
 
 package org.junit.jupiter.engine.execution;
 
+import java.io.Serial;
+
 import org.junit.jupiter.api.extension.ExecutionCondition;
 import org.junit.platform.commons.JUnitException;
 
@@ -22,6 +24,7 @@
  */
 class ConditionEvaluationException extends JUnitException {
 
+	@Serial
 	private static final long serialVersionUID = 1L;
 
 	public ConditionEvaluationException(String message, Throwable cause) {
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/ConditionEvaluator.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/ConditionEvaluator.java
index e51126bec2ef..c8c4ee3899c0 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/ConditionEvaluator.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/ConditionEvaluator.java
@@ -10,7 +10,6 @@
 
 package org.junit.jupiter.engine.execution;
 
-import static java.lang.String.format;
 import static org.apiguardian.api.API.Status.INTERNAL;
 
 import org.apiguardian.api.API;
@@ -71,14 +70,14 @@ private ConditionEvaluationResult evaluate(ExecutionCondition condition, Extensi
 	}
 
 	private void logResult(Class<?> conditionType, ConditionEvaluationResult result, ExtensionContext context) {
-		logger.trace(() -> format("Evaluation of condition [%s] on [%s] resulted in: %s", conditionType.getName(),
+		logger.trace(() -> "Evaluation of condition [%s] on [%s] resulted in: %s".formatted(conditionType.getName(),
 			context.getElement().orElse(null), result));
 	}
 
 	private ConditionEvaluationException evaluationException(Class<?> conditionType, Exception ex) {
 		String cause = StringUtils.isNotBlank(ex.getMessage()) ? ": " + ex.getMessage() : "";
 		return new ConditionEvaluationException(
-			format("Failed to evaluate condition [%s]%s", conditionType.getName(), cause), ex);
+			"Failed to evaluate condition [%s]%s".formatted(conditionType.getName(), cause), ex);
 	}
 
 }
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/ConstructorInvocation.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/ConstructorInvocation.java
index 79cbd46c6895..d046535c0a56 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/ConstructorInvocation.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/ConstructorInvocation.java
@@ -17,6 +17,7 @@
 import java.util.List;
 import java.util.Optional;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.extension.InvocationInterceptor.Invocation;
 import org.junit.jupiter.api.extension.ReflectiveInvocationContext;
 import org.junit.platform.commons.util.ReflectionUtils;
@@ -24,9 +25,9 @@
 class ConstructorInvocation<T> implements Invocation<T>, ReflectiveInvocationContext<Constructor<T>> {
 
 	private final Constructor<T> constructor;
-	private final Object[] arguments;
+	private final @Nullable Object[] arguments;
 
-	ConstructorInvocation(Constructor<T> constructor, Object[] arguments) {
+	ConstructorInvocation(Constructor<T> constructor, @Nullable Object[] arguments) {
 		this.constructor = constructor;
 		this.arguments = arguments;
 	}
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/DefaultExecutableInvoker.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/DefaultExecutableInvoker.java
index 226db46cf82d..37a663ebb0b8 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/DefaultExecutableInvoker.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/DefaultExecutableInvoker.java
@@ -18,9 +18,11 @@
 import java.util.Optional;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.extension.ExecutableInvoker;
 import org.junit.jupiter.api.extension.ExtensionContext;
 import org.junit.jupiter.engine.extension.ExtensionRegistry;
+import org.junit.jupiter.engine.support.MethodReflectionUtils;
 import org.junit.platform.commons.util.ReflectionUtils;
 
 /**
@@ -38,17 +40,19 @@ public DefaultExecutableInvoker(ExtensionContext extensionContext, ExtensionRegi
 	}
 
 	@Override
-	public <T> T invoke(Constructor<T> constructor, Object outerInstance) {
+	public <T> T invoke(Constructor<T> constructor, @Nullable Object outerInstance) {
+		@Nullable
 		Object[] arguments = resolveParameters(constructor, Optional.empty(), Optional.ofNullable(outerInstance),
 			extensionContext, extensionRegistry);
 		return ReflectionUtils.newInstance(constructor, arguments);
 	}
 
 	@Override
-	public Object invoke(Method method, Object target) {
+	public @Nullable Object invoke(Method method, @Nullable Object target) {
+		@Nullable
 		Object[] arguments = resolveParameters(method, Optional.ofNullable(target), extensionContext,
 			extensionRegistry);
-		return ReflectionUtils.invokeMethod(method, target, arguments);
+		return MethodReflectionUtils.invoke(method, target, arguments);
 	}
 
 }
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/DefaultParameterContext.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/DefaultParameterContext.java
index 23d2ada54331..4b4f48714d8b 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/DefaultParameterContext.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/DefaultParameterContext.java
@@ -23,17 +23,12 @@
 /**
  * @since 5.0
  */
-class DefaultParameterContext implements ParameterContext {
+record DefaultParameterContext(Parameter parameter, int index, Optional<Object> target) implements ParameterContext {
 
-	private final Parameter parameter;
-	private final int index;
-	private final Optional<Object> target;
-
-	DefaultParameterContext(Parameter parameter, int index, Optional<Object> target) {
+	DefaultParameterContext {
 		Preconditions.condition(index >= 0, "index must be greater than or equal to zero");
-		this.parameter = Preconditions.notNull(parameter, "parameter must not be null");
-		this.index = index;
-		this.target = Preconditions.notNull(target, "target must not be null");
+		Preconditions.notNull(parameter, "parameter must not be null");
+		Preconditions.notNull(target, "target must not be null");
 	}
 
 	@Override
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/ExtensionContextSupplier.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/ExtensionContextSupplier.java
index c813687bb8b4..c3be76eb148e 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/ExtensionContextSupplier.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/ExtensionContextSupplier.java
@@ -20,7 +20,7 @@
 
 /**
  * Container of two instances of {@link ExtensionContext} to simplify the legacy for
- * <a href="https://github.com/junit-team/junit5/issues/3445">#3445</a>.
+ * <a href="https://github.com/junit-team/junit-framework/issues/3445">#3445</a>.
  *
  * @since 5.12
  * @see TestInstantiationAwareExtension
@@ -51,6 +51,7 @@ private ScopeBasedExtensionContextSupplier(ExtensionContext currentExtensionCont
 			this.legacyExtensionContext = legacyExtensionContext;
 		}
 
+		@Override
 		public ExtensionContext get(TestInstantiationAwareExtension extension) {
 			return isTestScoped(extension) ? currentExtensionContext : legacyExtensionContext;
 		}
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/InterceptingExecutableInvoker.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/InterceptingExecutableInvoker.java
index 9454d5829302..416131d853cf 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/InterceptingExecutableInvoker.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/InterceptingExecutableInvoker.java
@@ -19,11 +19,13 @@
 import java.util.Optional;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.extension.ExtensionContext;
 import org.junit.jupiter.api.extension.InvocationInterceptor;
 import org.junit.jupiter.api.extension.InvocationInterceptor.Invocation;
 import org.junit.jupiter.api.extension.ParameterResolver;
 import org.junit.jupiter.api.extension.ReflectiveInvocationContext;
+import org.junit.jupiter.engine.execution.InterceptingExecutableInvoker.ReflectiveInterceptorCall.VoidMethodInterceptorCall;
 import org.junit.jupiter.engine.extension.ExtensionRegistry;
 
 /**
@@ -57,12 +59,19 @@ public <T> T invoke(Constructor<T> constructor, Optional<Object> outerInstance,
 			ExtensionContextSupplier extensionContext, ExtensionRegistry extensionRegistry,
 			ReflectiveInterceptorCall<Constructor<T>, T> interceptorCall) {
 
+		@Nullable
 		Object[] arguments = resolveParameters(constructor, Optional.empty(), outerInstance, extensionContext,
 			extensionRegistry);
 		ConstructorInvocation<T> invocation = new ConstructorInvocation<>(constructor, arguments);
 		return invoke(invocation, invocation, extensionContext, extensionRegistry, interceptorCall);
 	}
 
+	public void invokeVoid(Method method, @Nullable Object target, ExtensionContext extensionContext,
+			ExtensionRegistry extensionRegistry, VoidMethodInterceptorCall interceptorCall) {
+		this.<@Nullable Void> invoke(method, target, extensionContext, extensionRegistry,
+			ReflectiveInterceptorCall.ofVoidMethod(interceptorCall));
+	}
+
 	/**
 	 * Invoke the supplied method with dynamic parameter resolution.
 	 *
@@ -76,12 +85,14 @@ public <T> T invoke(Constructor<T> constructor, Optional<Object> outerInstance,
 	 * @param interceptorCall the call for intercepting this method invocation
 	 * via all registered {@linkplain InvocationInterceptor interceptors}
 	 */
-	public <T> T invoke(Method method, Object target, ExtensionContext extensionContext,
-			ExtensionRegistry extensionRegistry, ReflectiveInterceptorCall<Method, T> interceptorCall) {
+	public <T extends @Nullable Object> T invoke(Method method, @Nullable Object target,
+			ExtensionContext extensionContext, ExtensionRegistry extensionRegistry,
+			ReflectiveInterceptorCall<Method, T> interceptorCall) {
 
-		@SuppressWarnings("unchecked")
-		Optional<Object> optionalTarget = (target instanceof Optional ? (Optional<Object>) target
+		@SuppressWarnings({ "unchecked", "rawtypes" })
+		Optional<Object> optionalTarget = (target instanceof Optional optional ? optional
 				: Optional.ofNullable(target));
+		@Nullable
 		Object[] arguments = resolveParameters(method, optionalTarget, extensionContext, extensionRegistry);
 		MethodInvocation<T> invocation = new MethodInvocation<>(method, optionalTarget, arguments);
 		return invoke(invocation, invocation, extensionContext, extensionRegistry, interceptorCall);
@@ -102,12 +113,12 @@ private <E extends Executable, T> T invoke(Invocation<T> originalInvocation,
 				extensionContext.get(interceptor)));
 	}
 
-	public interface ReflectiveInterceptorCall<E extends Executable, T> {
+	public interface ReflectiveInterceptorCall<E extends Executable, T extends @Nullable Object> {
 
 		T apply(InvocationInterceptor interceptor, Invocation<T> invocation,
 				ReflectiveInvocationContext<E> invocationContext, ExtensionContext extensionContext) throws Throwable;
 
-		static ReflectiveInterceptorCall<Method, Void> ofVoidMethod(VoidMethodInterceptorCall call) {
+		static ReflectiveInterceptorCall<Method, @Nullable Void> ofVoidMethod(VoidMethodInterceptorCall call) {
 			return ((interceptorChain, invocation, invocationContext, extensionContext) -> {
 				call.apply(interceptorChain, invocation, invocationContext, extensionContext);
 				return null;
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/InvocationInterceptorChain.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/InvocationInterceptorChain.java
index 3b73cbc982e7..52a7fb65e12a 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/InvocationInterceptorChain.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/InvocationInterceptorChain.java
@@ -18,6 +18,7 @@
 import java.util.concurrent.atomic.AtomicBoolean;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.extension.InvocationInterceptor;
 import org.junit.jupiter.api.extension.InvocationInterceptor.Invocation;
 import org.junit.jupiter.engine.extension.ExtensionRegistry;
@@ -29,7 +30,8 @@
 @API(status = INTERNAL, since = "5.5")
 public class InvocationInterceptorChain {
 
-	public <T> T invoke(Invocation<T> invocation, ExtensionRegistry extensionRegistry, InterceptorCall<T> call) {
+	public <T extends @Nullable Object> T invoke(Invocation<T> invocation, ExtensionRegistry extensionRegistry,
+			InterceptorCall<T> call) {
 		List<InvocationInterceptor> interceptors = extensionRegistry.getExtensions(InvocationInterceptor.class);
 		if (interceptors.isEmpty()) {
 			return proceed(invocation);
@@ -69,15 +71,15 @@ private <T> T proceed(Invocation<T> invocation) {
 	}
 
 	@FunctionalInterface
-	public interface InterceptorCall<T> {
+	public interface InterceptorCall<T extends @Nullable Object> {
 
 		T apply(InvocationInterceptor interceptor, Invocation<T> invocation) throws Throwable;
 
-		static InterceptorCall<Void> ofVoid(VoidInterceptorCall call) {
-			return ((interceptorChain, invocation) -> {
+		static InterceptorCall<@Nullable Void> ofVoid(VoidInterceptorCall call) {
+			return (InvocationInterceptor interceptorChain, Invocation<@Nullable Void> invocation) -> {
 				call.apply(interceptorChain, invocation);
 				return null;
-			});
+			};
 		}
 
 	}
@@ -85,21 +87,12 @@ static InterceptorCall<Void> ofVoid(VoidInterceptorCall call) {
 	@FunctionalInterface
 	public interface VoidInterceptorCall {
 
-		void apply(InvocationInterceptor interceptor, Invocation<Void> invocation) throws Throwable;
+		void apply(InvocationInterceptor interceptor, Invocation<@Nullable Void> invocation) throws Throwable;
 
 	}
 
-	private static class InterceptedInvocation<T> implements Invocation<T> {
-
-		private final Invocation<T> invocation;
-		private final InterceptorCall<T> call;
-		private final InvocationInterceptor interceptor;
-
-		InterceptedInvocation(Invocation<T> invocation, InterceptorCall<T> call, InvocationInterceptor interceptor) {
-			this.invocation = invocation;
-			this.call = call;
-			this.interceptor = interceptor;
-		}
+	private record InterceptedInvocation<T>(Invocation<T> invocation, InterceptorCall<T> call,
+			InvocationInterceptor interceptor) implements Invocation<T> {
 
 		@Override
 		public T proceed() throws Throwable {
@@ -112,7 +105,7 @@ public void skip() {
 		}
 	}
 
-	private static class ValidatingInvocation<T> implements Invocation<T> {
+	private static class ValidatingInvocation<T extends @Nullable Object> implements Invocation<T> {
 
 		private static final Logger logger = LoggerFactory.getLogger(ValidatingInvocation.class);
 
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/JupiterEngineExecutionContext.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/JupiterEngineExecutionContext.java
index fab10b76024e..a70ae7c2d38d 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/JupiterEngineExecutionContext.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/JupiterEngineExecutionContext.java
@@ -10,9 +10,11 @@
 
 package org.junit.jupiter.engine.execution;
 
+import static java.util.Objects.requireNonNull;
 import static org.apiguardian.api.API.Status.INTERNAL;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.extension.ExtensionContext;
 import org.junit.jupiter.engine.config.JupiterConfiguration;
 import org.junit.jupiter.engine.descriptor.LauncherStoreFacade;
@@ -45,9 +47,9 @@ private JupiterEngineExecutionContext(State state) {
 
 	public void close() throws Exception {
 		ExtensionContext extensionContext = getExtensionContext();
-		if (extensionContext instanceof AutoCloseable) {
+		if (extensionContext instanceof @SuppressWarnings("resource") AutoCloseable closeable) {
 			try {
-				((AutoCloseable) extensionContext).close();
+				closeable.close();
 			}
 			catch (Exception e) {
 				throw new JUnitException("Failed to close extension context", e);
@@ -68,19 +70,19 @@ public LauncherStoreFacade getLauncherStoreFacade() {
 	}
 
 	public TestInstancesProvider getTestInstancesProvider() {
-		return this.state.testInstancesProvider;
+		return requireNonNull(this.state.testInstancesProvider);
 	}
 
 	public MutableExtensionRegistry getExtensionRegistry() {
-		return this.state.extensionRegistry;
+		return requireNonNull(this.state.extensionRegistry);
 	}
 
 	public ExtensionContext getExtensionContext() {
-		return this.state.extensionContext;
+		return requireNonNull(this.state.extensionContext);
 	}
 
 	public ThrowableCollector getThrowableCollector() {
-		return this.state.throwableCollector;
+		return requireNonNull(this.state.throwableCollector);
 	}
 
 	/**
@@ -125,9 +127,17 @@ private static final class State implements Cloneable {
 		final EngineExecutionListener executionListener;
 		final JupiterConfiguration configuration;
 		final LauncherStoreFacade launcherStoreFacade;
+
+		@Nullable
 		TestInstancesProvider testInstancesProvider;
+
+		@Nullable
 		MutableExtensionRegistry extensionRegistry;
+
+		@Nullable
 		ExtensionContext extensionContext;
+
+		@Nullable
 		ThrowableCollector throwableCollector;
 
 		State(EngineExecutionListener executionListener, JupiterConfiguration configuration,
@@ -152,6 +162,8 @@ public State clone() {
 	public static class Builder {
 
 		private State originalState;
+
+		@Nullable
 		private State newState = null;
 
 		private Builder(State originalState) {
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/MethodInvocation.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/MethodInvocation.java
index fb3f2e0c2810..6ef6f52f4bad 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/MethodInvocation.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/MethodInvocation.java
@@ -17,17 +17,18 @@
 import java.util.List;
 import java.util.Optional;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.extension.InvocationInterceptor.Invocation;
 import org.junit.jupiter.api.extension.ReflectiveInvocationContext;
-import org.junit.platform.commons.support.ReflectionSupport;
+import org.junit.jupiter.engine.support.MethodReflectionUtils;
 
-class MethodInvocation<T> implements Invocation<T>, ReflectiveInvocationContext<Method> {
+class MethodInvocation<T extends @Nullable Object> implements Invocation<T>, ReflectiveInvocationContext<Method> {
 
 	private final Method method;
 	private final Optional<Object> target;
-	private final Object[] arguments;
+	private final @Nullable Object[] arguments;
 
-	MethodInvocation(Method method, Optional<Object> target, Object[] arguments) {
+	MethodInvocation(Method method, Optional<Object> target, @Nullable Object[] arguments) {
 		this.method = method;
 		this.target = target;
 		this.arguments = arguments;
@@ -39,7 +40,6 @@ public Class<?> getTargetClass() {
 	}
 
 	@Override
-	@SuppressWarnings("unchecked")
 	public Optional<Object> getTarget() {
 		return this.target;
 	}
@@ -55,9 +55,10 @@ public List<Object> getArguments() {
 	}
 
 	@Override
-	@SuppressWarnings("unchecked")
+	@SuppressWarnings({ "unchecked", "NullAway" })
 	public T proceed() {
-		return (T) ReflectionSupport.invokeMethod(this.method, this.target.orElse(null), this.arguments);
+		var actualTarget = this.target.orElse(null);
+		return (T) MethodReflectionUtils.invoke(this.method, actualTarget, this.arguments);
 	}
 
 }
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/NamespaceAwareStore.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/NamespaceAwareStore.java
index d63c7f13a940..88535ea14931 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/NamespaceAwareStore.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/NamespaceAwareStore.java
@@ -16,6 +16,7 @@
 import java.util.function.Supplier;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.extension.ExtensionContext.Store;
 import org.junit.jupiter.api.extension.ExtensionContextException;
 import org.junit.platform.commons.util.Preconditions;
@@ -38,54 +39,64 @@ public NamespaceAwareStore(NamespacedHierarchicalStore<Namespace> valuesStore, N
 	}
 
 	@Override
-	public Object get(Object key) {
+	public @Nullable Object get(Object key) {
 		Preconditions.notNull(key, "key must not be null");
-		return accessStore(() -> this.valuesStore.get(this.namespace, key));
+		Supplier<@Nullable Object> action = () -> this.valuesStore.get(this.namespace, key);
+		return accessStore(action);
 	}
 
 	@Override
-	public <T> T get(Object key, Class<T> requiredType) {
+	public <T> @Nullable T get(Object key, Class<T> requiredType) {
 		Preconditions.notNull(key, "key must not be null");
 		Preconditions.notNull(requiredType, "requiredType must not be null");
-		return accessStore(() -> this.valuesStore.get(this.namespace, key, requiredType));
+		Supplier<@Nullable T> action = () -> this.valuesStore.get(this.namespace, key, requiredType);
+		return accessStore(action);
 	}
 
 	@Override
-	public <K, V> Object getOrComputeIfAbsent(K key, Function<K, V> defaultCreator) {
+	public <K, V extends @Nullable Object> @Nullable Object getOrComputeIfAbsent(K key,
+			Function<? super K, ? extends V> defaultCreator) {
 		Preconditions.notNull(key, "key must not be null");
 		Preconditions.notNull(defaultCreator, "defaultCreator function must not be null");
-		return accessStore(() -> this.valuesStore.getOrComputeIfAbsent(this.namespace, key, defaultCreator));
+		Supplier<@Nullable Object> action = () -> this.valuesStore.getOrComputeIfAbsent(this.namespace, key,
+			defaultCreator);
+		return accessStore(action);
 	}
 
 	@Override
-	public <K, V> V getOrComputeIfAbsent(K key, Function<K, V> defaultCreator, Class<V> requiredType) {
+	public <K, V extends @Nullable Object> @Nullable V getOrComputeIfAbsent(K key,
+			Function<? super K, ? extends V> defaultCreator, Class<V> requiredType) {
 		Preconditions.notNull(key, "key must not be null");
 		Preconditions.notNull(defaultCreator, "defaultCreator function must not be null");
 		Preconditions.notNull(requiredType, "requiredType must not be null");
-		return accessStore(
-			() -> this.valuesStore.getOrComputeIfAbsent(this.namespace, key, defaultCreator, requiredType));
+		Supplier<@Nullable V> action = () -> this.valuesStore.getOrComputeIfAbsent(this.namespace, key, defaultCreator,
+			requiredType);
+		return accessStore(action);
 	}
 
 	@Override
-	public void put(Object key, Object value) {
+	public void put(Object key, @Nullable Object value) {
 		Preconditions.notNull(key, "key must not be null");
-		accessStore(() -> this.valuesStore.put(this.namespace, key, value));
+		Supplier<@Nullable Object> action = () -> this.valuesStore.put(this.namespace, key, value);
+		accessStore(action);
 	}
 
 	@Override
-	public Object remove(Object key) {
+	public @Nullable Object remove(Object key) {
 		Preconditions.notNull(key, "key must not be null");
-		return accessStore(() -> this.valuesStore.remove(this.namespace, key));
+		Supplier<@Nullable Object> action = () -> this.valuesStore.remove(this.namespace, key);
+		return accessStore(action);
 	}
 
 	@Override
-	public <T> T remove(Object key, Class<T> requiredType) {
+	public <T> @Nullable T remove(Object key, Class<T> requiredType) {
 		Preconditions.notNull(key, "key must not be null");
 		Preconditions.notNull(requiredType, "requiredType must not be null");
-		return accessStore(() -> this.valuesStore.remove(this.namespace, key, requiredType));
+		Supplier<@Nullable T> action = () -> this.valuesStore.remove(this.namespace, key, requiredType);
+		return accessStore(action);
 	}
 
-	private <T> T accessStore(Supplier<T> action) {
+	private <T> @Nullable T accessStore(Supplier<@Nullable T> action) {
 		try {
 			return action.get();
 		}
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/ParameterResolutionUtils.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/ParameterResolutionUtils.java
index 65a4ddc0d38d..6b8379a56f1f 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/ParameterResolutionUtils.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/ParameterResolutionUtils.java
@@ -11,8 +11,9 @@
 package org.junit.jupiter.engine.execution;
 
 import static java.util.stream.Collectors.joining;
-import static java.util.stream.Collectors.toList;
 import static org.apiguardian.api.API.Status.INTERNAL;
+import static org.junit.platform.commons.util.KotlinReflectionUtils.getKotlinSuspendingFunctionParameters;
+import static org.junit.platform.commons.util.KotlinReflectionUtils.isKotlinSuspendingFunction;
 import static org.junit.platform.commons.util.ReflectionUtils.isAssignableTo;
 
 import java.lang.reflect.Constructor;
@@ -23,6 +24,7 @@
 import java.util.Optional;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.extension.ExtensionContext;
 import org.junit.jupiter.api.extension.ParameterContext;
 import org.junit.jupiter.api.extension.ParameterResolutionException;
@@ -58,10 +60,13 @@ public class ParameterResolutionUtils {
 	 * @return the array of Objects to be used as parameters in the executable
 	 * invocation; never {@code null} though potentially empty
 	 */
-	public static Object[] resolveParameters(Method method, Optional<Object> target, ExtensionContext extensionContext,
-			ExtensionRegistry extensionRegistry) {
+	public static @Nullable Object[] resolveParameters(Method method, Optional<Object> target,
+			ExtensionContext extensionContext, ExtensionRegistry extensionRegistry) {
 
-		return resolveParameters(method, target, Optional.empty(), extensionContext, extensionRegistry);
+		return resolveParameters(method, target, Optional.empty(), __ -> extensionContext, extensionRegistry,
+			isKotlinSuspendingFunction(method) //
+					? getKotlinSuspendingFunctionParameters(method) //
+					: method.getParameters());
 	}
 
 	/**
@@ -81,18 +86,26 @@ public static Object[] resolveParameters(Method method, Optional<Object> target,
 	 * @return the array of Objects to be used as parameters in the executable
 	 * invocation; never {@code null} though potentially empty
 	 */
-	public static Object[] resolveParameters(Executable executable, Optional<Object> target,
+	public static @Nullable Object[] resolveParameters(Executable executable, Optional<Object> target,
 			Optional<Object> outerInstance, ExtensionContext extensionContext, ExtensionRegistry extensionRegistry) {
 		return resolveParameters(executable, target, outerInstance, __ -> extensionContext, extensionRegistry);
 	}
 
-	public static Object[] resolveParameters(Executable executable, Optional<Object> target,
+	public static @Nullable Object[] resolveParameters(Executable executable, Optional<Object> target,
 			Optional<Object> outerInstance, ExtensionContextSupplier extensionContext,
 			ExtensionRegistry extensionRegistry) {
 
+		return resolveParameters(executable, target, outerInstance, extensionContext, extensionRegistry,
+			executable.getParameters());
+	}
+
+	private static @Nullable Object[] resolveParameters(Executable executable, Optional<Object> target,
+			Optional<Object> outerInstance, ExtensionContextSupplier extensionContext,
+			ExtensionRegistry extensionRegistry, Parameter[] parameters) {
+
 		Preconditions.notNull(target, "target must not be null");
 
-		Parameter[] parameters = executable.getParameters();
+		@Nullable
 		Object[] values = new Object[parameters.length];
 		int start = 0;
 
@@ -111,19 +124,19 @@ public static Object[] resolveParameters(Executable executable, Optional<Object>
 		return values;
 	}
 
-	private static Object resolveParameter(ParameterContext parameterContext, Executable executable,
+	private static @Nullable Object resolveParameter(ParameterContext parameterContext, Executable executable,
 			ExtensionContextSupplier extensionContext, ExtensionRegistry extensionRegistry) {
 
 		try {
 			// @formatter:off
 			List<ParameterResolver> matchingResolvers = extensionRegistry.stream(ParameterResolver.class)
 					.filter(resolver -> resolver.supportsParameter(parameterContext, extensionContext.get(resolver)))
-					.collect(toList());
+					.toList();
 			// @formatter:on
 
 			if (matchingResolvers.isEmpty()) {
 				throw new ParameterResolutionException(
-					String.format("No ParameterResolver registered for parameter [%s] in %s [%s].",
+					"No ParameterResolver registered for parameter [%s] in %s [%s].".formatted(
 						parameterContext.getParameter(), asLabel(executable), executable.toGenericString()));
 			}
 
@@ -134,7 +147,7 @@ private static Object resolveParameter(ParameterContext parameterContext, Execut
 						.collect(joining(", "));
 				// @formatter:on
 				throw new ParameterResolutionException(
-					String.format("Discovered multiple competing ParameterResolvers for parameter [%s] in %s [%s]: %s",
+					"Discovered multiple competing ParameterResolvers for parameter [%s] in %s [%s]: %s".formatted(
 						parameterContext.getParameter(), asLabel(executable), executable.toGenericString(), resolvers));
 			}
 
@@ -142,10 +155,10 @@ private static Object resolveParameter(ParameterContext parameterContext, Execut
 			Object value = resolver.resolveParameter(parameterContext, extensionContext.get(resolver));
 			validateResolvedType(parameterContext.getParameter(), value, executable, resolver);
 
-			logger.trace(() -> String.format(
-				"ParameterResolver [%s] resolved a value of type [%s] for parameter [%s] in %s [%s].",
-				resolver.getClass().getName(), (value != null ? value.getClass().getName() : null),
-				parameterContext.getParameter(), asLabel(executable), executable.toGenericString()));
+			logger.trace(
+				() -> "ParameterResolver [%s] resolved a value of type [%s] for parameter [%s] in %s [%s].".formatted(
+					resolver.getClass().getName(), (value != null ? value.getClass().getName() : null),
+					parameterContext.getParameter(), asLabel(executable), executable.toGenericString()));
 
 			return value;
 		}
@@ -155,8 +168,8 @@ private static Object resolveParameter(ParameterContext parameterContext, Execut
 		catch (Throwable throwable) {
 			UnrecoverableExceptions.rethrowIfUnrecoverable(throwable);
 
-			String message = String.format("Failed to resolve parameter [%s] in %s [%s]",
-				parameterContext.getParameter(), asLabel(executable), executable.toGenericString());
+			String message = "Failed to resolve parameter [%s] in %s [%s]".formatted(parameterContext.getParameter(),
+				asLabel(executable), executable.toGenericString());
 
 			if (StringUtils.isNotBlank(throwable.getMessage())) {
 				message += ": " + throwable.getMessage();
@@ -166,7 +179,7 @@ private static Object resolveParameter(ParameterContext parameterContext, Execut
 		}
 	}
 
-	private static void validateResolvedType(Parameter parameter, Object value, Executable executable,
+	private static void validateResolvedType(Parameter parameter, @Nullable Object value, Executable executable,
 			ParameterResolver resolver) {
 
 		Class<?> type = parameter.getType();
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/package-info.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/package-info.java
index 028111e0a0ca..cc5cec268e7d 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/package-info.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/package-info.java
@@ -2,4 +2,7 @@
  * Internal classes for test execution within the JUnit Jupiter test engine.
  */
 
+@NullMarked
 package org.junit.jupiter.engine.execution;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/AutoCloseExtension.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/AutoCloseExtension.java
index 07f10d636e4b..17652eef18ef 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/AutoCloseExtension.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/AutoCloseExtension.java
@@ -16,6 +16,7 @@
 import java.lang.reflect.Method;
 import java.util.function.Predicate;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.AutoClose;
 import org.junit.jupiter.api.extension.AfterAllCallback;
 import org.junit.jupiter.api.extension.ExtensionConfigurationException;
@@ -59,14 +60,16 @@ public void afterAll(ExtensionContext context) {
 		throwableCollector.assertEmpty();
 	}
 
-	private static void closeFields(Class<?> testClass, Object testInstance, ThrowableCollector throwableCollector) {
+	private static void closeFields(Class<?> testClass, @Nullable Object testInstance,
+			ThrowableCollector throwableCollector) {
+
 		Predicate<Field> predicate = (testInstance == null ? ModifierSupport::isStatic : ModifierSupport::isNotStatic);
-		AnnotationSupport.findAnnotatedFields(testClass, AutoClose.class, predicate, BOTTOM_UP).forEach(
-			field -> throwableCollector.execute(() -> closeField(field, testInstance)));
+		AnnotationSupport.findAnnotatedFields(testClass, AutoClose.class, predicate, BOTTOM_UP)//
+				.forEach(field -> throwableCollector.execute(() -> closeField(field, testInstance)));
 	}
 
-	private static void closeField(Field field, Object testInstance) throws Exception {
-		String methodName = AnnotationSupport.findAnnotation(field, AutoClose.class).get().value();
+	private static void closeField(Field field, @Nullable Object testInstance) throws Exception {
+		String methodName = AnnotationSupport.findAnnotation(field, AutoClose.class).orElseThrow().value();
 		Class<?> fieldType = field.getType();
 
 		checkCondition(StringUtils.isNotBlank(methodName), "@AutoClose on field %s must specify a method name.", field);
@@ -75,7 +78,7 @@ private static void closeField(Field field, Object testInstance) throws Exceptio
 
 		Object fieldValue = ReflectionSupport.tryToReadFieldValue(field, testInstance).get();
 		if (fieldValue == null) {
-			logger.warn(() -> String.format("Cannot @AutoClose field %s because it is null.", getQualifiedName(field)));
+			logger.warn(() -> "Cannot @AutoClose field %s because it is null.".formatted(getQualifiedName(field)));
 		}
 		else {
 			invokeCloseMethod(field, fieldValue, methodName.trim());
@@ -84,23 +87,23 @@ private static void closeField(Field field, Object testInstance) throws Exceptio
 
 	private static void invokeCloseMethod(Field field, Object target, String methodName) throws Exception {
 		// Avoid reflection if we can directly invoke close() via AutoCloseable.
-		if (target instanceof AutoCloseable && "close".equals(methodName)) {
-			((AutoCloseable) target).close();
+		if (target instanceof @SuppressWarnings("resource") AutoCloseable closeable && "close".equals(methodName)) {
+			closeable.close();
 			return;
 		}
 
 		Class<?> targetType = target.getClass();
 		Method closeMethod = ReflectionSupport.findMethod(targetType, methodName).orElseThrow(
 			() -> new ExtensionConfigurationException(
-				String.format("Cannot @AutoClose field %s because %s does not define method %s().",
-					getQualifiedName(field), targetType.getName(), methodName)));
+				"Cannot @AutoClose field %s because %s does not define method %s()."//
+						.formatted(getQualifiedName(field), targetType.getName(), methodName)));
 
 		closeMethod = ReflectionUtils.getInterfaceMethodIfPossible(closeMethod, targetType);
 		ReflectionSupport.invokeMethod(closeMethod, target);
 	}
 
 	private static void checkCondition(boolean condition, String messageFormat, Field field) {
-		Preconditions.condition(condition, () -> String.format(messageFormat, getQualifiedName(field)));
+		Preconditions.condition(condition, () -> messageFormat.formatted(getQualifiedName(field)));
 	}
 
 	private static String getQualifiedName(Field field) {
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/DefaultPreInterruptContext.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/DefaultPreInterruptContext.java
index 0e4be93b94e2..81fcd96f3228 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/DefaultPreInterruptContext.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/DefaultPreInterruptContext.java
@@ -17,12 +17,10 @@
 /**
  * @since 5.12
  */
-class DefaultPreInterruptContext implements PreInterruptContext {
-	private final Thread threadToInterrupt;
+record DefaultPreInterruptContext(Thread threadToInterrupt) implements PreInterruptContext {
 
-	DefaultPreInterruptContext(Thread threadToInterrupt) {
+	DefaultPreInterruptContext {
 		Preconditions.notNull(threadToInterrupt, "threadToInterrupt must not be null");
-		this.threadToInterrupt = threadToInterrupt;
 	}
 
 	@Override
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/DefaultRepetitionInfo.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/DefaultRepetitionInfo.java
index d9ecb54a3a68..3f92be90bf40 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/DefaultRepetitionInfo.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/DefaultRepetitionInfo.java
@@ -18,20 +18,8 @@
 /**
  * Default implementation of {@link RepetitionInfo}.
  */
-class DefaultRepetitionInfo implements RepetitionInfo {
-
-	final int currentRepetition;
-	final int totalRepetitions;
-	final AtomicInteger failureCount;
-	final int failureThreshold;
-
-	DefaultRepetitionInfo(int currentRepetition, int totalRepetitions, AtomicInteger failureCount,
-			int failureThreshold) {
-		this.currentRepetition = currentRepetition;
-		this.totalRepetitions = totalRepetitions;
-		this.failureCount = failureCount;
-		this.failureThreshold = failureThreshold;
-	}
+record DefaultRepetitionInfo(int currentRepetition, int totalRepetitions, AtomicInteger failureCount,
+		int failureThreshold) implements RepetitionInfo {
 
 	@Override
 	public int getCurrentRepetition() {
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/DisabledCondition.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/DisabledCondition.java
index 5dedc43e9107..9d4e1e4d3727 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/DisabledCondition.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/DisabledCondition.java
@@ -14,6 +14,7 @@
 
 import java.lang.reflect.AnnotatedElement;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.extension.ConditionEvaluationResult;
 import org.junit.jupiter.api.extension.ExecutionCondition;
@@ -44,7 +45,7 @@ public ConditionEvaluationResult evaluateExecutionCondition(ExtensionContext con
 				.orElse(ENABLED);
 	}
 
-	private ConditionEvaluationResult toResult(AnnotatedElement element, Disabled annotation) {
+	private ConditionEvaluationResult toResult(@Nullable AnnotatedElement element, Disabled annotation) {
 		String value = annotation.value();
 		String reason = StringUtils.isNotBlank(value) ? value : element + " is @Disabled";
 		return ConditionEvaluationResult.disabled(reason);
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/MutableExtensionRegistry.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/MutableExtensionRegistry.java
index eac99fe980f7..fdd84569d7e1 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/MutableExtensionRegistry.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/MutableExtensionRegistry.java
@@ -18,8 +18,6 @@
 import java.lang.reflect.Member;
 import java.lang.reflect.Method;
 import java.util.ArrayList;
-import java.util.Arrays;
-import java.util.Collections;
 import java.util.LinkedHashMap;
 import java.util.LinkedHashSet;
 import java.util.List;
@@ -29,10 +27,10 @@
 import java.util.Set;
 import java.util.function.Function;
 import java.util.function.Predicate;
-import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.extension.Extension;
 import org.junit.jupiter.engine.config.JupiterConfiguration;
 import org.junit.platform.commons.logging.Logger;
@@ -52,13 +50,14 @@ public class MutableExtensionRegistry implements ExtensionRegistry, ExtensionReg
 
 	private static final Logger logger = LoggerFactory.getLogger(MutableExtensionRegistry.class);
 
-	private static final List<Extension> DEFAULT_STATELESS_EXTENSIONS = Collections.unmodifiableList(Arrays.asList(//
+	private static final List<Extension> DEFAULT_STATELESS_EXTENSIONS = List.of( //
 		new DisabledCondition(), //
 		new AutoCloseExtension(), //
 		new TimeoutExtension(), //
 		new RepeatedTestExtension(), //
 		new TestInfoParameterResolver(), //
-		new TestReporterParameterResolver()));
+		new TestReporterParameterResolver() //
+	);
 
 	/**
 	 * Factory for creating and populating a new root registry with the default
@@ -122,10 +121,10 @@ private static void logExcludedExtensions(List<Class<? extends Extension>> exclu
 			List<String> excludeExtensionNames = excludedExtensions
 					.stream()
 					.map(Class::getName)
-					.collect(Collectors.toList());
+					.toList();
 			// @formatter:on
-			logger.config(() -> String.format(
-				"Excluded auto-detected extensions due to configured includes/excludes: %s", excludeExtensionNames));
+			logger.config(() -> "Excluded auto-detected extensions due to configured includes/excludes: %s".formatted(
+				excludeExtensionNames));
 		}
 	}
 
@@ -167,8 +166,7 @@ private MutableExtensionRegistry(Set<Class<? extends Extension>> registeredExten
 		this.lateInitExtensions = new LinkedHashMap<>();
 		registeredExtensions.forEach(entry -> {
 			Entry newEntry = entry;
-			if (entry instanceof LateInitEntry) {
-				LateInitEntry lateInitEntry = (LateInitEntry) entry;
+			if (entry instanceof LateInitEntry lateInitEntry) {
 				newEntry = lateInitEntry.getExtension() //
 						.map(Entry::of) //
 						.orElseGet(() -> getLateInitExtensions(lateInitEntry.getTestClass()).add(lateInitEntry.copy()));
@@ -218,8 +216,8 @@ public void registerUninitializedExtension(Class<?> testClass, Field source,
 		Preconditions.notNull(source, "source must not be null");
 		Preconditions.notNull(initializer, "initializer must not be null");
 
-		logger.trace(() -> String.format("Registering local extension (late-init) for [%s]%s",
-			source.getType().getName(), buildSourceInfo(source)));
+		logger.trace(() -> "Registering local extension (late-init) for [%s]%s".formatted(source.getType().getName(),
+			buildSourceInfo(source)));
 
 		LateInitEntry entry = getLateInitExtensions(testClass) //
 				.add(new LateInitEntry(testClass, initializer));
@@ -257,25 +255,23 @@ private void registerExtension(String category, Extension extension) {
 		registerExtension(category, extension, null);
 	}
 
-	private void registerExtension(String category, Extension extension, Object source) {
+	private void registerExtension(String category, Extension extension, @Nullable Object source) {
 		Preconditions.notBlank(category, "category must not be null or blank");
 		Preconditions.notNull(extension, "extension must not be null");
 
-		logger.trace(
-			() -> String.format("Registering %s extension [%s]%s", category, extension, buildSourceInfo(source)));
+		logger.trace(() -> "Registering %s extension [%s]%s".formatted(category, extension, buildSourceInfo(source)));
 
 		this.registeredExtensions.add(Entry.of(extension));
 		this.registeredExtensionTypes.add(extension.getClass());
 	}
 
-	private String buildSourceInfo(Object source) {
+	private String buildSourceInfo(@Nullable Object source) {
 		if (source == null) {
 			return "";
 		}
-		if (source instanceof Member) {
-			Member member = (Member) source;
+		if (source instanceof Member member) {
 			Object type = (member instanceof Method ? "method" : "field");
-			source = String.format("%s %s.%s", type, member.getDeclaringClass().getName(), member.getName());
+			source = "%s %s.%s".formatted(type, member.getDeclaringClass().getName(), member.getName());
 		}
 		return " from source [" + source + "]";
 	}
@@ -313,12 +309,12 @@ public Class<?> getTestClass() {
 		}
 
 		void initialize(Object testInstance) {
-			Preconditions.condition(!extension.isPresent(), "Extension already initialized");
+			Preconditions.condition(extension.isEmpty(), "Extension already initialized");
 			extension = Optional.of(initializer.apply(testInstance));
 		}
 
 		LateInitEntry copy() {
-			Preconditions.condition(!extension.isPresent(), "Extension already initialized");
+			Preconditions.condition(extension.isEmpty(), "Extension already initialized");
 			return new LateInitEntry(testClass, initializer);
 		}
 	}
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/PreInterruptThreadDumpPrinter.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/PreInterruptThreadDumpPrinter.java
index 40fa9e03e3bf..283710eb1f1e 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/PreInterruptThreadDumpPrinter.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/PreInterruptThreadDumpPrinter.java
@@ -18,24 +18,23 @@
 import org.junit.jupiter.engine.Constants;
 
 /**
- * The default implementation for {@link PreInterruptCallback},
- * which will print the stacks of all {@link Thread}s to {@code System.out}.
+ * Default implementation of {@link PreInterruptCallback}, which prints the stacks
+ * of all {@link Thread}s to {@code System.out}.
  *
- * <p>Note: This is disabled by default, and must be enabled with
- * {@link Constants#EXTENSIONS_TIMEOUT_THREAD_DUMP_ENABLED_PROPERTY_NAME}
+ * <p>Note: This is disabled by default and must be enabled via
+ * {@link Constants#EXTENSIONS_TIMEOUT_THREAD_DUMP_ENABLED_PROPERTY_NAME}.
  *
  * @since 5.12
  */
 final class PreInterruptThreadDumpPrinter implements PreInterruptCallback {
+
 	private static final String NL = "\n";
 
 	@Override
 	public void beforeThreadInterrupt(PreInterruptContext preInterruptContext, ExtensionContext extensionContext) {
-
 		Map<Thread, StackTraceElement[]> stackTraces = Thread.getAllStackTraces();
 
-		StringBuilder sb = new StringBuilder();
-		sb.append("Thread ");
+		StringBuilder sb = new StringBuilder("Thread ");
 		appendThreadName(sb, preInterruptContext.getThreadToInterrupt());
 		sb.append(" will be interrupted.");
 		sb.append(NL);
@@ -48,10 +47,9 @@ public void beforeThreadInterrupt(PreInterruptContext preInterruptContext, Exten
 				appendThreadName(sb, thread);
 				for (StackTraceElement stackTraceElement : stack) {
 					sb.append(NL);
-					//Do the same prefix as java.lang.Throwable.printStackTrace(java.lang.Throwable.PrintStreamOrWriter)
+					// Use the same prefix as java.lang.Throwable.printStackTrace(PrintStreamOrWriter)
 					sb.append("\tat ");
 					sb.append(stackTraceElement.toString());
-
 				}
 				sb.append(NL);
 			}
@@ -61,23 +59,25 @@ public void beforeThreadInterrupt(PreInterruptContext preInterruptContext, Exten
 	}
 
 	/**
-	 * Appends the {@link Thread} name and ID in a similar fashion as {@code jstack}.
-	 * @param sb the buffer
-	 * @param th the thread to append
+	 * Append the {@link Thread} name and ID in a similar fashion as {@code jstack}.
+	 * @param builder the builder to append to
+	 * @param thread the thread whose information should be appended
 	 */
-	private void appendThreadName(StringBuilder sb, Thread th) {
-		// Use same format as java.lang.management.ThreadInfo.toString
-		sb.append("\"");
-		sb.append(th.getName());
-		sb.append("\"");
-		if (th.isDaemon()) {
-			sb.append(" daemon");
+	@SuppressWarnings("deprecation") // Thread.getId() is deprecated on JDK 19+
+	private static void appendThreadName(StringBuilder builder, Thread thread) {
+		// Use same format as java.lang.management.ThreadInfo.toString()
+		builder.append("\"");
+		builder.append(thread.getName());
+		builder.append("\"");
+		if (thread.isDaemon()) {
+			builder.append(" daemon");
 		}
-		sb.append(" prio=");
-		sb.append(th.getPriority());
-		sb.append(" Id=");
-		sb.append(th.getId());
-		sb.append(" ");
-		sb.append(th.getState());
+		builder.append(" prio=");
+		builder.append(thread.getPriority());
+		builder.append(" Id=");
+		builder.append(thread.getId());
+		builder.append(" ");
+		builder.append(thread.getState());
 	}
+
 }
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/RepeatedTestExtension.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/RepeatedTestExtension.java
index efdcfdc8d679..46b91c5e8a77 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/RepeatedTestExtension.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/RepeatedTestExtension.java
@@ -57,8 +57,9 @@ public Stream<TestTemplateInvocationContext> provideTestTemplateInvocationContex
 
 	private int totalRepetitions(RepeatedTest repeatedTest, Method method) {
 		int repetitions = repeatedTest.value();
-		Preconditions.condition(repetitions > 0, () -> String.format(
-			"Configuration error: @RepeatedTest on method [%s] must be declared with a positive 'value'.", method));
+		Preconditions.condition(repetitions > 0,
+			() -> "Configuration error: @RepeatedTest on method [%s] must be declared with a positive 'value'.".formatted(
+				method));
 		return repetitions;
 	}
 
@@ -76,8 +77,9 @@ private int failureThreshold(RepeatedTest repeatedTest, Method method) {
 
 	private RepeatedTestDisplayNameFormatter displayNameFormatter(RepeatedTest repeatedTest, Method method,
 			String displayName) {
-		String pattern = Preconditions.notBlank(repeatedTest.name().trim(), () -> String.format(
-			"Configuration error: @RepeatedTest on method [%s] must be declared with a non-empty name.", method));
+		String pattern = Preconditions.notBlank(repeatedTest.name().trim(),
+			() -> "Configuration error: @RepeatedTest on method [%s] must be declared with a non-empty name.".formatted(
+				method));
 		return new RepeatedTestDisplayNameFormatter(pattern, displayName);
 	}
 
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/RepeatedTestInvocationContext.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/RepeatedTestInvocationContext.java
index b4f3f74e17b6..d8a735849d7e 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/RepeatedTestInvocationContext.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/RepeatedTestInvocationContext.java
@@ -36,7 +36,7 @@ public RepeatedTestInvocationContext(DefaultRepetitionInfo repetitionInfo,
 
 	@Override
 	public String getDisplayName(int invocationIndex) {
-		return this.formatter.format(this.repetitionInfo.currentRepetition, this.repetitionInfo.totalRepetitions);
+		return this.formatter.format(this.repetitionInfo.currentRepetition(), this.repetitionInfo.totalRepetitions());
 	}
 
 	@Override
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/RepetitionExtension.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/RepetitionExtension.java
index b22d07419534..388c8fa33840 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/RepetitionExtension.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/RepetitionExtension.java
@@ -13,6 +13,7 @@
 import static org.junit.jupiter.api.extension.ConditionEvaluationResult.disabled;
 import static org.junit.jupiter.api.extension.ConditionEvaluationResult.enabled;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.RepeatedTest;
 import org.junit.jupiter.api.RepetitionInfo;
 import org.junit.jupiter.api.extension.ConditionEvaluationResult;
@@ -61,14 +62,14 @@ public RepetitionInfo resolveParameter(ParameterContext parameterContext, Extens
 	}
 
 	@Override
-	public void testFailed(ExtensionContext context, Throwable cause) {
-		this.repetitionInfo.failureCount.incrementAndGet();
+	public void testFailed(ExtensionContext context, @Nullable Throwable cause) {
+		this.repetitionInfo.failureCount().incrementAndGet();
 	}
 
 	@Override
 	public ConditionEvaluationResult evaluateExecutionCondition(ExtensionContext context) {
-		int failureThreshold = this.repetitionInfo.failureThreshold;
-		if (this.repetitionInfo.failureCount.get() >= failureThreshold) {
+		int failureThreshold = this.repetitionInfo.getFailureThreshold();
+		if (this.repetitionInfo.getFailureCount() >= failureThreshold) {
 			return disabled("Failure threshold [" + failureThreshold + "] exceeded");
 		}
 		return enabled("Failure threshold not exceeded");
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/SameThreadTimeoutInvocation.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/SameThreadTimeoutInvocation.java
index 7a5a78ab1544..c1df07a23e43 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/SameThreadTimeoutInvocation.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/SameThreadTimeoutInvocation.java
@@ -16,13 +16,14 @@
 import java.util.concurrent.ScheduledFuture;
 import java.util.function.Supplier;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.extension.InvocationInterceptor.Invocation;
 import org.junit.platform.commons.util.UnrecoverableExceptions;
 
 /**
  * @since 5.5
  */
-class SameThreadTimeoutInvocation<T> implements Invocation<T> {
+class SameThreadTimeoutInvocation<T extends @Nullable Object> implements Invocation<T> {
 
 	private final Invocation<T> delegate;
 	private final TimeoutDuration timeout;
@@ -39,10 +40,11 @@ class SameThreadTimeoutInvocation<T> implements Invocation<T> {
 		this.preInterruptCallback = preInterruptCallback;
 	}
 
+	@SuppressWarnings("NullAway")
 	@Override
 	public T proceed() throws Throwable {
 		InterruptTask interruptTask = new InterruptTask(Thread.currentThread(), preInterruptCallback);
-		ScheduledFuture<?> future = executor.schedule(interruptTask, timeout.getValue(), timeout.getUnit());
+		ScheduledFuture<?> future = executor.schedule(interruptTask, timeout.value(), timeout.unit());
 		Throwable failure = null;
 		T result = null;
 		try {
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/SeparateThreadTimeoutInvocation.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/SeparateThreadTimeoutInvocation.java
index 5500f773720e..03635bddcc08 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/SeparateThreadTimeoutInvocation.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/SeparateThreadTimeoutInvocation.java
@@ -15,12 +15,13 @@
 import java.util.concurrent.TimeoutException;
 import java.util.function.Supplier;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.extension.InvocationInterceptor.Invocation;
 
 /**
  * @since 5.9
  */
-class SeparateThreadTimeoutInvocation<T> implements Invocation<T> {
+class SeparateThreadTimeoutInvocation<T extends @Nullable Object> implements Invocation<T> {
 
 	private final Invocation<T> delegate;
 	private final TimeoutDuration timeout;
@@ -36,11 +37,14 @@ class SeparateThreadTimeoutInvocation<T> implements Invocation<T> {
 	}
 
 	@Override
+	@SuppressWarnings("NullAway")
 	public T proceed() throws Throwable {
 		return assertTimeoutPreemptively(timeout.toDuration(), delegate::proceed, descriptionSupplier,
-			(__, messageSupplier, cause, testThread) -> {
-				TimeoutException exception = TimeoutExceptionFactory.create(messageSupplier.get(), timeout, null);
-				preInterruptCallback.executePreInterruptCallback(testThread, exception::addSuppressed);
+			(__, ___, cause, testThread) -> {
+				TimeoutException exception = TimeoutExceptionFactory.create(descriptionSupplier.get(), timeout, null);
+				if (testThread != null) {
+					preInterruptCallback.executePreInterruptCallback(testThread, exception::addSuppressed);
+				}
 				exception.initCause(cause);
 				return exception;
 			});
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/TempDirectory.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/TempDirectory.java
index d619da57f849..d352e94a358a 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/TempDirectory.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/TempDirectory.java
@@ -12,6 +12,7 @@
 
 import static java.nio.file.FileVisitResult.CONTINUE;
 import static java.nio.file.FileVisitResult.SKIP_SUBTREE;
+import static java.util.Objects.requireNonNull;
 import static java.util.stream.Collectors.joining;
 import static org.junit.jupiter.api.extension.TestInstantiationAwareExtension.ExtensionContextScope.TEST_METHOD;
 import static org.junit.jupiter.api.io.CleanupMode.DEFAULT;
@@ -36,7 +37,6 @@
 import java.nio.file.LinkOption;
 import java.nio.file.NoSuchFileException;
 import java.nio.file.Path;
-import java.nio.file.Paths;
 import java.nio.file.SimpleFileVisitor;
 import java.nio.file.attribute.BasicFileAttributes;
 import java.nio.file.attribute.DosFileAttributeView;
@@ -47,6 +47,7 @@
 import java.util.TreeMap;
 import java.util.function.Predicate;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.extension.AnnotatedElementContext;
 import org.junit.jupiter.api.extension.BeforeAllCallback;
 import org.junit.jupiter.api.extension.BeforeEachCallback;
@@ -59,7 +60,6 @@
 import org.junit.jupiter.api.io.CleanupMode;
 import org.junit.jupiter.api.io.TempDir;
 import org.junit.jupiter.api.io.TempDirFactory;
-import org.junit.jupiter.engine.config.EnumConfigurationParameterConverter;
 import org.junit.jupiter.engine.config.JupiterConfiguration;
 import org.junit.platform.commons.JUnitException;
 import org.junit.platform.commons.PreconditionViolationException;
@@ -148,20 +148,18 @@ private void injectInstanceFields(ExtensionContext context, Object instance) {
 		}
 	}
 
-	private void injectFields(ExtensionContext context, Object testInstance, Class<?> testClass,
+	private void injectFields(ExtensionContext context, @Nullable Object testInstance, Class<?> testClass,
 			Predicate<Field> predicate) {
 
-		Scope scope = getScope(context);
-
 		findAnnotatedFields(testClass, TempDir.class, predicate).forEach(field -> {
 			assertNonFinalField(field);
 			assertSupportedType("field", field.getType());
 
 			try {
 				CleanupMode cleanupMode = determineCleanupModeForField(field);
-				TempDirFactory factory = determineTempDirFactoryForField(field, scope);
+				TempDirFactory factory = determineTempDirFactoryForField(field);
 				makeAccessible(field).set(testInstance,
-					getPathOrFile(field.getType(), new FieldContext(field), factory, cleanupMode, scope, context));
+					getPathOrFile(field.getType(), new FieldContext(field), factory, cleanupMode, context));
 			}
 			catch (Throwable t) {
 				throw ExceptionUtils.throwAsUncheckedException(t);
@@ -187,9 +185,8 @@ public Object resolveParameter(ParameterContext parameterContext, ExtensionConte
 		Class<?> parameterType = parameterContext.getParameter().getType();
 		assertSupportedType("parameter", parameterType);
 		CleanupMode cleanupMode = determineCleanupModeForParameter(parameterContext);
-		Scope scope = getScope(extensionContext);
-		TempDirFactory factory = determineTempDirFactoryForParameter(parameterContext, scope);
-		return getPathOrFile(parameterType, parameterContext, factory, cleanupMode, scope, extensionContext);
+		TempDirFactory factory = determineTempDirFactoryForParameter(parameterContext);
+		return getPathOrFile(parameterType, parameterContext, factory, cleanupMode, extensionContext);
 	}
 
 	private CleanupMode determineCleanupModeForField(Field field) {
@@ -209,38 +206,21 @@ private CleanupMode determineCleanupMode(TempDir tempDir) {
 		return cleanupMode == DEFAULT ? this.configuration.getDefaultTempDirCleanupMode() : cleanupMode;
 	}
 
-	@SuppressWarnings("deprecation")
-	private Scope getScope(ExtensionContext context) {
-		return context.getRoot().getStore(NAMESPACE).getOrComputeIfAbsent( //
-			Scope.class, //
-			__ -> new EnumConfigurationParameterConverter<>(Scope.class, "@TempDir scope") //
-					.get(TempDir.SCOPE_PROPERTY_NAME, context::getConfigurationParameter, Scope.PER_DECLARATION), //
-			Scope.class //
-		);
-	}
-
-	private TempDirFactory determineTempDirFactoryForField(Field field, Scope scope) {
+	private TempDirFactory determineTempDirFactoryForField(Field field) {
 		TempDir tempDir = findAnnotation(field, TempDir.class).orElseThrow(
 			() -> new JUnitException("Field " + field + " must be annotated with @TempDir"));
-		return determineTempDirFactory(tempDir, scope);
+		return determineTempDirFactory(tempDir);
 	}
 
-	private TempDirFactory determineTempDirFactoryForParameter(ParameterContext parameterContext, Scope scope) {
+	private TempDirFactory determineTempDirFactoryForParameter(ParameterContext parameterContext) {
 		TempDir tempDir = parameterContext.findAnnotation(TempDir.class).orElseThrow(() -> new JUnitException(
 			"Parameter " + parameterContext.getParameter() + " must be annotated with @TempDir"));
-		return determineTempDirFactory(tempDir, scope);
+		return determineTempDirFactory(tempDir);
 	}
 
-	@SuppressWarnings("deprecation")
-	private TempDirFactory determineTempDirFactory(TempDir tempDir, Scope scope) {
+	private TempDirFactory determineTempDirFactory(TempDir tempDir) {
 		Class<? extends TempDirFactory> factory = tempDir.factory();
 
-		if (factory != TempDirFactory.class && scope == Scope.PER_CONTEXT) {
-			throw new ExtensionConfigurationException("Custom @TempDir factory is not supported with "
-					+ TempDir.SCOPE_PROPERTY_NAME + "=" + Scope.PER_CONTEXT.name().toLowerCase() + ". Use "
-					+ TempDir.DEFAULT_FACTORY_PROPERTY_NAME + " instead.");
-		}
-
 		return factory == TempDirFactory.class //
 				? this.configuration.getDefaultTempDirFactorySupplier().get()
 				: ReflectionSupport.newInstance(factory);
@@ -260,16 +240,13 @@ private static void assertSupportedType(String target, Class<?> type) {
 	}
 
 	private static Object getPathOrFile(Class<?> elementType, AnnotatedElementContext elementContext,
-			TempDirFactory factory, CleanupMode cleanupMode, Scope scope, ExtensionContext extensionContext) {
+			TempDirFactory factory, CleanupMode cleanupMode, ExtensionContext extensionContext) {
 
-		Namespace namespace = scope == Scope.PER_DECLARATION //
-				? NAMESPACE.append(elementContext) //
-				: NAMESPACE;
-		Path path = extensionContext.getStore(namespace) //
+		Path path = requireNonNull(extensionContext.getStore(NAMESPACE.append(elementContext)) //
 				.getOrComputeIfAbsent(KEY,
 					__ -> createTempDir(factory, cleanupMode, elementType, elementContext, extensionContext),
-					CloseablePath.class) //
-				.get();
+					CloseablePath.class)) //
+							.get();
 
 		return (elementType == Path.class) ? path : path.toFile();
 	}
@@ -335,7 +312,7 @@ public void close() throws IOException {
 			try {
 				if (this.cleanupMode == NEVER
 						|| (this.cleanupMode == ON_SUCCESS && selfOrChildFailed(this.extensionContext))) {
-					LOGGER.info(() -> String.format("Skipping cleanup of temp dir %s for %s due to CleanupMode.%s.",
+					LOGGER.info(() -> "Skipping cleanup of temp dir %s for %s due to CleanupMode.%s.".formatted(
 						this.dir, descriptionFor(this.annotatedElement), this.cleanupMode.name()));
 					return;
 				}
@@ -369,12 +346,10 @@ public void close() throws IOException {
 		 * @since 5.12
 		 */
 		private static String descriptionFor(AnnotatedElement annotatedElement) {
-			if (annotatedElement instanceof Field) {
-				Field field = (Field) annotatedElement;
+			if (annotatedElement instanceof Field field) {
 				return "field " + field.getDeclaringClass().getSimpleName() + "." + field.getName();
 			}
-			if (annotatedElement instanceof Parameter) {
-				Parameter parameter = (Parameter) annotatedElement;
+			if (annotatedElement instanceof Parameter parameter) {
 				Executable executable = parameter.getDeclaringExecutable();
 				return "parameter '" + parameter.getName() + "' in " + descriptionFor(executable);
 			}
@@ -388,7 +363,7 @@ private static String descriptionFor(Executable executable) {
 			boolean isConstructor = executable instanceof Constructor<?>;
 			String type = isConstructor ? "constructor" : "method";
 			String name = isConstructor ? executable.getDeclaringClass().getSimpleName() : executable.getName();
-			return String.format("%s %s(%s)", type, name,
+			return "%s %s(%s)".formatted(type, name,
 				ClassUtils.nullSafeToString(Class::getSimpleName, executable.getParameterTypes()));
 		}
 
@@ -538,7 +513,7 @@ private static void tryToResetPermissions(Path path) {
 		}
 
 		private IOException createIOExceptionWithAttachedFailures(SortedMap<Path, IOException> failures) {
-			Path emptyPath = Paths.get("");
+			Path emptyPath = Path.of("");
 			String joinedPaths = failures.keySet().stream() //
 					.map(this::tryToDeleteOnExit) //
 					.map(this::relativizeSafely) //
@@ -570,14 +545,6 @@ private Path relativizeSafely(Path path) {
 		}
 	}
 
-	enum Scope {
-
-		PER_CONTEXT,
-
-		PER_DECLARATION
-
-	}
-
 	interface FileOperations {
 
 		FileOperations DEFAULT = Files::delete;
@@ -586,9 +553,7 @@ interface FileOperations {
 
 	}
 
-	private static class FieldContext implements AnnotatedElementContext {
-
-		private final Field field;
+	private record FieldContext(Field field) implements AnnotatedElementContext {
 
 		private FieldContext(Field field) {
 			this.field = Preconditions.notNull(field, "field must not be null");
@@ -611,15 +576,8 @@ public String toString() {
 	}
 
 	@SuppressWarnings("deprecation")
-	private static class FailureTracker implements Store.CloseableResource, AutoCloseable {
-
-		private final ExtensionContext context;
-		private final ExtensionContext parentContext;
-
-		private FailureTracker(ExtensionContext context, ExtensionContext parentContext) {
-			this.context = context;
-			this.parentContext = parentContext;
-		}
+	private record FailureTracker(ExtensionContext context, ExtensionContext parentContext)
+			implements Store.CloseableResource, AutoCloseable {
 
 		@Override
 		public void close() {
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/TestInfoParameterResolver.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/TestInfoParameterResolver.java
index ad6c7f8f2143..c956ee43a956 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/TestInfoParameterResolver.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/TestInfoParameterResolver.java
@@ -14,6 +14,7 @@
 import java.util.Optional;
 import java.util.Set;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.TestInfo;
 import org.junit.jupiter.api.extension.ExtensionContext;
 import org.junit.jupiter.api.extension.ParameterContext;
@@ -89,7 +90,8 @@ public String toString() {
 			// @formatter:on
 		}
 
-		private static Object nullSafeGet(Optional<?> optional) {
+		@SuppressWarnings("OptionalAssignedToNull")
+		private static @Nullable Object nullSafeGet(@Nullable Optional<?> optional) {
 			return optional != null ? optional.orElse(null) : null;
 		}
 
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/TimeoutConfiguration.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/TimeoutConfiguration.java
index 60a8734db382..42831f0e737d 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/TimeoutConfiguration.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/TimeoutConfiguration.java
@@ -105,7 +105,7 @@ private Optional<TimeoutDuration> parseTimeoutDuration(String propertyName) {
 			}
 			catch (Exception e) {
 				logger.warn(e,
-					() -> String.format("Ignored invalid timeout '%s' set via the '%s' configuration parameter.", value,
+					() -> "Ignored invalid timeout '%s' set via the '%s' configuration parameter.".formatted(value,
 						key));
 				return null;
 			}
@@ -128,17 +128,17 @@ private Optional<ThreadMode> parseTimeoutThreadModeConfiguration() {
 			try {
 				ThreadMode threadMode = ThreadMode.valueOf(value.toUpperCase());
 				if (threadMode == ThreadMode.INFERRED) {
-					logger.warn(() -> String.format(
-						"Invalid timeout thread mode '%s', only %s and %s can be used as configuration parameter for %s.",
-						value, SAME_THREAD, SEPARATE_THREAD, DEFAULT_TIMEOUT_THREAD_MODE_PROPERTY_NAME));
+					logger.warn(
+						() -> "Invalid timeout thread mode '%s', only %s and %s can be used as configuration parameter for %s.".formatted(
+							value, SAME_THREAD, SEPARATE_THREAD, DEFAULT_TIMEOUT_THREAD_MODE_PROPERTY_NAME));
 					return null;
 				}
 				return threadMode;
 			}
 			catch (Exception e) {
 				logger.warn(e,
-					() -> String.format("Invalid timeout thread mode '%s' set via the '%s' configuration parameter.",
-						value, DEFAULT_TIMEOUT_THREAD_MODE_PROPERTY_NAME));
+					() -> "Invalid timeout thread mode '%s' set via the '%s' configuration parameter.".formatted(value,
+						DEFAULT_TIMEOUT_THREAD_MODE_PROPERTY_NAME));
 				return null;
 			}
 		});
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/TimeoutDuration.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/TimeoutDuration.java
index ac99448af8a9..66c154faba5a 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/TimeoutDuration.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/TimeoutDuration.java
@@ -12,7 +12,6 @@
 
 import java.time.Duration;
 import java.time.temporal.ChronoUnit;
-import java.util.Objects;
 import java.util.concurrent.TimeUnit;
 
 import org.junit.jupiter.api.Timeout;
@@ -22,46 +21,18 @@
 /**
  * @since 5.5
  */
-class TimeoutDuration {
+record TimeoutDuration(long value, TimeUnit unit) {
 
 	static TimeoutDuration from(Timeout timeout) {
 		return new TimeoutDuration(timeout.value(), timeout.unit());
 	}
 
-	private final long value;
-	private final TimeUnit unit;
-
 	TimeoutDuration(long value, TimeUnit unit) {
 		Preconditions.condition(value > 0, () -> "timeout duration must be a positive number: " + value);
 		this.value = value;
 		this.unit = Preconditions.notNull(unit, "timeout unit must not be null");
 	}
 
-	public long getValue() {
-		return value;
-	}
-
-	public TimeUnit getUnit() {
-		return unit;
-	}
-
-	@Override
-	public boolean equals(Object o) {
-		if (this == o) {
-			return true;
-		}
-		if (o == null || getClass() != o.getClass()) {
-			return false;
-		}
-		TimeoutDuration that = (TimeoutDuration) o;
-		return value == that.value && unit == that.unit;
-	}
-
-	@Override
-	public int hashCode() {
-		return Objects.hash(value, unit);
-	}
-
 	@Override
 	public String toString() {
 		String label = unit.name().toLowerCase();
@@ -76,23 +47,15 @@ public Duration toDuration() {
 	}
 
 	private ChronoUnit toChronoUnit() {
-		switch (unit) {
-			case NANOSECONDS:
-				return ChronoUnit.NANOS;
-			case MICROSECONDS:
-				return ChronoUnit.MICROS;
-			case MILLISECONDS:
-				return ChronoUnit.MILLIS;
-			case SECONDS:
-				return ChronoUnit.SECONDS;
-			case MINUTES:
-				return ChronoUnit.MINUTES;
-			case HOURS:
-				return ChronoUnit.HOURS;
-			case DAYS:
-				return ChronoUnit.DAYS;
-			default:
-				throw new JUnitException("Could not map TimeUnit " + unit + " to ChronoUnit");
-		}
+		return switch (unit) {
+			case NANOSECONDS -> ChronoUnit.NANOS;
+			case MICROSECONDS -> ChronoUnit.MICROS;
+			case MILLISECONDS -> ChronoUnit.MILLIS;
+			case SECONDS -> ChronoUnit.SECONDS;
+			case MINUTES -> ChronoUnit.MINUTES;
+			case HOURS -> ChronoUnit.HOURS;
+			case DAYS -> ChronoUnit.DAYS;
+			default -> throw new JUnitException("Could not map TimeUnit " + unit + " to ChronoUnit");
+		};
 	}
 }
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/TimeoutDurationParser.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/TimeoutDurationParser.java
index e5be5afefc3c..cba8abbc873e 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/TimeoutDurationParser.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/TimeoutDurationParser.java
@@ -10,6 +10,7 @@
 
 package org.junit.jupiter.engine.extension;
 
+import static java.util.Objects.requireNonNull;
 import static java.util.concurrent.TimeUnit.DAYS;
 import static java.util.concurrent.TimeUnit.HOURS;
 import static java.util.concurrent.TimeUnit.MICROSECONDS;
@@ -21,8 +22,6 @@
 import static java.util.regex.Pattern.UNICODE_CASE;
 
 import java.time.format.DateTimeParseException;
-import java.util.Collections;
-import java.util.HashMap;
 import java.util.Locale;
 import java.util.Map;
 import java.util.concurrent.TimeUnit;
@@ -36,19 +35,16 @@ class TimeoutDurationParser {
 
 	private static final Pattern PATTERN = Pattern.compile("([1-9]\\d*) ?((?:[nμm]?s)|m|h|d)?",
 		CASE_INSENSITIVE | UNICODE_CASE);
-	private static final Map<String, TimeUnit> UNITS_BY_ABBREVIATION;
 
-	static {
-		Map<String, TimeUnit> unitsByAbbreviation = new HashMap<>();
-		unitsByAbbreviation.put("ns", NANOSECONDS);
-		unitsByAbbreviation.put("μs", MICROSECONDS);
-		unitsByAbbreviation.put("ms", MILLISECONDS);
-		unitsByAbbreviation.put("s", SECONDS);
-		unitsByAbbreviation.put("m", MINUTES);
-		unitsByAbbreviation.put("h", HOURS);
-		unitsByAbbreviation.put("d", DAYS);
-		UNITS_BY_ABBREVIATION = Collections.unmodifiableMap(unitsByAbbreviation);
-	}
+	private static final Map<String, TimeUnit> UNITS_BY_ABBREVIATION = Map.of( //
+		"ns", NANOSECONDS, //
+		"μs", MICROSECONDS, //
+		"ms", MILLISECONDS, //
+		"s", SECONDS, //
+		"m", MINUTES, //
+		"h", HOURS, //
+		"d", DAYS //
+	);
 
 	TimeoutDuration parse(CharSequence text) throws DateTimeParseException {
 		Matcher matcher = PATTERN.matcher(text);
@@ -56,7 +52,7 @@ TimeoutDuration parse(CharSequence text) throws DateTimeParseException {
 			long value = Long.parseLong(matcher.group(1));
 			String unitAbbreviation = matcher.group(2);
 			TimeUnit unit = unitAbbreviation == null ? SECONDS
-					: UNITS_BY_ABBREVIATION.get(unitAbbreviation.toLowerCase(Locale.ENGLISH));
+					: requireNonNull(UNITS_BY_ABBREVIATION.get(unitAbbreviation.toLowerCase(Locale.ENGLISH)));
 			return new TimeoutDuration(value, unit);
 		}
 		throw new DateTimeParseException("Timeout duration is not in the expected format (<number> [ns|μs|ms|s|m|h|d])",
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/TimeoutExceptionFactory.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/TimeoutExceptionFactory.java
index 41174c609857..2c52407d0c82 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/TimeoutExceptionFactory.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/TimeoutExceptionFactory.java
@@ -12,6 +12,7 @@
 
 import java.util.concurrent.TimeoutException;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.util.Preconditions;
 
 /**
@@ -22,8 +23,9 @@ class TimeoutExceptionFactory {
 	private TimeoutExceptionFactory() {
 	}
 
-	static TimeoutException create(String methodSignature, TimeoutDuration timeoutDuration, Throwable failure) {
-		String message = String.format("%s timed out after %s",
+	static TimeoutException create(String methodSignature, TimeoutDuration timeoutDuration,
+			@Nullable Throwable failure) {
+		String message = "%s timed out after %s".formatted(
 			Preconditions.notNull(methodSignature, "method signature must not be null"),
 			Preconditions.notNull(timeoutDuration, "timeout duration must not be null"));
 		TimeoutException timeoutException = new TimeoutException(message);
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/TimeoutExtension.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/TimeoutExtension.java
index f7fd783d077a..4c8a611f3eed 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/TimeoutExtension.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/TimeoutExtension.java
@@ -10,6 +10,7 @@
 
 package org.junit.jupiter.engine.extension;
 
+import static java.util.Objects.requireNonNull;
 import static org.junit.jupiter.api.Timeout.TIMEOUT_MODE_PROPERTY_NAME;
 import static org.junit.jupiter.api.Timeout.ThreadMode.SAME_THREAD;
 
@@ -18,6 +19,7 @@
 import java.util.Optional;
 import java.util.function.Function;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Timeout;
 import org.junit.jupiter.api.Timeout.ThreadMode;
 import org.junit.jupiter.api.extension.BeforeAllCallback;
@@ -69,7 +71,7 @@ private void readAndStoreTimeoutSoChildrenInheritIt(ExtensionContext context) {
 	}
 
 	@Override
-	public void interceptBeforeAllMethod(Invocation<Void> invocation,
+	public void interceptBeforeAllMethod(Invocation<@Nullable Void> invocation,
 			ReflectiveInvocationContext<Method> invocationContext, ExtensionContext extensionContext) throws Throwable {
 
 		interceptLifecycleMethod(invocation, invocationContext, extensionContext,
@@ -77,7 +79,7 @@ public void interceptBeforeAllMethod(Invocation<Void> invocation,
 	}
 
 	@Override
-	public void interceptBeforeEachMethod(Invocation<Void> invocation,
+	public void interceptBeforeEachMethod(Invocation<@Nullable Void> invocation,
 			ReflectiveInvocationContext<Method> invocationContext, ExtensionContext extensionContext) throws Throwable {
 
 		interceptLifecycleMethod(invocation, invocationContext, extensionContext,
@@ -85,31 +87,31 @@ public void interceptBeforeEachMethod(Invocation<Void> invocation,
 	}
 
 	@Override
-	public void interceptTestMethod(Invocation<Void> invocation, ReflectiveInvocationContext<Method> invocationContext,
-			ExtensionContext extensionContext) throws Throwable {
+	public void interceptTestMethod(Invocation<@Nullable Void> invocation,
+			ReflectiveInvocationContext<Method> invocationContext, ExtensionContext extensionContext) throws Throwable {
 
-		interceptTestableMethod(invocation, invocationContext, extensionContext,
+		this.<@Nullable Void> interceptTestableMethod(invocation, invocationContext, extensionContext,
 			TimeoutConfiguration::getDefaultTestMethodTimeout);
 	}
 
 	@Override
-	public void interceptTestTemplateMethod(Invocation<Void> invocation,
+	public void interceptTestTemplateMethod(Invocation<@Nullable Void> invocation,
 			ReflectiveInvocationContext<Method> invocationContext, ExtensionContext extensionContext) throws Throwable {
 
-		interceptTestableMethod(invocation, invocationContext, extensionContext,
+		this.<@Nullable Void> interceptTestableMethod(invocation, invocationContext, extensionContext,
 			TimeoutConfiguration::getDefaultTestTemplateMethodTimeout);
 	}
 
 	@Override
-	public <T> T interceptTestFactoryMethod(Invocation<T> invocation,
+	public <T extends @Nullable Object> T interceptTestFactoryMethod(Invocation<T> invocation,
 			ReflectiveInvocationContext<Method> invocationContext, ExtensionContext extensionContext) throws Throwable {
 
-		return interceptTestableMethod(invocation, invocationContext, extensionContext,
+		return this.<T> interceptTestableMethod(invocation, invocationContext, extensionContext,
 			TimeoutConfiguration::getDefaultTestFactoryMethodTimeout);
 	}
 
 	@Override
-	public void interceptAfterEachMethod(Invocation<Void> invocation,
+	public void interceptAfterEachMethod(Invocation<@Nullable Void> invocation,
 			ReflectiveInvocationContext<Method> invocationContext, ExtensionContext extensionContext) throws Throwable {
 
 		interceptLifecycleMethod(invocation, invocationContext, extensionContext,
@@ -117,20 +119,21 @@ public void interceptAfterEachMethod(Invocation<Void> invocation,
 	}
 
 	@Override
-	public void interceptAfterAllMethod(Invocation<Void> invocation,
+	public void interceptAfterAllMethod(Invocation<@Nullable Void> invocation,
 			ReflectiveInvocationContext<Method> invocationContext, ExtensionContext extensionContext) throws Throwable {
 
 		interceptLifecycleMethod(invocation, invocationContext, extensionContext,
 			TimeoutConfiguration::getDefaultAfterAllMethodTimeout);
 	}
 
-	private void interceptLifecycleMethod(Invocation<Void> invocation,
+	private void interceptLifecycleMethod(Invocation<@Nullable Void> invocation,
 			ReflectiveInvocationContext<Method> invocationContext, ExtensionContext extensionContext,
 			TimeoutProvider defaultTimeoutProvider) throws Throwable {
 
 		TimeoutDuration timeout = readTimeoutFromAnnotation(Optional.of(invocationContext.getExecutable())).orElse(
 			null);
-		intercept(invocation, invocationContext, extensionContext, timeout, defaultTimeoutProvider);
+		this.<@Nullable Void> intercept(invocation, invocationContext, extensionContext, timeout,
+			defaultTimeoutProvider);
 	}
 
 	@SuppressWarnings("OptionalUsedAsFieldOrParameterType")
@@ -143,7 +146,7 @@ private Optional<ThreadMode> readTimeoutThreadModeFromAnnotation(Optional<Annota
 		return AnnotationSupport.findAnnotation(element, Timeout.class).map(Timeout::threadMode);
 	}
 
-	private <T> T interceptTestableMethod(Invocation<T> invocation,
+	private <T extends @Nullable Object> T interceptTestableMethod(Invocation<T> invocation,
 			ReflectiveInvocationContext<Method> invocationContext, ExtensionContext extensionContext,
 			TimeoutProvider defaultTimeoutProvider) throws Throwable {
 
@@ -152,16 +155,16 @@ private <T> T interceptTestableMethod(Invocation<T> invocation,
 		return intercept(invocation, invocationContext, extensionContext, timeout, defaultTimeoutProvider);
 	}
 
-	private <T> T intercept(Invocation<T> invocation, ReflectiveInvocationContext<Method> invocationContext,
-			ExtensionContext extensionContext, TimeoutDuration explicitTimeout, TimeoutProvider defaultTimeoutProvider)
-			throws Throwable {
+	private <T extends @Nullable Object> T intercept(Invocation<T> invocation,
+			ReflectiveInvocationContext<Method> invocationContext, ExtensionContext extensionContext,
+			@Nullable TimeoutDuration explicitTimeout, TimeoutProvider defaultTimeoutProvider) throws Throwable {
 
 		TimeoutDuration timeout = explicitTimeout == null ? getDefaultTimeout(extensionContext, defaultTimeoutProvider)
 				: explicitTimeout;
 		return decorate(invocation, invocationContext, extensionContext, timeout).proceed();
 	}
 
-	private TimeoutDuration getDefaultTimeout(ExtensionContext extensionContext,
+	private @Nullable TimeoutDuration getDefaultTimeout(ExtensionContext extensionContext,
 			TimeoutProvider defaultTimeoutProvider) {
 
 		return defaultTimeoutProvider.apply(getGlobalTimeoutConfiguration(extensionContext)).orElse(null);
@@ -169,12 +172,13 @@ private TimeoutDuration getDefaultTimeout(ExtensionContext extensionContext,
 
 	private TimeoutConfiguration getGlobalTimeoutConfiguration(ExtensionContext extensionContext) {
 		ExtensionContext root = extensionContext.getRoot();
-		return root.getStore(NAMESPACE).getOrComputeIfAbsent(GLOBAL_TIMEOUT_CONFIG_KEY,
-			key -> new TimeoutConfiguration(root), TimeoutConfiguration.class);
+		return requireNonNull(root.getStore(NAMESPACE).getOrComputeIfAbsent(GLOBAL_TIMEOUT_CONFIG_KEY,
+			key -> new TimeoutConfiguration(root), TimeoutConfiguration.class));
 	}
 
-	private <T> Invocation<T> decorate(Invocation<T> invocation, ReflectiveInvocationContext<Method> invocationContext,
-			ExtensionContext extensionContext, TimeoutDuration timeout) {
+	private <T extends @Nullable Object> Invocation<T> decorate(Invocation<T> invocation,
+			ReflectiveInvocationContext<Method> invocationContext, ExtensionContext extensionContext,
+			@Nullable TimeoutDuration timeout) {
 
 		if (timeout == null || isTimeoutDisabled(extensionContext)) {
 			return invocation;
@@ -194,7 +198,7 @@ private ThreadMode resolveTimeoutThreadMode(ExtensionContext extensionContext) {
 		return annotationThreadMode;
 	}
 
-	private ThreadMode getAnnotationThreadMode(ExtensionContext extensionContext) {
+	private @Nullable ThreadMode getAnnotationThreadMode(ExtensionContext extensionContext) {
 		return extensionContext.getStore(NAMESPACE).get(TESTABLE_METHOD_TIMEOUT_THREAD_MODE_KEY, ThreadMode.class);
 	}
 
@@ -202,7 +206,7 @@ private String describe(ReflectiveInvocationContext<Method> invocationContext, E
 		Method method = invocationContext.getExecutable();
 		Optional<Class<?>> testClass = extensionContext.getTestClass();
 		if (testClass.isPresent() && invocationContext.getTargetClass().equals(testClass.get())) {
-			return String.format("%s(%s)", method.getName(), ClassUtils.nullSafeToString(method.getParameterTypes()));
+			return "%s(%s)".formatted(method.getName(), ClassUtils.nullSafeToString(method.getParameterTypes()));
 		}
 		return ReflectionUtils.getFullyQualifiedMethodName(invocationContext.getTargetClass(), method);
 	}
@@ -219,16 +223,12 @@ private boolean isTimeoutDisabled(ExtensionContext extensionContext) {
 	 * Determine if timeouts are disabled for the supplied mode.
 	 */
 	private boolean isTimeoutDisabled(String mode) {
-		switch (mode) {
-			case ENABLED_MODE_VALUE:
-				return false;
-			case DISABLED_MODE_VALUE:
-				return true;
-			case DISABLED_ON_DEBUG_MODE_VALUE:
-				return RuntimeUtils.isDebugMode();
-			default:
-				throw new ExtensionConfigurationException("Unsupported timeout mode: " + mode);
-		}
+		return switch (mode) {
+			case ENABLED_MODE_VALUE -> false;
+			case DISABLED_MODE_VALUE -> true;
+			case DISABLED_ON_DEBUG_MODE_VALUE -> RuntimeUtils.isDebugMode();
+			default -> throw new ExtensionConfigurationException("Unsupported timeout mode: " + mode);
+		};
 	}
 
 	@FunctionalInterface
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/TimeoutInvocationFactory.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/TimeoutInvocationFactory.java
index 7843c012711b..41312b59d622 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/TimeoutInvocationFactory.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/TimeoutInvocationFactory.java
@@ -10,6 +10,8 @@
 
 package org.junit.jupiter.engine.extension;
 
+import static java.util.Objects.requireNonNull;
+
 import java.util.concurrent.Executors;
 import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.TimeUnit;
@@ -48,7 +50,7 @@ <T> Invocation<T> create(ThreadMode threadMode, TimeoutInvocationParameters<T> t
 	}
 
 	private ScheduledExecutorService getThreadExecutorForSameThreadInvocation() {
-		return store.getOrComputeIfAbsent(SingleThreadExecutorResource.class).get();
+		return requireNonNull(store.getOrComputeIfAbsent(SingleThreadExecutorResource.class)).get();
 	}
 
 	@SuppressWarnings({ "deprecation", "try" })
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/package-info.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/package-info.java
index ff29b09a9c8f..96ac809f2bb2 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/package-info.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/package-info.java
@@ -2,4 +2,7 @@
  * Test extensions specific to the JUnit Jupiter test engine.
  */
 
+@NullMarked
 package org.junit.jupiter.engine.extension;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/package-info.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/package-info.java
index 17af1fecb552..cb01093df2b9 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/package-info.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/package-info.java
@@ -2,4 +2,7 @@
  * Core package for the JUnit Jupiter test engine.
  */
 
+@NullMarked
 package org.junit.jupiter.engine;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/support/MethodReflectionUtils.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/support/MethodReflectionUtils.java
new file mode 100644
index 000000000000..a72d013134f4
--- /dev/null
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/support/MethodReflectionUtils.java
@@ -0,0 +1,47 @@
+/*
+ * Copyright 2015-2025 the original author or authors.
+ *
+ * All rights reserved. This program and the accompanying materials are
+ * made available under the terms of the Eclipse Public License v2.0 which
+ * accompanies this distribution and is available at
+ *
+ * https://www.eclipse.org/legal/epl-v20.html
+ */
+
+package org.junit.jupiter.engine.support;
+
+import static org.apiguardian.api.API.Status.INTERNAL;
+import static org.junit.platform.commons.util.KotlinReflectionUtils.getKotlinSuspendingFunctionGenericReturnType;
+import static org.junit.platform.commons.util.KotlinReflectionUtils.getKotlinSuspendingFunctionReturnType;
+import static org.junit.platform.commons.util.KotlinReflectionUtils.invokeKotlinSuspendingFunction;
+import static org.junit.platform.commons.util.KotlinReflectionUtils.isKotlinSuspendingFunction;
+
+import java.lang.reflect.Method;
+import java.lang.reflect.Type;
+
+import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
+import org.junit.platform.commons.support.ReflectionSupport;
+
+@API(status = INTERNAL, since = "6.0")
+public class MethodReflectionUtils {
+
+	public static Class<?> getReturnType(Method method) {
+		return isKotlinSuspendingFunction(method) //
+				? getKotlinSuspendingFunctionReturnType(method) //
+				: method.getReturnType();
+	}
+
+	public static Type getGenericReturnType(Method method) {
+		return isKotlinSuspendingFunction(method) //
+				? getKotlinSuspendingFunctionGenericReturnType(method) //
+				: method.getGenericReturnType();
+	}
+
+	public static @Nullable Object invoke(Method method, @Nullable Object target, @Nullable Object[] arguments) {
+		if (isKotlinSuspendingFunction(method)) {
+			return invokeKotlinSuspendingFunction(method, target, arguments);
+		}
+		return ReflectionSupport.invokeMethod(method, target, arguments);
+	}
+}
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/support/package-info.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/support/package-info.java
index 6eecfd0f5120..83ffb2de0923 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/support/package-info.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/support/package-info.java
@@ -2,4 +2,7 @@
  * Internal support classes for the JUnit Jupiter test engine.
  */
 
+@NullMarked
 package org.junit.jupiter.engine.support;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-jupiter-migrationsupport/README.md b/junit-jupiter-migrationsupport/README.md
index 730e2c8e94b1..a8b755cae594 100644
--- a/junit-jupiter-migrationsupport/README.md
+++ b/junit-jupiter-migrationsupport/README.md
@@ -9,11 +9,11 @@ implementations is not possible within the JUnit Jupiter extension model.
 
 The main purpose of this module is to facilitate the migration of large
 JUnit 4 codebases containing such JUnit 4 rules by minimizing the effort
-needed to run such legacy tests under JUnit 5.
+needed to run such legacy tests under JUnit Platform.
 By using one of the two provided class-level extensions on a test class
 such rules in legacy code bases can be left unchanged
 including the JUnit 4 rule import statements.
 
 However, if you intend to develop a *new* extension for
-JUnit 5 please use the new extension model of JUnit Jupiter instead
+JUnit please use the new extension model of JUnit Jupiter instead
 of the rule-based model of JUnit 4.
diff --git a/junit-jupiter-migrationsupport/junit-jupiter-migrationsupport.gradle.kts b/junit-jupiter-migrationsupport/junit-jupiter-migrationsupport.gradle.kts
index 0f28afd9ea94..810408bfd4c4 100644
--- a/junit-jupiter-migrationsupport/junit-jupiter-migrationsupport.gradle.kts
+++ b/junit-jupiter-migrationsupport/junit-jupiter-migrationsupport.gradle.kts
@@ -1,5 +1,6 @@
 plugins {
 	id("junitbuild.java-library-conventions")
+	id("junitbuild.java-nullability-conventions")
 	id("junitbuild.junit4-compatibility")
 }
 
@@ -11,22 +12,30 @@ dependencies {
 	api(projects.junitJupiterApi)
 
 	compileOnlyApi(libs.apiguardian)
+	compileOnly(libs.jspecify)
 
 	osgiVerification(projects.junitJupiterEngine)
 	osgiVerification(projects.junitPlatformLauncher)
 }
 
-tasks.jar {
-	bundle {
-		val importAPIGuardian: String by extra
-		bnd("""
-			# Import JUnit4 packages with a version
-			Import-Package: \
-				$importAPIGuardian,\
-				org.junit;version="[${libs.versions.junit4Min.get()},5)",\
-				org.junit.platform.commons.logging;status=INTERNAL,\
-				org.junit.rules;version="[${libs.versions.junit4Min.get()},5)",\
-				*
-		""")
+tasks {
+	compileJava {
+		options.compilerArgs.add("-Xlint:-requires-automatic,-requires-transitive-automatic") // JUnit 4
+	}
+	jar {
+		bundle {
+			val importAPIGuardian: String by extra
+			val importJSpecify: String by extra
+			bnd("""
+				# Import JUnit4 packages with a version
+				Import-Package: \
+					$importAPIGuardian,\
+					$importJSpecify,\
+					org.junit;version="[${libs.versions.junit4Min.get()},5)",\
+					org.junit.platform.commons.logging;status=INTERNAL,\
+					org.junit.rules;version="[${libs.versions.junit4Min.get()},5)",\
+					*
+			""")
+		}
 	}
 }
diff --git a/junit-jupiter-migrationsupport/src/module/org.junit.jupiter.migrationsupport/module-info.java b/junit-jupiter-migrationsupport/src/main/java/module-info.java
similarity index 96%
rename from junit-jupiter-migrationsupport/src/module/org.junit.jupiter.migrationsupport/module-info.java
rename to junit-jupiter-migrationsupport/src/main/java/module-info.java
index ced462bec0db..e89e043930e3 100644
--- a/junit-jupiter-migrationsupport/src/module/org.junit.jupiter.migrationsupport/module-info.java
+++ b/junit-jupiter-migrationsupport/src/main/java/module-info.java
@@ -14,8 +14,11 @@
  * @since 5.0
  */
 module org.junit.jupiter.migrationsupport {
-	requires transitive junit; // 4
+
 	requires static transitive org.apiguardian.api;
+	requires static org.jspecify;
+
+	requires transitive junit; // 4
 	requires transitive org.junit.jupiter.api;
 	requires org.junit.platform.commons;
 
diff --git a/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/EnableJUnit4MigrationSupport.java b/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/EnableJUnit4MigrationSupport.java
index 0c9c04778493..540b42ad5150 100644
--- a/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/EnableJUnit4MigrationSupport.java
+++ b/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/EnableJUnit4MigrationSupport.java
@@ -10,7 +10,7 @@
 
 package org.junit.jupiter.migrationsupport;
 
-import static org.apiguardian.api.API.Status.STABLE;
+import static org.apiguardian.api.API.Status.DEPRECATED;
 
 import java.lang.annotation.ElementType;
 import java.lang.annotation.Retention;
@@ -47,10 +47,14 @@
  * @see ExpectedExceptionSupport
  * @see IgnoreCondition
  * @see EnableRuleMigrationSupport
+ * @deprecated Please migrate to Jupiter extensions and use
+ * {@link org.junit.jupiter.api.Disabled @Disabled} instead.
  */
+@SuppressWarnings("removal")
 @Target(ElementType.TYPE)
 @Retention(RetentionPolicy.RUNTIME)
-@API(status = STABLE, since = "5.7")
+@API(status = DEPRECATED, since = "6.0")
+@Deprecated(since = "6.0", forRemoval = true)
 @EnableRuleMigrationSupport
 @ExtendWith(IgnoreCondition.class)
 public @interface EnableJUnit4MigrationSupport {
diff --git a/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/conditions/IgnoreCondition.java b/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/conditions/IgnoreCondition.java
index 59ab33098a59..ed8e2e434b37 100644
--- a/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/conditions/IgnoreCondition.java
+++ b/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/conditions/IgnoreCondition.java
@@ -10,12 +10,13 @@
 
 package org.junit.jupiter.migrationsupport.conditions;
 
-import static org.apiguardian.api.API.Status.STABLE;
+import static org.apiguardian.api.API.Status.DEPRECATED;
 import static org.junit.platform.commons.support.AnnotationSupport.findAnnotation;
 
 import java.lang.reflect.AnnotatedElement;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.Ignore;
 import org.junit.jupiter.api.extension.ConditionEvaluationResult;
 import org.junit.jupiter.api.extension.ExecutionCondition;
@@ -31,8 +32,10 @@
  * @see org.junit.jupiter.api.Disabled @Disabled
  * @see #evaluateExecutionCondition(ExtensionContext)
  * @see org.junit.jupiter.migrationsupport.EnableJUnit4MigrationSupport
+ * @deprecated Please use {@link org.junit.jupiter.api.Disabled @Disabled} instead.
  */
-@API(status = STABLE, since = "5.7")
+@API(status = DEPRECATED, since = "6.0")
+@Deprecated(since = "6.0", forRemoval = true)
 public class IgnoreCondition implements ExecutionCondition {
 
 	private static final ConditionEvaluationResult ENABLED = //
@@ -53,7 +56,7 @@ public ConditionEvaluationResult evaluateExecutionCondition(ExtensionContext con
 				.orElse(ENABLED);
 	}
 
-	private ConditionEvaluationResult toResult(AnnotatedElement element, Ignore annotation) {
+	private ConditionEvaluationResult toResult(@Nullable AnnotatedElement element, Ignore annotation) {
 		String value = annotation.value();
 		String reason = StringUtils.isNotBlank(value) ? value : element + " is disabled via @org.junit.Ignore";
 		return ConditionEvaluationResult.disabled(reason);
diff --git a/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/conditions/package-info.java b/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/conditions/package-info.java
index 530ff605d558..198cf1d1c686 100644
--- a/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/conditions/package-info.java
+++ b/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/conditions/package-info.java
@@ -1,7 +1,10 @@
 /**
- * Extensions which provide support for conditional test execution features of
- * JUnit 4 (e.g., the {@link org.junit.Ignore @Ignore} annotation) within JUnit
- * Jupiter.
+ * <em>Deprecated</em> extensions that provide support for conditional test
+ * execution features of JUnit 4 (e.g., the {@link org.junit.Ignore @Ignore}
+ * annotation) within JUnit Jupiter.
  */
 
+@NullMarked
 package org.junit.jupiter.migrationsupport.conditions;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/package-info.java b/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/package-info.java
index 236a13fded50..ad4c3815a608 100644
--- a/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/package-info.java
+++ b/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/package-info.java
@@ -1,5 +1,8 @@
 /**
- * Support for migrating from JUnit 4 to JUnit Jupiter.
+ * <em>Deprecated</em> support for migrating from JUnit 4 to JUnit Jupiter.
  */
 
+@NullMarked
 package org.junit.jupiter.migrationsupport;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/EnableRuleMigrationSupport.java b/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/EnableRuleMigrationSupport.java
index 243874b8265e..88d713067c3e 100644
--- a/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/EnableRuleMigrationSupport.java
+++ b/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/EnableRuleMigrationSupport.java
@@ -10,7 +10,7 @@
 
 package org.junit.jupiter.migrationsupport.rules;
 
-import static org.apiguardian.api.API.Status.STABLE;
+import static org.apiguardian.api.API.Status.DEPRECATED;
 
 import java.lang.annotation.ElementType;
 import java.lang.annotation.Retention;
@@ -36,10 +36,13 @@
  * @see VerifierSupport
  * @see ExpectedExceptionSupport
  * @see org.junit.jupiter.migrationsupport.EnableJUnit4MigrationSupport
+ * @deprecated Please migrate to Jupiter extensions.
  */
+@SuppressWarnings("removal")
 @Target(ElementType.TYPE)
 @Retention(RetentionPolicy.RUNTIME)
-@API(status = STABLE, since = "5.7")
+@API(status = DEPRECATED, since = "6.0")
+@Deprecated(since = "6.0", forRemoval = true)
 @ExtendWith(ExternalResourceSupport.class)
 @ExtendWith(VerifierSupport.class)
 @ExtendWith(ExpectedExceptionSupport.class)
diff --git a/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/ExpectedExceptionSupport.java b/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/ExpectedExceptionSupport.java
index adecfda66993..ec84443b488d 100644
--- a/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/ExpectedExceptionSupport.java
+++ b/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/ExpectedExceptionSupport.java
@@ -12,7 +12,7 @@
 
 import static java.lang.Boolean.FALSE;
 import static java.lang.Boolean.TRUE;
-import static org.apiguardian.api.API.Status.STABLE;
+import static org.apiguardian.api.API.Status.DEPRECATED;
 
 import org.apiguardian.api.API;
 import org.junit.jupiter.api.extension.AfterEachCallback;
@@ -20,6 +20,7 @@
 import org.junit.jupiter.api.extension.ExtensionContext.Namespace;
 import org.junit.jupiter.api.extension.ExtensionContext.Store;
 import org.junit.jupiter.api.extension.TestExecutionExceptionHandler;
+import org.junit.jupiter.api.function.Executable;
 import org.junit.jupiter.migrationsupport.rules.adapter.ExpectedExceptionAdapter;
 import org.junit.rules.ExpectedException;
 
@@ -38,8 +39,13 @@
  * @see org.junit.rules.ExpectedException
  * @see org.junit.rules.TestRule
  * @see org.junit.Rule
+ * @deprecated Please use
+ * {@link org.junit.jupiter.api.Assertions#assertThrows(Class, Executable)}
+ * instead.
  */
-@API(status = STABLE, since = "5.7")
+@SuppressWarnings("removal")
+@API(status = DEPRECATED, since = "6.0")
+@Deprecated(since = "6.0", forRemoval = true)
 public class ExpectedExceptionSupport implements AfterEachCallback, TestExecutionExceptionHandler {
 
 	private static final String EXCEPTION_WAS_HANDLED = "exceptionWasHandled";
@@ -57,8 +63,8 @@ public void handleTestExecutionException(ExtensionContext context, Throwable thr
 
 	@Override
 	public void afterEach(ExtensionContext context) throws Exception {
-		boolean handled = getStore(context).getOrComputeIfAbsent(EXCEPTION_WAS_HANDLED, key -> FALSE, Boolean.class);
-		if (!handled) {
+		Boolean handled = getStore(context).getOrComputeIfAbsent(EXCEPTION_WAS_HANDLED, key -> FALSE, Boolean.class);
+		if (handled != null && !handled) {
 			this.support.afterEach(context);
 		}
 	}
diff --git a/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/ExternalResourceSupport.java b/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/ExternalResourceSupport.java
index 347317733d4e..b5d77cfc6a7e 100644
--- a/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/ExternalResourceSupport.java
+++ b/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/ExternalResourceSupport.java
@@ -10,7 +10,7 @@
 
 package org.junit.jupiter.migrationsupport.rules;
 
-import static org.apiguardian.api.API.Status.STABLE;
+import static org.apiguardian.api.API.Status.DEPRECATED;
 
 import org.apiguardian.api.API;
 import org.junit.jupiter.api.extension.AfterEachCallback;
@@ -30,15 +30,18 @@
  * can be left unchanged including the JUnit 4 rule import statements.
  *
  * <p>However, if you intend to develop a <em>new</em> extension for
- * JUnit 5 please use the new extension model of JUnit Jupiter instead
+ * JUnit please use the new extension model of JUnit Jupiter instead
  * of the rule-based model of JUnit 4.
  *
  * @since 5.0
  * @see org.junit.rules.ExternalResource
  * @see org.junit.rules.TestRule
  * @see org.junit.Rule
+ * @deprecated Please use {@link org.junit.jupiter.api.AutoClose @AutoClose} instead.
  */
-@API(status = STABLE, since = "5.7")
+@SuppressWarnings("removal")
+@API(status = DEPRECATED, since = "6.0")
+@Deprecated(since = "6.0", forRemoval = true)
 public class ExternalResourceSupport implements BeforeEachCallback, AfterEachCallback {
 
 	private final TestRuleSupport support = new TestRuleSupport(ExternalResourceAdapter::new, ExternalResource.class);
diff --git a/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/TestRuleSupport.java b/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/TestRuleSupport.java
index f424126d6fdd..c13ac33b1985 100644
--- a/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/TestRuleSupport.java
+++ b/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/TestRuleSupport.java
@@ -11,6 +11,7 @@
 package org.junit.jupiter.migrationsupport.rules;
 
 import static java.util.Collections.unmodifiableList;
+import static java.util.Objects.requireNonNull;
 import static org.junit.platform.commons.support.AnnotationSupport.findPublicAnnotatedFields;
 import static org.junit.platform.commons.support.AnnotationSupport.isAnnotated;
 import static org.junit.platform.commons.support.HierarchyTraversalMode.TOP_DOWN;
@@ -101,7 +102,7 @@ public void handleTestExecutionException(ExtensionContext context, Throwable thr
 
 		// If no appropriate @Rule annotated members were discovered, we then
 		// have to rethrow the exception in order not to silently swallow it.
-		// Fixes bug: https://github.com/junit-team/junit5/issues/1069
+		// Fixes bug: https://github.com/junit-team/junit-framework/issues/1069
 		if (numRuleAnnotatedMembers == 0) {
 			throw throwable;
 		}
@@ -146,8 +147,8 @@ private List<TestRuleAnnotatedMember> getRuleAnnotatedMembers(ExtensionContext c
 		Object testInstance = context.getRequiredTestInstance();
 		Namespace namespace = Namespace.create(TestRuleSupport.class, context.getRequiredTestClass());
 		// @formatter:off
-		return new ArrayList<>(context.getStore(namespace)
-				.getOrComputeIfAbsent("rule-annotated-members", key -> findRuleAnnotatedMembers(testInstance), List.class));
+		return new ArrayList<>(requireNonNull(context.getStore(namespace)
+				.getOrComputeIfAbsent("rule-annotated-members", key -> findRuleAnnotatedMembers(testInstance), List.class)));
 		// @formatter:on
 	}
 
diff --git a/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/VerifierSupport.java b/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/VerifierSupport.java
index a5025818722d..1892be971501 100644
--- a/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/VerifierSupport.java
+++ b/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/VerifierSupport.java
@@ -10,7 +10,7 @@
 
 package org.junit.jupiter.migrationsupport.rules;
 
-import static org.apiguardian.api.API.Status.STABLE;
+import static org.apiguardian.api.API.Status.DEPRECATED;
 
 import org.apiguardian.api.API;
 import org.junit.jupiter.api.extension.AfterEachCallback;
@@ -29,15 +29,18 @@
  * can be left unchanged including the JUnit 4 rule import statements.
  *
  * <p>However, if you intend to develop a <em>new</em> extension for
- * JUnit 5 please use the new extension model of JUnit Jupiter instead
+ * JUnit please use the new extension model of JUnit Jupiter instead
  * of the rule-based model of JUnit 4.
  *
  * @since 5.0
  * @see org.junit.rules.Verifier
  * @see org.junit.rules.TestRule
  * @see org.junit.Rule
+ * @deprecated Please implement {@link org.junit.jupiter.api.extension.AfterTestExecutionCallback} instead.
  */
-@API(status = STABLE, since = "5.7")
+@SuppressWarnings("removal")
+@API(status = DEPRECATED, since = "6.0")
+@Deprecated(since = "6.0", forRemoval = true)
 public class VerifierSupport implements AfterEachCallback {
 
 	private final TestRuleSupport support = new TestRuleSupport(VerifierAdapter::new, Verifier.class);
diff --git a/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/adapter/AbstractTestRuleAdapter.java b/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/adapter/AbstractTestRuleAdapter.java
index 5c60dcf5df24..dce1c60fba92 100644
--- a/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/adapter/AbstractTestRuleAdapter.java
+++ b/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/adapter/AbstractTestRuleAdapter.java
@@ -17,6 +17,7 @@
 import java.lang.reflect.Method;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.migrationsupport.rules.member.TestRuleAnnotatedMember;
 import org.junit.platform.commons.JUnitException;
 import org.junit.platform.commons.util.ClassUtils;
@@ -37,13 +38,13 @@ public AbstractTestRuleAdapter(TestRuleAnnotatedMember annotatedMember, Class<?
 			() -> adapteeClass + " is not assignable from " + this.target.getClass());
 	}
 
-	protected Object executeMethod(String name) {
+	protected @Nullable Object executeMethod(String name) {
 		return executeMethod(name, new Class<?>[0]);
 	}
 
-	protected Object executeMethod(String methodName, Class<?>[] parameterTypes, Object... arguments) {
+	protected @Nullable Object executeMethod(String methodName, Class<?>[] parameterTypes, Object... arguments) {
 		Method method = findMethod(this.target.getClass(), methodName, parameterTypes).orElseThrow(
-			() -> new JUnitException(String.format("Failed to find method %s(%s) in class %s", methodName,
+			() -> new JUnitException("Failed to find method %s(%s) in class %s".formatted(methodName,
 				ClassUtils.nullSafeToString(parameterTypes), this.target.getClass().getName())));
 
 		return invokeMethod(method, this.target, arguments);
diff --git a/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/adapter/package-info.java b/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/adapter/package-info.java
index d69bee9757cc..043282b12ce0 100644
--- a/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/adapter/package-info.java
+++ b/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/adapter/package-info.java
@@ -1,5 +1,9 @@
 /**
- * Simple wrappers for JUnit 4 rules to overcome visibility limitations of the JUnit 4 implementations.
+ * <em>Internal</em> wrappers for JUnit 4 rules to overcome visibility
+ * limitations of the JUnit 4 implementations.
  */
 
+@NullMarked
 package org.junit.jupiter.migrationsupport.rules.adapter;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/member/AbstractTestRuleAnnotatedMember.java b/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/member/AbstractTestRuleAnnotatedMember.java
index be6ea055b87d..7e3557a0a085 100644
--- a/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/member/AbstractTestRuleAnnotatedMember.java
+++ b/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/member/AbstractTestRuleAnnotatedMember.java
@@ -10,6 +10,8 @@
 
 package org.junit.jupiter.migrationsupport.rules.member;
 
+import org.jspecify.annotations.Nullable;
+import org.junit.platform.commons.util.Preconditions;
 import org.junit.rules.TestRule;
 
 /**
@@ -19,8 +21,8 @@ abstract class AbstractTestRuleAnnotatedMember implements TestRuleAnnotatedMembe
 
 	private final TestRule testRule;
 
-	AbstractTestRuleAnnotatedMember(TestRule testRule) {
-		this.testRule = testRule;
+	AbstractTestRuleAnnotatedMember(@Nullable TestRule testRule) {
+		this.testRule = Preconditions.notNull(testRule, "TestRule must not be null");
 	}
 
 	@Override
diff --git a/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/member/TestRuleAnnotatedMember.java b/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/member/TestRuleAnnotatedMember.java
index 0b959f53bdaf..de68d64d1d15 100644
--- a/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/member/TestRuleAnnotatedMember.java
+++ b/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/member/TestRuleAnnotatedMember.java
@@ -18,7 +18,7 @@
 /**
  * @since 5.0
  */
-@API(status = INTERNAL, since = "5.0")
+@API(status = INTERNAL, since = "5.1")
 public interface TestRuleAnnotatedMember {
 
 	TestRule getTestRule();
diff --git a/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/member/package-info.java b/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/member/package-info.java
index 85ce964ae4f6..3d68cd8f27e4 100644
--- a/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/member/package-info.java
+++ b/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/member/package-info.java
@@ -1,5 +1,8 @@
 /**
- * Abstractions for members which can be targets of JUnit 4 rule annotations.
+ * <em>Internal</em> abstractions for members which can be targets of JUnit 4 rule annotations.
  */
 
+@NullMarked
 package org.junit.jupiter.migrationsupport.rules.member;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/package-info.java b/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/package-info.java
index 752ebb7e1e08..fa87e3fa0f3a 100644
--- a/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/package-info.java
+++ b/junit-jupiter-migrationsupport/src/main/java/org/junit/jupiter/migrationsupport/rules/package-info.java
@@ -1,5 +1,9 @@
 /**
- * Extensions which provide (limited) support for JUnit 4 rules within JUnit Jupiter.
+ * <em>Deprecated</em> extensions which provide (limited) support for JUnit 4
+ * rules within JUnit Jupiter.
  */
 
+@NullMarked
 package org.junit.jupiter.migrationsupport.rules;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-jupiter-params/LICENSE-univocity-parsers.md b/junit-jupiter-params/LICENSE-univocity-parsers.md
deleted file mode 100644
index f58ac2e9c2cf..000000000000
--- a/junit-jupiter-params/LICENSE-univocity-parsers.md
+++ /dev/null
@@ -1,168 +0,0 @@
-Apache License
-==============
-
-_Version 2.0, January 2004_
-_&lt;<https://www.apache.org/licenses/>&gt;_
-
-### Terms and Conditions for use, reproduction, and distribution
-
-#### 1. Definitions
-
-“License” shall mean the terms and conditions for use, reproduction, and
-distribution as defined by Sections 1 through 9 of this document.
-
-“Licensor” shall mean the copyright owner or entity authorized by the copyright
-owner that is granting the License.
-
-“Legal Entity” shall mean the union of the acting entity and all other entities
-that control, are controlled by, or are under common control with that entity.
-For the purposes of this definition, “control” means **(i)** the power, direct or
-indirect, to cause the direction or management of such entity, whether by
-contract or otherwise, or **(ii)** ownership of fifty percent (50%) or more of the
-outstanding shares, or **(iii)** beneficial ownership of such entity.
-
-“You” (or “Your”) shall mean an individual or Legal Entity exercising
-permissions granted by this License.
-
-“Source” form shall mean the preferred form for making modifications, including
-but not limited to software source code, documentation source, and configuration
-files.
-
-“Object” form shall mean any form resulting from mechanical transformation or
-translation of a Source form, including but not limited to compiled object code,
-generated documentation, and conversions to other media types.
-
-“Work” shall mean the work of authorship, whether in Source or Object form, made
-available under the License, as indicated by a copyright notice that is included
-in or attached to the work (an example is provided in the Appendix below).
-
-“Derivative Works” shall mean any work, whether in Source or Object form, that
-is based on (or derived from) the Work and for which the editorial revisions,
-annotations, elaborations, or other modifications represent, as a whole, an
-original work of authorship. For the purposes of this License, Derivative Works
-shall not include works that remain separable from, or merely link (or bind by
-name) to the interfaces of, the Work and Derivative Works thereof.
-
-“Contribution” shall mean any work of authorship, including the original version
-of the Work and any modifications or additions to that Work or Derivative Works
-thereof, that is intentionally submitted to Licensor for inclusion in the Work
-by the copyright owner or by an individual or Legal Entity authorized to submit
-on behalf of the copyright owner. For the purposes of this definition,
-“submitted” means any form of electronic, verbal, or written communication sent
-to the Licensor or its representatives, including but not limited to
-communication on electronic mailing lists, source code control systems, and
-issue tracking systems that are managed by, or on behalf of, the Licensor for
-the purpose of discussing and improving the Work, but excluding communication
-that is conspicuously marked or otherwise designated in writing by the copyright
-owner as “Not a Contribution.”
-
-“Contributor” shall mean Licensor and any individual or Legal Entity on behalf
-of whom a Contribution has been received by Licensor and subsequently
-incorporated within the Work.
-
-#### 2. Grant of Copyright License
-
-Subject to the terms and conditions of this License, each Contributor hereby
-grants to You a perpetual, worldwide, non-exclusive, no-charge, royalty-free,
-irrevocable copyright license to reproduce, prepare Derivative Works of,
-publicly display, publicly perform, sublicense, and distribute the Work and such
-Derivative Works in Source or Object form.
-
-#### 3. Grant of Patent License
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-Subject to the terms and conditions of this License, each Contributor hereby
-grants to You a perpetual, worldwide, non-exclusive, no-charge, royalty-free,
-irrevocable (except as stated in this section) patent license to make, have
-made, use, offer to sell, sell, import, and otherwise transfer the Work, where
-such license applies only to those patent claims licensable by such Contributor
-that are necessarily infringed by their Contribution(s) alone or by combination
-of their Contribution(s) with the Work to which such Contribution(s) was
-submitted. If You institute patent litigation against any entity (including a
-cross-claim or counterclaim in a lawsuit) alleging that the Work or a
-Contribution incorporated within the Work constitutes direct or contributory
-patent infringement, then any patent licenses granted to You under this License
-for that Work shall terminate as of the date such litigation is filed.
-
-#### 4. Redistribution
-
-You may reproduce and distribute copies of the Work or Derivative Works thereof
-in any medium, with or without modifications, and in Source or Object form,
-provided that You meet the following conditions:
-
-* **(a)** You must give any other recipients of the Work or Derivative Works a copy of
-this License; and
-* **(b)** You must cause any modified files to carry prominent notices stating that You
-changed the files; and
-* **(c)** You must retain, in the Source form of any Derivative Works that You distribute,
-all copyright, patent, trademark, and attribution notices from the Source form
-of the Work, excluding those notices that do not pertain to any part of the
-Derivative Works; and
-* **(d)** If the Work includes a “NOTICE” text file as part of its distribution, then any
-Derivative Works that You distribute must include a readable copy of the
-attribution notices contained within such NOTICE file, excluding those notices
-that do not pertain to any part of the Derivative Works, in at least one of the
-following places: within a NOTICE text file distributed as part of the
-Derivative Works; within the Source form or documentation, if provided along
-with the Derivative Works; or, within a display generated by the Derivative
-Works, if and wherever such third-party notices normally appear. The contents of
-the NOTICE file are for informational purposes only and do not modify the
-License. You may add Your own attribution notices within Derivative Works that
-You distribute, alongside or as an addendum to the NOTICE text from the Work,
-provided that such additional attribution notices cannot be construed as
-modifying the License.
-
-You may add Your own copyright statement to Your modifications and may provide
-additional or different license terms and conditions for use, reproduction, or
-distribution of Your modifications, or for any such Derivative Works as a whole,
-provided Your use, reproduction, and distribution of the Work otherwise complies
-with the conditions stated in this License.
-
-#### 5. Submission of Contributions
-
-Unless You explicitly state otherwise, any Contribution intentionally submitted
-for inclusion in the Work by You to the Licensor shall be under the terms and
-conditions of this License, without any additional terms or conditions.
-Notwithstanding the above, nothing herein shall supersede or modify the terms of
-any separate license agreement you may have executed with Licensor regarding
-such Contributions.
-
-#### 6. Trademarks
-
-This License does not grant permission to use the trade names, trademarks,
-service marks, or product names of the Licensor, except as required for
-reasonable and customary use in describing the origin of the Work and
-reproducing the content of the NOTICE file.
-
-#### 7. Disclaimer of Warranty
-
-Unless required by applicable law or agreed to in writing, Licensor provides the
-Work (and each Contributor provides its Contributions) on an “AS IS” BASIS,
-WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied,
-including, without limitation, any warranties or conditions of TITLE,
-NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A PARTICULAR PURPOSE. You are
-solely responsible for determining the appropriateness of using or
-redistributing the Work and assume any risks associated with Your exercise of
-permissions under this License.
-
-#### 8. Limitation of Liability
-
-In no event and under no legal theory, whether in tort (including negligence),
-contract, or otherwise, unless required by applicable law (such as deliberate
-and grossly negligent acts) or agreed to in writing, shall any Contributor be
-liable to You for damages, including any direct, indirect, special, incidental,
-or consequential damages of any character arising as a result of this License or
-out of the use or inability to use the Work (including but not limited to
-damages for loss of goodwill, work stoppage, computer failure or malfunction, or
-any and all other commercial damages or losses), even if such Contributor has
-been advised of the possibility of such damages.
-
-#### 9. Accepting Warranty or Additional Liability
-
-While redistributing the Work or Derivative Works thereof, You may choose to
-offer, and charge a fee for, acceptance of support, warranty, indemnity, or
-other liability obligations and/or rights consistent with this License. However,
-in accepting such obligations, You may act only on Your own behalf and on Your
-sole responsibility, not on behalf of any other Contributor, and only if You
-agree to indemnify, defend, and hold each Contributor harmless for any liability
-incurred by, or claims asserted against, such Contributor by reason of your
-accepting any such warranty or additional liability.
diff --git a/junit-jupiter-params/junit-jupiter-params.gradle.kts b/junit-jupiter-params/junit-jupiter-params.gradle.kts
index 7b3d65577455..6cb6fde4aa2a 100644
--- a/junit-jupiter-params/junit-jupiter-params.gradle.kts
+++ b/junit-jupiter-params/junit-jupiter-params.gradle.kts
@@ -1,6 +1,9 @@
 import junitbuild.extensions.javaModuleName
+import net.ltgt.gradle.errorprone.errorprone
+import net.ltgt.gradle.nullaway.nullaway
 
 plugins {
+	id("junitbuild.java-nullability-conventions")
 	id("junitbuild.kotlin-library-conventions")
 	id("junitbuild.shadow-conventions")
 	id("junitbuild.jmh-conventions")
@@ -14,8 +17,9 @@ dependencies {
 	api(projects.junitJupiterApi)
 
 	compileOnlyApi(libs.apiguardian)
+	compileOnly(libs.jspecify)
 
-	shadowed(libs.univocity.parsers)
+	shadowed(libs.fastcsv)
 
 	compileOnly(kotlin("stdlib"))
 
@@ -35,20 +39,36 @@ tasks {
 			""")
 		}
 	}
-}
-
-tasks {
-	shadowJar {
-		relocate("com.univocity", "org.junit.jupiter.params.shadow.com.univocity")
-		from(projectDir) {
-			include("LICENSE-univocity-parsers.md")
-			into("META-INF")
+	val extractFastCSVLicense by registering(Sync::class) {
+		from(zipTree(configurations.shadowedClasspath.flatMap { it.elements }.map { it.single { file -> file.asFile.name.contains("fastcsv") } })) {
+			include("META-INF/LICENSE")
+			rename { "LICENSE-fastcsv" }
 		}
+		into(layout.buildDirectory.dir("fastcsv"))
+	}
+	shadowJar {
+		relocate("de.siegmar.fastcsv", "org.junit.jupiter.params.shadow.de.siegmar.fastcsv")
+		exclude("META-INF/LICENSE")
+		from(extractFastCSVLicense)
 	}
-	compileModule {
+	compileJava {
 		options.compilerArgs.addAll(listOf(
-			"--add-modules", "univocity.parsers",
-			"--add-reads", "${javaModuleName}=univocity.parsers"
+			"--add-modules", "de.siegmar.fastcsv",
+			"--add-reads", "${javaModuleName}=de.siegmar.fastcsv"
 		))
 	}
+	compileJmhJava {
+		options.compilerArgs.add("-Xlint:-processing")
+		options.errorprone.nullaway {
+			customInitializerAnnotations.add(
+				"org.openjdk.jmh.annotations.Setup",
+			)
+		}
+	}
+	javadoc {
+		(options as StandardJavadocDocletOptions).apply {
+			addStringOption("-add-modules", "de.siegmar.fastcsv")
+			addStringOption("-add-reads", "${javaModuleName}=de.siegmar.fastcsv")
+		}
+	}
 }
diff --git a/junit-jupiter-params/src/jmh/java/org/junit/jupiter/params/ParameterizedInvocationNameFormatterBenchmarks.java b/junit-jupiter-params/src/jmh/java/org/junit/jupiter/params/ParameterizedInvocationNameFormatterBenchmarks.java
index 592be9f94445..0d57127007e1 100644
--- a/junit-jupiter-params/src/jmh/java/org/junit/jupiter/params/ParameterizedInvocationNameFormatterBenchmarks.java
+++ b/junit-jupiter-params/src/jmh/java/org/junit/jupiter/params/ParameterizedInvocationNameFormatterBenchmarks.java
@@ -10,6 +10,7 @@
 
 package org.junit.jupiter.params;
 
+import static java.util.Objects.requireNonNull;
 import static org.junit.jupiter.params.ParameterizedInvocationConstants.DEFAULT_DISPLAY_NAME;
 import static org.junit.jupiter.params.ParameterizedInvocationConstants.DISPLAY_NAME_PLACEHOLDER;
 
@@ -50,7 +51,9 @@ public void formatTestNames(Blackhole blackhole) throws Exception {
 		var method = TestCase.class.getDeclaredMethod("parameterizedTest", int.class);
 		var formatter = new ParameterizedInvocationNameFormatter(
 			DISPLAY_NAME_PLACEHOLDER + " " + DEFAULT_DISPLAY_NAME + " ({0})", "displayName",
-			new ParameterizedTestContext(TestCase.class, method, method.getAnnotation(ParameterizedTest.class)), 512);
+			new ParameterizedTestContext(TestCase.class, method,
+				requireNonNull(method.getAnnotation(ParameterizedTest.class))),
+			512);
 		for (int i = 0; i < argumentsList.size(); i++) {
 			Arguments arguments = argumentsList.get(i);
 			blackhole.consume(formatter.format(i, EvaluatedArgumentSet.allOf(arguments)));
diff --git a/junit-jupiter-params/src/module/org.junit.jupiter.params/module-info.java b/junit-jupiter-params/src/main/java/module-info.java
similarity index 96%
rename from junit-jupiter-params/src/module/org.junit.jupiter.params/module-info.java
rename to junit-jupiter-params/src/main/java/module-info.java
index 35569b82dd9d..f7ef36172179 100644
--- a/junit-jupiter-params/src/module/org.junit.jupiter.params/module-info.java
+++ b/junit-jupiter-params/src/main/java/module-info.java
@@ -14,7 +14,10 @@
  * @since 5.0
  */
 module org.junit.jupiter.params {
+
 	requires static transitive org.apiguardian.api;
+	requires static org.jspecify;
+
 	requires transitive org.junit.jupiter.api;
 	requires transitive org.junit.platform.commons;
 
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/AbstractParameterizedClassInvocationLifecycleMethodInvoker.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/AbstractParameterizedClassInvocationLifecycleMethodInvoker.java
index 0d20faee725b..2b836b9aed46 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/AbstractParameterizedClassInvocationLifecycleMethodInvoker.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/AbstractParameterizedClassInvocationLifecycleMethodInvoker.java
@@ -10,6 +10,8 @@
 
 package org.junit.jupiter.params;
 
+import static java.util.Objects.requireNonNull;
+
 import org.junit.jupiter.api.extension.ExecutableInvoker;
 import org.junit.jupiter.api.extension.ExtensionContext;
 import org.junit.jupiter.api.extension.ParameterContext;
@@ -52,9 +54,9 @@ public boolean supportsParameter(ParameterContext parameterContext, ExtensionCon
 	@Override
 	public Object resolveParameter(ParameterContext parameterContext, ExtensionContext extensionContext)
 			throws ParameterResolutionException {
-		return this.lifecycleMethod.parameterResolver //
+		return requireNonNull(this.lifecycleMethod.parameterResolver //
 				.resolve(parameterContext, extensionContext, this.arguments, this.invocationIndex,
-					this.resolutionCache);
+					this.resolutionCache));
 	}
 
 	protected void invoke(ExtensionContext context) {
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/AfterParameterizedClassInvocation.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/AfterParameterizedClassInvocation.java
index b7cb8fd6341a..1fe278f0267b 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/AfterParameterizedClassInvocation.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/AfterParameterizedClassInvocation.java
@@ -157,7 +157,7 @@
 @Target({ ElementType.ANNOTATION_TYPE, ElementType.METHOD })
 @Retention(RetentionPolicy.RUNTIME)
 @Documented
-@API(status = EXPERIMENTAL, since = "5.13")
+@API(status = EXPERIMENTAL, since = "6.0")
 @ClassTemplateInvocationLifecycleMethod(classTemplateAnnotation = ParameterizedClass.class, lifecycleMethodAnnotation = AfterParameterizedClassInvocation.class)
 public @interface AfterParameterizedClassInvocation {
 
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ArgumentCountValidationMode.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ArgumentCountValidationMode.java
index 2188d8a170b1..b73054060344 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ArgumentCountValidationMode.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ArgumentCountValidationMode.java
@@ -10,6 +10,8 @@
 
 package org.junit.jupiter.params;
 
+import static org.apiguardian.api.API.Status.MAINTAINED;
+
 import org.apiguardian.api.API;
 import org.junit.jupiter.params.provider.ArgumentsSource;
 
@@ -28,7 +30,7 @@
  * @see ParameterizedClass#argumentCountValidation()
  * @see ParameterizedTest#argumentCountValidation()
  */
-@API(status = API.Status.EXPERIMENTAL, since = "5.12")
+@API(status = MAINTAINED, since = "5.13.3")
 public enum ArgumentCountValidationMode {
 
 	/**
@@ -55,5 +57,6 @@ public enum ArgumentCountValidationMode {
 	 * <p>When there are more arguments provided than declared by the
 	 * parameterized class or method, this raises an error.
 	 */
-	STRICT,
+	STRICT
+
 }
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ArgumentCountValidator.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ArgumentCountValidator.java
index 322aa34d557d..135b4986a03c 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ArgumentCountValidator.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ArgumentCountValidator.java
@@ -10,6 +10,8 @@
 
 package org.junit.jupiter.params;
 
+import static java.util.Objects.requireNonNull;
+
 import java.util.Arrays;
 import java.util.Optional;
 
@@ -38,23 +40,21 @@ class ArgumentCountValidator {
 	void validate(ExtensionContext extensionContext) {
 		ArgumentCountValidationMode argumentCountValidationMode = getArgumentCountValidationMode(extensionContext);
 		switch (argumentCountValidationMode) {
-			case DEFAULT:
-			case NONE:
-				return;
-			case STRICT:
+			case DEFAULT, NONE -> {
+			}
+			case STRICT -> {
 				int consumedCount = this.declarationContext.getResolverFacade().determineConsumedArgumentCount(
 					this.arguments);
 				int totalCount = this.arguments.getTotalLength();
-				Preconditions.condition(consumedCount == totalCount, () -> String.format(
-					"Configuration error: @%s consumes %s %s but there %s %s %s provided.%nNote: the provided arguments were %s",
-					this.declarationContext.getAnnotationName(), consumedCount,
-					pluralize(consumedCount, "parameter", "parameters"), pluralize(totalCount, "was", "were"),
-					totalCount, pluralize(totalCount, "argument", "arguments"),
-					Arrays.toString(this.arguments.getAllPayloads())));
-				break;
-			default:
-				throw new ExtensionConfigurationException(
-					"Unsupported argument count validation mode: " + argumentCountValidationMode);
+				Preconditions.condition(consumedCount == totalCount,
+					() -> "Configuration error: @%s consumes %s %s but there %s %s %s provided.%nNote: the provided arguments were %s".formatted(
+						this.declarationContext.getAnnotationName(), consumedCount,
+						pluralize(consumedCount, "parameter", "parameters"), pluralize(totalCount, "was", "were"),
+						totalCount, pluralize(totalCount, "argument", "arguments"),
+						Arrays.toString(this.arguments.getAllPayloads())));
+			}
+			default -> throw new ExtensionConfigurationException(
+				"Unsupported argument count validation mode: " + argumentCountValidationMode);
 		}
 	}
 
@@ -72,7 +72,7 @@ private ArgumentCountValidationMode getArgumentCountValidationModeConfiguration(
 		String key = ARGUMENT_COUNT_VALIDATION_KEY;
 		ArgumentCountValidationMode fallback = ArgumentCountValidationMode.NONE;
 		ExtensionContext.Store store = getStore(extensionContext);
-		return store.getOrComputeIfAbsent(key, __ -> {
+		return requireNonNull(store.getOrComputeIfAbsent(key, __ -> {
 			Optional<String> optionalConfigValue = extensionContext.getConfigurationParameter(key);
 			if (optionalConfigValue.isPresent()) {
 				String configValue = optionalConfigValue.get();
@@ -80,9 +80,9 @@ private ArgumentCountValidationMode getArgumentCountValidationModeConfiguration(
 					ArgumentCountValidationMode.values()).filter(
 						mode -> mode.name().equalsIgnoreCase(configValue)).findFirst();
 				if (enumValue.isPresent()) {
-					logger.config(() -> String.format(
-						"Using ArgumentCountValidationMode '%s' set via the '%s' configuration parameter.",
-						enumValue.get().name(), key));
+					logger.config(
+						() -> "Using ArgumentCountValidationMode '%s' set via the '%s' configuration parameter.".formatted(
+							enumValue.get().name(), key));
 					return enumValue.get();
 				}
 				else {
@@ -96,7 +96,7 @@ private ArgumentCountValidationMode getArgumentCountValidationModeConfiguration(
 			else {
 				return fallback;
 			}
-		}, ArgumentCountValidationMode.class);
+		}, ArgumentCountValidationMode.class));
 	}
 
 	private static String pluralize(int count, String singular, String plural) {
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ArgumentSetLifecycleMethod.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ArgumentSetLifecycleMethod.java
index 13ed374ebf14..834cecb4fb2f 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ArgumentSetLifecycleMethod.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ArgumentSetLifecycleMethod.java
@@ -12,6 +12,7 @@
 
 import java.lang.reflect.Method;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.extension.ExtensionContext;
 import org.junit.jupiter.api.extension.ParameterContext;
 import org.junit.platform.commons.JUnitException;
@@ -51,6 +52,7 @@ public Object resolve(ParameterContext parameterContext, ExtensionContext extens
 
 		boolean supports(ParameterContext parameterContext);
 
+		@Nullable
 		Object resolve(ParameterContext parameterContext, ExtensionContext extensionContext,
 				EvaluatedArgumentSet arguments, int invocationIndex, ResolutionCache resolutionCache);
 
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/BeforeParameterizedClassInvocation.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/BeforeParameterizedClassInvocation.java
index 1391fd5a240e..ff08bd2d5c8d 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/BeforeParameterizedClassInvocation.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/BeforeParameterizedClassInvocation.java
@@ -158,7 +158,7 @@
 @Target({ ElementType.ANNOTATION_TYPE, ElementType.METHOD })
 @Retention(RetentionPolicy.RUNTIME)
 @Documented
-@API(status = EXPERIMENTAL, since = "5.13")
+@API(status = EXPERIMENTAL, since = "6.0")
 @ClassTemplateInvocationLifecycleMethod(classTemplateAnnotation = ParameterizedClass.class, lifecycleMethodAnnotation = BeforeParameterizedClassInvocation.class)
 public @interface BeforeParameterizedClassInvocation {
 
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/DefaultParameterInfo.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/DefaultParameterInfo.java
index 96fffa5039d5..c74ba724ea76 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/DefaultParameterInfo.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/DefaultParameterInfo.java
@@ -18,15 +18,7 @@
 /**
  * @since 5.13
  */
-class DefaultParameterInfo implements ParameterInfo {
-
-	private final ParameterDeclarations declarations;
-	private final ArgumentsAccessor arguments;
-
-	DefaultParameterInfo(ParameterDeclarations declarations, ArgumentsAccessor arguments) {
-		this.declarations = declarations;
-		this.arguments = arguments;
-	}
+record DefaultParameterInfo(ParameterDeclarations declarations, ArgumentsAccessor arguments) implements ParameterInfo {
 
 	@Override
 	public ParameterDeclarations getDeclarations() {
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/EvaluatedArgumentSet.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/EvaluatedArgumentSet.java
index 623f262ddc91..de8573073b55 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/EvaluatedArgumentSet.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/EvaluatedArgumentSet.java
@@ -15,6 +15,7 @@
 import java.util.function.Function;
 import java.util.function.IntUnaryOperator;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Named;
 import org.junit.jupiter.params.provider.Arguments;
 import org.junit.jupiter.params.provider.Arguments.ArgumentSet;
@@ -32,25 +33,29 @@
 class EvaluatedArgumentSet {
 
 	static EvaluatedArgumentSet allOf(Arguments arguments) {
+		@Nullable
 		Object[] all = arguments.get();
 		return create(all, all, arguments);
 	}
 
 	static EvaluatedArgumentSet of(Arguments arguments, IntUnaryOperator consumedLengthComputer) {
+		@Nullable
 		Object[] all = arguments.get();
+		@Nullable
 		Object[] consumed = dropSurplus(all, consumedLengthComputer.applyAsInt(all.length));
 		return create(all, consumed, arguments);
 	}
 
-	private static EvaluatedArgumentSet create(Object[] all, Object[] consumed, Arguments arguments) {
+	private static EvaluatedArgumentSet create(@Nullable Object[] all, @Nullable Object[] consumed,
+			Arguments arguments) {
 		return new EvaluatedArgumentSet(all, consumed, determineName(arguments));
 	}
 
-	private final Object[] all;
-	private final Object[] consumed;
+	private final @Nullable Object[] all;
+	private final @Nullable Object[] consumed;
 	private final Optional<String> name;
 
-	private EvaluatedArgumentSet(Object[] all, Object[] consumed, Optional<String> name) {
+	private EvaluatedArgumentSet(@Nullable Object[] all, @Nullable Object[] consumed, Optional<String> name) {
 		this.all = all;
 		this.consumed = consumed;
 		this.name = name;
@@ -60,6 +65,7 @@ int getTotalLength() {
 		return this.all.length;
 	}
 
+	@Nullable
 	Object[] getAllPayloads() {
 		return extractFromNamed(this.all, Named::getPayload);
 	}
@@ -68,14 +74,17 @@ int getConsumedLength() {
 		return this.consumed.length;
 	}
 
+	@Nullable
 	Object[] getConsumedNames() {
 		return extractFromNamed(this.consumed, Named::getName);
 	}
 
+	@Nullable
 	Object[] getConsumedPayloads() {
 		return extractFromNamed(this.consumed, Named::getPayload);
 	}
 
+	@Nullable
 	Object getConsumedPayload(int index) {
 		return extractFromNamed(this.consumed[index], Named::getPayload);
 	}
@@ -84,28 +93,30 @@ Optional<String> getName() {
 		return this.name;
 	}
 
-	private static Object[] dropSurplus(Object[] arguments, int newLength) {
+	private static @Nullable Object[] dropSurplus(@Nullable Object[] arguments, int newLength) {
 		Preconditions.condition(newLength <= arguments.length,
-			() -> String.format("New length %d must be less than or equal to the total length %d", newLength,
+			() -> "New length %d must be less than or equal to the total length %d".formatted(newLength,
 				arguments.length));
 		return arguments.length > newLength ? Arrays.copyOf(arguments, newLength) : arguments;
 	}
 
 	private static Optional<String> determineName(Arguments arguments) {
-		if (arguments instanceof ArgumentSet) {
-			return Optional.of(((ArgumentSet) arguments).getName());
+		if (arguments instanceof ArgumentSet set) {
+			return Optional.of(set.getName());
 		}
 		return Optional.empty();
 	}
 
-	private static Object[] extractFromNamed(Object[] arguments, Function<Named<?>, Object> mapper) {
+	private static @Nullable Object[] extractFromNamed(@Nullable Object[] arguments,
+			Function<Named<?>, @Nullable Object> mapper) {
 		return Arrays.stream(arguments) //
 				.map(argument -> extractFromNamed(argument, mapper)) //
 				.toArray();
 	}
 
-	private static Object extractFromNamed(Object argument, Function<Named<?>, Object> mapper) {
-		return argument instanceof Named ? mapper.apply((Named<?>) argument) : argument;
+	private static @Nullable Object extractFromNamed(@Nullable Object argument,
+			Function<Named<?>, @Nullable Object> mapper) {
+		return argument instanceof Named<?> named ? mapper.apply(named) : argument;
 	}
 
 }
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/Parameter.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/Parameter.java
index 70325ff71746..a68e943e4124 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/Parameter.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/Parameter.java
@@ -41,7 +41,7 @@
 @Retention(RetentionPolicy.RUNTIME)
 @Target({ ElementType.ANNOTATION_TYPE, ElementType.FIELD })
 @Documented
-@API(status = EXPERIMENTAL, since = "5.13")
+@API(status = EXPERIMENTAL, since = "6.0")
 public @interface Parameter {
 
 	/**
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedClass.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedClass.java
index cf64caaab50d..b01a72c12259 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedClass.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedClass.java
@@ -149,7 +149,7 @@
 @Retention(RetentionPolicy.RUNTIME)
 @Documented
 @Inherited
-@API(status = EXPERIMENTAL, since = "5.13")
+@API(status = EXPERIMENTAL, since = "6.0")
 @ClassTemplate
 @ExtendWith(ParameterizedClassExtension.class)
 @SuppressWarnings("exports")
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedClassContext.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedClassContext.java
index f73fff4e1e23..b6002a4ad817 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedClassContext.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedClassContext.java
@@ -12,14 +12,12 @@
 
 import static java.util.Collections.emptyList;
 import static java.util.Collections.reverse;
-import static org.junit.jupiter.api.TestInstance.Lifecycle.PER_METHOD;
 import static org.junit.platform.commons.support.AnnotationSupport.findAnnotatedMethods;
 import static org.junit.platform.commons.support.AnnotationSupport.findAnnotation;
 import static org.junit.platform.commons.support.AnnotationSupport.isAnnotated;
 import static org.junit.platform.commons.support.HierarchyTraversalMode.BOTTOM_UP;
 import static org.junit.platform.commons.support.HierarchyTraversalMode.TOP_DOWN;
 import static org.junit.platform.commons.support.ReflectionSupport.findFields;
-import static org.junit.platform.commons.util.CollectionUtils.toUnmodifiableList;
 import static org.junit.platform.commons.util.ReflectionUtils.isRecordClass;
 
 import java.lang.annotation.Annotation;
@@ -34,7 +32,6 @@
 import org.junit.jupiter.params.provider.Arguments;
 import org.junit.platform.commons.JUnitException;
 import org.junit.platform.commons.support.HierarchyTraversalMode;
-import org.junit.platform.commons.support.ModifierSupport;
 import org.junit.platform.commons.util.ReflectionUtils;
 
 class ParameterizedClassContext implements ParameterizedDeclarationContext<ClassTemplateInvocationContext> {
@@ -155,9 +152,6 @@ private static <A extends Annotation> List<ArgumentSetLifecycleMethod> findLifec
 		List<Method> methods = findAnnotatedMethods(testClass, annotationType, traversalMode);
 
 		return methods.stream() //
-				.filter(ModifierSupport::isNotPrivate) //
-				.filter(testInstanceLifecycle == PER_METHOD ? ModifierSupport::isStatic : __ -> true) //
-				.filter(ReflectionUtils::returnsPrimitiveVoid) //
 				.map(method -> {
 					A annotation = getAnnotation(method, annotationType);
 					if (injectArgumentsPredicate.test(annotation)) {
@@ -166,7 +160,7 @@ private static <A extends Annotation> List<ArgumentSetLifecycleMethod> findLifec
 					}
 					return new ArgumentSetLifecycleMethod(method);
 				}) //
-				.collect(toUnmodifiableList());
+				.toList();
 	}
 
 	private static <A extends Annotation> A getAnnotation(Method method, Class<A> annotationType) {
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedClassExtension.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedClassExtension.java
index db56de4f8f78..3f134156eba6 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedClassExtension.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedClassExtension.java
@@ -10,6 +10,7 @@
 
 package org.junit.jupiter.params;
 
+import static java.util.Objects.requireNonNull;
 import static org.junit.jupiter.api.TestInstance.Lifecycle.PER_CLASS;
 import static org.junit.jupiter.params.ParameterizedClassContext.InjectionType.CONSTRUCTOR;
 import static org.junit.platform.commons.support.AnnotationSupport.findAnnotation;
@@ -97,7 +98,7 @@ private boolean validateAndStoreClassContext(ExtensionContext extensionContext)
 
 		Optional<ParameterizedClass> annotation = findAnnotation(extensionContext.getTestClass(),
 			ParameterizedClass.class);
-		if (!annotation.isPresent()) {
+		if (annotation.isEmpty()) {
 			return false;
 		}
 
@@ -124,8 +125,8 @@ private static ParameterizedClassContext createClassContext(ExtensionContext ext
 	}
 
 	private ParameterizedClassContext getDeclarationContext(ExtensionContext extensionContext) {
-		return getStore(extensionContext)//
-				.get(DECLARATION_CONTEXT_KEY, ParameterizedClassContext.class);
+		return requireNonNull(getStore(extensionContext)//
+				.get(DECLARATION_CONTEXT_KEY, ParameterizedClassContext.class));
 	}
 
 	private Store getStore(ExtensionContext context) {
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedClassInvocationContext.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedClassInvocationContext.java
index 51f74401b29c..b4d8a5e63122 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedClassInvocationContext.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedClassInvocationContext.java
@@ -10,7 +10,6 @@
 
 package org.junit.jupiter.params;
 
-import static java.util.stream.Collectors.toList;
 import static org.junit.jupiter.api.TestInstance.Lifecycle.PER_METHOD;
 
 import java.util.List;
@@ -22,7 +21,6 @@
 import org.junit.jupiter.api.extension.ExtensionContext;
 import org.junit.jupiter.params.ParameterizedClassContext.InjectionType;
 import org.junit.jupiter.params.provider.Arguments;
-import org.junit.platform.commons.JUnitException;
 import org.junit.platform.commons.util.Preconditions;
 
 class ParameterizedClassInvocationContext extends ParameterizedInvocationContext<ParameterizedClassContext>
@@ -43,7 +41,7 @@ public String getDisplayName(int invocationIndex) {
 	@Override
 	public List<Extension> getAdditionalExtensions() {
 		return Stream.concat(Stream.of(createParameterInjector()), createLifecycleMethodInvokers()) //
-				.collect(toList());
+				.toList();
 	}
 
 	@Override
@@ -53,13 +51,10 @@ public void prepareInvocation(ExtensionContext context) {
 
 	private Extension createParameterInjector() {
 		InjectionType injectionType = this.declarationContext.getInjectionType();
-		switch (injectionType) {
-			case CONSTRUCTOR:
-				return createExtensionForConstructorInjection();
-			case FIELDS:
-				return createExtensionForFieldInjection();
-		}
-		throw new JUnitException("Unsupported injection type: " + injectionType);
+		return switch (injectionType) {
+			case CONSTRUCTOR -> createExtensionForConstructorInjection();
+			case FIELDS -> createExtensionForFieldInjection();
+		};
 	}
 
 	private ClassTemplateConstructorParameterResolver createExtensionForConstructorInjection() {
@@ -72,15 +67,12 @@ private ClassTemplateConstructorParameterResolver createExtensionForConstructorI
 	private Extension createExtensionForFieldInjection() {
 		ResolverFacade resolverFacade = this.declarationContext.getResolverFacade();
 		TestInstance.Lifecycle lifecycle = this.declarationContext.getTestInstanceLifecycle();
-		switch (lifecycle) {
-			case PER_CLASS:
-				return new BeforeClassTemplateInvocationFieldInjector(resolverFacade, this.arguments,
-					this.invocationIndex, this.resolutionCache);
-			case PER_METHOD:
-				return new InstancePostProcessingClassTemplateFieldInjector(resolverFacade, this.arguments,
-					this.invocationIndex, this.resolutionCache);
-		}
-		throw new JUnitException("Unsupported lifecycle: " + lifecycle);
+		return switch (lifecycle) {
+			case PER_CLASS -> new BeforeClassTemplateInvocationFieldInjector(resolverFacade, this.arguments,
+				this.invocationIndex, this.resolutionCache);
+			case PER_METHOD -> new InstancePostProcessingClassTemplateFieldInjector(resolverFacade, this.arguments,
+				this.invocationIndex, this.resolutionCache);
+		};
 	}
 
 	private Stream<Extension> createLifecycleMethodInvokers() {
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedInvocationConstants.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedInvocationConstants.java
index 04eff295b1a2..d3e171868873 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedInvocationConstants.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedInvocationConstants.java
@@ -10,7 +10,6 @@
 
 package org.junit.jupiter.params;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
 import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import org.apiguardian.api.API;
@@ -88,7 +87,7 @@ public class ParameterizedInvocationConstants {
 	 * @see #ARGUMENT_SET_NAME_OR_ARGUMENTS_WITH_NAMES_PLACEHOLDER
 	 * @see org.junit.jupiter.params.provider.Arguments#argumentSet(String, Object...)
 	 */
-	@API(status = EXPERIMENTAL, since = "5.11")
+	@API(status = MAINTAINED, since = "5.13.3")
 	public static final String ARGUMENT_SET_NAME_PLACEHOLDER = "{argumentSetName}";
 
 	/**
@@ -106,7 +105,7 @@ public class ParameterizedInvocationConstants {
 	 * @see #DEFAULT_DISPLAY_NAME
 	 * @see org.junit.jupiter.params.provider.Arguments#argumentSet(String, Object...)
 	 */
-	@API(status = EXPERIMENTAL, since = "5.11")
+	@API(status = MAINTAINED, since = "5.13.3")
 	public static final String ARGUMENT_SET_NAME_OR_ARGUMENTS_WITH_NAMES_PLACEHOLDER = "{argumentSetNameOrArgumentsWithNames}";
 
 	/**
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedInvocationContext.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedInvocationContext.java
index e310abb94843..01e1d1e7f6a7 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedInvocationContext.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedInvocationContext.java
@@ -15,6 +15,7 @@
 import java.util.Arrays;
 import java.util.concurrent.atomic.AtomicInteger;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.extension.ExtensionContext;
 import org.junit.jupiter.api.extension.ExtensionContext.Namespace;
 import org.junit.jupiter.params.aggregator.ArgumentsAccessor;
@@ -71,19 +72,15 @@ private void validateArgumentCount(ExtensionContext context) {
 	private void storeParameterInfo(ExtensionContext context) {
 		ParameterDeclarations declarations = this.declarationContext.getResolverFacade().getIndexedParameterDeclarations();
 		ClassLoader classLoader = getClassLoader(this.declarationContext.getTestClass());
+		@Nullable
 		Object[] arguments = this.arguments.getConsumedPayloads();
 		ArgumentsAccessor accessor = DefaultArgumentsAccessor.create(context, invocationIndex, classLoader, arguments);
 		new DefaultParameterInfo(declarations, accessor).store(context);
 	}
 
 	@SuppressWarnings({ "deprecation", "try" })
-	private static class CloseableArgument implements ExtensionContext.Store.CloseableResource, AutoCloseable {
-
-		private final AutoCloseable autoCloseable;
-
-		CloseableArgument(AutoCloseable autoCloseable) {
-			this.autoCloseable = autoCloseable;
-		}
+	private record CloseableArgument(AutoCloseable autoCloseable)
+			implements ExtensionContext.Store.CloseableResource, AutoCloseable {
 
 		@Override
 		public void close() throws Exception {
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedInvocationContextProvider.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedInvocationContextProvider.java
index 77e5a98059b7..bacf1504fded 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedInvocationContextProvider.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedInvocationContextProvider.java
@@ -55,8 +55,7 @@ protected Stream<T> provideInvocationContexts(ExtensionContext extensionContext,
 	private static <T> void validateInvokedAtLeastOnce(long invocationCount,
 			ParameterizedDeclarationContext<T> declarationContext) {
 		if (invocationCount == 0 && !declarationContext.isAllowingZeroInvocations()) {
-			String message = String.format(
-				"Configuration error: You must configure at least one set of arguments for this @%s",
+			String message = "Configuration error: You must configure at least one set of arguments for this @%s".formatted(
 				declarationContext.getAnnotationName());
 			throw new TemplateInvocationValidationException(message);
 		}
@@ -67,7 +66,7 @@ private static List<ArgumentsSource> collectArgumentSources(ParameterizedDeclara
 			ArgumentsSource.class);
 
 		Preconditions.notEmpty(argumentsSources,
-			() -> String.format("Configuration error: You must configure at least one arguments source for this @%s",
+			() -> "Configuration error: You must configure at least one arguments source for this @%s".formatted(
 				declarationContext.getAnnotationName()));
 
 		return argumentsSources;
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedInvocationNameFormatter.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedInvocationNameFormatter.java
index 1f1e9f103e65..82ac1a6f40a7 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedInvocationNameFormatter.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedInvocationNameFormatter.java
@@ -10,6 +10,7 @@
 
 package org.junit.jupiter.params;
 
+import static java.util.Objects.requireNonNull;
 import static java.util.stream.Collectors.joining;
 import static org.junit.jupiter.params.ParameterizedInvocationConstants.ARGUMENTS_PLACEHOLDER;
 import static org.junit.jupiter.params.ParameterizedInvocationConstants.ARGUMENTS_WITH_NAMES_PLACEHOLDER;
@@ -34,6 +35,7 @@
 import java.util.function.Function;
 import java.util.stream.IntStream;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.extension.ExtensionConfigurationException;
 import org.junit.jupiter.api.extension.ExtensionContext;
 import org.junit.platform.commons.JUnitException;
@@ -59,10 +61,10 @@ static ParameterizedInvocationNameFormatter create(ExtensionContext extensionCon
 				? extensionContext.getConfigurationParameter(DISPLAY_NAME_PATTERN_KEY) //
 						.orElse(DEFAULT_DISPLAY_NAME_PATTERN)
 				: name;
-		pattern = Preconditions.notBlank(pattern.trim(), () -> String.format(
-			"Configuration error: @%s on %s must be declared with a non-empty name.",
-			declarationContext.getAnnotationName(),
-			declarationContext.getResolverFacade().getIndexedParameterDeclarations().getSourceElementDescription()));
+		pattern = Preconditions.notBlank(pattern.trim(),
+			() -> "Configuration error: @%s on %s must be declared with a non-empty name.".formatted(
+				declarationContext.getAnnotationName(),
+				declarationContext.getResolverFacade().getIndexedParameterDeclarations().getSourceElementDescription()));
 
 		int argumentMaxLength = extensionContext.getConfigurationParameter(ARGUMENT_MAX_LENGTH_KEY, Integer::parseInt) //
 				.orElse(512);
@@ -130,7 +132,7 @@ private PartialFormatter[] parse(String pattern, String displayName,
 		return result.toArray(new PartialFormatter[0]);
 	}
 
-	private static PlaceholderPosition findFirstPlaceholder(PartialFormatters formatters, String segment) {
+	private static @Nullable PlaceholderPosition findFirstPlaceholder(PartialFormatters formatters, String segment) {
 		if (segment.length() < formatters.minimumPlaceholderLength) {
 			return null;
 		}
@@ -195,29 +197,11 @@ private static String argumentsPattern(int length) {
 				.collect(joining(", "));
 	}
 
-	private static class PlaceholderPosition {
-
-		final int index;
-		final String placeholder;
-
-		PlaceholderPosition(int index, String placeholder) {
-			this.index = index;
-			this.placeholder = placeholder;
-		}
-
+	private record PlaceholderPosition(int index, String placeholder) {
 	}
 
-	private static class ArgumentsContext {
-
-		private final int invocationIndex;
-		private final Object[] consumedArguments;
-		private final Optional<String> argumentSetName;
-
-		ArgumentsContext(int invocationIndex, Object[] consumedArguments, Optional<String> argumentSetName) {
-			this.invocationIndex = invocationIndex;
-			this.consumedArguments = consumedArguments;
-			this.argumentSetName = argumentSetName;
-		}
+	private record ArgumentsContext(int invocationIndex, @Nullable Object[] consumedArguments,
+			Optional<String> argumentSetName) {
 	}
 
 	@FunctionalInterface
@@ -229,13 +213,7 @@ private interface PartialFormatter {
 
 	}
 
-	private static class ArgumentSetNameFormatter implements PartialFormatter {
-
-		private final String annotationName;
-
-		ArgumentSetNameFormatter(String annotationName) {
-			this.annotationName = annotationName;
-		}
+	private record ArgumentSetNameFormatter(String annotationName) implements PartialFormatter {
 
 		@Override
 		public void append(ArgumentsContext context, StringBuffer result) {
@@ -243,9 +221,9 @@ public void append(ArgumentsContext context, StringBuffer result) {
 				result.append(context.argumentSetName.get());
 				return;
 			}
-			throw new ExtensionConfigurationException(String.format(
-				"When the display name pattern for a @%s contains %s, the arguments must be supplied as an ArgumentSet.",
-				this.annotationName, ARGUMENT_SET_NAME_PLACEHOLDER));
+			throw new ExtensionConfigurationException(
+				"When the display name pattern for a @%s contains %s, the arguments must be supplied as an ArgumentSet.".formatted(
+					this.annotationName, ARGUMENT_SET_NAME_PLACEHOLDER));
 		}
 	}
 
@@ -268,8 +246,9 @@ public synchronized void append(ArgumentsContext context, StringBuffer result) {
 			this.messageFormat.format(makeReadable(context.consumedArguments), result, new FieldPosition(0));
 		}
 
-		private Object[] makeReadable(Object[] arguments) {
+		private @Nullable Object[] makeReadable(@Nullable Object[] arguments) {
 			Format[] formats = messageFormat.getFormatsByArgumentIndex();
+			@Nullable
 			Object[] result = Arrays.copyOf(arguments, Math.min(arguments.length, formats.length), Object[].class);
 			for (int i = 0; i < result.length; i++) {
 				if (formats[i] == null) {
@@ -279,7 +258,7 @@ private Object[] makeReadable(Object[] arguments) {
 			return result;
 		}
 
-		private String truncateIfExceedsMaxLength(String argument) {
+		private @Nullable String truncateIfExceedsMaxLength(@Nullable String argument) {
 			if (argument != null && argument.length() > this.argumentMaxLength) {
 				return argument.substring(0, this.argumentMaxLength - 1) + ELLIPSIS;
 			}
@@ -316,7 +295,7 @@ void put(String placeholder, PartialFormatter formatter) {
 		}
 
 		PartialFormatter get(String placeholder) {
-			return formattersByPlaceholder.get(placeholder);
+			return requireNonNull(formattersByPlaceholder.get(placeholder));
 		}
 
 		Set<String> placeholders() {
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedInvocationParameterResolver.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedInvocationParameterResolver.java
index 84faf1971d23..193aff285e76 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedInvocationParameterResolver.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedInvocationParameterResolver.java
@@ -12,6 +12,7 @@
 
 import java.lang.reflect.Executable;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.extension.ExtensionContext;
 import org.junit.jupiter.api.extension.ParameterContext;
 import org.junit.jupiter.api.extension.ParameterResolutionException;
@@ -50,7 +51,7 @@ public final boolean supportsParameter(ParameterContext parameterContext, Extens
 	}
 
 	@Override
-	public final Object resolveParameter(ParameterContext parameterContext, ExtensionContext extensionContext)
+	public final @Nullable Object resolveParameter(ParameterContext parameterContext, ExtensionContext extensionContext)
 			throws ParameterResolutionException {
 
 		return this.resolverFacade.resolve(parameterContext, extensionContext, this.arguments, this.invocationIndex,
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedTest.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedTest.java
index eb841a9bdc5b..129bde582290 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedTest.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedTest.java
@@ -11,7 +11,7 @@
 package org.junit.jupiter.params;
 
 import static org.apiguardian.api.API.Status.DEPRECATED;
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
 
 import java.lang.annotation.Documented;
@@ -313,7 +313,7 @@
 	 *
 	 * @since 5.12
 	 */
-	@API(status = EXPERIMENTAL, since = "5.12")
+	@API(status = MAINTAINED, since = "5.13.3")
 	boolean allowZeroInvocations() default false;
 
 	/**
@@ -334,7 +334,7 @@
 	 * @since 5.12
 	 * @see ArgumentCountValidationMode
 	 */
-	@API(status = EXPERIMENTAL, since = "5.12")
+	@API(status = MAINTAINED, since = "5.13.3")
 	ArgumentCountValidationMode argumentCountValidation() default ArgumentCountValidationMode.DEFAULT;
 
 }
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedTestExtension.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedTestExtension.java
index 5097d9f02322..31de4ad836aa 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedTestExtension.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedTestExtension.java
@@ -10,6 +10,7 @@
 
 package org.junit.jupiter.params;
 
+import static java.util.Objects.requireNonNull;
 import static org.junit.platform.commons.support.AnnotationSupport.findAnnotation;
 
 import java.util.Optional;
@@ -31,7 +32,7 @@ class ParameterizedTestExtension extends ParameterizedInvocationContextProvider<
 	@Override
 	public boolean supportsTestTemplate(ExtensionContext context) {
 		Optional<ParameterizedTest> annotation = findAnnotation(context.getTestMethod(), ParameterizedTest.class);
-		if (!annotation.isPresent()) {
+		if (annotation.isEmpty()) {
 			return false;
 		}
 
@@ -56,8 +57,8 @@ public boolean mayReturnZeroTestTemplateInvocationContexts(ExtensionContext exte
 	}
 
 	private ParameterizedTestContext getDeclarationContext(ExtensionContext extensionContext) {
-		return getStore(extensionContext)//
-				.get(DECLARATION_CONTEXT_KEY, ParameterizedTestContext.class);
+		return requireNonNull(getStore(extensionContext)//
+				.get(DECLARATION_CONTEXT_KEY, ParameterizedTestContext.class));
 	}
 
 	private ExtensionContext.Store getStore(ExtensionContext context) {
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedTestSpiInstantiator.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedTestSpiInstantiator.java
index 1545d292a062..bed7e1b61a3b 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedTestSpiInstantiator.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedTestSpiInstantiator.java
@@ -49,7 +49,7 @@ private static <T> Constructor<?> findBestConstructor(Class<T> spiInterface,
 			Class<? extends T> implementationClass) {
 
 		Preconditions.condition(!ReflectionUtils.isInnerClass(implementationClass),
-			() -> String.format("The %s [%s] must be either a top-level class or a static nested class",
+			() -> "The %s [%s] must be either a top-level class or a static nested class".formatted(
 				spiInterface.getSimpleName(), implementationClass.getName()));
 
 		Constructor<?>[] constructors = implementationClass.getDeclaredConstructors();
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ResolutionCache.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ResolutionCache.java
index eeec256dccd0..ac013d0ceb70 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ResolutionCache.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ResolutionCache.java
@@ -14,6 +14,7 @@
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.function.Supplier;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.params.support.ParameterDeclaration;
 
 /**
@@ -27,14 +28,15 @@ static ResolutionCache enabled() {
 
 	ResolutionCache DISABLED = (__, resolver) -> resolver.get();
 
-	Object resolve(ParameterDeclaration declaration, Supplier<Object> resolver);
+	@Nullable
+	Object resolve(ParameterDeclaration declaration, Supplier<?> resolver);
 
 	class Concurrent implements ResolutionCache {
 
 		private final Map<ParameterDeclaration, Object> cache = new ConcurrentHashMap<>();
 
 		@Override
-		public Object resolve(ParameterDeclaration declaration, Supplier<Object> resolver) {
+		public @Nullable Object resolve(ParameterDeclaration declaration, Supplier<?> resolver) {
 			return cache.computeIfAbsent(declaration, __ -> resolver.get());
 		}
 	}
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ResolverFacade.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ResolverFacade.java
index a1cad8e98419..3aebf1fe27b1 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ResolverFacade.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/ResolverFacade.java
@@ -11,13 +11,14 @@
 package org.junit.jupiter.params;
 
 import static java.lang.System.lineSeparator;
-import static java.util.Collections.unmodifiableList;
+import static java.util.Objects.requireNonNull;
 import static java.util.stream.Collectors.joining;
-import static java.util.stream.Collectors.toList;
 import static java.util.stream.Collectors.toMap;
 import static org.junit.platform.commons.support.AnnotationSupport.findAnnotation;
 import static org.junit.platform.commons.support.AnnotationSupport.isAnnotated;
 import static org.junit.platform.commons.support.ReflectionSupport.makeAccessible;
+import static org.junit.platform.commons.util.KotlinReflectionUtils.getKotlinSuspendingFunctionParameters;
+import static org.junit.platform.commons.util.KotlinReflectionUtils.isKotlinSuspendingFunction;
 import static org.junit.platform.commons.util.ReflectionUtils.isInnerClass;
 
 import java.lang.annotation.Annotation;
@@ -39,6 +40,7 @@
 import java.util.function.Supplier;
 import java.util.stream.Stream;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.extension.AnnotatedElementContext;
 import org.junit.jupiter.api.extension.ExtensionConfigurationException;
 import org.junit.jupiter.api.extension.ExtensionContext;
@@ -107,6 +109,9 @@ static ResolverFacade create(Constructor<?> constructor, ParameterizedClass anno
 	}
 
 	static ResolverFacade create(Method method, Annotation annotation) {
+		if (isKotlinSuspendingFunction(method)) {
+			return create(method, annotation, 0, getKotlinSuspendingFunctionParameters(method));
+		}
 		return create(method, annotation, 0);
 	}
 
@@ -124,9 +129,13 @@ static ResolverFacade create(Method method, Annotation annotation) {
 	 * </ol>
 	 */
 	private static ResolverFacade create(Executable executable, Annotation annotation, int indexOffset) {
+		return create(executable, annotation, indexOffset, executable.getParameters());
+	}
+
+	private static ResolverFacade create(Executable executable, Annotation annotation, int indexOffset,
+			java.lang.reflect.Parameter[] parameters) {
 		NavigableMap<Integer, ExecutableParameterDeclaration> indexedParameters = new TreeMap<>();
 		NavigableMap<Integer, ExecutableParameterDeclaration> aggregatorParameters = new TreeMap<>();
-		java.lang.reflect.Parameter[] parameters = executable.getParameters();
 		for (int index = indexOffset; index < parameters.length; index++) {
 			ExecutableParameterDeclaration declaration = new ExecutableParameterDeclaration(parameters[index], index,
 				indexOffset);
@@ -232,8 +241,8 @@ ArgumentSetLifecycleMethod.ParameterResolver createLifecycleMethodParameterResol
 				.call(() -> configurationErrorOrSuccess(errors,
 					() -> new DefaultArgumentSetLifecycleMethodParameterResolver(originalResolverFacade,
 						lifecycleMethodResolverFacade, parameterDeclarationMapping))) //
-				.getOrThrow(cause -> new ExtensionConfigurationException(
-					String.format("Invalid @%s lifecycle method declaration: %s",
+				.getNonNullOrThrow(cause -> new ExtensionConfigurationException(
+					"Invalid @%s lifecycle method declaration: %s".formatted(
 						annotation.annotationType().getSimpleName(), method.toGenericString()),
 					cause));
 	}
@@ -242,6 +251,7 @@ ArgumentSetLifecycleMethod.ParameterResolver createLifecycleMethodParameterResol
 	 * Resolve the parameter for the supplied context using the supplied
 	 * arguments.
 	 */
+	@Nullable
 	Object resolve(ParameterContext parameterContext, ExtensionContext extensionContext, EvaluatedArgumentSet arguments,
 			int invocationIndex, ResolutionCache resolutionCache) {
 
@@ -295,8 +305,9 @@ private void setField(Object testInstance, FieldParameterDeclaration declaration
 		}
 	}
 
-	private Object resolve(ResolvableParameterDeclaration parameterDeclaration, ExtensionContext extensionContext,
-			EvaluatedArgumentSet arguments, int invocationIndex, Optional<ParameterContext> parameterContext) {
+	private @Nullable Object resolve(ResolvableParameterDeclaration parameterDeclaration,
+			ExtensionContext extensionContext, EvaluatedArgumentSet arguments, int invocationIndex,
+			Optional<ParameterContext> parameterContext) {
 		Resolver resolver = getResolver(extensionContext, parameterDeclaration);
 		return parameterDeclaration.resolve(resolver, extensionContext, arguments, invocationIndex, parameterContext);
 	}
@@ -338,13 +349,13 @@ private static List<String> validateLifecycleMethodParameters(Method method, Ann
 				break;
 			}
 			if (!actualDeclaration.getParameterType().equals(originalDeclaration.getParameterType())) {
-				errors.add(String.format(
-					"parameter%s with index %d is incompatible with the parameter declared on the parameterized class: expected type '%s' but found '%s'",
-					parameterName(actualDeclaration), parameterIndex, originalDeclaration.getParameterType(),
-					actualDeclaration.getParameterType()));
+				errors.add(
+					"parameter%s with index %d is incompatible with the parameter declared on the parameterized class: expected type '%s' but found '%s'".formatted(
+						parameterName(actualDeclaration), parameterIndex, originalDeclaration.getParameterType(),
+						actualDeclaration.getParameterType()));
 			}
 			else if (findAnnotation(actualDeclaration.getAnnotatedElement(), ConvertWith.class).isPresent()) {
-				errors.add(String.format("parameter%s with index %d must not be annotated with @ConvertWith",
+				errors.add("parameter%s with index %d must not be annotated with @ConvertWith".formatted(
 					parameterName(actualDeclaration), parameterIndex));
 			}
 			else if (errors.isEmpty()) {
@@ -366,7 +377,7 @@ else if (errors.size() == 1) {
 			throw new PreconditionViolationException("Configuration error: " + errors.get(0) + ".");
 		}
 		else {
-			throw new PreconditionViolationException(String.format("%d configuration errors:%n%s", errors.size(),
+			throw new PreconditionViolationException("%d configuration errors:%n%s".formatted(errors.size(),
 				errors.stream().collect(joining(lineSeparator() + "- ", "- ", ""))));
 		}
 	}
@@ -383,28 +394,27 @@ private static void validateIndexedParameters(
 
 		for (int index = 0; index <= indexedParameters.lastKey(); index++) {
 			if (!indexedParameters.containsKey(index)) {
-				errors.add(String.format("no field annotated with @Parameter(%d) declared", index));
+				errors.add("no field annotated with @Parameter(%d) declared".formatted(index));
 			}
 		}
 	}
 
 	private static void validateIndexedParameterDeclarations(int index, List<FieldParameterDeclaration> declarations,
 			List<String> errors) {
-		List<Field> fields = declarations.stream().map(FieldParameterDeclaration::getField).collect(toList());
+		List<Field> fields = declarations.stream().map(FieldParameterDeclaration::getField).toList();
 		if (index < 0) {
 			declarations.stream() //
-					.map(declaration -> String.format(
-						"index must be greater than or equal to zero in @Parameter(%d) annotation on field [%s]", index,
-						declaration.getField())) //
+					.map(
+						declaration -> "index must be greater than or equal to zero in @Parameter(%d) annotation on field [%s]".formatted(
+							index, declaration.getField())) //
 					.forEach(errors::add);
 		}
 		else if (declarations.size() > 1) {
-			errors.add(
-				String.format("duplicate index declared in @Parameter(%d) annotation on fields %s", index, fields));
+			errors.add("duplicate index declared in @Parameter(%d) annotation on fields %s".formatted(index, fields));
 		}
 		fields.stream() //
 				.filter(ModifierSupport::isFinal) //
-				.map(field -> String.format("@Parameter field [%s] must not be declared as final", field)) //
+				.map("@Parameter field [%s] must not be declared as final"::formatted) //
 				.forEach(errors::add);
 	}
 
@@ -412,9 +422,9 @@ private static void validateAggregatorParameters(Set<FieldParameterDeclaration>
 			List<String> errors) {
 		aggregatorParameters.stream() //
 				.filter(declaration -> declaration.getParameterIndex() != Parameter.UNSET_INDEX) //
-				.map(declaration -> String.format(
-					"no index may be declared in @Parameter(%d) annotation on aggregator field [%s]",
-					declaration.getParameterIndex(), declaration.getField())) //
+				.map(
+					declaration -> "no index may be declared in @Parameter(%d) annotation on aggregator field [%s]".formatted(
+						declaration.getParameterIndex(), declaration.getField())) //
 				.forEach(errors::add);
 	}
 
@@ -457,29 +467,25 @@ private static ParameterResolutionException parameterResolutionException(String
 
 	private interface Resolver {
 
+		@Nullable
 		Object resolve(ParameterContext parameterContext, int parameterIndex, ExtensionContext extensionContext,
 				EvaluatedArgumentSet arguments, int invocationIndex);
 
+		@Nullable
 		Object resolve(FieldContext fieldContext, ExtensionContext extensionContext, EvaluatedArgumentSet arguments,
 				int invocationIndex);
 
 	}
 
-	private static class Converter implements Resolver {
-
-		private final ArgumentConverter argumentConverter;
+	private record Converter(ArgumentConverter argumentConverter) implements Resolver {
 
 		private static Converter createDefault(ExtensionContext context) {
 			return new Converter(new DefaultArgumentConverter(context));
 		}
 
-		Converter(ArgumentConverter argumentConverter) {
-			this.argumentConverter = argumentConverter;
-		}
-
 		@Override
-		public Object resolve(ParameterContext parameterContext, int parameterIndex, ExtensionContext extensionContext,
-				EvaluatedArgumentSet arguments, int invocationIndex) {
+		public @Nullable Object resolve(ParameterContext parameterContext, int parameterIndex,
+				ExtensionContext extensionContext, EvaluatedArgumentSet arguments, int invocationIndex) {
 			Object argument = arguments.getConsumedPayload(parameterIndex);
 			try {
 				return this.argumentConverter.convert(argument, parameterContext);
@@ -490,7 +496,7 @@ public Object resolve(ParameterContext parameterContext, int parameterIndex, Ext
 		}
 
 		@Override
-		public Object resolve(FieldContext fieldContext, ExtensionContext extensionContext,
+		public @Nullable Object resolve(FieldContext fieldContext, ExtensionContext extensionContext,
 				EvaluatedArgumentSet arguments, int invocationIndex) {
 			Object argument = arguments.getConsumedPayload(fieldContext.getParameterIndex());
 			try {
@@ -502,7 +508,7 @@ public Object resolve(FieldContext fieldContext, ExtensionContext extensionConte
 		}
 	}
 
-	private static class Aggregator implements Resolver {
+	private record Aggregator(ArgumentsAggregator argumentsAggregator) implements Resolver {
 
 		private static final Aggregator DEFAULT = new Aggregator(new SimpleArgumentsAggregator() {
 			@Override
@@ -512,16 +518,10 @@ protected Object aggregateArguments(ArgumentsAccessor accessor, Class<?> targetT
 			}
 		});
 
-		private final ArgumentsAggregator argumentsAggregator;
-
-		Aggregator(ArgumentsAggregator argumentsAggregator) {
-			this.argumentsAggregator = argumentsAggregator;
-		}
-
 		@Override
-		public Object resolve(ParameterContext parameterContext, int parameterIndex, ExtensionContext extensionContext,
-				EvaluatedArgumentSet arguments, int invocationIndex) {
-			ArgumentsAccessor accessor = ParameterInfo.get(extensionContext).getArguments();
+		public @Nullable Object resolve(ParameterContext parameterContext, int parameterIndex,
+				ExtensionContext extensionContext, EvaluatedArgumentSet arguments, int invocationIndex) {
+			ArgumentsAccessor accessor = requireNonNull(ParameterInfo.get(extensionContext)).getArguments();
 			try {
 				return this.argumentsAggregator.aggregateArguments(accessor, parameterContext);
 			}
@@ -532,9 +532,9 @@ public Object resolve(ParameterContext parameterContext, int parameterIndex, Ext
 		}
 
 		@Override
-		public Object resolve(FieldContext fieldContext, ExtensionContext extensionContext,
+		public @Nullable Object resolve(FieldContext fieldContext, ExtensionContext extensionContext,
 				EvaluatedArgumentSet arguments, int invocationIndex) {
-			ArgumentsAccessor accessor = ParameterInfo.get(extensionContext).getArguments();
+			ArgumentsAccessor accessor = requireNonNull(ParameterInfo.get(extensionContext)).getArguments();
 			try {
 				return this.argumentsAggregator.aggregateArguments(accessor, fieldContext);
 			}
@@ -545,16 +545,9 @@ public Object resolve(FieldContext fieldContext, ExtensionContext extensionConte
 		}
 	}
 
-	private static class DefaultParameterDeclarations implements ParameterDeclarations {
-
-		private final AnnotatedElement sourceElement;
-		private final NavigableMap<Integer, ? extends ResolvableParameterDeclaration> declarationsByIndex;
-
-		DefaultParameterDeclarations(AnnotatedElement sourceElement,
-				NavigableMap<Integer, ? extends ResolvableParameterDeclaration> declarationsByIndex) {
-			this.sourceElement = sourceElement;
-			this.declarationsByIndex = declarationsByIndex;
-		}
+	private record DefaultParameterDeclarations(AnnotatedElement sourceElement,
+			NavigableMap<Integer, ? extends ResolvableParameterDeclaration> declarationsByIndex)
+			implements ParameterDeclarations {
 
 		@Override
 		public AnnotatedElement getSourceElement() {
@@ -570,7 +563,7 @@ public Optional<ParameterDeclaration> getFirst() {
 
 		@Override
 		public List<ParameterDeclaration> getAll() {
-			return unmodifiableList(new ArrayList<>(this.declarationsByIndex.values()));
+			return List.copyOf(this.declarationsByIndex.values());
 		}
 
 		@Override
@@ -584,14 +577,14 @@ public String getSourceElementDescription() {
 		}
 
 		static String describe(AnnotatedElement sourceElement) {
-			if (sourceElement instanceof Method) {
-				return String.format("method [%s]", ((Method) sourceElement).toGenericString());
+			if (sourceElement instanceof Method method) {
+				return "method [%s]".formatted(method.toGenericString());
 			}
-			if (sourceElement instanceof Constructor) {
-				return String.format("constructor [%s]", ((Constructor<?>) sourceElement).toGenericString());
+			if (sourceElement instanceof Constructor<?> constructor) {
+				return "constructor [%s]".formatted(constructor.toGenericString());
 			}
-			if (sourceElement instanceof Class) {
-				return String.format("class [%s]", ((Class<?>) sourceElement).getName());
+			if (sourceElement instanceof Class<?> clazz) {
+				return "class [%s]".formatted(clazz.getName());
 			}
 			return sourceElement.toString();
 		}
@@ -610,7 +603,7 @@ boolean isAggregator() {
 					|| isAnnotated(getAnnotatedElement(), AggregateWith.class);
 		}
 
-		protected abstract Object resolve(Resolver resolver, ExtensionContext extensionContext,
+		protected abstract @Nullable Object resolve(Resolver resolver, ExtensionContext extensionContext,
 				EvaluatedArgumentSet arguments, int invocationIndex,
 				Optional<ParameterContext> originalParameterContext);
 	}
@@ -651,8 +644,9 @@ public Optional<String> getParameterName() {
 		}
 
 		@Override
-		public Object resolve(Resolver resolver, ExtensionContext extensionContext, EvaluatedArgumentSet arguments,
-				int invocationIndex, Optional<ParameterContext> originalParameterContext) {
+		public @Nullable Object resolve(Resolver resolver, ExtensionContext extensionContext,
+				EvaluatedArgumentSet arguments, int invocationIndex,
+				Optional<ParameterContext> originalParameterContext) {
 			return resolver.resolve(this, extensionContext, arguments, invocationIndex);
 		}
 	}
@@ -690,8 +684,9 @@ public Optional<String> getParameterName() {
 		}
 
 		@Override
-		public Object resolve(Resolver resolver, ExtensionContext extensionContext, EvaluatedArgumentSet arguments,
-				int invocationIndex, Optional<ParameterContext> originalParameterContext) {
+		public @Nullable Object resolve(Resolver resolver, ExtensionContext extensionContext,
+				EvaluatedArgumentSet arguments, int invocationIndex,
+				Optional<ParameterContext> originalParameterContext) {
 			ParameterContext parameterContext = originalParameterContext //
 					.filter(it -> it.getParameter().equals(this.parameter)) //
 					.orElseGet(() -> toParameterContext(extensionContext, originalParameterContext));
@@ -702,7 +697,7 @@ public Object resolve(Resolver resolver, ExtensionContext extensionContext, Eval
 		private ParameterContext toParameterContext(ExtensionContext extensionContext,
 				Optional<ParameterContext> originalParameterContext) {
 			Optional<Object> target = originalParameterContext.flatMap(ParameterContext::getTarget);
-			if (!target.isPresent()) {
+			if (target.isEmpty()) {
 				target = extensionContext.getTestInstance();
 			}
 			return toParameterContext(target);
@@ -728,21 +723,11 @@ public Optional<Object> getTarget() {
 		}
 	}
 
-	private static class DefaultArgumentSetLifecycleMethodParameterResolver
+	private record DefaultArgumentSetLifecycleMethodParameterResolver(ResolverFacade originalResolverFacade,
+			ResolverFacade lifecycleMethodResolverFacade,
+			Map<ParameterDeclaration, ResolvableParameterDeclaration> parameterDeclarationMapping)
 			implements ArgumentSetLifecycleMethod.ParameterResolver {
 
-		private final ResolverFacade originalResolverFacade;
-		private final ResolverFacade lifecycleMethodResolverFacade;
-		private final Map<ParameterDeclaration, ResolvableParameterDeclaration> parameterDeclarationMapping;
-
-		DefaultArgumentSetLifecycleMethodParameterResolver(ResolverFacade originalResolverFacade,
-				ResolverFacade lifecycleMethodResolverFacade,
-				Map<ParameterDeclaration, ResolvableParameterDeclaration> parameterDeclarationMapping) {
-			this.originalResolverFacade = originalResolverFacade;
-			this.lifecycleMethodResolverFacade = lifecycleMethodResolverFacade;
-			this.parameterDeclarationMapping = parameterDeclarationMapping;
-		}
-
 		@Override
 		public boolean supports(ParameterContext parameterContext) {
 			return this.lifecycleMethodResolverFacade.findDeclaration(parameterContext.getIndex()) //
@@ -751,7 +736,7 @@ public boolean supports(ParameterContext parameterContext) {
 		}
 
 		@Override
-		public Object resolve(ParameterContext parameterContext, ExtensionContext extensionContext,
+		public @Nullable Object resolve(ParameterContext parameterContext, ExtensionContext extensionContext,
 				EvaluatedArgumentSet arguments, int invocationIndex, ResolutionCache resolutionCache) {
 
 			ResolvableParameterDeclaration actualDeclaration = this.lifecycleMethodResolverFacade //
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/aggregator/ArgumentAccessException.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/aggregator/ArgumentAccessException.java
index dbdad3cf0d7f..3a52c9812a4b 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/aggregator/ArgumentAccessException.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/aggregator/ArgumentAccessException.java
@@ -12,6 +12,8 @@
 
 import static org.apiguardian.api.API.Status.STABLE;
 
+import java.io.Serial;
+
 import org.apiguardian.api.API;
 import org.junit.platform.commons.JUnitException;
 
@@ -26,6 +28,7 @@
 @API(status = STABLE, since = "5.7")
 public class ArgumentAccessException extends JUnitException {
 
+	@Serial
 	private static final long serialVersionUID = 1L;
 
 	public ArgumentAccessException(String message) {
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/aggregator/ArgumentsAccessor.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/aggregator/ArgumentsAccessor.java
index 5e31a35d288c..536c19db6a19 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/aggregator/ArgumentsAccessor.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/aggregator/ArgumentsAccessor.java
@@ -15,6 +15,7 @@
 import java.util.List;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 
 /**
  * {@code ArgumentsAccessor} defines the public API for accessing arguments provided
@@ -52,6 +53,7 @@ public interface ArgumentsAccessor {
 	 * equal to zero and less than {@link #size}
 	 * @return the value at the given index, potentially {@code null}
 	 */
+	@Nullable
 	Object get(int index) throws ArgumentAccessException;
 
 	/**
@@ -63,7 +65,7 @@ public interface ArgumentsAccessor {
 	 * @param requiredType the required type of the value; never {@code null}
 	 * @return the value at the given index, potentially {@code null}
 	 */
-	<T> T get(int index, Class<T> requiredType) throws ArgumentAccessException;
+	<T> @Nullable T get(int index, Class<T> requiredType) throws ArgumentAccessException;
 
 	/**
 	 * Get the value of the argument at the given index as a {@link Character},
@@ -75,6 +77,7 @@ public interface ArgumentsAccessor {
 	 * @throws ArgumentAccessException if the value cannot be accessed
 	 * or converted to the desired type
 	 */
+	@Nullable
 	Character getCharacter(int index) throws ArgumentAccessException;
 
 	/**
@@ -87,6 +90,7 @@ public interface ArgumentsAccessor {
 	 * @throws ArgumentAccessException if the value cannot be accessed
 	 * or converted to the desired type
 	 */
+	@Nullable
 	Boolean getBoolean(int index) throws ArgumentAccessException;
 
 	/**
@@ -99,6 +103,7 @@ public interface ArgumentsAccessor {
 	 * @throws ArgumentAccessException if the value cannot be accessed
 	 * or converted to the desired type
 	 */
+	@Nullable
 	Byte getByte(int index) throws ArgumentAccessException;
 
 	/**
@@ -111,6 +116,7 @@ public interface ArgumentsAccessor {
 	 * @throws ArgumentAccessException if the value cannot be accessed
 	 * or converted to the desired type
 	 */
+	@Nullable
 	Short getShort(int index) throws ArgumentAccessException;
 
 	/**
@@ -123,6 +129,7 @@ public interface ArgumentsAccessor {
 	 * @throws ArgumentAccessException if the value cannot be accessed
 	 * or converted to the desired type
 	 */
+	@Nullable
 	Integer getInteger(int index) throws ArgumentAccessException;
 
 	/**
@@ -135,6 +142,7 @@ public interface ArgumentsAccessor {
 	 * @throws ArgumentAccessException if the value cannot be accessed
 	 * or converted to the desired type
 	 */
+	@Nullable
 	Long getLong(int index) throws ArgumentAccessException;
 
 	/**
@@ -147,6 +155,7 @@ public interface ArgumentsAccessor {
 	 * @throws ArgumentAccessException if the value cannot be accessed
 	 * or converted to the desired type
 	 */
+	@Nullable
 	Float getFloat(int index) throws ArgumentAccessException;
 
 	/**
@@ -159,6 +168,7 @@ public interface ArgumentsAccessor {
 	 * @throws ArgumentAccessException if the value cannot be accessed
 	 * or converted to the desired type
 	 */
+	@Nullable
 	Double getDouble(int index) throws ArgumentAccessException;
 
 	/**
@@ -171,6 +181,7 @@ public interface ArgumentsAccessor {
 	 * @throws ArgumentAccessException if the value cannot be accessed
 	 * or converted to the desired type
 	 */
+	@Nullable
 	String getString(int index) throws ArgumentAccessException;
 
 	/**
@@ -181,12 +192,13 @@ public interface ArgumentsAccessor {
 	/**
 	 * Get all arguments in this accessor as an array.
 	 */
+	@Nullable
 	Object[] toArray();
 
 	/**
 	 * Get all arguments in this accessor as an immutable list.
 	 */
-	List<Object> toList();
+	List<@Nullable Object> toList();
 
 	/**
 	 * Get the index of the current test invocation.
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/aggregator/ArgumentsAggregationException.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/aggregator/ArgumentsAggregationException.java
index f2c80d0910b7..af251259e560 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/aggregator/ArgumentsAggregationException.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/aggregator/ArgumentsAggregationException.java
@@ -12,6 +12,8 @@
 
 import static org.apiguardian.api.API.Status.STABLE;
 
+import java.io.Serial;
+
 import org.apiguardian.api.API;
 import org.junit.platform.commons.JUnitException;
 
@@ -26,6 +28,7 @@
 @API(status = STABLE, since = "5.7")
 public class ArgumentsAggregationException extends JUnitException {
 
+	@Serial
 	private static final long serialVersionUID = 1L;
 
 	public ArgumentsAggregationException(String message) {
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/aggregator/ArgumentsAggregator.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/aggregator/ArgumentsAggregator.java
index 905b69e8fe33..9dd598971388 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/aggregator/ArgumentsAggregator.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/aggregator/ArgumentsAggregator.java
@@ -14,6 +14,7 @@
 import static org.apiguardian.api.API.Status.STABLE;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.extension.ParameterContext;
 import org.junit.jupiter.api.extension.ParameterResolver;
 import org.junit.jupiter.params.support.FieldContext;
@@ -65,6 +66,7 @@ public interface ArgumentsAggregator {
 	 * @throws ArgumentsAggregationException if an error occurs during the
 	 * aggregation
 	 */
+	@Nullable
 	Object aggregateArguments(ArgumentsAccessor accessor, ParameterContext context)
 			throws ArgumentsAggregationException;
 
@@ -82,8 +84,8 @@ Object aggregateArguments(ArgumentsAccessor accessor, ParameterContext context)
 	 * aggregation
 	 * @since 5.13
 	 */
-	@API(status = EXPERIMENTAL, since = "5.13")
-	default Object aggregateArguments(ArgumentsAccessor accessor, FieldContext context)
+	@API(status = EXPERIMENTAL, since = "6.0")
+	default @Nullable Object aggregateArguments(ArgumentsAccessor accessor, FieldContext context)
 			throws ArgumentsAggregationException {
 		throw new JUnitException(
 			String.format("ArgumentsAggregator does not override the convert(ArgumentsAccessor, FieldContext) method. "
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/aggregator/DefaultArgumentsAccessor.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/aggregator/DefaultArgumentsAccessor.java
index 40bf7213e1c7..80376859b3da 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/aggregator/DefaultArgumentsAccessor.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/aggregator/DefaultArgumentsAccessor.java
@@ -10,7 +10,6 @@
 
 package org.junit.jupiter.params.aggregator;
 
-import static java.lang.String.format;
 import static org.apiguardian.api.API.Status.INTERNAL;
 
 import java.util.Arrays;
@@ -19,6 +18,7 @@
 import java.util.function.BiFunction;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.extension.ExtensionContext;
 import org.junit.jupiter.params.converter.DefaultArgumentConverter;
 import org.junit.platform.commons.util.ClassUtils;
@@ -38,35 +38,38 @@
 public class DefaultArgumentsAccessor implements ArgumentsAccessor {
 
 	private final int invocationIndex;
-	private final Object[] arguments;
-	private final BiFunction<Object, Class<?>, Object> converter;
+	private final @Nullable Object[] arguments;
+	private final BiFunction<@Nullable Object, Class<?>, @Nullable Object> converter;
 
 	public static DefaultArgumentsAccessor create(ExtensionContext context, int invocationIndex,
-			ClassLoader classLoader, Object[] arguments) {
+			ClassLoader classLoader, @Nullable Object[] arguments) {
 		Preconditions.notNull(classLoader, "ClassLoader must not be null");
 
-		BiFunction<Object, Class<?>, Object> converter = (source, targetType) -> new DefaultArgumentConverter(context) //
-				.convert(source, targetType, classLoader);
+		BiFunction<@Nullable Object, Class<?>, @Nullable Object> converter = (source,
+				targetType) -> new DefaultArgumentConverter(context) //
+						.convert(source, targetType, classLoader);
 		return new DefaultArgumentsAccessor(converter, invocationIndex, arguments);
 	}
 
-	private DefaultArgumentsAccessor(BiFunction<Object, Class<?>, Object> converter, int invocationIndex,
-			Object... arguments) {
+	private DefaultArgumentsAccessor(BiFunction<@Nullable Object, Class<?>, @Nullable Object> converter,
+			int invocationIndex, @Nullable Object... arguments) {
+		Preconditions.notNull(converter, "Converter must not be null");
 		Preconditions.condition(invocationIndex >= 1, () -> "Invocation index must be >= 1");
-		this.converter = Preconditions.notNull(converter, "Converter must not be null");
+		Preconditions.notNull(arguments, "Arguments array must not be null");
+		this.converter = converter;
 		this.invocationIndex = invocationIndex;
-		this.arguments = Preconditions.notNull(arguments, "Arguments array must not be null");
+		this.arguments = arguments;
 	}
 
 	@Override
-	public Object get(int index) {
+	public @Nullable Object get(int index) {
 		Preconditions.condition(index >= 0 && index < this.arguments.length,
-			() -> format("index must be >= 0 and < %d", this.arguments.length));
+			() -> "index must be >= 0 and < %d".formatted(this.arguments.length));
 		return this.arguments[index];
 	}
 
 	@Override
-	public <T> T get(int index, Class<T> requiredType) {
+	public <T> @Nullable T get(int index, Class<T> requiredType) {
 		Preconditions.notNull(requiredType, "requiredType must not be null");
 		Object value = get(index);
 		try {
@@ -74,8 +77,7 @@ public <T> T get(int index, Class<T> requiredType) {
 			return requiredType.cast(convertedValue);
 		}
 		catch (Exception ex) {
-			String message = format(
-				"Argument at index [%d] with value [%s] and type [%s] could not be converted or cast to type [%s].",
+			String message = "Argument at index [%d] with value [%s] and type [%s] could not be converted or cast to type [%s].".formatted(
 				index, value, ClassUtils.nullSafeToString(value == null ? null : value.getClass()),
 				requiredType.getName());
 			throw new ArgumentAccessException(message, ex);
@@ -83,47 +85,47 @@ public <T> T get(int index, Class<T> requiredType) {
 	}
 
 	@Override
-	public Character getCharacter(int index) {
+	public @Nullable Character getCharacter(int index) {
 		return get(index, Character.class);
 	}
 
 	@Override
-	public Boolean getBoolean(int index) {
+	public @Nullable Boolean getBoolean(int index) {
 		return get(index, Boolean.class);
 	}
 
 	@Override
-	public Byte getByte(int index) {
+	public @Nullable Byte getByte(int index) {
 		return get(index, Byte.class);
 	}
 
 	@Override
-	public Short getShort(int index) {
+	public @Nullable Short getShort(int index) {
 		return get(index, Short.class);
 	}
 
 	@Override
-	public Integer getInteger(int index) {
+	public @Nullable Integer getInteger(int index) {
 		return get(index, Integer.class);
 	}
 
 	@Override
-	public Long getLong(int index) {
+	public @Nullable Long getLong(int index) {
 		return get(index, Long.class);
 	}
 
 	@Override
-	public Float getFloat(int index) {
+	public @Nullable Float getFloat(int index) {
 		return get(index, Float.class);
 	}
 
 	@Override
-	public Double getDouble(int index) {
+	public @Nullable Double getDouble(int index) {
 		return get(index, Double.class);
 	}
 
 	@Override
-	public String getString(int index) {
+	public @Nullable String getString(int index) {
 		return get(index, String.class);
 	}
 
@@ -133,13 +135,13 @@ public int size() {
 	}
 
 	@Override
-	public Object[] toArray() {
+	public @Nullable Object[] toArray() {
 		return Arrays.copyOf(this.arguments, this.arguments.length);
 	}
 
 	@Override
-	public List<Object> toList() {
-		return Collections.unmodifiableList(Arrays.asList(this.arguments));
+	public List<@Nullable Object> toList() {
+		return Collections.<@Nullable Object> unmodifiableList(Arrays.asList(this.arguments));
 	}
 
 	@Override
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/aggregator/SimpleArgumentsAggregator.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/aggregator/SimpleArgumentsAggregator.java
index 25373b624f75..e05b83e1d1c0 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/aggregator/SimpleArgumentsAggregator.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/aggregator/SimpleArgumentsAggregator.java
@@ -13,6 +13,7 @@
 import static org.apiguardian.api.API.Status.EXPERIMENTAL;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.extension.AnnotatedElementContext;
 import org.junit.jupiter.api.extension.ParameterContext;
 import org.junit.jupiter.params.support.FieldContext;
@@ -25,24 +26,24 @@
  * @since 5.0
  * @see ArgumentsAggregator
  */
-@API(status = EXPERIMENTAL, since = "5.13")
+@API(status = EXPERIMENTAL, since = "6.0")
 public abstract class SimpleArgumentsAggregator implements ArgumentsAggregator {
 
 	public SimpleArgumentsAggregator() {
 	}
 
 	@Override
-	public Object aggregateArguments(ArgumentsAccessor accessor, ParameterContext context)
+	public @Nullable Object aggregateArguments(ArgumentsAccessor accessor, ParameterContext context)
 			throws ArgumentsAggregationException {
 		return aggregateArguments(accessor, context.getParameter().getType(), context, context.getIndex());
 	}
 
 	@Override
-	public Object aggregateArguments(ArgumentsAccessor accessor, FieldContext context)
+	public @Nullable Object aggregateArguments(ArgumentsAccessor accessor, FieldContext context)
 			throws ArgumentsAggregationException {
-		return aggregateArguments(accessor, null, context, context.getParameterIndex());
+		return aggregateArguments(accessor, context.getField().getType(), context, context.getParameterIndex());
 	}
 
-	protected abstract Object aggregateArguments(ArgumentsAccessor accessor, Class<?> targetType,
+	protected abstract @Nullable Object aggregateArguments(ArgumentsAccessor accessor, Class<?> targetType,
 			AnnotatedElementContext context, int parameterIndex) throws ArgumentsAggregationException;
 }
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/aggregator/package-info.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/aggregator/package-info.java
index e7129488d84f..a56f2a1280a1 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/aggregator/package-info.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/aggregator/package-info.java
@@ -4,4 +4,7 @@
  * {@link org.junit.jupiter.params.aggregator.AggregateWith} annotation.
  */
 
+@NullMarked
 package org.junit.jupiter.params.aggregator;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/converter/AnnotationBasedArgumentConverter.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/converter/AnnotationBasedArgumentConverter.java
index 40dc578f40b4..5619958a28d8 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/converter/AnnotationBasedArgumentConverter.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/converter/AnnotationBasedArgumentConverter.java
@@ -10,11 +10,13 @@
 
 package org.junit.jupiter.params.converter;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static java.util.Objects.requireNonNull;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import java.lang.annotation.Annotation;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.extension.ParameterContext;
 import org.junit.jupiter.params.support.AnnotationConsumer;
 import org.junit.jupiter.params.support.FieldContext;
@@ -30,29 +32,31 @@
  * @see AnnotationConsumer
  * @see SimpleArgumentConverter
  */
-@API(status = EXPERIMENTAL, since = "5.10")
+@API(status = MAINTAINED, since = "5.13.3")
 public abstract class AnnotationBasedArgumentConverter<A extends Annotation>
 		implements ArgumentConverter, AnnotationConsumer<A> {
 
+	private @Nullable A annotation;
+
 	public AnnotationBasedArgumentConverter() {
 	}
 
-	private A annotation;
-
 	@Override
 	public final void accept(A annotation) {
-		Preconditions.notNull(annotation, "annotation must not be null");
-		this.annotation = annotation;
+		this.annotation = Preconditions.notNull(annotation, "annotation must not be null");
+
 	}
 
 	@Override
-	public final Object convert(Object source, ParameterContext context) throws ArgumentConversionException {
-		return convert(source, context.getParameter().getType(), this.annotation);
+	public final @Nullable Object convert(@Nullable Object source, ParameterContext context)
+			throws ArgumentConversionException {
+		return convert(source, context.getParameter().getType(), requireNonNull(this.annotation));
 	}
 
 	@Override
-	public final Object convert(Object source, FieldContext context) throws ArgumentConversionException {
-		return convert(source, context.getField().getType(), this.annotation);
+	public final @Nullable Object convert(@Nullable Object source, FieldContext context)
+			throws ArgumentConversionException {
+		return convert(source, context.getField().getType(), requireNonNull(this.annotation));
 	}
 
 	/**
@@ -68,7 +72,7 @@ public final Object convert(Object source, FieldContext context) throws Argument
 	 * @throws ArgumentConversionException in case an error occurs during the
 	 * conversion
 	 */
-	protected abstract Object convert(Object source, Class<?> targetType, A annotation)
+	protected abstract @Nullable Object convert(@Nullable Object source, Class<?> targetType, A annotation)
 			throws ArgumentConversionException;
 
 }
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/converter/ArgumentConversionException.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/converter/ArgumentConversionException.java
index 358d6e122c74..64d5b304aceb 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/converter/ArgumentConversionException.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/converter/ArgumentConversionException.java
@@ -12,7 +12,10 @@
 
 import static org.apiguardian.api.API.Status.STABLE;
 
+import java.io.Serial;
+
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.JUnitException;
 
 /**
@@ -26,13 +29,14 @@
 @API(status = STABLE, since = "5.7")
 public class ArgumentConversionException extends JUnitException {
 
+	@Serial
 	private static final long serialVersionUID = 1L;
 
-	public ArgumentConversionException(String message) {
+	public ArgumentConversionException(@Nullable String message) {
 		super(message);
 	}
 
-	public ArgumentConversionException(String message, Throwable cause) {
+	public ArgumentConversionException(@Nullable String message, @Nullable Throwable cause) {
 		super(message, cause);
 	}
 
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/converter/ArgumentConverter.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/converter/ArgumentConverter.java
index eae935d66e75..16003b8b2c2f 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/converter/ArgumentConverter.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/converter/ArgumentConverter.java
@@ -14,6 +14,7 @@
 import static org.apiguardian.api.API.Status.STABLE;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.extension.ParameterContext;
 import org.junit.jupiter.api.extension.ParameterResolver;
 import org.junit.jupiter.params.support.FieldContext;
@@ -25,8 +26,12 @@
  *
  * <p>Such an {@code ArgumentConverter} is applied to the method parameter
  * of a {@link org.junit.jupiter.params.ParameterizedTest @ParameterizedTest}
- * method with the help of a
- * {@link org.junit.jupiter.params.converter.ConvertWith @ConvertWith} annotation.
+ * or a constructor parameter or
+ * {@link org.junit.jupiter.params.Parameter @Parameter}-annotated field of a
+ * {@link org.junit.jupiter.params.ParameterizedClass @ParameterizedClass} with
+ * the help of a
+ * {@link org.junit.jupiter.params.converter.ConvertWith @ConvertWith}
+ * annotation.
  *
  * <p>Implementations must provide a no-args constructor or a single unambiguous
  * constructor to use {@linkplain ParameterResolver parameter resolution}. They
@@ -64,7 +69,8 @@ public interface ArgumentConverter {
 	 * @throws ArgumentConversionException if an error occurs during the
 	 * conversion
 	 */
-	Object convert(Object source, ParameterContext context) throws ArgumentConversionException;
+	@Nullable
+	Object convert(@Nullable Object source, ParameterContext context) throws ArgumentConversionException;
 
 	/**
 	 * Convert the supplied {@code source} object according to the supplied
@@ -79,8 +85,8 @@ public interface ArgumentConverter {
 	 * conversion
 	 * @since 5.13
 	 */
-	@API(status = EXPERIMENTAL, since = "5.13")
-	default Object convert(Object source, FieldContext context) throws ArgumentConversionException {
+	@API(status = EXPERIMENTAL, since = "6.0")
+	default @Nullable Object convert(@Nullable Object source, FieldContext context) throws ArgumentConversionException {
 		throw new JUnitException(
 			String.format("ArgumentConverter does not override the convert(Object, FieldContext) method. "
 					+ "Please report this issue to the maintainers of %s.",
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/converter/DefaultArgumentConverter.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/converter/DefaultArgumentConverter.java
index eea0e734508a..46c29d6a9cc0 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/converter/DefaultArgumentConverter.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/converter/DefaultArgumentConverter.java
@@ -24,6 +24,7 @@
 import java.util.function.Function;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.extension.ExtensionContext;
 import org.junit.jupiter.api.extension.ParameterContext;
 import org.junit.jupiter.params.support.FieldContext;
@@ -80,20 +81,22 @@ public DefaultArgumentConverter(ExtensionContext context) {
 	}
 
 	@Override
-	public final Object convert(Object source, ParameterContext context) {
+	public final @Nullable Object convert(@Nullable Object source, ParameterContext context) {
 		Class<?> targetType = context.getParameter().getType();
 		ClassLoader classLoader = getClassLoader(context.getDeclaringExecutable().getDeclaringClass());
 		return convert(source, targetType, classLoader);
 	}
 
 	@Override
-	public final Object convert(Object source, FieldContext context) throws ArgumentConversionException {
+	public final @Nullable Object convert(@Nullable Object source, FieldContext context)
+			throws ArgumentConversionException {
+
 		Class<?> targetType = context.getField().getType();
 		ClassLoader classLoader = getClassLoader(context.getField().getDeclaringClass());
 		return convert(source, targetType, classLoader);
 	}
 
-	public final Object convert(Object source, Class<?> targetType, ClassLoader classLoader) {
+	public final @Nullable Object convert(@Nullable Object source, Class<?> targetType, ClassLoader classLoader) {
 		if (source == null) {
 			if (targetType.isPrimitive()) {
 				throw new ArgumentConversionException(
@@ -106,22 +109,21 @@ public final Object convert(Object source, Class<?> targetType, ClassLoader clas
 			return source;
 		}
 
-		if (source instanceof String) {
+		if (source instanceof String string) {
 			if (targetType == Locale.class && getLocaleConversionFormat() == LocaleConversionFormat.BCP_47) {
-				return Locale.forLanguageTag((String) source);
+				return Locale.forLanguageTag(string);
 			}
 
 			try {
-				return convert((String) source, targetType, classLoader);
+				return convert(string, targetType, classLoader);
 			}
 			catch (ConversionException ex) {
 				throw new ArgumentConversionException(ex.getMessage(), ex);
 			}
 		}
 
-		throw new ArgumentConversionException(
-			String.format("No built-in converter for source type %s and target type %s",
-				source.getClass().getTypeName(), targetType.getTypeName()));
+		throw new ArgumentConversionException("No built-in converter for source type %s and target type %s".formatted(
+			source.getClass().getTypeName(), targetType.getTypeName()));
 	}
 
 	private LocaleConversionFormat getLocaleConversionFormat() {
@@ -129,7 +131,8 @@ private LocaleConversionFormat getLocaleConversionFormat() {
 				.orElse(LocaleConversionFormat.BCP_47);
 	}
 
-	Object convert(String source, Class<?> targetType, ClassLoader classLoader) {
+	@Nullable
+	Object convert(@Nullable String source, Class<?> targetType, ClassLoader classLoader) {
 		return ConversionSupport.convert(source, targetType, classLoader);
 	}
 
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/converter/JavaTimeArgumentConverter.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/converter/JavaTimeArgumentConverter.java
index 6684b472ff18..f91d22d0cf65 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/converter/JavaTimeArgumentConverter.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/converter/JavaTimeArgumentConverter.java
@@ -27,6 +27,8 @@
 import java.util.LinkedHashMap;
 import java.util.Map;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * @since 5.0
  */
@@ -50,7 +52,9 @@ class JavaTimeArgumentConverter extends AnnotationBasedArgumentConverter<JavaTim
 	}
 
 	@Override
-	protected Object convert(Object input, Class<?> targetClass, JavaTimeConversionPattern annotation) {
+	protected @Nullable Object convert(@Nullable Object input, Class<?> targetClass,
+			JavaTimeConversionPattern annotation) {
+
 		if (input == null) {
 			if (annotation.nullable()) {
 				return null;
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/converter/JavaTimeConversionPattern.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/converter/JavaTimeConversionPattern.java
index c667722c6d8f..8559eebab160 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/converter/JavaTimeConversionPattern.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/converter/JavaTimeConversionPattern.java
@@ -10,7 +10,7 @@
 
 package org.junit.jupiter.params.converter;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
 
 import java.lang.annotation.Documented;
@@ -57,7 +57,7 @@
 	 *
 	 * @since 5.12
 	 */
-	@API(status = EXPERIMENTAL, since = "5.12")
+	@API(status = MAINTAINED, since = "5.13.3")
 	boolean nullable() default false;
 
 }
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/converter/SimpleArgumentConverter.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/converter/SimpleArgumentConverter.java
index 2cb0f3f922a6..8ef7a6235104 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/converter/SimpleArgumentConverter.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/converter/SimpleArgumentConverter.java
@@ -13,6 +13,7 @@
 import static org.apiguardian.api.API.Status.STABLE;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.extension.ParameterContext;
 import org.junit.jupiter.params.support.FieldContext;
 
@@ -33,12 +34,14 @@ public SimpleArgumentConverter() {
 	}
 
 	@Override
-	public final Object convert(Object source, ParameterContext context) throws ArgumentConversionException {
+	public final @Nullable Object convert(@Nullable Object source, ParameterContext context)
+			throws ArgumentConversionException {
 		return convert(source, context.getParameter().getType());
 	}
 
 	@Override
-	public final Object convert(Object source, FieldContext context) throws ArgumentConversionException {
+	public final @Nullable Object convert(@Nullable Object source, FieldContext context)
+			throws ArgumentConversionException {
 		return convert(source, context.getField().getType());
 	}
 
@@ -54,6 +57,7 @@ public final Object convert(Object source, FieldContext context) throws Argument
 	 * @throws ArgumentConversionException in case an error occurs during the
 	 * conversion
 	 */
-	protected abstract Object convert(Object source, Class<?> targetType) throws ArgumentConversionException;
+	protected abstract @Nullable Object convert(@Nullable Object source, Class<?> targetType)
+			throws ArgumentConversionException;
 
 }
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/converter/TypedArgumentConverter.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/converter/TypedArgumentConverter.java
index 949cba18590c..b2dda27b4639 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/converter/TypedArgumentConverter.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/converter/TypedArgumentConverter.java
@@ -13,6 +13,7 @@
 import static org.apiguardian.api.API.Status.STABLE;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.extension.ParameterContext;
 import org.junit.jupiter.params.support.FieldContext;
 import org.junit.platform.commons.util.Preconditions;
@@ -30,7 +31,7 @@
  * @see SimpleArgumentConverter
  */
 @API(status = STABLE, since = "5.10")
-public abstract class TypedArgumentConverter<S, T> implements ArgumentConverter {
+public abstract class TypedArgumentConverter<S, T extends @Nullable Object> implements ArgumentConverter {
 
 	private final Class<S> sourceType;
 	private final Class<T> targetType;
@@ -48,27 +49,30 @@ protected TypedArgumentConverter(Class<S> sourceType, Class<T> targetType) {
 	}
 
 	@Override
-	public final Object convert(Object source, ParameterContext context) throws ArgumentConversionException {
+	public final @Nullable Object convert(@Nullable Object source, ParameterContext context)
+			throws ArgumentConversionException {
+
 		return convert(source, context.getParameter().getType());
 	}
 
 	@Override
-	public final Object convert(Object source, FieldContext context) throws ArgumentConversionException {
+	public final @Nullable Object convert(@Nullable Object source, FieldContext context)
+			throws ArgumentConversionException {
+
 		return convert(source, context.getField().getType());
 	}
 
-	private T convert(Object source, Class<?> actualTargetType) {
+	private T convert(@Nullable Object source, Class<?> actualTargetType) {
 		if (source == null) {
 			return convert(null);
 		}
 		if (!this.sourceType.isInstance(source)) {
-			String message = String.format(
-				"%s cannot convert objects of type [%s]. Only source objects of type [%s] are supported.",
+			String message = "%s cannot convert objects of type [%s]. Only source objects of type [%s] are supported.".formatted(
 				getClass().getSimpleName(), source.getClass().getName(), this.sourceType.getName());
 			throw new ArgumentConversionException(message);
 		}
 		if (!ReflectionUtils.isAssignableTo(this.targetType, actualTargetType)) {
-			String message = String.format("%s cannot convert to type [%s]. Only target type [%s] is supported.",
+			String message = "%s cannot convert to type [%s]. Only target type [%s] is supported.".formatted(
 				getClass().getSimpleName(), actualTargetType.getName(), this.targetType.getName());
 			throw new ArgumentConversionException(message);
 		}
@@ -85,6 +89,6 @@ private T convert(Object source, Class<?> actualTargetType) {
 	 * @throws ArgumentConversionException if an error occurs during the
 	 * conversion
 	 */
-	protected abstract T convert(S source) throws ArgumentConversionException;
+	protected abstract T convert(@Nullable S source) throws ArgumentConversionException;
 
 }
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/converter/package-info.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/converter/package-info.java
index ff813c1864f7..6459e382e89f 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/converter/package-info.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/converter/package-info.java
@@ -4,4 +4,7 @@
  * {@link org.junit.jupiter.params.converter.ConvertWith @ConvertWith} annotation.
  */
 
+@NullMarked
 package org.junit.jupiter.params.converter;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/package-info.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/package-info.java
index aa0820df67a8..1261a4a90940 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/package-info.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/package-info.java
@@ -2,4 +2,7 @@
  * JUnit Jupiter extension for parameterized tests.
  */
 
+@NullMarked
 package org.junit.jupiter.params;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/AnnotationBasedArgumentsProvider.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/AnnotationBasedArgumentsProvider.java
index 3abbbe760d15..307e2f4d930e 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/AnnotationBasedArgumentsProvider.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/AnnotationBasedArgumentsProvider.java
@@ -11,7 +11,7 @@
 package org.junit.jupiter.params.provider;
 
 import static org.apiguardian.api.API.Status.DEPRECATED;
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import java.lang.annotation.Annotation;
 import java.util.ArrayList;
@@ -38,7 +38,7 @@
  * @see org.junit.jupiter.params.provider.ArgumentsProvider
  * @see org.junit.jupiter.params.support.AnnotationConsumer
  */
-@API(status = EXPERIMENTAL, since = "5.10")
+@API(status = MAINTAINED, since = "5.13.3")
 public abstract class AnnotationBasedArgumentsProvider<A extends Annotation>
 		implements ArgumentsProvider, AnnotationConsumer<A> {
 
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/Arguments.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/Arguments.java
index bb525eb94648..9b11b7a84f92 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/Arguments.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/Arguments.java
@@ -10,10 +10,11 @@
 
 package org.junit.jupiter.params.provider;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.util.Preconditions;
 
 /**
@@ -24,17 +25,16 @@
  * typically be provided by an {@link ArgumentsProvider}.
  *
  * @apiNote <p>This interface is specifically designed as a simple holder of
- * arguments of a parameterized test. Therefore, if you end up
- * {@linkplain java.util.stream.Stream#map(java.util.function.Function) transforming}
- * or
+ * arguments for a parameterized test. Therefore, if you end up
+ * {@linkplain java.util.stream.Stream#map(java.util.function.Function) transforming} or
  * {@linkplain java.util.stream.Stream#filter(java.util.function.Predicate) filtering}
  * the arguments, you should consider using one of the following in intermediate
  * steps:
  *
  * <ul>
- *   <li>The standard collections</li>
- *   <li>Tuples from third-party libraries, e.g.,
- *   <a href="https://commons.apache.org/proper/commons-lang/apidocs/org/apache/commons/lang3/tuple/package-summary.html">Commons Lang</a>,
+ *   <li>The standard Java collections</li>
+ *   <li>Tuples from third-party libraries &mdash; for example,
+ *   <a href="https://commons.apache.org/proper/commons-lang/apidocs/org/apache/commons/lang3/tuple/package-summary.html">Commons Lang</a>
  *   or <a href="https://www.javatuples.org">javatuples</a></li>
  *   <li>Your own data class</li>
  * </ul>
@@ -50,6 +50,7 @@
  * @see org.junit.jupiter.params.provider.ArgumentsProvider
  * @see org.junit.jupiter.params.converter.ArgumentConverter
  */
+@FunctionalInterface
 @API(status = STABLE, since = "5.7")
 public interface Arguments {
 
@@ -60,8 +61,9 @@ public interface Arguments {
 	 * @apiNote If you need a type-safe way to access some or all of the arguments,
 	 * please read the {@linkplain Arguments class-level API note}.
 	 *
-	 * @return the arguments; never {@code null}
+	 * @return the arguments; never {@code null} but may contain {@code null}
 	 */
+	@Nullable
 	Object[] get();
 
 	/**
@@ -69,12 +71,12 @@ public interface Arguments {
 	 * the supplied {@code arguments}.
 	 *
 	 * @param arguments the arguments to be used for an invocation of the test
-	 * method; must not be {@code null}
+	 * method; must not be {@code null} but may contain {@code null}
 	 * @return an instance of {@code Arguments}; never {@code null}
 	 * @see #arguments(Object...)
 	 * @see #argumentSet(String, Object...)
 	 */
-	static Arguments of(Object... arguments) {
+	static Arguments of(@Nullable Object... arguments) {
 		Preconditions.notNull(arguments, "arguments array must not be null");
 		return () -> arguments;
 	}
@@ -88,12 +90,12 @@ static Arguments of(Object... arguments) {
 	 * {@code import static org.junit.jupiter.params.provider.Arguments.arguments;}
 	 *
 	 * @param arguments the arguments to be used for an invocation of the test
-	 * method; must not be {@code null}
+	 * method; must not be {@code null} but may contain {@code null}
 	 * @return an instance of {@code Arguments}; never {@code null}
 	 * @since 5.3
 	 * @see #argumentSet(String, Object...)
 	 */
-	static Arguments arguments(Object... arguments) {
+	static Arguments arguments(@Nullable Object... arguments) {
 		return of(arguments);
 	}
 
@@ -111,15 +113,15 @@ static Arguments arguments(Object... arguments) {
 	 *
 	 * @param name the name of the argument set; must not be {@code null} or blank
 	 * @param arguments the arguments to be used for an invocation of the test
-	 * method; must not be {@code null}
+	 * method; must not be {@code null} but may contain {@code null}
 	 * @return an {@code ArgumentSet}; never {@code null}
 	 * @since 5.11
 	 * @see ArgumentSet
 	 * @see org.junit.jupiter.params.ParameterizedTest#ARGUMENT_SET_NAME_PLACEHOLDER
 	 * @see org.junit.jupiter.params.ParameterizedTest#ARGUMENT_SET_NAME_OR_ARGUMENTS_WITH_NAMES_PLACEHOLDER
 	 */
-	@API(status = EXPERIMENTAL, since = "5.11")
-	static ArgumentSet argumentSet(String name, Object... arguments) {
+	@API(status = MAINTAINED, since = "5.13.3")
+	static ArgumentSet argumentSet(String name, @Nullable Object... arguments) {
 		return new ArgumentSet(name, arguments);
 	}
 
@@ -132,14 +134,14 @@ static ArgumentSet argumentSet(String name, Object... arguments) {
 	 * @see org.junit.jupiter.params.ParameterizedTest#ARGUMENT_SET_NAME_PLACEHOLDER
 	 * @see org.junit.jupiter.params.ParameterizedTest#ARGUMENT_SET_NAME_OR_ARGUMENTS_WITH_NAMES_PLACEHOLDER
 	 */
-	@API(status = EXPERIMENTAL, since = "5.11")
+	@API(status = MAINTAINED, since = "5.13.3")
 	final class ArgumentSet implements Arguments {
 
 		private final String name;
 
-		private final Object[] arguments;
+		private final @Nullable Object[] arguments;
 
-		private ArgumentSet(String name, Object[] arguments) {
+		private ArgumentSet(String name, @Nullable Object[] arguments) {
 			Preconditions.notBlank(name, "name must not be null or blank");
 			Preconditions.notNull(arguments, "arguments array must not be null");
 			this.name = name;
@@ -155,7 +157,7 @@ public String getName() {
 		}
 
 		@Override
-		public Object[] get() {
+		public @Nullable Object[] get() {
 			return this.arguments;
 		}
 
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/ArgumentsProvider.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/ArgumentsProvider.java
index 058ab4803634..c7f24ed01038 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/ArgumentsProvider.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/ArgumentsProvider.java
@@ -72,7 +72,7 @@ default Stream<? extends Arguments> provideArguments(@SuppressWarnings("unused")
 	 * @return a stream of arguments; never {@code null}
 	 * @since 5.13
 	 */
-	@API(status = EXPERIMENTAL, since = "5.13")
+	@API(status = EXPERIMENTAL, since = "6.0")
 	default Stream<? extends Arguments> provideArguments(ParameterDeclarations parameters, ExtensionContext context)
 			throws Exception {
 		try {
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/ArgumentsUtils.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/ArgumentsUtils.java
index 105d85354079..6c08432e1442 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/ArgumentsUtils.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/ArgumentsUtils.java
@@ -30,20 +30,20 @@ private ArgumentsUtils() {
 	 */
 	static Arguments toArguments(Object item) {
 		// Nothing to do except cast.
-		if (item instanceof Arguments) {
-			return (Arguments) item;
+		if (item instanceof Arguments arguments) {
+			return arguments;
 		}
 
 		// Pass all multidimensional arrays "as is", in contrast to Object[].
-		// See https://github.com/junit-team/junit5/issues/1665
+		// See https://github.com/junit-team/junit-framework/issues/1665
 		if (ReflectionUtils.isMultidimensionalArray(item)) {
 			return arguments(item);
 		}
 
 		// Special treatment for one-dimensional reference arrays.
-		// See https://github.com/junit-team/junit5/issues/1665
-		if (item instanceof Object[]) {
-			return arguments((Object[]) item);
+		// See https://github.com/junit-team/junit-framework/issues/1665
+		if (item instanceof Object[] objects) {
+			return arguments(objects);
 		}
 
 		// Pass everything else "as is".
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/CsvArgumentsProvider.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/CsvArgumentsProvider.java
index f5d25363c379..9a7c4ee47184 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/CsvArgumentsProvider.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/CsvArgumentsProvider.java
@@ -10,20 +10,15 @@
 
 package org.junit.jupiter.params.provider;
 
-import static org.junit.jupiter.params.provider.CsvParserFactory.createParserFor;
-import static org.junit.platform.commons.util.CollectionUtils.toSet;
-
-import java.io.StringReader;
 import java.lang.annotation.Annotation;
 import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.List;
-import java.util.Set;
-import java.util.concurrent.atomic.AtomicInteger;
 import java.util.stream.Stream;
 
-import com.univocity.parsers.csv.CsvParser;
+import de.siegmar.fastcsv.reader.CsvRecord;
+import de.siegmar.fastcsv.reader.NamedCsvRecord;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Named;
 import org.junit.jupiter.api.extension.ExtensionContext;
 import org.junit.jupiter.params.support.ParameterDeclarations;
@@ -36,79 +31,43 @@
  */
 class CsvArgumentsProvider extends AnnotationBasedArgumentsProvider<CsvSource> {
 
-	private static final String LINE_SEPARATOR = "\n";
-
-	private Set<String> nullValues;
-	private CsvParser csvParser;
-
 	@Override
 	protected Stream<? extends Arguments> provideArguments(ParameterDeclarations parameters, ExtensionContext context,
 			CsvSource csvSource) {
-		this.nullValues = toSet(csvSource.nullValues());
-		this.csvParser = createParserFor(csvSource);
-		final boolean textBlockDeclared = !csvSource.textBlock().isEmpty();
-		Preconditions.condition(csvSource.value().length > 0 ^ textBlockDeclared,
-			() -> "@CsvSource must be declared with either `value` or `textBlock` but not both");
 
-		return textBlockDeclared ? parseTextBlock(csvSource) : parseValueArray(csvSource);
-	}
+		CsvReaderFactory.validate(csvSource);
+
+		List<Arguments> arguments = new ArrayList<>();
 
-	private Stream<Arguments> parseTextBlock(CsvSource csvSource) {
-		String textBlock = csvSource.textBlock();
-		boolean useHeadersInDisplayName = csvSource.useHeadersInDisplayName();
-		List<Arguments> argumentsList = new ArrayList<>();
-
-		try {
-			List<String[]> csvRecords = this.csvParser.parseAll(new StringReader(textBlock));
-			String[] headers = useHeadersInDisplayName ? getHeaders(this.csvParser) : null;
-
-			AtomicInteger index = new AtomicInteger(0);
-			for (String[] csvRecord : csvRecords) {
-				index.incrementAndGet();
-				Preconditions.notNull(csvRecord,
-					() -> "Record at index " + index + " contains invalid CSV: \"\"\"\n" + textBlock + "\n\"\"\"");
-				argumentsList.add(processCsvRecord(csvRecord, this.nullValues, useHeadersInDisplayName, headers));
+		try (var reader = CsvReaderFactory.createReaderFor(csvSource, getData(csvSource))) {
+			boolean useHeadersInDisplayName = csvSource.useHeadersInDisplayName();
+			for (CsvRecord record : reader) {
+				arguments.add(processCsvRecord(record, useHeadersInDisplayName));
 			}
 		}
 		catch (Throwable throwable) {
 			throw handleCsvException(throwable, csvSource);
 		}
 
-		return argumentsList.stream();
+		return arguments.stream();
 	}
 
-	private Stream<Arguments> parseValueArray(CsvSource csvSource) {
-		boolean useHeadersInDisplayName = csvSource.useHeadersInDisplayName();
-		List<Arguments> argumentsList = new ArrayList<>();
-
-		try {
-			String[] headers = null;
-			AtomicInteger index = new AtomicInteger(0);
-			for (String input : csvSource.value()) {
-				index.incrementAndGet();
-				String[] csvRecord = this.csvParser.parseLine(input + LINE_SEPARATOR);
-				// Lazily retrieve headers if necessary.
-				if (useHeadersInDisplayName && headers == null) {
-					headers = getHeaders(this.csvParser);
-					continue;
-				}
-				Preconditions.notNull(csvRecord,
-					() -> "Record at index " + index + " contains invalid CSV: \"" + input + "\"");
-				argumentsList.add(processCsvRecord(csvRecord, this.nullValues, useHeadersInDisplayName, headers));
-			}
+	private static String getData(CsvSource csvSource) {
+		var values = csvSource.value();
+		Preconditions.condition(values.length > 0 ^ !csvSource.textBlock().isEmpty(),
+			() -> "@CsvSource must be declared with either `value` or `textBlock` but not both");
+
+		if (!csvSource.textBlock().isEmpty()) {
+			return csvSource.textBlock();
 		}
-		catch (Throwable throwable) {
-			throw handleCsvException(throwable, csvSource);
+		else {
+			for (int i = 0; i < values.length; i++) {
+				int finalI = i;
+				Preconditions.notBlank(values[i],
+					() -> "CSV record at index %d must not be blank".formatted(finalI + 1));
+			}
+			return String.join("\n", values);
 		}
-
-		return argumentsList.stream();
-	}
-
-	// Cannot get parsed headers until after parsing has started.
-	static String[] getHeaders(CsvParser csvParser) {
-		return Arrays.stream(csvParser.getContext().parsedHeaders())//
-				.map(String::trim)//
-				.toArray(String[]::new);
 	}
 
 	/**
@@ -116,33 +75,42 @@ static String[] getHeaders(CsvParser csvParser) {
 	 * {@link Named} if necessary (for CSV header support), and returns the
 	 * CSV record wrapped in an {@link Arguments} instance.
 	 */
-	static Arguments processCsvRecord(Object[] csvRecord, Set<String> nullValues, boolean useHeadersInDisplayName,
-			String[] headers) {
+	static Arguments processCsvRecord(CsvRecord record, boolean useHeadersInDisplayName) {
+		List<String> fields = record.getFields();
+		List<String> headers = useHeadersInDisplayName ? getHeaders(record) : List.of();
 
-		// Nothing to process?
-		if (nullValues.isEmpty() && !useHeadersInDisplayName) {
-			return Arguments.of(csvRecord);
-		}
+		Preconditions.condition(!useHeadersInDisplayName || fields.size() <= headers.size(), //
+			() -> String.format( //
+				"The number of columns (%d) exceeds the number of supplied headers (%d) in CSV record: %s", //
+				fields.size(), headers.size(), fields)); //
 
-		Preconditions.condition(!useHeadersInDisplayName || (csvRecord.length <= headers.length),
-			() -> String.format(
-				"The number of columns (%d) exceeds the number of supplied headers (%d) in CSV record: %s",
-				csvRecord.length, headers.length, Arrays.toString(csvRecord)));
+		@Nullable
+		Object[] arguments = new Object[fields.size()];
 
-		Object[] arguments = new Object[csvRecord.length];
-		for (int i = 0; i < csvRecord.length; i++) {
-			Object column = csvRecord[i];
-			if (nullValues.contains(column)) {
-				column = null;
-			}
+		for (int i = 0; i < fields.size(); i++) {
+			Object argument = resolveNullMarker(fields.get(i));
 			if (useHeadersInDisplayName) {
-				column = Named.of(headers[i] + " = " + column, column);
+				String header = resolveNullMarker(headers.get(i));
+				argument = asNamed(header + " = " + argument, argument);
 			}
-			arguments[i] = column;
+			arguments[i] = argument;
 		}
+
 		return Arguments.of(arguments);
 	}
 
+	private static List<String> getHeaders(CsvRecord record) {
+		return ((NamedCsvRecord) record).getHeader();
+	}
+
+	private static @Nullable String resolveNullMarker(String record) {
+		return record == CsvReaderFactory.DefaultFieldModifier.NULL_MARKER ? null : record;
+	}
+
+	private static Named<@Nullable Object> asNamed(String name, @Nullable Object column) {
+		return Named.<@Nullable Object> of(name, column);
+	}
+
 	/**
 	 * @return this method always throws an exception and therefore never
 	 * returns anything; the return type is merely present to allow this
@@ -150,8 +118,8 @@ static Arguments processCsvRecord(Object[] csvRecord, Set<String> nullValues, bo
 	 */
 	static RuntimeException handleCsvException(Throwable throwable, Annotation annotation) {
 		UnrecoverableExceptions.rethrowIfUnrecoverable(throwable);
-		if (throwable instanceof PreconditionViolationException) {
-			throw (PreconditionViolationException) throwable;
+		if (throwable instanceof PreconditionViolationException exception) {
+			throw exception;
 		}
 		throw new CsvParsingException("Failed to parse CSV input configured via " + annotation, throwable);
 	}
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/CsvFileArgumentsProvider.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/CsvFileArgumentsProvider.java
index f514bb74bed7..128416d91bd7 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/CsvFileArgumentsProvider.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/CsvFileArgumentsProvider.java
@@ -10,28 +10,20 @@
 
 package org.junit.jupiter.params.provider;
 
-import static java.util.Spliterators.spliteratorUnknownSize;
-import static java.util.stream.Collectors.toList;
-import static java.util.stream.StreamSupport.stream;
-import static org.junit.jupiter.params.provider.CsvArgumentsProvider.getHeaders;
-import static org.junit.jupiter.params.provider.CsvArgumentsProvider.handleCsvException;
-import static org.junit.jupiter.params.provider.CsvArgumentsProvider.processCsvRecord;
-import static org.junit.jupiter.params.provider.CsvParserFactory.createParserFor;
-import static org.junit.platform.commons.util.CollectionUtils.toSet;
-
 import java.io.IOException;
 import java.io.InputStream;
 import java.nio.charset.Charset;
 import java.nio.file.Files;
-import java.nio.file.Paths;
+import java.nio.file.Path;
 import java.util.Arrays;
-import java.util.Iterator;
 import java.util.List;
-import java.util.Set;
 import java.util.Spliterator;
+import java.util.function.Consumer;
 import java.util.stream.Stream;
+import java.util.stream.StreamSupport;
 
-import com.univocity.parsers.csv.CsvParser;
+import de.siegmar.fastcsv.reader.CsvReader;
+import de.siegmar.fastcsv.reader.CsvRecord;
 
 import org.junit.jupiter.api.extension.ExtensionContext;
 import org.junit.jupiter.params.support.ParameterDeclarations;
@@ -46,10 +38,6 @@ class CsvFileArgumentsProvider extends AnnotationBasedArgumentsProvider<CsvFileS
 
 	private final InputStreamProvider inputStreamProvider;
 
-	private Charset charset;
-	private int numLinesToSkip;
-	private CsvParser csvParser;
-
 	CsvFileArgumentsProvider() {
 		this(DefaultInputStreamProvider.INSTANCE);
 	}
@@ -61,24 +49,25 @@ class CsvFileArgumentsProvider extends AnnotationBasedArgumentsProvider<CsvFileS
 	@Override
 	protected Stream<? extends Arguments> provideArguments(ParameterDeclarations parameters, ExtensionContext context,
 			CsvFileSource csvFileSource) {
-		this.charset = getCharsetFrom(csvFileSource);
-		this.numLinesToSkip = csvFileSource.numLinesToSkip();
-		this.csvParser = createParserFor(csvFileSource);
+
+		Charset charset = getCharsetFrom(csvFileSource);
+
+		CsvReaderFactory.validate(csvFileSource);
 
 		Stream<Source> resources = Arrays.stream(csvFileSource.resources()).map(inputStreamProvider::classpathResource);
 		Stream<Source> files = Arrays.stream(csvFileSource.files()).map(inputStreamProvider::file);
-		List<Source> sources = Stream.concat(resources, files).collect(toList());
+		List<Source> sources = Stream.concat(resources, files).toList();
 
 		// @formatter:off
 		return Preconditions.notEmpty(sources, "Resources or files must not be empty")
 				.stream()
 				.map(source -> source.open(context))
-				.map(inputStream -> beginParsing(inputStream, csvFileSource))
-				.flatMap(parser -> toStream(parser, csvFileSource));
+				.map(inputStream -> CsvReaderFactory.createReaderFor(csvFileSource, inputStream, charset))
+				.flatMap(reader -> toStream(reader, csvFileSource));
 		// @formatter:on
 	}
 
-	private Charset getCharsetFrom(CsvFileSource csvFileSource) {
+	private static Charset getCharsetFrom(CsvFileSource csvFileSource) {
 		try {
 			return Charset.forName(csvFileSource.encoding());
 		}
@@ -87,79 +76,59 @@ private Charset getCharsetFrom(CsvFileSource csvFileSource) {
 		}
 	}
 
-	private CsvParser beginParsing(InputStream inputStream, CsvFileSource csvFileSource) {
-		try {
-			this.csvParser.beginParsing(inputStream, this.charset);
-		}
-		catch (Throwable throwable) {
-			throw handleCsvException(throwable, csvFileSource);
-		}
-		return this.csvParser;
-	}
-
-	private Stream<Arguments> toStream(CsvParser csvParser, CsvFileSource csvFileSource) {
-		CsvParserIterator iterator = new CsvParserIterator(csvParser, csvFileSource);
-		return stream(spliteratorUnknownSize(iterator, Spliterator.ORDERED), false) //
-				.skip(this.numLinesToSkip) //
+	private static Stream<Arguments> toStream(CsvReader<? extends CsvRecord> reader, CsvFileSource csvFileSource) {
+		var spliterator = CsvExceptionHandlingSpliterator.delegatingTo(reader.spliterator(), csvFileSource);
+		boolean useHeadersInDisplayName = csvFileSource.useHeadersInDisplayName();
+		// @formatter:off
+		return StreamSupport.stream(spliterator, false)
+				.skip(csvFileSource.numLinesToSkip())
+				.map(record -> CsvArgumentsProvider.processCsvRecord(
+						record, useHeadersInDisplayName)
+				)
 				.onClose(() -> {
 					try {
-						csvParser.stopParsing();
+						reader.close();
 					}
 					catch (Throwable throwable) {
-						throw handleCsvException(throwable, csvFileSource);
+						throw CsvArgumentsProvider.handleCsvException(throwable, csvFileSource);
 					}
 				});
+		// @formatter:on
 	}
 
-	private static class CsvParserIterator implements Iterator<Arguments> {
-
-		private final CsvParser csvParser;
-		private final CsvFileSource csvFileSource;
-		private final boolean useHeadersInDisplayName;
-		private final Set<String> nullValues;
-		private Arguments nextArguments;
-		private String[] headers;
-
-		CsvParserIterator(CsvParser csvParser, CsvFileSource csvFileSource) {
-			this.csvParser = csvParser;
-			this.csvFileSource = csvFileSource;
-			this.useHeadersInDisplayName = csvFileSource.useHeadersInDisplayName();
-			this.nullValues = toSet(csvFileSource.nullValues());
-			advance();
-		}
+	private record CsvExceptionHandlingSpliterator<T>(Spliterator<T> delegate, CsvFileSource csvFileSource)
+			implements Spliterator<T> {
 
-		@Override
-		public boolean hasNext() {
-			return this.nextArguments != null;
+		static <T> CsvExceptionHandlingSpliterator<T> delegatingTo(Spliterator<T> delegate,
+				CsvFileSource csvFileSource) {
+			return new CsvExceptionHandlingSpliterator<>(delegate, csvFileSource);
 		}
 
 		@Override
-		public Arguments next() {
-			Arguments result = this.nextArguments;
-			advance();
-			return result;
-		}
-
-		private void advance() {
+		public boolean tryAdvance(final Consumer<? super T> action) {
 			try {
-				String[] csvRecord = this.csvParser.parseNext();
-				if (csvRecord != null) {
-					// Lazily retrieve headers if necessary.
-					if (this.useHeadersInDisplayName && this.headers == null) {
-						this.headers = getHeaders(this.csvParser);
-					}
-					this.nextArguments = processCsvRecord(csvRecord, this.nullValues, this.useHeadersInDisplayName,
-						this.headers);
-				}
-				else {
-					this.nextArguments = null;
-				}
+				return delegate.tryAdvance(action);
 			}
 			catch (Throwable throwable) {
-				throw handleCsvException(throwable, this.csvFileSource);
+				throw CsvArgumentsProvider.handleCsvException(throwable, csvFileSource);
 			}
 		}
 
+		@Override
+		public Spliterator<T> trySplit() {
+			return delegate.trySplit();
+		}
+
+		@Override
+		public long estimateSize() {
+			return delegate.estimateSize();
+		}
+
+		@Override
+		public int characteristics() {
+			return delegate.characteristics();
+		}
+
 	}
 
 	@FunctionalInterface
@@ -201,7 +170,7 @@ public InputStream openClasspathResource(Class<?> baseClass, String path) {
 		public InputStream openFile(String path) {
 			Preconditions.notBlank(path, () -> "File [" + path + "] must not be null or blank");
 			try {
-				return Files.newInputStream(Paths.get(path));
+				return Files.newInputStream(Path.of(path));
 			}
 			catch (IOException e) {
 				throw new JUnitException("File [" + path + "] could not be read", e);
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/CsvFileSource.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/CsvFileSource.java
index 3f06e2ff62f0..b51f27b61637 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/CsvFileSource.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/CsvFileSource.java
@@ -41,6 +41,9 @@
  * <p>The column delimiter (which defaults to a comma ({@code ,})) can be customized
  * via either {@link #delimiter} or {@link #delimiterString}.
  *
+ * <p>The line separator is detected automatically, meaning that any of
+ * {@code "\r"}, {@code "\n"}, or {@code "\r\n"} is treated as a line separator.
+ *
  * <p>In contrast to the default syntax used in {@code @CsvSource}, {@code @CsvFileSource}
  * uses a double quote ({@code "}) as its quote character by default, but this can
  * be changed via {@link #quoteCharacter}. An empty, quoted value ({@code ""})
@@ -101,14 +104,6 @@
 	 */
 	String encoding() default "UTF-8";
 
-	/**
-	 * The line separator to use when reading the CSV files; must consist of 1
-	 * or 2 characters, typically {@code "\r"}, {@code "\n"}, or {@code "\r\n"}.
-	 *
-	 * <p>Defaults to {@code "\n"}.
-	 */
-	String lineSeparator() default "\n";
-
 	/**
 	 * Configures whether the first CSV record should be treated as header names
 	 * for columns.
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/CsvParserFactory.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/CsvParserFactory.java
deleted file mode 100644
index ba1b1c0c34ac..000000000000
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/CsvParserFactory.java
+++ /dev/null
@@ -1,90 +0,0 @@
-/*
- * Copyright 2015-2025 the original author or authors.
- *
- * All rights reserved. This program and the accompanying materials are
- * made available under the terms of the Eclipse Public License v2.0 which
- * accompanies this distribution and is available at
- *
- * https://www.eclipse.org/legal/epl-v20.html
- */
-
-package org.junit.jupiter.params.provider;
-
-import java.lang.annotation.Annotation;
-
-import com.univocity.parsers.csv.CsvParser;
-import com.univocity.parsers.csv.CsvParserSettings;
-
-import org.junit.platform.commons.util.Preconditions;
-
-/**
- * @since 5.6
- */
-class CsvParserFactory {
-
-	private static final String DEFAULT_DELIMITER = ",";
-	private static final String LINE_SEPARATOR = "\n";
-	private static final char EMPTY_CHAR = '\0';
-	private static final boolean COMMENT_PROCESSING_FOR_CSV_FILE_SOURCE = true;
-
-	static CsvParser createParserFor(CsvSource annotation) {
-		String delimiter = selectDelimiter(annotation, annotation.delimiter(), annotation.delimiterString());
-		boolean commentProcessingEnabled = !annotation.textBlock().isEmpty();
-		return createParser(delimiter, LINE_SEPARATOR, annotation.quoteCharacter(), annotation.emptyValue(),
-			annotation.maxCharsPerColumn(), commentProcessingEnabled, annotation.useHeadersInDisplayName(),
-			annotation.ignoreLeadingAndTrailingWhitespace());
-	}
-
-	static CsvParser createParserFor(CsvFileSource annotation) {
-		String delimiter = selectDelimiter(annotation, annotation.delimiter(), annotation.delimiterString());
-		return createParser(delimiter, annotation.lineSeparator(), annotation.quoteCharacter(), annotation.emptyValue(),
-			annotation.maxCharsPerColumn(), COMMENT_PROCESSING_FOR_CSV_FILE_SOURCE,
-			annotation.useHeadersInDisplayName(), annotation.ignoreLeadingAndTrailingWhitespace());
-	}
-
-	private static String selectDelimiter(Annotation annotation, char delimiter, String delimiterString) {
-		Preconditions.condition(delimiter == EMPTY_CHAR || delimiterString.isEmpty(),
-			() -> "The delimiter and delimiterString attributes cannot be set simultaneously in " + annotation);
-
-		if (delimiter != EMPTY_CHAR) {
-			return String.valueOf(delimiter);
-		}
-		if (!delimiterString.isEmpty()) {
-			return delimiterString;
-		}
-		return DEFAULT_DELIMITER;
-	}
-
-	private static CsvParser createParser(String delimiter, String lineSeparator, char quote, String emptyValue,
-			int maxCharsPerColumn, boolean commentProcessingEnabled, boolean headerExtractionEnabled,
-			boolean ignoreLeadingAndTrailingWhitespace) {
-		return new CsvParser(createParserSettings(delimiter, lineSeparator, quote, emptyValue, maxCharsPerColumn,
-			commentProcessingEnabled, headerExtractionEnabled, ignoreLeadingAndTrailingWhitespace));
-	}
-
-	private static CsvParserSettings createParserSettings(String delimiter, String lineSeparator, char quote,
-			String emptyValue, int maxCharsPerColumn, boolean commentProcessingEnabled, boolean headerExtractionEnabled,
-			boolean ignoreLeadingAndTrailingWhitespace) {
-
-		CsvParserSettings settings = new CsvParserSettings();
-		settings.setHeaderExtractionEnabled(headerExtractionEnabled);
-		settings.getFormat().setDelimiter(delimiter);
-		settings.getFormat().setLineSeparator(lineSeparator);
-		settings.getFormat().setQuote(quote);
-		settings.getFormat().setQuoteEscape(quote);
-		settings.setEmptyValue(emptyValue);
-		settings.setCommentProcessingEnabled(commentProcessingEnabled);
-		settings.setAutoConfigurationEnabled(false);
-		settings.setIgnoreLeadingWhitespaces(ignoreLeadingAndTrailingWhitespace);
-		settings.setIgnoreTrailingWhitespaces(ignoreLeadingAndTrailingWhitespace);
-		Preconditions.condition(maxCharsPerColumn > 0 || maxCharsPerColumn == -1,
-			() -> "maxCharsPerColumn must be a positive number or -1: " + maxCharsPerColumn);
-		settings.setMaxCharsPerColumn(maxCharsPerColumn);
-		// Do not use the built-in support for skipping rows/lines since it will
-		// throw an IllegalArgumentException if the file does not contain at least
-		// the number of specified lines to skip.
-		// settings.setNumberOfRowsToSkip(annotation.numLinesToSkip());
-		return settings;
-	}
-
-}
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/CsvParsingException.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/CsvParsingException.java
index b0db31d48b2f..3528e62ee819 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/CsvParsingException.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/CsvParsingException.java
@@ -12,6 +12,8 @@
 
 import static org.apiguardian.api.API.Status.STABLE;
 
+import java.io.Serial;
+
 import org.apiguardian.api.API;
 import org.junit.platform.commons.JUnitException;
 
@@ -25,6 +27,7 @@
 @API(status = STABLE, since = "5.7")
 public class CsvParsingException extends JUnitException {
 
+	@Serial
 	private static final long serialVersionUID = 1L;
 
 	public CsvParsingException(String message) {
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/CsvReaderFactory.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/CsvReaderFactory.java
new file mode 100644
index 000000000000..24420b9eef51
--- /dev/null
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/CsvReaderFactory.java
@@ -0,0 +1,177 @@
+/*
+ * Copyright 2015-2025 the original author or authors.
+ *
+ * All rights reserved. This program and the accompanying materials are
+ * made available under the terms of the Eclipse Public License v2.0 which
+ * accompanies this distribution and is available at
+ *
+ * https://www.eclipse.org/legal/epl-v20.html
+ */
+
+package org.junit.jupiter.params.provider;
+
+import static de.siegmar.fastcsv.reader.CommentStrategy.NONE;
+import static de.siegmar.fastcsv.reader.CommentStrategy.SKIP;
+
+import java.io.InputStream;
+import java.lang.annotation.Annotation;
+import java.nio.charset.Charset;
+import java.util.Set;
+import java.util.UUID;
+
+import de.siegmar.fastcsv.reader.CsvCallbackHandler;
+import de.siegmar.fastcsv.reader.CsvReader;
+import de.siegmar.fastcsv.reader.CsvRecord;
+import de.siegmar.fastcsv.reader.CsvRecordHandler;
+import de.siegmar.fastcsv.reader.FieldModifier;
+import de.siegmar.fastcsv.reader.NamedCsvRecordHandler;
+
+import org.junit.platform.commons.util.Preconditions;
+
+/**
+ * @since 6.0
+ */
+class CsvReaderFactory {
+
+	private static final String DEFAULT_DELIMITER = ",";
+	private static final char EMPTY_CHAR = '\0';
+	private static final boolean SKIP_EMPTY_LINES = true;
+	private static final boolean TRIM_WHITESPACES_AROUND_QUOTES = true;
+	private static final boolean ALLOW_EXTRA_FIELDS = true;
+	private static final boolean ALLOW_MISSING_FIELDS = true;
+	private static final boolean ALLOW_DUPLICATE_HEADER_FIELDS = true;
+	private static final int MAX_FIELDS = 512;
+	private static final int MAX_RECORD_SIZE = Integer.MAX_VALUE;
+
+	static void validate(CsvSource csvSource) {
+		validateMaxCharsPerColumn(csvSource.maxCharsPerColumn());
+		validateDelimiter(csvSource.delimiter(), csvSource.delimiterString(), csvSource);
+	}
+
+	static void validate(CsvFileSource csvFileSource) {
+		validateMaxCharsPerColumn(csvFileSource.maxCharsPerColumn());
+		validateDelimiter(csvFileSource.delimiter(), csvFileSource.delimiterString(), csvFileSource);
+	}
+
+	private static void validateMaxCharsPerColumn(int maxCharsPerColumn) {
+		Preconditions.condition(maxCharsPerColumn > 0 || maxCharsPerColumn == -1,
+			() -> "maxCharsPerColumn must be a positive number or -1: " + maxCharsPerColumn);
+	}
+
+	private static void validateDelimiter(char delimiter, String delimiterString, Annotation annotation) {
+		Preconditions.condition(delimiter == EMPTY_CHAR || delimiterString.isEmpty(),
+			() -> "The delimiter and delimiterString attributes cannot be set simultaneously in " + annotation);
+	}
+
+	static CsvReader<? extends CsvRecord> createReaderFor(CsvSource csvSource, String data) {
+		String delimiter = selectDelimiter(csvSource.delimiter(), csvSource.delimiterString());
+		// @formatter:off
+		var builder = CsvReader.builder()
+				.skipEmptyLines(SKIP_EMPTY_LINES)
+				.trimWhitespacesAroundQuotes(TRIM_WHITESPACES_AROUND_QUOTES)
+				.allowExtraFields(ALLOW_EXTRA_FIELDS)
+				.allowMissingFields(ALLOW_MISSING_FIELDS)
+				.fieldSeparator(delimiter)
+				.quoteCharacter(csvSource.quoteCharacter())
+				.commentStrategy(csvSource.textBlock().isEmpty() ? NONE : SKIP);
+
+		var callbackHandler = createCallbackHandler(
+				csvSource.emptyValue(),
+				Set.of(csvSource.nullValues()),
+				csvSource.ignoreLeadingAndTrailingWhitespace(),
+				csvSource.maxCharsPerColumn(),
+				csvSource.useHeadersInDisplayName()
+		);
+		// @formatter:on
+		return builder.build(callbackHandler, data);
+	}
+
+	static CsvReader<? extends CsvRecord> createReaderFor(CsvFileSource csvFileSource, InputStream inputStream,
+			Charset charset) {
+
+		String delimiter = selectDelimiter(csvFileSource.delimiter(), csvFileSource.delimiterString());
+		// @formatter:off
+		var builder = CsvReader.builder()
+				.skipEmptyLines(SKIP_EMPTY_LINES)
+				.trimWhitespacesAroundQuotes(TRIM_WHITESPACES_AROUND_QUOTES)
+				.allowExtraFields(ALLOW_EXTRA_FIELDS)
+				.allowMissingFields(ALLOW_MISSING_FIELDS)
+				.fieldSeparator(delimiter)
+				.quoteCharacter(csvFileSource.quoteCharacter())
+				.commentStrategy(SKIP);
+
+		var callbackHandler = createCallbackHandler(
+				csvFileSource.emptyValue(),
+				Set.of(csvFileSource.nullValues()),
+				csvFileSource.ignoreLeadingAndTrailingWhitespace(),
+				csvFileSource.maxCharsPerColumn(),
+				csvFileSource.useHeadersInDisplayName()
+		);
+		// @formatter:on
+		return builder.build(callbackHandler, inputStream, charset);
+	}
+
+	private static String selectDelimiter(char delimiter, String delimiterString) {
+		if (delimiter != EMPTY_CHAR) {
+			return String.valueOf(delimiter);
+		}
+		if (!delimiterString.isEmpty()) {
+			return delimiterString;
+		}
+		return DEFAULT_DELIMITER;
+	}
+
+	private static CsvCallbackHandler<? extends CsvRecord> createCallbackHandler(String emptyValue,
+			Set<String> nullValues, boolean ignoreLeadingAndTrailingWhitespaces, int maxCharsPerColumn,
+			boolean useHeadersInDisplayName) {
+
+		int maxFieldSize = maxCharsPerColumn == -1 ? Integer.MAX_VALUE : maxCharsPerColumn;
+		FieldModifier modifier = new DefaultFieldModifier(emptyValue, nullValues, ignoreLeadingAndTrailingWhitespaces);
+
+		// @formatter:off
+		if (useHeadersInDisplayName) {
+			return NamedCsvRecordHandler.builder()
+					.allowDuplicateHeaderFields(ALLOW_DUPLICATE_HEADER_FIELDS)
+					.maxFields(MAX_FIELDS)
+					.maxRecordSize(MAX_RECORD_SIZE)
+					.maxFieldSize(maxFieldSize)
+					.fieldModifier(modifier)
+					.build();
+		}
+		return CsvRecordHandler.builder()
+				.maxFields(MAX_FIELDS)
+				.maxRecordSize(MAX_RECORD_SIZE)
+				.maxFieldSize(maxFieldSize)
+				.fieldModifier(modifier)
+				.build();
+		// @formatter:on
+	}
+
+	record DefaultFieldModifier(String emptyValue, Set<String> nullValues, boolean ignoreLeadingAndTrailingWhitespaces)
+			implements FieldModifier {
+		/**
+		 * Represents a {@code null} value and serves as a workaround
+		 * since FastCSV does not allow the modified field value to be {@code null}.
+		 * <p>
+		 * The marker is generated with a unique ID to ensure it cannot conflict with actual CSV content.
+		 */
+		static final String NULL_MARKER = String.format("<null marker with unique id: %s>", UUID.randomUUID());
+
+		@Override
+		public String modify(long unusedStartingLineNumber, int unusedFieldIdx, boolean quoted, String field) {
+			if (quoted && field.isEmpty() && !emptyValue.isEmpty()) {
+				return emptyValue;
+			}
+			if (!quoted && field.isBlank()) {
+				return NULL_MARKER;
+			}
+			String modifiedField = (!quoted && ignoreLeadingAndTrailingWhitespaces) ? field.strip() : field;
+			if (nullValues.contains(modifiedField)) {
+				return NULL_MARKER;
+			}
+			return modifiedField;
+		}
+
+	}
+
+}
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/CsvSource.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/CsvSource.java
index a06ef984acdd..295add81b394 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/CsvSource.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/CsvSource.java
@@ -91,7 +91,8 @@
 	 * <p>Each value corresponds to a record in a CSV file and will be split using
 	 * the specified {@link #delimiter} or {@link #delimiterString}. Note that
 	 * the first value may optionally be used to supply CSV headers (see
-	 * {@link #useHeadersInDisplayName}).
+	 * {@link #useHeadersInDisplayName}). Moreover, each specified value must
+	 * not be blank.
 	 *
 	 * <p>If <em>text block</em> syntax is supported by your programming language,
 	 * you may find it more convenient to declare your CSV content via the
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/EmptyArgumentsProvider.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/EmptyArgumentsProvider.java
index 65657724932e..9c9b4f5a8173 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/EmptyArgumentsProvider.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/EmptyArgumentsProvider.java
@@ -45,7 +45,7 @@ public Stream<? extends Arguments> provideArguments(ParameterDeclarations parame
 		Optional<ParameterDeclaration> firstParameter = parameters.getFirst();
 
 		Preconditions.condition(firstParameter.isPresent(),
-			() -> String.format("@EmptySource cannot provide an empty argument to %s: no formal parameters declared.",
+			() -> "@EmptySource cannot provide an empty argument to %s: no formal parameters declared.".formatted(
 				parameters.getSourceElementDescription()));
 
 		Class<?> parameterType = firstParameter.get().getParameterType();
@@ -89,7 +89,7 @@ public Stream<? extends Arguments> provideArguments(ParameterDeclarations parame
 		}
 		// else
 		throw new PreconditionViolationException(
-			String.format("@EmptySource cannot provide an empty argument to %s: [%s] is not a supported type.",
+			"@EmptySource cannot provide an empty argument to %s: [%s] is not a supported type.".formatted(
 				parameters.getSourceElementDescription(), parameterType.getName()));
 	}
 
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/EnumArgumentsProvider.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/EnumArgumentsProvider.java
index e234e3a7f722..ce657e281418 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/EnumArgumentsProvider.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/EnumArgumentsProvider.java
@@ -56,8 +56,7 @@ private <E extends Enum<E>> Set<? extends E> getEnumConstants(ParameterDeclarati
 		E from = enumSource.from().isEmpty() ? constants[0] : Enum.valueOf(enumClass, enumSource.from());
 		E to = enumSource.to().isEmpty() ? constants[constants.length - 1] : Enum.valueOf(enumClass, enumSource.to());
 		Preconditions.condition(from.compareTo(to) <= 0,
-			() -> String.format(
-				"Invalid enum range: 'from' (%s) must come before 'to' (%s) in the natural order of enum constants.",
+			() -> "Invalid enum range: 'from' (%s) must come before 'to' (%s) in the natural order of enum constants.".formatted(
 				from, to));
 		return EnumSet.range(from, to);
 	}
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/EnumSource.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/EnumSource.java
index a41b1af29455..000e3460f211 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/EnumSource.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/EnumSource.java
@@ -11,7 +11,7 @@
 package org.junit.jupiter.params.provider;
 
 import static java.util.stream.Collectors.toSet;
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
 
 import java.lang.annotation.Documented;
@@ -109,7 +109,7 @@
 	 *
 	 * @since 5.12
 	 */
-	@API(status = EXPERIMENTAL, since = "5.12")
+	@API(status = MAINTAINED, since = "5.13.3")
 	String from() default "";
 
 	/**
@@ -125,7 +125,7 @@
 	 *
 	 * @since 5.12
 	 */
-	@API(status = EXPERIMENTAL, since = "5.12")
+	@API(status = MAINTAINED, since = "5.13.3")
 	String to() default "";
 
 	/**
@@ -188,7 +188,7 @@ enum Mode {
 		 * @since 5.9
 		 * @see java.util.stream.Stream#noneMatch(java.util.function.Predicate)
 		 */
-		@API(status = EXPERIMENTAL, since = "5.9")
+		@API(status = MAINTAINED, since = "5.13.3")
 		MATCH_NONE(Mode::validatePatterns, (name, patterns) -> patterns.stream().noneMatch(name::matches));
 
 		private final Validator validator;
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/FieldArgumentsProvider.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/FieldArgumentsProvider.java
index 944419c351a6..fb4b47373981 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/FieldArgumentsProvider.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/FieldArgumentsProvider.java
@@ -24,6 +24,7 @@
 import java.util.stream.BaseStream;
 import java.util.stream.Stream;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.extension.ExtensionContext;
 import org.junit.jupiter.params.support.ParameterDeclarations;
 import org.junit.platform.commons.JUnitException;
@@ -60,8 +61,8 @@ protected Stream<? extends Arguments> provideArguments(ParameterDeclarations par
 				.map(field -> validateField(field, testInstance))
 				.map(field -> readField(field, testInstance))
 				.flatMap(fieldValue -> {
-					if (fieldValue instanceof Supplier<?>) {
-						fieldValue = ((Supplier<?>) fieldValue).get();
+					if (fieldValue instanceof Supplier<?> supplier) {
+						fieldValue = supplier.get();
 					}
 					return CollectionUtils.toStream(fieldValue);
 				})
@@ -90,12 +91,12 @@ static Field findField(Class<?> testClass, String fieldName) {
 				.findFirst()//
 				.orElse(null);
 
-		Preconditions.notNull(field,
-			() -> format("Could not find field named [%s] in class [%s]", resolvedFieldName, resolvedClass.getName()));
-		return field;
+		return Preconditions.notNull(field,
+			() -> "Could not find field named [%s] in class [%s]".formatted(resolvedFieldName,
+				resolvedClass.getName()));
 	}
 
-	private static Field validateField(Field field, Object testInstance) {
+	private static Field validateField(Field field, @Nullable Object testInstance) {
 		Preconditions.condition(field.getDeclaringClass().isInstance(testInstance) || ModifierSupport.isStatic(field),
 			() -> format("Field '%s' must be static: local @FieldSource fields must be static "
 					+ "unless the PER_CLASS @TestInstance lifecycle mode is used; "
@@ -104,24 +105,25 @@ private static Field validateField(Field field, Object testInstance) {
 		return field;
 	}
 
-	private static Object readField(Field field, Object testInstance) {
+	@SuppressWarnings("NullAway")
+	private static Object readField(Field field, @Nullable Object testInstance) {
 		Object value = ReflectionSupport.tryToReadFieldValue(field, testInstance).getOrThrow(
-			cause -> new JUnitException(format("Could not read field [%s]", field.getName()), cause));
+			cause -> new JUnitException("Could not read field [%s]".formatted(field.getName()), cause));
 
 		String fieldName = field.getName();
 		String declaringClass = field.getDeclaringClass().getName();
 
 		Preconditions.notNull(value,
-			() -> format("The value of field [%s] in class [%s] must not be null", fieldName, declaringClass));
+			() -> "The value of field [%s] in class [%s] must not be null".formatted(fieldName, declaringClass));
 
 		Preconditions.condition(!(value instanceof BaseStream),
-			() -> format("The value of field [%s] in class [%s] must not be a stream", fieldName, declaringClass));
+			() -> "The value of field [%s] in class [%s] must not be a stream".formatted(fieldName, declaringClass));
 
 		Preconditions.condition(!(value instanceof Iterator),
-			() -> format("The value of field [%s] in class [%s] must not be an Iterator", fieldName, declaringClass));
+			() -> "The value of field [%s] in class [%s] must not be an Iterator".formatted(fieldName, declaringClass));
 
 		Preconditions.condition(isConvertibleToStream(field, value),
-			() -> format("The value of field [%s] in class [%s] must be convertible to a Stream", fieldName,
+			() -> "The value of field [%s] in class [%s] must be convertible to a Stream".formatted(fieldName,
 				declaringClass));
 
 		return value;
@@ -141,21 +143,18 @@ private static boolean isConvertibleToStream(Field field, Object value) {
 		// Check declared type T of Supplier<T>.
 		if (Supplier.class.isAssignableFrom(field.getType())) {
 			Type genericType = field.getGenericType();
-			if (genericType instanceof ParameterizedType) {
-				ParameterizedType parameterizedType = (ParameterizedType) genericType;
+			if (genericType instanceof ParameterizedType parameterizedType) {
 				Type[] typeArguments = parameterizedType.getActualTypeArguments();
 				if (typeArguments.length == 1) {
 					Type type = typeArguments[0];
 					// Handle cases such as Supplier<IntStream>
-					if (type instanceof Class) {
-						Class<?> clazz = (Class<?>) type;
+					if (type instanceof Class<?> clazz) {
 						return CollectionUtils.isConvertibleToStream(clazz);
 					}
 					// Handle cases such as Supplier<Stream<String>>
-					if (type instanceof ParameterizedType) {
-						Type rawType = ((ParameterizedType) type).getRawType();
-						if (rawType instanceof Class<?>) {
-							Class<?> clazz = (Class<?>) rawType;
+					if (type instanceof ParameterizedType innerParameterizedType) {
+						Type rawType = innerParameterizedType.getRawType();
+						if (rawType instanceof Class<?> clazz) {
 							return CollectionUtils.isConvertibleToStream(clazz);
 						}
 					}
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/FieldSource.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/FieldSource.java
index 32666855bb9c..1b01d6c4de90 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/FieldSource.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/FieldSource.java
@@ -10,7 +10,7 @@
 
 package org.junit.jupiter.params.provider;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import java.lang.annotation.Documented;
 import java.lang.annotation.ElementType;
@@ -134,7 +134,7 @@
 @Documented
 @Inherited
 @Repeatable(FieldSources.class)
-@API(status = EXPERIMENTAL, since = "5.11")
+@API(status = MAINTAINED, since = "5.13.3")
 @ArgumentsSource(FieldArgumentsProvider.class)
 @SuppressWarnings("exports")
 public @interface FieldSource {
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/FieldSources.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/FieldSources.java
index b49836cd2543..96f6b0f368dc 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/FieldSources.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/FieldSources.java
@@ -10,7 +10,7 @@
 
 package org.junit.jupiter.params.provider;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import java.lang.annotation.Documented;
 import java.lang.annotation.ElementType;
@@ -41,7 +41,7 @@
 @Retention(RetentionPolicy.RUNTIME)
 @Documented
 @Inherited
-@API(status = EXPERIMENTAL, since = "5.11")
+@API(status = MAINTAINED, since = "5.13.3")
 public @interface FieldSources {
 
 	/**
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/MethodArgumentsProvider.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/MethodArgumentsProvider.java
index 4a67985cac84..227fefc9aa17 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/MethodArgumentsProvider.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/MethodArgumentsProvider.java
@@ -12,7 +12,6 @@
 
 import static java.lang.String.format;
 import static java.util.Arrays.stream;
-import static java.util.stream.Collectors.toList;
 import static org.junit.platform.commons.support.AnnotationSupport.isAnnotated;
 import static org.junit.platform.commons.util.CollectionUtils.isConvertibleToStream;
 
@@ -22,6 +21,7 @@
 import java.util.function.Predicate;
 import java.util.stream.Stream;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.TestFactory;
 import org.junit.jupiter.api.TestTemplate;
@@ -53,7 +53,7 @@ protected Stream<? extends Arguments> provideArguments(ParameterDeclarations par
 		return stream(methodNames)
 				.map(factoryMethodName -> findFactoryMethod(testClass, testMethod, factoryMethodName))
 				.map(factoryMethod -> validateFactoryMethod(factoryMethod, testInstance))
-				.map(factoryMethod -> context.getExecutableInvoker().invoke(factoryMethod, testInstance))
+				.map(factoryMethod -> Preconditions.notNull(context.getExecutableInvoker().invoke(factoryMethod, testInstance), () -> "@MethodSource-referenced method [%s] must not return null".formatted(factoryMethod.toGenericString())))
 				.flatMap(CollectionUtils::toStream)
 				.map(ArgumentsUtils::toArguments);
 		// @formatter:on
@@ -80,9 +80,9 @@ private static Method findFactoryMethod(Class<?> testClass, Optional<Method> tes
 		Method factoryMethod = findFactoryMethodByFullyQualifiedName(testClass, testMethod, factoryMethodName);
 
 		// Ensure factory method has a valid return type and is not a test method.
-		Preconditions.condition(isFactoryMethod.test(factoryMethod), () -> format(
-			"Could not find valid factory method [%s] for test class [%s] but found the following invalid candidate: %s",
-			originalFactoryMethodName, testClass.getName(), factoryMethod));
+		Preconditions.condition(isFactoryMethod.test(factoryMethod),
+			() -> "Could not find valid factory method [%s] for test class [%s] but found the following invalid candidate: %s".formatted(
+				originalFactoryMethodName, testClass.getName(), factoryMethod));
 
 		return factoryMethod;
 	}
@@ -129,7 +129,7 @@ static Method findFactoryMethodByFullyQualifiedName(Class<?> testClass, Optional
 		// If we didn't find an exact match but an explicit parameter list was specified,
 		// that's a user configuration error.
 		Preconditions.condition(!explicitParameterListSpecified,
-			() -> format("Could not find factory method [%s(%s)] in class [%s]", methodName, methodParameters,
+			() -> "Could not find factory method [%s(%s)] in class [%s]".formatted(methodName, methodParameters,
 				className));
 
 		// Otherwise, fall back to the same lenient search semantics that are used
@@ -153,22 +153,21 @@ private static Method findFactoryMethodBySimpleName(Class<?> clazz, Optional<Met
 				&& !candidate.equals(testMethod.orElse(null));
 		List<Method> candidates = ReflectionUtils.findMethods(clazz, isCandidate);
 
-		List<Method> factoryMethods = candidates.stream().filter(isFactoryMethod).collect(toList());
+		List<Method> factoryMethods = candidates.stream().filter(isFactoryMethod).toList();
 
 		Preconditions.notEmpty(factoryMethods, () -> {
 			if (candidates.isEmpty()) {
 				// Report that we didn't find anything.
-				return format("Could not find factory method [%s] in class [%s]", factoryMethodName, clazz.getName());
+				return "Could not find factory method [%s] in class [%s]".formatted(factoryMethodName, clazz.getName());
 			}
 			// If we didn't find the factory method using the isFactoryMethod Predicate, perhaps
 			// the specified factory method has an invalid return type or is a test method.
 			// In that case, we report the invalid candidates that were found.
-			return format(
-				"Could not find valid factory method [%s] in class [%s] but found the following invalid candidates: %s",
+			return "Could not find valid factory method [%s] in class [%s] but found the following invalid candidates: %s".formatted(
 				factoryMethodName, clazz.getName(), candidates);
 		});
 		Preconditions.condition(factoryMethods.size() == 1,
-			() -> format("%d factory methods named [%s] were found in class [%s]: %s", factoryMethods.size(),
+			() -> "%d factory methods named [%s] were found in class [%s]: %s".formatted(factoryMethods.size(),
 				factoryMethodName, clazz.getName(), factoryMethods));
 		return factoryMethods.get(0);
 	}
@@ -178,7 +177,7 @@ private static boolean isTestMethod(Method candidate) {
 				|| isAnnotated(candidate, TestFactory.class);
 	}
 
-	private static Method validateFactoryMethod(Method factoryMethod, Object testInstance) {
+	private static Method validateFactoryMethod(Method factoryMethod, @Nullable Object testInstance) {
 		Preconditions.condition(
 			factoryMethod.getDeclaringClass().isInstance(testInstance) || ReflectionUtils.isStatic(factoryMethod),
 			() -> format("Method '%s' must be static: local factory methods must be static "
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/NullArgumentsProvider.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/NullArgumentsProvider.java
index 8cafbb51e3cf..87ffaf0a38f2 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/NullArgumentsProvider.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/NullArgumentsProvider.java
@@ -14,6 +14,7 @@
 
 import java.util.stream.Stream;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.extension.ExtensionContext;
 import org.junit.jupiter.params.support.ParameterDeclarations;
 import org.junit.platform.commons.util.Preconditions;
@@ -24,12 +25,12 @@
  */
 class NullArgumentsProvider implements ArgumentsProvider {
 
-	private static final Arguments nullArguments = arguments(new Object[] { null });
+	private static final Arguments nullArguments = arguments(new @Nullable Object[] { null });
 
 	@Override
 	public Stream<? extends Arguments> provideArguments(ParameterDeclarations parameters, ExtensionContext context) {
 		Preconditions.condition(parameters.getFirst().isPresent(),
-			() -> String.format("@NullSource cannot provide a null argument to %s: no formal parameters declared.",
+			() -> "@NullSource cannot provide a null argument to %s: no formal parameters declared.".formatted(
 				parameters.getSourceElementDescription()));
 
 		return Stream.of(nullArguments);
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/ValueArgumentsProvider.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/ValueArgumentsProvider.java
index a3a929dfa2ba..2872c51e5ae8 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/ValueArgumentsProvider.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/ValueArgumentsProvider.java
@@ -10,8 +10,6 @@
 
 package org.junit.jupiter.params.provider;
 
-import static java.util.stream.Collectors.toList;
-
 import java.lang.reflect.Array;
 import java.util.Arrays;
 import java.util.List;
@@ -36,7 +34,7 @@ protected Stream<? extends Arguments> provideArguments(ParameterDeclarations par
 
 	private Object[] getArgumentsFromSource(ValueSource valueSource) {
 		// @formatter:off
-		List<Object> arrays =
+		List<?> arrays =
 			Stream.of(
 				valueSource.shorts(),
 				valueSource.bytes(),
@@ -50,7 +48,7 @@ private Object[] getArgumentsFromSource(ValueSource valueSource) {
 				valueSource.classes()
 			)
 			.filter(array -> Array.getLength(array) > 0)
-			.collect(toList());
+			.toList();
 		// @formatter:on
 
 		Preconditions.condition(arrays.size() == 1, () -> "Exactly one type of input must be provided in the @"
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/package-info.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/package-info.java
index a41697ab81e3..adb442e423e5 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/package-info.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/package-info.java
@@ -5,4 +5,7 @@
  * annotations.
  */
 
+@NullMarked
 package org.junit.jupiter.params.provider;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/support/AnnotationConsumerInitializer.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/support/AnnotationConsumerInitializer.java
index 785c9e571fc4..e48a5995a4ea 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/support/AnnotationConsumerInitializer.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/support/AnnotationConsumerInitializer.java
@@ -41,6 +41,7 @@ public final class AnnotationConsumerInitializer {
 	private static final List<AnnotationConsumingMethodSignature> annotationConsumingMethodSignatures = asList( //
 		new AnnotationConsumingMethodSignature("accept", 1, 0), //
 		new AnnotationConsumingMethodSignature("provideArguments", 3, 2), //
+		new AnnotationConsumingMethodSignature("provideArguments", 2, 1), //
 		new AnnotationConsumingMethodSignature("convert", 3, 2));
 
 	private AnnotationConsumerInitializer() {
@@ -49,7 +50,7 @@ private AnnotationConsumerInitializer() {
 
 	@SuppressWarnings({ "unchecked", "rawtypes" })
 	public static <T> T initialize(AnnotatedElement annotatedElement, T annotationConsumerInstance) {
-		if (annotationConsumerInstance instanceof AnnotationConsumer) {
+		if (annotationConsumerInstance instanceof AnnotationConsumer consumer) {
 			Class<? extends Annotation> annotationType = findConsumedAnnotationType(annotationConsumerInstance);
 			List<? extends Annotation> annotations = findAnnotations(annotatedElement, annotationType);
 
@@ -58,8 +59,7 @@ public static <T> T initialize(AnnotatedElement annotatedElement, T annotationCo
 						+ " must be used with an annotation of type " + annotationType.getName());
 			}
 
-			annotations.forEach(annotation -> initializeAnnotationConsumer(
-				(AnnotationConsumer) annotationConsumerInstance, annotation));
+			annotations.forEach(annotation -> initializeAnnotationConsumer(consumer, annotation));
 		}
 		return annotationConsumerInstance;
 	}
@@ -85,7 +85,7 @@ private static Class<? extends Annotation> getAnnotationType(Method method) {
 		int annotationIndex = annotationConsumingMethodSignatures.stream() //
 				.filter(signature -> signature.isMatchingWith(method)) //
 				.findFirst() //
-				.map(AnnotationConsumingMethodSignature::getAnnotationParameterIndex) //
+				.map(AnnotationConsumingMethodSignature::annotationParameterIndex) //
 				.orElse(0);
 
 		return (Class<? extends Annotation>) method.getParameterTypes()[annotationIndex];
@@ -101,17 +101,8 @@ private static <A extends Annotation> void initializeAnnotationConsumer(Annotati
 		}
 	}
 
-	private static class AnnotationConsumingMethodSignature {
-
-		private final String methodName;
-		private final int parameterCount;
-		private final int annotationParameterIndex;
-
-		AnnotationConsumingMethodSignature(String methodName, int parameterCount, int annotationParameterIndex) {
-			this.methodName = methodName;
-			this.parameterCount = parameterCount;
-			this.annotationParameterIndex = annotationParameterIndex;
-		}
+	private record AnnotationConsumingMethodSignature(String methodName, int parameterCount,
+			int annotationParameterIndex) {
 
 		boolean isMatchingWith(Method method) {
 			return method.getName().equals(methodName) //
@@ -119,10 +110,6 @@ boolean isMatchingWith(Method method) {
 					&& method.getParameterTypes()[annotationParameterIndex].isAnnotation();
 		}
 
-		int getAnnotationParameterIndex() {
-			return annotationParameterIndex;
-		}
-
 	}
 
 }
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/support/FieldContext.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/support/FieldContext.java
index 355da13d126e..facf6a65faed 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/support/FieldContext.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/support/FieldContext.java
@@ -28,7 +28,7 @@
  * @see ParameterizedClass
  * @see Parameter
  */
-@API(status = EXPERIMENTAL, since = "5.13")
+@API(status = EXPERIMENTAL, since = "6.0")
 public interface FieldContext extends AnnotatedElementContext {
 
 	/**
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/support/ParameterDeclaration.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/support/ParameterDeclaration.java
index fca970de9df6..1c6bc5e302a5 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/support/ParameterDeclaration.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/support/ParameterDeclaration.java
@@ -24,7 +24,7 @@
  * @since 5.13
  * @see ParameterDeclarations
  */
-@API(status = EXPERIMENTAL, since = "5.13")
+@API(status = EXPERIMENTAL, since = "6.0")
 public interface ParameterDeclaration {
 
 	/**
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/support/ParameterDeclarations.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/support/ParameterDeclarations.java
index bc30402ad63f..07bb229fd5f3 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/support/ParameterDeclarations.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/support/ParameterDeclarations.java
@@ -40,7 +40,7 @@
  * @see org.junit.jupiter.params.ParameterizedClass
  * @see org.junit.jupiter.params.ParameterizedTest
  */
-@API(status = EXPERIMENTAL, since = "5.13")
+@API(status = EXPERIMENTAL, since = "6.0")
 public interface ParameterDeclarations {
 
 	/**
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/support/ParameterInfo.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/support/ParameterInfo.java
index 03fd6b2a811d..9b54ba41125a 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/support/ParameterInfo.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/support/ParameterInfo.java
@@ -13,6 +13,7 @@
 import static org.apiguardian.api.API.Status.EXPERIMENTAL;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.extension.Extension;
 import org.junit.jupiter.api.extension.ExtensionContext;
@@ -49,7 +50,7 @@
  * @see ParameterizedClass
  * @see ParameterizedTest
  */
-@API(status = EXPERIMENTAL, since = "5.13")
+@API(status = EXPERIMENTAL, since = "6.0")
 public interface ParameterInfo {
 
 	/**
@@ -68,7 +69,7 @@ public interface ParameterInfo {
 	 * {@return the closest {@code ParameterInfo} instance for the supplied
 	 * {@code ExtensionContext}; potentially {@code null}}
 	 */
-	static ParameterInfo get(ExtensionContext context) {
+	static @Nullable ParameterInfo get(ExtensionContext context) {
 		return context.getStore(NAMESPACE).get(KEY, ParameterInfo.class);
 	}
 
diff --git a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/support/package-info.java b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/support/package-info.java
index 56772a43120d..866ac5d3c0df 100644
--- a/junit-jupiter-params/src/main/java/org/junit/jupiter/params/support/package-info.java
+++ b/junit-jupiter-params/src/main/java/org/junit/jupiter/params/support/package-info.java
@@ -6,4 +6,7 @@
  * for arguments.
  */
 
+@NullMarked
 package org.junit.jupiter.params.support;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-jupiter-params/src/main/kotlin/org/junit/jupiter/params/aggregator/ArgumentsAccessor.kt b/junit-jupiter-params/src/main/kotlin/org/junit/jupiter/params/aggregator/ArgumentsAccessor.kt
index 7d06dc0aa071..d8a791419aef 100644
--- a/junit-jupiter-params/src/main/kotlin/org/junit/jupiter/params/aggregator/ArgumentsAccessor.kt
+++ b/junit-jupiter-params/src/main/kotlin/org/junit/jupiter/params/aggregator/ArgumentsAccessor.kt
@@ -26,4 +26,4 @@ import org.apiguardian.api.API
  */
 @Suppress("EXTENSION_SHADOWED_BY_MEMBER") // method is in fact not shadowed due to reified type
 inline fun <reified T : Any> ArgumentsAccessor.get(index: Int): T =
-    this.get(index, T::class.java)
+    this.get(index, T::class.java)!!
diff --git a/junit-jupiter-params/src/testFixtures/java/org/junit/jupiter/params/provider/RecordArguments.java b/junit-jupiter-params/src/testFixtures/java/org/junit/jupiter/params/provider/RecordArguments.java
index 96213c64e57e..1ecc810c460c 100644
--- a/junit-jupiter-params/src/testFixtures/java/org/junit/jupiter/params/provider/RecordArguments.java
+++ b/junit-jupiter-params/src/testFixtures/java/org/junit/jupiter/params/provider/RecordArguments.java
@@ -12,12 +12,13 @@
 
 import java.util.Arrays;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.support.ReflectionSupport;
 
 public interface RecordArguments extends Arguments {
 
 	@Override
-	default Object[] get() {
+	default @Nullable Object[] get() {
 		return Arrays.stream(getClass().getRecordComponents()) //
 				.map(component -> ReflectionSupport.invokeMethod(component.getAccessor(), this)) //
 				.toArray();
diff --git a/junit-jupiter/junit-jupiter.gradle.kts b/junit-jupiter/junit-jupiter.gradle.kts
index 83230d0b4226..17073c730817 100644
--- a/junit-jupiter/junit-jupiter.gradle.kts
+++ b/junit-jupiter/junit-jupiter.gradle.kts
@@ -1,5 +1,5 @@
 plugins {
-	id("junitbuild.java-library-conventions")
+	id("junitbuild.java-aggregator-conventions")
 }
 
 description = "JUnit Jupiter (Aggregator)"
@@ -9,7 +9,7 @@ dependencies {
 	api(projects.junitJupiterApi)
 	api(projects.junitJupiterParams)
 
-	runtimeOnly(projects.junitJupiterEngine)
+	implementation(projects.junitJupiterEngine)
 
 	osgiVerification(projects.junitJupiterEngine)
 	osgiVerification(projects.junitPlatformLauncher)
diff --git a/junit-jupiter/src/module/org.junit.jupiter/module-info.java b/junit-jupiter/src/main/java/module-info.java
similarity index 100%
rename from junit-jupiter/src/module/org.junit.jupiter/module-info.java
rename to junit-jupiter/src/main/java/module-info.java
diff --git a/junit-platform-commons/junit-platform-commons.gradle.kts b/junit-platform-commons/junit-platform-commons.gradle.kts
index 3465b0078020..36ebd5359aa9 100644
--- a/junit-platform-commons/junit-platform-commons.gradle.kts
+++ b/junit-platform-commons/junit-platform-commons.gradle.kts
@@ -1,8 +1,8 @@
-import junitbuild.java.UpdateJarAction
+import junitbuild.extensions.javaModuleName
 
 plugins {
-	id("junitbuild.java-library-conventions")
-	id("junitbuild.java-multi-release-sources")
+	id("junitbuild.java-nullability-conventions")
+	id("junitbuild.kotlin-library-conventions")
 	`java-test-fixtures`
 }
 
@@ -12,29 +12,33 @@ dependencies {
 	api(platform(projects.junitBom))
 
 	compileOnlyApi(libs.apiguardian)
-}
+	compileOnlyApi(libs.jspecify)
 
-tasks.jar {
-	val release9ClassesDir = sourceSets.mainRelease9.get().output.classesDirs.singleFile
-	inputs.dir(release9ClassesDir).withPathSensitivity(PathSensitivity.RELATIVE)
-	doLast(objects.newInstance(UpdateJarAction::class).apply {
-		javaLauncher = javaToolchains.launcherFor(java.toolchain)
-		args.addAll(
-			"--file", archiveFile.get().asFile.absolutePath,
-			"--release", "9",
-			"-C", release9ClassesDir.absolutePath, "."
-		)
-	})
+	compileOnly(kotlin("stdlib"))
+	compileOnly(kotlin("reflect"))
+	compileOnly(libs.kotlinx.coroutines)
 }
 
-tasks.codeCoverageClassesJar {
-	exclude("org/junit/platform/commons/util/ModuleUtils.class")
-	exclude("org/junit/platform/commons/util/PackageNameUtils.class")
-	exclude("org/junit/platform/commons/util/ServiceLoaderUtils.class")
+tasks.compileJava {
+	options.compilerArgs.add("-Xlint:-module") // due to qualified exports
+	val moduleName = javaModuleName
+	val mainOutput = files(sourceSets.main.get().output)
+	options.compilerArgumentProviders.add(CommandLineArgumentProvider {
+		listOf("--patch-module", "${moduleName}=${mainOutput.asPath}")
+	})
 }
 
-eclipse {
-	classpath {
-		sourceSets -= project.sourceSets.mainRelease9.get()
+tasks.jar {
+	bundle {
+		val importAPIGuardian: String by extra
+		val importJSpecify: String by extra
+		bnd("""
+			Import-Package: \
+				$importAPIGuardian,\
+				$importJSpecify,\
+				kotlin.*;resolution:="optional",\
+				kotlinx.*;resolution:="optional",\
+				*
+		""")
 	}
 }
diff --git a/junit-platform-commons/src/module/org.junit.platform.commons/module-info.java b/junit-platform-commons/src/main/java/module-info.java
similarity index 92%
rename from junit-platform-commons/src/module/org.junit.platform.commons/module-info.java
rename to junit-platform-commons/src/main/java/module-info.java
index bb545c577f82..c500d7624f09 100644
--- a/junit-platform-commons/src/module/org.junit.platform.commons/module-info.java
+++ b/junit-platform-commons/src/main/java/module-info.java
@@ -16,7 +16,13 @@
 module org.junit.platform.commons {
 	requires java.logging;
 	requires java.management; // needed by RuntimeUtils to determine input arguments
+
 	requires static transitive org.apiguardian.api;
+	requires static transitive org.jspecify;
+
+	requires static kotlin.stdlib;
+	requires static kotlin.reflect;
+	requires static kotlinx.coroutines.core;
 
 	exports org.junit.platform.commons;
 	exports org.junit.platform.commons.annotation;
@@ -30,7 +36,6 @@
 			org.junit.platform.engine,
 			org.junit.platform.launcher,
 			org.junit.platform.reporting,
-			org.junit.platform.runner,
 			org.junit.platform.suite.api,
 			org.junit.platform.suite.engine,
 			org.junit.platform.testkit,
@@ -45,10 +50,8 @@
 			org.junit.jupiter.params,
 			org.junit.platform.console,
 			org.junit.platform.engine,
-			org.junit.platform.jfr,
 			org.junit.platform.launcher,
 			org.junit.platform.reporting,
-			org.junit.platform.runner,
 			org.junit.platform.suite.api,
 			org.junit.platform.suite.commons,
 			org.junit.platform.suite.engine,
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/JUnitException.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/JUnitException.java
index 2dbc032984fd..162514bec3fc 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/JUnitException.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/JUnitException.java
@@ -13,7 +13,10 @@
 import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
 
+import java.io.Serial;
+
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 
 /**
  * Base class for all {@link RuntimeException RuntimeExceptions} thrown
@@ -24,13 +27,14 @@
 @API(status = STABLE, since = "1.5")
 public class JUnitException extends RuntimeException {
 
+	@Serial
 	private static final long serialVersionUID = 1L;
 
-	public JUnitException(String message) {
+	public JUnitException(@Nullable String message) {
 		super(message);
 	}
 
-	public JUnitException(String message, Throwable cause) {
+	public JUnitException(@Nullable String message, @Nullable Throwable cause) {
 		super(message, cause);
 	}
 
@@ -38,7 +42,8 @@ public JUnitException(String message, Throwable cause) {
 	 * @since 1.13
 	 */
 	@API(status = MAINTAINED, since = "1.13")
-	protected JUnitException(String message, Throwable cause, boolean enableSuppression, boolean writableStackTrace) {
+	protected JUnitException(@Nullable String message, @Nullable Throwable cause, boolean enableSuppression,
+			boolean writableStackTrace) {
 		super(message, cause, enableSuppression, writableStackTrace);
 	}
 
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/PreconditionViolationException.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/PreconditionViolationException.java
index 4ae58db3adec..2d9e1a5385f4 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/PreconditionViolationException.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/PreconditionViolationException.java
@@ -12,7 +12,10 @@
 
 import static org.apiguardian.api.API.Status.STABLE;
 
+import java.io.Serial;
+
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 
 /**
  * Thrown if a <em>precondition</em> is violated.
@@ -20,16 +23,16 @@
  * @since 1.5
  */
 @API(status = STABLE, since = "1.5")
-@SuppressWarnings({ "deprecation", "exports" })
-public class PreconditionViolationException extends org.junit.platform.commons.util.PreconditionViolationException {
+public class PreconditionViolationException extends JUnitException {
 
+	@Serial
 	private static final long serialVersionUID = 1L;
 
 	public PreconditionViolationException(String message) {
 		super(message);
 	}
 
-	public PreconditionViolationException(String message, Throwable cause) {
+	public PreconditionViolationException(String message, @Nullable Throwable cause) {
 		super(message, cause);
 	}
 
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/annotation/package-info.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/annotation/package-info.java
index f5f0eaf51493..1221aebb8f50 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/annotation/package-info.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/annotation/package-info.java
@@ -2,4 +2,7 @@
  * Common annotations for the JUnit Platform.
  */
 
+@NullMarked
 package org.junit.platform.commons.annotation;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/function/Try.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/function/Try.java
index 04403c18a34d..115ccb8e8ef2 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/function/Try.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/function/Try.java
@@ -10,6 +10,7 @@
 
 package org.junit.platform.commons.function;
 
+import static org.apiguardian.api.API.Status.EXPERIMENTAL;
 import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import java.util.Objects;
@@ -20,6 +21,8 @@
 import java.util.function.Supplier;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.NonNull;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.JUnitException;
 
 /**
@@ -39,7 +42,7 @@
  * @since 1.4
  */
 @API(status = MAINTAINED, since = "1.4")
-public abstract class Try<V> {
+public abstract class Try<V extends @Nullable Object> {
 
 	/**
 	 * Call the supplied {@link Callable} and return a successful {@code Try}
@@ -52,7 +55,7 @@ public abstract class Try<V> {
 	 * @see #success(Object)
 	 * @see #failure(Exception)
 	 */
-	public static <V> Try<V> call(Callable<V> action) {
+	public static <V extends @Nullable Object> Try<V> call(Callable<V> action) {
 		checkNotNull(action, "action");
 		return Try.of(() -> success(action.call()));
 	}
@@ -64,7 +67,7 @@ public static <V> Try<V> call(Callable<V> action) {
 	 * @return a succeeded {@code Try} that contains the supplied value; never
 	 * {@code null}
 	 */
-	public static <V> Try<V> success(V value) {
+	public static <V extends @Nullable Object> Try<V> success(V value) {
 		return new Success<>(value);
 	}
 
@@ -80,7 +83,7 @@ public static <V> Try<V> failure(Exception cause) {
 	}
 
 	// Cannot use Preconditions due to package cycle
-	private static <T> T checkNotNull(T input, String title) {
+	private static <T> T checkNotNull(@Nullable T input, String title) {
 		if (input == null) {
 			// Cannot use PreconditionViolationException due to package cycle
 			throw new JUnitException(title + " must not be null");
@@ -149,6 +152,22 @@ private Try() {
 	 */
 	public abstract V get() throws Exception;
 
+	/**
+	 * If this {@code Try} is a success, get the contained value; if this
+	 * {@code Try} is a failure, throw the contained exception.
+	 *
+	 * @return the contained value, if available
+	 * @throws Exception if this {@code Try} is a failure or the contained value
+	 * is {@code null}
+	 *
+	 * @since 6.0
+	 */
+	@API(status = EXPERIMENTAL, since = "6.0")
+	public final @NonNull V getNonNull() throws Exception {
+		var value = get();
+		return checkNotNull(value, "value");
+	}
+
 	/**
 	 * If this {@code Try} is a success, get the contained value; if this
 	 * {@code Try} is a failure, call the supplied {@link Function} with the
@@ -161,6 +180,27 @@ private Try() {
 	 */
 	public abstract <E extends Exception> V getOrThrow(Function<? super Exception, E> exceptionTransformer) throws E;
 
+	/**
+	 * If this {@code Try} is a success, get the contained value; if this
+	 * {@code Try} is a failure, call the supplied {@link Function} with the
+	 * contained exception and throw the resulting {@link Exception}.
+	 *
+	 * @param exceptionTransformer the transformer to be called with the
+	 * contained exception, if available; must not be {@code null}
+	 * @return the contained value, if available and not {@code null}
+	 * @throws E if this {@code Try} is a failure or the contained value
+	 * is {@code null}
+	 */
+	@API(status = EXPERIMENTAL, since = "6.0")
+	public final <E extends Exception> @NonNull V getNonNullOrThrow(
+			Function<@Nullable Exception, E> exceptionTransformer) throws E {
+		var value = getOrThrow(exceptionTransformer);
+		if (value == null) {
+			throw exceptionTransformer.apply(null);
+		}
+		return value;
+	}
+
 	/**
 	 * If this {@code Try} is a success, call the supplied {@link Consumer} with
 	 * the contained value; otherwise, do nothing.
@@ -198,7 +238,7 @@ private Try() {
 	 * except that a {@code Transformer} may throw an exception.
 	 */
 	@FunctionalInterface
-	public interface Transformer<S, T> {
+	public interface Transformer<S extends @Nullable Object, T extends @Nullable Object> {
 
 		/**
 		 * Apply this transformer to the supplied value.
@@ -209,7 +249,7 @@ public interface Transformer<S, T> {
 
 	}
 
-	private static class Success<V> extends Try<V> {
+	private static class Success<V extends @Nullable Object> extends Try<V> {
 
 		private final V value;
 
@@ -287,7 +327,7 @@ public int hashCode() {
 		}
 	}
 
-	private static class Failure<V> extends Try<V> {
+	private static class Failure<V extends @Nullable Object> extends Try<V> {
 
 		private final Exception cause;
 
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/function/package-info.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/function/package-info.java
index 8f031faf22e0..79d053801103 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/function/package-info.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/function/package-info.java
@@ -2,4 +2,7 @@
  * Functional interfaces and support classes.
  */
 
+@NullMarked
 package org.junit.platform.commons.function;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/logging/LogRecordListener.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/logging/LogRecordListener.java
index 22a53d59453b..e5ac90f9d8fb 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/logging/LogRecordListener.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/logging/LogRecordListener.java
@@ -75,6 +75,7 @@ public Stream<LogRecord> stream() {
 	 * @see #stream(Class)
 	 * @see #stream(Class, Level)
 	 */
+	@SuppressWarnings("ConstantValue")
 	public Stream<LogRecord> stream(Level level) {
 		// NOTE: we cannot use org.junit.platform.commons.util.Preconditions here
 		// since that would introduce a package cycle.
@@ -100,6 +101,7 @@ public Stream<LogRecord> stream(Level level) {
 	 * @see #stream(Level)
 	 * @see #stream(Class, Level)
 	 */
+	@SuppressWarnings("ConstantValue")
 	public Stream<LogRecord> stream(Class<?> clazz) {
 		// NOTE: we cannot use org.junit.platform.commons.util.Preconditions here
 		// since that would introduce a package cycle.
@@ -127,6 +129,7 @@ public Stream<LogRecord> stream(Class<?> clazz) {
 	 * @see #stream(Level)
 	 * @see #stream(Class)
 	 */
+	@SuppressWarnings("ConstantValue")
 	public Stream<LogRecord> stream(Class<?> clazz, Level level) {
 		// NOTE: we cannot use org.junit.platform.commons.util.Preconditions here
 		// since that would introduce a package cycle.
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/logging/Logger.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/logging/Logger.java
index 09d4d3c93918..caa1dff66a17 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/logging/Logger.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/logging/Logger.java
@@ -15,6 +15,7 @@
 import java.util.function.Supplier;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 
 /**
  * The {@code Logger} API serves as a simple logging facade for
@@ -38,7 +39,7 @@ public interface Logger {
 	 *
 	 * <p>Maps to {@link java.util.logging.Level#SEVERE} in JUL.
 	 */
-	void error(Throwable throwable, Supplier<String> messageSupplier);
+	void error(@Nullable Throwable throwable, Supplier<String> messageSupplier);
 
 	/**
 	 * Log the message from the provided {@code messageSupplier} at warning level.
@@ -53,7 +54,7 @@ public interface Logger {
 	 *
 	 * <p>Maps to {@link java.util.logging.Level#WARNING} in JUL.
 	 */
-	void warn(Throwable throwable, Supplier<String> messageSupplier);
+	void warn(@Nullable Throwable throwable, Supplier<String> messageSupplier);
 
 	/**
 	 * Log the message from the provided {@code messageSupplier} at info level.
@@ -68,7 +69,7 @@ public interface Logger {
 	 *
 	 * <p>Maps to {@link java.util.logging.Level#INFO} in JUL.
 	 */
-	void info(Throwable throwable, Supplier<String> messageSupplier);
+	void info(@Nullable Throwable throwable, Supplier<String> messageSupplier);
 
 	/**
 	 * Log the message from the provided {@code messageSupplier} at config level.
@@ -83,7 +84,7 @@ public interface Logger {
 	 *
 	 * <p>Maps to {@link java.util.logging.Level#CONFIG} in JUL.
 	 */
-	void config(Throwable throwable, Supplier<String> messageSupplier);
+	void config(@Nullable Throwable throwable, Supplier<String> messageSupplier);
 
 	/**
 	 * Log the message from the provided {@code messageSupplier} at debug level.
@@ -98,7 +99,7 @@ public interface Logger {
 	 *
 	 * <p>Maps to {@link java.util.logging.Level#FINE} in JUL.
 	 */
-	void debug(Throwable throwable, Supplier<String> messageSupplier);
+	void debug(@Nullable Throwable throwable, Supplier<String> messageSupplier);
 
 	/**
 	 * Log the message from the provided {@code messageSupplier} at trace level.
@@ -113,6 +114,6 @@ public interface Logger {
 	 *
 	 * <p>Maps to {@link java.util.logging.Level#FINER} in JUL.
 	 */
-	void trace(Throwable throwable, Supplier<String> messageSupplier);
+	void trace(@Nullable Throwable throwable, Supplier<String> messageSupplier);
 
 }
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/logging/LoggerFactory.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/logging/LoggerFactory.java
index c6b3ce3b44e4..711b42d6c658 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/logging/LoggerFactory.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/logging/LoggerFactory.java
@@ -19,6 +19,7 @@
 import java.util.logging.LogRecord;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.JUnitException;
 
 /**
@@ -41,6 +42,7 @@ private LoggerFactory() {
 	 * @param clazz the class for which to get the logger; never {@code null}
 	 * @return the logger
 	 */
+	@SuppressWarnings("ConstantValue")
 	public static Logger getLogger(Class<?> clazz) {
 		// NOTE: we cannot use org.junit.platform.commons.util.Preconditions here
 		// since that would introduce a package cycle.
@@ -86,7 +88,7 @@ public void error(Supplier<String> messageSupplier) {
 		}
 
 		@Override
-		public void error(Throwable throwable, Supplier<String> messageSupplier) {
+		public void error(@Nullable Throwable throwable, Supplier<String> messageSupplier) {
 			log(Level.SEVERE, throwable, messageSupplier);
 		}
 
@@ -96,7 +98,7 @@ public void warn(Supplier<String> messageSupplier) {
 		}
 
 		@Override
-		public void warn(Throwable throwable, Supplier<String> messageSupplier) {
+		public void warn(@Nullable Throwable throwable, Supplier<String> messageSupplier) {
 			log(Level.WARNING, throwable, messageSupplier);
 		}
 
@@ -106,7 +108,7 @@ public void info(Supplier<String> messageSupplier) {
 		}
 
 		@Override
-		public void info(Throwable throwable, Supplier<String> messageSupplier) {
+		public void info(@Nullable Throwable throwable, Supplier<String> messageSupplier) {
 			log(Level.INFO, throwable, messageSupplier);
 		}
 
@@ -116,7 +118,7 @@ public void config(Supplier<String> messageSupplier) {
 		}
 
 		@Override
-		public void config(Throwable throwable, Supplier<String> messageSupplier) {
+		public void config(@Nullable Throwable throwable, Supplier<String> messageSupplier) {
 			log(Level.CONFIG, throwable, messageSupplier);
 		}
 
@@ -126,7 +128,7 @@ public void debug(Supplier<String> messageSupplier) {
 		}
 
 		@Override
-		public void debug(Throwable throwable, Supplier<String> messageSupplier) {
+		public void debug(@Nullable Throwable throwable, Supplier<String> messageSupplier) {
 			log(Level.FINE, throwable, messageSupplier);
 		}
 
@@ -136,14 +138,14 @@ public void trace(Supplier<String> messageSupplier) {
 		}
 
 		@Override
-		public void trace(Throwable throwable, Supplier<String> messageSupplier) {
+		public void trace(@Nullable Throwable throwable, Supplier<String> messageSupplier) {
 			log(Level.FINER, throwable, messageSupplier);
 		}
 
-		private void log(Level level, Throwable throwable, Supplier<String> messageSupplier) {
+		private void log(Level level, @Nullable Throwable throwable, Supplier<String> messageSupplier) {
 			boolean loggable = this.julLogger.isLoggable(level);
 			if (loggable || !listeners.isEmpty()) {
-				LogRecord logRecord = createLogRecord(level, throwable, nullSafeGet(messageSupplier));
+				LogRecord logRecord = createLogRecord(level, throwable, messageSupplier.get());
 				if (loggable) {
 					this.julLogger.log(logRecord);
 				}
@@ -151,7 +153,7 @@ private void log(Level level, Throwable throwable, Supplier<String> messageSuppl
 			}
 		}
 
-		private LogRecord createLogRecord(Level level, Throwable throwable, String message) {
+		private LogRecord createLogRecord(Level level, @Nullable Throwable throwable, String message) {
 			String sourceClassName = null;
 			String sourceMethodName = null;
 			boolean found = false;
@@ -178,10 +180,6 @@ else if (found) {
 			return logRecord;
 		}
 
-		private static String nullSafeGet(Supplier<String> messageSupplier) {
-			return (messageSupplier != null ? messageSupplier.get() : null);
-		}
-
 	}
 
 }
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/logging/package-info.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/logging/package-info.java
index 75260c34a99a..9fe567592387 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/logging/package-info.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/logging/package-info.java
@@ -8,4 +8,7 @@
  * Use at your own risk!
  */
 
+@NullMarked
 package org.junit.platform.commons.logging;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/package-info.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/package-info.java
index 66e1cf2aa51c..18945b31c25e 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/package-info.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/package-info.java
@@ -8,4 +8,7 @@
  * APIs by external parties is not supported!</strong>
  */
 
+@NullMarked
 package org.junit.platform.commons;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/AnnotationSupport.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/AnnotationSupport.java
index 1f30697db788..24044ac09e27 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/AnnotationSupport.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/AnnotationSupport.java
@@ -11,7 +11,6 @@
 package org.junit.platform.commons.support;
 
 import static org.apiguardian.api.API.Status.DEPRECATED;
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
 import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import java.lang.annotation.Annotation;
@@ -24,6 +23,7 @@
 import java.util.function.Predicate;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.util.AnnotationUtils;
 import org.junit.platform.commons.util.Preconditions;
 import org.junit.platform.commons.util.ReflectionUtils;
@@ -70,7 +70,7 @@ private AnnotationSupport() {
 	 * @see #findRepeatableAnnotations(Optional, Class)
 	 */
 	@API(status = MAINTAINED, since = "1.3")
-	public static boolean isAnnotated(Optional<? extends AnnotatedElement> element,
+	public static boolean isAnnotated(@Nullable Optional<? extends AnnotatedElement> element,
 			Class<? extends Annotation> annotationType) {
 
 		return AnnotationUtils.isAnnotated(element, annotationType);
@@ -93,7 +93,7 @@ public static boolean isAnnotated(Optional<? extends AnnotatedElement> element,
 	 * @see #findAnnotation(AnnotatedElement, Class)
 	 * @see #findRepeatableAnnotations(AnnotatedElement, Class)
 	 */
-	public static boolean isAnnotated(AnnotatedElement element, Class<? extends Annotation> annotationType) {
+	public static boolean isAnnotated(@Nullable AnnotatedElement element, Class<? extends Annotation> annotationType) {
 		return AnnotationUtils.isAnnotated(element, annotationType);
 	}
 
@@ -112,8 +112,8 @@ public static boolean isAnnotated(AnnotatedElement element, Class<? extends Anno
 	 * @see #findAnnotation(AnnotatedElement, Class)
 	 */
 	@API(status = MAINTAINED, since = "1.1")
-	public static <A extends Annotation> Optional<A> findAnnotation(Optional<? extends AnnotatedElement> element,
-			Class<A> annotationType) {
+	public static <A extends Annotation> Optional<A> findAnnotation(
+			@Nullable Optional<? extends AnnotatedElement> element, Class<A> annotationType) {
 
 		return AnnotationUtils.findAnnotation(element, annotationType);
 	}
@@ -135,7 +135,8 @@ public static <A extends Annotation> Optional<A> findAnnotation(Optional<? exten
 	 * @return an {@code Optional} containing the annotation; never {@code null} but
 	 * potentially empty
 	 */
-	public static <A extends Annotation> Optional<A> findAnnotation(AnnotatedElement element, Class<A> annotationType) {
+	public static <A extends Annotation> Optional<A> findAnnotation(@Nullable AnnotatedElement element,
+			Class<A> annotationType) {
 		return AnnotationUtils.findAnnotation(element, annotationType);
 	}
 
@@ -173,7 +174,7 @@ public static <A extends Annotation> Optional<A> findAnnotation(AnnotatedElement
 	@Deprecated
 	@API(status = DEPRECATED, since = "1.12")
 	@SuppressWarnings("deprecation")
-	public static <A extends Annotation> Optional<A> findAnnotation(Class<?> clazz, Class<A> annotationType,
+	public static <A extends Annotation> Optional<A> findAnnotation(@Nullable Class<?> clazz, Class<A> annotationType,
 			SearchOption searchOption) {
 
 		Preconditions.notNull(searchOption, "SearchOption must not be null");
@@ -213,14 +214,14 @@ public static <A extends Annotation> Optional<A> findAnnotation(Class<?> clazz,
 	 * @since 1.12
 	 * @see #findAnnotation(AnnotatedElement, Class)
 	 */
-	@API(status = EXPERIMENTAL, since = "1.12")
-	public static <A extends Annotation> Optional<A> findAnnotation(Class<?> clazz, Class<A> annotationType,
+	@API(status = MAINTAINED, since = "1.13.3")
+	public static <A extends Annotation> Optional<A> findAnnotation(@Nullable Class<?> clazz, Class<A> annotationType,
 			List<Class<?>> enclosingInstanceTypes) {
 
 		Preconditions.notNull(enclosingInstanceTypes, "enclosingInstanceTypes must not be null");
 
 		Optional<A> annotation = findAnnotation(clazz, annotationType);
-		if (!annotation.isPresent()) {
+		if (annotation.isEmpty()) {
 			ListIterator<Class<?>> iterator = enclosingInstanceTypes.listIterator(enclosingInstanceTypes.size());
 			while (iterator.hasPrevious()) {
 				annotation = findAnnotation(iterator.previous(), annotationType);
@@ -252,8 +253,8 @@ public static <A extends Annotation> Optional<A> findAnnotation(Class<?> clazz,
 	 * @see #findRepeatableAnnotations(AnnotatedElement, Class)
 	 */
 	@API(status = MAINTAINED, since = "1.5")
-	public static <A extends Annotation> List<A> findRepeatableAnnotations(Optional<? extends AnnotatedElement> element,
-			Class<A> annotationType) {
+	public static <A extends Annotation> List<A> findRepeatableAnnotations(
+			@Nullable Optional<? extends AnnotatedElement> element, Class<A> annotationType) {
 
 		return AnnotationUtils.findRepeatableAnnotations(element, annotationType);
 	}
@@ -297,7 +298,7 @@ public static <A extends Annotation> List<A> findRepeatableAnnotations(Optional<
 	 * @see java.lang.annotation.Repeatable
 	 * @see java.lang.annotation.Inherited
 	 */
-	public static <A extends Annotation> List<A> findRepeatableAnnotations(AnnotatedElement element,
+	public static <A extends Annotation> List<A> findRepeatableAnnotations(@Nullable AnnotatedElement element,
 			Class<A> annotationType) {
 
 		return AnnotationUtils.findRepeatableAnnotations(element, annotationType);
@@ -441,13 +442,16 @@ public static List<Field> findAnnotatedFields(Class<?> clazz, Class<? extends An
 	 * @see ReflectionSupport#tryToReadFieldValue(Field, Object)
 	 */
 	@API(status = MAINTAINED, since = "1.4")
-	public static List<Object> findAnnotatedFieldValues(Object instance, Class<? extends Annotation> annotationType) {
+	public static List<@Nullable Object> findAnnotatedFieldValues(Object instance,
+			Class<? extends Annotation> annotationType) {
 		Preconditions.notNull(instance, "instance must not be null");
 
 		List<Field> fields = findAnnotatedFields(instance.getClass(), annotationType, ModifierSupport::isNotStatic,
 			HierarchyTraversalMode.TOP_DOWN);
 
-		return ReflectionUtils.readFieldValues(fields, instance);
+		@SuppressWarnings("unchecked")
+		List<@Nullable Object> result = (List<@Nullable Object>) ReflectionUtils.readFieldValues(fields, instance);
+		return result;
 	}
 
 	/**
@@ -473,12 +477,15 @@ public static List<Object> findAnnotatedFieldValues(Object instance, Class<? ext
 	 * @see ReflectionSupport#tryToReadFieldValue(Field, Object)
 	 */
 	@API(status = MAINTAINED, since = "1.4")
-	public static List<Object> findAnnotatedFieldValues(Class<?> clazz, Class<? extends Annotation> annotationType) {
+	public static List<@Nullable Object> findAnnotatedFieldValues(Class<?> clazz,
+			Class<? extends Annotation> annotationType) {
 
 		List<Field> fields = findAnnotatedFields(clazz, annotationType, ModifierSupport::isStatic,
 			HierarchyTraversalMode.TOP_DOWN);
 
-		return ReflectionUtils.readFieldValues(fields, null);
+		@SuppressWarnings("unchecked")
+		List<@Nullable Object> result = (List<@Nullable Object>) ReflectionUtils.readFieldValues(fields, null);
+		return result;
 	}
 
 	/**
@@ -508,8 +515,8 @@ public static List<Object> findAnnotatedFieldValues(Class<?> clazz, Class<? exte
 	 */
 	@SuppressWarnings("unchecked")
 	@API(status = MAINTAINED, since = "1.4")
-	public static <T> List<T> findAnnotatedFieldValues(Object instance, Class<? extends Annotation> annotationType,
-			Class<T> fieldType) {
+	public static <T extends @Nullable Object> List<T> findAnnotatedFieldValues(Object instance,
+			Class<? extends Annotation> annotationType, Class<T> fieldType) {
 
 		Preconditions.notNull(instance, "instance must not be null");
 		Preconditions.notNull(fieldType, "fieldType must not be null");
@@ -550,8 +557,8 @@ public static <T> List<T> findAnnotatedFieldValues(Object instance, Class<? exte
 	 */
 	@SuppressWarnings("unchecked")
 	@API(status = MAINTAINED, since = "1.4")
-	public static <T> List<T> findAnnotatedFieldValues(Class<?> clazz, Class<? extends Annotation> annotationType,
-			Class<T> fieldType) {
+	public static <T extends @Nullable Object> List<T> findAnnotatedFieldValues(Class<?> clazz,
+			Class<? extends Annotation> annotationType, Class<T> fieldType) {
 
 		Preconditions.notNull(fieldType, "fieldType must not be null");
 
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/DefaultResource.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/DefaultResource.java
index 26df8c0f876c..d8df57d38fdf 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/DefaultResource.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/DefaultResource.java
@@ -13,7 +13,6 @@
 import static org.apiguardian.api.API.Status.INTERNAL;
 
 import java.net.URI;
-import java.util.Objects;
 
 import org.apiguardian.api.API;
 import org.junit.platform.commons.util.Preconditions;
@@ -29,14 +28,11 @@
  * @since 1.11
  */
 @API(status = INTERNAL, since = "1.12")
-public class DefaultResource implements Resource {
+public record DefaultResource(String name, URI uri) implements Resource {
 
-	private final String name;
-	private final URI uri;
-
-	public DefaultResource(String name, URI uri) {
-		this.name = Preconditions.notNull(name, "name must not be null");
-		this.uri = Preconditions.notNull(uri, "uri must not be null");
+	public DefaultResource {
+		Preconditions.notNull(name, "name must not be null");
+		Preconditions.notNull(uri, "uri must not be null");
 	}
 
 	@Override
@@ -49,21 +45,6 @@ public URI getUri() {
 		return uri;
 	}
 
-	@Override
-	public boolean equals(Object o) {
-		if (this == o)
-			return true;
-		if (o == null || getClass() != o.getClass())
-			return false;
-		DefaultResource that = (DefaultResource) o;
-		return name.equals(that.name) && uri.equals(that.uri);
-	}
-
-	@Override
-	public int hashCode() {
-		return Objects.hash(name, uri);
-	}
-
 	@Override
 	public String toString() {
 		return new ToStringBuilder(this) //
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/ModifierSupport.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/ModifierSupport.java
index e92289ecc05e..536cc908dc76 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/ModifierSupport.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/ModifierSupport.java
@@ -151,7 +151,7 @@ public static boolean isAbstract(Member member) {
 	 * @since 1.13
 	 * @see java.lang.reflect.Modifier#isAbstract(int)
 	 */
-	@API(status = EXPERIMENTAL, since = "1.13")
+	@API(status = EXPERIMENTAL, since = "6.0")
 	public static boolean isNotAbstract(Class<?> clazz) {
 		return ReflectionUtils.isNotAbstract(clazz);
 	}
@@ -164,7 +164,7 @@ public static boolean isNotAbstract(Class<?> clazz) {
 	 * @since 1.13
 	 * @see java.lang.reflect.Modifier#isAbstract(int)
 	 */
-	@API(status = EXPERIMENTAL, since = "1.13")
+	@API(status = EXPERIMENTAL, since = "6.0")
 	public static boolean isNotAbstract(Member member) {
 		return ReflectionUtils.isNotAbstract(member);
 	}
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/ReflectionSupport.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/ReflectionSupport.java
index 5f8d2cbeffc4..4e57d4b727d5 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/ReflectionSupport.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/ReflectionSupport.java
@@ -10,8 +10,6 @@
 
 package org.junit.platform.commons.support;
 
-import static org.apiguardian.api.API.Status.DEPRECATED;
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
 import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import java.lang.reflect.Field;
@@ -24,6 +22,7 @@
 import java.util.stream.Stream;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.JUnitException;
 import org.junit.platform.commons.function.Try;
 import org.junit.platform.commons.util.ExceptionUtils;
@@ -51,28 +50,6 @@ private ReflectionSupport() {
 		/* no-op */
 	}
 
-	/**
-	 * Load a class by its <em>primitive name</em> or <em>fully qualified name</em>,
-	 * using the default {@link ClassLoader}.
-	 *
-	 * <p>Class names for arrays may be specified using either the JVM's internal
-	 * String representation (e.g., {@code [[I} for {@code int[][]},
-	 * {@code [Ljava.lang.String;} for {@code java.lang.String[]}, etc.) or
-	 * <em>source code syntax</em> (e.g., {@code int[][]}, {@code java.lang.String[]},
-	 * etc.).
-	 *
-	 * @param name the name of the class to load; never {@code null} or blank
-	 * @return an {@code Optional} containing the loaded class; never {@code null}
-	 * but potentially empty if no such class could be loaded
-	 * @deprecated Please use {@link #tryToLoadClass(String)} instead.
-	 */
-	@API(status = DEPRECATED, since = "1.4")
-	@Deprecated
-	@SuppressWarnings("deprecation")
-	public static Optional<Class<?>> loadClass(String name) {
-		return ReflectionUtils.loadClass(name);
-	}
-
 	/**
 	 * Try to load a class by its <em>primitive name</em> or <em>fully qualified
 	 * name</em>, using the default {@link ClassLoader}.
@@ -110,7 +87,7 @@ public static Try<Class<?>> tryToLoadClass(String name) {
 	 * @since 1.10
 	 * @see #tryToLoadClass(String)
 	 */
-	@API(status = EXPERIMENTAL, since = "1.10")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public static Try<Class<?>> tryToLoadClass(String name, ClassLoader classLoader) {
 		return ReflectionUtils.tryToLoadClass(name, classLoader);
 	}
@@ -133,7 +110,7 @@ public static Try<Class<?>> tryToLoadClass(String name, ClassLoader classLoader)
 	 * @since 1.12
 	 * @see #tryToGetResources(String, ClassLoader)
 	 */
-	@API(status = EXPERIMENTAL, since = "1.12")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public static Try<Set<Resource>> tryToGetResources(String classpathResourceName) {
 		return ReflectionUtils.tryToGetResources(classpathResourceName);
 	}
@@ -157,7 +134,7 @@ public static Try<Set<Resource>> tryToGetResources(String classpathResourceName)
 	 * @since 1.12
 	 * @see #tryToGetResources(String)
 	 */
-	@API(status = EXPERIMENTAL, since = "1.12")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public static Try<Set<Resource>> tryToGetResources(String classpathResourceName, ClassLoader classLoader) {
 		return ReflectionUtils.tryToGetResources(classpathResourceName, classLoader);
 	}
@@ -201,7 +178,7 @@ public static List<Class<?>> findAllClassesInClasspathRoot(URI root, Predicate<C
 	 * @see #findAllResourcesInPackage(String, Predicate)
 	 * @see #findAllResourcesInModule(String, Predicate)
 	 */
-	@API(status = EXPERIMENTAL, since = "1.11")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public static List<Resource> findAllResourcesInClasspathRoot(URI root, Predicate<Resource> resourceFilter) {
 		return ReflectionUtils.findAllResourcesInClasspathRoot(root, resourceFilter);
 	}
@@ -247,7 +224,7 @@ public static Stream<Class<?>> streamAllClassesInClasspathRoot(URI root, Predica
 	 * @see #streamAllResourcesInPackage(String, Predicate)
 	 * @see #streamAllResourcesInModule(String, Predicate)
 	 */
-	@API(status = EXPERIMENTAL, since = "1.11")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public static Stream<Resource> streamAllResourcesInClasspathRoot(URI root, Predicate<Resource> resourceFilter) {
 		return ReflectionUtils.streamAllResourcesInClasspathRoot(root, resourceFilter);
 	}
@@ -294,7 +271,7 @@ public static List<Class<?>> findAllClassesInPackage(String basePackageName, Pre
 	 * @see #findAllResourcesInClasspathRoot(URI, Predicate)
 	 * @see #findAllResourcesInModule(String, Predicate)
 	 */
-	@API(status = EXPERIMENTAL, since = "1.11")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public static List<Resource> findAllResourcesInPackage(String basePackageName, Predicate<Resource> resourceFilter) {
 		return ReflectionUtils.findAllResourcesInPackage(basePackageName, resourceFilter);
 	}
@@ -344,7 +321,7 @@ public static Stream<Class<?>> streamAllClassesInPackage(String basePackageName,
 	 * @see #streamAllResourcesInClasspathRoot(URI, Predicate)
 	 * @see #streamAllResourcesInModule(String, Predicate)
 	 */
-	@API(status = EXPERIMENTAL, since = "1.11")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public static Stream<Resource> streamAllResourcesInPackage(String basePackageName,
 			Predicate<Resource> resourceFilter) {
 
@@ -392,7 +369,7 @@ public static List<Class<?>> findAllClassesInModule(String moduleName, Predicate
 	 * @see #findAllResourcesInClasspathRoot(URI, Predicate)
 	 * @see #findAllResourcesInPackage(String, Predicate)
 	 */
-	@API(status = EXPERIMENTAL, since = "1.11")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public static List<Resource> findAllResourcesInModule(String moduleName, Predicate<Resource> resourceFilter) {
 		return ReflectionUtils.findAllResourcesInModule(moduleName, resourceFilter);
 	}
@@ -438,7 +415,7 @@ public static Stream<Class<?>> streamAllClassesInModule(String moduleName, Predi
 	 * @see #streamAllResourcesInClasspathRoot(URI, Predicate)
 	 * @see #streamAllResourcesInPackage(String, Predicate)
 	 */
-	@API(status = EXPERIMENTAL, since = "1.11")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public static Stream<Resource> streamAllResourcesInModule(String moduleName, Predicate<Resource> resourceFilter) {
 		return ReflectionUtils.streamAllResourcesInModule(moduleName, resourceFilter);
 	}
@@ -470,12 +447,12 @@ public static <T> T newInstance(Class<T> clazz, Object... args) {
 	 * @param method the method to invoke; never {@code null}
 	 * @param target the object on which to invoke the method; may be
 	 * {@code null} if the method is {@code static}
-	 * @param args the arguments to pass to the method
+	 * @param args the arguments to pass to the method; never {@code null}
 	 * @return the value returned by the method invocation or {@code null}
 	 * if the return type is {@code void}
 	 * @see ExceptionUtils#throwAsUncheckedException(Throwable)
 	 */
-	public static Object invokeMethod(Method method, Object target, Object... args) {
+	public static @Nullable Object invokeMethod(Method method, @Nullable Object target, @Nullable Object... args) {
 		return ReflectionUtils.invokeMethod(method, target, args);
 	}
 
@@ -545,7 +522,7 @@ public static Stream<Field> streamFields(Class<?> clazz, Predicate<Field> predic
 	 * @since 1.4
 	 */
 	@API(status = MAINTAINED, since = "1.4")
-	public static Try<Object> tryToReadFieldValue(Field field, Object instance) {
+	public static Try<@Nullable Object> tryToReadFieldValue(Field field, @Nullable Object instance) {
 		return ReflectionUtils.tryToReadFieldValue(field, instance);
 	}
 
@@ -570,7 +547,7 @@ public static Try<Object> tryToReadFieldValue(Field field, Object instance) {
 	 * but potentially empty if no such method could be found
 	 * @see #findMethod(Class, String, Class...)
 	 */
-	public static Optional<Method> findMethod(Class<?> clazz, String methodName, String parameterTypeNames) {
+	public static Optional<Method> findMethod(Class<?> clazz, String methodName, @Nullable String parameterTypeNames) {
 		return ReflectionUtils.findMethod(clazz, methodName, parameterTypeNames);
 	}
 
@@ -712,7 +689,7 @@ public static Stream<Class<?>> streamNestedClasses(Class<?> clazz, Predicate<Cla
 	 * @since 1.12
 	 * @see Field#setAccessible(boolean)
 	 */
-	@API(status = EXPERIMENTAL, since = "1.12")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public static Field makeAccessible(Field field) {
 		return ReflectionUtils.makeAccessible(Preconditions.notNull(field, "field must not be null"));
 	}
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/Resource.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/Resource.java
index 4080d12a5bbe..07cc0ce75642 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/Resource.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/Resource.java
@@ -10,7 +10,7 @@
 
 package org.junit.platform.commons.support;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import java.io.IOException;
 import java.io.InputStream;
@@ -30,7 +30,7 @@
  * @see ReflectionSupport#streamAllResourcesInPackage(String, Predicate)
  * @see ReflectionSupport#streamAllResourcesInModule(String, Predicate)
  */
-@API(status = EXPERIMENTAL, since = "1.11")
+@API(status = MAINTAINED, since = "1.13.3")
 public interface Resource {
 
 	/**
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/conversion/ConversionException.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/conversion/ConversionException.java
index 1e3474d27c6c..d5fe3902f8fb 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/conversion/ConversionException.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/conversion/ConversionException.java
@@ -10,7 +10,9 @@
 
 package org.junit.platform.commons.support.conversion;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
+
+import java.io.Serial;
 
 import org.apiguardian.api.API;
 import org.junit.platform.commons.JUnitException;
@@ -21,9 +23,10 @@
  *
  * @since 1.11
  */
-@API(status = EXPERIMENTAL, since = "1.11")
+@API(status = MAINTAINED, since = "1.13.3")
 public class ConversionException extends JUnitException {
 
+	@Serial
 	private static final long serialVersionUID = 1L;
 
 	public ConversionException(String message) {
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/conversion/ConversionSupport.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/conversion/ConversionSupport.java
index fa95826f5ddd..34ed6ef458f4 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/conversion/ConversionSupport.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/conversion/ConversionSupport.java
@@ -10,15 +10,14 @@
 
 package org.junit.platform.commons.support.conversion;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.junit.platform.commons.util.ReflectionUtils.getWrapperType;
 
 import java.util.List;
 import java.util.Optional;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.util.ClassLoaderUtils;
 
 /**
@@ -27,10 +26,10 @@
  *
  * @since 1.11
  */
-@API(status = EXPERIMENTAL, since = "1.11")
+@API(status = MAINTAINED, since = "1.13.3")
 public final class ConversionSupport {
 
-	private static final List<StringToObjectConverter> stringToObjectConverters = unmodifiableList(asList( //
+	private static final List<StringToObjectConverter> stringToObjectConverters = List.of( //
 		new StringToBooleanConverter(), //
 		new StringToCharacterConverter(), //
 		new StringToNumberConverter(), //
@@ -39,7 +38,7 @@ public final class ConversionSupport {
 		new StringToJavaTimeConverter(), //
 		new StringToCommonJavaTypesConverter(), //
 		new FallbackStringToObjectConverter() //
-	));
+	);
 
 	private ConversionSupport() {
 		/* no-op */
@@ -99,7 +98,8 @@ private ConversionSupport() {
 	 * @since 1.11
 	 */
 	@SuppressWarnings("unchecked")
-	public static <T> T convert(String source, Class<T> targetType, ClassLoader classLoader) {
+	public static <T> @Nullable T convert(@Nullable String source, Class<T> targetType,
+			@Nullable ClassLoader classLoader) {
 		if (source == null) {
 			if (targetType.isPrimitive()) {
 				throw new ConversionException(
@@ -122,13 +122,13 @@ public static <T> T convert(String source, Class<T> targetType, ClassLoader clas
 				return (T) converter.get().convert(source, targetTypeToUse, classLoaderToUse);
 			}
 			catch (Exception ex) {
-				if (ex instanceof ConversionException) {
+				if (ex instanceof ConversionException conversionException) {
 					// simply rethrow it
-					throw (ConversionException) ex;
+					throw conversionException;
 				}
 				// else
 				throw new ConversionException(
-					String.format("Failed to convert String \"%s\" to type %s", source, targetType.getTypeName()), ex);
+					"Failed to convert String \"%s\" to type %s".formatted(source, targetType.getTypeName()), ex);
 			}
 		}
 
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/conversion/FallbackStringToObjectConverter.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/conversion/FallbackStringToObjectConverter.java
index aeea2d9e119d..916406e3fbcb 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/conversion/FallbackStringToObjectConverter.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/conversion/FallbackStringToObjectConverter.java
@@ -26,6 +26,7 @@
 import java.util.function.Function;
 import java.util.function.Predicate;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.util.Preconditions;
 
 /**
@@ -66,7 +67,7 @@ class FallbackStringToObjectConverter implements StringToObjectConverter {
 	 * This prevents the framework from repeatedly searching for things which
 	 * are already known not to exist.
 	 */
-	private static final ConcurrentHashMap<Class<?>, Function<String, Object>> factoryExecutableCache //
+	private static final ConcurrentHashMap<Class<?>, Function<String, @Nullable Object>> factoryExecutableCache //
 		= new ConcurrentHashMap<>(64);
 
 	@Override
@@ -75,15 +76,15 @@ public boolean canConvertTo(Class<?> targetType) {
 	}
 
 	@Override
-	public Object convert(String source, Class<?> targetType) throws Exception {
-		Function<String, Object> executable = findFactoryExecutable(targetType);
+	public @Nullable Object convert(String source, Class<?> targetType) throws Exception {
+		Function<String, @Nullable Object> executable = findFactoryExecutable(targetType);
 		Preconditions.condition(executable != NULL_EXECUTABLE,
 			"Illegal state: convert() must not be called if canConvert() returned false");
 
 		return executable.apply(source);
 	}
 
-	private static Function<String, Object> findFactoryExecutable(Class<?> targetType) {
+	private static Function<String, @Nullable Object> findFactoryExecutable(Class<?> targetType) {
 		return factoryExecutableCache.computeIfAbsent(targetType, type -> {
 			Method factoryMethod = findFactoryMethod(type);
 			if (factoryMethod != null) {
@@ -97,7 +98,7 @@ private static Function<String, Object> findFactoryExecutable(Class<?> targetTyp
 		});
 	}
 
-	private static Method findFactoryMethod(Class<?> targetType) {
+	private static @Nullable Method findFactoryMethod(Class<?> targetType) {
 		List<Method> factoryMethods = findMethods(targetType, new IsFactoryMethod(targetType), BOTTOM_UP);
 		if (factoryMethods.size() == 1) {
 			return factoryMethods.get(0);
@@ -105,7 +106,7 @@ private static Method findFactoryMethod(Class<?> targetType) {
 		return null;
 	}
 
-	private static Constructor<?> findFactoryConstructor(Class<?> targetType) {
+	private static @Nullable Constructor<?> findFactoryConstructor(Class<?> targetType) {
 		List<Constructor<?>> constructors = findConstructors(targetType, new IsFactoryConstructor(targetType));
 		if (constructors.size() == 1) {
 			return constructors.get(0);
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/conversion/StringToClassConverter.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/conversion/StringToClassConverter.java
index ad16fb18edf3..a2d5cbb9322e 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/conversion/StringToClassConverter.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/conversion/StringToClassConverter.java
@@ -10,6 +10,7 @@
 
 package org.junit.platform.commons.support.conversion;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.support.ReflectionSupport;
 
 class StringToClassConverter implements StringToObjectConverter {
@@ -25,7 +26,7 @@ public Object convert(String source, Class<?> targetType) throws Exception {
 	}
 
 	@Override
-	public Object convert(String className, Class<?> targetType, ClassLoader classLoader) throws Exception {
+	public @Nullable Object convert(String className, Class<?> targetType, ClassLoader classLoader) throws Exception {
 		// @formatter:off
 		return ReflectionSupport.tryToLoadClass(className, classLoader)
 				.getOrThrow(cause -> new ConversionException(
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/conversion/StringToCommonJavaTypesConverter.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/conversion/StringToCommonJavaTypesConverter.java
index 17aa357439ae..7eb2bd31bd16 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/conversion/StringToCommonJavaTypesConverter.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/conversion/StringToCommonJavaTypesConverter.java
@@ -10,8 +10,6 @@
 
 package org.junit.platform.commons.support.conversion;
 
-import static java.util.Collections.unmodifiableMap;
-
 import java.io.File;
 import java.net.MalformedURLException;
 import java.net.URI;
@@ -20,33 +18,29 @@
 import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.util.Currency;
-import java.util.HashMap;
 import java.util.Locale;
 import java.util.Map;
 import java.util.UUID;
 import java.util.function.Function;
 
-class StringToCommonJavaTypesConverter implements StringToObjectConverter {
-
-	private static final Map<Class<?>, Function<String, ?>> CONVERTERS;
+import org.junit.platform.commons.util.Preconditions;
 
-	static {
-		Map<Class<?>, Function<String, ?>> converters = new HashMap<>();
+class StringToCommonJavaTypesConverter implements StringToObjectConverter {
 
+	@SuppressWarnings("deprecation")
+	private static final Map<Class<?>, Function<String, ?>> CONVERTERS = Map.of( //
 		// java.io and java.nio
-		converters.put(File.class, File::new);
-		converters.put(Charset.class, Charset::forName);
-		converters.put(Path.class, Paths::get);
+		File.class, File::new, //
+		Charset.class, Charset::forName, //
+		Path.class, Paths::get,
 		// java.net
-		converters.put(URI.class, URI::create);
-		converters.put(URL.class, StringToCommonJavaTypesConverter::toURL);
+		URI.class, URI::create, //
+		URL.class, StringToCommonJavaTypesConverter::toURL,
 		// java.util
-		converters.put(Currency.class, Currency::getInstance);
-		converters.put(Locale.class, Locale::new);
-		converters.put(UUID.class, UUID::fromString);
-
-		CONVERTERS = unmodifiableMap(converters);
-	}
+		Currency.class, Currency::getInstance, //
+		Locale.class, Locale::new, //
+		UUID.class, UUID::fromString //
+	);
 
 	@Override
 	public boolean canConvertTo(Class<?> targetType) {
@@ -55,7 +49,9 @@ public boolean canConvertTo(Class<?> targetType) {
 
 	@Override
 	public Object convert(String source, Class<?> targetType) throws Exception {
-		return CONVERTERS.get(targetType).apply(source);
+		Function<String, ?> converter = Preconditions.notNull(CONVERTERS.get(targetType),
+			() -> "No registered converter for %s".formatted(targetType.getName()));
+		return converter.apply(source);
 	}
 
 	private static URL toURL(String url) {
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/conversion/StringToJavaTimeConverter.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/conversion/StringToJavaTimeConverter.java
index 0e544f39a3a4..c49bd2bc8bdf 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/conversion/StringToJavaTimeConverter.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/conversion/StringToJavaTimeConverter.java
@@ -10,7 +10,7 @@
 
 package org.junit.platform.commons.support.conversion;
 
-import static java.util.Collections.unmodifiableMap;
+import static java.util.Map.entry;
 
 import java.time.Duration;
 import java.time.Instant;
@@ -26,31 +26,29 @@
 import java.time.ZoneId;
 import java.time.ZoneOffset;
 import java.time.ZonedDateTime;
-import java.util.HashMap;
 import java.util.Map;
 import java.util.function.Function;
 
+import org.junit.platform.commons.util.Preconditions;
+
 class StringToJavaTimeConverter implements StringToObjectConverter {
 
-	private static final Map<Class<?>, Function<String, ?>> CONVERTERS;
-	static {
-		Map<Class<?>, Function<String, ?>> converters = new HashMap<>();
-		converters.put(Duration.class, Duration::parse);
-		converters.put(Instant.class, Instant::parse);
-		converters.put(LocalDate.class, LocalDate::parse);
-		converters.put(LocalDateTime.class, LocalDateTime::parse);
-		converters.put(LocalTime.class, LocalTime::parse);
-		converters.put(MonthDay.class, MonthDay::parse);
-		converters.put(OffsetDateTime.class, OffsetDateTime::parse);
-		converters.put(OffsetTime.class, OffsetTime::parse);
-		converters.put(Period.class, Period::parse);
-		converters.put(Year.class, Year::parse);
-		converters.put(YearMonth.class, YearMonth::parse);
-		converters.put(ZonedDateTime.class, ZonedDateTime::parse);
-		converters.put(ZoneId.class, ZoneId::of);
-		converters.put(ZoneOffset.class, ZoneOffset::of);
-		CONVERTERS = unmodifiableMap(converters);
-	}
+	private static final Map<Class<?>, Function<String, ?>> CONVERTERS = Map.ofEntries( //
+		entry(Duration.class, Duration::parse), //
+		entry(Instant.class, Instant::parse), //
+		entry(LocalDate.class, LocalDate::parse), //
+		entry(LocalDateTime.class, LocalDateTime::parse), //
+		entry(LocalTime.class, LocalTime::parse), //
+		entry(MonthDay.class, MonthDay::parse), //
+		entry(OffsetDateTime.class, OffsetDateTime::parse), //
+		entry(OffsetTime.class, OffsetTime::parse), //
+		entry(Period.class, Period::parse), //
+		entry(Year.class, Year::parse), //
+		entry(YearMonth.class, YearMonth::parse), //
+		entry(ZonedDateTime.class, ZonedDateTime::parse), //
+		entry(ZoneId.class, ZoneId::of), //
+		entry(ZoneOffset.class, ZoneOffset::of) //
+	);
 
 	@Override
 	public boolean canConvertTo(Class<?> targetType) {
@@ -59,7 +57,9 @@ public boolean canConvertTo(Class<?> targetType) {
 
 	@Override
 	public Object convert(String source, Class<?> targetType) throws Exception {
-		return CONVERTERS.get(targetType).apply(source);
+		Function<String, ?> converter = Preconditions.notNull(CONVERTERS.get(targetType),
+			() -> "No registered converter for %s".formatted(targetType.getName()));
+		return converter.apply(source);
 	}
 
 }
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/conversion/StringToNumberConverter.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/conversion/StringToNumberConverter.java
index 21a7a0fc2e62..f21ee0429c1b 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/conversion/StringToNumberConverter.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/conversion/StringToNumberConverter.java
@@ -10,32 +10,28 @@
 
 package org.junit.platform.commons.support.conversion;
 
-import static java.util.Collections.unmodifiableMap;
-
 import java.math.BigDecimal;
 import java.math.BigInteger;
-import java.util.HashMap;
 import java.util.Map;
 import java.util.function.Function;
 
+import org.junit.platform.commons.util.Preconditions;
+
 class StringToNumberConverter implements StringToObjectConverter {
 
-	private static final Map<Class<?>, Function<String, ?>> CONVERTERS;
-	static {
-		Map<Class<?>, Function<String, ?>> converters = new HashMap<>();
-		converters.put(Byte.class, Byte::decode);
-		converters.put(Short.class, Short::decode);
-		converters.put(Integer.class, Integer::decode);
-		converters.put(Long.class, Long::decode);
-		converters.put(Float.class, Float::valueOf);
-		converters.put(Double.class, Double::valueOf);
+	private static final Map<Class<?>, Function<String, ?>> CONVERTERS = Map.of( //
+		Byte.class, Byte::decode, //
+		Short.class, Short::decode, //
+		Integer.class, Integer::decode, //
+		Long.class, Long::decode, //
+		Float.class, Float::valueOf, //
+		Double.class, Double::valueOf, //
 		// Technically, BigInteger and BigDecimal constructors are covered by
 		// FallbackStringToObjectConverter, but we have explicit conversion
 		// configured for them anyway.
-		converters.put(BigInteger.class, BigInteger::new);
-		converters.put(BigDecimal.class, BigDecimal::new);
-		CONVERTERS = unmodifiableMap(converters);
-	}
+		BigInteger.class, BigInteger::new, //
+		BigDecimal.class, BigDecimal::new //
+	);
 
 	@Override
 	public boolean canConvertTo(Class<?> targetType) {
@@ -44,7 +40,9 @@ public boolean canConvertTo(Class<?> targetType) {
 
 	@Override
 	public Object convert(String source, Class<?> targetType) {
-		return CONVERTERS.get(targetType).apply(source.replace("_", ""));
+		Function<String, ?> converter = Preconditions.notNull(CONVERTERS.get(targetType),
+			() -> "No registered converter for %s".formatted(targetType.getName()));
+		return converter.apply(source.replace("_", ""));
 	}
 
 }
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/conversion/StringToObjectConverter.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/conversion/StringToObjectConverter.java
index ceb00e2e95d8..6c3bfffae363 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/conversion/StringToObjectConverter.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/conversion/StringToObjectConverter.java
@@ -10,6 +10,8 @@
 
 package org.junit.platform.commons.support.conversion;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * Internal API for converting arguments of type {@link String} to a specified
  * target type.
@@ -31,6 +33,7 @@ interface StringToObjectConverter {
 	 * <p>This method will only be invoked in {@link #canConvertTo(Class)}
 	 * returned {@code true} for the same target type.
 	 */
+	@Nullable
 	Object convert(String source, Class<?> targetType) throws Exception;
 
 	/**
@@ -45,7 +48,7 @@ interface StringToObjectConverter {
 	 * Can be overridden by concrete implementations of this interface that need
 	 * access to the supplied {@link ClassLoader}.
 	 */
-	default Object convert(String source, Class<?> targetType, ClassLoader classLoader) throws Exception {
+	default @Nullable Object convert(String source, Class<?> targetType, ClassLoader classLoader) throws Exception {
 		return convert(source, targetType);
 	}
 
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/conversion/package-info.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/conversion/package-info.java
index 18807d6a4e90..79ba440a7609 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/conversion/package-info.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/conversion/package-info.java
@@ -2,4 +2,7 @@
  * Conversion APIs provided by the JUnit Platform.
  */
 
+@NullMarked
 package org.junit.platform.commons.support.conversion;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/package-info.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/package-info.java
index fae0c2a81547..68a77ec1bf22 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/package-info.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/package-info.java
@@ -8,4 +8,7 @@
  * extensions with the same semantics as within the JUnit Platform itself.
  */
 
+@NullMarked
 package org.junit.platform.commons.support;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/scanning/ClassFilter.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/scanning/ClassFilter.java
index c8bc48b6b0a4..8c4502d4814d 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/scanning/ClassFilter.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/scanning/ClassFilter.java
@@ -10,7 +10,7 @@
 
 package org.junit.platform.commons.support.scanning;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import java.util.function.Predicate;
 
@@ -22,7 +22,7 @@
  *
  * @since 1.1
  */
-@API(status = EXPERIMENTAL, since = "1.12")
+@API(status = MAINTAINED, since = "1.13.3")
 public class ClassFilter {
 
 	/**
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/scanning/ClasspathFileVisitor.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/scanning/ClasspathFileVisitor.java
index 2bc01963da99..3387e121f6e7 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/scanning/ClasspathFileVisitor.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/scanning/ClasspathFileVisitor.java
@@ -20,6 +20,7 @@
 import java.util.function.BiConsumer;
 import java.util.function.Predicate;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.logging.Logger;
 import org.junit.platform.commons.logging.LoggerFactory;
 
@@ -55,7 +56,7 @@ public FileVisitResult visitFileFailed(Path file, IOException ex) {
 	}
 
 	@Override
-	public FileVisitResult postVisitDirectory(Path dir, IOException ex) {
+	public FileVisitResult postVisitDirectory(Path dir, @Nullable IOException ex) {
 		if (ex != null) {
 			logger.warn(ex, () -> "I/O error visiting directory: " + dir);
 		}
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/scanning/ClasspathScanner.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/scanning/ClasspathScanner.java
index 344863ad6dac..348932108c4f 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/scanning/ClasspathScanner.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/scanning/ClasspathScanner.java
@@ -28,7 +28,7 @@
  *
  * @since 1.12
  */
-@API(status = Status.EXPERIMENTAL, since = "1.12")
+@API(status = Status.MAINTAINED, since = "1.13.3")
 public interface ClasspathScanner {
 
 	/**
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/scanning/CloseablePath.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/scanning/CloseablePath.java
index 0cb4977d9477..aa18d1b587de 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/scanning/CloseablePath.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/scanning/CloseablePath.java
@@ -20,13 +20,14 @@
 import java.nio.file.FileSystem;
 import java.nio.file.FileSystems;
 import java.nio.file.Path;
-import java.nio.file.Paths;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ConcurrentMap;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.function.Function;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * @since 1.0
  */
@@ -65,7 +66,7 @@ static CloseablePath create(URI uri, FileSystemProvider fileSystemProvider) thro
 			return createForJarFileSystem(new URI(JAR_URI_SCHEME + ':' + uri),
 				fileSystem -> fileSystem.getRootDirectories().iterator().next(), fileSystemProvider);
 		}
-		return new CloseablePath(Paths.get(uri), NULL_CLOSEABLE);
+		return new CloseablePath(Path.of(uri), NULL_CLOSEABLE);
 	}
 
 	private static CloseablePath createForJarFileSystem(URI jarUri, Function<FileSystem, Path> pathProvider,
@@ -114,7 +115,7 @@ private ManagedFileSystem retain() {
 			return this;
 		}
 
-		private ManagedFileSystem release() {
+		private @Nullable ManagedFileSystem release() {
 			if (referenceCount.decrementAndGet() == 0) {
 				close();
 				return null;
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/scanning/DefaultClasspathScanner.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/scanning/DefaultClasspathScanner.java
index f4ff533b000c..427b8867d946 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/scanning/DefaultClasspathScanner.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/scanning/DefaultClasspathScanner.java
@@ -10,10 +10,8 @@
 
 package org.junit.platform.commons.support.scanning;
 
-import static java.lang.String.format;
 import static java.util.Collections.emptyList;
 import static java.util.stream.Collectors.joining;
-import static java.util.stream.Collectors.toList;
 import static org.apiguardian.api.API.Status.INTERNAL;
 import static org.junit.platform.commons.support.scanning.ClasspathFilters.CLASS_FILE_SUFFIX;
 import static org.junit.platform.commons.util.StringUtils.isNotBlank;
@@ -132,7 +130,7 @@ private List<Class<?>> findClassesForUris(List<URI> baseUris, String basePackage
 				.map(baseUri -> findClassesForUri(baseUri, basePackageName, classFilter))
 				.flatMap(Collection::stream)
 				.distinct()
-				.collect(toList());
+				.toList();
 		// @formatter:on
 	}
 
@@ -156,7 +154,7 @@ private List<Resource> findResourcesForUris(List<URI> baseUris, String basePacka
 				.map(baseUri -> findResourcesForUri(baseUri, basePackageName, resourceFilter))
 				.flatMap(Collection::stream)
 				.distinct()
-				.collect(toList());
+				.toList();
 		// @formatter:on
 	}
 
@@ -297,8 +295,9 @@ private void handleThrowable(Path classFile, Throwable throwable) {
 
 	private void logMalformedClassName(Path classFile, String fullyQualifiedClassName, InternalError ex) {
 		try {
-			logger.debug(ex, () -> format("The java.lang.Class loaded from path [%s] has a malformed class name [%s].",
-				classFile.toAbsolutePath(), fullyQualifiedClassName));
+			logger.debug(ex,
+				() -> "The java.lang.Class loaded from path [%s] has a malformed class name [%s].".formatted(
+					classFile.toAbsolutePath(), fullyQualifiedClassName));
 		}
 		catch (Throwable t) {
 			UnrecoverableExceptions.rethrowIfUnrecoverable(t);
@@ -309,7 +308,7 @@ private void logMalformedClassName(Path classFile, String fullyQualifiedClassNam
 
 	private void logGenericFileProcessingException(Path classpathFile, Throwable throwable) {
 		logger.debug(throwable,
-			() -> format("Failed to load [%s] during classpath scanning.", classpathFile.toAbsolutePath()));
+			() -> "Failed to load [%s] during classpath scanning.".formatted(classpathFile.toAbsolutePath()));
 	}
 
 	private ClassLoader getClassLoader() {
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/scanning/package-info.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/scanning/package-info.java
index 769733a65aef..2da61c5d8ce9 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/support/scanning/package-info.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/support/scanning/package-info.java
@@ -2,4 +2,7 @@
  * Classpath scanning APIs provided by the JUnit Platform.
  */
 
+@NullMarked
 package org.junit.platform.commons.support.scanning;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/AnnotationUtils.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/AnnotationUtils.java
index 15d47bb253ce..0e7d7b7e2441 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/AnnotationUtils.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/AnnotationUtils.java
@@ -11,8 +11,8 @@
 package org.junit.platform.commons.util;
 
 import static java.util.Arrays.asList;
+import static java.util.Objects.requireNonNull;
 import static org.apiguardian.api.API.Status.INTERNAL;
-import static org.junit.platform.commons.util.CollectionUtils.toUnmodifiableList;
 import static org.junit.platform.commons.util.ReflectionUtils.isInnerClass;
 
 import java.lang.annotation.Annotation;
@@ -24,7 +24,6 @@
 import java.lang.reflect.Field;
 import java.lang.reflect.Method;
 import java.lang.reflect.Parameter;
-import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
@@ -37,6 +36,7 @@
 import java.util.function.Predicate;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.JUnitException;
 import org.junit.platform.commons.util.ReflectionUtils.HierarchyTraversalMode;
 
@@ -75,7 +75,8 @@ private AnnotationUtils() {
 	 * @see #findAnnotation(Optional, Class)
 	 * @see org.junit.platform.commons.support.AnnotationSupport#isAnnotated(Optional, Class)
 	 */
-	public static boolean isAnnotated(Optional<? extends AnnotatedElement> element,
+	@SuppressWarnings("NullableOptional")
+	public static boolean isAnnotated(@Nullable Optional<? extends AnnotatedElement> element,
 			Class<? extends Annotation> annotationType) {
 
 		return findAnnotation(element, annotationType).isPresent();
@@ -101,17 +102,18 @@ public static boolean isAnnotated(Parameter parameter, int index, Class<? extend
 	 * @see #findAnnotation(AnnotatedElement, Class)
 	 * @see org.junit.platform.commons.support.AnnotationSupport#isAnnotated(AnnotatedElement, Class)
 	 */
-	public static boolean isAnnotated(AnnotatedElement element, Class<? extends Annotation> annotationType) {
+	public static boolean isAnnotated(@Nullable AnnotatedElement element, Class<? extends Annotation> annotationType) {
 		return findAnnotation(element, annotationType).isPresent();
 	}
 
 	/**
 	 * @see org.junit.platform.commons.support.AnnotationSupport#findAnnotation(Optional, Class)
 	 */
-	public static <A extends Annotation> Optional<A> findAnnotation(Optional<? extends AnnotatedElement> element,
-			Class<A> annotationType) {
+	@SuppressWarnings({ "OptionalAssignedToNull", "NullableOptional" })
+	public static <A extends Annotation> Optional<A> findAnnotation(
+			@Nullable Optional<? extends AnnotatedElement> element, Class<A> annotationType) {
 
-		if (element == null || !element.isPresent()) {
+		if (element == null || element.isEmpty()) {
 			return Optional.empty();
 		}
 
@@ -131,14 +133,15 @@ public static <A extends Annotation> Optional<A> findAnnotation(Parameter parame
 	/**
 	 * @see org.junit.platform.commons.support.AnnotationSupport#findAnnotation(AnnotatedElement, Class)
 	 */
-	public static <A extends Annotation> Optional<A> findAnnotation(AnnotatedElement element, Class<A> annotationType) {
+	public static <A extends Annotation> Optional<A> findAnnotation(@Nullable AnnotatedElement element,
+			Class<A> annotationType) {
 		Preconditions.notNull(annotationType, "annotationType must not be null");
 		boolean inherited = annotationType.isAnnotationPresent(Inherited.class);
 		return findAnnotation(element, annotationType, inherited, new HashSet<>());
 	}
 
-	private static <A extends Annotation> Optional<A> findAnnotation(AnnotatedElement element, Class<A> annotationType,
-			boolean inherited, Set<Annotation> visited) {
+	private static <A extends Annotation> Optional<A> findAnnotation(@Nullable AnnotatedElement element,
+			Class<A> annotationType, boolean inherited, Set<Annotation> visited) {
 
 		Preconditions.notNull(annotationType, "annotationType must not be null");
 
@@ -159,8 +162,7 @@ private static <A extends Annotation> Optional<A> findAnnotation(AnnotatedElemen
 			return directMetaAnnotation;
 		}
 
-		if (element instanceof Class) {
-			Class<?> clazz = (Class<?>) element;
+		if (element instanceof Class<?> clazz) {
 
 			// Search on interfaces
 			for (Class<?> ifc : clazz.getInterfaces()) {
@@ -224,7 +226,7 @@ private static <A extends Annotation> Optional<A> findMetaAnnotation(Class<A> an
 	 * @since 1.8
 	 * @see #findAnnotation(AnnotatedElement, Class)
 	 */
-	public static <A extends Annotation> Optional<A> findAnnotation(Class<?> clazz, Class<A> annotationType,
+	public static <A extends Annotation> Optional<A> findAnnotation(@Nullable Class<?> clazz, Class<A> annotationType,
 			boolean searchEnclosingClasses) {
 
 		Preconditions.notNull(annotationType, "annotationType must not be null");
@@ -248,10 +250,11 @@ public static <A extends Annotation> Optional<A> findAnnotation(Class<?> clazz,
 	 * @since 1.5
 	 * @see org.junit.platform.commons.support.AnnotationSupport#findRepeatableAnnotations(Optional, Class)
 	 */
-	public static <A extends Annotation> List<A> findRepeatableAnnotations(Optional<? extends AnnotatedElement> element,
-			Class<A> annotationType) {
+	@SuppressWarnings({ "OptionalAssignedToNull", "NullableOptional" })
+	public static <A extends Annotation> List<A> findRepeatableAnnotations(
+			@Nullable Optional<? extends AnnotatedElement> element, Class<A> annotationType) {
 
-		if (element == null || !element.isPresent()) {
+		if (element == null || element.isEmpty()) {
 			return Collections.emptyList();
 		}
 
@@ -271,7 +274,7 @@ public static <A extends Annotation> List<A> findRepeatableAnnotations(Parameter
 	/**
 	 * @see org.junit.platform.commons.support.AnnotationSupport#findRepeatableAnnotations(AnnotatedElement, Class)
 	 */
-	public static <A extends Annotation> List<A> findRepeatableAnnotations(AnnotatedElement element,
+	public static <A extends Annotation> List<A> findRepeatableAnnotations(@Nullable AnnotatedElement element,
 			Class<A> annotationType) {
 
 		Preconditions.notNull(annotationType, "annotationType must not be null");
@@ -290,15 +293,14 @@ public static <A extends Annotation> List<A> findRepeatableAnnotations(Annotated
 		Set<A> found = new LinkedHashSet<>(16);
 		findRepeatableAnnotations(element, annotationType, containerType, inherited, found, new HashSet<>(16));
 		// unmodifiable since returned from public, non-internal method(s)
-		return Collections.unmodifiableList(new ArrayList<>(found));
+		return List.copyOf(found);
 	}
 
 	private static <A extends Annotation> void findRepeatableAnnotations(AnnotatedElement element,
 			Class<A> annotationType, Class<? extends Annotation> containerType, boolean inherited, Set<A> found,
 			Set<Annotation> visited) {
 
-		if (element instanceof Class) {
-			Class<?> clazz = (Class<?>) element;
+		if (element instanceof Class<?> clazz) {
 
 			// Recurse first in order to support top-down semantics for inherited, repeatable annotations.
 			if (inherited) {
@@ -342,19 +344,20 @@ else if (candidateAnnotationType.equals(containerType)) {
 					// a 'value' attribute that returns an array of the contained annotation type.
 					// See https://docs.oracle.com/javase/specs/jls/se8/html/jls-9.html#jls-9.6.3
 					Method method = ReflectionUtils.tryToGetMethod(containerType, "value").getOrThrow(
-						cause -> new JUnitException(String.format(
-							"Container annotation type '%s' must declare a 'value' attribute of type %s[].",
-							containerType, annotationType), cause));
+						cause -> new JUnitException(
+							"Container annotation type '%s' must declare a 'value' attribute of type %s[].".formatted(
+								containerType, annotationType),
+							cause));
 
 					Annotation[] containedAnnotations = (Annotation[]) ReflectionUtils.invokeMethod(method, candidate);
-					found.addAll((Collection<? extends A>) asList(containedAnnotations));
+					found.addAll((Collection<? extends A>) asList(requireNonNull(containedAnnotations)));
 				}
 				// Nested container annotation?
 				else if (isRepeatableAnnotationContainer(candidateAnnotationType)) {
 					Method method = ReflectionUtils.tryToGetMethod(candidateAnnotationType, "value").toOptional().get();
 					Annotation[] containedAnnotations = (Annotation[]) ReflectionUtils.invokeMethod(method, candidate);
 
-					for (Annotation containedAnnotation : containedAnnotations) {
+					for (Annotation containedAnnotation : requireNonNull(containedAnnotations)) {
 						findRepeatableAnnotations(containedAnnotation.getClass(), annotationType, containerType,
 							inherited, found, visited);
 					}
@@ -420,7 +423,7 @@ private static boolean isRepeatableAnnotationContainer(Class<? extends Annotatio
 	 * the supplied {@code index} is {@code 0}
 	 * @since 1.8
 	 */
-	private static AnnotatedElement getEffectiveAnnotatedParameter(Parameter parameter, int index) {
+	private static @Nullable AnnotatedElement getEffectiveAnnotatedParameter(Parameter parameter, int index) {
 		Preconditions.notNull(parameter, "Parameter must not be null");
 		Executable executable = parameter.getDeclaringExecutable();
 
@@ -450,7 +453,7 @@ public static List<Field> findPublicAnnotatedFields(Class<?> clazz, Class<?> fie
 		// @formatter:off
 		return Arrays.stream(clazz.getFields())
 				.filter(field -> fieldType.isAssignableFrom(field.getType()) && isAnnotated(field, annotationType))
-				.collect(toUnmodifiableList());
+				.toList();
 		// @formatter:on
 	}
 
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/BlacklistedExceptions.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/BlacklistedExceptions.java
deleted file mode 100644
index f51c6ca8fc75..000000000000
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/BlacklistedExceptions.java
+++ /dev/null
@@ -1,60 +0,0 @@
-/*
- * Copyright 2015-2025 the original author or authors.
- *
- * All rights reserved. This program and the accompanying materials are
- * made available under the terms of the Eclipse Public License v2.0 which
- * accompanies this distribution and is available at
- *
- * https://www.eclipse.org/legal/epl-v20.html
- */
-
-package org.junit.platform.commons.util;
-
-import static org.apiguardian.api.API.Status.DEPRECATED;
-
-import org.apiguardian.api.API;
-
-/**
- * Internal utilities for working with <em>unrecoverable</em> exceptions.
- *
- * <p><em>Unrecoverable</em> exceptions are those that should always terminate
- * test plan execution immediately.
- *
- * <h2>Currently Unrecoverable Exceptions</h2>
- * <ul>
- * <li>{@link OutOfMemoryError}</li>
- * </ul>
- *
- * <h2>DISCLAIMER</h2>
- *
- * <p>These utilities are intended solely for usage within the JUnit framework
- * itself. <strong>Any usage by external parties is not supported.</strong>
- * Use at your own risk!
- *
- * @since 1.0
- * @deprecated Use {@link UnrecoverableExceptions} instead.
- */
-@Deprecated
-@API(status = DEPRECATED, since = "1.7")
-public final class BlacklistedExceptions {
-
-	private BlacklistedExceptions() {
-		/* no-op */
-	}
-
-	/**
-	 * Rethrow the supplied {@link Throwable exception} if it is
-	 * <em>unrecoverable</em>.
-	 *
-	 * <p>If the supplied {@code exception} is not <em>unrecoverable</em>, this
-	 * method does nothing.
-	 *
-	 * @deprecated Use {@link UnrecoverableExceptions#rethrowIfUnrecoverable}
-	 * instead.
-	 */
-	@Deprecated
-	public static void rethrowIfBlacklisted(Throwable exception) {
-		UnrecoverableExceptions.rethrowIfUnrecoverable(exception);
-	}
-
-}
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/ClassNamePatternFilterUtils.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/ClassNamePatternFilterUtils.java
index efca1d2dcdb6..bfe483dd0957 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/ClassNamePatternFilterUtils.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/ClassNamePatternFilterUtils.java
@@ -10,7 +10,6 @@
 
 package org.junit.platform.commons.util;
 
-import static java.util.stream.Collectors.toList;
 import static org.apiguardian.api.API.Status.INTERNAL;
 
 import java.util.Arrays;
@@ -22,6 +21,7 @@
 import java.util.regex.Pattern;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 
 /**
  * Collection of utilities for creating filters based on class names.
@@ -52,7 +52,7 @@ private ClassNamePatternFilterUtils() {
 	 *
 	 * @param patterns a comma-separated list of patterns
 	 */
-	public static <T> Predicate<T> excludeMatchingClasses(String patterns) {
+	public static <T> Predicate<T> excludeMatchingClasses(@Nullable String patterns) {
 		return matchingClasses(patterns, object -> object.getClass().getName(), FilterType.EXCLUDE);
 	}
 
@@ -62,7 +62,7 @@ public static <T> Predicate<T> excludeMatchingClasses(String patterns) {
 	 *
 	 * @param patterns a comma-separated list of patterns
 	 */
-	public static Predicate<String> excludeMatchingClassNames(String patterns) {
+	public static Predicate<String> excludeMatchingClassNames(@Nullable String patterns) {
 		return matchingClasses(patterns, Function.identity(), FilterType.EXCLUDE);
 	}
 
@@ -73,7 +73,7 @@ public static Predicate<String> excludeMatchingClassNames(String patterns) {
 	 *
 	 * @param patterns a comma-separated list of patterns
 	 */
-	public static <T> Predicate<T> includeMatchingClasses(String patterns) {
+	public static <T> Predicate<T> includeMatchingClasses(@Nullable String patterns) {
 		return matchingClasses(patterns, object -> object.getClass().getName(), FilterType.INCLUDE);
 	}
 
@@ -83,7 +83,7 @@ public static <T> Predicate<T> includeMatchingClasses(String patterns) {
 	 *
 	 * @param patterns a comma-separated list of patterns
 	 */
-	public static Predicate<String> includeMatchingClassNames(String patterns) {
+	public static Predicate<String> includeMatchingClassNames(@Nullable String patterns) {
 		return matchingClasses(patterns, Function.identity(), FilterType.INCLUDE);
 	}
 
@@ -91,7 +91,7 @@ private enum FilterType {
 		INCLUDE, EXCLUDE
 	}
 
-	private static <T> Predicate<T> matchingClasses(String patterns, Function<T, String> classNameProvider,
+	private static <T> Predicate<T> matchingClasses(@Nullable String patterns, Function<T, String> classNameProvider,
 			FilterType type) {
 		// @formatter:off
 		return Optional.ofNullable(patterns)
@@ -123,7 +123,7 @@ private static List<Pattern> convertToRegularExpressions(String patterns) {
 				.map(String::trim)
 				.map(ClassNamePatternFilterUtils::replaceRegExElements)
 				.map(Pattern::compile)
-				.collect(toList());
+				.toList();
 		// @formatter:on
 	}
 
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/ClassUtils.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/ClassUtils.java
index 9fc01426c2f6..51a6eb26f20c 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/ClassUtils.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/ClassUtils.java
@@ -17,6 +17,7 @@
 import java.util.function.Function;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 
 /**
  * Collection of utilities for working with {@link Class classes}.
@@ -49,7 +50,7 @@ private ClassUtils() {
 	 * @see #nullSafeToString(Class...)
 	 * @see StringUtils#nullSafeToString(Object)
 	 */
-	public static String nullSafeToString(Class<?> clazz) {
+	public static String nullSafeToString(@Nullable Class<?> clazz) {
 		return clazz == null ? "null" : clazz.getName();
 	}
 
@@ -64,7 +65,7 @@ public static String nullSafeToString(Class<?> clazz) {
 	 * @see #nullSafeToString(Function, Class...)
 	 * @see StringUtils#nullSafeToString(Object)
 	 */
-	public static String nullSafeToString(Class<?>... classes) {
+	public static String nullSafeToString(@Nullable Class<?> @Nullable... classes) {
 		return nullSafeToString(Class::getName, classes);
 	}
 
@@ -83,13 +84,16 @@ public static String nullSafeToString(Class<?>... classes) {
 	 * @see #nullSafeToString(Class...)
 	 * @see StringUtils#nullSafeToString(Object)
 	 */
-	public static String nullSafeToString(Function<? super Class<?>, ? extends String> mapper, Class<?>... classes) {
+	public static String nullSafeToString(Function<? super Class<?>, ? extends String> mapper,
+			@Nullable Class<?> @Nullable... classes) {
 		Preconditions.notNull(mapper, "Mapping function must not be null");
 
 		if (classes == null || classes.length == 0) {
 			return "";
 		}
-		return stream(classes).map(clazz -> clazz == null ? "null" : mapper.apply(clazz)).collect(joining(", "));
+		return stream(classes) //
+				.map(clazz -> clazz == null ? "null" : mapper.apply(clazz)) //
+				.collect(joining(", "));
 	}
 
 }
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/ClasspathScannerLoader.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/ClasspathScannerLoader.java
index 67c919d930b2..cfa60d58369b 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/ClasspathScannerLoader.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/ClasspathScannerLoader.java
@@ -10,7 +10,6 @@
 
 package org.junit.platform.commons.util;
 
-import static java.util.stream.Collectors.toList;
 import static java.util.stream.StreamSupport.stream;
 
 import java.util.List;
@@ -29,16 +28,16 @@ static ClasspathScanner getInstance() {
 		ServiceLoader<ClasspathScanner> serviceLoader = ServiceLoader.load(ClasspathScanner.class,
 			ClassLoaderUtils.getDefaultClassLoader());
 
-		List<ClasspathScanner> classpathScanners = stream(serviceLoader.spliterator(), false).collect(toList());
+		List<ClasspathScanner> classpathScanners = stream(serviceLoader.spliterator(), false).toList();
 
 		if (classpathScanners.size() == 1) {
 			return classpathScanners.get(0);
 		}
 
 		if (classpathScanners.size() > 1) {
-			throw new JUnitException(String.format(
-				"There should not be more than one ClasspathScanner implementation present on the classpath but there were %d: %s",
-				classpathScanners.size(), classpathScanners));
+			throw new JUnitException(
+				"There should not be more than one ClasspathScanner implementation present on the classpath but there were %d: %s".formatted(
+					classpathScanners.size(), classpathScanners));
 		}
 
 		return new DefaultClasspathScanner(ClassLoaderUtils::getDefaultClassLoader, ReflectionUtils::tryToLoadClass);
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/CollectionUtils.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/CollectionUtils.java
index c50a4b178518..cd6a1b6f2190 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/CollectionUtils.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/CollectionUtils.java
@@ -12,8 +12,6 @@
 
 import static java.util.Spliterator.ORDERED;
 import static java.util.Spliterators.spliteratorUnknownSize;
-import static java.util.stream.Collectors.collectingAndThen;
-import static java.util.stream.Collectors.toList;
 import static java.util.stream.StreamSupport.stream;
 import static org.apiguardian.api.API.Status.INTERNAL;
 import static org.junit.platform.commons.support.ReflectionSupport.invokeMethod;
@@ -22,21 +20,18 @@
 import java.lang.reflect.Method;
 import java.util.Arrays;
 import java.util.Collection;
-import java.util.Collections;
-import java.util.HashSet;
 import java.util.Iterator;
 import java.util.List;
 import java.util.ListIterator;
 import java.util.Optional;
-import java.util.Set;
 import java.util.function.Consumer;
-import java.util.stream.Collector;
 import java.util.stream.DoubleStream;
 import java.util.stream.IntStream;
 import java.util.stream.LongStream;
 import java.util.stream.Stream;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.PreconditionViolationException;
 import org.junit.platform.commons.support.ReflectionSupport;
 
@@ -82,63 +77,19 @@ public static <T> T getOnlyElement(Collection<T> collection) {
 	 * @since 1.11
 	 */
 	@API(status = INTERNAL, since = "1.11")
-	public static <T> Optional<T> getFirstElement(Collection<T> collection) {
+	public static <T extends @Nullable Object> Optional<T> getFirstElement(Collection<T> collection) {
 		Preconditions.notNull(collection, "collection must not be null");
 		return collection.isEmpty() //
 				? Optional.empty() //
 				: Optional.ofNullable(firstElement(collection));
 	}
 
-	private static <T> T firstElement(Collection<T> collection) {
-		return collection instanceof List //
-				? ((List<T>) collection).get(0) //
+	private static <T extends @Nullable Object> T firstElement(Collection<T> collection) {
+		return collection instanceof List<T> list //
+				? list.get(0) //
 				: collection.iterator().next();
 	}
 
-	/**
-	 * Convert the supplied array of values to a {@link Set}.
-	 *
-	 * @param values the array of values; never {@code null}
-	 * @return a set of the values
-	 * @throws PreconditionViolationException if the array is {@code null}
-	 * @since 1.6
-	 */
-	@API(status = INTERNAL, since = "1.6")
-	public static <T> Set<T> toSet(T[] values) {
-		Preconditions.notNull(values, "values array must not be null");
-		if (values.length == 0) {
-			return Collections.emptySet();
-		}
-		if (values.length == 1) {
-			return Collections.singleton(values[0]);
-		}
-		Set<T> set = new HashSet<>();
-		Collections.addAll(set, values);
-		return set;
-	}
-
-	/**
-	 * Return a {@code Collector} that accumulates the input elements into a
-	 * new unmodifiable list, in encounter order.
-	 *
-	 * <p>There are no guarantees on the type or serializability of the list
-	 * returned, so if more control over the returned list is required,
-	 * consider creating a new {@code Collector} implementation like the
-	 * following:
-	 *
-	 * <pre class="code">
-	 * public static &lt;T&gt; Collector&lt;T, ?, List&lt;T&gt;&gt; toUnmodifiableList(Supplier&lt;List&lt;T&gt;&gt; listSupplier) {
-	 *     return Collectors.collectingAndThen(Collectors.toCollection(listSupplier), Collections::unmodifiableList);
-	 * }</pre>
-	 *
-	 * @param <T> the type of the input elements
-	 * @return a {@code Collector} which collects all the input elements into
-	 * an unmodifiable list, in encounter order
-	 */
-	public static <T> Collector<T, ?, List<T>> toUnmodifiableList() {
-		return collectingAndThen(toList(), Collections::unmodifiableList);
-	}
-
 	/**
 	 * Determine if an instance of the supplied type can be converted into a
 	 * {@code Stream}.
@@ -153,7 +104,7 @@ public static <T> Set<T> toSet(T[] values) {
 	 * @see #toStream(Object)
 	 */
 	@API(status = INTERNAL, since = "1.9.1")
-	public static boolean isConvertibleToStream(Class<?> type) {
+	public static boolean isConvertibleToStream(@Nullable Class<?> type) {
 		if (type == null || type == void.class) {
 			return false;
 		}
@@ -194,38 +145,38 @@ public static boolean isConvertibleToStream(Class<?> type) {
 	 */
 	public static Stream<?> toStream(Object object) {
 		Preconditions.notNull(object, "Object must not be null");
-		if (object instanceof Stream) {
-			return (Stream<?>) object;
+		if (object instanceof Stream<?> stream) {
+			return stream;
 		}
-		if (object instanceof DoubleStream) {
-			return ((DoubleStream) object).boxed();
+		if (object instanceof DoubleStream stream) {
+			return stream.boxed();
 		}
-		if (object instanceof IntStream) {
-			return ((IntStream) object).boxed();
+		if (object instanceof IntStream stream) {
+			return stream.boxed();
 		}
-		if (object instanceof LongStream) {
-			return ((LongStream) object).boxed();
+		if (object instanceof LongStream stream) {
+			return stream.boxed();
 		}
-		if (object instanceof Collection) {
-			return ((Collection<?>) object).stream();
+		if (object instanceof Collection<?> collection) {
+			return collection.stream();
 		}
-		if (object instanceof Iterable) {
-			return stream(((Iterable<?>) object).spliterator(), false);
+		if (object instanceof Iterable<?> iterable) {
+			return stream(iterable.spliterator(), false);
 		}
-		if (object instanceof Iterator) {
-			return stream(spliteratorUnknownSize((Iterator<?>) object, ORDERED), false);
+		if (object instanceof Iterator<?> iterator) {
+			return stream(spliteratorUnknownSize(iterator, ORDERED), false);
 		}
-		if (object instanceof Object[]) {
-			return Arrays.stream((Object[]) object);
+		if (object instanceof Object[] array) {
+			return Arrays.stream(array);
 		}
-		if (object instanceof double[]) {
-			return DoubleStream.of((double[]) object).boxed();
+		if (object instanceof double[] array) {
+			return DoubleStream.of(array).boxed();
 		}
-		if (object instanceof int[]) {
-			return IntStream.of((int[]) object).boxed();
+		if (object instanceof int[] array) {
+			return IntStream.of(array).boxed();
 		}
-		if (object instanceof long[]) {
-			return LongStream.of((long[]) object).boxed();
+		if (object instanceof long[] array) {
+			return LongStream.of(array).boxed();
 		}
 		if (object.getClass().isArray() && object.getClass().getComponentType().isPrimitive()) {
 			return IntStream.range(0, Array.getLength(object)).mapToObj(i -> Array.get(object, i));
@@ -238,8 +189,8 @@ private static Stream<?> tryConvertToStreamByReflection(Object object) {
 				.map(method -> (Iterator<?>) invokeMethod(method, object)) //
 				.map(iterator -> spliteratorUnknownSize(iterator, ORDERED)) //
 				.map(spliterator -> stream(spliterator, false)) //
-				.orElseThrow(() -> new PreconditionViolationException(String.format(
-					"Cannot convert instance of %s into a Stream: %s", object.getClass().getName(), object)));
+				.orElseThrow(() -> new PreconditionViolationException(
+					"Cannot convert instance of %s into a Stream: %s".formatted(object.getClass().getName(), object)));
 	}
 
 	private static Optional<Method> findIteratorMethod(Class<?> type) {
@@ -251,7 +202,7 @@ private static Optional<Method> findIteratorMethod(Class<?> type) {
 	 * Call the supplied action on each element of the supplied {@link List} from last to first element.
 	 */
 	@API(status = INTERNAL, since = "1.9.2")
-	public static <T> void forEachInReverseOrder(List<T> list, Consumer<? super T> action) {
+	public static <T extends @Nullable Object> void forEachInReverseOrder(List<T> list, Consumer<? super T> action) {
 		if (list.isEmpty()) {
 			return;
 		}
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/ExceptionUtils.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/ExceptionUtils.java
index c2056951ddf8..8874905af32a 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/ExceptionUtils.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/ExceptionUtils.java
@@ -171,7 +171,7 @@ public static List<Throwable> findNestedThrowables(Throwable rootThrowable) {
 			}
 		}
 
-		return Collections.unmodifiableList(new ArrayList<>(visited));
+		return List.copyOf(visited);
 	}
 
 }
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/FunctionUtils.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/FunctionUtils.java
index 9546914e2c6a..0e7470fbf099 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/FunctionUtils.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/FunctionUtils.java
@@ -16,6 +16,7 @@
 import java.util.function.Predicate;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 
 /**
  * Collection of utilities for working with {@link Function Functions},
@@ -43,7 +44,8 @@ private FunctionUtils() {
 	 * @param function the function to apply
 	 * @param predicate the predicate to test against the result of the function
 	 */
-	public static <T, V> Predicate<T> where(Function<T, V> function, Predicate<? super V> predicate) {
+	public static <T extends @Nullable Object, V extends @Nullable Object> Predicate<T> where(Function<T, V> function,
+			Predicate<? super V> predicate) {
 		Preconditions.notNull(function, "function must not be null");
 		Preconditions.notNull(predicate, "predicate must not be null");
 		return input -> predicate.test(function.apply(input));
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/KotlinReflectionUtils.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/KotlinReflectionUtils.java
new file mode 100644
index 000000000000..926ae651ee99
--- /dev/null
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/KotlinReflectionUtils.java
@@ -0,0 +1,115 @@
+/*
+ * Copyright 2015-2025 the original author or authors.
+ *
+ * All rights reserved. This program and the accompanying materials are
+ * made available under the terms of the Eclipse Public License v2.0 which
+ * accompanies this distribution and is available at
+ *
+ * https://www.eclipse.org/legal/epl-v20.html
+ */
+
+package org.junit.platform.commons.util;
+
+import static org.apiguardian.api.API.Status.INTERNAL;
+import static org.junit.platform.commons.util.ReflectionUtils.tryToLoadClass;
+
+import java.lang.annotation.Annotation;
+import java.lang.reflect.Method;
+import java.lang.reflect.Parameter;
+import java.lang.reflect.Type;
+
+import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
+import org.junit.platform.commons.function.Try;
+
+/**
+ * Internal Kotlin-specific reflection utilities
+ *
+ * @since 6.0
+ */
+@API(status = INTERNAL, since = "6.0")
+public class KotlinReflectionUtils {
+
+	private static final @Nullable Class<? extends Annotation> kotlinMetadata;
+	private static final @Nullable Class<?> kotlinCoroutineContinuation;
+	private static final boolean kotlinReflectPresent;
+	private static final boolean kotlinxCoroutinesPresent;
+
+	static {
+		var metadata = tryToLoadKotlinMetadataClass();
+		kotlinMetadata = metadata.toOptional().orElse(null);
+		kotlinCoroutineContinuation = metadata //
+				.andThen(__ -> tryToLoadClass("kotlin.coroutines.Continuation")) //
+				.toOptional() //
+				.orElse(null);
+		kotlinReflectPresent = metadata.andThen(__ -> tryToLoadClass("kotlin.reflect.jvm.ReflectJvmMapping")) //
+				.toOptional() //
+				.isPresent();
+		kotlinxCoroutinesPresent = metadata.andThen(__ -> tryToLoadClass("kotlinx.coroutines.BuildersKt")) //
+				.toOptional() //
+				.isPresent();
+	}
+
+	@SuppressWarnings("unchecked")
+	private static Try<Class<? extends Annotation>> tryToLoadKotlinMetadataClass() {
+		return tryToLoadClass("kotlin.Metadata") //
+				.andThenTry(it -> (Class<? extends Annotation>) it);
+	}
+
+	public static boolean isKotlinSuspendingFunction(Method method) {
+		if (kotlinCoroutineContinuation != null && isKotlinType(method.getDeclaringClass())) {
+			int parameterCount = method.getParameterCount();
+			return parameterCount > 0 //
+					&& method.getParameterTypes()[parameterCount - 1] == kotlinCoroutineContinuation;
+		}
+		return false;
+	}
+
+	private static boolean isKotlinType(Class<?> clazz) {
+		return kotlinMetadata != null //
+				&& clazz.getDeclaredAnnotation(kotlinMetadata) != null;
+	}
+
+	public static Class<?> getKotlinSuspendingFunctionReturnType(Method method) {
+		requireKotlinReflect(method);
+		return KotlinSuspendingFunctionUtils.getReturnType(method);
+	}
+
+	public static Type getKotlinSuspendingFunctionGenericReturnType(Method method) {
+		requireKotlinReflect(method);
+		return KotlinSuspendingFunctionUtils.getGenericReturnType(method);
+	}
+
+	public static Parameter[] getKotlinSuspendingFunctionParameters(Method method) {
+		requireKotlinReflect(method);
+		return KotlinSuspendingFunctionUtils.getParameters(method);
+	}
+
+	public static Class<?>[] getKotlinSuspendingFunctionParameterTypes(Method method) {
+		requireKotlinReflect(method);
+		return KotlinSuspendingFunctionUtils.getParameterTypes(method);
+	}
+
+	public static @Nullable Object invokeKotlinSuspendingFunction(Method method, @Nullable Object target,
+			@Nullable Object[] args) {
+		requireKotlinReflect(method);
+		requireKotlinxCoroutines(method);
+		return KotlinSuspendingFunctionUtils.invoke(method, target, args);
+	}
+
+	private static void requireKotlinReflect(Method method) {
+		requireDependency(method, kotlinReflectPresent, "org.jetbrains.kotlin:kotlin-reflect");
+	}
+
+	private static void requireKotlinxCoroutines(Method method) {
+		requireDependency(method, kotlinxCoroutinesPresent, "org.jetbrains.kotlinx:kotlinx-coroutines-core");
+	}
+
+	private static void requireDependency(Method method, boolean condition, String dependencyNotation) {
+		Preconditions.condition(condition,
+			() -> ("Kotlin suspending function [%s] requires %s to be on the classpath or module path. "
+					+ "Please add a corresponding dependency.").formatted(method.toGenericString(),
+						dependencyNotation));
+	}
+
+}
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/KotlinSuspendingFunctionUtils.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/KotlinSuspendingFunctionUtils.java
new file mode 100644
index 000000000000..363af7fcffc3
--- /dev/null
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/KotlinSuspendingFunctionUtils.java
@@ -0,0 +1,112 @@
+/*
+ * Copyright 2015-2025 the original author or authors.
+ *
+ * All rights reserved. This program and the accompanying materials are
+ * made available under the terms of the Eclipse Public License v2.0 which
+ * accompanies this distribution and is available at
+ *
+ * https://www.eclipse.org/legal/epl-v20.html
+ */
+
+package org.junit.platform.commons.util;
+
+import static kotlin.jvm.JvmClassMappingKt.getJavaClass;
+import static kotlin.reflect.full.KCallables.callSuspendBy;
+import static kotlin.reflect.jvm.KCallablesJvm.isAccessible;
+import static kotlin.reflect.jvm.KCallablesJvm.setAccessible;
+import static kotlin.reflect.jvm.KTypesJvm.getJvmErasure;
+import static kotlin.reflect.jvm.ReflectJvmMapping.getJavaType;
+import static kotlinx.coroutines.BuildersKt.runBlocking;
+import static org.junit.platform.commons.util.ExceptionUtils.throwAsUncheckedException;
+import static org.junit.platform.commons.util.ReflectionUtils.getUnderlyingCause;
+
+import java.lang.reflect.Method;
+import java.lang.reflect.Parameter;
+import java.lang.reflect.Type;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.Map;
+
+import org.jspecify.annotations.Nullable;
+
+import kotlin.Unit;
+import kotlin.coroutines.EmptyCoroutineContext;
+import kotlin.reflect.KFunction;
+import kotlin.reflect.KParameter;
+import kotlin.reflect.jvm.ReflectJvmMapping;
+
+class KotlinSuspendingFunctionUtils {
+
+	static Class<?> getReturnType(Method method) {
+		var returnType = getJavaClass(getJvmErasure(getKotlinFunction(method).getReturnType()));
+		if (Unit.class.equals(returnType)) {
+			return void.class;
+		}
+		return returnType;
+	}
+
+	static Type getGenericReturnType(Method method) {
+		return getJavaType(getKotlinFunction(method).getReturnType());
+	}
+
+	static Parameter[] getParameters(Method method) {
+		var parameterCount = method.getParameterCount();
+		if (parameterCount == 1) {
+			return new Parameter[0];
+		}
+		return Arrays.copyOf(method.getParameters(), parameterCount - 1);
+	}
+
+	static Class<?>[] getParameterTypes(Method method) {
+		var parameterCount = method.getParameterCount();
+		if (parameterCount == 1) {
+			return new Class<?>[0];
+		}
+		return Arrays.stream(method.getParameterTypes()).limit(parameterCount - 1).toArray(Class<?>[]::new);
+	}
+
+	static @Nullable Object invoke(Method method, @Nullable Object target, @Nullable Object[] args) {
+		try {
+			return invoke(getKotlinFunction(method), target, args);
+		}
+		catch (InterruptedException e) {
+			throw throwAsUncheckedException(e);
+		}
+	}
+
+	private static <T> @Nullable T invoke(KFunction<T> function, @Nullable Object target, @Nullable Object[] args)
+			throws InterruptedException {
+		if (!isAccessible(function)) {
+			setAccessible(function, true);
+		}
+		return runBlocking(EmptyCoroutineContext.INSTANCE, (__, continuation) -> {
+			try {
+				return callSuspendBy(function, toArgumentMap(target, args, function), continuation);
+			}
+			catch (Exception e) {
+				throw throwAsUncheckedException(getUnderlyingCause(e));
+			}
+		});
+	}
+
+	private static Map<KParameter, @Nullable Object> toArgumentMap(@Nullable Object target, @Nullable Object[] args,
+			KFunction<?> function) {
+		Map<KParameter, @Nullable Object> arguments = new HashMap<>(args.length + 1);
+		int index = 0;
+		for (KParameter parameter : function.getParameters()) {
+			switch (parameter.getKind()) {
+				case INSTANCE -> arguments.put(parameter, target);
+				case VALUE, EXTENSION_RECEIVER -> {
+					arguments.put(parameter, args[index]);
+					index++;
+				}
+			}
+		}
+		return arguments;
+	}
+
+	private static KFunction<?> getKotlinFunction(Method method) {
+		return Preconditions.notNull(ReflectJvmMapping.getKotlinFunction(method),
+			() -> "Failed to get Kotlin function for method: " + method);
+	}
+}
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/LruCache.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/LruCache.java
index 83a56c172608..b4fd94c246db 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/LruCache.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/LruCache.java
@@ -12,6 +12,7 @@
 
 import static org.apiguardian.api.API.Status.INTERNAL;
 
+import java.io.Serial;
 import java.util.LinkedHashMap;
 import java.util.Map;
 
@@ -29,6 +30,7 @@
 @API(status = INTERNAL, since = "1.6")
 public class LruCache<K, V> extends LinkedHashMap<K, V> {
 
+	@Serial
 	private static final long serialVersionUID = 1L;
 
 	private final int maxSize;
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/ModuleUtils.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/ModuleUtils.java
index 980c06394ea2..40208636bd4c 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/ModuleUtils.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/ModuleUtils.java
@@ -10,18 +10,33 @@
 
 package org.junit.platform.commons.util;
 
-import static java.util.Collections.emptyList;
-import static java.util.Collections.emptySet;
+import static java.util.Objects.requireNonNull;
+import static java.util.function.Predicate.isEqual;
+import static java.util.stream.Collectors.toCollection;
+import static java.util.stream.Collectors.toSet;
 import static org.apiguardian.api.API.Status.INTERNAL;
 
+import java.io.IOException;
+import java.lang.module.Configuration;
+import java.lang.module.ModuleFinder;
+import java.lang.module.ModuleReader;
+import java.lang.module.ModuleReference;
+import java.lang.module.ResolvedModule;
+import java.net.URI;
+import java.net.URISyntaxException;
+import java.util.ArrayList;
+import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Optional;
 import java.util.Set;
 import java.util.function.Predicate;
+import java.util.stream.Stream;
 
 import org.apiguardian.api.API;
+import org.junit.platform.commons.JUnitException;
 import org.junit.platform.commons.logging.Logger;
 import org.junit.platform.commons.logging.LoggerFactory;
+import org.junit.platform.commons.support.DefaultResource;
 import org.junit.platform.commons.support.Resource;
 import org.junit.platform.commons.support.scanning.ClassFilter;
 
@@ -49,42 +64,40 @@ public class ModuleUtils {
 	 * potentially empty
 	 */
 	public static Set<String> findAllNonSystemBootModuleNames() {
-		logger.config(() -> "Basic version of findAllNonSystemBootModuleNames() always returns an empty set!");
-		return emptySet();
+		// @formatter:off
+		Set<String> systemModules = ModuleFinder.ofSystem().findAll().stream()
+				.map(reference -> reference.descriptor().name())
+				.collect(toSet());
+		return streamResolvedModules(name -> !systemModules.contains(name))
+				.map(ResolvedModule::name)
+				.collect(toCollection(LinkedHashSet::new));
+		// @formatter:on
 	}
 
 	/**
-	 * Determine if the current Java runtime supports the Java Platform Module System.
+	 * Java 9+ runtime supports the Java Platform Module System.
 	 *
-	 * @return {@code true} if the Java Platform Module System is available,
-	 * otherwise {@code false}
+	 * @return {@code true}
 	 */
 	public static boolean isJavaPlatformModuleSystemAvailable() {
-		return false;
+		return true;
 	}
 
-	/**
-	 * Return the name of the module that the class or interface is a member of.
-	 *
-	 * @param type class or interface to analyze
-	 * @return the module name; never {@code null} but potentially empty
-	 */
 	public static Optional<String> getModuleName(Class<?> type) {
-		return Optional.empty();
+		Preconditions.notNull(type, "Class type must not be null");
+
+		return Optional.ofNullable(type.getModule().getName());
 	}
 
-	/**
-	 * Return the raw version of the module that the class or interface is a member of.
-	 *
-	 * @param type class or interface to analyze
-	 * @return the raw module version; never {@code null} but potentially empty
-	 */
 	public static Optional<String> getModuleVersion(Class<?> type) {
-		return Optional.empty();
+		Preconditions.notNull(type, "Class type must not be null");
+
+		Module module = type.getModule();
+		return module.isNamed() ? module.getDescriptor().rawVersion() : Optional.empty();
 	}
 
 	/**
-	 * Find all classes for the given module name.
+	 * Find all {@linkplain Class classes} for the given module name.
 	 *
 	 * @param moduleName the name of the module to scan; never {@code null} or
 	 * <em>empty</em>
@@ -96,12 +109,17 @@ public static List<Class<?>> findAllClassesInModule(String moduleName, ClassFilt
 		Preconditions.notBlank(moduleName, "Module name must not be null or empty");
 		Preconditions.notNull(filter, "Class filter must not be null");
 
-		logger.config(() -> "Basic version of findAllClassesInModule() always returns an empty list!");
-		return emptyList();
+		logger.debug(() -> "Looking for classes in module: " + moduleName);
+		// @formatter:off
+		Set<ModuleReference> moduleReferences = streamResolvedModules(isEqual(moduleName))
+				.map(ResolvedModule::reference)
+				.collect(toSet());
+		// @formatter:on
+		return scan(moduleReferences, filter, ModuleUtils.class.getClassLoader());
 	}
 
 	/**
-	 * Find all resources for the given module name.
+	 * Find all {@linkplain Resource resources} for the given module name.
 	 *
 	 * @param moduleName the name of the module to scan; never {@code null} or
 	 * <em>empty</em>
@@ -115,8 +133,178 @@ public static List<Resource> findAllResourcesInModule(String moduleName, Predica
 		Preconditions.notBlank(moduleName, "Module name must not be null or empty");
 		Preconditions.notNull(filter, "Resource filter must not be null");
 
-		logger.config(() -> "Basic version of findAllResourcesInModule() always returns an empty list!");
-		return emptyList();
+		logger.debug(() -> "Looking for classes in module: " + moduleName);
+		// @formatter:off
+		Set<ModuleReference> moduleReferences = streamResolvedModules(isEqual(moduleName))
+				.map(ResolvedModule::reference)
+				.collect(toSet());
+		// @formatter:on
+		return scan(moduleReferences, filter, ModuleUtils.class.getClassLoader());
+	}
+
+	/**
+	 * Stream resolved modules from current (or boot) module layer.
+	 */
+	private static Stream<ResolvedModule> streamResolvedModules(Predicate<String> moduleNamePredicate) {
+		Module module = ModuleUtils.class.getModule();
+		ModuleLayer layer = module.getLayer();
+		if (layer == null) {
+			logger.config(() -> ModuleUtils.class + " is a member of " + module
+					+ " - using boot layer returned by ModuleLayer.boot() as fall-back.");
+			layer = ModuleLayer.boot();
+		}
+		return streamResolvedModules(moduleNamePredicate, layer);
+	}
+
+	/**
+	 * Stream resolved modules from the supplied layer.
+	 */
+	private static Stream<ResolvedModule> streamResolvedModules(Predicate<String> moduleNamePredicate,
+			ModuleLayer layer) {
+		logger.debug(() -> "Streaming modules for layer @" + System.identityHashCode(layer) + ": " + layer);
+		Configuration configuration = layer.configuration();
+		logger.debug(() -> "Module layer configuration: " + configuration);
+		Stream<ResolvedModule> stream = configuration.modules().stream();
+		return stream.filter(module -> moduleNamePredicate.test(module.name()));
+	}
+
+	/**
+	 * Scan for classes using the supplied set of module references, class
+	 * filter, and loader.
+	 */
+	private static List<Class<?>> scan(Set<ModuleReference> references, ClassFilter filter, ClassLoader loader) {
+		logger.debug(() -> "Scanning " + references.size() + " module references: " + references);
+		ModuleReferenceClassScanner scanner = new ModuleReferenceClassScanner(filter, loader);
+		List<Class<?>> classes = new ArrayList<>();
+		for (ModuleReference reference : references) {
+			classes.addAll(scanner.scan(reference));
+		}
+		logger.debug(() -> "Found " + classes.size() + " classes: " + classes);
+		return List.copyOf(classes);
+	}
+
+	/**
+	 * Scan for classes using the supplied set of module references, class
+	 * filter, and loader.
+	 */
+	private static List<Resource> scan(Set<ModuleReference> references, Predicate<Resource> filter,
+			ClassLoader loader) {
+		logger.debug(() -> "Scanning " + references.size() + " module references: " + references);
+		ModuleReferenceResourceScanner scanner = new ModuleReferenceResourceScanner(filter, loader);
+		List<Resource> classes = new ArrayList<>();
+		for (ModuleReference reference : references) {
+			classes.addAll(scanner.scan(reference));
+		}
+		logger.debug(() -> "Found " + classes.size() + " classes: " + classes);
+		return List.copyOf(classes);
+	}
+
+	/**
+	 * {@link ModuleReference} class scanner.
+	 *
+	 * @since 1.1
+	 */
+	static class ModuleReferenceClassScanner {
+
+		private final ClassFilter classFilter;
+		private final ClassLoader classLoader;
+
+		ModuleReferenceClassScanner(ClassFilter classFilter, ClassLoader classLoader) {
+			this.classFilter = classFilter;
+			this.classLoader = classLoader;
+		}
+
+		/**
+		 * Scan module reference for classes that potentially contain testable methods.
+		 */
+		List<Class<?>> scan(ModuleReference reference) {
+			try (ModuleReader reader = reference.open()) {
+				try (Stream<String> names = reader.list()) {
+					// @formatter:off
+					return names.filter(name -> name.endsWith(".class"))
+							.map(this::className)
+							.filter(name -> !name.equals("module-info"))
+							.filter(classFilter::match)
+							.<Class<?>> map(this::loadClassUnchecked)
+							.filter(classFilter::match)
+							.toList();
+					// @formatter:on
+				}
+			}
+			catch (IOException e) {
+				throw new JUnitException("Failed to read contents of " + reference + ".", e);
+			}
+		}
+
+		/**
+		 * Convert resource name to binary class name.
+		 */
+		private String className(String resourceName) {
+			resourceName = resourceName.substring(0, resourceName.length() - 6); // 6 = ".class".length()
+			resourceName = resourceName.replace('/', '.');
+			return resourceName;
+		}
+
+		/**
+		 * Load class by its binary name.
+		 *
+		 * @see ClassLoader#loadClass(String)
+		 */
+		private Class<?> loadClassUnchecked(String binaryName) {
+			try {
+				return classLoader.loadClass(binaryName);
+			}
+			catch (ClassNotFoundException e) {
+				throw new JUnitException("Failed to load class with name '" + binaryName + "'.", e);
+			}
+		}
+
+	}
+
+	/**
+	 * {@link ModuleReference} resource class scanner.
+	 *
+	 * @since 1.11
+	 */
+	static class ModuleReferenceResourceScanner {
+
+		private final Predicate<Resource> resourceFilter;
+		private final ClassLoader classLoader;
+
+		ModuleReferenceResourceScanner(Predicate<Resource> resourceFilter, ClassLoader classLoader) {
+			this.resourceFilter = resourceFilter;
+			this.classLoader = classLoader;
+		}
+
+		/**
+		 * Scan module reference for resources that potentially contain testable resources.
+		 */
+		List<Resource> scan(ModuleReference reference) {
+			try (ModuleReader reader = reference.open()) {
+				try (Stream<String> names = reader.list()) {
+					// @formatter:off
+					return names.filter(name -> !name.endsWith(".class"))
+							.map(this::loadResourceUnchecked)
+							.filter(resourceFilter)
+							.toList();
+					// @formatter:on
+				}
+			}
+			catch (IOException e) {
+				throw new JUnitException("Failed to read contents of " + reference + ".", e);
+			}
+		}
+
+		private Resource loadResourceUnchecked(String binaryName) {
+			try {
+				URI uri = requireNonNull(classLoader.getResource(binaryName)).toURI();
+				return new DefaultResource(binaryName, uri);
+			}
+			catch (NullPointerException | URISyntaxException e) {
+				throw new JUnitException("Failed to load resource with name '" + binaryName + "'.", e);
+			}
+		}
+
 	}
 
 }
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/PackageNameUtils.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/PackageNameUtils.java
deleted file mode 100644
index 2a0094dda4c4..000000000000
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/PackageNameUtils.java
+++ /dev/null
@@ -1,38 +0,0 @@
-/*
- * Copyright 2015-2025 the original author or authors.
- *
- * All rights reserved. This program and the accompanying materials are
- * made available under the terms of the Eclipse Public License v2.0 which
- * accompanies this distribution and is available at
- *
- * https://www.eclipse.org/legal/epl-v20.html
- */
-
-package org.junit.platform.commons.util;
-
-import static org.junit.platform.commons.util.PackageUtils.DEFAULT_PACKAGE_NAME;
-
-/**
- * Collection of utilities for working with package names.
- *
- * <h2>DISCLAIMER</h2>
- *
- * <p>These utilities are intended solely for usage within the JUnit framework
- * itself. <strong>Any usage by external parties is not supported.</strong>
- * Use at your own risk!
- *
- * @since 1.11.3
- */
-class PackageNameUtils {
-
-	static String getPackageName(Class<?> clazz) {
-		Package p = clazz.getPackage();
-		if (p != null) {
-			return p.getName();
-		}
-		String className = clazz.getName();
-		int index = className.lastIndexOf('.');
-		return index == -1 ? DEFAULT_PACKAGE_NAME : className.substring(0, index);
-	}
-
-}
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/PreconditionViolationException.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/PreconditionViolationException.java
deleted file mode 100644
index e28c0372d53a..000000000000
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/PreconditionViolationException.java
+++ /dev/null
@@ -1,39 +0,0 @@
-/*
- * Copyright 2015-2025 the original author or authors.
- *
- * All rights reserved. This program and the accompanying materials are
- * made available under the terms of the Eclipse Public License v2.0 which
- * accompanies this distribution and is available at
- *
- * https://www.eclipse.org/legal/epl-v20.html
- */
-
-package org.junit.platform.commons.util;
-
-import static org.apiguardian.api.API.Status.DEPRECATED;
-
-import org.apiguardian.api.API;
-import org.junit.platform.commons.JUnitException;
-
-/**
- * Thrown if a <em>precondition</em> is violated.
- *
- * @since 1.0
- * @see Preconditions
- * @deprecated Use {@linkplain org.junit.platform.commons.PreconditionViolationException} instead.
- */
-@API(status = DEPRECATED, since = "1.5")
-@Deprecated
-public class PreconditionViolationException extends JUnitException {
-
-	private static final long serialVersionUID = 1L;
-
-	public PreconditionViolationException(String message) {
-		super(message);
-	}
-
-	public PreconditionViolationException(String message, Throwable cause) {
-		super(message, cause);
-	}
-
-}
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/Preconditions.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/Preconditions.java
index 99c8ae49e6e6..c5e3e502c7c7 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/Preconditions.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/Preconditions.java
@@ -17,6 +17,7 @@
 import java.util.function.Supplier;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.PreconditionViolationException;
 
 /**
@@ -50,8 +51,10 @@ private Preconditions() {
 	 * @throws PreconditionViolationException if the supplied object is {@code null}
 	 * @see #notNull(Object, Supplier)
 	 */
-	public static <T> T notNull(T object, String message) throws PreconditionViolationException {
-		condition(object != null, message);
+	public static <T> T notNull(@Nullable T object, String message) throws PreconditionViolationException {
+		if (object == null) {
+			throw new PreconditionViolationException(message);
+		}
 		return object;
 	}
 
@@ -64,8 +67,12 @@ public static <T> T notNull(T object, String message) throws PreconditionViolati
 	 * @throws PreconditionViolationException if the supplied object is {@code null}
 	 * @see #condition(boolean, Supplier)
 	 */
-	public static <T> T notNull(T object, Supplier<String> messageSupplier) throws PreconditionViolationException {
-		condition(object != null, messageSupplier);
+	public static <T> T notNull(@Nullable T object, Supplier<String> messageSupplier)
+			throws PreconditionViolationException {
+
+		if (object == null) {
+			throw new PreconditionViolationException(messageSupplier.get());
+		}
 		return object;
 	}
 
@@ -81,8 +88,10 @@ public static <T> T notNull(T object, Supplier<String> messageSupplier) throws P
 	 * @see #condition(boolean, String)
 	 */
 	@API(status = INTERNAL, since = "1.11")
-	public static int[] notEmpty(int[] array, String message) throws PreconditionViolationException {
-		condition(array != null && array.length > 0, message);
+	public static int[] notEmpty(int @Nullable [] array, String message) throws PreconditionViolationException {
+		if (array == null || array.length == 0) {
+			throw new PreconditionViolationException(message);
+		}
 		return array;
 	}
 
@@ -100,8 +109,10 @@ public static int[] notEmpty(int[] array, String message) throws PreconditionVio
 	 * @see #containsNoNullElements(Object[], String)
 	 * @see #condition(boolean, String)
 	 */
-	public static <T> T[] notEmpty(T[] array, String message) throws PreconditionViolationException {
-		condition(array != null && array.length > 0, message);
+	public static <T> T[] notEmpty(T @Nullable [] array, String message) throws PreconditionViolationException {
+		if (array == null || array.length == 0) {
+			throw new PreconditionViolationException(message);
+		}
 		return array;
 	}
 
@@ -119,8 +130,12 @@ public static <T> T[] notEmpty(T[] array, String message) throws PreconditionVio
 	 * @see #containsNoNullElements(Object[], String)
 	 * @see #condition(boolean, String)
 	 */
-	public static <T> T[] notEmpty(T[] array, Supplier<String> messageSupplier) throws PreconditionViolationException {
-		condition(array != null && array.length > 0, messageSupplier);
+	public static <T> T[] notEmpty(T @Nullable [] array, Supplier<String> messageSupplier)
+			throws PreconditionViolationException {
+
+		if (array == null || array.length == 0) {
+			throw new PreconditionViolationException(messageSupplier.get());
+		}
 		return array;
 	}
 
@@ -137,10 +152,12 @@ public static <T> T[] notEmpty(T[] array, Supplier<String> messageSupplier) thro
 	 * @see #containsNoNullElements(Collection, String)
 	 * @see #condition(boolean, String)
 	 */
-	public static <T extends Collection<?>> T notEmpty(T collection, String message)
+	public static <T extends Collection<?>> T notEmpty(@Nullable T collection, String message)
 			throws PreconditionViolationException {
 
-		condition(collection != null && !collection.isEmpty(), message);
+		if (collection == null || collection.isEmpty()) {
+			throw new PreconditionViolationException(message);
+		}
 		return collection;
 	}
 
@@ -157,10 +174,12 @@ public static <T extends Collection<?>> T notEmpty(T collection, String message)
 	 * @see #containsNoNullElements(Collection, String)
 	 * @see #condition(boolean, String)
 	 */
-	public static <T extends Collection<?>> T notEmpty(T collection, Supplier<String> messageSupplier)
+	public static <T extends Collection<?>> T notEmpty(@Nullable T collection, Supplier<String> messageSupplier)
 			throws PreconditionViolationException {
 
-		condition(collection != null && !collection.isEmpty(), messageSupplier);
+		if (collection == null || collection.isEmpty()) {
+			throw new PreconditionViolationException(messageSupplier.get());
+		}
 		return collection;
 	}
 
@@ -177,7 +196,10 @@ public static <T extends Collection<?>> T notEmpty(T collection, Supplier<String
 	 * any {@code null} elements
 	 * @see #notNull(Object, String)
 	 */
-	public static <T> T[] containsNoNullElements(T[] array, String message) throws PreconditionViolationException {
+
+	public static <T> T @Nullable [] containsNoNullElements(T @Nullable [] array, String message)
+			throws PreconditionViolationException {
+
 		if (array != null) {
 			Arrays.stream(array).forEach(object -> notNull(object, message));
 		}
@@ -197,7 +219,7 @@ public static <T> T[] containsNoNullElements(T[] array, String message) throws P
 	 * any {@code null} elements
 	 * @see #notNull(Object, String)
 	 */
-	public static <T> T[] containsNoNullElements(T[] array, Supplier<String> messageSupplier)
+	public static <T> T @Nullable [] containsNoNullElements(T @Nullable [] array, Supplier<String> messageSupplier)
 			throws PreconditionViolationException {
 
 		if (array != null) {
@@ -219,7 +241,7 @@ public static <T> T[] containsNoNullElements(T[] array, Supplier<String> message
 	 * any {@code null} elements
 	 * @see #notNull(Object, String)
 	 */
-	public static <T extends Collection<?>> T containsNoNullElements(T collection, String message)
+	public static <T extends Collection<?>> @Nullable T containsNoNullElements(@Nullable T collection, String message)
 			throws PreconditionViolationException {
 
 		if (collection != null) {
@@ -241,8 +263,8 @@ public static <T extends Collection<?>> T containsNoNullElements(T collection, S
 	 * any {@code null} elements
 	 * @see #notNull(Object, String)
 	 */
-	public static <T extends Collection<?>> T containsNoNullElements(T collection, Supplier<String> messageSupplier)
-			throws PreconditionViolationException {
+	public static <T extends Collection<?>> @Nullable T containsNoNullElements(@Nullable T collection,
+			Supplier<String> messageSupplier) throws PreconditionViolationException {
 
 		if (collection != null) {
 			collection.forEach(object -> notNull(object, messageSupplier));
@@ -262,8 +284,10 @@ public static <T extends Collection<?>> T containsNoNullElements(T collection, S
 	 * @throws PreconditionViolationException if the supplied string is blank
 	 * @see #notBlank(String, Supplier)
 	 */
-	public static String notBlank(String str, String message) throws PreconditionViolationException {
-		condition(StringUtils.isNotBlank(str), message);
+	public static String notBlank(@Nullable String str, String message) throws PreconditionViolationException {
+		if (str == null || StringUtils.isBlank(str)) {
+			throw new PreconditionViolationException(message);
+		}
 		return str;
 	}
 
@@ -280,8 +304,12 @@ public static String notBlank(String str, String message) throws PreconditionVio
 	 * @see StringUtils#isNotBlank(String)
 	 * @see #condition(boolean, Supplier)
 	 */
-	public static String notBlank(String str, Supplier<String> messageSupplier) throws PreconditionViolationException {
-		condition(StringUtils.isNotBlank(str), messageSupplier);
+	public static String notBlank(@Nullable String str, Supplier<String> messageSupplier)
+			throws PreconditionViolationException {
+
+		if (str == null || StringUtils.isBlank(str)) {
+			throw new PreconditionViolationException(messageSupplier.get());
+		}
 		return str;
 	}
 
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/ReflectionUtils.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/ReflectionUtils.java
index f122e8c77958..d9bd8e4b4849 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/ReflectionUtils.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/ReflectionUtils.java
@@ -14,11 +14,8 @@
 import static java.util.Collections.synchronizedMap;
 import static java.util.stream.Collectors.toCollection;
 import static java.util.stream.Collectors.toSet;
-import static org.apiguardian.api.API.Status.DEPRECATED;
 import static org.apiguardian.api.API.Status.INTERNAL;
 import static org.apiguardian.api.API.Status.STABLE;
-import static org.junit.platform.commons.util.CollectionUtils.toUnmodifiableList;
-import static org.junit.platform.commons.util.PackageNameUtils.getPackageName;
 import static org.junit.platform.commons.util.ReflectionUtils.HierarchyTraversalMode.BOTTOM_UP;
 import static org.junit.platform.commons.util.ReflectionUtils.HierarchyTraversalMode.TOP_DOWN;
 
@@ -52,12 +49,15 @@
 import java.util.Optional;
 import java.util.Set;
 import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.function.Consumer;
 import java.util.function.Predicate;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 import java.util.stream.Stream;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.JUnitException;
 import org.junit.platform.commons.function.Try;
 import org.junit.platform.commons.logging.Logger;
@@ -85,27 +85,6 @@
 @API(status = INTERNAL, since = "1.0")
 public final class ReflectionUtils {
 
-	/**
-	 * Property name used to signal that legacy semantics should be used when
-	 * searching for fields and methods within a type hierarchy: {@value}.
-	 *
-	 * <p>Value must be either {@code true} or {@code false} (ignoring case);
-	 * defaults to {@code false}.
-	 *
-	 * <p>When set to {@code false} (either explicitly or implicitly), field and
-	 * method searches will adhere to Java semantics regarding whether a given
-	 * field or method is visible or overridden, where the latter only applies
-	 * to methods. When set to {@code true}, the semantics used in JUnit 5 prior
-	 * to JUnit 5.11 (JUnit Platform 1.11) will be used, which means that fields
-	 * and methods can hide, shadow, or supersede fields and methods in supertypes
-	 * based solely on the field's name or the method's signature, disregarding
-	 * the actual Java language semantics for visibility and whether a method
-	 * overrides another method.
-	 *
-	 * @since 1.11
-	 */
-	private static final String USE_LEGACY_SEARCH_SEMANTICS_PROPERTY_NAME = "junit.platform.reflection.search.useLegacySemantics";
-
 	private static final Logger logger = LoggerFactory.getLogger(ReflectionUtils.class);
 
 	private ReflectionUtils() {
@@ -151,7 +130,7 @@ public enum HierarchyTraversalMode {
 	 * <p>This serves as a cache to avoid repeated cycle detection for classes
 	 * that have already been checked.
 	 * @since 1.6
-	 * @see #detectInnerClassCycle(Class)
+	 * @see #detectInnerClassCycle(Class, CycleErrorHandling)
 	 */
 	private static final Set<String> noCyclesDetectedCache = ConcurrentHashMap.newKeySet();
 
@@ -238,7 +217,7 @@ public enum HierarchyTraversalMode {
 
 		classNameToTypeMap = Collections.unmodifiableMap(classNamesToTypes);
 
-		Map<Class<?>, Class<?>> primitivesToWrappers = new IdentityHashMap<>(9);
+		Map<Class<?>, Class<?>> primitivesToWrappers = new IdentityHashMap<>(8);
 
 		primitivesToWrappers.put(boolean.class, Boolean.class);
 		primitivesToWrappers.put(byte.class, Byte.class);
@@ -252,8 +231,6 @@ public enum HierarchyTraversalMode {
 		primitiveToWrapperMap = Collections.unmodifiableMap(primitivesToWrappers);
 	}
 
-	static volatile boolean useLegacySearchSemantics = getLegacySearchSemanticsFlag();
-
 	public static boolean isPublic(Class<?> clazz) {
 		Preconditions.notNull(clazz, "Class must not be null");
 		return Modifier.isPublic(clazz.getModifiers());
@@ -380,7 +357,7 @@ public static boolean isInnerClass(Class<?> clazz) {
 	 * @since 1.12
 	 */
 	@API(status = INTERNAL, since = "1.12")
-	public static boolean isRecordObject(Object object) {
+	public static boolean isRecordObject(@Nullable Object object) {
 		return object != null && isRecordClass(object.getClass());
 	}
 
@@ -390,8 +367,7 @@ public static boolean isRecordObject(Object object) {
 	 */
 	@API(status = INTERNAL, since = "1.12")
 	public static boolean isRecordClass(Class<?> clazz) {
-		Class<?> superclass = clazz.getSuperclass();
-		return superclass != null && "java.lang.Record".equals(superclass.getName());
+		return clazz.isRecord();
 	}
 
 	/**
@@ -410,7 +386,7 @@ public static boolean returnsPrimitiveVoid(Method method) {
 	 * @param obj the object to test; potentially {@code null}
 	 * @return {@code true} if the object is an array
 	 */
-	public static boolean isArray(Object obj) {
+	public static boolean isArray(@Nullable Object obj) {
 		return (obj != null && obj.getClass().isArray());
 	}
 
@@ -422,7 +398,7 @@ public static boolean isArray(Object obj) {
 	 * @since 1.3.2
 	 */
 	@API(status = INTERNAL, since = "1.3.2")
-	public static boolean isMultidimensionalArray(Object obj) {
+	public static boolean isMultidimensionalArray(@Nullable Object obj) {
 		return (obj != null && obj.getClass().isArray() && obj.getClass().getComponentType().isArray());
 	}
 
@@ -482,7 +458,7 @@ public static boolean isAssignableTo(Class<?> sourceType, Class<?> targetType) {
 	 * @see Class#isAssignableFrom(Class)
 	 * @see #isAssignableTo(Class, Class)
 	 */
-	public static boolean isAssignableTo(Object obj, Class<?> targetType) {
+	public static boolean isAssignableTo(@Nullable Object obj, Class<?> targetType) {
 		Preconditions.notNull(targetType, "target type must not be null");
 
 		if (obj == null) {
@@ -565,9 +541,9 @@ static boolean isWideningConversion(Class<?> sourceType, Class<?> targetType) {
 	 *
 	 * @param type the primitive type for which to retrieve the wrapper type
 	 * @return the corresponding wrapper type or {@code null} if the
-	 * supplied type is {@code null} or not a primitive type
+	 * supplied type is not a primitive type
 	 */
-	public static Class<?> getWrapperType(Class<?> type) {
+	public static @Nullable Class<?> getWrapperType(Class<?> type) {
 		return primitiveToWrapperMap.get(type);
 	}
 
@@ -603,7 +579,7 @@ public static <T> T newInstance(Class<T> clazz, Object... args) {
 	 * @see #newInstance(Class, Object...)
 	 * @see ExceptionUtils#throwAsUncheckedException(Throwable)
 	 */
-	public static <T> T newInstance(Constructor<T> constructor, Object... args) {
+	public static <T> T newInstance(Constructor<T> constructor, @Nullable Object... args) {
 		Preconditions.notNull(constructor, "Constructor must not be null");
 
 		try {
@@ -614,27 +590,6 @@ public static <T> T newInstance(Constructor<T> constructor, Object... args) {
 		}
 	}
 
-	/**
-	 * Read the value of a potentially inaccessible or nonexistent field.
-	 *
-	 * <p>If the field does not exist or the value of the field is {@code null},
-	 * an empty {@link Optional} will be returned.
-	 *
-	 * @param clazz the class where the field is declared; never {@code null}
-	 * @param fieldName the name of the field; never {@code null} or empty
-	 * @param instance the instance from where the value is to be read; may
-	 * be {@code null} for a static field
-	 * @see #readFieldValue(Field)
-	 * @see #readFieldValue(Field, Object)
-	 * @deprecated Please use {@link #tryToReadFieldValue(Class, String, Object)}
-	 * instead.
-	 */
-	@API(status = DEPRECATED, since = "1.4")
-	@Deprecated
-	public static <T> Optional<Object> readFieldValue(Class<T> clazz, String fieldName, T instance) {
-		return tryToReadFieldValue(clazz, fieldName, instance).toOptional();
-	}
-
 	/**
 	 * Try to read the value of a potentially inaccessible or nonexistent field.
 	 *
@@ -650,7 +605,7 @@ public static <T> Optional<Object> readFieldValue(Class<T> clazz, String fieldNa
 	 * @see #tryToReadFieldValue(Field, Object)
 	 */
 	@API(status = INTERNAL, since = "1.4")
-	public static <T> Try<Object> tryToReadFieldValue(Class<T> clazz, String fieldName, T instance) {
+	public static <T> Try<Object> tryToReadFieldValue(Class<T> clazz, String fieldName, @Nullable T instance) {
 		Preconditions.notNull(clazz, "Class must not be null");
 		Preconditions.notBlank(fieldName, "Field name must not be null or blank");
 
@@ -660,25 +615,6 @@ public static <T> Try<Object> tryToReadFieldValue(Class<T> clazz, String fieldNa
 		// @formatter:on
 	}
 
-	/**
-	 * Read the value of the supplied static field, making it accessible if
-	 * necessary and {@linkplain ExceptionUtils#throwAsUncheckedException masking}
-	 * any checked exception as an unchecked exception.
-	 *
-	 * <p>If the value of the field is {@code null}, an empty {@link Optional}
-	 * will be returned.
-	 *
-	 * @param field the field to read; never {@code null}
-	 * @see #readFieldValue(Field, Object)
-	 * @see #readFieldValue(Class, String, Object)
-	 * @deprecated Please use {@link #tryToReadFieldValue(Field)} instead.
-	 */
-	@API(status = DEPRECATED, since = "1.4")
-	@Deprecated
-	public static Optional<Object> readFieldValue(Field field) {
-		return tryToReadFieldValue(field).toOptional();
-	}
-
 	/**
 	 * Try to read the value of a potentially inaccessible static field.
 	 *
@@ -691,39 +627,18 @@ public static Optional<Object> readFieldValue(Field field) {
 	 * @see #tryToReadFieldValue(Class, String, Object)
 	 */
 	@API(status = INTERNAL, since = "1.4")
-	public static Try<Object> tryToReadFieldValue(Field field) {
+	public static Try<@Nullable Object> tryToReadFieldValue(Field field) {
 		return tryToReadFieldValue(field, null);
 	}
 
-	/**
-	 * Read the value of the supplied field, making it accessible if necessary
-	 * and {@linkplain ExceptionUtils#throwAsUncheckedException masking} any
-	 * checked exception as an unchecked exception.
-	 *
-	 * <p>If the value of the field is {@code null}, an empty {@link Optional}
-	 * will be returned.
-	 *
-	 * @param field the field to read; never {@code null}
-	 * @param instance the instance from which the value is to be read; may
-	 * be {@code null} for a static field
-	 * @see #readFieldValue(Field)
-	 * @see #readFieldValue(Class, String, Object)
-	 * @deprecated Please use {@link #tryToReadFieldValue(Field, Object)}
-	 * instead.
-	 */
-	@API(status = DEPRECATED, since = "1.4")
-	@Deprecated
-	public static Optional<Object> readFieldValue(Field field, Object instance) {
-		return tryToReadFieldValue(field, instance).toOptional();
-	}
-
 	/**
 	 * @since 1.4
 	 * @see org.junit.platform.commons.support.ReflectionSupport#tryToReadFieldValue(Field, Object)
 	 * @see #tryToReadFieldValue(Class, String, Object)
 	 */
 	@API(status = INTERNAL, since = "1.4")
-	public static Try<Object> tryToReadFieldValue(Field field, Object instance) {
+	@SuppressWarnings("NullAway")
+	public static Try<@Nullable Object> tryToReadFieldValue(Field field, @Nullable Object instance) {
 		Preconditions.notNull(field, "Field must not be null");
 		Preconditions.condition((instance != null || isStatic(field)),
 			() -> String.format("Cannot read non-static field [%s] on a null instance.", field));
@@ -742,7 +657,7 @@ public static Try<Object> tryToReadFieldValue(Field field, Object instance) {
 	 * @return an immutable list of the values of the specified fields; never
 	 * {@code null} but may be empty or contain {@code null} entries
 	 */
-	public static List<Object> readFieldValues(List<Field> fields, Object instance) {
+	public static List<?> readFieldValues(List<Field> fields, @Nullable Object instance) {
 		return readFieldValues(fields, instance, field -> true);
 	}
 
@@ -759,7 +674,7 @@ public static List<Object> readFieldValues(List<Field> fields, Object instance)
 	 * @return an immutable list of the values of the specified fields; never
 	 * {@code null} but may be empty or contain {@code null} entries
 	 */
-	public static List<Object> readFieldValues(List<Field> fields, Object instance, Predicate<Field> predicate) {
+	public static List<?> readFieldValues(List<Field> fields, @Nullable Object instance, Predicate<Field> predicate) {
 		Preconditions.notNull(fields, "fields list must not be null");
 		Preconditions.notNull(predicate, "Predicate must not be null");
 
@@ -767,16 +682,15 @@ public static List<Object> readFieldValues(List<Field> fields, Object instance,
 		return fields.stream()
 				.filter(predicate)
 				.map(field ->
-					tryToReadFieldValue(field, instance)
-						.getOrThrow(ExceptionUtils::throwAsUncheckedException))
-				.collect(toUnmodifiableList());
+					tryToReadFieldValue(field, instance).getOrThrow(ExceptionUtils::throwAsUncheckedException))
+				.toList();
 		// @formatter:on
 	}
 
 	/**
 	 * @see org.junit.platform.commons.support.ReflectionSupport#invokeMethod(Method, Object, Object...)
 	 */
-	public static Object invokeMethod(Method method, Object target, Object... args) {
+	public static @Nullable Object invokeMethod(Method method, @Nullable Object target, @Nullable Object... args) {
 		Preconditions.notNull(method, "Method must not be null");
 		Preconditions.condition((target != null || isStatic(method)),
 			() -> String.format("Cannot invoke non-static method [%s] on a null target.", method.toGenericString()));
@@ -789,16 +703,6 @@ public static Object invokeMethod(Method method, Object target, Object... args)
 		}
 	}
 
-	/**
-	 * @see org.junit.platform.commons.support.ReflectionSupport#loadClass(String)
-	 * @deprecated Please use {@link #tryToLoadClass(String)} instead.
-	 */
-	@API(status = DEPRECATED, since = "1.4")
-	@Deprecated
-	public static Optional<Class<?>> loadClass(String name) {
-		return tryToLoadClass(name).toOptional();
-	}
-
 	/**
 	 * @since 1.4
 	 * @see org.junit.platform.commons.support.ReflectionSupport#tryToLoadClass(String)
@@ -808,25 +712,6 @@ public static Try<Class<?>> tryToLoadClass(String name) {
 		return tryToLoadClass(name, ClassLoaderUtils.getDefaultClassLoader());
 	}
 
-	/**
-	 * Load a class by its <em>primitive name</em> or <em>fully qualified name</em>,
-	 * using the supplied {@link ClassLoader}.
-	 *
-	 * <p>See {@link org.junit.platform.commons.support.ReflectionSupport#loadClass(String)}
-	 * for details on support for class names for arrays.
-	 *
-	 * @param name the name of the class to load; never {@code null} or blank
-	 * @param classLoader the {@code ClassLoader} to use; never {@code null}
-	 * @see #loadClass(String)
-	 * @deprecated Please use {@link #tryToLoadClass(String, ClassLoader)}
-	 * instead.
-	 */
-	@API(status = DEPRECATED, since = "1.4")
-	@Deprecated
-	public static Optional<Class<?>> loadClass(String name, ClassLoader classLoader) {
-		return tryToLoadClass(name, classLoader).toOptional();
-	}
-
 	/**
 	 * Load a class by its <em>primitive name</em> or <em>fully qualified name</em>,
 	 * using the supplied {@link ClassLoader}.
@@ -842,7 +727,7 @@ public static Optional<Class<?>> loadClass(String name, ClassLoader classLoader)
 	 */
 	@API(status = INTERNAL, since = "1.11")
 	public static Class<?> loadRequiredClass(String name, ClassLoader classLoader) throws JUnitException {
-		return tryToLoadClass(name, classLoader).getOrThrow(
+		return tryToLoadClass(name, classLoader).getNonNullOrThrow(
 			cause -> new JUnitException(format("Could not load class [%s]", name), cause));
 	}
 
@@ -974,7 +859,8 @@ public static String getFullyQualifiedMethodName(Class<?> clazz, Method method)
 	 * @param parameterTypes the parameter types of the method; may be {@code null} or empty
 	 * @return fully qualified method name; never {@code null}
 	 */
-	public static String getFullyQualifiedMethodName(Class<?> clazz, String methodName, Class<?>... parameterTypes) {
+	public static String getFullyQualifiedMethodName(Class<?> clazz, String methodName,
+			Class<?> @Nullable... parameterTypes) {
 		Preconditions.notNull(clazz, "Class must not be null");
 
 		return getFullyQualifiedMethodName(clazz.getName(), methodName, ClassUtils.nullSafeToString(parameterTypes));
@@ -1109,14 +995,14 @@ public static Stream<Class<?>> streamAllClassesInClasspathRoot(URI root, Predica
 	 * @since 1.1
 	 */
 	public static List<Class<?>> findAllClassesInClasspathRoot(URI root, ClassFilter classFilter) {
-		return Collections.unmodifiableList(classpathScanner.scanForClassesInClasspathRoot(root, classFilter));
+		return List.copyOf(classpathScanner.scanForClassesInClasspathRoot(root, classFilter));
 	}
 
 	/**
 	 * @since 1.11
 	 */
 	public static List<Resource> findAllResourcesInClasspathRoot(URI root, Predicate<Resource> resourceFilter) {
-		return Collections.unmodifiableList(classpathScanner.scanForResourcesInClasspathRoot(root, resourceFilter));
+		return List.copyOf(classpathScanner.scanForResourcesInClasspathRoot(root, resourceFilter));
 	}
 
 	/**
@@ -1155,15 +1041,14 @@ public static Stream<Class<?>> streamAllClassesInPackage(String basePackageName,
 	 * @since 1.1
 	 */
 	public static List<Class<?>> findAllClassesInPackage(String basePackageName, ClassFilter classFilter) {
-		return Collections.unmodifiableList(classpathScanner.scanForClassesInPackage(basePackageName, classFilter));
+		return List.copyOf(classpathScanner.scanForClassesInPackage(basePackageName, classFilter));
 	}
 
 	/**
 	 * @since 1.11
 	 */
 	public static List<Resource> findAllResourcesInPackage(String basePackageName, Predicate<Resource> resourceFilter) {
-		return Collections.unmodifiableList(
-			classpathScanner.scanForResourcesInPackage(basePackageName, resourceFilter));
+		return List.copyOf(classpathScanner.scanForResourcesInPackage(basePackageName, resourceFilter));
 	}
 
 	/**
@@ -1204,14 +1089,14 @@ public static Stream<Class<?>> streamAllClassesInModule(String moduleName, Predi
 	 * @since 1.1.1
 	 */
 	public static List<Class<?>> findAllClassesInModule(String moduleName, ClassFilter classFilter) {
-		return Collections.unmodifiableList(ModuleUtils.findAllClassesInModule(moduleName, classFilter));
+		return List.copyOf(ModuleUtils.findAllClassesInModule(moduleName, classFilter));
 	}
 
 	/**
 	 * @since 1.11
 	 */
 	public static List<Resource> findAllResourcesInModule(String moduleName, Predicate<Resource> resourceFilter) {
-		return Collections.unmodifiableList(ModuleUtils.findAllResourcesInModule(moduleName, resourceFilter));
+		return List.copyOf(ModuleUtils.findAllResourcesInModule(moduleName, resourceFilter));
 	}
 
 	/**
@@ -1232,15 +1117,18 @@ public static Stream<Resource> streamAllResourcesInModule(String moduleName, Pre
 	 * @see org.junit.platform.commons.support.ReflectionSupport#findNestedClasses(Class, Predicate)
 	 */
 	public static List<Class<?>> findNestedClasses(Class<?> clazz, Predicate<Class<?>> predicate) {
+		return findNestedClasses(clazz, predicate, CycleErrorHandling.THROW_EXCEPTION);
+	}
+
+	@API(status = INTERNAL, since = "5.13.2")
+	public static List<Class<?>> findNestedClasses(Class<?> clazz, Predicate<Class<?>> predicate,
+			CycleErrorHandling errorHandling) {
 		Preconditions.notNull(clazz, "Class must not be null");
 		Preconditions.notNull(predicate, "Predicate must not be null");
 
 		Set<Class<?>> candidates = new LinkedHashSet<>();
-		visitNestedClasses(clazz, predicate, nestedClass -> {
-			candidates.add(nestedClass);
-			return true;
-		});
-		return Collections.unmodifiableList(new ArrayList<>(candidates));
+		visitAllNestedClasses(clazz, predicate, candidates::add, errorHandling);
+		return List.copyOf(candidates);
 	}
 
 	/**
@@ -1250,19 +1138,28 @@ public static List<Class<?>> findNestedClasses(Class<?> clazz, Predicate<Class<?
 	 * <p>This method does <strong>not</strong> search for nested classes
 	 * recursively.
 	 *
+	 * <p>This method detects cycles in <em>inner</em> class hierarchies &mdash;
+	 * from the supplied class up to the outermost enclosing class &mdash; and
+	 * throws a {@link JUnitException} if such a cycle is detected. Cycles within
+	 * inner class hierarchies <em>below</em> the supplied class are not detected
+	 * by this method.
+	 *
 	 * @param clazz the class to be searched; never {@code null}
 	 * @param predicate the predicate against which the list of nested classes is
 	 * checked; never {@code null}
 	 * @return {@code true} if such a nested class is present
 	 * @throws JUnitException if a cycle is detected within an inner class hierarchy
 	 */
-	@API(status = INTERNAL, since = "1.13")
-	public static boolean isNestedClassPresent(Class<?> clazz, Predicate<Class<?>> predicate) {
+	@API(status = INTERNAL, since = "1.13.2")
+	public static boolean isNestedClassPresent(Class<?> clazz, Predicate<Class<?>> predicate,
+			CycleErrorHandling errorHandling) {
 		Preconditions.notNull(clazz, "Class must not be null");
 		Preconditions.notNull(predicate, "Predicate must not be null");
+		Preconditions.notNull(errorHandling, "CycleErrorHandling must not be null");
 
-		boolean visitorWasNotCalled = visitNestedClasses(clazz, predicate, __ -> false);
-		return !visitorWasNotCalled;
+		AtomicBoolean foundNestedClass = new AtomicBoolean(false);
+		visitAllNestedClasses(clazz, predicate, __ -> foundNestedClass.setPlain(true), errorHandling);
+		return foundNestedClass.getPlain();
 	}
 
 	/**
@@ -1273,24 +1170,36 @@ public static Stream<Class<?>> streamNestedClasses(Class<?> clazz, Predicate<Cla
 		return findNestedClasses(clazz, predicate).stream();
 	}
 
-	private static boolean visitNestedClasses(Class<?> clazz, Predicate<Class<?>> predicate,
-			Visitor<Class<?>> visitor) {
+	@API(status = INTERNAL, since = "5.13.2")
+	public static Stream<Class<?>> streamNestedClasses(Class<?> clazz, Predicate<Class<?>> predicate,
+			CycleErrorHandling errorHandling) {
+		return findNestedClasses(clazz, predicate, errorHandling).stream();
+	}
+
+	/**
+	 * Visit <em>all</em> nested classes without support for short-circuiting
+	 * in order to ensure all of them are checked for class cycles.
+	 */
+	private static void visitAllNestedClasses(Class<?> clazz, Predicate<Class<?>> predicate,
+			Consumer<Class<?>> consumer, CycleErrorHandling errorHandling) {
+
 		if (!isSearchable(clazz)) {
-			return true;
+			return;
 		}
 
 		if (isInnerClass(clazz) && predicate.test(clazz)) {
-			detectInnerClassCycle(clazz);
+			if (detectInnerClassCycle(clazz, errorHandling)) {
+				return;
+			}
 		}
 
 		try {
 			// Candidates in current class
 			for (Class<?> nestedClass : clazz.getDeclaredClasses()) {
 				if (predicate.test(nestedClass)) {
-					detectInnerClassCycle(nestedClass);
-					boolean shouldContinue = visitor.accept(nestedClass);
-					if (!shouldContinue) {
-						return false;
+					consumer.accept(nestedClass);
+					if (detectInnerClassCycle(nestedClass, errorHandling)) {
+						return;
 					}
 				}
 			}
@@ -1300,30 +1209,20 @@ private static boolean visitNestedClasses(Class<?> clazz, Predicate<Class<?>> pr
 		}
 
 		// Search class hierarchy
-		boolean shouldContinue = visitNestedClasses(clazz.getSuperclass(), predicate, visitor);
-		if (!shouldContinue) {
-			return false;
-		}
+		visitAllNestedClasses(clazz.getSuperclass(), predicate, consumer, errorHandling);
 
 		// Search interface hierarchy
 		for (Class<?> ifc : clazz.getInterfaces()) {
-			shouldContinue = visitNestedClasses(ifc, predicate, visitor);
-			if (!shouldContinue) {
-				return false;
-			}
+			visitAllNestedClasses(ifc, predicate, consumer, errorHandling);
 		}
-
-		return true;
 	}
 
 	/**
 	 * Detect a cycle in the inner class hierarchy in which the supplied class
 	 * resides &mdash; from the supplied class up to the outermost enclosing class
 	 * &mdash; and throw a {@link JUnitException} if a cycle is detected.
-	 *
 	 * <p>This method does <strong>not</strong> detect cycles within inner class
 	 * hierarchies <em>below</em> the supplied class.
-	 *
 	 * <p>If the supplied class is not an inner class and does not have a
 	 * searchable superclass, this method is effectively a no-op.
 	 *
@@ -1331,25 +1230,26 @@ private static boolean visitNestedClasses(Class<?> clazz, Predicate<Class<?>> pr
 	 * @see #isInnerClass(Class)
 	 * @see #isSearchable(Class)
 	 */
-	private static void detectInnerClassCycle(Class<?> clazz) {
+	private static boolean detectInnerClassCycle(Class<?> clazz, CycleErrorHandling errorHandling) {
 		Preconditions.notNull(clazz, "Class must not be null");
 		String className = clazz.getName();
 
 		if (noCyclesDetectedCache.contains(className)) {
-			return;
+			return false;
 		}
 
 		Class<?> superclass = clazz.getSuperclass();
 		if (isInnerClass(clazz) && isSearchable(superclass)) {
 			for (Class<?> enclosing = clazz.getEnclosingClass(); enclosing != null; enclosing = enclosing.getEnclosingClass()) {
 				if (superclass.equals(enclosing)) {
-					throw new JUnitException(String.format("Detected cycle in inner class hierarchy between %s and %s",
-						className, enclosing.getName()));
+					errorHandling.handle(clazz, enclosing);
+					return true;
 				}
 			}
 		}
 
 		noCyclesDetectedCache.add(className);
+		return false;
 	}
 
 	/**
@@ -1404,7 +1304,7 @@ public static List<Constructor<?>> findConstructors(Class<?> clazz, Predicate<Co
 			// @formatter:off
 			return Arrays.stream(clazz.getDeclaredConstructors())
 					.filter(predicate)
-					.collect(toUnmodifiableList());
+					.toList();
 			// @formatter:on
 		}
 		catch (Throwable t) {
@@ -1418,7 +1318,7 @@ public static List<Constructor<?>> findConstructors(Class<?> clazz, Predicate<Co
 	public static List<Field> findFields(Class<?> clazz, Predicate<Field> predicate,
 			HierarchyTraversalMode traversalMode) {
 
-		return streamFields(clazz, predicate, traversalMode).collect(toUnmodifiableList());
+		return streamFields(clazz, predicate, traversalMode).toList();
 	}
 
 	/**
@@ -1447,23 +1347,19 @@ private static List<Field> findAllFieldsInHierarchy(Class<?> clazz, HierarchyTra
 		Field[] localFields = getDeclaredFields(clazz).stream()
 				.filter(field -> !field.isSynthetic())
 				.toArray(Field[]::new);
-		Field[] superclassFields = getSuperclassFields(clazz, traversalMode).stream()
-				.filter(field -> isNotShadowedByLocalFields(field, localFields))
-				.toArray(Field[]::new);
-		Field[] interfaceFields = getInterfaceFields(clazz, traversalMode).stream()
-				.filter(field -> isNotShadowedByLocalFields(field, localFields))
-				.toArray(Field[]::new);
 		// @formatter:on
+		List<Field> superclassFields = getSuperclassFields(clazz, traversalMode);
+		List<Field> interfaceFields = getInterfaceFields(clazz, traversalMode);
 
-		List<Field> fields = new ArrayList<>(superclassFields.length + interfaceFields.length + localFields.length);
+		List<Field> fields = new ArrayList<>(superclassFields.size() + interfaceFields.size() + localFields.length);
 		if (traversalMode == TOP_DOWN) {
-			Collections.addAll(fields, superclassFields);
-			Collections.addAll(fields, interfaceFields);
+			fields.addAll(superclassFields);
+			fields.addAll(interfaceFields);
 		}
 		Collections.addAll(fields, localFields);
 		if (traversalMode == BOTTOM_UP) {
-			Collections.addAll(fields, interfaceFields);
-			Collections.addAll(fields, superclassFields);
+			fields.addAll(interfaceFields);
+			fields.addAll(superclassFields);
 		}
 		return fields;
 	}
@@ -1489,29 +1385,6 @@ public static boolean isMethodPresent(Class<?> clazz, Predicate<Method> predicat
 		return findMethod(clazz, predicate).isPresent();
 	}
 
-	/**
-	 * Get the {@link Method} in the specified class with the specified name
-	 * and parameter types.
-	 *
-	 * <p>This method delegates to {@link Class#getMethod(String, Class...)} but
-	 * swallows any exception thrown.
-	 *
-	 * @param clazz the class in which to search for the method; never {@code null}
-	 * @param methodName the name of the method to get; never {@code null} or blank
-	 * @param parameterTypes the parameter types of the method; may be {@code null}
-	 * or empty
-	 * @return an {@code Optional} containing the method; never {@code null} but
-	 * empty if the invocation of {@code Class#getMethod()} throws a
-	 * {@link NoSuchMethodException}
-	 * @deprecated Please use {@link #tryToGetMethod(Class, String, Class[])}
-	 * instead.
-	 */
-	@API(status = DEPRECATED, since = "1.4")
-	@Deprecated
-	static Optional<Method> getMethod(Class<?> clazz, String methodName, Class<?>... parameterTypes) {
-		return tryToGetMethod(clazz, methodName, parameterTypes).toOptional();
-	}
-
 	/**
 	 * Try to get the {@link Method} in the specified class with the specified
 	 * name and parameter types.
@@ -1529,7 +1402,7 @@ static Optional<Method> getMethod(Class<?> clazz, String methodName, Class<?>...
 	 * @since 1.4
 	 */
 	@API(status = INTERNAL, since = "1.4")
-	public static Try<Method> tryToGetMethod(Class<?> clazz, String methodName, Class<?>... parameterTypes) {
+	public static Try<Method> tryToGetMethod(Class<?> clazz, String methodName, Class<?> @Nullable... parameterTypes) {
 		Preconditions.notNull(clazz, "Class must not be null");
 		Preconditions.notBlank(methodName, "Method name must not be null or blank");
 
@@ -1548,7 +1421,7 @@ public static Try<Method> tryToGetMethod(Class<?> clazz, String methodName, Clas
 	 * @since 1.11
 	 */
 	@API(status = INTERNAL, since = "1.11")
-	public static Method getInterfaceMethodIfPossible(Method method, Class<?> targetClass) {
+	public static Method getInterfaceMethodIfPossible(Method method, @Nullable Class<?> targetClass) {
 		if (!isPublic(method) || method.getDeclaringClass().isInterface()) {
 			return method;
 		}
@@ -1586,15 +1459,17 @@ private static Method findInterfaceMethodIfPossible(Method method, Class<?>[] pa
 	/**
 	 * @see org.junit.platform.commons.support.ReflectionSupport#findMethod(Class, String, String)
 	 */
-	public static Optional<Method> findMethod(Class<?> clazz, String methodName, String parameterTypeNames) {
+	public static Optional<Method> findMethod(Class<?> clazz, String methodName, @Nullable String parameterTypeNames) {
 		Preconditions.notNull(clazz, "Class must not be null");
 		Preconditions.notBlank(methodName, "Method name must not be null or blank");
 		return findMethod(clazz, methodName, resolveParameterTypes(clazz, methodName, parameterTypeNames));
 	}
 
 	@API(status = INTERNAL, since = "1.10")
-	public static Class<?>[] resolveParameterTypes(Class<?> clazz, String methodName, String parameterTypeNames) {
-		if (StringUtils.isBlank(parameterTypeNames)) {
+	public static Class<?>[] resolveParameterTypes(Class<?> clazz, String methodName,
+			@Nullable String parameterTypeNames) {
+
+		if (parameterTypeNames == null || StringUtils.isBlank(parameterTypeNames)) {
 			return EMPTY_CLASS_ARRAY;
 		}
 
@@ -1611,7 +1486,7 @@ private static Class<?> loadRequiredParameterType(Class<?> clazz, String methodN
 
 		// @formatter:off
 		return tryToLoadClass(typeName, classLoader)
-				.getOrThrow(cause -> new JUnitException(
+				.getNonNullOrThrow(cause -> new JUnitException(
 						String.format("Failed to load parameter type [%s] for method [%s] in class [%s].",
 								typeName, methodName, clazz.getName()), cause));
 		// @formatter:on
@@ -1705,7 +1580,7 @@ public static List<Method> findMethods(Class<?> clazz, Predicate<Method> predica
 	public static List<Method> findMethods(Class<?> clazz, Predicate<Method> predicate,
 			HierarchyTraversalMode traversalMode) {
 
-		return streamMethods(clazz, predicate, traversalMode).collect(toUnmodifiableList());
+		return streamMethods(clazz, predicate, traversalMode).toList();
 	}
 
 	/**
@@ -1760,14 +1635,6 @@ private static List<Method> findAllMethodsInHierarchy(Class<?> clazz, HierarchyT
 		return methods;
 	}
 
-	/**
-	 * Custom alternative to {@link Class#getFields()} that sorts the fields
-	 * and converts them to a mutable list.
-	 */
-	private static List<Field> getFields(Class<?> clazz) {
-		return toSortedMutableList(clazz.getFields());
-	}
-
 	/**
 	 * Custom alternative to {@link Class#getDeclaredFields()} that sorts the
 	 * fields and converts them to a mutable list.
@@ -1903,21 +1770,18 @@ private static List<Method> getInterfaceMethods(Class<?> clazz, HierarchyTravers
 	private static List<Field> getInterfaceFields(Class<?> clazz, HierarchyTraversalMode traversalMode) {
 		List<Field> allInterfaceFields = new ArrayList<>();
 		for (Class<?> ifc : clazz.getInterfaces()) {
+
 			Field[] localInterfaceFields = ifc.getFields();
 			Arrays.sort(localInterfaceFields, ReflectionUtils::defaultFieldSorter);
 
-			// @formatter:off
-			Field[] superinterfaceFields = getInterfaceFields(ifc, traversalMode).stream()
-					.filter(field -> isNotShadowedByLocalFields(field, localInterfaceFields))
-					.toArray(Field[]::new);
-			// @formatter:on
+			List<Field> superinterfaceFields = getInterfaceFields(ifc, traversalMode);
 
 			if (traversalMode == TOP_DOWN) {
-				Collections.addAll(allInterfaceFields, superinterfaceFields);
+				allInterfaceFields.addAll(superinterfaceFields);
 			}
 			Collections.addAll(allInterfaceFields, localInterfaceFields);
 			if (traversalMode == BOTTOM_UP) {
-				Collections.addAll(allInterfaceFields, superinterfaceFields);
+				allInterfaceFields.addAll(superinterfaceFields);
 			}
 		}
 		return allInterfaceFields;
@@ -1931,18 +1795,6 @@ private static List<Field> getSuperclassFields(Class<?> clazz, HierarchyTraversa
 		return findAllFieldsInHierarchy(superclass, traversalMode);
 	}
 
-	private static boolean isNotShadowedByLocalFields(Field field, Field[] localFields) {
-		if (useLegacySearchSemantics) {
-			for (Field local : localFields) {
-				if (local.getName().equals(field.getName())) {
-					return false;
-				}
-			}
-			return true;
-		}
-		return true;
-	}
-
 	private static List<Method> getSuperclassMethods(Class<?> clazz, HierarchyTraversalMode traversalMode) {
 		Class<?> superclass = clazz.getSuperclass();
 		if (!isSearchable(superclass)) {
@@ -1961,23 +1813,20 @@ private static boolean isNotOverriddenByLocalMethods(Method method, Method[] loc
 	}
 
 	private static boolean isMethodOverriddenBy(Method upper, Method lower) {
-		// If legacy search semantics are enabled, skip to hasCompatibleSignature() check.
-		if (!useLegacySearchSemantics) {
-			// A static method cannot override anything.
-			if (Modifier.isStatic(lower.getModifiers())) {
-				return false;
-			}
+		// A static method cannot override anything.
+		if (Modifier.isStatic(lower.getModifiers())) {
+			return false;
+		}
 
-			// Cannot override a private, static, or final method.
-			int modifiers = upper.getModifiers();
-			if (Modifier.isPrivate(modifiers) || Modifier.isStatic(modifiers) || Modifier.isFinal(modifiers)) {
-				return false;
-			}
+		// Cannot override a private, static, or final method.
+		int modifiers = upper.getModifiers();
+		if (Modifier.isPrivate(modifiers) || Modifier.isStatic(modifiers) || Modifier.isFinal(modifiers)) {
+			return false;
+		}
 
-			// Cannot override a package-private method in another package.
-			if (isPackagePrivate(upper) && !declaredInSamePackage(upper, lower)) {
-				return false;
-			}
+		// Cannot override a package-private method in another package.
+		if (isPackagePrivate(upper) && !declaredInSamePackage(upper, lower)) {
+			return false;
 		}
 
 		return hasCompatibleSignature(upper, lower.getName(), lower.getParameterTypes());
@@ -1989,7 +1838,7 @@ private static boolean isPackagePrivate(Member member) {
 	}
 
 	private static boolean declaredInSamePackage(Method m1, Method m2) {
-		return getPackageName(m1.getDeclaringClass()).equals(getPackageName(m2.getDeclaringClass()));
+		return m1.getDeclaringClass().getPackageName().equals(m2.getDeclaringClass().getPackageName());
 	}
 
 	/**
@@ -2020,10 +1869,7 @@ private static boolean hasCompatibleSignature(Method candidate, String methodNam
 			}
 		}
 		// lower is sub-signature of upper: check for generics in upper method
-		if (isGeneric(candidate)) {
-			return true;
-		}
-		return false;
+		return isGeneric(candidate);
 	}
 
 	static boolean isGeneric(Method method) {
@@ -2087,7 +1933,7 @@ private static void getAllAssignmentCompatibleClasses(Class<?> clazz, Set<Class<
 	 * searched but may be applicable for other use cases as well.
 	 * @since 1.6
 	 */
-	private static boolean isSearchable(Class<?> clazz) {
+	private static boolean isSearchable(@Nullable Class<?> clazz) {
 		return (clazz != null && clazz != Object.class);
 	}
 
@@ -2100,33 +1946,32 @@ private static boolean isSearchable(Class<?> clazz) {
 	 * {@linkplain InvocationTargetException#getTargetException() target
 	 * exception}; otherwise, this method returns the supplied {@code Throwable}.
 	 */
-	private static Throwable getUnderlyingCause(Throwable t) {
-		if (t instanceof InvocationTargetException) {
-			return getUnderlyingCause(((InvocationTargetException) t).getTargetException());
+	static Throwable getUnderlyingCause(Throwable t) {
+		if (t instanceof InvocationTargetException ite) {
+			return getUnderlyingCause(ite.getTargetException());
 		}
 		return t;
 	}
 
-	private static boolean getLegacySearchSemanticsFlag() {
-		String rawValue = System.getProperty(USE_LEGACY_SEARCH_SEMANTICS_PROPERTY_NAME);
-		if (StringUtils.isBlank(rawValue)) {
-			return false;
-		}
-		String value = rawValue.trim().toLowerCase();
-		boolean isTrue = "true".equals(value);
-		Preconditions.condition(isTrue || "false".equals(value), () -> USE_LEGACY_SEARCH_SEMANTICS_PROPERTY_NAME
-				+ " property must be 'true' or 'false' (ignoring case): " + rawValue);
-		return isTrue;
-	}
+	@API(status = INTERNAL, since = "5.13.2")
+	public enum CycleErrorHandling {
 
-	private interface Visitor<T> {
+		THROW_EXCEPTION {
+			@Override
+			void handle(Class<?> clazz, Class<?> enclosing) {
+				throw new JUnitException(String.format("Detected cycle in inner class hierarchy between %s and %s",
+					clazz.getName(), enclosing.getName()));
+			}
+		},
 
-		/**
-		 * @return {@code true} if the visitor should continue searching;
-		 * {@code false} if the visitor should stop
-		 */
-		boolean accept(T value);
+		ABORT_VISIT {
+			@Override
+			void handle(Class<?> clazz, Class<?> enclosing) {
+				// ignore
+			}
+		};
 
+		abstract void handle(Class<?> clazz, Class<?> enclosing);
 	}
 
 }
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/RuntimeUtils.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/RuntimeUtils.java
index e738aea49d8c..192e3f2c4d6b 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/RuntimeUtils.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/RuntimeUtils.java
@@ -52,7 +52,7 @@ public static boolean isDebugMode() {
 	static Optional<List<String>> getInputArguments() {
 		Optional<Class<?>> managementFactoryClass = ReflectionUtils.tryToLoadClass(
 			"java.lang.management.ManagementFactory").toOptional();
-		if (!managementFactoryClass.isPresent()) {
+		if (managementFactoryClass.isEmpty()) {
 			return Optional.empty();
 		}
 		// Can't use "java.lang.management.ManagementFactory.getRuntimeMXBean().getInputArguments()"
@@ -61,7 +61,7 @@ static Optional<List<String>> getInputArguments() {
 		// See https://github.com/junit-team/junit4/pull/1187
 		try {
 			Object bean = managementFactoryClass.get().getMethod("getRuntimeMXBean").invoke(null);
-			Class<?> mx = ReflectionUtils.tryToLoadClass("java.lang.management.RuntimeMXBean").get();
+			Class<?> mx = ReflectionUtils.tryToLoadClass("java.lang.management.RuntimeMXBean").getNonNull();
 			@SuppressWarnings("unchecked")
 			List<String> args = (List<String>) mx.getMethod("getInputArguments").invoke(bean);
 			return Optional.of(args);
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/ServiceLoaderUtils.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/ServiceLoaderUtils.java
index 0a060bee0999..d9f179b6b381 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/ServiceLoaderUtils.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/ServiceLoaderUtils.java
@@ -13,9 +13,9 @@
 import java.util.ServiceLoader;
 import java.util.function.Predicate;
 import java.util.stream.Stream;
-import java.util.stream.StreamSupport;
 
 import org.apiguardian.api.API;
+import org.apiguardian.api.API.Status;
 
 /**
  * Collection of utilities for working with {@link ServiceLoader}.
@@ -28,7 +28,7 @@
  *
  * @since 1.11
  */
-@API(status = API.Status.INTERNAL, since = "1.11")
+@API(status = Status.INTERNAL, since = "1.11")
 public class ServiceLoaderUtils {
 
 	private ServiceLoaderUtils() {
@@ -45,11 +45,16 @@ private ServiceLoaderUtils() {
 	 */
 	public static <T> Stream<T> filter(ServiceLoader<T> serviceLoader,
 			Predicate<? super Class<? extends T>> providerPredicate) {
-		return StreamSupport.stream(serviceLoader.spliterator(), false).filter(it -> {
-			@SuppressWarnings("unchecked")
-			Class<? extends T> type = (Class<? extends T>) it.getClass();
-			return providerPredicate.test(type);
-		});
+
+		Preconditions.notNull(serviceLoader, "serviceLoader must not be null");
+		Preconditions.notNull(providerPredicate, "providerPredicate must not be null");
+
+		// @formatter:off
+		return serviceLoader
+				.stream()
+				.filter(provider -> providerPredicate.test(provider.type()))
+				.map(ServiceLoader.Provider::get);
+		// @formatter:on
 	}
 
 }
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/StringUtils.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/StringUtils.java
index 9989cb33a93b..5c387ad209bf 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/StringUtils.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/StringUtils.java
@@ -20,6 +20,7 @@
 import java.util.regex.Pattern;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 
 /**
  * Collection of utilities for working with {@link String Strings},
@@ -41,7 +42,7 @@ public final class StringUtils {
 
 	/**
 	 * Guard against "IllegalArgumentException: Unsupported flags: 256" errors.
-	 * @see <a href="https://github.com/junit-team/junit5/issues/1800">#1800</a>
+	 * @see <a href="https://github.com/junit-team/junit-framework/issues/1800">#1800</a>
 	 */
 	static Pattern compileIsoControlPattern() {
 		// https://docs.oracle.com/javase/8/docs/api/java/util/regex/Pattern.html#posix
@@ -67,7 +68,7 @@ private StringUtils() {
 	 * @return {@code true} if the string is blank
 	 * @see #isNotBlank(String)
 	 */
-	public static boolean isBlank(String str) {
+	public static boolean isBlank(@Nullable String str) {
 		return (str == null || str.trim().isEmpty());
 	}
 
@@ -79,7 +80,7 @@ public static boolean isBlank(String str) {
 	 * @return {@code true} if the string is not blank
 	 * @see #isBlank(String)
 	 */
-	public static boolean isNotBlank(String str) {
+	public static boolean isNotBlank(@Nullable String str) {
 		return !isBlank(str);
 	}
 
@@ -91,7 +92,7 @@ public static boolean isNotBlank(String str) {
 	 * @see #containsIsoControlCharacter(String)
 	 * @see Character#isWhitespace(int)
 	 */
-	public static boolean containsWhitespace(String str) {
+	public static boolean containsWhitespace(@Nullable String str) {
 		return str != null && str.codePoints().anyMatch(Character::isWhitespace);
 	}
 
@@ -105,7 +106,7 @@ public static boolean containsWhitespace(String str) {
 	 * @see #containsIsoControlCharacter(String)
 	 * @see Character#isWhitespace(int)
 	 */
-	public static boolean doesNotContainWhitespace(String str) {
+	public static boolean doesNotContainWhitespace(@Nullable String str) {
 		return !containsWhitespace(str);
 	}
 
@@ -117,7 +118,7 @@ public static boolean doesNotContainWhitespace(String str) {
 	 * @see #containsWhitespace(String)
 	 * @see Character#isISOControl(int)
 	 */
-	public static boolean containsIsoControlCharacter(String str) {
+	public static boolean containsIsoControlCharacter(@Nullable String str) {
 		return str != null && str.codePoints().anyMatch(Character::isISOControl);
 	}
 
@@ -131,7 +132,7 @@ public static boolean containsIsoControlCharacter(String str) {
 	 * @see #containsWhitespace(String)
 	 * @see Character#isISOControl(int)
 	 */
-	public static boolean doesNotContainIsoControlCharacter(String str) {
+	public static boolean doesNotContainIsoControlCharacter(@Nullable String str) {
 		return !containsIsoControlCharacter(str);
 	}
 
@@ -157,7 +158,7 @@ public static boolean doesNotContainIsoControlCharacter(String str) {
 	 * @see Arrays#deepToString(Object[])
 	 * @see ClassUtils#nullSafeToString(Class...)
 	 */
-	public static String nullSafeToString(Object obj) {
+	public static String nullSafeToString(@Nullable Object obj) {
 		if (obj == null) {
 			return "null";
 		}
@@ -165,29 +166,29 @@ public static String nullSafeToString(Object obj) {
 		try {
 			if (obj.getClass().isArray()) {
 				if (obj.getClass().getComponentType().isPrimitive()) {
-					if (obj instanceof boolean[]) {
-						return Arrays.toString((boolean[]) obj);
+					if (obj instanceof boolean[] booleans) {
+						return Arrays.toString(booleans);
 					}
-					if (obj instanceof char[]) {
-						return Arrays.toString((char[]) obj);
+					if (obj instanceof char[] chars) {
+						return Arrays.toString(chars);
 					}
-					if (obj instanceof short[]) {
-						return Arrays.toString((short[]) obj);
+					if (obj instanceof short[] shorts) {
+						return Arrays.toString(shorts);
 					}
-					if (obj instanceof byte[]) {
-						return Arrays.toString((byte[]) obj);
+					if (obj instanceof byte[] bytes) {
+						return Arrays.toString(bytes);
 					}
-					if (obj instanceof int[]) {
-						return Arrays.toString((int[]) obj);
+					if (obj instanceof int[] ints) {
+						return Arrays.toString(ints);
 					}
-					if (obj instanceof long[]) {
-						return Arrays.toString((long[]) obj);
+					if (obj instanceof long[] longs) {
+						return Arrays.toString(longs);
 					}
-					if (obj instanceof float[]) {
-						return Arrays.toString((float[]) obj);
+					if (obj instanceof float[] floats) {
+						return Arrays.toString(floats);
 					}
-					if (obj instanceof double[]) {
-						return Arrays.toString((double[]) obj);
+					if (obj instanceof double[] doubles) {
+						return Arrays.toString(doubles);
 					}
 				}
 				return Arrays.deepToString((Object[]) obj);
@@ -221,7 +222,7 @@ public static String nullSafeToString(Object obj) {
 	 * @see #nullSafeToString(Object)
 	 * @see ClassUtils#nullSafeToString(Class...)
 	 */
-	public static String defaultToString(Object obj) {
+	public static String defaultToString(@Nullable Object obj) {
 		if (obj == null) {
 			return "null";
 		}
@@ -239,7 +240,7 @@ public static String defaultToString(Object obj) {
 	 * @since 1.4
 	 */
 	@API(status = INTERNAL, since = "1.4")
-	public static String replaceIsoControlCharacters(String str, String replacement) {
+	public static @Nullable String replaceIsoControlCharacters(@Nullable String str, String replacement) {
 		Preconditions.notNull(replacement, "replacement must not be null");
 		return str == null ? null : ISO_CONTROL_PATTERN.matcher(str).replaceAll(replacement);
 	}
@@ -254,7 +255,7 @@ public static String replaceIsoControlCharacters(String str, String replacement)
 	 * @since 1.4
 	 */
 	@API(status = INTERNAL, since = "1.4")
-	public static String replaceWhitespaceCharacters(String str, String replacement) {
+	public static @Nullable String replaceWhitespaceCharacters(@Nullable String str, String replacement) {
 		Preconditions.notNull(replacement, "replacement must not be null");
 		return str == null ? null : WHITESPACE_PATTERN.matcher(str).replaceAll(replacement);
 	}
@@ -303,7 +304,7 @@ private static TwoPartSplitResult splitIntoTwo(String value, int index, int leng
 	 * @see StringUtils#splitIntoTwo(String, String)
 	 */
 	@API(status = INTERNAL, since = "1.11")
-	public interface TwoPartSplitResult {
+	public sealed interface TwoPartSplitResult {
 
 		/**
 		 * Map the result of splitting a string into two parts or throw an exception.
@@ -330,13 +331,7 @@ default <T> T mapTwo(Supplier<? extends RuntimeException> onePartExceptionCreato
 
 	}
 
-	private static final class OnePart implements TwoPartSplitResult {
-
-		private final String value;
-
-		OnePart(String value) {
-			this.value = value;
-		}
+	private record OnePart(String value) implements TwoPartSplitResult {
 
 		@Override
 		public <T> T map(Function<String, ? extends T> onePartMapper,
@@ -345,15 +340,7 @@ public <T> T map(Function<String, ? extends T> onePartMapper,
 		}
 	}
 
-	private static final class TwoParts implements TwoPartSplitResult {
-
-		private final String first;
-		private final String second;
-
-		TwoParts(String first, String second) {
-			this.first = first;
-			this.second = second;
-		}
+	private record TwoParts(String first, String second) implements TwoPartSplitResult {
 
 		@Override
 		public <T> T map(Function<String, ? extends T> onePartMapper,
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/ToStringBuilder.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/ToStringBuilder.java
index eabaf3dcc09a..97bfb1a6cc30 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/ToStringBuilder.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/ToStringBuilder.java
@@ -17,6 +17,7 @@
 import java.util.List;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 
 /**
  * Simple builder for generating strings in custom implementations of
@@ -50,13 +51,13 @@ public ToStringBuilder(String typeName) {
 		this.typeName = Preconditions.notNull(typeName, "Type name must not be null");
 	}
 
-	public ToStringBuilder append(String name, Object value) {
+	public ToStringBuilder append(String name, @Nullable Object value) {
 		Preconditions.notBlank(name, "Name must not be null or blank");
 		this.values.add(name + " = " + toString(value));
 		return this;
 	}
 
-	private String toString(Object obj) {
+	private String toString(@Nullable Object obj) {
 		return (obj instanceof CharSequence) ? ("'" + obj + "'") : StringUtils.nullSafeToString(obj);
 	}
 
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/UnrecoverableExceptions.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/UnrecoverableExceptions.java
index 23589c2a1672..7799476137a1 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/UnrecoverableExceptions.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/UnrecoverableExceptions.java
@@ -13,6 +13,7 @@
 import static org.apiguardian.api.API.Status.INTERNAL;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 
 /**
  * Internal utilities for working with <em>unrecoverable</em> exceptions.
@@ -47,7 +48,7 @@ private UnrecoverableExceptions() {
 	 * <p>If the supplied {@code exception} is not <em>unrecoverable</em>, this
 	 * method does nothing.
 	 */
-	public static void rethrowIfUnrecoverable(Throwable exception) {
+	public static void rethrowIfUnrecoverable(@Nullable Throwable exception) {
 		if (exception instanceof OutOfMemoryError) {
 			throw ExceptionUtils.throwAsUncheckedException(exception);
 		}
diff --git a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/package-info.java b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/package-info.java
index 119940686c89..3d9e974b50f9 100644
--- a/junit-platform-commons/src/main/java/org/junit/platform/commons/util/package-info.java
+++ b/junit-platform-commons/src/main/java/org/junit/platform/commons/util/package-info.java
@@ -8,4 +8,7 @@
  * Use at your own risk!
  */
 
+@NullMarked
 package org.junit.platform.commons.util;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-platform-commons/src/main/java9/org/junit/platform/commons/util/ModuleUtils.java b/junit-platform-commons/src/main/java9/org/junit/platform/commons/util/ModuleUtils.java
deleted file mode 100644
index 9f20d964f471..000000000000
--- a/junit-platform-commons/src/main/java9/org/junit/platform/commons/util/ModuleUtils.java
+++ /dev/null
@@ -1,311 +0,0 @@
-/*
- * Copyright 2015-2025 the original author or authors.
- *
- * All rights reserved. This program and the accompanying materials are
- * made available under the terms of the Eclipse Public License v2.0 which
- * accompanies this distribution and is available at
- *
- * https://www.eclipse.org/legal/epl-v20.html
- */
-
-package org.junit.platform.commons.util;
-
-import static java.util.function.Predicate.isEqual;
-import static java.util.stream.Collectors.toCollection;
-import static java.util.stream.Collectors.toSet;
-import static org.apiguardian.api.API.Status.INTERNAL;
-
-import java.io.IOException;
-import java.lang.module.Configuration;
-import java.lang.module.ModuleFinder;
-import java.lang.module.ModuleReader;
-import java.lang.module.ModuleReference;
-import java.lang.module.ResolvedModule;
-import java.net.URI;
-import java.net.URISyntaxException;
-import java.util.ArrayList;
-import java.util.Collections;
-import java.util.LinkedHashSet;
-import java.util.List;
-import java.util.Optional;
-import java.util.Set;
-import java.util.function.Predicate;
-import java.util.stream.Collectors;
-import java.util.stream.Stream;
-
-import org.apiguardian.api.API;
-import org.junit.platform.commons.JUnitException;
-import org.junit.platform.commons.logging.Logger;
-import org.junit.platform.commons.logging.LoggerFactory;
-import org.junit.platform.commons.support.DefaultResource;
-import org.junit.platform.commons.support.Resource;
-import org.junit.platform.commons.support.scanning.ClassFilter;
-
-/**
- * Collection of utilities for working with {@code java.lang.Module}
- * and friends.
- *
- * <h2>DISCLAIMER</h2>
- *
- * <p>These utilities are intended solely for usage within the JUnit framework
- * itself. <strong>Any usage by external parties is not supported.</strong>
- * Use at your own risk!
- *
- * @since 1.1
- */
-@API(status = INTERNAL, since = "1.1")
-public class ModuleUtils {
-
-	private static final Logger logger = LoggerFactory.getLogger(ModuleUtils.class);
-
-	/**
-	 * Find all non-system boot modules names.
-	 *
-	 * @return a set of all such module names; never {@code null} but
-	 * potentially empty
-	 */
-	public static Set<String> findAllNonSystemBootModuleNames() {
-		// @formatter:off
-		Set<String> systemModules = ModuleFinder.ofSystem().findAll().stream()
-				.map(reference -> reference.descriptor().name())
-				.collect(toSet());
-		return streamResolvedModules(name -> !systemModules.contains(name))
-				.map(ResolvedModule::name)
-				.collect(toCollection(LinkedHashSet::new));
-		// @formatter:on
-	}
-
-	/**
-	 * Java 9+ runtime supports the Java Platform Module System.
-	 *
-	 * @return {@code true}
-	 */
-	public static boolean isJavaPlatformModuleSystemAvailable() {
-		return true;
-	}
-
-	public static Optional<String> getModuleName(Class<?> type) {
-		Preconditions.notNull(type, "Class type must not be null");
-
-		return Optional.ofNullable(type.getModule().getName());
-	}
-
-	public static Optional<String> getModuleVersion(Class<?> type) {
-		Preconditions.notNull(type, "Class type must not be null");
-
-		Module module = type.getModule();
-		return module.isNamed() ? module.getDescriptor().rawVersion() : Optional.empty();
-	}
-
-	/**
-	 * Find all {@linkplain Class classes} for the given module name.
-	 *
-	 * @param moduleName the name of the module to scan; never {@code null} or
-	 * <em>empty</em>
-	 * @param filter the class filter to apply; never {@code null}
-	 * @return an immutable list of all such classes found; never {@code null}
-	 * but potentially empty
-	 */
-	public static List<Class<?>> findAllClassesInModule(String moduleName, ClassFilter filter) {
-		Preconditions.notBlank(moduleName, "Module name must not be null or empty");
-		Preconditions.notNull(filter, "Class filter must not be null");
-
-		logger.debug(() -> "Looking for classes in module: " + moduleName);
-		// @formatter:off
-		Set<ModuleReference> moduleReferences = streamResolvedModules(isEqual(moduleName))
-				.map(ResolvedModule::reference)
-				.collect(toSet());
-		// @formatter:on
-		return scan(moduleReferences, filter, ModuleUtils.class.getClassLoader());
-	}
-
-	/**
-	 * Find all {@linkplain Resource resources} for the given module name.
-	 *
-	 * @param moduleName the name of the module to scan; never {@code null} or
-	 * <em>empty</em>
-	 * @param filter the class filter to apply; never {@code null}
-	 * @return an immutable list of all such resources found; never {@code null}
-	 * but potentially empty
-	 * @since 1.11
-	 */
-	@API(status = INTERNAL, since = "1.11")
-	public static List<Resource> findAllResourcesInModule(String moduleName, Predicate<Resource> filter) {
-		Preconditions.notBlank(moduleName, "Module name must not be null or empty");
-		Preconditions.notNull(filter, "Resource filter must not be null");
-
-		logger.debug(() -> "Looking for classes in module: " + moduleName);
-		// @formatter:off
-		Set<ModuleReference> moduleReferences = streamResolvedModules(isEqual(moduleName))
-				.map(ResolvedModule::reference)
-				.collect(toSet());
-		// @formatter:on
-		return scan(moduleReferences, filter, ModuleUtils.class.getClassLoader());
-	}
-
-	/**
-	 * Stream resolved modules from current (or boot) module layer.
-	 */
-	private static Stream<ResolvedModule> streamResolvedModules(Predicate<String> moduleNamePredicate) {
-		Module module = ModuleUtils.class.getModule();
-		ModuleLayer layer = module.getLayer();
-		if (layer == null) {
-			logger.config(() -> ModuleUtils.class + " is a member of " + module
-					+ " - using boot layer returned by ModuleLayer.boot() as fall-back.");
-			layer = ModuleLayer.boot();
-		}
-		return streamResolvedModules(moduleNamePredicate, layer);
-	}
-
-	/**
-	 * Stream resolved modules from the supplied layer.
-	 */
-	private static Stream<ResolvedModule> streamResolvedModules(Predicate<String> moduleNamePredicate,
-			ModuleLayer layer) {
-		logger.debug(() -> "Streaming modules for layer @" + System.identityHashCode(layer) + ": " + layer);
-		Configuration configuration = layer.configuration();
-		logger.debug(() -> "Module layer configuration: " + configuration);
-		Stream<ResolvedModule> stream = configuration.modules().stream();
-		return stream.filter(module -> moduleNamePredicate.test(module.name()));
-	}
-
-	/**
-	 * Scan for classes using the supplied set of module references, class
-	 * filter, and loader.
-	 */
-	private static List<Class<?>> scan(Set<ModuleReference> references, ClassFilter filter, ClassLoader loader) {
-		logger.debug(() -> "Scanning " + references.size() + " module references: " + references);
-		ModuleReferenceClassScanner scanner = new ModuleReferenceClassScanner(filter, loader);
-		List<Class<?>> classes = new ArrayList<>();
-		for (ModuleReference reference : references) {
-			classes.addAll(scanner.scan(reference));
-		}
-		logger.debug(() -> "Found " + classes.size() + " classes: " + classes);
-		return Collections.unmodifiableList(classes);
-	}
-
-	/**
-	 * Scan for classes using the supplied set of module references, class
-	 * filter, and loader.
-	 */
-	private static List<Resource> scan(Set<ModuleReference> references, Predicate<Resource> filter,
-			ClassLoader loader) {
-		logger.debug(() -> "Scanning " + references.size() + " module references: " + references);
-		ModuleReferenceResourceScanner scanner = new ModuleReferenceResourceScanner(filter, loader);
-		List<Resource> classes = new ArrayList<>();
-		for (ModuleReference reference : references) {
-			classes.addAll(scanner.scan(reference));
-		}
-		logger.debug(() -> "Found " + classes.size() + " classes: " + classes);
-		return Collections.unmodifiableList(classes);
-	}
-
-	/**
-	 * {@link ModuleReference} class scanner.
-	 *
-	 * @since 1.1
-	 */
-	static class ModuleReferenceClassScanner {
-
-		private final ClassFilter classFilter;
-		private final ClassLoader classLoader;
-
-		ModuleReferenceClassScanner(ClassFilter classFilter, ClassLoader classLoader) {
-			this.classFilter = classFilter;
-			this.classLoader = classLoader;
-		}
-
-		/**
-		 * Scan module reference for classes that potentially contain testable methods.
-		 */
-		List<Class<?>> scan(ModuleReference reference) {
-			try (ModuleReader reader = reference.open()) {
-				try (Stream<String> names = reader.list()) {
-					// @formatter:off
-					return names.filter(name -> name.endsWith(".class"))
-							.map(this::className)
-							.filter(name -> !name.equals("module-info"))
-							.filter(classFilter::match)
-							.map(this::loadClassUnchecked)
-							.filter(classFilter::match)
-							.collect(Collectors.toList());
-					// @formatter:on
-				}
-			}
-			catch (IOException e) {
-				throw new JUnitException("Failed to read contents of " + reference + ".", e);
-			}
-		}
-
-		/**
-		 * Convert resource name to binary class name.
-		 */
-		private String className(String resourceName) {
-			resourceName = resourceName.substring(0, resourceName.length() - 6); // 6 = ".class".length()
-			resourceName = resourceName.replace('/', '.');
-			return resourceName;
-		}
-
-		/**
-		 * Load class by its binary name.
-		 *
-		 * @see ClassLoader#loadClass(String)
-		 */
-		private Class<?> loadClassUnchecked(String binaryName) {
-			try {
-				return classLoader.loadClass(binaryName);
-			}
-			catch (ClassNotFoundException e) {
-				throw new JUnitException("Failed to load class with name '" + binaryName + "'.", e);
-			}
-		}
-
-	}
-
-	/**
-	 * {@link ModuleReference} resource class scanner.
-	 *
-	 * @since 1.11
-	 */
-	static class ModuleReferenceResourceScanner {
-
-		private final Predicate<Resource> resourceFilter;
-		private final ClassLoader classLoader;
-
-		ModuleReferenceResourceScanner(Predicate<Resource> resourceFilter, ClassLoader classLoader) {
-			this.resourceFilter = resourceFilter;
-			this.classLoader = classLoader;
-		}
-
-		/**
-		 * Scan module reference for resources that potentially contain testable resources.
-		 */
-		List<Resource> scan(ModuleReference reference) {
-			try (ModuleReader reader = reference.open()) {
-				try (Stream<String> names = reader.list()) {
-					// @formatter:off
-					return names.filter(name -> !name.endsWith(".class"))
-							.map(this::loadResourceUnchecked)
-							.filter(resourceFilter)
-							.collect(Collectors.toList());
-					// @formatter:on
-				}
-			}
-			catch (IOException e) {
-				throw new JUnitException("Failed to read contents of " + reference + ".", e);
-			}
-		}
-
-		private Resource loadResourceUnchecked(String binaryName) {
-			try {
-				URI uri = classLoader.getResource(binaryName).toURI();
-				return new DefaultResource(binaryName, uri);
-			}
-			catch (URISyntaxException e) {
-				throw new JUnitException("Failed to load resource with name '" + binaryName + "'.", e);
-			}
-		}
-
-	}
-
-}
diff --git a/junit-platform-commons/src/main/java9/org/junit/platform/commons/util/PackageNameUtils.java b/junit-platform-commons/src/main/java9/org/junit/platform/commons/util/PackageNameUtils.java
deleted file mode 100644
index 0cb6aec9e8d8..000000000000
--- a/junit-platform-commons/src/main/java9/org/junit/platform/commons/util/PackageNameUtils.java
+++ /dev/null
@@ -1,30 +0,0 @@
-/*
- * Copyright 2015-2025 the original author or authors.
- *
- * All rights reserved. This program and the accompanying materials are
- * made available under the terms of the Eclipse Public License v2.0 which
- * accompanies this distribution and is available at
- *
- * https://www.eclipse.org/legal/epl-v20.html
- */
-
-package org.junit.platform.commons.util;
-
-/**
- * Collection of utilities for working with package names.
- *
- * <h2>DISCLAIMER</h2>
- *
- * <p>These utilities are intended solely for usage within the JUnit framework
- * itself. <strong>Any usage by external parties is not supported.</strong>
- * Use at your own risk!
- *
- * @since 1.11.3
- */
-class PackageNameUtils {
-
-	static String getPackageName(Class<?> clazz) {
-		return clazz.getPackageName();
-	}
-
-}
diff --git a/junit-platform-commons/src/main/java9/org/junit/platform/commons/util/ServiceLoaderUtils.java b/junit-platform-commons/src/main/java9/org/junit/platform/commons/util/ServiceLoaderUtils.java
deleted file mode 100644
index db209116b615..000000000000
--- a/junit-platform-commons/src/main/java9/org/junit/platform/commons/util/ServiceLoaderUtils.java
+++ /dev/null
@@ -1,56 +0,0 @@
-/*
- * Copyright 2015-2025 the original author or authors.
- *
- * All rights reserved. This program and the accompanying materials are
- * made available under the terms of the Eclipse Public License v2.0 which
- * accompanies this distribution and is available at
- *
- * https://www.eclipse.org/legal/epl-v20.html
- */
-
-package org.junit.platform.commons.util;
-
-import java.util.ServiceLoader;
-import java.util.function.Predicate;
-import java.util.stream.Stream;
-
-import org.apiguardian.api.API;
-import org.apiguardian.api.API.Status;
-
-/**
- * Collection of utilities for working with {@link ServiceLoader}.
- *
- * <h2>DISCLAIMER</h2>
- *
- * <p>These utilities are intended solely for usage within the JUnit framework
- * itself. <strong>Any usage by external parties is not supported.</strong>
- * Use at your own risk!
- *
- * @since 1.11
- */
-@API(status = Status.INTERNAL, since = "1.11")
-public class ServiceLoaderUtils {
-
-	private ServiceLoaderUtils() {
-		/* no-op */
-	}
-
-	/**
-	 * Filters the supplied service loader using the supplied predicate.
-	 *
-	 * @param <T> the type of the service
-	 * @param serviceLoader the service loader to be filtered
-	 * @param providerPredicate the predicate to filter the loaded services
-	 * @return a stream of loaded services that match the predicate
-	 */
-	public static <T> Stream<T> filter(ServiceLoader<T> serviceLoader,
-			Predicate<? super Class<? extends T>> providerPredicate) {
-		// @formatter:off
-		return serviceLoader
-				.stream()
-				.filter(provider -> providerPredicate.test(provider.type()))
-				.map(ServiceLoader.Provider::get);
-		// @formatter:on
-	}
-
-}
diff --git a/junit-platform-commons/src/testFixtures/java/org/junit/platform/commons/test/ConcurrencyTestingUtils.java b/junit-platform-commons/src/testFixtures/java/org/junit/platform/commons/test/ConcurrencyTestingUtils.java
index e0ae6d6c762e..6f63ab1d7432 100644
--- a/junit-platform-commons/src/testFixtures/java/org/junit/platform/commons/test/ConcurrencyTestingUtils.java
+++ b/junit-platform-commons/src/testFixtures/java/org/junit/platform/commons/test/ConcurrencyTestingUtils.java
@@ -21,16 +21,19 @@
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 
+import org.jspecify.annotations.Nullable;
+
 public class ConcurrencyTestingUtils {
 
 	public static void executeConcurrently(int threads, Runnable action) throws Exception {
-		executeConcurrently(threads, () -> {
+		ConcurrencyTestingUtils.<@Nullable Object> executeConcurrently(threads, () -> {
 			action.run();
 			return null;
 		});
 	}
 
-	public static <T> List<T> executeConcurrently(int threads, Callable<T> action) throws Exception {
+	public static <T extends @Nullable Object> List<T> executeConcurrently(int threads, Callable<T> action)
+			throws Exception {
 		ExecutorService executorService = Executors.newFixedThreadPool(threads);
 		try {
 			CountDownLatch latch = new CountDownLatch(threads);
diff --git a/junit-platform-commons/src/testFixtures/java/org/junit/platform/commons/test/IdeUtils.java b/junit-platform-commons/src/testFixtures/java/org/junit/platform/commons/test/IdeUtils.java
new file mode 100644
index 000000000000..1b20c64c8113
--- /dev/null
+++ b/junit-platform-commons/src/testFixtures/java/org/junit/platform/commons/test/IdeUtils.java
@@ -0,0 +1,27 @@
+/*
+ * Copyright 2015-2025 the original author or authors.
+ *
+ * All rights reserved. This program and the accompanying materials are
+ * made available under the terms of the Eclipse Public License v2.0 which
+ * accompanies this distribution and is available at
+ *
+ * https://www.eclipse.org/legal/epl-v20.html
+ */
+
+package org.junit.platform.commons.test;
+
+/**
+ * Collection of test utilities for IDEs.
+ */
+public class IdeUtils {
+
+	/**
+	 * Determine if the current code is running in the Eclipse IDE.
+	 * <p>Copied from {@code org.springframework.core.testfixture.ide.IdeUtils}.
+	 */
+	public static boolean runningInEclipse() {
+		return StackWalker.getInstance().walk(
+			stream -> stream.anyMatch(stackFrame -> stackFrame.getClassName().startsWith("org.eclipse.jdt")));
+	}
+
+}
diff --git a/junit-platform-commons/src/testFixtures/java/org/junit/platform/commons/test/package-info.java b/junit-platform-commons/src/testFixtures/java/org/junit/platform/commons/test/package-info.java
new file mode 100644
index 000000000000..72143b56db41
--- /dev/null
+++ b/junit-platform-commons/src/testFixtures/java/org/junit/platform/commons/test/package-info.java
@@ -0,0 +1,5 @@
+
+@NullMarked
+package org.junit.platform.commons.test;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-platform-console-standalone/junit-platform-console-standalone.gradle.kts b/junit-platform-console-standalone/junit-platform-console-standalone.gradle.kts
index 503f1a4a744c..632c2fe94568 100644
--- a/junit-platform-console-standalone/junit-platform-console-standalone.gradle.kts
+++ b/junit-platform-console-standalone/junit-platform-console-standalone.gradle.kts
@@ -1,4 +1,4 @@
-import junitbuild.extensions.dependencyProject
+import junitbuild.extensions.withArchiveOperations
 import junitbuild.java.WriteArtifactsFile
 
 plugins {
@@ -22,9 +22,6 @@ dependencies {
 	osgiVerification(libs.openTestReporting.tooling.spi)
 }
 
-val jupiterVersion = rootProject.version
-val vintageVersion: String by project
-
 tasks {
 	jar {
 		manifest {
@@ -36,19 +33,33 @@ tasks {
 		from(configurations.shadowedClasspath)
 		outputFile = layout.buildDirectory.file("shadowed-artifacts")
 	}
+	val extractThirdPartyLicenses by registering(Sync::class) {
+		from(withArchiveOperations { ops -> configurations.shadowedClasspath.flatMap { it.elements }.map { it.map(ops::zipTree) } })
+		into(layout.buildDirectory.dir("thirdPartyLicenses"))
+		include("LICENSE.txt")
+		include("LICENSE-junit.txt")
+		include("META-INF/LICENSE-*")
+		exclude("META-INF/LICENSE-notice.md")
+		eachFile {
+			val fileName = relativePath.lastName
+			relativePath = RelativePath(true, when (fileName) {
+				"LICENSE.txt" -> "LICENSE-hamcrest"
+				"LICENSE-junit.txt" -> "LICENSE-junit4"
+				else -> fileName
+			})
+		}
+		includeEmptyDirs = false
+	}
 	shadowJar {
-		// https://github.com/junit-team/junit5/issues/2557
+		// https://github.com/junit-team/junit-framework/issues/2557
 		// exclude compiled module declarations from any source (e.g. /*, /META-INF/versions/N/*)
 		exclude("**/module-info.class")
-		// https://github.com/junit-team/junit5/issues/761
+		// https://github.com/junit-team/junit-framework/issues/761
 		// prevent duplicates, add 3rd-party licenses explicitly
-		exclude("META-INF/LICENSE*.md")
-		from(dependencyProject(project.projects.junitPlatformConsole).projectDir) {
-			include("LICENSE-picocli.md")
-			into("META-INF")
-		}
-		from(dependencyProject(project.projects.junitJupiterParams).projectDir) {
-			include("LICENSE-univocity-parsers.md")
+		exclude("**/COPYRIGHT*")
+		exclude("META-INF/LICENSE*")
+		exclude("LICENSE*.txt") // JUnit 4 and Hamcrest
+		from(extractThirdPartyLicenses) {
 			into("META-INF")
 		}
 		from(shadowedArtifactsFile) {
@@ -57,11 +68,14 @@ tasks {
 
 		bundle {
 			val importAPIGuardian: String by extra
+			val importJSpecify: String by extra
 			bnd("""
 				# Customize the imports because this is an aggregate jar
 				Import-Package: \
 					$importAPIGuardian,\
+					$importJSpecify,\
 					kotlin.*;resolution:="optional",\
+					kotlinx.*;resolution:="optional",\
 					*
 				# Disable the APIGuardian plugin since everything was already
 				# processed, again because this is an aggregate jar
@@ -77,8 +91,8 @@ tasks {
 					"Implementation-Title" to project.name,
 					// Generate test engine version information in single shared manifest file.
 					// Pattern of key and value: `"Engine-Version-{YourTestEngine#getId()}": "47.11"`
-					"Engine-Version-junit-jupiter" to jupiterVersion,
-					"Engine-Version-junit-vintage" to vintageVersion,
+					"Engine-Version-junit-jupiter" to project.version,
+					"Engine-Version-junit-vintage" to project.version,
 					// Version-aware binaries are already included - set Multi-Release flag here.
 					// See https://openjdk.java.net/jeps/238 for details
 					// Note: the "jar --update ... --release X" command does not work with the
@@ -87,12 +101,4 @@ tasks {
 			))
 		}
 	}
-
-	// This jar contains some Java 9 code
-	// (org.junit.platform.console.ConsoleLauncherToolProvider which implements
-	// java.util.spi.ToolProvider which is @since 9).
-	// So in order to resolve this, it can only run on Java 9
-	osgiProperties {
-		property("-runee", "JavaSE-9")
-	}
 }
diff --git a/junit-platform-console/junit-platform-console.gradle.kts b/junit-platform-console/junit-platform-console.gradle.kts
index 7a032e5ae482..0dd0f1b66209 100644
--- a/junit-platform-console/junit-platform-console.gradle.kts
+++ b/junit-platform-console/junit-platform-console.gradle.kts
@@ -1,10 +1,12 @@
 import junitbuild.extensions.javaModuleName
 import junitbuild.java.UpdateJarAction
+import net.ltgt.gradle.errorprone.errorprone
+import net.ltgt.gradle.nullaway.nullaway
 
 plugins {
 	id("junitbuild.java-library-conventions")
+	id("junitbuild.java-nullability-conventions")
 	id("junitbuild.shadow-conventions")
-	id("junitbuild.java-multi-release-sources")
 }
 
 description = "JUnit Platform Console"
@@ -14,8 +16,7 @@ dependencies {
 	api(projects.junitPlatformReporting)
 
 	compileOnlyApi(libs.apiguardian)
-
-	compileOnly(libs.openTestReporting.events)
+	compileOnly(libs.jspecify)
 
 	shadowed(libs.picocli)
 
@@ -25,31 +26,37 @@ dependencies {
 }
 
 tasks {
-	compileModule {
+	compileJava {
 		options.compilerArgs.addAll(listOf(
-			"--add-modules", "org.opentest4j.reporting.events",
-			"--add-reads", "${project.projects.junitPlatformReporting.javaModuleName}=org.opentest4j.reporting.events",
 			"--add-modules", "info.picocli",
 			"--add-reads", "${javaModuleName}=info.picocli"
 		))
+		options.errorprone.nullaway {
+			excludedFieldAnnotations.addAll(
+				"picocli.CommandLine.ArgGroup",
+				"picocli.CommandLine.Mixin",
+				"picocli.CommandLine.Spec",
+			)
+		}
+	}
+	javadoc {
+		(options as StandardJavadocDocletOptions).apply {
+			addStringOption("-add-modules", "info.picocli")
+			addStringOption("-add-reads", "${javaModuleName}=info.picocli")
+		}
 	}
 	shadowJar {
-		val release17ClassesDir = sourceSets.mainRelease17.get().output.classesDirs.singleFile
-		inputs.dir(release17ClassesDir).withPathSensitivity(PathSensitivity.RELATIVE)
 		exclude("META-INF/versions/9/module-info.class")
 		relocate("picocli", "org.junit.platform.console.shadow.picocli")
 		from(projectDir) {
 			include("LICENSE-picocli.md")
 			into("META-INF")
 		}
-		from(sourceSets.mainRelease9.get().output.classesDirs)
 		doLast(objects.newInstance(UpdateJarAction::class).apply {
 			javaLauncher = project.javaToolchains.launcherFor(java.toolchain)
 			args.addAll(
 				"--file", archiveFile.get().asFile.absolutePath,
 				"--main-class", "org.junit.platform.console.ConsoleLauncher",
-				"--release", "17",
-				"-C", release17ClassesDir.absolutePath, "."
 			)
 		})
 	}
@@ -61,19 +68,4 @@ tasks {
 			attributes("Main-Class" to "org.junit.platform.console.ConsoleLauncher")
 		}
 	}
-
-	// This jar contains some Java 9 code
-	// (org.junit.platform.console.ConsoleLauncherToolProvider which implements
-	// java.util.spi.ToolProvider which is @since 9).
-	// So in order to resolve this, it can only run on Java 9
-	osgiProperties {
-		property("-runee", "JavaSE-9")
-	}
-}
-
-eclipse {
-	classpath {
-		sourceSets -= project.sourceSets.mainRelease9.get()
-		sourceSets -= project.sourceSets.mainRelease17.get()
-	}
 }
diff --git a/junit-platform-console/src/module/org.junit.platform.console/module-info.java b/junit-platform-console/src/main/java/module-info.java
similarity index 95%
rename from junit-platform-console/src/module/org.junit.platform.console/module-info.java
rename to junit-platform-console/src/main/java/module-info.java
index 166aff5ee795..0fe1a03f0cf7 100644
--- a/junit-platform-console/src/module/org.junit.platform.console/module-info.java
+++ b/junit-platform-console/src/main/java/module-info.java
@@ -15,7 +15,10 @@
  * @provides java.util.spi.ToolProvider
  */
 module org.junit.platform.console {
+
 	requires static org.apiguardian.api;
+	requires static org.jspecify;
+
 	requires org.junit.platform.commons;
 	requires org.junit.platform.engine;
 	requires org.junit.platform.launcher;
diff --git a/junit-platform-console/src/main/java9/org/junit/platform/console/ConsoleLauncherToolProvider.java b/junit-platform-console/src/main/java/org/junit/platform/console/ConsoleLauncherToolProvider.java
similarity index 100%
rename from junit-platform-console/src/main/java9/org/junit/platform/console/ConsoleLauncherToolProvider.java
rename to junit-platform-console/src/main/java/org/junit/platform/console/ConsoleLauncherToolProvider.java
diff --git a/junit-platform-console/src/main/java/org/junit/platform/console/options/AnsiColorOptionMixin.java b/junit-platform-console/src/main/java/org/junit/platform/console/options/AnsiColorOptionMixin.java
index 4e9ee00ee6ac..3467e3129f95 100644
--- a/junit-platform-console/src/main/java/org/junit/platform/console/options/AnsiColorOptionMixin.java
+++ b/junit-platform-console/src/main/java/org/junit/platform/console/options/AnsiColorOptionMixin.java
@@ -39,9 +39,4 @@ public void setDisableAnsiColors(boolean disableAnsiColors) {
 		this.disableAnsiColors = disableAnsiColors;
 	}
 
-	@Option(names = "-disable-ansi-colors", hidden = true)
-	public void setDisableAnsiColors2(boolean disableAnsiColors) {
-		setDisableAnsiColors(disableAnsiColors);
-	}
-
 }
diff --git a/junit-platform-console/src/main/java/org/junit/platform/console/options/BannerOptionMixin.java b/junit-platform-console/src/main/java/org/junit/platform/console/options/BannerOptionMixin.java
deleted file mode 100644
index 813bb0937d29..000000000000
--- a/junit-platform-console/src/main/java/org/junit/platform/console/options/BannerOptionMixin.java
+++ /dev/null
@@ -1,27 +0,0 @@
-/*
- * Copyright 2015-2025 the original author or authors.
- *
- * All rights reserved. This program and the accompanying materials are
- * made available under the terms of the Eclipse Public License v2.0 which
- * accompanies this distribution and is available at
- *
- * https://www.eclipse.org/legal/epl-v20.html
- */
-
-package org.junit.platform.console.options;
-
-import picocli.CommandLine.Option;
-
-class BannerOptionMixin {
-
-	@Option(names = "--disable-banner", description = "Disable print out of the welcome message.")
-	private boolean disableBanner;
-
-	@Option(names = "-disable-banner", hidden = true)
-	private boolean disableBanner2;
-
-	public boolean isDisableBanner() {
-		return disableBanner || disableBanner2;
-	}
-
-}
diff --git a/junit-platform-console/src/main/java/org/junit/platform/console/options/BaseCommand.java b/junit-platform-console/src/main/java/org/junit/platform/console/options/BaseCommand.java
index 5f904aa2d2f0..d9153ecc7a04 100644
--- a/junit-platform-console/src/main/java/org/junit/platform/console/options/BaseCommand.java
+++ b/junit-platform-console/src/main/java/org/junit/platform/console/options/BaseCommand.java
@@ -30,8 +30,8 @@ abstract class BaseCommand<T> implements Callable<T> {
 	@Mixin
 	AnsiColorOptionMixin ansiColorOption;
 
-	@Mixin
-	BannerOptionMixin bannerOption;
+	@Option(names = "--disable-banner", description = "Disable print out of the welcome message.")
+	private boolean disableBanner;
 
 	@SuppressWarnings("unused")
 	@Option(names = { "-h", "--help" }, usageHelp = true, description = "Display help information.")
@@ -39,7 +39,7 @@ abstract class BaseCommand<T> implements Callable<T> {
 
 	@SuppressWarnings("unused")
 	@Option(names = "--version", versionHelp = true, description = "Display version information.")
-	private boolean versionHelpRequested;
+	private boolean versionRequested;
 
 	void execute(String... args) {
 		toCommandLine().execute(args);
@@ -74,7 +74,7 @@ static CommandLine initialize(CommandLine commandLine) {
 	@Override
 	public final T call() {
 		PrintWriter out = getOut();
-		if (!bannerOption.isDisableBanner()) {
+		if (!disableBanner) {
 			displayBanner(out);
 		}
 		try {
diff --git a/junit-platform-console/src/main/java/org/junit/platform/console/options/ClasspathEntriesConverter.java b/junit-platform-console/src/main/java/org/junit/platform/console/options/ClasspathEntriesConverter.java
index a0f2fa15774d..9de9395df764 100644
--- a/junit-platform-console/src/main/java/org/junit/platform/console/options/ClasspathEntriesConverter.java
+++ b/junit-platform-console/src/main/java/org/junit/platform/console/options/ClasspathEntriesConverter.java
@@ -14,7 +14,6 @@
 import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.util.List;
-import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
 import picocli.CommandLine;
@@ -23,7 +22,7 @@ class ClasspathEntriesConverter implements CommandLine.ITypeConverter<List<Path>
 
 	@Override
 	public List<Path> convert(String value) {
-		return Stream.of(value.split(File.pathSeparator)).map(Paths::get).collect(Collectors.toList());
+		return Stream.of(value.split(File.pathSeparator)).map(Paths::get).toList();
 	}
 
 }
diff --git a/junit-platform-console/src/main/java/org/junit/platform/console/options/CommandResult.java b/junit-platform-console/src/main/java/org/junit/platform/console/options/CommandResult.java
index 87a202e0560a..ff0031b9e5ec 100644
--- a/junit-platform-console/src/main/java/org/junit/platform/console/options/CommandResult.java
+++ b/junit-platform-console/src/main/java/org/junit/platform/console/options/CommandResult.java
@@ -15,6 +15,7 @@
 import java.util.Optional;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 
 /**
  * @since 1.10
@@ -40,14 +41,15 @@ public static <T> CommandResult<T> failure() {
 		return create(FAILURE, null);
 	}
 
-	public static <T> CommandResult<T> create(int exitCode, T value) {
+	public static <T> CommandResult<T> create(int exitCode, @Nullable T value) {
 		return new CommandResult<>(exitCode, value);
 	}
 
 	private final int exitCode;
-	private final T value;
 
-	private CommandResult(int exitCode, T value) {
+	private final @Nullable T value;
+
+	private CommandResult(int exitCode, @Nullable T value) {
 		this.exitCode = exitCode;
 		this.value = value;
 	}
diff --git a/junit-platform-console/src/main/java/org/junit/platform/console/options/ConsoleUtils.java b/junit-platform-console/src/main/java/org/junit/platform/console/options/ConsoleUtils.java
index 680e3381df6a..bd39bff687da 100644
--- a/junit-platform-console/src/main/java/org/junit/platform/console/options/ConsoleUtils.java
+++ b/junit-platform-console/src/main/java/org/junit/platform/console/options/ConsoleUtils.java
@@ -12,6 +12,7 @@
 
 import static org.apiguardian.api.API.Status.INTERNAL;
 
+import java.io.Console;
 import java.nio.charset.Charset;
 
 import org.apiguardian.api.API;
@@ -35,7 +36,8 @@ public class ConsoleUtils {
 	 * {@return the charset of the console}
 	 */
 	public static Charset charset() {
-		return Charset.defaultCharset();
+		Console console = System.console();
+		return console != null ? console.charset() : Charset.defaultCharset();
 	}
 
 }
diff --git a/junit-platform-console/src/main/java/org/junit/platform/console/options/ExecuteTestsCommand.java b/junit-platform-console/src/main/java/org/junit/platform/console/options/ExecuteTestsCommand.java
index 079a1b740b12..ca6c4d0281c8 100644
--- a/junit-platform-console/src/main/java/org/junit/platform/console/options/ExecuteTestsCommand.java
+++ b/junit-platform-console/src/main/java/org/junit/platform/console/options/ExecuteTestsCommand.java
@@ -16,6 +16,7 @@
 import java.nio.file.Path;
 import java.util.Optional;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.console.tasks.ConsoleTestExecutor;
 import org.junit.platform.launcher.listeners.TestExecutionSummary;
 
@@ -23,6 +24,7 @@
 import picocli.CommandLine.ArgGroup;
 import picocli.CommandLine.Command;
 import picocli.CommandLine.Mixin;
+import picocli.CommandLine.Option;
 
 @Command(//
 		name = "execute", //
@@ -93,17 +95,15 @@ public int getExitCode() {
 
 	static class ReportingOptions {
 
-		@CommandLine.Option(names = "--fail-if-no-tests", description = "Fail and return exit status code 2 if no tests are found.")
+		@Option(names = "--fail-if-no-tests", description = "Fail and return exit status code 2 if no tests are found.")
 		private boolean failIfNoTests; // no single-dash equivalent: was introduced in 5.3-M1
 
-		@CommandLine.Option(names = "--reports-dir", paramLabel = "DIR", description = "Enable report output into a specified local directory (will be created if it does not exist).")
+		@Nullable
+		@Option(names = "--reports-dir", paramLabel = "DIR", description = "Enable report output into a specified local directory (will be created if it does not exist).")
 		private Path reportsDir;
 
-		@CommandLine.Option(names = "-reports-dir", hidden = true)
-		private Path reportsDir2;
-
 		Optional<Path> getReportsDir() {
-			return reportsDir == null ? Optional.ofNullable(reportsDir2) : Optional.of(reportsDir);
+			return Optional.ofNullable(reportsDir);
 		}
 	}
 
diff --git a/junit-platform-console/src/main/java/org/junit/platform/console/options/ListTestEnginesCommand.java b/junit-platform-console/src/main/java/org/junit/platform/console/options/ListTestEnginesCommand.java
index a83ac4530e7c..6e17282662b8 100644
--- a/junit-platform-console/src/main/java/org/junit/platform/console/options/ListTestEnginesCommand.java
+++ b/junit-platform-console/src/main/java/org/junit/platform/console/options/ListTestEnginesCommand.java
@@ -46,7 +46,7 @@ private void displayEngine(PrintWriter out, TestEngine engine) {
 		engine.getGroupId().ifPresent(details::add);
 		engine.getArtifactId().ifPresent(details::add);
 		engine.getVersion().ifPresent(details::add);
-		out.println(getColorScheme().string(String.format("@|bold %s|@%s", engine.getId(), details)));
+		out.println(getColorScheme().string("@|bold %s|@%s".formatted(engine.getId(), details)));
 	}
 
 }
diff --git a/junit-platform-console/src/main/java/org/junit/platform/console/options/MainCommand.java b/junit-platform-console/src/main/java/org/junit/platform/console/options/MainCommand.java
index 177a17913681..6d309e5b3985 100644
--- a/junit-platform-console/src/main/java/org/junit/platform/console/options/MainCommand.java
+++ b/junit-platform-console/src/main/java/org/junit/platform/console/options/MainCommand.java
@@ -10,27 +10,26 @@
 
 package org.junit.platform.console.options;
 
-import java.io.PrintWriter;
-import java.util.ArrayList;
-import java.util.List;
+import static java.util.Objects.requireNonNull;
+
 import java.util.Optional;
-import java.util.concurrent.Callable;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.console.tasks.ConsoleTestExecutor;
 
 import picocli.CommandLine;
 import picocli.CommandLine.Command;
-import picocli.CommandLine.Help.ColorScheme;
 import picocli.CommandLine.IExitCodeGenerator;
 import picocli.CommandLine.Mixin;
 import picocli.CommandLine.Model.CommandSpec;
 import picocli.CommandLine.Option;
+import picocli.CommandLine.ParameterException;
 import picocli.CommandLine.Spec;
-import picocli.CommandLine.Unmatched;
 
 @Command(//
 		name = "junit", //
 		abbreviateSynopsis = true, //
+		synopsisSubcommandLabel = "COMMAND", //
 		sortOptions = false, //
 		usageHelpWidth = 95, //
 		showAtFileInUsageHelp = true, //
@@ -38,34 +37,29 @@
 		description = "Launches the JUnit Platform for test discovery and execution.", //
 		footerHeading = "%n", //
 		footer = "For more information, please refer to the JUnit User Guide at%n" //
-				+ "@|underline https://junit.org/junit5/docs/${junit.docs.version}/user-guide/|@", //
+				+ "@|underline https://docs.junit.org/${junit.docs.version}/user-guide/|@", //
 		scope = CommandLine.ScopeType.INHERIT, //
 		exitCodeOnInvalidInput = CommandResult.FAILURE, //
 		exitCodeOnExecutionException = CommandResult.FAILURE, //
 		versionProvider = ManifestVersionProvider.class //
 )
-class MainCommand implements Callable<Object>, IExitCodeGenerator {
+class MainCommand implements Runnable, IExitCodeGenerator {
 
 	private final ConsoleTestExecutor.Factory consoleTestExecutorFactory;
 
 	@Option(names = { "-h", "--help" }, help = true, description = "Display help information.")
 	private boolean helpRequested;
 
-	@Option(names = { "--h", "-help" }, help = true, hidden = true)
-	private boolean helpRequested2;
-
 	@Option(names = "--version", versionHelp = true, description = "Display version information.")
-	private boolean versionHelpRequested;
+	private boolean versionRequested;
 
 	@Mixin
 	AnsiColorOptionMixin ansiColorOption;
 
-	@Unmatched
-	private final List<String> allParameters = new ArrayList<>();
-
 	@Spec
 	CommandSpec commandSpec;
 
+	@Nullable
 	CommandResult<?> commandResult;
 
 	MainCommand(ConsoleTestExecutor.Factory consoleTestExecutorFactory) {
@@ -73,65 +67,27 @@ class MainCommand implements Callable<Object>, IExitCodeGenerator {
 	}
 
 	@Override
-	public Object call() {
-		if (helpRequested || helpRequested2) {
+	public void run() {
+		if (helpRequested) {
 			commandSpec.commandLine().usage(commandSpec.commandLine().getOut());
 			commandResult = CommandResult.success();
-			return null;
 		}
-		if (versionHelpRequested) {
+		else if (versionRequested) {
 			commandSpec.commandLine().printVersionHelp(commandSpec.commandLine().getOut());
 			commandResult = CommandResult.success();
-			return null;
 		}
-		if (allParameters.contains("--list-engines")) {
-			return runCommand("engines", Optional.of("--list-engines"));
+		else {
+			throw new ParameterException(commandSpec.commandLine(), "Missing required subcommand");
 		}
-		return runCommand("execute", Optional.empty());
 	}
 
 	@Override
 	public int getExitCode() {
-		return commandResult.getExitCode();
-	}
-
-	@SuppressWarnings("OptionalUsedAsFieldOrParameterType")
-	private Object runCommand(String subcommand, Optional<String> triggeringOption) {
-		CommandLine commandLine = commandSpec.commandLine();
-		commandLine.setUnmatchedArgumentsAllowed(false);
-		Object command = commandLine.getSubcommands().get(subcommand).getCommandSpec().userObject();
-
-		List<String> args = new ArrayList<>(commandLine.getParseResult().expandedArgs());
-		triggeringOption.ifPresent(args::remove);
-		CommandResult<?> result = runCommand( //
-			new CommandLine(command), //
-			args.toArray(new String[0]), //
-			Optional.of(new OutputStreamConfig(commandLine)) //
-		);
-		this.commandResult = result;
-
-		printDeprecationWarning(subcommand, triggeringOption, commandLine);
-
-		return result.getValue().orElse(null);
-	}
-
-	private static void printDeprecationWarning(String subcommand, Optional<String> triggeringOption,
-			CommandLine commandLine) {
-		PrintWriter err = commandLine.getErr();
-		String reason = triggeringOption.map(it -> " due to use of '" + it + "'").orElse("");
-
-		commandLine.getOut().flush();
-		err.println();
-		ColorScheme colorScheme = commandLine.getColorScheme();
-		err.println(colorScheme.string(
-			String.format("@|yellow,bold WARNING:|@ Delegated to the '%s' command%s.", subcommand, reason)));
-		err.println(
-			colorScheme.string("         This behaviour has been deprecated and will be removed in a future release."));
-		err.println(colorScheme.string("         Please use the '" + subcommand + "' command directly."));
-		err.flush();
+		return requireNonNull(commandResult).getExitCode();
 	}
 
-	CommandResult<?> run(String[] args, Optional<OutputStreamConfig> outputStreamConfig) {
+	CommandResult<?> run(String[] args,
+			@SuppressWarnings("OptionalUsedAsFieldOrParameterType") Optional<OutputStreamConfig> outputStreamConfig) {
 		CommandLine commandLine = new CommandLine(this) //
 				.addSubcommand(new DiscoverTestsCommand(consoleTestExecutorFactory)) //
 				.addSubcommand(new ExecuteTestsCommand(consoleTestExecutorFactory)) //
@@ -140,7 +96,7 @@ CommandResult<?> run(String[] args, Optional<OutputStreamConfig> outputStreamCon
 	}
 
 	private static CommandResult<?> runCommand(CommandLine commandLine, String[] args,
-			Optional<OutputStreamConfig> outputStreamConfig) {
+			@SuppressWarnings("OptionalUsedAsFieldOrParameterType") Optional<OutputStreamConfig> outputStreamConfig) {
 		BaseCommand.initialize(commandLine);
 		outputStreamConfig.ifPresent(it -> it.applyTo(commandLine));
 		int exitCode = commandLine.execute(args);
diff --git a/junit-platform-console/src/main/java/org/junit/platform/console/options/ManifestVersionProvider.java b/junit-platform-console/src/main/java/org/junit/platform/console/options/ManifestVersionProvider.java
index 8f41f9f8c894..45a0c1bdb070 100644
--- a/junit-platform-console/src/main/java/org/junit/platform/console/options/ManifestVersionProvider.java
+++ b/junit-platform-console/src/main/java/org/junit/platform/console/options/ManifestVersionProvider.java
@@ -25,8 +25,7 @@ public static Optional<String> getImplementationVersion() {
 	@Override
 	public String[] getVersion() {
 		return new String[] { //
-				String.format("@|bold JUnit Platform Console Launcher %s|@",
-					getImplementationVersion().orElse("<unknown>")), //
+				"@|bold JUnit Platform Console Launcher %s|@".formatted(getImplementationVersion().orElse("<unknown>")), //
 				"JVM: ${java.version} (${java.vendor} ${java.vm.name} ${java.vm.version})", //
 				"OS: ${os.name} ${os.version} ${os.arch}" //
 		};
diff --git a/junit-platform-console/src/main/java/org/junit/platform/console/options/TestConsoleOutputOptions.java b/junit-platform-console/src/main/java/org/junit/platform/console/options/TestConsoleOutputOptions.java
index 73f4fc4a2416..396f74fd7cef 100644
--- a/junit-platform-console/src/main/java/org/junit/platform/console/options/TestConsoleOutputOptions.java
+++ b/junit-platform-console/src/main/java/org/junit/platform/console/options/TestConsoleOutputOptions.java
@@ -16,6 +16,7 @@
 import java.util.Locale;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 
 /**
  * @since 1.10
@@ -28,12 +29,16 @@ public class TestConsoleOutputOptions {
 	static final Theme DEFAULT_THEME = Theme.valueOf(ConsoleUtils.charset());
 
 	private boolean ansiColorOutputDisabled;
-	private Path colorPalettePath;
+
+	private @Nullable Path colorPalettePath;
+
 	private boolean isSingleColorPalette;
 	private Details details = DEFAULT_DETAILS;
 	private Theme theme = DEFAULT_THEME;
-	private Path stdoutPath;
-	private Path stderrPath;
+
+	private @Nullable Path stdoutPath;
+
+	private @Nullable Path stderrPath;
 
 	public boolean isAnsiColorOutputDisabled() {
 		return this.ansiColorOutputDisabled;
@@ -43,11 +48,11 @@ public void setAnsiColorOutputDisabled(boolean ansiColorOutputDisabled) {
 		this.ansiColorOutputDisabled = ansiColorOutputDisabled;
 	}
 
-	public Path getColorPalettePath() {
+	public @Nullable Path getColorPalettePath() {
 		return colorPalettePath;
 	}
 
-	public void setColorPalettePath(Path colorPalettePath) {
+	public void setColorPalettePath(@Nullable Path colorPalettePath) {
 		this.colorPalettePath = colorPalettePath;
 	}
 
@@ -76,22 +81,22 @@ public void setTheme(Theme theme) {
 	}
 
 	@API(status = INTERNAL, since = "1.13")
-	public Path getStdoutPath() {
+	public @Nullable Path getStdoutPath() {
 		return this.stdoutPath;
 	}
 
 	@API(status = INTERNAL, since = "1.13")
-	public void setStdoutPath(Path stdoutPath) {
+	public void setStdoutPath(@Nullable Path stdoutPath) {
 		this.stdoutPath = stdoutPath;
 	}
 
 	@API(status = INTERNAL, since = "1.13")
-	public Path getStderrPath() {
+	public @Nullable Path getStderrPath() {
 		return this.stderrPath;
 	}
 
 	@API(status = INTERNAL, since = "1.13")
-	public void setStderrPath(Path stderrPath) {
+	public void setStderrPath(@Nullable Path stderrPath) {
 		this.stderrPath = stderrPath;
 	}
 
diff --git a/junit-platform-console/src/main/java/org/junit/platform/console/options/TestConsoleOutputOptionsMixin.java b/junit-platform-console/src/main/java/org/junit/platform/console/options/TestConsoleOutputOptionsMixin.java
index 20103a737d99..54d3cbd34a29 100644
--- a/junit-platform-console/src/main/java/org/junit/platform/console/options/TestConsoleOutputOptionsMixin.java
+++ b/junit-platform-console/src/main/java/org/junit/platform/console/options/TestConsoleOutputOptionsMixin.java
@@ -16,6 +16,8 @@
 
 import java.nio.file.Path;
 
+import org.jspecify.annotations.Nullable;
+
 import picocli.CommandLine.ArgGroup;
 import picocli.CommandLine.Option;
 
@@ -26,42 +28,35 @@ class TestConsoleOutputOptionsMixin {
 
 	static class ConsoleOutputOptions {
 
+		@Nullable
 		@Option(names = "--color-palette", paramLabel = "FILE", description = "Specify a path to a properties file to customize ANSI style of output (not supported by all terminals).")
 		private Path colorPalette;
-		@Option(names = "-color-palette", hidden = true)
-		private Path colorPalette2;
 
 		@Option(names = "--single-color", description = "Style test output using only text attributes, no color (not supported by all terminals).")
 		private boolean singleColorPalette;
-		@Option(names = "-single-color", hidden = true)
-		private boolean singleColorPalette2;
 
 		@Option(names = "--details", paramLabel = "MODE", defaultValue = DEFAULT_DETAILS_NAME, description = "Select an output details mode for when tests are executed. " //
 				+ "Use one of: ${COMPLETION-CANDIDATES}. If 'none' is selected, " //
 				+ "then only the summary and test failures are shown. Default: ${DEFAULT-VALUE}.")
 		private final Details details = DEFAULT_DETAILS;
 
-		@Option(names = "-details", hidden = true, defaultValue = DEFAULT_DETAILS_NAME)
-		private final Details details2 = DEFAULT_DETAILS;
-
 		@Option(names = "--details-theme", paramLabel = "THEME", description = "Select an output details tree theme for when tests are executed. "
 				+ "Use one of: ${COMPLETION-CANDIDATES}. Default is detected based on default character encoding.")
 		private final Theme theme = DEFAULT_THEME;
 
-		@Option(names = "-details-theme", hidden = true)
-		private final Theme theme2 = DEFAULT_THEME;
-
+		@Nullable
 		@Option(names = "--redirect-stdout", paramLabel = "FILE", description = "Redirect test output to stdout to a file.")
 		private Path stdout;
 
+		@Nullable
 		@Option(names = "--redirect-stderr", paramLabel = "FILE", description = "Redirect test output to stderr to a file.")
 		private Path stderr;
 
 		private void applyTo(TestConsoleOutputOptions result) {
-			result.setColorPalettePath(choose(colorPalette, colorPalette2, null));
-			result.setSingleColorPalette(singleColorPalette || singleColorPalette2);
-			result.setDetails(choose(details, details2, DEFAULT_DETAILS));
-			result.setTheme(choose(theme, theme2, DEFAULT_THEME));
+			result.setColorPalettePath(colorPalette);
+			result.setSingleColorPalette(singleColorPalette);
+			result.setDetails(details);
+			result.setTheme(theme);
 			result.setStdoutPath(stdout);
 			result.setStderrPath(stderr);
 		}
@@ -75,8 +70,4 @@ TestConsoleOutputOptions toTestConsoleOutputOptions() {
 		return result;
 	}
 
-	private static <T> T choose(T left, T right, T defaultValue) {
-		return left == right ? left : (left == defaultValue ? right : left);
-	}
-
 }
diff --git a/junit-platform-console/src/main/java/org/junit/platform/console/options/TestDiscoveryOptions.java b/junit-platform-console/src/main/java/org/junit/platform/console/options/TestDiscoveryOptions.java
index 0345dde65603..3e368c90ae94 100644
--- a/junit-platform-console/src/main/java/org/junit/platform/console/options/TestDiscoveryOptions.java
+++ b/junit-platform-console/src/main/java/org/junit/platform/console/options/TestDiscoveryOptions.java
@@ -13,7 +13,6 @@
 import static java.util.Collections.emptyList;
 import static java.util.Collections.emptyMap;
 import static java.util.Collections.singletonList;
-import static java.util.stream.Collectors.toList;
 import static org.apiguardian.api.API.Status.INTERNAL;
 import static org.junit.platform.engine.discovery.ClassNameFilter.STANDARD_INCLUDE_PATTERN;
 
@@ -24,6 +23,7 @@
 import java.util.Map;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.engine.DiscoverySelector;
 import org.junit.platform.engine.DiscoverySelectorIdentifier;
 import org.junit.platform.engine.discovery.ClassSelector;
@@ -46,7 +46,8 @@ public class TestDiscoveryOptions {
 
 	private boolean scanClasspath;
 	private List<Path> additionalClasspathEntries = emptyList();
-	private List<Path> selectedClasspathEntries = emptyList();
+
+	private @Nullable List<Path> selectedClasspathEntries = emptyList();
 
 	private boolean scanModulepath;
 
@@ -93,7 +94,7 @@ public void setScanClasspath(boolean scanClasspath) {
 	}
 
 	public List<Path> getExistingAdditionalClasspathEntries() {
-		return this.additionalClasspathEntries.stream().filter(Files::exists).collect(toList());
+		return this.additionalClasspathEntries.stream().filter(Files::exists).toList();
 	}
 
 	public List<Path> getAdditionalClasspathEntries() {
@@ -104,11 +105,11 @@ public void setAdditionalClasspathEntries(List<Path> additionalClasspathEntries)
 		this.additionalClasspathEntries = additionalClasspathEntries;
 	}
 
-	public List<Path> getSelectedClasspathEntries() {
+	public @Nullable List<Path> getSelectedClasspathEntries() {
 		return this.selectedClasspathEntries;
 	}
 
-	public void setSelectedClasspathEntries(List<Path> selectedClasspathEntries) {
+	public void setSelectedClasspathEntries(@Nullable List<Path> selectedClasspathEntries) {
 		this.selectedClasspathEntries = selectedClasspathEntries;
 	}
 
@@ -202,6 +203,7 @@ public void setSelectorIdentifiers(List<DiscoverySelectorIdentifier> selectorIde
 
 	public List<DiscoverySelector> getExplicitSelectors() {
 		List<DiscoverySelector> selectors = new ArrayList<>();
+		selectors.addAll(getSelectedUniqueIds());
 		selectors.addAll(getSelectedUris());
 		selectors.addAll(getSelectedFiles());
 		selectors.addAll(getSelectedDirectories());
diff --git a/junit-platform-console/src/main/java/org/junit/platform/console/options/TestDiscoveryOptionsMixin.java b/junit-platform-console/src/main/java/org/junit/platform/console/options/TestDiscoveryOptionsMixin.java
index 7d423f17c9bd..b95b5a43f44b 100644
--- a/junit-platform-console/src/main/java/org/junit/platform/console/options/TestDiscoveryOptionsMixin.java
+++ b/junit-platform-console/src/main/java/org/junit/platform/console/options/TestDiscoveryOptionsMixin.java
@@ -12,11 +12,11 @@
 
 import java.nio.file.Path;
 import java.util.ArrayList;
-import java.util.Collections;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.engine.DiscoverySelectorIdentifier;
 import org.junit.platform.engine.discovery.ClassNameFilter;
 import org.junit.platform.engine.discovery.ClassSelector;
@@ -42,7 +42,7 @@ class TestDiscoveryOptionsMixin {
 	SelectorOptions selectorOptions;
 
 	@ArgGroup(validate = false, order = 3, heading = "%n  For more information on selectors including syntax examples, see"
-			+ "%n  @|underline https://junit.org/junit5/docs/${junit.docs.version}/user-guide/#running-tests-discovery-selectors|@"
+			+ "%n  @|underline https://docs.junit.org/${junit.docs.version}/user-guide/#running-tests-discovery-selectors|@"
 			+ "%n%n@|bold FILTERS|@%n%n")
 	FilterOptions filterOptions;
 
@@ -51,6 +51,7 @@ class TestDiscoveryOptionsMixin {
 
 	static class SelectorOptions {
 
+		@Nullable
 		@Option(names = { "--scan-classpath",
 				"--scan-class-path" }, converter = ClasspathEntriesConverter.class, paramLabel = "PATH", arity = "0..1", description = "Scan all directories on the classpath or explicit classpath roots. " //
 						+ "Without arguments, only directories on the system classpath as well as additional classpath " //
@@ -59,24 +60,13 @@ static class SelectorOptions {
 						+ "This option can be repeated.")
 		private List<Path> selectedClasspathEntries;
 
-		@Option(names = { "-scan-class-path",
-				"-scan-classpath" }, converter = ClasspathEntriesConverter.class, arity = "0..1", hidden = true)
-		private List<Path> selectedClasspathEntries2;
-
 		@Option(names = "--scan-modules", description = "Scan all resolved modules for test discovery.")
 		private boolean scanModulepath;
 
-		@Option(names = "-scan-modules", hidden = true)
-		private boolean scanModulepath2;
-
 		@Option(names = { "-u",
 				"--select-uri" }, paramLabel = "URI", arity = "1..*", converter = SelectorConverter.Uri.class, description = "Select a URI for test discovery. This option can be repeated.")
 		private final List<UriSelector> selectedUris = new ArrayList<>();
 
-		@Option(names = { "--u",
-				"-select-uri" }, arity = "1..*", hidden = true, converter = SelectorConverter.Uri.class)
-		private final List<UriSelector> selectedUris2 = new ArrayList<>();
-
 		@Option(names = { "-f",
 				"--select-file" }, paramLabel = "FILE", arity = "1..*", converter = SelectorConverter.File.class, //
 				description = "Select a file for test discovery. "
@@ -84,58 +74,30 @@ static class SelectorOptions {
 						+ "This option can be repeated.")
 		private final List<FileSelector> selectedFiles = new ArrayList<>();
 
-		@Option(names = { "--f",
-				"-select-file" }, arity = "1..*", hidden = true, converter = SelectorConverter.File.class)
-		private final List<FileSelector> selectedFiles2 = new ArrayList<>();
-
 		@Option(names = { "-d",
 				"--select-directory" }, paramLabel = "DIR", arity = "1..*", converter = SelectorConverter.Directory.class, description = "Select a directory for test discovery. This option can be repeated.")
 		private final List<DirectorySelector> selectedDirectories = new ArrayList<>();
 
-		@Option(names = { "--d",
-				"-select-directory" }, arity = "1..*", hidden = true, converter = SelectorConverter.Directory.class)
-		private final List<DirectorySelector> selectedDirectories2 = new ArrayList<>();
-
 		@Option(names = { "-o",
 				"--select-module" }, paramLabel = "NAME", arity = "1..*", converter = SelectorConverter.Module.class, description = "Select single module for test discovery. This option can be repeated.")
 		private final List<ModuleSelector> selectedModules = new ArrayList<>();
 
-		@Option(names = { "--o",
-				"-select-module" }, arity = "1..*", converter = SelectorConverter.Module.class, hidden = true)
-		private final List<ModuleSelector> selectedModules2 = new ArrayList<>();
-
 		@Option(names = { "-p",
 				"--select-package" }, paramLabel = "PKG", arity = "1..*", converter = SelectorConverter.Package.class, description = "Select a package for test discovery. This option can be repeated.")
 		private final List<PackageSelector> selectedPackages = new ArrayList<>();
 
-		@Option(names = { "--p",
-				"-select-package" }, arity = "1..*", hidden = true, converter = SelectorConverter.Package.class)
-		private final List<PackageSelector> selectedPackages2 = new ArrayList<>();
-
 		@Option(names = { "-c",
 				"--select-class" }, paramLabel = "CLASS", arity = "1..*", converter = SelectorConverter.Class.class, description = "Select a class for test discovery. This option can be repeated.")
 		private final List<ClassSelector> selectedClasses = new ArrayList<>();
 
-		@Option(names = { "--c",
-				"-select-class" }, arity = "1..*", hidden = true, converter = SelectorConverter.Class.class)
-		private final List<ClassSelector> selectedClasses2 = new ArrayList<>();
-
 		@Option(names = { "-m",
 				"--select-method" }, paramLabel = "NAME", arity = "1..*", converter = SelectorConverter.Method.class, description = "Select a method for test discovery. This option can be repeated.")
 		private final List<MethodSelector> selectedMethods = new ArrayList<>();
 
-		@Option(names = { "--m",
-				"-select-method" }, arity = "1..*", hidden = true, converter = SelectorConverter.Method.class)
-		private final List<MethodSelector> selectedMethods2 = new ArrayList<>();
-
 		@Option(names = { "-r",
 				"--select-resource" }, paramLabel = "RESOURCE", arity = "1..*", converter = SelectorConverter.ClasspathResource.class, description = "Select a classpath resource for test discovery. This option can be repeated.")
 		private final List<ClasspathResourceSelector> selectedClasspathResources = new ArrayList<>();
 
-		@Option(names = { "--r",
-				"-select-resource" }, arity = "1..*", hidden = true, converter = SelectorConverter.ClasspathResource.class)
-		private final List<ClasspathResourceSelector> selectedClasspathResources2 = new ArrayList<>();
-
 		@Option(names = { "-i",
 				"--select-iteration" }, paramLabel = "PREFIX:VALUE[INDEX(..INDEX)?(,INDEX(..INDEX)?)*]", arity = "1..*", converter = SelectorConverter.Iteration.class, //
 				description = "Select iterations for test discovery via a prefixed identifier and a list of indexes or index ranges "
@@ -143,10 +105,6 @@ static class SelectorOptions {
 						+ "This option can be repeated.")
 		private final List<IterationSelector> selectedIterations = new ArrayList<>();
 
-		@Option(names = { "--i",
-				"-select-iteration" }, arity = "1..*", hidden = true, converter = SelectorConverter.Iteration.class)
-		private final List<IterationSelector> selectedIterations2 = new ArrayList<>();
-
 		@Option(names = { "--select-unique-id",
 				"--uid" }, paramLabel = "UNIQUE-ID", arity = "1..*", converter = SelectorConverter.UniqueId.class, //
 				description = "Select a unique id for test discovery. This option can be repeated.")
@@ -161,19 +119,18 @@ static class SelectorOptions {
 		}
 
 		private void applyTo(TestDiscoveryOptions result) {
-			result.setScanClasspath(this.selectedClasspathEntries != null || this.selectedClasspathEntries2 != null); // flag was specified
-			result.setScanModulepath(this.scanModulepath || this.scanModulepath2);
-			result.setSelectedModules(merge(this.selectedModules, this.selectedModules2));
-			result.setSelectedClasspathEntries(merge(this.selectedClasspathEntries, this.selectedClasspathEntries2));
-			result.setSelectedUris(merge(this.selectedUris, this.selectedUris2));
-			result.setSelectedFiles(merge(this.selectedFiles, this.selectedFiles2));
-			result.setSelectedDirectories(merge(this.selectedDirectories, this.selectedDirectories2));
-			result.setSelectedPackages(merge(this.selectedPackages, this.selectedPackages2));
-			result.setSelectedClasses(merge(this.selectedClasses, this.selectedClasses2));
-			result.setSelectedMethods(merge(this.selectedMethods, this.selectedMethods2));
-			result.setSelectedClasspathResources(
-				merge(this.selectedClasspathResources, this.selectedClasspathResources2));
-			result.setSelectedIterations(merge(this.selectedIterations, this.selectedIterations2));
+			result.setScanClasspath(this.selectedClasspathEntries != null); // flag was specified
+			result.setScanModulepath(this.scanModulepath);
+			result.setSelectedModules(this.selectedModules);
+			result.setSelectedClasspathEntries(this.selectedClasspathEntries);
+			result.setSelectedUris(this.selectedUris);
+			result.setSelectedFiles(this.selectedFiles);
+			result.setSelectedDirectories(this.selectedDirectories);
+			result.setSelectedPackages(this.selectedPackages);
+			result.setSelectedClasses(this.selectedClasses);
+			result.setSelectedMethods(this.selectedMethods);
+			result.setSelectedClasspathResources(this.selectedClasspathResources);
+			result.setSelectedIterations(this.selectedIterations);
 			result.setSelectedUniqueId(this.selectedUniqueIds);
 			result.setSelectorIdentifiers(this.selectorIdentifiers);
 		}
@@ -189,31 +146,19 @@ static class FilterOptions {
 						+ "Default: ${DEFAULT-VALUE}")
 		private final List<String> includeClassNamePatterns = new ArrayList<>();
 
-		@Option(names = { "--n", "-include-classname" }, arity = "1", hidden = true)
-		private final List<String> includeClassNamePatterns2 = new ArrayList<>();
-
 		@Option(names = { "-N",
 				"--exclude-classname" }, paramLabel = "PATTERN", arity = "1", description = "Provide a regular expression to exclude those classes whose fully qualified names match. " //
 						+ "When this option is repeated, all patterns will be combined using OR semantics.")
 		private final List<String> excludeClassNamePatterns = new ArrayList<>();
 
-		@Option(names = { "--N", "-exclude-classname" }, arity = "1", hidden = true)
-		private final List<String> excludeClassNamePatterns2 = new ArrayList<>();
-
 		@Option(names = {
 				"--include-package" }, paramLabel = "PKG", arity = "1", description = "Provide a package to be included in the test run. This option can be repeated.")
 		private final List<String> includePackages = new ArrayList<>();
 
-		@Option(names = { "-include-package" }, arity = "1", hidden = true)
-		private final List<String> includePackages2 = new ArrayList<>();
-
 		@Option(names = {
 				"--exclude-package" }, paramLabel = "PKG", arity = "1", description = "Provide a package to be excluded from the test run. This option can be repeated.")
 		private final List<String> excludePackages = new ArrayList<>();
 
-		@Option(names = { "-exclude-package" }, arity = "1", hidden = true)
-		private final List<String> excludePackages2 = new ArrayList<>();
-
 		@Option(names = {
 				"--include-methodname" }, paramLabel = "PATTERN", arity = "1", description = "Provide a regular expression to include only methods whose fully qualified names without parameters match. " //
 						+ "When this option is repeated, all patterns will be combined using OR semantics.")
@@ -230,43 +175,31 @@ static class FilterOptions {
 						"When this option is repeated, all patterns will be combined using OR semantics.")
 		private final List<String> includedTags = new ArrayList<>();
 
-		@Option(names = { "--t", "-include-tag" }, arity = "1", hidden = true)
-		private final List<String> includedTags2 = new ArrayList<>();
-
 		@Option(names = { "-T",
 				"--exclude-tag" }, paramLabel = "TAG", arity = "1", description = "Provide a tag or tag expression to exclude those tests whose tags match. "
 						+ //
 						"When this option is repeated, all patterns will be combined using OR semantics.")
 		private final List<String> excludedTags = new ArrayList<>();
 
-		@Option(names = { "--T", "-exclude-tag" }, arity = "1", hidden = true)
-		private final List<String> excludedTags2 = new ArrayList<>();
-
 		@Option(names = { "-e",
 				"--include-engine" }, paramLabel = "ID", arity = "1", description = "Provide the ID of an engine to be included in the test run. This option can be repeated.")
 		private final List<String> includedEngines = new ArrayList<>();
 
-		@Option(names = { "--e", "-include-engine" }, arity = "1", hidden = true)
-		private final List<String> includedEngines2 = new ArrayList<>();
-
 		@Option(names = { "-E",
 				"--exclude-engine" }, paramLabel = "ID", arity = "1", description = "Provide the ID of an engine to be excluded from the test run. This option can be repeated.")
 		private final List<String> excludedEngines = new ArrayList<>();
 
-		@Option(names = { "--E", "-exclude-engine" }, arity = "1", hidden = true)
-		private final List<String> excludedEngines2 = new ArrayList<>();
-
 		private void applyTo(TestDiscoveryOptions result) {
-			result.setIncludedClassNamePatterns(merge(this.includeClassNamePatterns, this.includeClassNamePatterns2));
-			result.setExcludedClassNamePatterns(merge(this.excludeClassNamePatterns, this.excludeClassNamePatterns2));
-			result.setIncludedPackages(merge(this.includePackages, this.includePackages2));
-			result.setExcludedPackages(merge(this.excludePackages, this.excludePackages2));
+			result.setIncludedClassNamePatterns(this.includeClassNamePatterns);
+			result.setExcludedClassNamePatterns(this.excludeClassNamePatterns);
+			result.setIncludedPackages(this.includePackages);
+			result.setExcludedPackages(this.excludePackages);
 			result.setIncludedMethodNamePatterns(new ArrayList<>(this.includeMethodNamePatterns));
 			result.setExcludedMethodNamePatterns(new ArrayList<>(this.excludeMethodNamePatterns));
-			result.setIncludedTagExpressions(merge(this.includedTags, this.includedTags2));
-			result.setExcludedTagExpressions(merge(this.excludedTags, this.excludedTags2));
-			result.setIncludedEngines(merge(this.includedEngines, this.includedEngines2));
-			result.setExcludedEngines(merge(this.excludedEngines, this.excludedEngines2));
+			result.setIncludedTagExpressions(this.includedTags);
+			result.setExcludedTagExpressions(this.excludedTags);
+			result.setIncludedEngines(this.includedEngines);
+			result.setExcludedEngines(this.excludedEngines);
 		}
 	}
 
@@ -277,10 +210,6 @@ static class RuntimeConfigurationOptions {
 						+ "-- for example, for adding engines and their dependencies. This option can be repeated.")
 		private final List<Path> additionalClasspathEntries = new ArrayList<>();
 
-		@Option(names = { "--cp", "-classpath",
-				"-class-path" }, converter = ClasspathEntriesConverter.class, hidden = true)
-		private final List<Path> additionalClasspathEntries2 = new ArrayList<>();
-
 		// Implementation note: the @Option annotation is on a setter method to allow validation.
 		private final Map<String, String> configurationParameters = new LinkedHashMap<>();
 
@@ -291,11 +220,6 @@ static class RuntimeConfigurationOptions {
 		@CommandLine.Spec
 		private CommandLine.Model.CommandSpec spec;
 
-		@Option(names = { "-config" }, arity = "1", hidden = true)
-		public void setConfigurationParameters2(Map<String, String> keyValuePairs) {
-			setConfigurationParameters(keyValuePairs);
-		}
-
 		/**
 		 * Adds the specified key-value pair (or pairs) to the configuration parameters.
 		 * A {@code ParameterException} is thrown if the same key is specified multiple times
@@ -303,7 +227,7 @@ public void setConfigurationParameters2(Map<String, String> keyValuePairs) {
 		 *
 		 * @param map the key-value pairs to add
 		 * @throws CommandLine.ParameterException if the map already contains this key
-		 * @see <a href="https://github.com/junit-team/junit5/issues/1308">#1308</a>
+		 * @see <a href="https://github.com/junit-team/junit-framework/issues/1308">#1308</a>
 		 */
 		@Option(names = "--config", paramLabel = "KEY=VALUE", arity = "1", description = "Set a configuration parameter for test discovery and execution. This option can be repeated.")
 		public void setConfigurationParameters(Map<String, String> map) {
@@ -318,12 +242,12 @@ private void validateUnique(String key, String newValue) {
 			String existing = configurationParameters.get(key);
 			if (existing != null && !existing.equals(newValue)) {
 				throw new CommandLine.ParameterException(spec.commandLine(),
-					String.format("Duplicate key '%s' for values '%s' and '%s'.", key, existing, newValue));
+					"Duplicate key '%s' for values '%s' and '%s'.".formatted(key, existing, newValue));
 			}
 		}
 
 		private void applyTo(TestDiscoveryOptions result) {
-			result.setAdditionalClasspathEntries(merge(additionalClasspathEntries, additionalClasspathEntries2));
+			result.setAdditionalClasspathEntries(additionalClasspathEntries);
 			result.setConfigurationParametersResources(configurationParametersResources);
 			result.setConfigurationParameters(configurationParameters);
 		}
@@ -343,10 +267,4 @@ TestDiscoveryOptions toTestDiscoveryOptions() {
 		return result;
 	}
 
-	private static <T> List<T> merge(List<T> list1, List<T> list2) {
-		List<T> result = new ArrayList<>(list1 == null ? Collections.emptyList() : list1);
-		result.addAll(list2 == null ? Collections.emptyList() : list2);
-		return result;
-	}
-
 }
diff --git a/junit-platform-console/src/main/java/org/junit/platform/console/options/Theme.java b/junit-platform-console/src/main/java/org/junit/platform/console/options/Theme.java
index 83d75d08fc8f..1abf7f8e0084 100644
--- a/junit-platform-console/src/main/java/org/junit/platform/console/options/Theme.java
+++ b/junit-platform-console/src/main/java/org/junit/platform/console/options/Theme.java
@@ -116,16 +116,11 @@ public final String skipped() {
 	}
 
 	public final String status(TestExecutionResult result) {
-		switch (result.getStatus()) {
-			case SUCCESSFUL:
-				return successful();
-			case ABORTED:
-				return aborted();
-			case FAILED:
-				return failed();
-			default:
-				return result.getStatus().name();
-		}
+		return switch (result.getStatus()) {
+			case SUCCESSFUL -> successful();
+			case ABORTED -> aborted();
+			case FAILED -> failed();
+		};
 	}
 
 	/**
diff --git a/junit-platform-console/src/main/java/org/junit/platform/console/options/package-info.java b/junit-platform-console/src/main/java/org/junit/platform/console/options/package-info.java
index babb46e295da..f06150fae4b5 100644
--- a/junit-platform-console/src/main/java/org/junit/platform/console/options/package-info.java
+++ b/junit-platform-console/src/main/java/org/junit/platform/console/options/package-info.java
@@ -2,4 +2,7 @@
  * Configuration options for JUnit's console launcher.
  */
 
+@NullMarked
 package org.junit.platform.console.options;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-platform-console/src/main/java/org/junit/platform/console/package-info.java b/junit-platform-console/src/main/java/org/junit/platform/console/package-info.java
index 73bc1b41dceb..3b0816fca102 100644
--- a/junit-platform-console/src/main/java/org/junit/platform/console/package-info.java
+++ b/junit-platform-console/src/main/java/org/junit/platform/console/package-info.java
@@ -2,4 +2,7 @@
  * Support for launching the JUnit Platform from the console.
  */
 
+@NullMarked
 package org.junit.platform.console;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-platform-console/src/main/java/org/junit/platform/console/tasks/ColorPalette.java b/junit-platform-console/src/main/java/org/junit/platform/console/tasks/ColorPalette.java
index 7ff8e3f6809b..120f2de48a6f 100644
--- a/junit-platform-console/src/main/java/org/junit/platform/console/tasks/ColorPalette.java
+++ b/junit-platform-console/src/main/java/org/junit/platform/console/tasks/ColorPalette.java
@@ -122,7 +122,7 @@ public String paint(Style style, String text) {
 	}
 
 	private String getAnsiFormatter(Style style) {
-		return String.format("\u001B[%sm", this.colorsToAnsiSequences.get(style));
+		return "\u001B[%sm".formatted(this.colorsToAnsiSequences.get(style));
 	}
 
 }
diff --git a/junit-platform-console/src/main/java/org/junit/platform/console/tasks/ConsoleTestExecutor.java b/junit-platform-console/src/main/java/org/junit/platform/console/tasks/ConsoleTestExecutor.java
index eb0f3874a8e3..4c001b4d806f 100644
--- a/junit-platform-console/src/main/java/org/junit/platform/console/tasks/ConsoleTestExecutor.java
+++ b/junit-platform-console/src/main/java/org/junit/platform/console/tasks/ConsoleTestExecutor.java
@@ -180,21 +180,16 @@ private SummaryGeneratingListener registerListeners(PrintWriter out, Optional<Pa
 	private Optional<DetailsPrintingListener> createDetailsPrintingListener(PrintWriter out) {
 		ColorPalette colorPalette = getColorPalette();
 		Theme theme = outputOptions.getTheme();
-		switch (outputOptions.getDetails()) {
-			case SUMMARY:
-				// summary listener is always created and registered
-				return Optional.empty();
-			case FLAT:
-				return Optional.of(new FlatPrintingListener(out, colorPalette));
-			case TREE:
-				return Optional.of(new TreePrintingListener(out, colorPalette, theme));
-			case VERBOSE:
-				return Optional.of(new VerboseTreePrintingListener(out, colorPalette, 16, theme));
-			case TESTFEED:
-				return Optional.of(new TestFeedPrintingListener(out, colorPalette));
-			default:
-				return Optional.empty();
-		}
+		return switch (outputOptions.getDetails()) {
+			case SUMMARY ->
+					// summary listener is always created and registered
+					Optional.empty();
+			case FLAT -> Optional.of(new FlatPrintingListener(out, colorPalette));
+			case TREE -> Optional.of(new TreePrintingListener(out, colorPalette, theme));
+			case VERBOSE -> Optional.of(new VerboseTreePrintingListener(out, colorPalette, 16, theme));
+			case TESTFEED -> Optional.of(new TestFeedPrintingListener(out, colorPalette));
+			case NONE -> Optional.empty();
+		};
 	}
 
 	private ColorPalette getColorPalette() {
diff --git a/junit-platform-console/src/main/java/org/junit/platform/console/tasks/CustomClassLoaderCloseStrategy.java b/junit-platform-console/src/main/java/org/junit/platform/console/tasks/CustomClassLoaderCloseStrategy.java
index 8a4694ba2156..a5221b569334 100644
--- a/junit-platform-console/src/main/java/org/junit/platform/console/tasks/CustomClassLoaderCloseStrategy.java
+++ b/junit-platform-console/src/main/java/org/junit/platform/console/tasks/CustomClassLoaderCloseStrategy.java
@@ -31,17 +31,13 @@ public enum CustomClassLoaderCloseStrategy {
 
 		@Override
 		public void handle(ClassLoader customClassLoader) {
-			if (customClassLoader instanceof AutoCloseable) {
-				close((AutoCloseable) customClassLoader);
-			}
-		}
-
-		private void close(AutoCloseable customClassLoader) {
-			try {
-				customClassLoader.close();
-			}
-			catch (Exception e) {
-				throw new JUnitException("Failed to close custom class loader", e);
+			if (customClassLoader instanceof @SuppressWarnings("resource") AutoCloseable closeable) {
+				try {
+					closeable.close();
+				}
+				catch (Exception ex) {
+					throw new JUnitException("Failed to close custom class loader", ex);
+				}
 			}
 		}
 	},
@@ -54,6 +50,7 @@ private void close(AutoCloseable customClassLoader) {
 	 * afterward.
 	 */
 	KEEP_OPEN {
+
 		@Override
 		public void handle(ClassLoader customClassLoader) {
 			// do nothing
diff --git a/junit-platform-console/src/main/java/org/junit/platform/console/tasks/DiscoveryRequestCreator.java b/junit-platform-console/src/main/java/org/junit/platform/console/tasks/DiscoveryRequestCreator.java
index 75934df963ac..fd687ba632be 100644
--- a/junit-platform-console/src/main/java/org/junit/platform/console/tasks/DiscoveryRequestCreator.java
+++ b/junit-platform-console/src/main/java/org/junit/platform/console/tasks/DiscoveryRequestCreator.java
@@ -82,12 +82,14 @@ private static List<ClasspathRootSelector> createClasspathRootSelectors(TestDisc
 	}
 
 	private static Set<Path> determineClasspathRoots(TestDiscoveryOptions options) {
-		if (options.getSelectedClasspathEntries().isEmpty()) {
+		var selectedClasspathEntries = Preconditions.notNull(options.getSelectedClasspathEntries(),
+			() -> "No classpath entries selected");
+		if (selectedClasspathEntries.isEmpty()) {
 			Set<Path> rootDirs = new LinkedHashSet<>(ReflectionUtils.getAllClasspathRootDirectories());
 			rootDirs.addAll(options.getExistingAdditionalClasspathEntries());
 			return rootDirs;
 		}
-		return new LinkedHashSet<>(options.getSelectedClasspathEntries());
+		return new LinkedHashSet<>(selectedClasspathEntries);
 	}
 
 	private static void addFilters(LauncherDiscoveryRequestBuilder requestBuilder, TestDiscoveryOptions options,
@@ -137,15 +139,15 @@ private static ClassNameFilter includedClassNamePatterns(TestDiscoveryOptions op
 		Stream<String> patternStreams = Stream.concat( //
 			options.getIncludedClassNamePatterns().stream(), //
 			selectors.stream() //
-					.map(selector -> selector instanceof IterationSelector
-							? ((IterationSelector) selector).getParentSelector()
+					.map(selector -> selector instanceof IterationSelector iterationSelector
+							? iterationSelector.getParentSelector()
 							: selector) //
 					.map(selector -> {
-						if (selector instanceof ClassSelector) {
-							return ((ClassSelector) selector).getClassName();
+						if (selector instanceof ClassSelector classSelector) {
+							return classSelector.getClassName();
 						}
-						if (selector instanceof MethodSelector) {
-							return ((MethodSelector) selector).getClassName();
+						if (selector instanceof MethodSelector methodSelector) {
+							return methodSelector.getClassName();
 						}
 						return null;
 					}) //
diff --git a/junit-platform-console/src/main/java/org/junit/platform/console/tasks/FlatPrintingListener.java b/junit-platform-console/src/main/java/org/junit/platform/console/tasks/FlatPrintingListener.java
index f1b0e755b2a2..abdb07208f7a 100644
--- a/junit-platform-console/src/main/java/org/junit/platform/console/tasks/FlatPrintingListener.java
+++ b/junit-platform-console/src/main/java/org/junit/platform/console/tasks/FlatPrintingListener.java
@@ -93,7 +93,7 @@ private void printlnMessage(Style style, String message, String detail) {
 	}
 
 	private void println(Style style, String format, Object... args) {
-		this.out.println(colorPalette.paint(style, String.format(format, args)));
+		this.out.println(colorPalette.paint(style, format.formatted(args)));
 	}
 
 	/**
diff --git a/junit-platform-console/src/main/java/org/junit/platform/console/tasks/StandardStreamsHandler.java b/junit-platform-console/src/main/java/org/junit/platform/console/tasks/StandardStreamsHandler.java
index 50bcb1309054..5f7b8bca1307 100644
--- a/junit-platform-console/src/main/java/org/junit/platform/console/tasks/StandardStreamsHandler.java
+++ b/junit-platform-console/src/main/java/org/junit/platform/console/tasks/StandardStreamsHandler.java
@@ -15,13 +15,14 @@
 import java.nio.file.Files;
 import java.nio.file.Path;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.JUnitException;
 
 class StandardStreamsHandler implements AutoCloseable {
 
-	private PrintStream stdout;
+	private @Nullable PrintStream stdout;
 
-	private PrintStream stderr;
+	private @Nullable PrintStream stderr;
 
 	public StandardStreamsHandler() {
 	}
@@ -39,7 +40,7 @@ public StandardStreamsHandler() {
 	 * @param stderrPath the file path for standard error, or {@code null} to
 	 * indicate no redirection
 	 */
-	public void redirectStandardStreams(Path stdoutPath, Path stderrPath) {
+	public void redirectStandardStreams(@Nullable Path stdoutPath, @Nullable Path stderrPath) {
 		if (isSameFile(stdoutPath, stderrPath)) {
 			try {
 				PrintStream commonStream = new PrintStream(Files.newOutputStream(stdoutPath), true);
@@ -92,7 +93,7 @@ public void close() {
 		}
 	}
 
-	private static boolean isSameFile(Path path1, Path path2) {
+	private static boolean isSameFile(@Nullable Path path1, @Nullable Path path2) {
 		if (path1 == null || path2 == null) {
 			return false;
 		}
diff --git a/junit-platform-console/src/main/java/org/junit/platform/console/tasks/Style.java b/junit-platform-console/src/main/java/org/junit/platform/console/tasks/Style.java
index 72b2dc83ff22..5a74c39738be 100644
--- a/junit-platform-console/src/main/java/org/junit/platform/console/tasks/Style.java
+++ b/junit-platform-console/src/main/java/org/junit/platform/console/tasks/Style.java
@@ -21,16 +21,11 @@ enum Style {
 	NONE, SUCCESSFUL, ABORTED, FAILED, SKIPPED, CONTAINER, TEST, DYNAMIC, REPORTED;
 
 	static Style valueOf(TestExecutionResult result) {
-		switch (result.getStatus()) {
-			case SUCCESSFUL:
-				return Style.SUCCESSFUL;
-			case ABORTED:
-				return Style.ABORTED;
-			case FAILED:
-				return Style.FAILED;
-			default:
-				return Style.NONE;
-		}
+		return switch (result.getStatus()) {
+			case SUCCESSFUL -> Style.SUCCESSFUL;
+			case ABORTED -> Style.ABORTED;
+			case FAILED -> Style.FAILED;
+		};
 	}
 
 	static Style valueOf(TestIdentifier testIdentifier) {
diff --git a/junit-platform-console/src/main/java/org/junit/platform/console/tasks/TestFeedPrintingListener.java b/junit-platform-console/src/main/java/org/junit/platform/console/tasks/TestFeedPrintingListener.java
index f0be524edaab..cfe4ecb37a60 100644
--- a/junit-platform-console/src/main/java/org/junit/platform/console/tasks/TestFeedPrintingListener.java
+++ b/junit-platform-console/src/main/java/org/junit/platform/console/tasks/TestFeedPrintingListener.java
@@ -10,12 +10,14 @@
 
 package org.junit.platform.console.tasks;
 
+import static java.util.Objects.requireNonNull;
 import static org.junit.platform.engine.TestExecutionResult.Status.SUCCESSFUL;
 
 import java.io.PrintWriter;
 import java.util.ArrayList;
 import java.util.List;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.util.ExceptionUtils;
 import org.junit.platform.engine.TestExecutionResult;
 import org.junit.platform.engine.UniqueId;
@@ -29,7 +31,8 @@ class TestFeedPrintingListener implements DetailsPrintingListener {
 
 	private final PrintWriter out;
 	private final ColorPalette colorPalette;
-	private TestPlan testPlan;
+
+	private @Nullable TestPlan testPlan;
 
 	TestFeedPrintingListener(PrintWriter out, ColorPalette colorPalette) {
 		this.out = out;
@@ -50,7 +53,7 @@ public void testPlanExecutionFinished(TestPlan testPlan) {
 	public void executionSkipped(TestIdentifier testIdentifier, String reason) {
 		if (shouldPrint(testIdentifier)) {
 			String msg = formatTestIdentifier(testIdentifier);
-			String indentedReason = indented(String.format("Reason: %s", reason));
+			String indentedReason = indented("Reason: %s".formatted(reason));
 			println(Style.SKIPPED,
 				String.format("%s" + STATUS_SEPARATOR + "SKIPPED%n" + INDENTATION + "%s", msg, indentedReason));
 		}
@@ -94,7 +97,7 @@ private List<String> collectDisplayNames(UniqueId uniqueId) {
 		int size = uniqueId.getSegments().size();
 		List<String> displayNames = new ArrayList<>(size);
 		for (int i = 0; i < size; i++) {
-			displayNames.add(0, testPlan.getTestIdentifier(uniqueId).getDisplayName());
+			displayNames.add(0, requireNonNull(testPlan).getTestIdentifier(uniqueId).getDisplayName());
 			if (i < size - 1) {
 				uniqueId = uniqueId.removeLastSegment();
 			}
diff --git a/junit-platform-console/src/main/java/org/junit/platform/console/tasks/TreeNode.java b/junit-platform-console/src/main/java/org/junit/platform/console/tasks/TreeNode.java
index e60a07146fa2..03de24ef6bd4 100644
--- a/junit-platform-console/src/main/java/org/junit/platform/console/tasks/TreeNode.java
+++ b/junit-platform-console/src/main/java/org/junit/platform/console/tasks/TreeNode.java
@@ -10,10 +10,13 @@
 
 package org.junit.platform.console.tasks;
 
+import static java.util.Objects.requireNonNull;
+
 import java.util.Optional;
 import java.util.Queue;
 import java.util.concurrent.ConcurrentLinkedQueue;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.util.StringUtils;
 import org.junit.platform.engine.TestExecutionResult;
 import org.junit.platform.engine.reporting.FileEntry;
@@ -28,9 +31,13 @@ class TreeNode {
 	private final String caption;
 	private final long creation;
 	long duration;
-	private String reason;
-	private TestIdentifier identifier;
-	private TestExecutionResult result;
+
+	private @Nullable String reason;
+
+	private @Nullable TestIdentifier identifier;
+
+	private @Nullable TestExecutionResult result;
+
 	final Queue<ReportEntry> reports = new ConcurrentLinkedQueue<>();
 	final Queue<FileEntry> files = new ConcurrentLinkedQueue<>();
 	final Queue<TreeNode> children = new ConcurrentLinkedQueue<>();
@@ -94,6 +101,6 @@ static String createCaption(String displayName) {
 		boolean normal = displayName.length() <= 80;
 		String caption = normal ? displayName : displayName.substring(0, 80) + "...";
 		String whites = StringUtils.replaceWhitespaceCharacters(caption, " ");
-		return StringUtils.replaceIsoControlCharacters(whites, ".");
+		return requireNonNull(StringUtils.replaceIsoControlCharacters(whites, "."));
 	}
 }
diff --git a/junit-platform-console/src/main/java/org/junit/platform/console/tasks/TreePrinter.java b/junit-platform-console/src/main/java/org/junit/platform/console/tasks/TreePrinter.java
index c1997f52d342..f6df0f45c825 100644
--- a/junit-platform-console/src/main/java/org/junit/platform/console/tasks/TreePrinter.java
+++ b/junit-platform-console/src/main/java/org/junit/platform/console/tasks/TreePrinter.java
@@ -10,6 +10,7 @@
 
 package org.junit.platform.console.tasks;
 
+import static java.util.Objects.requireNonNull;
 import static org.junit.platform.commons.util.CollectionUtils.getOnlyElement;
 
 import java.io.PrintWriter;
@@ -80,7 +81,7 @@ private void printVisible(TreeNode node, String indent, boolean continuous) {
 			out.print(" ");
 			out.print(duration);
 		}
-		boolean nodeIsBeingListed = node.duration == 0 && !node.result().isPresent() && !node.reason().isPresent();
+		boolean nodeIsBeingListed = node.duration == 0 && node.result().isEmpty() && node.reason().isEmpty();
 		if (!nodeIsBeingListed) {
 			out.print(" ");
 			out.print(icon);
@@ -96,7 +97,7 @@ private String tab(TreeNode node, boolean continuous) {
 		// We might be the "last" node in this level, that means
 		// `continuous == false`, but still need to include a vertical
 		// bar for printing stack traces, messages and reports.
-		// See https://github.com/junit-team/junit5/issues/1531
+		// See https://github.com/junit-team/junit-framework/issues/1531
 		if (node.children.size() > 0) {
 			return theme.blank() + theme.vertical();
 		}
@@ -120,7 +121,7 @@ private String colorCaption(TreeNode node) {
 	}
 
 	private void printThrowable(String indent, TestExecutionResult result) {
-		if (!result.getThrowable().isPresent()) {
+		if (result.getThrowable().isEmpty()) {
 			return;
 		}
 		Throwable throwable = result.getThrowable().get();
@@ -128,7 +129,7 @@ private void printThrowable(String indent, TestExecutionResult result) {
 		if (StringUtils.isBlank(message)) {
 			message = throwable.toString();
 		}
-		printMessage(Style.FAILED, indent, message);
+		printMessage(Style.FAILED, indent, requireNonNull(message));
 	}
 
 	private void printReportEntry(String indent, ReportEntry reportEntry) {
diff --git a/junit-platform-console/src/main/java/org/junit/platform/console/tasks/TreePrintingListener.java b/junit-platform-console/src/main/java/org/junit/platform/console/tasks/TreePrintingListener.java
index 49ec53d48ec8..36351d035a0a 100644
--- a/junit-platform-console/src/main/java/org/junit/platform/console/tasks/TreePrintingListener.java
+++ b/junit-platform-console/src/main/java/org/junit/platform/console/tasks/TreePrintingListener.java
@@ -10,10 +10,14 @@
 
 package org.junit.platform.console.tasks;
 
+import static java.util.Objects.requireNonNull;
+import static java.util.Objects.requireNonNullElse;
+
 import java.io.PrintWriter;
 import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.console.options.Theme;
 import org.junit.platform.engine.TestExecutionResult;
 import org.junit.platform.engine.UniqueId;
@@ -28,20 +32,22 @@
 class TreePrintingListener implements DetailsPrintingListener {
 
 	private final Map<UniqueId, TreeNode> nodesByUniqueId = new ConcurrentHashMap<>();
-	private TreeNode root;
 	private final TreePrinter treePrinter;
 
+	private @Nullable TreeNode root;
+
 	TreePrintingListener(PrintWriter out, ColorPalette colorPalette, Theme theme) {
 		this.treePrinter = new TreePrinter(out, theme, colorPalette);
 	}
 
 	private void addNode(TestIdentifier testIdentifier, TreeNode node) {
 		nodesByUniqueId.put(testIdentifier.getUniqueIdObject(), node);
-		testIdentifier.getParentIdObject().map(nodesByUniqueId::get).orElse(root).addChild(node);
+		TreeNode parent = testIdentifier.getParentIdObject().map(nodesByUniqueId::get).orElse(null);
+		requireNonNullElse(parent, root).addChild(node);
 	}
 
 	private TreeNode getNode(TestIdentifier testIdentifier) {
-		return nodesByUniqueId.get(testIdentifier.getUniqueIdObject());
+		return requireNonNull(nodesByUniqueId.get(testIdentifier.getUniqueIdObject()));
 	}
 
 	@Override
@@ -51,7 +57,7 @@ public void testPlanExecutionStarted(TestPlan testPlan) {
 
 	@Override
 	public void testPlanExecutionFinished(TestPlan testPlan) {
-		treePrinter.print(root);
+		treePrinter.print(requireNonNull(root));
 	}
 
 	@Override
diff --git a/junit-platform-console/src/main/java/org/junit/platform/console/tasks/package-info.java b/junit-platform-console/src/main/java/org/junit/platform/console/tasks/package-info.java
index bcfe3d83e71c..39f268bb129d 100644
--- a/junit-platform-console/src/main/java/org/junit/platform/console/tasks/package-info.java
+++ b/junit-platform-console/src/main/java/org/junit/platform/console/tasks/package-info.java
@@ -2,4 +2,7 @@
  * Internal execution tasks for JUnit's console launcher.
  */
 
+@NullMarked
 package org.junit.platform.console.tasks;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-platform-console/src/main/java17/org/junit/platform/console/options/ConsoleUtils.java b/junit-platform-console/src/main/java17/org/junit/platform/console/options/ConsoleUtils.java
deleted file mode 100644
index 145ebed63fd4..000000000000
--- a/junit-platform-console/src/main/java17/org/junit/platform/console/options/ConsoleUtils.java
+++ /dev/null
@@ -1,42 +0,0 @@
-/*
- * Copyright 2015-2025 the original author or authors.
- *
- * All rights reserved. This program and the accompanying materials are
- * made available under the terms of the Eclipse Public License v2.0 which
- * accompanies this distribution and is available at
- *
- * https://www.eclipse.org/legal/epl-v20.html
- */
-
-package org.junit.platform.console.options;
-
-import static org.apiguardian.api.API.Status.INTERNAL;
-
-import java.io.Console;
-import java.nio.charset.Charset;
-
-import org.apiguardian.api.API;
-
-/**
- * Collection of utilities for working with {@code java.io.Console}
- * and friends.
- *
- * <h2>DISCLAIMER</h2>
- *
- * <p>These utilities are intended solely for usage within the JUnit framework
- * itself. <strong>Any usage by external parties is not supported.</strong>
- * Use at your own risk!
- *
- * @since 1.9
- */
-@API(status = INTERNAL, since = "1.9")
-public class ConsoleUtils {
-
-	/**
-	 * {@return the charset of the console}
-	 */
-	public static Charset charset() {
-		Console console = System.console();
-		return console != null ? console.charset() : Charset.defaultCharset();
-	}
-}
diff --git a/junit-platform-engine/junit-platform-engine.gradle.kts b/junit-platform-engine/junit-platform-engine.gradle.kts
index 416b227b00c1..09282c6e49f3 100644
--- a/junit-platform-engine/junit-platform-engine.gradle.kts
+++ b/junit-platform-engine/junit-platform-engine.gradle.kts
@@ -1,5 +1,6 @@
 plugins {
 	id("junitbuild.java-library-conventions")
+	id("junitbuild.java-nullability-conventions")
 	`java-test-fixtures`
 }
 
@@ -11,6 +12,7 @@ dependencies {
 	api(projects.junitPlatformCommons)
 
 	compileOnlyApi(libs.apiguardian)
+	compileOnlyApi(libs.jspecify)
 
 	testImplementation(libs.assertj)
 
diff --git a/junit-platform-engine/src/module/org.junit.platform.engine/module-info.java b/junit-platform-engine/src/main/java/module-info.java
similarity index 97%
rename from junit-platform-engine/src/module/org.junit.platform.engine/module-info.java
rename to junit-platform-engine/src/main/java/module-info.java
index d595f8bdcd1b..d23c9872dad9 100644
--- a/junit-platform-engine/src/module/org.junit.platform.engine/module-info.java
+++ b/junit-platform-engine/src/main/java/module-info.java
@@ -17,7 +17,10 @@
  * @since 1.0
  */
 module org.junit.platform.engine {
+
 	requires static transitive org.apiguardian.api;
+	requires static org.jspecify;
+
 	requires transitive org.junit.platform.commons;
 	requires transitive org.opentest4j;
 
@@ -28,7 +31,6 @@
 	exports org.junit.platform.engine.support.config;
 	exports org.junit.platform.engine.support.descriptor;
 	exports org.junit.platform.engine.support.discovery;
-	exports org.junit.platform.engine.support.filter;
 	exports org.junit.platform.engine.support.hierarchical;
 	exports org.junit.platform.engine.support.store;
 
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/CompositeFilter.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/CompositeFilter.java
index 6a29af05e7bf..de40e2256c9b 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/CompositeFilter.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/CompositeFilter.java
@@ -10,7 +10,6 @@
 
 package org.junit.platform.engine;
 
-import static java.lang.String.format;
 import static java.util.stream.Collectors.joining;
 import static org.junit.platform.engine.FilterResult.included;
 
@@ -82,7 +81,7 @@ public String toString() {
 		// @formatter:off
 		return filters.stream()
 				.map(Object::toString)
-				.map(value -> format("(%s)", value))
+				.map("(%s)"::formatted)
 				.collect(joining(" and "));
 		// @formatter:on
 	}
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/ConfigurationParameters.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/ConfigurationParameters.java
index c28f9229d9ce..48f2b3d1b0bb 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/ConfigurationParameters.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/ConfigurationParameters.java
@@ -10,7 +10,6 @@
 
 package org.junit.platform.engine;
 
-import static org.apiguardian.api.API.Status.DEPRECATED;
 import static org.apiguardian.api.API.Status.STABLE;
 
 import java.util.Optional;
@@ -18,6 +17,7 @@
 import java.util.function.Function;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.JUnitException;
 import org.junit.platform.commons.util.Preconditions;
 
@@ -117,29 +117,20 @@ public interface ConfigurationParameters {
 	 * @see #CONFIG_FILE_NAME
 	 */
 	@API(status = STABLE, since = "1.3")
-	default <T> Optional<T> get(String key, Function<String, T> transformer) {
+	default <T> Optional<T> get(String key, Function<? super String, ? extends @Nullable T> transformer) {
 		Preconditions.notNull(transformer, "transformer must not be null");
 		return get(key).map(input -> {
 			try {
 				return transformer.apply(input);
 			}
 			catch (Exception ex) {
-				String message = String.format(
-					"Failed to transform configuration parameter with key '%s' and initial value '%s'", key, input);
+				String message = "Failed to transform configuration parameter with key '%s' and initial value '%s'".formatted(
+					key, input);
 				throw new JUnitException(message, ex);
 			}
 		});
 	}
 
-	/**
-	 * Get the number of configuration parameters stored directly in this
-	 * {@code ConfigurationParameters}.
-	 * @deprecated as of JUnit Platform 1.9 in favor of {@link #keySet()}
-	 */
-	@Deprecated
-	@API(status = DEPRECATED, since = "1.9")
-	int size();
-
 	/**
 	 * Get the keys of all configuration parameters stored in this
 	 * {@code ConfigurationParameters}.
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/DefaultDiscoveryIssue.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/DefaultDiscoveryIssue.java
index 055aa4029191..1f82ef3487b2 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/DefaultDiscoveryIssue.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/DefaultDiscoveryIssue.java
@@ -13,6 +13,7 @@
 import java.util.Objects;
 import java.util.Optional;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.util.ToStringBuilder;
 
 /**
@@ -22,8 +23,10 @@ final class DefaultDiscoveryIssue implements DiscoveryIssue {
 
 	private final Severity severity;
 	private final String message;
-	private final TestSource source;
-	private final Throwable cause;
+
+	private final @Nullable TestSource source;
+
+	private final @Nullable Throwable cause;
 
 	DefaultDiscoveryIssue(Builder builder) {
 		this.severity = builder.severity;
@@ -54,8 +57,9 @@ public Optional<Throwable> cause() {
 
 	@Override
 	public boolean equals(Object o) {
-		if (o == null || getClass() != o.getClass())
+		if (o == null || getClass() != o.getClass()) {
 			return false;
+		}
 		DefaultDiscoveryIssue that = (DefaultDiscoveryIssue) o;
 		return this.severity == that.severity //
 				&& Objects.equals(this.message, that.message) //
@@ -86,7 +90,11 @@ static class Builder implements DiscoveryIssue.Builder {
 
 		private final Severity severity;
 		private final String message;
+
+		@Nullable
 		private TestSource source;
+
+		@Nullable
 		public Throwable cause;
 
 		Builder(Severity severity, String message) {
@@ -95,13 +103,13 @@ static class Builder implements DiscoveryIssue.Builder {
 		}
 
 		@Override
-		public Builder source(TestSource source) {
+		public Builder source(@Nullable TestSource source) {
 			this.source = source;
 			return this;
 		}
 
 		@Override
-		public Builder cause(Throwable cause) {
+		public Builder cause(@Nullable Throwable cause) {
 			this.cause = cause;
 			return this;
 		}
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/DiscoveryIssue.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/DiscoveryIssue.java
index 287523181921..caf8dd40efa3 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/DiscoveryIssue.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/DiscoveryIssue.java
@@ -16,6 +16,7 @@
 import java.util.function.UnaryOperator;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.util.Preconditions;
 
 /**
@@ -24,7 +25,7 @@
  *
  * @since 1.13
  */
-@API(status = EXPERIMENTAL, since = "1.13")
+@API(status = EXPERIMENTAL, since = "6.0")
 public interface DiscoveryIssue {
 
 	/**
@@ -138,7 +139,7 @@ default Builder source(Optional<TestSource> source) {
 		 * @param source the {@link TestSource} for the {@code DiscoveryIssue};
 		 * may be {@code null}
 		 */
-		Builder source(TestSource source);
+		Builder source(@Nullable TestSource source);
 
 		/**
 		 * Set the {@link Throwable} that caused the {@code DiscoveryIssue}.
@@ -157,7 +158,7 @@ default Builder cause(Optional<Throwable> cause) {
 		 * @param cause the {@link Throwable} that caused the
 		 * {@code DiscoveryIssue}; may be {@code null}
 		 */
-		Builder cause(Throwable cause);
+		Builder cause(@Nullable Throwable cause);
 
 		/**
 		 * Build the {@code DiscoveryIssue}.
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/DiscoverySelector.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/DiscoverySelector.java
index 5284d19ee03e..35b0a5919df6 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/DiscoverySelector.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/DiscoverySelector.java
@@ -10,7 +10,7 @@
 
 package org.junit.platform.engine;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
 
 import java.util.Optional;
@@ -45,7 +45,7 @@ public interface DiscoverySelector {
 	 * identifiers
 	 * @since 1.11
 	 */
-	@API(status = EXPERIMENTAL, since = "1.11")
+	@API(status = MAINTAINED, since = "1.13.3")
 	default Optional<DiscoverySelectorIdentifier> toIdentifier() {
 		return Optional.empty();
 	}
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/DiscoverySelectorIdentifier.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/DiscoverySelectorIdentifier.java
index 0a24baa5f0fe..d885f08a851c 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/DiscoverySelectorIdentifier.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/DiscoverySelectorIdentifier.java
@@ -10,7 +10,7 @@
 
 package org.junit.platform.engine;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import java.util.Objects;
 
@@ -29,7 +29,7 @@
  * @see org.junit.platform.engine.discovery.DiscoverySelectors#parse(String)
  * @see org.junit.platform.engine.discovery.DiscoverySelectorIdentifierParser
  */
-@API(status = EXPERIMENTAL, since = "1.11")
+@API(status = MAINTAINED, since = "1.13.3")
 public final class DiscoverySelectorIdentifier {
 
 	private final String prefix;
@@ -108,7 +108,7 @@ public int hashCode() {
 	 */
 	@Override
 	public String toString() {
-		return String.format("%s:%s", this.prefix, this.value);
+		return "%s:%s".formatted(this.prefix, this.value);
 	}
 
 }
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/EngineDiscoveryListener.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/EngineDiscoveryListener.java
index 5fad4a0b5dd3..f03bec90e09d 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/EngineDiscoveryListener.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/EngineDiscoveryListener.java
@@ -63,7 +63,7 @@ default void selectorProcessed(UniqueId engineId, DiscoverySelector selector, Se
 	 * @since 1.13
 	 * @see DiscoveryIssue
 	 */
-	@API(status = EXPERIMENTAL, since = "1.13")
+	@API(status = EXPERIMENTAL, since = "6.0")
 	default void issueEncountered(UniqueId engineId, DiscoveryIssue issue) {
 	}
 
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/EngineDiscoveryRequest.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/EngineDiscoveryRequest.java
index 3bdacace4401..f18442f27d91 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/EngineDiscoveryRequest.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/EngineDiscoveryRequest.java
@@ -10,7 +10,7 @@
 
 package org.junit.platform.engine;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
 
 import java.util.List;
@@ -46,7 +46,8 @@ public interface EngineDiscoveryRequest {
 	 * Get the {@link DiscoverySelector DiscoverySelectors} for this request,
 	 * filtered by a particular type.
 	 *
-	 * @param selectorType the type of {@link DiscoverySelector} to filter by
+	 * @param selectorType the type of {@link DiscoverySelector} to filter by;
+	 * never {@code null}
 	 * @return all selectors of this request that are instances of
 	 * {@code selectorType}; never {@code null} but potentially empty
 	 */
@@ -59,7 +60,8 @@ public interface EngineDiscoveryRequest {
 	 * <p>The returned filters are to be combined using AND semantics, i.e. all
 	 * of them have to include a resource for it to end up in the test plan.
 	 *
-	 * @param filterType the type of {@link DiscoveryFilter} to filter by
+	 * @param filterType the type of {@link DiscoveryFilter} to filter by;
+	 * never {@code null}
 	 * @return all filters of this request that are instances of
 	 * {@code filterType}; never {@code null} but potentially empty
 	 */
@@ -89,7 +91,7 @@ default EngineDiscoveryListener getDiscoveryListener() {
 	 * @return the output directory provider; never {@code null}
 	 * @since 1.12
 	 */
-	@API(status = EXPERIMENTAL, since = "1.12")
+	@API(status = MAINTAINED, since = "1.13.3")
 	default OutputDirectoryProvider getOutputDirectoryProvider() {
 		throw new JUnitException(
 			"OutputDirectoryProvider not available; probably due to unaligned versions of the junit-platform-engine and junit-platform-launcher jars on the classpath/module path.");
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/EngineExecutionListener.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/EngineExecutionListener.java
index 8affe7aad78c..8c764d120b19 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/EngineExecutionListener.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/EngineExecutionListener.java
@@ -10,7 +10,7 @@
 
 package org.junit.platform.engine;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
 
 import org.apiguardian.api.API;
@@ -156,7 +156,7 @@ default void reportingEntryPublished(TestDescriptor testDescriptor, ReportEntry
 	* the file entry belongs
 	 * @param file a {@code FileEntry} instance to be attached
 	 */
-	@API(status = EXPERIMENTAL, since = "1.12")
+	@API(status = MAINTAINED, since = "1.13.3")
 	default void fileEntryPublished(TestDescriptor testDescriptor, FileEntry file) {
 	}
 }
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/ExecutionRequest.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/ExecutionRequest.java
index 1267551da486..620f6057b94b 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/ExecutionRequest.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/ExecutionRequest.java
@@ -13,9 +13,11 @@
 import static org.apiguardian.api.API.Status.DEPRECATED;
 import static org.apiguardian.api.API.Status.EXPERIMENTAL;
 import static org.apiguardian.api.API.Status.INTERNAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.PreconditionViolationException;
 import org.junit.platform.commons.util.Preconditions;
 import org.junit.platform.engine.reporting.OutputDirectoryProvider;
@@ -41,8 +43,10 @@ public class ExecutionRequest {
 	private final TestDescriptor rootTestDescriptor;
 	private final EngineExecutionListener engineExecutionListener;
 	private final ConfigurationParameters configurationParameters;
-	private final OutputDirectoryProvider outputDirectoryProvider;
-	private final NamespacedHierarchicalStore<Namespace> requestLevelStore;
+
+	private final @Nullable OutputDirectoryProvider outputDirectoryProvider;
+
+	private final @Nullable NamespacedHierarchicalStore<Namespace> requestLevelStore;
 
 	@Deprecated
 	@API(status = DEPRECATED, since = "1.11")
@@ -52,8 +56,8 @@ public ExecutionRequest(TestDescriptor rootTestDescriptor, EngineExecutionListen
 	}
 
 	private ExecutionRequest(TestDescriptor rootTestDescriptor, EngineExecutionListener engineExecutionListener,
-			ConfigurationParameters configurationParameters, OutputDirectoryProvider outputDirectoryProvider,
-			NamespacedHierarchicalStore<Namespace> requestLevelStore) {
+			ConfigurationParameters configurationParameters, @Nullable OutputDirectoryProvider outputDirectoryProvider,
+			@Nullable NamespacedHierarchicalStore<Namespace> requestLevelStore) {
 		this.rootTestDescriptor = Preconditions.notNull(rootTestDescriptor, "rootTestDescriptor must not be null");
 		this.engineExecutionListener = Preconditions.notNull(engineExecutionListener,
 			"engineExecutionListener must not be null");
@@ -144,7 +148,7 @@ public ConfigurationParameters getConfigurationParameters() {
 	 * is not available
 	 * @since 1.12
 	 */
-	@API(status = EXPERIMENTAL, since = "1.12")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public OutputDirectoryProvider getOutputDirectoryProvider() {
 		return Preconditions.notNull(this.outputDirectoryProvider,
 			"No OutputDirectoryProvider was configured for this request");
@@ -161,7 +165,7 @@ public OutputDirectoryProvider getOutputDirectoryProvider() {
 	 * @since 1.13
 	 * @see NamespacedHierarchicalStore
 	 */
-	@API(status = EXPERIMENTAL, since = "1.13")
+	@API(status = EXPERIMENTAL, since = "6.0")
 	public NamespacedHierarchicalStore<Namespace> getStore() {
 		return Preconditions.notNull(this.requestLevelStore,
 			"No NamespacedHierarchicalStore was configured for this request");
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/Filter.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/Filter.java
index b500a1320a2b..83511c09bdf8 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/Filter.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/Filter.java
@@ -11,6 +11,7 @@
 package org.junit.platform.engine;
 
 import static java.util.Arrays.asList;
+import static org.apiguardian.api.API.Status.DEPRECATED;
 import static org.apiguardian.api.API.Status.STABLE;
 import static org.junit.platform.commons.util.CollectionUtils.getOnlyElement;
 import static org.junit.platform.engine.CompositeFilter.alwaysIncluded;
@@ -94,6 +95,8 @@ static <T> Filter<T> composeFilters(Collection<? extends Filter<T>> filters) {
 	 * @param adaptee the filter to be adapted
 	 * @param converter the converter function to apply
 	 */
+	@API(status = DEPRECATED, since = "6.0")
+	@Deprecated(since = "6.0", forRemoval = true)
 	static <T, V> Filter<T> adaptFilter(Filter<V> adaptee, Function<T, V> converter) {
 		return input -> adaptee.apply(converter.apply(input));
 	}
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/FilterResult.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/FilterResult.java
index b2bfae49122b..eabfcfe20815 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/FilterResult.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/FilterResult.java
@@ -16,6 +16,7 @@
 import java.util.function.Supplier;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.util.ToStringBuilder;
 
 /**
@@ -32,7 +33,7 @@ public class FilterResult {
 	 * @param reason the reason why the filtered object was included
 	 * @return an included {@code FilterResult} with the given reason
 	 */
-	public static FilterResult included(String reason) {
+	public static FilterResult included(@Nullable String reason) {
 		return new FilterResult(true, reason);
 	}
 
@@ -42,14 +43,14 @@ public static FilterResult included(String reason) {
 	 * @param reason the reason why the filtered object was excluded
 	 * @return an excluded {@code FilterResult} with the given reason
 	 */
-	public static FilterResult excluded(String reason) {
+	public static FilterResult excluded(@Nullable String reason) {
 		return new FilterResult(false, reason);
 	}
 
 	/**
 	 * Factory for creating filter results based on the condition given.
 	 *
-	 * @param included whether or not the filtered object should be included
+	 * @param included whether the filtered object should be included
 	 * @return a valid {@code FilterResult} for the given condition
 	 */
 	public static FilterResult includedIf(boolean included) {
@@ -59,13 +60,13 @@ public static FilterResult includedIf(boolean included) {
 	/**
 	 * Factory for creating filter results based on the condition given.
 	 *
-	 * @param included whether or not the filtered object should be included
+	 * @param included whether the filtered object should be included
 	 * @param inclusionReasonSupplier supplier for the reason in case of inclusion
 	 * @param exclusionReasonSupplier supplier for the reason in case of exclusion
 	 * @return a valid {@code FilterResult} for the given condition
 	 */
-	public static FilterResult includedIf(boolean included, Supplier<String> inclusionReasonSupplier,
-			Supplier<String> exclusionReasonSupplier) {
+	public static FilterResult includedIf(boolean included, Supplier<@Nullable String> inclusionReasonSupplier,
+			Supplier<@Nullable String> exclusionReasonSupplier) {
 		return included ? included(inclusionReasonSupplier.get()) : excluded(exclusionReasonSupplier.get());
 	}
 
@@ -73,7 +74,7 @@ public static FilterResult includedIf(boolean included, Supplier<String> inclusi
 
 	private final Optional<String> reason;
 
-	private FilterResult(boolean included, String reason) {
+	private FilterResult(boolean included, @Nullable String reason) {
 		this.included = included;
 		this.reason = Optional.ofNullable(reason);
 	}
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/SelectorResolutionResult.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/SelectorResolutionResult.java
index 105bf9d09e7d..8ddad4ab5560 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/SelectorResolutionResult.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/SelectorResolutionResult.java
@@ -15,6 +15,7 @@
 import java.util.Optional;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.util.ToStringBuilder;
 
 /**
@@ -86,9 +87,10 @@ public static SelectorResolutionResult failed(Throwable throwable) {
 	}
 
 	private final Status status;
-	private final Throwable throwable;
 
-	private SelectorResolutionResult(Status status, Throwable throwable) {
+	private final @Nullable Throwable throwable;
+
+	private SelectorResolutionResult(Status status, @Nullable Throwable throwable) {
 		this.status = status;
 		this.throwable = throwable;
 	}
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/TestDescriptor.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/TestDescriptor.java
index b23d2d79ed09..2039ecf8ba11 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/TestDescriptor.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/TestDescriptor.java
@@ -11,6 +11,7 @@
 package org.junit.platform.engine;
 
 import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
 
 import java.util.ArrayList;
@@ -22,6 +23,7 @@
 import java.util.function.UnaryOperator;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.util.Preconditions;
 
 /**
@@ -99,7 +101,7 @@ default String getLegacyReportingName() {
 	 *
 	 * @param parent the new parent of this descriptor; may be {@code null}.
 	 */
-	void setParent(TestDescriptor parent);
+	void setParent(@Nullable TestDescriptor parent);
 
 	/**
 	 * Get the immutable set of <em>children</em> of this descriptor.
@@ -120,7 +122,7 @@ default String getLegacyReportingName() {
 	 */
 	@API(status = STABLE, since = "1.10")
 	default Set<? extends TestDescriptor> getAncestors() {
-		if (!getParent().isPresent()) {
+		if (getParent().isEmpty()) {
 			return Collections.emptySet();
 		}
 		TestDescriptor parent = getParent().get();
@@ -188,7 +190,7 @@ default Set<? extends TestDescriptor> getDescendants() {
 	 * @param orderer a unary operator to order the children of this test descriptor
 	 * @since 1.12
 	 */
-	@API(since = "1.12", status = EXPERIMENTAL)
+	@API(status = MAINTAINED, since = "1.13.3")
 	default void orderChildren(UnaryOperator<List<TestDescriptor>> orderer) {
 		Preconditions.notNull(orderer, "orderer must not be null");
 		Set<? extends TestDescriptor> originalChildren = getChildren();
@@ -215,7 +217,7 @@ default void orderChildren(UnaryOperator<List<TestDescriptor>> orderer) {
 	 * <p>A <em>root</em> descriptor is a descriptor without a parent.
 	 */
 	default boolean isRoot() {
-		return !getParent().isPresent();
+		return getParent().isEmpty();
 	}
 
 	/**
@@ -333,7 +335,7 @@ interface Visitor {
 		 * is empty
 		 * @since 1.13
 		 */
-		@API(status = EXPERIMENTAL, since = "1.13")
+		@API(status = EXPERIMENTAL, since = "6.0")
 		static Visitor composite(Visitor... visitors) {
 			return CompositeTestDescriptorVisitor.from(visitors);
 		}
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/TestExecutionResult.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/TestExecutionResult.java
index 4bd69d935d05..f7e2ddcd889b 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/TestExecutionResult.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/TestExecutionResult.java
@@ -18,6 +18,7 @@
 import java.util.Optional;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.util.Preconditions;
 import org.junit.platform.commons.util.ToStringBuilder;
 
@@ -77,7 +78,7 @@ public static TestExecutionResult successful() {
 	 * {@code null}
 	 * @return the {@code TestExecutionResult}; never {@code null}
 	 */
-	public static TestExecutionResult aborted(Throwable throwable) {
+	public static TestExecutionResult aborted(@Nullable Throwable throwable) {
 		return new TestExecutionResult(ABORTED, throwable);
 	}
 
@@ -89,14 +90,15 @@ public static TestExecutionResult aborted(Throwable throwable) {
 	 * {@code null}
 	 * @return the {@code TestExecutionResult}; never {@code null}
 	 */
-	public static TestExecutionResult failed(Throwable throwable) {
+	public static TestExecutionResult failed(@Nullable Throwable throwable) {
 		return new TestExecutionResult(FAILED, throwable);
 	}
 
 	private final Status status;
-	private final Throwable throwable;
 
-	private TestExecutionResult(Status status, Throwable throwable) {
+	private final @Nullable Throwable throwable;
+
+	private TestExecutionResult(Status status, @Nullable Throwable throwable) {
 		this.status = Preconditions.notNull(status, "Status must not be null");
 		this.throwable = throwable;
 	}
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/TestTag.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/TestTag.java
index ba0834df4dfa..0a2e7002a330 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/TestTag.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/TestTag.java
@@ -12,14 +12,13 @@
 
 import static org.apiguardian.api.API.Status.STABLE;
 
+import java.io.Serial;
 import java.io.Serializable;
-import java.util.Arrays;
-import java.util.Collections;
-import java.util.HashSet;
 import java.util.Objects;
 import java.util.Set;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.PreconditionViolationException;
 import org.junit.platform.commons.util.Preconditions;
 import org.junit.platform.commons.util.StringUtils;
@@ -35,6 +34,7 @@
 @API(status = STABLE, since = "1.0")
 public final class TestTag implements Serializable {
 
+	@Serial
 	private static final long serialVersionUID = 1L;
 
 	private final String name;
@@ -51,8 +51,7 @@ public final class TestTag implements Serializable {
 	 * <li>{@code !}: <em>exclamation point</em></li>
 	 * </ul>
 	 */
-	public static final Set<String> RESERVED_CHARACTERS = Collections.unmodifiableSet(
-		new HashSet<>(Arrays.asList(",", "(", ")", "&", "|", "!")));
+	public static final Set<String> RESERVED_CHARACTERS = Set.of(",", "(", ")", "&", "|", "!");
 
 	/**
 	 * Determine if the supplied tag name is valid with regard to the supported
@@ -82,7 +81,7 @@ public final class TestTag implements Serializable {
 	 * @see #RESERVED_CHARACTERS
 	 * @see TestTag#create(String)
 	 */
-	public static boolean isValid(String name) {
+	public static boolean isValid(@Nullable String name) {
 		if (name == null) {
 			return false;
 		}
@@ -118,7 +117,7 @@ public static TestTag create(String name) throws PreconditionViolationException
 
 	private TestTag(String name) {
 		Preconditions.condition(TestTag.isValid(name),
-			() -> String.format("Tag name [%s] must be syntactically valid", name));
+			() -> "Tag name [%s] must be syntactically valid".formatted(name));
 		this.name = name.trim();
 	}
 
@@ -133,11 +132,7 @@ public String getName() {
 
 	@Override
 	public boolean equals(Object obj) {
-		if (obj instanceof TestTag) {
-			TestTag that = (TestTag) obj;
-			return Objects.equals(this.name, that.name);
-		}
-		return false;
+		return (obj instanceof TestTag that && Objects.equals(this.name, that.name));
 	}
 
 	@Override
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/UniqueId.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/UniqueId.java
index acd4fe3d4d2c..c60e716d54ec 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/UniqueId.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/UniqueId.java
@@ -10,10 +10,9 @@
 
 package org.junit.platform.engine;
 
-import static java.util.Collections.singletonList;
-import static java.util.Collections.unmodifiableList;
 import static org.apiguardian.api.API.Status.STABLE;
 
+import java.io.Serial;
 import java.io.Serializable;
 import java.lang.ref.SoftReference;
 import java.util.ArrayList;
@@ -22,6 +21,7 @@
 import java.util.Optional;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.JUnitException;
 import org.junit.platform.commons.util.Preconditions;
 import org.junit.platform.commons.util.ToStringBuilder;
@@ -37,6 +37,7 @@
 @API(status = STABLE, since = "1.0")
 public class UniqueId implements Cloneable, Serializable {
 
+	@Serial
 	private static final long serialVersionUID = 1L;
 
 	private static final String ENGINE_SEGMENT_TYPE = "engine";
@@ -90,10 +91,10 @@ public static UniqueId root(String segmentType, String value) {
 	private transient int hashCode;
 
 	// lazily computed
-	private transient SoftReference<String> toString;
+	private transient @Nullable SoftReference<String> toString;
 
 	private UniqueId(UniqueIdFormat uniqueIdFormat, Segment segment) {
-		this(uniqueIdFormat, singletonList(segment));
+		this(uniqueIdFormat, List.of(segment));
 	}
 
 	/**
@@ -105,7 +106,7 @@ private UniqueId(UniqueIdFormat uniqueIdFormat, Segment segment) {
 	 */
 	UniqueId(UniqueIdFormat uniqueIdFormat, List<Segment> segments) {
 		this.uniqueIdFormat = uniqueIdFormat;
-		this.segments = segments;
+		this.segments = List.copyOf(segments);
 	}
 
 	final Optional<Segment> getRoot() {
@@ -126,7 +127,7 @@ public final Optional<String> getEngineId() {
 	 * {@code UniqueId}.
 	 */
 	public final List<Segment> getSegments() {
-		return unmodifiableList(this.segments);
+		return this.segments;
 	}
 
 	/**
@@ -214,7 +215,7 @@ public boolean hasPrefix(UniqueId potentialPrefix) {
 	@API(status = STABLE, since = "1.5")
 	public UniqueId removeLastSegment() {
 		Preconditions.condition(this.segments.size() > 1, "Cannot remove last remaining segment");
-		return new UniqueId(uniqueIdFormat, new ArrayList<>(this.segments.subList(0, this.segments.size() - 1)));
+		return new UniqueId(uniqueIdFormat, List.copyOf(this.segments.subList(0, this.segments.size() - 1)));
 	}
 
 	/**
@@ -296,6 +297,7 @@ public String toString() {
 	@API(status = STABLE, since = "1.0")
 	public static class Segment implements Serializable {
 
+		@Serial
 		private static final long serialVersionUID = 1L;
 
 		private final String type;
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/UniqueIdFormat.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/UniqueIdFormat.java
index 2aaebf38eb18..87275e54ba4d 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/UniqueIdFormat.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/UniqueIdFormat.java
@@ -11,10 +11,9 @@
 package org.junit.platform.engine;
 
 import static java.util.stream.Collectors.joining;
-import static java.util.stream.Collectors.toList;
 
+import java.io.Serial;
 import java.io.Serializable;
-import java.io.UnsupportedEncodingException;
 import java.net.URLDecoder;
 import java.net.URLEncoder;
 import java.nio.charset.StandardCharsets;
@@ -36,6 +35,7 @@
  */
 class UniqueIdFormat implements Serializable {
 
+	@Serial
 	private static final long serialVersionUID = 1L;
 
 	private static final UniqueIdFormat defaultFormat = new UniqueIdFormat('[', ':', ']', '/');
@@ -49,12 +49,7 @@ private static String quote(char c) {
 	}
 
 	private static String encode(char c) {
-		try {
-			return URLEncoder.encode(String.valueOf(c), StandardCharsets.UTF_8.name());
-		}
-		catch (UnsupportedEncodingException e) {
-			throw new AssertionError("UTF-8 should be supported", e);
-		}
+		return URLEncoder.encode(String.valueOf(c), StandardCharsets.UTF_8);
 	}
 
 	private final char openSegment;
@@ -70,7 +65,7 @@ private static String encode(char c) {
 		this.closeSegment = closeSegment;
 		this.segmentDelimiter = segmentDelimiter;
 		this.segmentPattern = Pattern.compile(
-			String.format("%s(.+)%s(.+)%s", quote(openSegment), quote(typeValueSeparator), quote(closeSegment)),
+			"%s(.+)%s(.+)%s".formatted(quote(openSegment), quote(typeValueSeparator), quote(closeSegment)),
 			Pattern.DOTALL);
 
 		// Compute "forbidden" character encoding map.
@@ -92,14 +87,14 @@ private static String encode(char c) {
 	 */
 	UniqueId parse(String source) throws JUnitException {
 		String[] parts = source.split(String.valueOf(this.segmentDelimiter));
-		List<Segment> segments = Arrays.stream(parts).map(this::createSegment).collect(toList());
+		List<Segment> segments = Arrays.stream(parts).map(this::createSegment).toList();
 		return new UniqueId(this, segments);
 	}
 
 	private Segment createSegment(String segmentString) throws JUnitException {
 		Matcher segmentMatcher = this.segmentPattern.matcher(segmentString);
 		if (!segmentMatcher.matches()) {
-			throw new JUnitException(String.format("'%s' is not a well-formed UniqueId segment", segmentString));
+			throw new JUnitException("'%s' is not a well-formed UniqueId segment".formatted(segmentString));
 		}
 		String type = decode(checkAllowed(segmentMatcher.group(1)));
 		String value = decode(checkAllowed(segmentMatcher.group(2)));
@@ -116,7 +111,7 @@ private String checkAllowed(String typeOrValue) {
 
 	private void checkDoesNotContain(String typeOrValue, char forbiddenCharacter) {
 		Preconditions.condition(typeOrValue.indexOf(forbiddenCharacter) < 0,
-			() -> String.format("type or value '%s' must not contain '%s'", typeOrValue, forbiddenCharacter));
+			() -> "type or value '%s' must not contain '%s'".formatted(typeOrValue, forbiddenCharacter));
 	}
 
 	/**
@@ -150,12 +145,7 @@ private String encode(String s) {
 	}
 
 	private static String decode(String s) {
-		try {
-			return URLDecoder.decode(s, StandardCharsets.UTF_8.name());
-		}
-		catch (UnsupportedEncodingException e) {
-			throw new JUnitException("UTF-8 should be supported", e);
-		}
+		return URLDecoder.decode(s, StandardCharsets.UTF_8);
 	}
 
 }
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/AbstractClassNameFilter.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/AbstractClassNameFilter.java
index ae047beed04c..94ac57e783e4 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/AbstractClassNameFilter.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/AbstractClassNameFilter.java
@@ -11,7 +11,6 @@
 package org.junit.platform.engine.discovery;
 
 import static java.util.stream.Collectors.joining;
-import static java.util.stream.Collectors.toList;
 
 import java.util.Arrays;
 import java.util.List;
@@ -36,7 +35,7 @@ abstract class AbstractClassNameFilter implements ClassNameFilter {
 	AbstractClassNameFilter(String... patterns) {
 		Preconditions.notEmpty(patterns, "patterns array must not be null or empty");
 		Preconditions.containsNoNullElements(patterns, "patterns array must not contain null elements");
-		this.patterns = Arrays.stream(patterns).map(Pattern::compile).collect(toList());
+		this.patterns = Arrays.stream(patterns).map(Pattern::compile).toList();
 		this.patternDescription = Arrays.stream(patterns).collect(joining("' OR '", "'", "'"));
 	}
 
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/ClassSelector.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/ClassSelector.java
index 38c412c1e5c1..82a0b305ee65 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/ClassSelector.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/ClassSelector.java
@@ -10,14 +10,15 @@
 
 package org.junit.platform.engine.discovery;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
 import static org.apiguardian.api.API.Status.INTERNAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
 
 import java.util.Objects;
 import java.util.Optional;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.PreconditionViolationException;
 import org.junit.platform.commons.function.Try;
 import org.junit.platform.commons.support.ReflectionSupport;
@@ -47,12 +48,13 @@
 @API(status = STABLE, since = "1.0")
 public class ClassSelector implements DiscoverySelector {
 
-	private final ClassLoader classLoader;
+	private final @Nullable ClassLoader classLoader;
+
 	private final String className;
 
-	private Class<?> javaClass;
+	private @Nullable Class<?> javaClass;
 
-	ClassSelector(ClassLoader classLoader, String className) {
+	ClassSelector(@Nullable ClassLoader classLoader, String className) {
 		this.className = className;
 		this.classLoader = classLoader;
 	}
@@ -69,8 +71,8 @@ public class ClassSelector implements DiscoverySelector {
 	 * @return the {@code ClassLoader}; potentially {@code null}
 	 * @since 1.10
 	 */
-	@API(status = EXPERIMENTAL, since = "1.10")
-	public ClassLoader getClassLoader() {
+	@API(status = MAINTAINED, since = "1.13.3")
+	public @Nullable ClassLoader getClassLoader() {
 		return this.classLoader;
 	}
 
@@ -94,7 +96,7 @@ public Class<?> getJavaClass() {
 			Try<Class<?>> tryToLoadClass = this.classLoader == null
 				? ReflectionSupport.tryToLoadClass(this.className)
 				: ReflectionSupport.tryToLoadClass(this.className, this.classLoader);
-			this.javaClass = tryToLoadClass.getOrThrow(cause ->
+			this.javaClass = tryToLoadClass.getNonNullOrThrow(cause ->
 				new PreconditionViolationException("Could not load class with name: " + this.className, cause));
 			// @formatter:on
 		}
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/ClasspathResourceSelector.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/ClasspathResourceSelector.java
index d703b5da7d2b..a7f83f3b4715 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/ClasspathResourceSelector.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/ClasspathResourceSelector.java
@@ -11,8 +11,8 @@
 package org.junit.platform.engine.discovery;
 
 import static java.util.Collections.unmodifiableSet;
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
 import static org.apiguardian.api.API.Status.INTERNAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
 
 import java.util.LinkedHashSet;
@@ -21,6 +21,7 @@
 import java.util.Set;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.PreconditionViolationException;
 import org.junit.platform.commons.function.Try;
 import org.junit.platform.commons.support.Resource;
@@ -55,10 +56,12 @@
 public class ClasspathResourceSelector implements DiscoverySelector {
 
 	private final String classpathResourceName;
-	private final FilePosition position;
-	private Set<Resource> classpathResources;
 
-	ClasspathResourceSelector(String classpathResourceName, FilePosition position) {
+	private final @Nullable FilePosition position;
+
+	private @Nullable Set<Resource> classpathResources;
+
+	ClasspathResourceSelector(String classpathResourceName, @Nullable FilePosition position) {
 		boolean startsWithSlash = classpathResourceName.startsWith("/");
 		this.classpathResourceName = (startsWithSlash ? classpathResourceName.substring(1) : classpathResourceName);
 		this.position = position;
@@ -93,7 +96,7 @@ public String getClasspathResourceName() {
 	 *
 	 * @since 1.12
 	 */
-	@API(status = EXPERIMENTAL, since = "1.12")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public Set<Resource> getClasspathResources() {
 		if (this.classpathResources == null) {
 			Try<Set<Resource>> tryToGetResource = ReflectionUtils.tryToGetResources(this.classpathResourceName);
@@ -159,7 +162,7 @@ public Optional<DiscoverySelectorIdentifier> toIdentifier() {
 		}
 		else {
 			return Optional.of(DiscoverySelectorIdentifier.create(IdentifierParser.PREFIX,
-				String.format("%s?%s", this.classpathResourceName, this.position.toQueryPart())));
+				"%s?%s".formatted(this.classpathResourceName, this.position.toQueryPart())));
 		}
 	}
 
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/ClasspathRootSelector.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/ClasspathRootSelector.java
index 133572b909ff..27708e10f8f2 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/ClasspathRootSelector.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/ClasspathRootSelector.java
@@ -17,7 +17,6 @@
 
 import java.net.URI;
 import java.nio.file.Path;
-import java.nio.file.Paths;
 import java.util.Objects;
 import java.util.Optional;
 
@@ -114,7 +113,7 @@ public String getPrefix() {
 
 		@Override
 		public Optional<ClasspathRootSelector> parse(DiscoverySelectorIdentifier identifier, Context context) {
-			Path path = Paths.get(URI.create(identifier.getValue()));
+			Path path = Path.of(URI.create(identifier.getValue()));
 			return getFirstElement(DiscoverySelectors.selectClasspathRoots(singleton(path)));
 		}
 
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/DirectorySelector.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/DirectorySelector.java
index fe74b2a1fdc8..577b97bc93a1 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/DirectorySelector.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/DirectorySelector.java
@@ -17,7 +17,6 @@
 import java.nio.file.FileSystem;
 import java.nio.file.FileSystems;
 import java.nio.file.Path;
-import java.nio.file.Paths;
 import java.util.Objects;
 import java.util.Optional;
 
@@ -67,7 +66,7 @@ public File getDirectory() {
 	 * @see #getRawPath()
 	 */
 	public Path getPath() {
-		return Paths.get(this.path);
+		return Path.of(this.path);
 	}
 
 	/**
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/DiscoverySelectorIdentifierParser.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/DiscoverySelectorIdentifierParser.java
index a643a21d89fc..857d5c2835a9 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/DiscoverySelectorIdentifierParser.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/DiscoverySelectorIdentifierParser.java
@@ -10,7 +10,7 @@
 
 package org.junit.platform.engine.discovery;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import java.util.Optional;
 
@@ -28,7 +28,7 @@
  * @since 1.11
  * @see DiscoverySelectors#parse(String)
  */
-@API(status = EXPERIMENTAL, since = "1.11")
+@API(status = MAINTAINED, since = "1.13.3")
 public interface DiscoverySelectorIdentifierParser {
 
 	/**
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/DiscoverySelectorIdentifierParsers.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/DiscoverySelectorIdentifierParsers.java
index 0f2d195eeb8d..f844100d44d6 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/DiscoverySelectorIdentifierParsers.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/DiscoverySelectorIdentifierParsers.java
@@ -37,16 +37,14 @@ static Stream<? extends DiscoverySelector> parseAll(String... identifiers) {
 		Preconditions.notNull(identifiers, "identifiers must not be null");
 		return Stream.of(identifiers) //
 				.map(DiscoverySelectorIdentifierParsers::parse) //
-				.filter(Optional::isPresent) //
-				.map(Optional::get);
+				.flatMap(Optional::stream);
 	}
 
 	static Stream<? extends DiscoverySelector> parseAll(Collection<DiscoverySelectorIdentifier> identifiers) {
 		Preconditions.notNull(identifiers, "identifiers must not be null");
 		return identifiers.stream() //
 				.map(DiscoverySelectorIdentifierParsers::parse) //
-				.filter(Optional::isPresent) //
-				.map(Optional::get);
+				.flatMap(Optional::stream);
 	}
 
 	static Optional<? extends DiscoverySelector> parse(String identifier) {
@@ -56,8 +54,9 @@ static Optional<? extends DiscoverySelector> parse(String identifier) {
 
 	static Optional<? extends DiscoverySelector> parse(DiscoverySelectorIdentifier identifier) {
 		Preconditions.notNull(identifier, "identifier must not be null");
-		DiscoverySelectorIdentifierParser parser = Singleton.INSTANCE.parsersByPrefix.get(identifier.getPrefix());
-		Preconditions.notNull(parser, "No parser for prefix: " + identifier.getPrefix());
+		DiscoverySelectorIdentifierParser parser = Preconditions.notNull(
+			Singleton.INSTANCE.parsersByPrefix.get(identifier.getPrefix()),
+			"No parser for prefix: " + identifier.getPrefix());
 
 		return parser.parse(identifier, DiscoverySelectorIdentifierParsers::parse);
 	}
@@ -75,7 +74,7 @@ private enum Singleton {
 			for (DiscoverySelectorIdentifierParser parser : loadedParsers) {
 				DiscoverySelectorIdentifierParser previous = parsersByPrefix.put(parser.getPrefix(), parser);
 				Preconditions.condition(previous == null,
-					() -> String.format("Duplicate parser for prefix: [%s]; candidate a: [%s]; candidate b: [%s]",
+					() -> "Duplicate parser for prefix: [%s]; candidate a: [%s]; candidate b: [%s]".formatted(
 						parser.getPrefix(), requireNonNull(previous).getClass().getName(),
 						parser.getClass().getName()));
 			}
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/DiscoverySelectors.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/DiscoverySelectors.java
index 299204c35677..af0862827b3e 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/DiscoverySelectors.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/DiscoverySelectors.java
@@ -10,10 +10,8 @@
 
 package org.junit.platform.engine.discovery;
 
-import static java.util.stream.Collectors.toList;
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
-import static org.junit.platform.commons.util.CollectionUtils.toUnmodifiableList;
 
 import java.io.File;
 import java.io.IOException;
@@ -29,6 +27,7 @@
 import java.util.stream.Stream;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.PreconditionViolationException;
 import org.junit.platform.commons.support.ReflectionSupport;
 import org.junit.platform.commons.support.Resource;
@@ -153,7 +152,7 @@ public static FileSelector selectFile(File file) {
 	 * @see #selectDirectory(String)
 	 * @see #selectDirectory(File)
 	 */
-	public static FileSelector selectFile(String path, FilePosition position) {
+	public static FileSelector selectFile(String path, @Nullable FilePosition position) {
 		Preconditions.notBlank(path, "File path must not be null or blank");
 		return new FileSelector(path, position);
 	}
@@ -174,10 +173,10 @@ public static FileSelector selectFile(String path, FilePosition position) {
 	 * @see #selectDirectory(String)
 	 * @see #selectDirectory(File)
 	 */
-	public static FileSelector selectFile(File file, FilePosition position) {
+	public static FileSelector selectFile(File file, @Nullable FilePosition position) {
 		Preconditions.notNull(file, "File must not be null");
 		Preconditions.condition(file.isFile(),
-			() -> String.format("The supplied java.io.File [%s] must represent an existing file", file));
+			() -> "The supplied java.io.File [%s] must represent an existing file".formatted(file));
 		try {
 			return new FileSelector(file.getCanonicalPath(), position);
 		}
@@ -219,7 +218,7 @@ public static DirectorySelector selectDirectory(String path) {
 	public static DirectorySelector selectDirectory(File directory) {
 		Preconditions.notNull(directory, "Directory must not be null");
 		Preconditions.condition(directory.isDirectory(),
-			() -> String.format("The supplied java.io.File [%s] must represent an existing directory", directory));
+			() -> "The supplied java.io.File [%s] must represent an existing directory".formatted(directory));
 		try {
 			return new DirectorySelector(directory.getCanonicalPath());
 		}
@@ -261,7 +260,7 @@ public static List<ClasspathRootSelector> selectClasspathRoots(Set<Path> classpa
 				.map(Path::toUri)
 				.map(ClasspathRootSelector::new)
 				// unmodifiable since selectClasspathRoots is a public, non-internal method
-				.collect(toUnmodifiableList());
+				.toList();
 		// @formatter:on
 	}
 
@@ -321,7 +320,7 @@ public static ClasspathResourceSelector selectClasspathResource(String classpath
 	 * @see ClassLoader#getResources(String)
 	 */
 	public static ClasspathResourceSelector selectClasspathResource(String classpathResourceName,
-			FilePosition position) {
+			@Nullable FilePosition position) {
 		Preconditions.notBlank(classpathResourceName, "classpath resource name must not be null or blank");
 		return new ClasspathResourceSelector(classpathResourceName, position);
 	}
@@ -349,11 +348,11 @@ public static ClasspathResourceSelector selectClasspathResource(String classpath
 	 * @see ClasspathResourceSelector
 	 * @see ReflectionSupport#tryToGetResources(String)
 	 */
-	@API(status = EXPERIMENTAL, since = "1.12")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public static ClasspathResourceSelector selectClasspathResource(Set<Resource> classpathResources) {
 		Preconditions.notEmpty(classpathResources, "classpath resources must not be null or empty");
 		Preconditions.containsNoNullElements(classpathResources, "individual classpath resources must not be null");
-		List<String> resourceNames = classpathResources.stream().map(Resource::getName).distinct().collect(toList());
+		List<String> resourceNames = classpathResources.stream().map(Resource::getName).distinct().toList();
 		Preconditions.condition(resourceNames.size() == 1, "all classpath resources must have the same name");
 		Preconditions.notBlank(resourceNames.get(0), "classpath resource names must not be null or blank");
 		return new ClasspathResourceSelector(classpathResources);
@@ -393,7 +392,7 @@ public static List<ModuleSelector> selectModules(Set<String> moduleNames) {
 		return moduleNames.stream()
 				.map(DiscoverySelectors::selectModule)
 				// unmodifiable since this is a public, non-internal method
-				.collect(toUnmodifiableList());
+				.toList();
 		// @formatter:on
 	}
 
@@ -445,8 +444,8 @@ public static ClassSelector selectClass(String className) {
 	 * @since 1.10
 	 * @see ClassSelector
 	 */
-	@API(status = EXPERIMENTAL, since = "1.10")
-	public static ClassSelector selectClass(ClassLoader classLoader, String className) {
+	@API(status = MAINTAINED, since = "1.13.3")
+	public static ClassSelector selectClass(@Nullable ClassLoader classLoader, String className) {
 		Preconditions.notBlank(className, "Class name must not be null or blank");
 		return new ClassSelector(classLoader, className);
 	}
@@ -513,8 +512,8 @@ public static MethodSelector selectMethod(String fullyQualifiedMethodName) throw
 	 * @see #selectMethod(String)
 	 * @see MethodSelector
 	 */
-	@API(status = EXPERIMENTAL, since = "1.10")
-	public static MethodSelector selectMethod(ClassLoader classLoader, String fullyQualifiedMethodName)
+	@API(status = MAINTAINED, since = "1.13.3")
+	public static MethodSelector selectMethod(@Nullable ClassLoader classLoader, String fullyQualifiedMethodName)
 			throws PreconditionViolationException {
 		String[] methodParts = ReflectionUtils.parseFullyQualifiedMethodName(fullyQualifiedMethodName);
 		return selectMethod(classLoader, methodParts[0], methodParts[1], methodParts[2]);
@@ -545,8 +544,8 @@ public static MethodSelector selectMethod(String className, String methodName) {
 	 * @since 1.10
 	 * @see MethodSelector
 	 */
-	@API(status = EXPERIMENTAL, since = "1.10")
-	public static MethodSelector selectMethod(ClassLoader classLoader, String className, String methodName) {
+	@API(status = MAINTAINED, since = "1.13.3")
+	public static MethodSelector selectMethod(@Nullable ClassLoader classLoader, String className, String methodName) {
 		return selectMethod(classLoader, className, methodName, "");
 	}
 
@@ -589,8 +588,8 @@ public static MethodSelector selectMethod(String className, String methodName, S
 	 * @since 1.10
 	 * @see MethodSelector
 	 */
-	@API(status = EXPERIMENTAL, since = "1.10")
-	public static MethodSelector selectMethod(ClassLoader classLoader, String className, String methodName,
+	@API(status = MAINTAINED, since = "1.13.3")
+	public static MethodSelector selectMethod(@Nullable ClassLoader classLoader, String className, String methodName,
 			String parameterTypeNames) {
 		Preconditions.notBlank(className, "Class name must not be null or blank");
 		Preconditions.notBlank(methodName, "Method name must not be null or blank");
@@ -645,7 +644,7 @@ public static MethodSelector selectMethod(Class<?> javaClass, String methodName,
 	 * @since 1.10
 	 * @see MethodSelector
 	 */
-	@API(status = EXPERIMENTAL, since = "1.10")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public static MethodSelector selectMethod(String className, String methodName, Class<?>... parameterTypes) {
 		Preconditions.notBlank(className, "Class name must not be null or blank");
 		Preconditions.notBlank(methodName, "Method name must not be null or blank");
@@ -666,7 +665,7 @@ public static MethodSelector selectMethod(String className, String methodName, C
 	 * @since 1.10
 	 * @see MethodSelector
 	 */
-	@API(status = EXPERIMENTAL, since = "1.10")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public static MethodSelector selectMethod(Class<?> javaClass, String methodName, Class<?>... parameterTypes) {
 		Preconditions.notNull(javaClass, "Class must not be null");
 		Preconditions.notBlank(methodName, "Method name must not be null or blank");
@@ -730,9 +729,9 @@ public static NestedClassSelector selectNestedClass(List<String> enclosingClassN
 	 * @since 1.10
 	 * @see NestedClassSelector
 	 */
-	@API(status = EXPERIMENTAL, since = "1.10")
-	public static NestedClassSelector selectNestedClass(ClassLoader classLoader, List<String> enclosingClassNames,
-			String nestedClassName) {
+	@API(status = MAINTAINED, since = "1.13.3")
+	public static NestedClassSelector selectNestedClass(@Nullable ClassLoader classLoader,
+			List<String> enclosingClassNames, String nestedClassName) {
 		Preconditions.notEmpty(enclosingClassNames, "Enclosing class names must not be null or empty");
 		Preconditions.notBlank(nestedClassName, "Nested class name must not be null or blank");
 		return new NestedClassSelector(classLoader, enclosingClassNames, nestedClassName);
@@ -766,9 +765,10 @@ public static NestedMethodSelector selectNestedMethod(List<String> enclosingClas
 	 * @since 1.10
 	 * @see NestedMethodSelector
 	 */
-	@API(status = EXPERIMENTAL, since = "1.10")
-	public static NestedMethodSelector selectNestedMethod(ClassLoader classLoader, List<String> enclosingClassNames,
-			String nestedClassName, String methodName) throws PreconditionViolationException {
+	@API(status = MAINTAINED, since = "1.13.3")
+	public static NestedMethodSelector selectNestedMethod(@Nullable ClassLoader classLoader,
+			List<String> enclosingClassNames, String nestedClassName, String methodName)
+			throws PreconditionViolationException {
 		Preconditions.notEmpty(enclosingClassNames, "Enclosing class names must not be null or empty");
 		Preconditions.notBlank(nestedClassName, "Nested class name must not be null or blank");
 		Preconditions.notBlank(methodName, "Method name must not be null or blank");
@@ -814,9 +814,9 @@ public static NestedMethodSelector selectNestedMethod(List<String> enclosingClas
 	 * @since 1.10
 	 * @see #selectNestedMethod(List, String, String, String)
 	 */
-	@API(status = EXPERIMENTAL, since = "1.10")
-	public static NestedMethodSelector selectNestedMethod(ClassLoader classLoader, List<String> enclosingClassNames,
-			String nestedClassName, String methodName, String parameterTypeNames) {
+	@API(status = MAINTAINED, since = "1.13.3")
+	public static NestedMethodSelector selectNestedMethod(@Nullable ClassLoader classLoader,
+			List<String> enclosingClassNames, String nestedClassName, String methodName, String parameterTypeNames) {
 
 		Preconditions.notEmpty(enclosingClassNames, "Enclosing class names must not be null or empty");
 		Preconditions.notBlank(nestedClassName, "Nested class name must not be null or blank");
@@ -840,7 +840,7 @@ public static NestedMethodSelector selectNestedMethod(ClassLoader classLoader, L
 	 * @since 1.10
 	 * @see NestedMethodSelector
 	 */
-	@API(status = EXPERIMENTAL, since = "1.10")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public static NestedMethodSelector selectNestedMethod(List<String> enclosingClassNames, String nestedClassName,
 			String methodName, Class<?>... parameterTypes) {
 
@@ -909,7 +909,7 @@ public static NestedMethodSelector selectNestedMethod(List<Class<?>> enclosingCl
 	 * @since 1.10
 	 * @see NestedMethodSelector
 	 */
-	@API(status = EXPERIMENTAL, since = "1.10")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public static NestedMethodSelector selectNestedMethod(List<Class<?>> enclosingClasses, Class<?> nestedClass,
 			String methodName, Class<?>... parameterTypes) {
 
@@ -973,7 +973,7 @@ public static UniqueIdSelector selectUniqueId(String uniqueId) {
 	 * @since 1.9
 	 * @see IterationSelector
 	 */
-	@API(status = EXPERIMENTAL, since = "1.9")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public static IterationSelector selectIteration(DiscoverySelector parentSelector, int... iterationIndices) {
 		Preconditions.notNull(parentSelector, "Parent selector must not be null");
 		Preconditions.notEmpty(iterationIndices, "iteration indices must not be empty");
@@ -990,7 +990,7 @@ public static IterationSelector selectIteration(DiscoverySelector parentSelector
 	 * @since 1.11
 	 * @see DiscoverySelectorIdentifierParser
 	 */
-	@API(status = EXPERIMENTAL, since = "1.11")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public static Optional<? extends DiscoverySelector> parse(String identifier) {
 		return DiscoverySelectorIdentifierParsers.parse(identifier);
 	}
@@ -1005,7 +1005,7 @@ public static Optional<? extends DiscoverySelector> parse(String identifier) {
 	 * @since 1.11
 	 * @see DiscoverySelectorIdentifierParser
 	 */
-	@API(status = EXPERIMENTAL, since = "1.11")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public static Optional<? extends DiscoverySelector> parse(DiscoverySelectorIdentifier identifier) {
 		return DiscoverySelectorIdentifierParsers.parse(identifier);
 	}
@@ -1021,7 +1021,7 @@ public static Optional<? extends DiscoverySelector> parse(DiscoverySelectorIdent
 	 * @since 1.11
 	 * @see DiscoverySelectorIdentifierParser
 	 */
-	@API(status = EXPERIMENTAL, since = "1.11")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public static Stream<? extends DiscoverySelector> parseAll(String... identifiers) {
 		return DiscoverySelectorIdentifierParsers.parseAll(identifiers);
 	}
@@ -1037,7 +1037,7 @@ public static Stream<? extends DiscoverySelector> parseAll(String... identifiers
 	 * @since 1.11
 	 * @see DiscoverySelectorIdentifierParser
 	 */
-	@API(status = EXPERIMENTAL, since = "1.11")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public static Stream<? extends DiscoverySelector> parseAll(Collection<DiscoverySelectorIdentifier> identifiers) {
 		return DiscoverySelectorIdentifierParsers.parseAll(identifiers);
 	}
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/ExcludeClassNameFilter.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/ExcludeClassNameFilter.java
index 3a1733d00775..f98d90de6966 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/ExcludeClassNameFilter.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/ExcludeClassNameFilter.java
@@ -41,21 +41,21 @@ public FilterResult apply(String className) {
 	}
 
 	private String formatInclusionReason(String className) {
-		return String.format("Class name [%s] does not match any excluded pattern: %s", className, patternDescription);
+		return "Class name [%s] does not match any excluded pattern: %s".formatted(className, patternDescription);
 	}
 
 	private String formatExclusionReason(String className, Pattern pattern) {
-		return String.format("Class name [%s] matches excluded pattern: '%s'", className, pattern);
+		return "Class name [%s] matches excluded pattern: '%s'".formatted(className, pattern);
 	}
 
 	@Override
 	public Predicate<String> toPredicate() {
-		return className -> !findMatchingPattern(className).isPresent();
+		return className -> findMatchingPattern(className).isEmpty();
 	}
 
 	@Override
 	public String toString() {
-		return String.format("%s that excludes class names that match one of the following regular expressions: %s",
+		return "%s that excludes class names that match one of the following regular expressions: %s".formatted(
 			getClass().getSimpleName(), this.patternDescription);
 	}
 
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/ExcludePackageNameFilter.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/ExcludePackageNameFilter.java
index eb649b634c3f..49986e06fd92 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/ExcludePackageNameFilter.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/ExcludePackageNameFilter.java
@@ -51,17 +51,17 @@ public FilterResult apply(String packageName) {
 	}
 
 	private String formatInclusionReason(String packageName) {
-		return String.format("Package name [%s] does not match any excluded names: %s", packageName,
+		return "Package name [%s] does not match any excluded names: %s".formatted(packageName,
 			this.patternDescription);
 	}
 
 	private String formatExclusionReason(String packageName, String matchedName) {
-		return String.format("Package name [%s] matches excluded name: '%s'", packageName, matchedName);
+		return "Package name [%s] matches excluded name: '%s'".formatted(packageName, matchedName);
 	}
 
 	@Override
 	public Predicate<String> toPredicate() {
-		return packageName -> !findMatchingName(packageName).isPresent();
+		return packageName -> findMatchingName(packageName).isEmpty();
 	}
 
 	private Optional<String> findMatchingName(String packageName) {
@@ -71,8 +71,7 @@ private Optional<String> findMatchingName(String packageName) {
 
 	@Override
 	public String toString() {
-		return String.format(
-			"%s that excludes packages whose names are either equal to or start with one of the following: %s",
+		return "%s that excludes packages whose names are either equal to or start with one of the following: %s".formatted(
 			getClass().getSimpleName(), this.patternDescription);
 	}
 
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/FilePosition.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/FilePosition.java
index 48cb72eb7e73..74973ef3fa90 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/FilePosition.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/FilePosition.java
@@ -12,11 +12,13 @@
 
 import static org.apiguardian.api.API.Status.STABLE;
 
+import java.io.Serial;
 import java.io.Serializable;
 import java.util.Objects;
 import java.util.Optional;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.logging.Logger;
 import org.junit.platform.commons.logging.LoggerFactory;
 import org.junit.platform.commons.util.Preconditions;
@@ -37,6 +39,7 @@
 @API(status = STABLE, since = "1.7")
 public class FilePosition implements Serializable {
 
+	@Serial
 	private static final long serialVersionUID = 1L;
 
 	private static final Logger logger = LoggerFactory.getLogger(FilePosition.class);
@@ -119,7 +122,8 @@ else if (column == null && "column".equals(key)) {
 	}
 
 	private final int line;
-	private final Integer column;
+
+	private final @Nullable Integer column;
 
 	private FilePosition(int line) {
 		Preconditions.condition(line > 0, "line number must be greater than zero");
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/FileSelector.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/FileSelector.java
index 80333c12af9d..ac01e74b5379 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/FileSelector.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/FileSelector.java
@@ -17,11 +17,11 @@
 import java.nio.file.FileSystem;
 import java.nio.file.FileSystems;
 import java.nio.file.Path;
-import java.nio.file.Paths;
 import java.util.Objects;
 import java.util.Optional;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.util.StringUtils;
 import org.junit.platform.commons.util.ToStringBuilder;
 import org.junit.platform.engine.DiscoverySelector;
@@ -45,9 +45,10 @@
 public class FileSelector implements DiscoverySelector {
 
 	private final String path;
-	private final FilePosition position;
 
-	FileSelector(String path, FilePosition position) {
+	private final @Nullable FilePosition position;
+
+	FileSelector(String path, @Nullable FilePosition position) {
 		this.path = path;
 		this.position = position;
 	}
@@ -70,7 +71,7 @@ public File getFile() {
 	 * @see #getRawPath()
 	 */
 	public Path getPath() {
-		return Paths.get(this.path);
+		return Path.of(this.path);
 	}
 
 	/**
@@ -127,7 +128,7 @@ public Optional<DiscoverySelectorIdentifier> toIdentifier() {
 		}
 		else {
 			return Optional.of(DiscoverySelectorIdentifier.create(IdentifierParser.PREFIX,
-				String.format("%s?%s", this.path, this.position.toQueryPart())));
+				"%s?%s".formatted(this.path, this.position.toQueryPart())));
 		}
 	}
 
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/IncludeClassNameFilter.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/IncludeClassNameFilter.java
index 8e233bb002fd..6c44a92ad0e5 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/IncludeClassNameFilter.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/IncludeClassNameFilter.java
@@ -41,12 +41,11 @@ public FilterResult apply(String className) {
 	}
 
 	private String formatInclusionReason(String className, Pattern pattern) {
-		return String.format("Class name [%s] matches included pattern: '%s'", className, pattern);
+		return "Class name [%s] matches included pattern: '%s'".formatted(className, pattern);
 	}
 
 	private String formatExclusionReason(String className) {
-		return String.format("Class name [%s] does not match any included pattern: %s", className,
-			this.patternDescription);
+		return "Class name [%s] does not match any included pattern: %s".formatted(className, this.patternDescription);
 	}
 
 	@Override
@@ -56,7 +55,7 @@ public Predicate<String> toPredicate() {
 
 	@Override
 	public String toString() {
-		return String.format("%s that includes class names that match one of the following regular expressions: %s",
+		return "%s that includes class names that match one of the following regular expressions: %s".formatted(
 			getClass().getSimpleName(), this.patternDescription);
 	}
 
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/IncludePackageNameFilter.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/IncludePackageNameFilter.java
index 322f840ae94d..4317b42f3e5b 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/IncludePackageNameFilter.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/IncludePackageNameFilter.java
@@ -51,11 +51,11 @@ public FilterResult apply(String packageName) {
 	}
 
 	private String formatInclusionReason(String packageName, String matchedName) {
-		return String.format("Package name [%s] matches included name: '%s'", packageName, matchedName);
+		return "Package name [%s] matches included name: '%s'".formatted(packageName, matchedName);
 	}
 
 	private String formatExclusionReason(String packageName) {
-		return String.format("Package name [%s] does not match any included names: %s", packageName,
+		return "Package name [%s] does not match any included names: %s".formatted(packageName,
 			this.patternDescription);
 	}
 
@@ -71,8 +71,7 @@ private Optional<String> findMatchingName(String packageName) {
 
 	@Override
 	public String toString() {
-		return String.format(
-			"%s that includes packages whose names are either equal to or start with one of the following: %s",
+		return "%s that includes packages whose names are either equal to or start with one of the following: %s".formatted(
 			getClass().getSimpleName(), this.patternDescription);
 	}
 
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/IterationSelector.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/IterationSelector.java
index dd603097263b..8b63b8a01a77 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/IterationSelector.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/IterationSelector.java
@@ -13,8 +13,8 @@
 import static java.util.stream.Collectors.collectingAndThen;
 import static java.util.stream.Collectors.joining;
 import static java.util.stream.Collectors.toCollection;
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
 import static org.apiguardian.api.API.Status.INTERNAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -44,7 +44,7 @@
  * @since 1.9
  * @see DiscoverySelectors#selectIteration(DiscoverySelector, int...)
  */
-@API(status = EXPERIMENTAL, since = "1.9")
+@API(status = MAINTAINED, since = "1.13.3")
 public class IterationSelector implements DiscoverySelector {
 
 	private final DiscoverySelector parentSelector;
@@ -106,7 +106,7 @@ public String toString() {
 	public Optional<DiscoverySelectorIdentifier> toIdentifier() {
 		return this.parentSelector.toIdentifier().map(parentSelectorString -> DiscoverySelectorIdentifier.create( //
 			IdentifierParser.PREFIX, //
-			String.format("%s[%s]", parentSelectorString, formatIterationIndicesAsRanges())) //
+			"%s[%s]".formatted(parentSelectorString, formatIterationIndicesAsRanges())) //
 		);
 	}
 
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/MethodSelector.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/MethodSelector.java
index 2bbe3ca08411..74efbcf9c5f2 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/MethodSelector.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/MethodSelector.java
@@ -10,9 +10,8 @@
 
 package org.junit.platform.engine.discovery;
 
-import static org.apiguardian.api.API.Status.DEPRECATED;
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
 import static org.apiguardian.api.API.Status.INTERNAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
 
 import java.lang.reflect.Method;
@@ -20,6 +19,7 @@
 import java.util.Optional;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.JUnitException;
 import org.junit.platform.commons.PreconditionViolationException;
 import org.junit.platform.commons.function.Try;
@@ -60,19 +60,21 @@
 @API(status = STABLE, since = "1.0")
 public class MethodSelector implements DiscoverySelector {
 
-	private final ClassLoader classLoader;
+	private final @Nullable ClassLoader classLoader;
 	private final String className;
 	private final String methodName;
 	private final String parameterTypeNames;
 
-	private volatile Class<?> javaClass;
-	private volatile Method javaMethod;
-	private volatile Class<?>[] parameterTypes;
+	private volatile @Nullable Class<?> javaClass;
+
+	private volatile @Nullable Method javaMethod;
+
+	private volatile Class<?> @Nullable [] parameterTypes;
 
 	/**
 	 * @since 1.10
 	 */
-	MethodSelector(ClassLoader classLoader, String className, String methodName, String parameterTypeNames) {
+	MethodSelector(@Nullable ClassLoader classLoader, String className, String methodName, String parameterTypeNames) {
 		this.classLoader = classLoader;
 		this.className = className;
 		this.methodName = methodName;
@@ -90,7 +92,7 @@ public class MethodSelector implements DiscoverySelector {
 	/**
 	 * @since 1.10
 	 */
-	MethodSelector(ClassLoader classLoader, String className, String methodName, Class<?>... parameterTypes) {
+	MethodSelector(@Nullable ClassLoader classLoader, String className, String methodName, Class<?>... parameterTypes) {
 		this.classLoader = classLoader;
 		this.className = className;
 		this.methodName = methodName;
@@ -126,8 +128,8 @@ public class MethodSelector implements DiscoverySelector {
 	 * @return the {@code ClassLoader}; potentially {@code null}
 	 * @since 1.10
 	 */
-	@API(status = EXPERIMENTAL, since = "1.10")
-	public ClassLoader getClassLoader() {
+	@API(status = MAINTAINED, since = "1.13.3")
+	public @Nullable ClassLoader getClassLoader() {
 		return this.classLoader;
 	}
 
@@ -145,23 +147,6 @@ public String getMethodName() {
 		return this.methodName;
 	}
 
-	/**
-	 * Get the names of parameter types for the selected method.
-	 *
-	 * <p>See {@link #getParameterTypeNames()} for details.
-	 *
-	 * @return the names of parameter types
-	 * @since 1.0
-	 * @see #getParameterTypeNames()
-	 * @see #getParameterTypes()
-	 * @deprecated since 1.10 in favor of {@link #getParameterTypeNames()}
-	 */
-	@Deprecated
-	@API(status = DEPRECATED, since = "1.10")
-	public String getMethodParameterTypes() {
-		return getParameterTypeNames();
-	}
-
 	/**
 	 * Get the names of parameter types for the selected method as a {@link String},
 	 * typically a comma-separated list of primitive types, fully qualified class
@@ -194,8 +179,7 @@ public String getParameterTypeNames() {
 	 * @see #getJavaMethod()
 	 */
 	public Class<?> getJavaClass() {
-		lazyLoadJavaClass();
-		return this.javaClass;
+		return lazyLoadJavaClass();
 	}
 
 	/**
@@ -208,8 +192,7 @@ public Class<?> getJavaClass() {
 	 * @see #getJavaClass()
 	 */
 	public Method getJavaMethod() {
-		lazyLoadJavaMethod();
-		return this.javaMethod;
+		return lazyLoadJavaMethod();
 	}
 
 	/**
@@ -227,50 +210,56 @@ public Method getJavaMethod() {
 	 * @see #getParameterTypeNames()
 	 * @see Method#getParameterTypes()
 	 */
-	@API(status = EXPERIMENTAL, since = "1.10")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public Class<?>[] getParameterTypes() {
-		lazyLoadParameterTypes();
-		return this.parameterTypes.clone();
+		return lazyLoadParameterTypes().clone();
 	}
 
-	private void lazyLoadJavaClass() {
-		// @formatter:off
-		if (this.javaClass == null) {
+	private Class<?> lazyLoadJavaClass() {
+		Class<?> value = this.javaClass;
+		if (value == null) {
+			// @formatter:off
 			Try<Class<?>> tryToLoadClass = this.classLoader == null
 				? ReflectionSupport.tryToLoadClass(this.className)
 				: ReflectionSupport.tryToLoadClass(this.className, this.classLoader);
-			this.javaClass = tryToLoadClass.getOrThrow(cause ->
+			value = tryToLoadClass.getNonNullOrThrow(cause ->
 				new PreconditionViolationException("Could not load class with name: " + this.className, cause));
+			// @formatter:on
+			this.javaClass = value;
 		}
-		// @formatter:on
+		return value;
 	}
 
-	private void lazyLoadJavaMethod() {
-		if (this.javaMethod == null) {
-			lazyLoadJavaClass();
-			lazyLoadParameterTypes();
-			if (this.parameterTypes.length > 0) {
-				this.javaMethod = ReflectionSupport.findMethod(this.javaClass, this.methodName,
-					this.parameterTypes).orElseThrow(
-						() -> new PreconditionViolationException(String.format(
-							"Could not find method with name [%s] and parameter types [%s] in class [%s].",
-							this.methodName, this.parameterTypeNames, this.javaClass.getName())));
+	private Method lazyLoadJavaMethod() {
+		var value = this.javaMethod;
+		if (value == null) {
+			Class<?> javaClass = lazyLoadJavaClass();
+			var parameterTypes = lazyLoadParameterTypes();
+			if (parameterTypes.length > 0) {
+				value = ReflectionSupport.findMethod(javaClass, this.methodName, parameterTypes).orElseThrow(
+					() -> new PreconditionViolationException(
+						"Could not find method with name [%s] and parameter types [%s] in class [%s].".formatted(
+							this.methodName, this.parameterTypeNames, javaClass.getName())));
 			}
 			else {
-				this.javaMethod = ReflectionSupport.findMethod(this.javaClass, this.methodName).orElseThrow(
+				value = ReflectionSupport.findMethod(javaClass, this.methodName).orElseThrow(
 					() -> new PreconditionViolationException(
-						String.format("Could not find method with name [%s] in class [%s].", this.methodName,
-							this.javaClass.getName())));
+						"Could not find method with name [%s] in class [%s].".formatted(this.methodName,
+							javaClass.getName())));
 			}
+			this.javaMethod = value;
 		}
+		return value;
 	}
 
-	private void lazyLoadParameterTypes() {
-		if (this.parameterTypes == null) {
-			lazyLoadJavaClass();
-			this.parameterTypes = ReflectionUtils.resolveParameterTypes(this.javaClass, this.methodName,
+	private Class<?>[] lazyLoadParameterTypes() {
+		var value = this.parameterTypes;
+		if (value == null) {
+			value = ReflectionUtils.resolveParameterTypes(lazyLoadJavaClass(), this.methodName,
 				this.parameterTypeNames);
+			this.parameterTypes = value;
 		}
+		return value;
 	}
 
 	/**
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/NestedClassSelector.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/NestedClassSelector.java
index c61f68d6df18..30996cd3e167 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/NestedClassSelector.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/NestedClassSelector.java
@@ -11,11 +11,9 @@
 package org.junit.platform.engine.discovery;
 
 import static java.util.stream.Collectors.joining;
-import static java.util.stream.Collectors.toList;
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
 import static org.apiguardian.api.API.Status.INTERNAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
-import static org.junit.platform.commons.util.CollectionUtils.toUnmodifiableList;
 
 import java.util.Arrays;
 import java.util.List;
@@ -24,6 +22,7 @@
 import java.util.stream.Stream;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.PreconditionViolationException;
 import org.junit.platform.commons.util.ToStringBuilder;
 import org.junit.platform.engine.DiscoverySelector;
@@ -54,21 +53,22 @@
 @API(status = STABLE, since = "1.6")
 public class NestedClassSelector implements DiscoverySelector {
 
-	private final ClassLoader classLoader;
+	private final @Nullable ClassLoader classLoader;
+
 	private final List<ClassSelector> enclosingClassSelectors;
 	private final ClassSelector nestedClassSelector;
 
-	NestedClassSelector(ClassLoader classLoader, List<String> enclosingClassNames, String nestedClassName) {
+	NestedClassSelector(@Nullable ClassLoader classLoader, List<String> enclosingClassNames, String nestedClassName) {
 		this.classLoader = classLoader;
 		this.enclosingClassSelectors = enclosingClassNames.stream() //
 				.map(className -> new ClassSelector(classLoader, className)) //
-				.collect(toUnmodifiableList());
+				.toList();
 		this.nestedClassSelector = new ClassSelector(classLoader, nestedClassName);
 	}
 
 	NestedClassSelector(List<Class<?>> enclosingClasses, Class<?> nestedClass) {
 		this.classLoader = nestedClass.getClassLoader();
-		this.enclosingClassSelectors = enclosingClasses.stream().map(ClassSelector::new).collect(toList());
+		this.enclosingClassSelectors = enclosingClasses.stream().map(ClassSelector::new).toList();
 		this.nestedClassSelector = new ClassSelector(nestedClass);
 	}
 
@@ -78,8 +78,8 @@ public class NestedClassSelector implements DiscoverySelector {
 	 * @return the {@code ClassLoader}; potentially {@code null}
 	 * @since 1.10
 	 */
-	@API(status = EXPERIMENTAL, since = "1.10")
-	public ClassLoader getClassLoader() {
+	@API(status = MAINTAINED, since = "1.13.3")
+	public @Nullable ClassLoader getClassLoader() {
 		return this.classLoader;
 	}
 
@@ -87,7 +87,7 @@ public ClassLoader getClassLoader() {
 	 * Get the names of the classes enclosing the selected nested class.
 	 */
 	public List<String> getEnclosingClassNames() {
-		return this.enclosingClassSelectors.stream().map(ClassSelector::getClassName).collect(toList());
+		return this.enclosingClassSelectors.stream().map(ClassSelector::getClassName).toList();
 	}
 
 	/**
@@ -100,7 +100,7 @@ public List<String> getEnclosingClassNames() {
 	 * {@link PreconditionViolationException} if the classes cannot be loaded.
 	 */
 	public List<Class<?>> getEnclosingClasses() {
-		return this.enclosingClassSelectors.stream().map(ClassSelector::getJavaClass).collect(toList());
+		return this.enclosingClassSelectors.stream().<Class<?>> map(ClassSelector::getJavaClass).toList();
 	}
 
 	/**
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/NestedMethodSelector.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/NestedMethodSelector.java
index 25f17d67ca92..9fc6415b63a7 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/NestedMethodSelector.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/NestedMethodSelector.java
@@ -10,9 +10,8 @@
 
 package org.junit.platform.engine.discovery;
 
-import static org.apiguardian.api.API.Status.DEPRECATED;
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
 import static org.apiguardian.api.API.Status.INTERNAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
 
 import java.lang.reflect.Method;
@@ -22,6 +21,7 @@
 import java.util.Optional;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.PreconditionViolationException;
 import org.junit.platform.commons.util.ReflectionUtils;
 import org.junit.platform.commons.util.ToStringBuilder;
@@ -61,7 +61,7 @@ public class NestedMethodSelector implements DiscoverySelector {
 	private final NestedClassSelector nestedClassSelector;
 	private final MethodSelector methodSelector;
 
-	NestedMethodSelector(ClassLoader classLoader, List<String> enclosingClassNames, String nestedClassName,
+	NestedMethodSelector(@Nullable ClassLoader classLoader, List<String> enclosingClassNames, String nestedClassName,
 			String methodName, String parameterTypeNames) {
 		this.nestedClassSelector = new NestedClassSelector(classLoader, enclosingClassNames, nestedClassName);
 		this.methodSelector = new MethodSelector(classLoader, nestedClassName, methodName, parameterTypeNames);
@@ -70,7 +70,7 @@ public class NestedMethodSelector implements DiscoverySelector {
 	/**
 	 * @since 1.10
 	 */
-	NestedMethodSelector(ClassLoader classLoader, List<String> enclosingClassNames, String nestedClassName,
+	NestedMethodSelector(@Nullable ClassLoader classLoader, List<String> enclosingClassNames, String nestedClassName,
 			String methodName, Class<?>... parameterTypes) {
 		this.nestedClassSelector = new NestedClassSelector(classLoader, enclosingClassNames, nestedClassName);
 		this.methodSelector = new MethodSelector(classLoader, nestedClassName, methodName, parameterTypes);
@@ -101,8 +101,8 @@ public class NestedMethodSelector implements DiscoverySelector {
 	 *
 	 * @since 1.10
 	 */
-	@API(status = EXPERIMENTAL, since = "1.10")
-	public ClassLoader getClassLoader() {
+	@API(status = MAINTAINED, since = "1.13.3")
+	public @Nullable ClassLoader getClassLoader() {
 		return this.nestedClassSelector.getClassLoader();
 	}
 
@@ -164,23 +164,6 @@ public Method getMethod() {
 		return this.methodSelector.getJavaMethod();
 	}
 
-	/**
-	 * Get the names of parameter types for the selected method.
-	 *
-	 * <p>See {@link #getParameterTypeNames()} for details.
-	 *
-	 * @return the names of parameter types
-	 * @since 1.6
-	 * @see #getParameterTypeNames()
-	 * @see #getParameterTypes()
-	 * @deprecated since 1.10 in favor or {@link #getParameterTypeNames()}
-	 */
-	@Deprecated
-	@API(status = DEPRECATED, since = "1.10")
-	public String getMethodParameterTypes() {
-		return getParameterTypeNames();
-	}
-
 	/**
 	 * Get the names of parameter types for the selected method as a {@link String}.
 	 *
@@ -209,7 +192,7 @@ public String getParameterTypeNames() {
 	 * @see #getParameterTypeNames()
 	 * @see MethodSelector#getParameterTypes()
 	 */
-	@API(status = EXPERIMENTAL, since = "1.10")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public Class<?>[] getParameterTypes() {
 		return this.methodSelector.getParameterTypes();
 	}
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/package-info.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/package-info.java
index 55321771b8e4..9f8135af9449 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/package-info.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/discovery/package-info.java
@@ -4,4 +4,7 @@
  * {@linkplain org.junit.platform.engine.EngineDiscoveryRequest discovery requests}.
  */
 
+@NullMarked
 package org.junit.platform.engine.discovery;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/package-info.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/package-info.java
index 63bb41729648..02ab768dc6f8 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/package-info.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/package-info.java
@@ -2,4 +2,7 @@
  * Public API for test engines.
  */
 
+@NullMarked
 package org.junit.platform.engine;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/reporting/FileEntry.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/reporting/FileEntry.java
index 13ad5f022b52..3d02c01f797a 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/reporting/FileEntry.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/reporting/FileEntry.java
@@ -10,13 +10,14 @@
 
 package org.junit.platform.engine.reporting;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import java.nio.file.Path;
 import java.time.LocalDateTime;
 import java.util.Optional;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.util.Preconditions;
 import org.junit.platform.commons.util.ToStringBuilder;
 
@@ -27,7 +28,7 @@
  * @since 1.12
  * @see #from(Path, String)
  */
-@API(status = EXPERIMENTAL, since = "1.12")
+@API(status = MAINTAINED, since = "1.13.3")
 public final class FileEntry {
 
 	/**
@@ -38,15 +39,16 @@ public final class FileEntry {
 	 * @param mediaType the media type of the path to publish; may be
 	 * {@code null}
 	 */
-	public static FileEntry from(Path path, String mediaType) {
+	public static FileEntry from(Path path, @Nullable String mediaType) {
 		return new FileEntry(path, mediaType);
 	}
 
 	private final LocalDateTime timestamp = LocalDateTime.now();
 	private final Path path;
-	private final String mediaType;
 
-	private FileEntry(Path path, String mediaType) {
+	private final @Nullable String mediaType;
+
+	private FileEntry(Path path, @Nullable String mediaType) {
 		this.path = Preconditions.notNull(path, "path must not be null");
 		this.mediaType = mediaType;
 	}
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/reporting/OutputDirectoryProvider.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/reporting/OutputDirectoryProvider.java
index 60fc831b9822..c1e55406c456 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/reporting/OutputDirectoryProvider.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/reporting/OutputDirectoryProvider.java
@@ -10,7 +10,7 @@
 
 package org.junit.platform.engine.reporting;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import java.io.IOException;
 import java.nio.file.Path;
@@ -26,7 +26,7 @@
  * @since 1.12
  * @see EngineDiscoveryRequest#getOutputDirectoryProvider()
  */
-@API(status = EXPERIMENTAL, since = "1.12")
+@API(status = MAINTAINED, since = "1.13.3")
 public interface OutputDirectoryProvider {
 
 	/**
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/reporting/ReportEntry.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/reporting/ReportEntry.java
index 0af74b590121..28587cfe0615 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/reporting/ReportEntry.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/reporting/ReportEntry.java
@@ -10,7 +10,6 @@
 
 package org.junit.platform.engine.reporting;
 
-import static org.apiguardian.api.API.Status.DEPRECATED;
 import static org.apiguardian.api.API.Status.STABLE;
 
 import java.time.LocalDateTime;
@@ -36,12 +35,7 @@ public final class ReportEntry {
 	private final LocalDateTime timestamp = LocalDateTime.now();
 	private final Map<String, String> keyValuePairs = new LinkedHashMap<>();
 
-	/**
-	 * @deprecated Use {@link #from(String, String)} or {@link #from(Map)}
-	 */
-	@API(status = DEPRECATED, since = "1.8")
-	@Deprecated
-	public ReportEntry() {
+	private ReportEntry() {
 	}
 
 	/**
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/reporting/package-info.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/reporting/package-info.java
index 11965058d1ab..6cafad5c020e 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/reporting/package-info.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/reporting/package-info.java
@@ -3,4 +3,7 @@
  * listeners.
  */
 
+@NullMarked
 package org.junit.platform.engine.reporting;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/config/PrefixedConfigurationParameters.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/config/PrefixedConfigurationParameters.java
index 31454eca91cd..61a55c72830c 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/config/PrefixedConfigurationParameters.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/config/PrefixedConfigurationParameters.java
@@ -17,6 +17,7 @@
 import java.util.function.Function;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.util.Preconditions;
 import org.junit.platform.engine.ConfigurationParameters;
 
@@ -57,7 +58,7 @@ public Optional<Boolean> getBoolean(String key) {
 	}
 
 	@Override
-	public <T> Optional<T> get(String key, Function<String, T> transformer) {
+	public <T> Optional<T> get(String key, Function<? super String, ? extends @Nullable T> transformer) {
 		return delegate.get(prefixed(key), transformer);
 	}
 
@@ -65,12 +66,6 @@ private String prefixed(String key) {
 		return prefix + key;
 	}
 
-	@Override
-	@SuppressWarnings("deprecation")
-	public int size() {
-		return delegate.size();
-	}
-
 	@Override
 	public Set<String> keySet() {
 		return delegate.keySet();
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/config/package-info.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/config/package-info.java
index 05f555a220ea..76d01748f8e3 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/config/package-info.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/config/package-info.java
@@ -3,4 +3,7 @@
  * classes intended to be used by test engine implementations.
  */
 
+@NullMarked
 package org.junit.platform.engine.support.config;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/AbstractTestDescriptor.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/AbstractTestDescriptor.java
index 336b6d686d95..4292bc7f6028 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/AbstractTestDescriptor.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/AbstractTestDescriptor.java
@@ -22,6 +22,7 @@
 import java.util.function.UnaryOperator;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.util.Preconditions;
 import org.junit.platform.engine.TestDescriptor;
 import org.junit.platform.engine.TestSource;
@@ -44,9 +45,9 @@ public abstract class AbstractTestDescriptor implements TestDescriptor {
 
 	private final String displayName;
 
-	private final TestSource source;
+	private final @Nullable TestSource source;
 
-	private TestDescriptor parent;
+	private @Nullable TestDescriptor parent;
 
 	/**
 	 * The synchronized set of children associated with this {@code TestDescriptor}.
@@ -87,7 +88,7 @@ protected AbstractTestDescriptor(UniqueId uniqueId, String displayName) {
 	 * {@code TestDescriptor}; can be {@code null}
 	 * @see #AbstractTestDescriptor(UniqueId, String)
 	 */
-	protected AbstractTestDescriptor(UniqueId uniqueId, String displayName, TestSource source) {
+	protected AbstractTestDescriptor(UniqueId uniqueId, String displayName, @Nullable TestSource source) {
 		this.uniqueId = Preconditions.notNull(uniqueId, "UniqueId must not be null");
 		this.displayName = Preconditions.notBlank(displayName, "displayName must not be null or blank");
 		this.source = source;
@@ -119,7 +120,7 @@ public final Optional<TestDescriptor> getParent() {
 	}
 
 	@Override
-	public final void setParent(TestDescriptor parent) {
+	public final void setParent(@Nullable TestDescriptor parent) {
 		this.parent = parent;
 	}
 
@@ -144,8 +145,8 @@ public void removeChild(TestDescriptor child) {
 
 	@Override
 	public void removeFromHierarchy() {
-		Preconditions.condition(!isRoot(), "cannot remove the root of a hierarchy");
-		this.parent.removeChild(this);
+		var parent = Preconditions.notNull(this.parent, "cannot remove the root of a hierarchy");
+		parent.removeChild(this);
 		this.children.forEach(child -> child.setParent(null));
 		this.children.clear();
 	}
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/ClassSource.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/ClassSource.java
index 186cf149b07d..7852ba45b8a0 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/ClassSource.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/ClassSource.java
@@ -12,11 +12,13 @@
 
 import static org.apiguardian.api.API.Status.STABLE;
 
+import java.io.Serial;
 import java.net.URI;
 import java.util.Objects;
 import java.util.Optional;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.PreconditionViolationException;
 import org.junit.platform.commons.support.ReflectionSupport;
 import org.junit.platform.commons.util.Preconditions;
@@ -43,6 +45,7 @@
 @API(status = STABLE, since = "1.0")
 public class ClassSource implements TestSource {
 
+	@Serial
 	private static final long serialVersionUID = 1L;
 
 	/**
@@ -69,7 +72,7 @@ public static ClassSource from(String className) {
 	 * @param className the class name; must not be {@code null} or blank
 	 * @param filePosition the position in the source file; may be {@code null}
 	 */
-	public static ClassSource from(String className, FilePosition filePosition) {
+	public static ClassSource from(String className, @Nullable FilePosition filePosition) {
 		return new ClassSource(className, filePosition);
 	}
 
@@ -130,14 +133,16 @@ public static ClassSource from(URI uri) {
 	}
 
 	private final String className;
-	private final FilePosition filePosition;
-	private Class<?> javaClass;
+
+	private final @Nullable FilePosition filePosition;
+
+	private @Nullable Class<?> javaClass;
 
 	private ClassSource(String className) {
 		this(className, null);
 	}
 
-	private ClassSource(String className, FilePosition filePosition) {
+	private ClassSource(String className, @Nullable FilePosition filePosition) {
 		this.className = Preconditions.notBlank(className, "Class name must not be null or blank");
 		this.filePosition = filePosition;
 	}
@@ -146,7 +151,7 @@ private ClassSource(Class<?> javaClass) {
 		this(javaClass, null);
 	}
 
-	private ClassSource(Class<?> javaClass, FilePosition filePosition) {
+	private ClassSource(Class<?> javaClass, @Nullable FilePosition filePosition) {
 		this.javaClass = Preconditions.notNull(javaClass, "Class must not be null");
 		this.className = this.javaClass.getName();
 		this.filePosition = filePosition;
@@ -175,7 +180,7 @@ public final String getClassName() {
 	public final Class<?> getJavaClass() {
 		if (this.javaClass == null) {
 			// @formatter:off
-			this.javaClass = ReflectionSupport.tryToLoadClass(this.className).getOrThrow(
+			this.javaClass = ReflectionSupport.tryToLoadClass(this.className).getNonNullOrThrow(
 				cause -> new PreconditionViolationException("Could not load class with name: " + this.className, cause));
 			// @formatter:on
 		}
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/ClasspathResourceSource.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/ClasspathResourceSource.java
index a49f65ed040b..838b92d9ad8e 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/ClasspathResourceSource.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/ClasspathResourceSource.java
@@ -12,11 +12,13 @@
 
 import static org.apiguardian.api.API.Status.STABLE;
 
+import java.io.Serial;
 import java.net.URI;
 import java.util.Objects;
 import java.util.Optional;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.PreconditionViolationException;
 import org.junit.platform.commons.util.Preconditions;
 import org.junit.platform.commons.util.ResourceUtils;
@@ -33,6 +35,7 @@
 @API(status = STABLE, since = "1.0")
 public class ClasspathResourceSource implements TestSource {
 
+	@Serial
 	private static final long serialVersionUID = 1L;
 
 	/**
@@ -77,7 +80,7 @@ public static ClasspathResourceSource from(String classpathResourceName) {
 	 * {@code null} or blank
 	 * @param filePosition the position in the classpath resource; may be {@code null}
 	 */
-	public static ClasspathResourceSource from(String classpathResourceName, FilePosition filePosition) {
+	public static ClasspathResourceSource from(String classpathResourceName, @Nullable FilePosition filePosition) {
 		return new ClasspathResourceSource(classpathResourceName, filePosition);
 	}
 
@@ -110,13 +113,14 @@ public static ClasspathResourceSource from(URI uri) {
 	}
 
 	private final String classpathResourceName;
-	private final FilePosition filePosition;
+
+	private final @Nullable FilePosition filePosition;
 
 	private ClasspathResourceSource(String classpathResourceName) {
 		this(classpathResourceName, null);
 	}
 
-	private ClasspathResourceSource(String classpathResourceName, FilePosition filePosition) {
+	private ClasspathResourceSource(String classpathResourceName, @Nullable FilePosition filePosition) {
 		Preconditions.notBlank(classpathResourceName, "Classpath resource name must not be null or blank");
 		boolean startsWithSlash = classpathResourceName.startsWith("/");
 		this.classpathResourceName = (startsWithSlash ? classpathResourceName.substring(1) : classpathResourceName);
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/CompositeTestSource.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/CompositeTestSource.java
index 43a396a221b5..15438b93c4b1 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/CompositeTestSource.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/CompositeTestSource.java
@@ -10,10 +10,9 @@
 
 package org.junit.platform.engine.support.descriptor;
 
-import static java.util.Collections.unmodifiableList;
 import static org.apiguardian.api.API.Status.STABLE;
 
-import java.util.ArrayList;
+import java.io.Serial;
 import java.util.Collection;
 import java.util.List;
 
@@ -32,6 +31,7 @@
 @API(status = STABLE, since = "1.0")
 public class CompositeTestSource implements TestSource {
 
+	@Serial
 	private static final long serialVersionUID = 1L;
 
 	/**
@@ -55,7 +55,7 @@ public static CompositeTestSource from(Collection<? extends TestSource> sources)
 	private CompositeTestSource(Collection<? extends TestSource> sources) {
 		Preconditions.notEmpty(sources, "TestSource collection must not be null or empty");
 		Preconditions.containsNoNullElements(sources, "individual TestSources must not be null");
-		this.sources = unmodifiableList(new ArrayList<>(sources));
+		this.sources = List.copyOf(sources);
 	}
 
 	/**
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/DefaultUriSource.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/DefaultUriSource.java
index 54ae69de460a..a11f3af851a8 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/DefaultUriSource.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/DefaultUriSource.java
@@ -10,8 +10,8 @@
 
 package org.junit.platform.engine.support.descriptor;
 
+import java.io.Serial;
 import java.net.URI;
-import java.util.Objects;
 
 import org.junit.platform.commons.util.Preconditions;
 import org.junit.platform.commons.util.ToStringBuilder;
@@ -21,14 +21,13 @@
  *
  * @since 1.3
  */
-class DefaultUriSource implements UriSource {
+record DefaultUriSource(URI uri) implements UriSource {
 
+	@Serial
 	private static final long serialVersionUID = 1L;
 
-	private final URI uri;
-
-	DefaultUriSource(URI uri) {
-		this.uri = Preconditions.notNull(uri, "URI must not be null");
+	DefaultUriSource {
+		Preconditions.notNull(uri, "URI must not be null");
 	}
 
 	@Override
@@ -36,23 +35,6 @@ public URI getUri() {
 		return uri;
 	}
 
-	@Override
-	public boolean equals(Object o) {
-		if (this == o) {
-			return true;
-		}
-		if (o == null || getClass() != o.getClass()) {
-			return false;
-		}
-		DefaultUriSource that = (DefaultUriSource) o;
-		return Objects.equals(this.uri, that.uri);
-	}
-
-	@Override
-	public int hashCode() {
-		return this.uri.hashCode();
-	}
-
 	@Override
 	public String toString() {
 		return new ToStringBuilder(this).append("uri", this.uri).toString();
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/DirectorySource.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/DirectorySource.java
index 04cc46369d5f..a2b3645bd203 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/DirectorySource.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/DirectorySource.java
@@ -14,6 +14,7 @@
 
 import java.io.File;
 import java.io.IOException;
+import java.io.Serial;
 import java.net.URI;
 
 import org.apiguardian.api.API;
@@ -30,6 +31,7 @@
 @API(status = STABLE, since = "1.0")
 public class DirectorySource implements FileSystemSource {
 
+	@Serial
 	private static final long serialVersionUID = 1L;
 
 	/**
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/FilePosition.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/FilePosition.java
index 859006090008..7d8d9b5500ff 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/FilePosition.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/FilePosition.java
@@ -12,11 +12,13 @@
 
 import static org.apiguardian.api.API.Status.STABLE;
 
+import java.io.Serial;
 import java.io.Serializable;
 import java.util.Objects;
 import java.util.Optional;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.logging.Logger;
 import org.junit.platform.commons.logging.LoggerFactory;
 import org.junit.platform.commons.util.Preconditions;
@@ -32,6 +34,7 @@
 @API(status = STABLE, since = "1.0")
 public class FilePosition implements Serializable {
 
+	@Serial
 	private static final long serialVersionUID = 1L;
 
 	private static final Logger logger = LoggerFactory.getLogger(FilePosition.class);
@@ -114,7 +117,8 @@ else if (column == null && "column".equals(key)) {
 	}
 
 	private final int line;
-	private final Integer column;
+
+	private final @Nullable Integer column;
 
 	private FilePosition(int line) {
 		Preconditions.condition(line > 0, "line number must be greater than zero");
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/FileSource.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/FileSource.java
index 0e6e42acba94..577f602659db 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/FileSource.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/FileSource.java
@@ -14,11 +14,13 @@
 
 import java.io.File;
 import java.io.IOException;
+import java.io.Serial;
 import java.net.URI;
 import java.util.Objects;
 import java.util.Optional;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.JUnitException;
 import org.junit.platform.commons.util.Preconditions;
 import org.junit.platform.commons.util.ToStringBuilder;
@@ -33,6 +35,7 @@
 @API(status = STABLE, since = "1.0")
 public class FileSource implements FileSystemSource {
 
+	@Serial
 	private static final long serialVersionUID = 1L;
 
 	/**
@@ -51,18 +54,19 @@ public static FileSource from(File file) {
 	 * @param file the source file; must not be {@code null}
 	 * @param filePosition the position in the source file; may be {@code null}
 	 */
-	public static FileSource from(File file, FilePosition filePosition) {
+	public static FileSource from(File file, @Nullable FilePosition filePosition) {
 		return new FileSource(file, filePosition);
 	}
 
 	private final File file;
-	private final FilePosition filePosition;
+
+	private final @Nullable FilePosition filePosition;
 
 	private FileSource(File file) {
 		this(file, null);
 	}
 
-	private FileSource(File file, FilePosition filePosition) {
+	private FileSource(File file, @Nullable FilePosition filePosition) {
 		Preconditions.notNull(file, "file must not be null");
 		try {
 			this.file = file.getCanonicalFile();
@@ -109,7 +113,8 @@ public boolean equals(Object o) {
 			return false;
 		}
 		FileSource that = (FileSource) o;
-		return Objects.equals(this.file, that.file) && Objects.equals(this.filePosition, that.filePosition);
+		return Objects.equals(this.file, that.file) //
+				&& Objects.equals(this.filePosition, that.filePosition);
 	}
 
 	@Override
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/MethodSource.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/MethodSource.java
index 3f2f876a49ba..1917dd19b168 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/MethodSource.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/MethodSource.java
@@ -13,10 +13,12 @@
 import static org.apiguardian.api.API.Status.STABLE;
 import static org.junit.platform.commons.util.ClassUtils.nullSafeToString;
 
+import java.io.Serial;
 import java.lang.reflect.Method;
 import java.util.Objects;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.PreconditionViolationException;
 import org.junit.platform.commons.support.ReflectionSupport;
 import org.junit.platform.commons.util.Preconditions;
@@ -36,6 +38,7 @@
 @API(status = STABLE, since = "1.0")
 public class MethodSource implements TestSource {
 
+	@Serial
 	private static final long serialVersionUID = 1L;
 
 	/**
@@ -106,15 +109,18 @@ public static MethodSource from(Class<?> testClass, Method testMethod) {
 
 	private final String className;
 	private final String methodName;
-	private final String methodParameterTypes;
-	private Class<?> javaClass;
-	private transient Method javaMethod;
+
+	private final @Nullable String methodParameterTypes;
+
+	private @Nullable Class<?> javaClass;
+
+	private transient @Nullable Method javaMethod;
 
 	private MethodSource(String className, String methodName) {
 		this(className, methodName, null);
 	}
 
-	private MethodSource(String className, String methodName, String methodParameterTypes) {
+	private MethodSource(String className, String methodName, @Nullable String methodParameterTypes) {
 		Preconditions.notBlank(className, "Class name must not be null or blank");
 		Preconditions.notBlank(methodName, "Method name must not be null or blank");
 		this.className = className;
@@ -156,7 +162,7 @@ public final String getMethodName() {
 	/**
 	 * Get the method parameter types of this source.
 	 */
-	public final String getMethodParameterTypes() {
+	public final @Nullable String getMethodParameterTypes() {
 		return this.methodParameterTypes;
 	}
 
@@ -172,8 +178,7 @@ public final String getMethodParameterTypes() {
 	 */
 	@API(status = STABLE, since = "1.7")
 	public final Class<?> getJavaClass() {
-		lazyLoadJavaClass();
-		return this.javaClass;
+		return lazyLoadJavaClass();
 	}
 
 	/**
@@ -188,37 +193,37 @@ public final Class<?> getJavaClass() {
 	 */
 	@API(status = STABLE, since = "1.7")
 	public final Method getJavaMethod() {
-		lazyLoadJavaMethod();
-		return this.javaMethod;
+		return lazyLoadJavaMethod();
 	}
 
-	private void lazyLoadJavaClass() {
+	private Class<?> lazyLoadJavaClass() {
 		if (this.javaClass == null) {
 			// @formatter:off
-			this.javaClass = ReflectionSupport.tryToLoadClass(this.className).getOrThrow(
+			this.javaClass = ReflectionSupport.tryToLoadClass(this.className).getNonNullOrThrow(
 				cause -> new PreconditionViolationException("Could not load class with name: " + this.className, cause));
 			// @formatter:on
 		}
+		return this.javaClass;
 	}
 
-	private void lazyLoadJavaMethod() {
-		lazyLoadJavaClass();
-
+	private Method lazyLoadJavaMethod() {
 		if (this.javaMethod == null) {
+			Class<?> javaClass = getJavaClass();
 			if (StringUtils.isNotBlank(this.methodParameterTypes)) {
-				this.javaMethod = ReflectionSupport.findMethod(this.javaClass, this.methodName,
+				this.javaMethod = ReflectionSupport.findMethod(javaClass, this.methodName,
 					this.methodParameterTypes).orElseThrow(
-						() -> new PreconditionViolationException(String.format(
-							"Could not find method with name [%s] and parameter types [%s] in class [%s].",
-							this.methodName, this.methodParameterTypes, this.javaClass.getName())));
+						() -> new PreconditionViolationException(
+							"Could not find method with name [%s] and parameter types [%s] in class [%s].".formatted(
+								this.methodName, this.methodParameterTypes, javaClass.getName())));
 			}
 			else {
-				this.javaMethod = ReflectionSupport.findMethod(this.javaClass, this.methodName).orElseThrow(
+				this.javaMethod = ReflectionSupport.findMethod(javaClass, this.methodName).orElseThrow(
 					() -> new PreconditionViolationException(
-						String.format("Could not find method with name [%s] in class [%s].", this.methodName,
-							this.javaClass.getName())));
+						"Could not find method with name [%s] in class [%s].".formatted(this.methodName,
+							javaClass.getName())));
 			}
 		}
+		return this.javaMethod;
 	}
 
 	@Override
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/PackageSource.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/PackageSource.java
index c6bca4e9c0ff..d3c46953a3f9 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/PackageSource.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/PackageSource.java
@@ -12,6 +12,7 @@
 
 import static org.apiguardian.api.API.Status.STABLE;
 
+import java.io.Serial;
 import java.util.Objects;
 
 import org.apiguardian.api.API;
@@ -31,6 +32,7 @@
 @API(status = STABLE, since = "1.0")
 public class PackageSource implements TestSource {
 
+	@Serial
 	private static final long serialVersionUID = 1L;
 
 	/**
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/UriSource.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/UriSource.java
index 58efdba0a566..d27d8dd8f1e3 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/UriSource.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/UriSource.java
@@ -15,7 +15,6 @@
 import java.net.URI;
 import java.nio.file.Files;
 import java.nio.file.Path;
-import java.nio.file.Paths;
 
 import org.apiguardian.api.API;
 import org.junit.platform.commons.logging.LoggerFactory;
@@ -59,7 +58,7 @@ static UriSource from(URI uri) {
 
 		try {
 			URI uriWithoutQuery = ResourceUtils.stripQueryComponent(uri);
-			Path path = Paths.get(uriWithoutQuery);
+			Path path = Path.of(uriWithoutQuery);
 			if (Files.isRegularFile(path)) {
 				return FileSource.from(path.toFile(), FilePosition.fromQuery(uri.getQuery()).orElse(null));
 			}
@@ -68,8 +67,9 @@ static UriSource from(URI uri) {
 			}
 		}
 		catch (RuntimeException ex) {
-			LoggerFactory.getLogger(UriSource.class).debug(ex, () -> String.format(
-				"The supplied URI [%s] is not path-based. Falling back to default UriSource implementation.", uri));
+			LoggerFactory.getLogger(UriSource.class).debug(ex,
+				() -> "The supplied URI [%s] is not path-based. Falling back to default UriSource implementation.".formatted(
+					uri));
 		}
 
 		// Store supplied URI as-is
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/package-info.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/package-info.java
index 9f063532a19a..eabc3dab0055 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/package-info.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/descriptor/package-info.java
@@ -4,4 +4,7 @@
  * the launcher.
  */
 
+@NullMarked
 package org.junit.platform.engine.support.descriptor;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/discovery/DiscoveryIssueReporter.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/discovery/DiscoveryIssueReporter.java
index 8226df455562..bfe4a854902c 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/discovery/DiscoveryIssueReporter.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/discovery/DiscoveryIssueReporter.java
@@ -34,7 +34,7 @@
  * @since 1.13
  * @see SelectorResolver.Context
  */
-@API(status = EXPERIMENTAL, since = "1.13")
+@API(status = EXPERIMENTAL, since = "6.0")
 public interface DiscoveryIssueReporter {
 
 	/**
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/discovery/EngineDiscoveryRequestResolution.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/discovery/EngineDiscoveryRequestResolution.java
index 36a939414a7d..1726376ffa67 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/discovery/EngineDiscoveryRequestResolution.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/discovery/EngineDiscoveryRequestResolution.java
@@ -10,6 +10,7 @@
 
 package org.junit.platform.engine.support.discovery;
 
+import static java.util.Objects.requireNonNullElse;
 import static java.util.stream.Collectors.joining;
 import static org.junit.platform.commons.util.CollectionUtils.getOnlyElement;
 import static org.junit.platform.engine.SelectorResolutionResult.failed;
@@ -28,6 +29,7 @@
 import java.util.function.Function;
 import java.util.function.Supplier;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.JUnitException;
 import org.junit.platform.commons.util.UnrecoverableExceptions;
 import org.junit.platform.engine.DiscoverySelector;
@@ -120,46 +122,46 @@ private Optional<Resolution> resolve(DiscoverySelector selector) {
 		if (resolvedSelectors.containsKey(selector)) {
 			return Optional.of(resolvedSelectors.get(selector));
 		}
-		if (selector instanceof UniqueIdSelector) {
-			return resolveUniqueId((UniqueIdSelector) selector);
+		if (selector instanceof UniqueIdSelector uniqueIdSelector) {
+			return resolveUniqueId(uniqueIdSelector);
 		}
 		return resolve(selector, resolver -> {
 			Context context = getContext(selector);
-			if (selector instanceof ClasspathResourceSelector) {
-				return resolver.resolve((ClasspathResourceSelector) selector, context);
+			if (selector instanceof ClasspathResourceSelector classpathResourceSelector) {
+				return resolver.resolve(classpathResourceSelector, context);
 			}
-			if (selector instanceof ClasspathRootSelector) {
-				return resolver.resolve((ClasspathRootSelector) selector, context);
+			if (selector instanceof ClasspathRootSelector classpathRootSelector) {
+				return resolver.resolve(classpathRootSelector, context);
 			}
-			if (selector instanceof ClassSelector) {
-				return resolver.resolve((ClassSelector) selector, context);
+			if (selector instanceof ClassSelector classSelector) {
+				return resolver.resolve(classSelector, context);
 			}
-			if (selector instanceof IterationSelector) {
-				return resolver.resolve((IterationSelector) selector, context);
+			if (selector instanceof IterationSelector iterationSelector) {
+				return resolver.resolve(iterationSelector, context);
 			}
-			if (selector instanceof NestedClassSelector) {
-				return resolver.resolve((NestedClassSelector) selector, context);
+			if (selector instanceof NestedClassSelector nestedClassSelector) {
+				return resolver.resolve(nestedClassSelector, context);
 			}
-			if (selector instanceof DirectorySelector) {
-				return resolver.resolve((DirectorySelector) selector, context);
+			if (selector instanceof DirectorySelector directorySelector) {
+				return resolver.resolve(directorySelector, context);
 			}
-			if (selector instanceof FileSelector) {
-				return resolver.resolve((FileSelector) selector, context);
+			if (selector instanceof FileSelector fileSelector) {
+				return resolver.resolve(fileSelector, context);
 			}
-			if (selector instanceof MethodSelector) {
-				return resolver.resolve((MethodSelector) selector, context);
+			if (selector instanceof MethodSelector methodSelector) {
+				return resolver.resolve(methodSelector, context);
 			}
-			if (selector instanceof NestedMethodSelector) {
-				return resolver.resolve((NestedMethodSelector) selector, context);
+			if (selector instanceof NestedMethodSelector nestedMethodSelector) {
+				return resolver.resolve(nestedMethodSelector, context);
 			}
-			if (selector instanceof ModuleSelector) {
-				return resolver.resolve((ModuleSelector) selector, context);
+			if (selector instanceof ModuleSelector moduleSelector) {
+				return resolver.resolve(moduleSelector, context);
 			}
-			if (selector instanceof PackageSelector) {
-				return resolver.resolve((PackageSelector) selector, context);
+			if (selector instanceof PackageSelector packageSelector) {
+				return resolver.resolve(packageSelector, context);
 			}
-			if (selector instanceof UriSelector) {
-				return resolver.resolve((UriSelector) selector, context);
+			if (selector instanceof UriSelector uriSelector) {
+				return resolver.resolve(uriSelector, context);
 			}
 			return resolver.resolve(selector, context);
 		});
@@ -199,18 +201,16 @@ private Optional<Resolution> resolve(DiscoverySelector selector,
 
 	private class DefaultContext implements Context {
 
+		@Nullable
 		private final TestDescriptor parent;
 
-		DefaultContext(TestDescriptor parent) {
+		DefaultContext(@Nullable TestDescriptor parent) {
 			this.parent = parent;
 		}
 
 		@Override
 		public <T extends TestDescriptor> Optional<T> addToParent(Function<TestDescriptor, Optional<T>> creator) {
-			if (parent != null) {
-				return createAndAdd(parent, creator);
-			}
-			return createAndAdd(engineDescriptor, creator);
+			return createAndAdd(requireNonNullElse(parent, engineDescriptor), creator);
 		}
 
 		@Override
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/discovery/EngineDiscoveryRequestResolver.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/discovery/EngineDiscoveryRequestResolver.java
index 4c5dbf3037d9..e38072e58355 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/discovery/EngineDiscoveryRequestResolver.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/discovery/EngineDiscoveryRequestResolver.java
@@ -12,6 +12,7 @@
 
 import static java.util.stream.Collectors.toCollection;
 import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
 
 import java.util.ArrayList;
@@ -136,7 +137,7 @@ public void resolve(EngineDiscoveryRequest request, T engineDescriptor) {
 	 * @see SelectorResolver
 	 * @see TestDescriptor.Visitor
 	 */
-	@API(status = EXPERIMENTAL, since = "1.13")
+	@API(status = EXPERIMENTAL, since = "6.0")
 	public void resolve(EngineDiscoveryRequest request, T engineDescriptor, DiscoveryIssueReporter issueReporter) {
 		Preconditions.notNull(request, "request must not be null");
 		Preconditions.notNull(engineDescriptor, "engineDescriptor must not be null");
@@ -207,7 +208,7 @@ public Builder<T> addClassContainerSelectorResolver(Predicate<Class<?>> classFil
 		 * {@code null}
 		 * @return this builder for method chaining
 		 */
-		@API(status = EXPERIMENTAL, since = "1.13")
+		@API(status = EXPERIMENTAL, since = "6.0")
 		public Builder<T> addClassContainerSelectorResolverWithContext(
 				Function<InitializationContext<T>, Predicate<Class<?>>> classFilterCreator) {
 			Preconditions.notNull(classFilterCreator, "classFilterCreator must not be null");
@@ -227,7 +228,7 @@ public Builder<T> addClassContainerSelectorResolverWithContext(
 		 * @return this builder for method chaining
 		 * @since 1.12
 		 */
-		@API(status = EXPERIMENTAL, since = "1.12")
+		@API(status = MAINTAINED, since = "1.13.3")
 		public Builder<T> addResourceContainerSelectorResolver(Predicate<Resource> resourceFilter) {
 			Preconditions.notNull(resourceFilter, "resourceFilter must not be null");
 			return addSelectorResolver(
@@ -336,7 +337,7 @@ public interface InitializationContext<T extends TestDescriptor> {
 		 * {@code null}
 		 * @since 1.12
 		 */
-		@API(status = EXPERIMENTAL, since = "1.12")
+		@API(status = MAINTAINED, since = "1.13.3")
 		Predicate<String> getPackageFilter();
 
 		/**
@@ -345,7 +346,7 @@ public interface InitializationContext<T extends TestDescriptor> {
 		 *
 		 * @since 1.13
 		 */
-		@API(status = EXPERIMENTAL, since = "1.13")
+		@API(status = EXPERIMENTAL, since = "6.0")
 		DiscoveryIssueReporter getIssueReporter();
 	}
 
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/discovery/SelectorResolver.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/discovery/SelectorResolver.java
index a402a4679152..e507cf47fc10 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/discovery/SelectorResolver.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/discovery/SelectorResolver.java
@@ -12,7 +12,7 @@
 
 import static java.util.Collections.emptySet;
 import static java.util.Collections.singleton;
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
 
 import java.util.Collections;
@@ -315,7 +315,7 @@ default Resolution resolve(UriSelector selector, Context context) {
 	 * Resolution#matches(Set) matches()}; never {@code null}
 	 * @see #resolve(DiscoverySelector, Context)
 	 */
-	@API(status = EXPERIMENTAL, since = "1.9")
+	@API(status = MAINTAINED, since = "1.13.3")
 	default Resolution resolve(IterationSelector selector, Context context) {
 		return resolve((DiscoverySelector) selector, context);
 	}
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/discovery/package-info.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/discovery/package-info.java
index 1f0ea1ff308a..3d6b8dd4a0aa 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/discovery/package-info.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/discovery/package-info.java
@@ -6,4 +6,7 @@
  * @see org.junit.platform.engine.support.discovery.SelectorResolver
  */
 
+@NullMarked
 package org.junit.platform.engine.support.discovery;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/filter/ClasspathScanningSupport.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/filter/ClasspathScanningSupport.java
deleted file mode 100644
index 1eabfbdd8475..000000000000
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/filter/ClasspathScanningSupport.java
+++ /dev/null
@@ -1,71 +0,0 @@
-/*
- * Copyright 2015-2025 the original author or authors.
- *
- * All rights reserved. This program and the accompanying materials are
- * made available under the terms of the Eclipse Public License v2.0 which
- * accompanies this distribution and is available at
- *
- * https://www.eclipse.org/legal/epl-v20.html
- */
-
-package org.junit.platform.engine.support.filter;
-
-import static org.apiguardian.api.API.Status.DEPRECATED;
-import static org.junit.platform.engine.Filter.composeFilters;
-
-import java.util.ArrayList;
-import java.util.List;
-import java.util.function.Predicate;
-
-import org.apiguardian.api.API;
-import org.junit.platform.commons.support.scanning.ClassFilter;
-import org.junit.platform.engine.DiscoveryFilter;
-import org.junit.platform.engine.EngineDiscoveryRequest;
-import org.junit.platform.engine.discovery.ClassNameFilter;
-import org.junit.platform.engine.discovery.PackageNameFilter;
-
-/**
- * Support utility methods for classpath scanning.
- *
- * @since 1.0
- * @deprecated Please use {@link org.junit.platform.engine.support.discovery.EngineDiscoveryRequestResolver} instead.
- */
-@Deprecated
-@API(status = DEPRECATED, since = "1.5")
-public final class ClasspathScanningSupport {
-
-	private ClasspathScanningSupport() {
-		/* no-op */
-	}
-
-	/**
-	 * Build a {@link Predicate} for fully qualified class names to be used for
-	 * classpath scanning from an {@link EngineDiscoveryRequest}.
-	 *
-	 * @param request the request to build a predicate from
-	 * @deprecated Please use {@link org.junit.platform.engine.support.discovery.EngineDiscoveryRequestResolver} instead.
-	 */
-	@Deprecated
-	public static Predicate<String> buildClassNamePredicate(EngineDiscoveryRequest request) {
-		List<DiscoveryFilter<String>> filters = new ArrayList<>();
-		filters.addAll(request.getFiltersByType(ClassNameFilter.class));
-		filters.addAll(request.getFiltersByType(PackageNameFilter.class));
-		return composeFilters(filters).toPredicate();
-	}
-
-	/**
-	 * Build a {@link ClassFilter} by combining the name predicate built by
-	 * {@link #buildClassNamePredicate(EngineDiscoveryRequest)} and the passed-in
-	 * class predicate.
-	 *
-	 * @param request the request to build a name predicate from
-	 * @param classPredicate the class predicate
-	 * @deprecated Please use {@link org.junit.platform.engine.support.discovery.EngineDiscoveryRequestResolver} instead.
-	 */
-	@Deprecated
-	@SuppressWarnings("exports")
-	public static ClassFilter buildClassFilter(EngineDiscoveryRequest request, Predicate<Class<?>> classPredicate) {
-		return ClassFilter.of(buildClassNamePredicate(request), classPredicate);
-	}
-
-}
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/filter/package-info.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/filter/package-info.java
deleted file mode 100644
index c074ecf00bf0..000000000000
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/filter/package-info.java
+++ /dev/null
@@ -1,6 +0,0 @@
-/**
- * {@link org.junit.platform.engine.Filter}-related support classes intended to be
- * used by test engine implementations.
- */
-
-package org.junit.platform.engine.support.filter;
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/CompositeLock.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/CompositeLock.java
index 76dbbb6b984c..7ac65a73e6a1 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/CompositeLock.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/CompositeLock.java
@@ -10,8 +10,6 @@
 
 package org.junit.platform.engine.support.hierarchical;
 
-import static java.util.Collections.unmodifiableList;
-
 import java.util.ArrayList;
 import java.util.List;
 import java.util.concurrent.ForkJoinPool;
@@ -31,7 +29,7 @@ class CompositeLock implements ResourceLock {
 
 	CompositeLock(List<ExclusiveResource> resources, List<Lock> locks) {
 		Preconditions.condition(resources.size() == locks.size(), "Resources and locks must have the same size");
-		this.resources = unmodifiableList(resources);
+		this.resources = List.copyOf(resources);
 		this.locks = Preconditions.notEmpty(locks, "Locks must not be empty");
 		this.exclusive = resources.stream().anyMatch(
 			resource -> resource.getLockMode() == ExclusiveResource.LockMode.READ_WRITE);
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/DefaultParallelExecutionConfigurationStrategy.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/DefaultParallelExecutionConfigurationStrategy.java
index 304c9e943f58..47e88a603deb 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/DefaultParallelExecutionConfigurationStrategy.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/DefaultParallelExecutionConfigurationStrategy.java
@@ -10,7 +10,8 @@
 
 package org.junit.platform.engine.support.hierarchical;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static java.util.Objects.requireNonNull;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
 
 import java.math.BigDecimal;
@@ -40,8 +41,8 @@ public enum DefaultParallelExecutionConfigurationStrategy implements ParallelExe
 		public ParallelExecutionConfiguration createConfiguration(ConfigurationParameters configurationParameters) {
 			int parallelism = configurationParameters.get(CONFIG_FIXED_PARALLELISM_PROPERTY_NAME,
 				Integer::valueOf).orElseThrow(
-					() -> new JUnitException(String.format("Configuration parameter '%s' must be set",
-						CONFIG_FIXED_PARALLELISM_PROPERTY_NAME)));
+					() -> new JUnitException(
+						"Configuration parameter '%s' must be set".formatted(CONFIG_FIXED_PARALLELISM_PROPERTY_NAME)));
 
 			int maxPoolSize = configurationParameters.get(CONFIG_FIXED_MAX_POOL_SIZE_PROPERTY_NAME,
 				Integer::valueOf).orElse(parallelism + 256);
@@ -66,8 +67,8 @@ public ParallelExecutionConfiguration createConfiguration(ConfigurationParameter
 				BigDecimal::new).orElse(BigDecimal.ONE);
 
 			Preconditions.condition(factor.compareTo(BigDecimal.ZERO) > 0,
-				() -> String.format("Factor '%s' specified via configuration parameter '%s' must be greater than 0",
-					factor, CONFIG_DYNAMIC_FACTOR_PROPERTY_NAME));
+				() -> "Factor '%s' specified via configuration parameter '%s' must be greater than 0".formatted(factor,
+					CONFIG_DYNAMIC_FACTOR_PROPERTY_NAME));
 
 			int parallelism = Math.max(1,
 				factor.multiply(BigDecimal.valueOf(Runtime.getRuntime().availableProcessors())).intValue());
@@ -75,8 +76,7 @@ public ParallelExecutionConfiguration createConfiguration(ConfigurationParameter
 			int maxPoolSize = configurationParameters.get(CONFIG_DYNAMIC_MAX_POOL_SIZE_FACTOR_PROPERTY_NAME,
 				BigDecimal::new).map(maxPoolSizeFactor -> {
 					Preconditions.condition(maxPoolSizeFactor.compareTo(BigDecimal.ONE) >= 0,
-						() -> String.format(
-							"Factor '%s' specified via configuration parameter '%s' must be greater than or equal to 1",
+						() -> "Factor '%s' specified via configuration parameter '%s' must be greater than or equal to 1".formatted(
 							factor, CONFIG_DYNAMIC_MAX_POOL_SIZE_FACTOR_PROPERTY_NAME));
 					return maxPoolSizeFactor.multiply(BigDecimal.valueOf(parallelism)).intValue();
 				}).orElseGet(() -> 256 + parallelism);
@@ -107,8 +107,8 @@ public ParallelExecutionConfiguration createConfiguration(ConfigurationParameter
 									+ ParallelExecutionConfigurationStrategy.class);
 						return (ParallelExecutionConfigurationStrategy) ReflectionSupport.newInstance(strategyClass);
 					}) //
-					.andThenTry(strategy -> strategy.createConfiguration(configurationParameters)) //
-					.getOrThrow(cause -> new JUnitException(
+					.andThenTry(strategy -> requireNonNull(strategy).createConfiguration(configurationParameters)) //
+					.getNonNullOrThrow(cause -> new JUnitException(
 						"Could not create configuration for strategy class: " + className, cause));
 		}
 	};
@@ -144,7 +144,7 @@ public ParallelExecutionConfiguration createConfiguration(ConfigurationParameter
 	 * @since 1.10
 	 * @see #FIXED
 	 */
-	@API(status = EXPERIMENTAL, since = "1.10")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public static final String CONFIG_FIXED_MAX_POOL_SIZE_PROPERTY_NAME = "fixed.max-pool-size";
 
 	/**
@@ -160,7 +160,7 @@ public ParallelExecutionConfiguration createConfiguration(ConfigurationParameter
 	 * @see #FIXED
 	 * @see #CONFIG_FIXED_MAX_POOL_SIZE_PROPERTY_NAME
 	 */
-	@API(status = EXPERIMENTAL, since = "1.10")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public static final String CONFIG_FIXED_SATURATE_PROPERTY_NAME = "fixed.saturate";
 
 	/**
@@ -188,7 +188,7 @@ public ParallelExecutionConfiguration createConfiguration(ConfigurationParameter
 	 * @since 1.10
 	 * @see #DYNAMIC
 	 */
-	@API(status = EXPERIMENTAL, since = "1.10")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public static final String CONFIG_DYNAMIC_MAX_POOL_SIZE_FACTOR_PROPERTY_NAME = "dynamic.max-pool-size-factor";
 
 	/**
@@ -204,7 +204,7 @@ public ParallelExecutionConfiguration createConfiguration(ConfigurationParameter
 	 * @see #DYNAMIC
 	 * @see #CONFIG_DYNAMIC_FACTOR_PROPERTY_NAME
 	 */
-	@API(status = EXPERIMENTAL, since = "1.10")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public static final String CONFIG_DYNAMIC_SATURATE_PROPERTY_NAME = "dynamic.saturate";
 
 	/**
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/ForkJoinPoolHierarchicalTestExecutorService.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/ForkJoinPoolHierarchicalTestExecutorService.java
index 9ccb3747680f..60677dea7bac 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/ForkJoinPoolHierarchicalTestExecutorService.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/ForkJoinPoolHierarchicalTestExecutorService.java
@@ -35,6 +35,7 @@
 import java.util.function.Predicate;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.JUnitException;
 import org.junit.platform.commons.function.Try;
 import org.junit.platform.commons.logging.LoggerFactory;
@@ -126,7 +127,8 @@ private static Callable<ForkJoinPool> sinceJava7ConstructorInvocation(ParallelEx
 	}
 
 	@Override
-	public Future<Void> submit(TestTask testTask) {
+	@SuppressWarnings("NullAway")
+	public Future<@Nullable Void> submit(TestTask testTask) {
 		ExclusiveTask exclusiveTask = new ExclusiveTask(testTask);
 		if (!isAlreadyRunningInForkJoinPool()) {
 			// ensure we're running inside the ForkJoinPool so we
@@ -233,6 +235,7 @@ class ExclusiveTask extends ForkJoinTask<Void> {
 		 *
 		 * @return {@code null} always
 		 */
+		@Override
 		public final Void getRawResult() {
 			return null;
 		}
@@ -240,6 +243,7 @@ public final Void getRawResult() {
 		/**
 		 * Requires null completion value.
 		 */
+		@Override
 		protected final void setRawResult(Void mustBeNull) {
 		}
 
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/HierarchicalTestExecutor.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/HierarchicalTestExecutor.java
index 3ce7e541cf43..68549dbf632a 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/HierarchicalTestExecutor.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/HierarchicalTestExecutor.java
@@ -12,6 +12,7 @@
 
 import java.util.concurrent.Future;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.engine.EngineExecutionListener;
 import org.junit.platform.engine.ExecutionRequest;
 import org.junit.platform.engine.TestDescriptor;
@@ -46,7 +47,7 @@ class HierarchicalTestExecutor<C extends EngineExecutionContext> {
 		this.throwableCollectorFactory = throwableCollectorFactory;
 	}
 
-	Future<Void> execute() {
+	Future<@Nullable Void> execute() {
 		TestDescriptor rootTestDescriptor = this.request.getRootTestDescriptor();
 		EngineExecutionListener executionListener = this.request.getEngineExecutionListener();
 		NodeExecutionAdvisor executionAdvisor = new NodeTreeWalker().walk(rootTestDescriptor);
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/HierarchicalTestExecutorService.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/HierarchicalTestExecutorService.java
index d879aa2b5978..1fed0663e519 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/HierarchicalTestExecutorService.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/HierarchicalTestExecutorService.java
@@ -16,6 +16,7 @@
 import java.util.concurrent.Future;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.engine.ExecutionRequest;
 import org.junit.platform.engine.support.hierarchical.Node.ExecutionMode;
 
@@ -49,7 +50,7 @@ public interface HierarchicalTestExecutorService extends AutoCloseable {
 	 * to be finished
 	 * @see #invokeAll(List)
 	 */
-	Future<Void> submit(TestTask testTask);
+	Future<@Nullable Void> submit(TestTask testTask);
 
 	/**
 	 * Invoke all supplied {@linkplain TestTask test tasks} and block until
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/LockManager.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/LockManager.java
index 988d52efb69e..3171c31d2b66 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/LockManager.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/LockManager.java
@@ -15,7 +15,6 @@
 import static java.util.stream.Collectors.groupingBy;
 import static java.util.stream.Collectors.toList;
 import static org.junit.platform.commons.util.CollectionUtils.getOnlyElement;
-import static org.junit.platform.commons.util.CollectionUtils.toUnmodifiableList;
 import static org.junit.platform.engine.support.hierarchical.ExclusiveResource.GLOBAL_READ;
 import static org.junit.platform.engine.support.hierarchical.ExclusiveResource.GLOBAL_READ_WRITE;
 import static org.junit.platform.engine.support.hierarchical.ExclusiveResource.LockMode.READ;
@@ -66,19 +65,16 @@ private List<ExclusiveResource> toDistinctSortedResources(Collection<ExclusiveRe
 
 		return resourcesByKey.values().stream()
 				.map(resourcesWithSameKey -> resourcesWithSameKey.get(0))
-				.collect(toUnmodifiableList());
+				.toList();
 		// @formatter:on
 	}
 
 	private ResourceLock toResourceLock(List<ExclusiveResource> resources) {
-		switch (resources.size()) {
-			case 0:
-				return NopLock.INSTANCE;
-			case 1:
-				return toSingleLock(getOnlyElement(resources));
-			default:
-				return new CompositeLock(resources, toLocks(resources));
-		}
+		return switch (resources.size()) {
+			case 0 -> NopLock.INSTANCE;
+			case 1 -> toSingleLock(getOnlyElement(resources));
+			default -> new CompositeLock(resources, toLocks(resources));
+		};
 	}
 
 	private SingleLock toSingleLock(ExclusiveResource resource) {
@@ -92,7 +88,7 @@ private SingleLock toSingleLock(ExclusiveResource resource) {
 	}
 
 	private List<Lock> toLocks(List<ExclusiveResource> resources) {
-		return resources.stream().map(this::toLock).collect(toUnmodifiableList());
+		return resources.stream().map(this::toLock).toList();
 	}
 
 	private Lock toLock(ExclusiveResource resource) {
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/Node.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/Node.java
index f2616e60a6cb..1fa014c92d14 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/Node.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/Node.java
@@ -19,6 +19,7 @@
 import java.util.concurrent.Future;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.util.ToStringBuilder;
 import org.junit.platform.engine.EngineExecutionListener;
 import org.junit.platform.engine.TestDescriptor;
@@ -218,7 +219,7 @@ class SkipResult {
 		 * may be {@code null}
 		 * @return a skipped {@code SkipResult} with the given reason
 		 */
-		public static SkipResult skip(String reason) {
+		public static SkipResult skip(@Nullable String reason) {
 			return new SkipResult(true, reason);
 		}
 
@@ -233,7 +234,7 @@ public static SkipResult doNotSkip() {
 			return alwaysExecuteSkipResult;
 		}
 
-		private SkipResult(boolean skipped, String reason) {
+		private SkipResult(boolean skipped, @Nullable String reason) {
 			this.skipped = skipped;
 			this.reason = Optional.ofNullable(reason);
 		}
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/NodeTestTask.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/NodeTestTask.java
index 928b6d21e55a..5249236fd729 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/NodeTestTask.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/NodeTestTask.java
@@ -10,6 +10,8 @@
 
 package org.junit.platform.engine.support.hierarchical;
 
+import static java.util.Objects.requireNonNull;
+import static java.util.Objects.requireNonNullElse;
 import static java.util.concurrent.CompletableFuture.completedFuture;
 import static java.util.stream.Collectors.toCollection;
 import static org.junit.platform.engine.TestExecutionResult.failed;
@@ -23,6 +25,7 @@
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.Future;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.JUnitException;
 import org.junit.platform.commons.logging.Logger;
 import org.junit.platform.commons.logging.LoggerFactory;
@@ -51,12 +54,15 @@ class NodeTestTask<C extends EngineExecutionContext> implements TestTask {
 	private final Node<C> node;
 	private final Runnable finalizer;
 
-	private C parentContext;
-	private C context;
+	private @Nullable C parentContext;
+
+	private @Nullable C context;
+
+	private @Nullable SkipResult skipResult;
 
-	private SkipResult skipResult;
 	private boolean started;
-	private ThrowableCollector throwableCollector;
+
+	private @Nullable ThrowableCollector throwableCollector;
 
 	NodeTestTask(NodeTestTaskContext taskContext, TestDescriptor testDescriptor) {
 		this(taskContext, testDescriptor, NOOP);
@@ -71,12 +77,12 @@ class NodeTestTask<C extends EngineExecutionContext> implements TestTask {
 
 	@Override
 	public ResourceLock getResourceLock() {
-		return taskContext.getExecutionAdvisor().getResourceLock(testDescriptor);
+		return taskContext.executionAdvisor().getResourceLock(testDescriptor);
 	}
 
 	@Override
 	public ExecutionMode getExecutionMode() {
-		return taskContext.getExecutionAdvisor().getForcedExecutionMode(testDescriptor) //
+		return taskContext.executionAdvisor().getForcedExecutionMode(testDescriptor) //
 				.orElseGet(node::getExecutionMode);
 	}
 
@@ -85,19 +91,19 @@ public String toString() {
 		return "NodeTestTask [" + testDescriptor + "]";
 	}
 
-	void setParentContext(C parentContext) {
+	void setParentContext(@Nullable C parentContext) {
 		this.parentContext = parentContext;
 	}
 
 	@Override
 	public void execute() {
 		try {
-			throwableCollector = taskContext.getThrowableCollectorFactory().create();
+			throwableCollector = taskContext.throwableCollectorFactory().create();
 			prepare();
 			if (throwableCollector.isEmpty()) {
 				checkWhetherSkipped();
 			}
-			if (throwableCollector.isEmpty() && !skipResult.isSkipped()) {
+			if (throwableCollector.isEmpty() && !requiredSkipResult().isSkipped()) {
 				executeRecursively();
 			}
 			if (context != null) {
@@ -108,7 +114,7 @@ public void execute() {
 		finally {
 			// Ensure that the 'interrupted status' flag for the current thread
 			// is cleared for reuse of the thread in subsequent task executions.
-			// See https://github.com/junit-team/junit5/issues/1688
+			// See https://github.com/junit-team/junit-framework/issues/1688
 			if (Thread.interrupted()) {
 				logger.debug(() -> String.format(
 					"Execution of TestDescriptor with display name [%s] "
@@ -121,28 +127,30 @@ public void execute() {
 		}
 
 		// Clear reference to context to allow it to be garbage collected.
-		// See https://github.com/junit-team/junit5/issues/1578
+		// See https://github.com/junit-team/junit-framework/issues/1578
 		context = null;
 	}
 
 	private void prepare() {
-		throwableCollector.execute(() -> context = node.prepare(parentContext));
+		requiredThrowableCollector().execute(() -> context = node.prepare(requireNonNull(parentContext)));
 
 		// Clear reference to parent context to allow it to be garbage collected.
-		// See https://github.com/junit-team/junit5/issues/1578
+		// See https://github.com/junit-team/junit-framework/issues/1578
 		parentContext = null;
 	}
 
 	private void checkWhetherSkipped() {
-		throwableCollector.execute(() -> skipResult = node.shouldBeSkipped(context));
+		requiredThrowableCollector().execute(() -> skipResult = node.shouldBeSkipped(requiredContext()));
 	}
 
 	private void executeRecursively() {
-		taskContext.getListener().executionStarted(testDescriptor);
+		taskContext.listener().executionStarted(testDescriptor);
 		started = true;
 
+		var throwableCollector = requiredThrowableCollector();
+
 		throwableCollector.execute(() -> {
-			node.around(context, ctx -> {
+			node.around(requiredContext(), ctx -> {
 				context = ctx;
 				throwableCollector.execute(() -> {
 					// @formatter:off
@@ -151,55 +159,71 @@ private void executeRecursively() {
 							.collect(toCollection(ArrayList::new));
 					// @formatter:on
 
-					context = node.before(context);
+					context = node.before(requiredContext());
 
 					final DynamicTestExecutor dynamicTestExecutor = new DefaultDynamicTestExecutor();
-					context = node.execute(context, dynamicTestExecutor);
+					context = node.execute(requiredContext(), dynamicTestExecutor);
 
 					if (!children.isEmpty()) {
 						children.forEach(child -> child.setParentContext(context));
-						taskContext.getExecutorService().invokeAll(children);
+						taskContext.executorService().invokeAll(children);
 					}
 
 					throwableCollector.execute(dynamicTestExecutor::awaitFinished);
 				});
 
-				throwableCollector.execute(() -> node.after(context));
+				throwableCollector.execute(() -> node.after(requiredContext()));
 			});
 		});
 	}
 
 	private void cleanUp() {
-		throwableCollector.execute(() -> node.cleanUp(context));
+		requiredThrowableCollector().execute(() -> node.cleanUp(requiredContext()));
 	}
 
 	private void reportCompletion() {
-		if (throwableCollector.isEmpty() && skipResult.isSkipped()) {
+
+		var throwableCollector = requiredThrowableCollector();
+
+		if (throwableCollector.isEmpty() && requiredSkipResult().isSkipped()) {
+			var skipResult = requiredSkipResult();
 			try {
-				node.nodeSkipped(context, testDescriptor, skipResult);
+				node.nodeSkipped(requiredContext(), testDescriptor, skipResult);
 			}
 			catch (Throwable throwable) {
 				UnrecoverableExceptions.rethrowIfUnrecoverable(throwable);
 				logger.debug(throwable,
-					() -> String.format("Failed to invoke nodeSkipped() on Node %s", testDescriptor.getUniqueId()));
+					() -> "Failed to invoke nodeSkipped() on Node %s".formatted(testDescriptor.getUniqueId()));
 			}
-			taskContext.getListener().executionSkipped(testDescriptor, skipResult.getReason().orElse("<unknown>"));
+			taskContext.listener().executionSkipped(testDescriptor, skipResult.getReason().orElse("<unknown>"));
 			return;
 		}
 		if (!started) {
 			// Call executionStarted first to comply with the contract of EngineExecutionListener.
-			taskContext.getListener().executionStarted(testDescriptor);
+			taskContext.listener().executionStarted(testDescriptor);
 		}
 		try {
-			node.nodeFinished(context, testDescriptor, throwableCollector.toTestExecutionResult());
+			node.nodeFinished(requiredContext(), testDescriptor, throwableCollector.toTestExecutionResult());
 		}
 		catch (Throwable throwable) {
 			UnrecoverableExceptions.rethrowIfUnrecoverable(throwable);
 			logger.debug(throwable,
-				() -> String.format("Failed to invoke nodeFinished() on Node %s", testDescriptor.getUniqueId()));
+				() -> "Failed to invoke nodeFinished() on Node %s".formatted(testDescriptor.getUniqueId()));
 		}
-		taskContext.getListener().executionFinished(testDescriptor, throwableCollector.toTestExecutionResult());
-		throwableCollector = null;
+		taskContext.listener().executionFinished(testDescriptor, throwableCollector.toTestExecutionResult());
+		this.throwableCollector = null;
+	}
+
+	private C requiredContext() {
+		return requireNonNull(context);
+	}
+
+	private SkipResult requiredSkipResult() {
+		return requireNonNull(skipResult);
+	}
+
+	private ThrowableCollector requiredThrowableCollector() {
+		return requireNonNull(throwableCollector);
 	}
 
 	private class DefaultDynamicTestExecutor implements DynamicTestExecutor {
@@ -207,7 +231,7 @@ private class DefaultDynamicTestExecutor implements DynamicTestExecutor {
 
 		@Override
 		public void execute(TestDescriptor testDescriptor) {
-			execute(testDescriptor, taskContext.getListener());
+			execute(testDescriptor, taskContext.listener());
 		}
 
 		@Override
@@ -229,7 +253,7 @@ public Future<?> execute(TestDescriptor testDescriptor, EngineExecutionListener
 					testDescriptor, () -> unfinishedTasks.remove(uniqueId));
 				nodeTestTask.setParentContext(context);
 				unfinishedTasks.put(uniqueId, DynamicTaskState.unscheduled());
-				Future<Void> future = taskContext.getExecutorService().submit(nodeTestTask);
+				Future<@Nullable Void> future = taskContext.executorService().submit(nodeTestTask);
 				unfinishedTasks.computeIfPresent(uniqueId, (__, state) -> DynamicTaskState.scheduled(future));
 				return future;
 			}
@@ -245,7 +269,7 @@ public void awaitFinished() throws InterruptedException {
 					// Futures returned by execute() may have been cancelled
 				}
 				catch (ExecutionException e) {
-					throw ExceptionUtils.throwAsUncheckedException(e.getCause());
+					throw ExceptionUtils.throwAsUncheckedException(requireNonNullElse(e.getCause(), e));
 				}
 			}
 		}
@@ -261,7 +285,7 @@ static DynamicTaskState unscheduled() {
 			return UNSCHEDULED;
 		}
 
-		static DynamicTaskState scheduled(Future<Void> future) {
+		static DynamicTaskState scheduled(Future<@Nullable Void> future) {
 			return future::get;
 		}
 
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/NodeTestTaskContext.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/NodeTestTaskContext.java
index a6298847d59a..005d8ab6d02c 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/NodeTestTaskContext.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/NodeTestTaskContext.java
@@ -15,20 +15,8 @@
 /**
  * @since 1.3.1
  */
-class NodeTestTaskContext {
-
-	private final EngineExecutionListener listener;
-	private final HierarchicalTestExecutorService executorService;
-	private final ThrowableCollector.Factory throwableCollectorFactory;
-	private final NodeExecutionAdvisor executionAdvisor;
-
-	public NodeTestTaskContext(EngineExecutionListener listener, HierarchicalTestExecutorService executorService,
-			ThrowableCollector.Factory throwableCollectorFactory, NodeExecutionAdvisor executionAdvisor) {
-		this.listener = listener;
-		this.executorService = executorService;
-		this.throwableCollectorFactory = throwableCollectorFactory;
-		this.executionAdvisor = executionAdvisor;
-	}
+record NodeTestTaskContext(EngineExecutionListener listener, HierarchicalTestExecutorService executorService,
+		ThrowableCollector.Factory throwableCollectorFactory, NodeExecutionAdvisor executionAdvisor) {
 
 	NodeTestTaskContext withListener(EngineExecutionListener listener) {
 		if (this.listener == listener) {
@@ -37,19 +25,4 @@ NodeTestTaskContext withListener(EngineExecutionListener listener) {
 		return new NodeTestTaskContext(listener, executorService, throwableCollectorFactory, executionAdvisor);
 	}
 
-	EngineExecutionListener getListener() {
-		return listener;
-	}
-
-	HierarchicalTestExecutorService getExecutorService() {
-		return executorService;
-	}
-
-	ThrowableCollector.Factory getThrowableCollectorFactory() {
-		return throwableCollectorFactory;
-	}
-
-	NodeExecutionAdvisor getExecutionAdvisor() {
-		return executionAdvisor;
-	}
 }
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/NodeUtils.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/NodeUtils.java
index 4f916837c32c..a624f2300efa 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/NodeUtils.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/NodeUtils.java
@@ -21,9 +21,9 @@ private NodeUtils() {
 		/* no-op */
 	}
 
-	@SuppressWarnings("unchecked")
+	@SuppressWarnings({ "unchecked", "rawtypes" })
 	static <C extends EngineExecutionContext> Node<C> asNode(TestDescriptor testDescriptor) {
-		return (testDescriptor instanceof Node ? (Node<C>) testDescriptor : noOpNode);
+		return (testDescriptor instanceof Node node ? node : noOpNode);
 	}
 
 	@SuppressWarnings("rawtypes")
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/ParallelExecutionConfiguration.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/ParallelExecutionConfiguration.java
index 15f9a3184e7e..b7cd9cb64ffe 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/ParallelExecutionConfiguration.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/ParallelExecutionConfiguration.java
@@ -16,6 +16,7 @@
 import java.util.function.Predicate;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 
 /**
  * Configuration to use for parallel test execution.
@@ -66,10 +67,10 @@ public interface ParallelExecutionConfiguration {
 	 * @return the saturate predicate to be passed to the {@code ForkJoinPool} constructor; may be {@code null}
 	 * @since 1.9
 	 * @see ForkJoinPool#ForkJoinPool(int, ForkJoinPool.ForkJoinWorkerThreadFactory, Thread.UncaughtExceptionHandler,
-	 * boolean, int, int, int, Predicate, long, TimeUnit)
+	 * boolean, int, int, int, Predicate, long, java.util.concurrent.TimeUnit)
 	 */
 	@API(status = STABLE, since = "1.11")
-	default Predicate<? super ForkJoinPool> getSaturatePredicate() {
+	default @Nullable Predicate<? super ForkJoinPool> getSaturatePredicate() {
 		return null;
 	}
 
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/ResourceLock.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/ResourceLock.java
index 4f62637aa6ef..5022d88d0101 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/ResourceLock.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/ResourceLock.java
@@ -90,6 +90,6 @@ default boolean isCompatible(ResourceLock other) {
 				.filter(resource -> ExclusiveResource.COMPARATOR.compare(resource,
 					ownResources.get(ownResources.size() - 1)) < 0);
 
-		return !(potentiallyDeadlockCausingAdditionalResource.isPresent());
+		return potentiallyDeadlockCausingAdditionalResource.isEmpty();
 	}
 }
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/SameThreadHierarchicalTestExecutorService.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/SameThreadHierarchicalTestExecutorService.java
index d6293ed7874b..aa05f4330ebb 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/SameThreadHierarchicalTestExecutorService.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/SameThreadHierarchicalTestExecutorService.java
@@ -17,6 +17,7 @@
 import java.util.concurrent.Future;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 
 /**
  * A simple {@linkplain HierarchicalTestExecutorService executor service} that
@@ -31,7 +32,8 @@ public SameThreadHierarchicalTestExecutorService() {
 	}
 
 	@Override
-	public Future<Void> submit(TestTask testTask) {
+	@SuppressWarnings("NullAway")
+	public Future<@Nullable Void> submit(TestTask testTask) {
 		testTask.execute();
 		return completedFuture(null);
 	}
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/SingleTestExecutor.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/SingleTestExecutor.java
deleted file mode 100644
index 3aa0ab4aea6b..000000000000
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/SingleTestExecutor.java
+++ /dev/null
@@ -1,83 +0,0 @@
-/*
- * Copyright 2015-2025 the original author or authors.
- *
- * All rights reserved. This program and the accompanying materials are
- * made available under the terms of the Eclipse Public License v2.0 which
- * accompanies this distribution and is available at
- *
- * https://www.eclipse.org/legal/epl-v20.html
- */
-
-package org.junit.platform.engine.support.hierarchical;
-
-import static org.apiguardian.api.API.Status.DEPRECATED;
-import static org.junit.platform.engine.TestExecutionResult.aborted;
-import static org.junit.platform.engine.TestExecutionResult.failed;
-import static org.junit.platform.engine.TestExecutionResult.successful;
-
-import org.apiguardian.api.API;
-import org.junit.platform.commons.util.UnrecoverableExceptions;
-import org.junit.platform.engine.TestExecutionResult;
-import org.opentest4j.TestAbortedException;
-
-/**
- * {@code SingleTestExecutor} encapsulates the execution of a single test
- * wrapped in an {@link Executable}.
- *
- * @since 1.0
- * @see #executeSafely(Executable)
- * @deprecated Please use {@link ThrowableCollector#execute} and
- * {@link ThrowableCollector#toTestExecutionResult} instead.
- */
-@Deprecated
-@API(status = DEPRECATED, since = "1.2")
-@SuppressWarnings("missing-explicit-ctor")
-public class SingleTestExecutor {
-
-	/**
-	 * Functional interface for a single test to be executed by
-	 * {@link SingleTestExecutor}.
-	 */
-	@FunctionalInterface
-	public interface Executable {
-
-		/**
-		 * Execute the test.
-		 *
-		 * @throws TestAbortedException to signal aborted execution
-		 * @throws Throwable to signal failure
-		 */
-		void execute() throws TestAbortedException, Throwable;
-
-	}
-
-	/**
-	 * Execute the supplied {@link Executable} and return a
-	 * {@link TestExecutionResult} based on the outcome.
-	 *
-	 * <p>If the {@code Executable} throws an <em>unrecoverable</em> exception
-	 * &mdash; for example, an {@link OutOfMemoryError} &mdash; this method will
-	 * rethrow it.
-	 *
-	 * @param executable the test to be executed
-	 * @return {@linkplain TestExecutionResult#aborted aborted} if the
-	 * {@code Executable} throws a {@link TestAbortedException};
-	 * {@linkplain TestExecutionResult#failed failed} if any other
-	 * {@link Throwable} is thrown; and {@linkplain TestExecutionResult#successful
-	 * successful} otherwise
-	 */
-	public TestExecutionResult executeSafely(Executable executable) {
-		try {
-			executable.execute();
-			return successful();
-		}
-		catch (TestAbortedException e) {
-			return aborted(e);
-		}
-		catch (Throwable t) {
-			UnrecoverableExceptions.rethrowIfUnrecoverable(t);
-			return failed(t);
-		}
-	}
-
-}
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/ThrowableCollector.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/ThrowableCollector.java
index 88e83cdb9ed5..04282d8b151e 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/ThrowableCollector.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/ThrowableCollector.java
@@ -18,6 +18,7 @@
 import java.util.function.Predicate;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.util.ExceptionUtils;
 import org.junit.platform.commons.util.Preconditions;
 import org.junit.platform.commons.util.UnrecoverableExceptions;
@@ -42,7 +43,7 @@ public class ThrowableCollector {
 
 	private final Predicate<? super Throwable> abortedExecutionPredicate;
 
-	private Throwable throwable;
+	private @Nullable Throwable throwable;
 
 	/**
 	 * Create a new {@code ThrowableCollector} that uses the supplied
@@ -121,7 +122,7 @@ else if (throwable != t) {
 	 * @see #isEmpty()
 	 * @see #assertEmpty()
 	 */
-	public Throwable getThrowable() {
+	public @Nullable Throwable getThrowable() {
 		return this.throwable;
 	}
 
@@ -157,7 +158,7 @@ public boolean isNotEmpty() {
 	 * @see ExceptionUtils#throwAsUncheckedException(Throwable)
 	 */
 	public void assertEmpty() {
-		if (!isEmpty()) {
+		if (this.throwable != null) {
 			throw ExceptionUtils.throwAsUncheckedException(this.throwable);
 		}
 	}
@@ -174,13 +175,13 @@ public void assertEmpty() {
 	 */
 	@API(status = MAINTAINED, since = "1.6")
 	public TestExecutionResult toTestExecutionResult() {
-		if (isEmpty()) {
+		if (this.throwable == null) {
 			return successful();
 		}
-		if (hasAbortedExecution(throwable)) {
-			return aborted(throwable);
+		if (hasAbortedExecution(this.throwable)) {
+			return aborted(this.throwable);
 		}
-		return failed(throwable);
+		return failed(this.throwable);
 	}
 
 	private boolean hasAbortedExecution(Throwable t) {
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/package-info.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/package-info.java
index 033745ba7795..925cfac6bfec 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/package-info.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/hierarchical/package-info.java
@@ -5,4 +5,7 @@
  * {@link org.junit.platform.engine.support.hierarchical.Node} abstraction.
  */
 
+@NullMarked
 package org.junit.platform.engine.support.hierarchical;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/store/Namespace.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/store/Namespace.java
index dcf06d571833..d18935b75c4f 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/store/Namespace.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/store/Namespace.java
@@ -13,7 +13,6 @@
 import static org.apiguardian.api.API.Status.EXPERIMENTAL;
 
 import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
 
@@ -28,7 +27,7 @@
  * mixing data between extensions or across different invocations within the
  * lifecycle of a single extension.
  */
-@API(status = EXPERIMENTAL, since = "1.13")
+@API(status = EXPERIMENTAL, since = "6.0")
 public class Namespace {
 
 	/**
@@ -48,7 +47,7 @@ public class Namespace {
 	public static Namespace create(Object... parts) {
 		Preconditions.notEmpty(parts, "parts array must not be null or empty");
 		Preconditions.containsNoNullElements(parts, "individual parts must not be null");
-		return new Namespace(Arrays.asList(parts));
+		return new Namespace(List.of(parts));
 	}
 
 	/**
@@ -68,7 +67,7 @@ public static Namespace create(List<Object> objects) {
 	private final List<Object> parts;
 
 	private Namespace(List<Object> parts) {
-		this.parts = new ArrayList<>(parts);
+		this.parts = List.copyOf(parts);
 	}
 
 	@Override
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/store/NamespacedHierarchicalStore.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/store/NamespacedHierarchicalStore.java
index bd27996973b1..72826970014a 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/store/NamespacedHierarchicalStore.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/store/NamespacedHierarchicalStore.java
@@ -11,12 +11,13 @@
 package org.junit.platform.engine.support.store;
 
 import static java.util.Comparator.comparing;
+import static java.util.Objects.requireNonNull;
 import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.junit.platform.commons.util.ReflectionUtils.getWrapperType;
 import static org.junit.platform.commons.util.ReflectionUtils.isAssignableTo;
 
 import java.util.Comparator;
-import java.util.Objects;
 import java.util.Optional;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ConcurrentMap;
@@ -25,6 +26,7 @@
 import java.util.function.Supplier;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.util.ExceptionUtils;
 import org.junit.platform.commons.util.Preconditions;
 import org.junit.platform.commons.util.UnrecoverableExceptions;
@@ -44,16 +46,16 @@
  * @param <N> Namespace type
  * @since 1.10
  */
-@API(status = EXPERIMENTAL, since = "1.10")
+@API(status = MAINTAINED, since = "1.13.3")
 public final class NamespacedHierarchicalStore<N> implements AutoCloseable {
 
 	private final AtomicInteger insertOrderSequence = new AtomicInteger();
 
 	private final ConcurrentMap<CompositeKey<N>, StoredValue> storedValues = new ConcurrentHashMap<>(4);
 
-	private final NamespacedHierarchicalStore<N> parentStore;
+	private final @Nullable NamespacedHierarchicalStore<N> parentStore;
 
-	private final CloseAction<N> closeAction;
+	private final @Nullable CloseAction<N> closeAction;
 
 	private volatile boolean closed = false;
 
@@ -62,7 +64,7 @@ public final class NamespacedHierarchicalStore<N> implements AutoCloseable {
 	 *
 	 * @param parentStore the parent store to use for lookups; may be {@code null}
 	 */
-	public NamespacedHierarchicalStore(NamespacedHierarchicalStore<N> parentStore) {
+	public NamespacedHierarchicalStore(@Nullable NamespacedHierarchicalStore<N> parentStore) {
 		this(parentStore, null);
 	}
 
@@ -73,7 +75,8 @@ public NamespacedHierarchicalStore(NamespacedHierarchicalStore<N> parentStore) {
 	 * @param closeAction the action to be called for each stored value when this
 	 * store is closed; may be {@code null}
 	 */
-	public NamespacedHierarchicalStore(NamespacedHierarchicalStore<N> parentStore, CloseAction<N> closeAction) {
+	public NamespacedHierarchicalStore(@Nullable NamespacedHierarchicalStore<N> parentStore,
+			@Nullable CloseAction<N> closeAction) {
 		this.parentStore = parentStore;
 		this.closeAction = closeAction;
 	}
@@ -94,7 +97,7 @@ public NamespacedHierarchicalStore<N> newChild() {
 	 * @return an {@code Optional} containing the parent store, or an empty {@code Optional} if there is no parent
 	 * @since 5.13
 	 */
-	@API(status = EXPERIMENTAL, since = "5.13")
+	@API(status = EXPERIMENTAL, since = "6.0")
 	public Optional<NamespacedHierarchicalStore<N>> getParent() {
 		return Optional.ofNullable(this.parentStore);
 	}
@@ -106,7 +109,7 @@ public Optional<NamespacedHierarchicalStore<N>> getParent() {
 	 * @since 1.11
 	 * @see #close()
 	 */
-	@API(status = EXPERIMENTAL, since = "1.11")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public boolean isClosed() {
 		return this.closed;
 	}
@@ -152,7 +155,7 @@ public void close() {
 	 * @throws NamespacedHierarchicalStoreException if this store has already been
 	 * closed
 	 */
-	public Object get(N namespace, Object key) {
+	public @Nullable Object get(N namespace, Object key) {
 		StoredValue storedValue = getStoredValue(new CompositeKey<>(namespace, key));
 		return StoredValue.evaluateIfNotNull(storedValue);
 	}
@@ -168,7 +171,8 @@ public Object get(N namespace, Object key) {
 	 * @throws NamespacedHierarchicalStoreException if the stored value cannot
 	 * be cast to the required type, or if this store has already been closed
 	 */
-	public <T> T get(N namespace, Object key, Class<T> requiredType) throws NamespacedHierarchicalStoreException {
+	public <T> @Nullable T get(N namespace, Object key, Class<T> requiredType)
+			throws NamespacedHierarchicalStoreException {
 		Object value = get(namespace, key);
 		return castToRequiredType(key, value, requiredType);
 	}
@@ -185,13 +189,14 @@ public <T> T get(N namespace, Object key, Class<T> requiredType) throws Namespac
 	 * @throws NamespacedHierarchicalStoreException if this store has already been
 	 * closed
 	 */
-	public <K, V> Object getOrComputeIfAbsent(N namespace, K key, Function<K, V> defaultCreator) {
+	public <K, V extends @Nullable Object> @Nullable Object getOrComputeIfAbsent(N namespace, K key,
+			Function<? super K, ? extends V> defaultCreator) {
 		Preconditions.notNull(defaultCreator, "defaultCreator must not be null");
 		CompositeKey<N> compositeKey = new CompositeKey<>(namespace, key);
 		StoredValue storedValue = getStoredValue(compositeKey);
 		if (storedValue == null) {
 			storedValue = this.storedValues.computeIfAbsent(compositeKey,
-				__ -> storedValue(new MemoizingSupplier(() -> {
+				__ -> newStoredValue(new MemoizingSupplier(() -> {
 					rejectIfClosed();
 					return defaultCreator.apply(key);
 				})));
@@ -213,7 +218,8 @@ public <K, V> Object getOrComputeIfAbsent(N namespace, K key, Function<K, V> def
 	 * @throws NamespacedHierarchicalStoreException if the stored value cannot
 	 * be cast to the required type, or if this store has already been closed
 	 */
-	public <K, V> V getOrComputeIfAbsent(N namespace, K key, Function<K, V> defaultCreator, Class<V> requiredType)
+	public <K, V extends @Nullable Object> @Nullable V getOrComputeIfAbsent(N namespace, K key,
+			Function<? super K, ? extends V> defaultCreator, Class<V> requiredType)
 			throws NamespacedHierarchicalStoreException {
 
 		Object value = getOrComputeIfAbsent(namespace, key, defaultCreator);
@@ -234,9 +240,10 @@ public <K, V> V getOrComputeIfAbsent(N namespace, K key, Function<K, V> defaultC
 	 * @throws NamespacedHierarchicalStoreException if an error occurs while
 	 * storing the value, or if this store has already been closed
 	 */
-	public Object put(N namespace, Object key, Object value) throws NamespacedHierarchicalStoreException {
+	public @Nullable Object put(N namespace, Object key, @Nullable Object value)
+			throws NamespacedHierarchicalStoreException {
 		rejectIfClosed();
-		StoredValue oldValue = this.storedValues.put(new CompositeKey<>(namespace, key), storedValue(() -> value));
+		StoredValue oldValue = this.storedValues.put(new CompositeKey<>(namespace, key), newStoredValue(() -> value));
 		return StoredValue.evaluateIfNotNull(oldValue);
 	}
 
@@ -253,7 +260,7 @@ public Object put(N namespace, Object key, Object value) throws NamespacedHierar
 	 * @throws NamespacedHierarchicalStoreException if this store has already been
 	 * closed
 	 */
-	public Object remove(N namespace, Object key) {
+	public @Nullable Object remove(N namespace, Object key) {
 		rejectIfClosed();
 		StoredValue previous = this.storedValues.remove(new CompositeKey<>(namespace, key));
 		return StoredValue.evaluateIfNotNull(previous);
@@ -273,17 +280,18 @@ public Object remove(N namespace, Object key) {
 	 * @throws NamespacedHierarchicalStoreException if the stored value cannot
 	 * be cast to the required type, or if this store has already been closed
 	 */
-	public <T> T remove(N namespace, Object key, Class<T> requiredType) throws NamespacedHierarchicalStoreException {
+	public <T> @Nullable T remove(N namespace, Object key, Class<T> requiredType)
+			throws NamespacedHierarchicalStoreException {
 		rejectIfClosed();
 		Object value = remove(namespace, key);
 		return castToRequiredType(key, value, requiredType);
 	}
 
-	private StoredValue storedValue(Supplier<Object> value) {
+	private StoredValue newStoredValue(Supplier<@Nullable Object> value) {
 		return new StoredValue(this.insertOrderSequence.getAndIncrement(), value);
 	}
 
-	private StoredValue getStoredValue(CompositeKey<N> compositeKey) {
+	private @Nullable StoredValue getStoredValue(CompositeKey<N> compositeKey) {
 		StoredValue storedValue = this.storedValues.get(compositeKey);
 		if (storedValue != null) {
 			return storedValue;
@@ -295,20 +303,20 @@ private StoredValue getStoredValue(CompositeKey<N> compositeKey) {
 	}
 
 	@SuppressWarnings("unchecked")
-	private <T> T castToRequiredType(Object key, Object value, Class<T> requiredType) {
+	private <T> @Nullable T castToRequiredType(Object key, @Nullable Object value, Class<T> requiredType) {
 		Preconditions.notNull(requiredType, "requiredType must not be null");
 		if (value == null) {
 			return null;
 		}
 		if (isAssignableTo(value, requiredType)) {
 			if (requiredType.isPrimitive()) {
-				return (T) getWrapperType(requiredType).cast(value);
+				return (T) requireNonNull(getWrapperType(requiredType)).cast(value);
 			}
 			return requiredType.cast(value);
 		}
 		// else
 		throw new NamespacedHierarchicalStoreException(
-			String.format("Object stored under key [%s] is not of required type [%s], but was [%s]: %s", key,
+			"Object stored under key [%s] is not of required type [%s], but was [%s]: %s".formatted(key,
 				requiredType.getName(), value.getClass().getName(), value));
 	}
 
@@ -319,46 +327,18 @@ private void rejectIfClosed() {
 		}
 	}
 
-	private static class CompositeKey<N> {
-
-		private final N namespace;
-		private final Object key;
-
-		private CompositeKey(N namespace, Object key) {
-			this.namespace = Preconditions.notNull(namespace, "namespace must not be null");
-			this.key = Preconditions.notNull(key, "key must not be null");
-		}
-
-		@Override
-		public boolean equals(Object o) {
-			if (this == o) {
-				return true;
-			}
-			if (o == null || getClass() != o.getClass()) {
-				return false;
-			}
-			CompositeKey<?> that = (CompositeKey<?>) o;
-			return this.namespace.equals(that.namespace) && this.key.equals(that.key);
-		}
+	private record CompositeKey<N>(N namespace, Object key) {
 
-		@Override
-		public int hashCode() {
-			return Objects.hash(this.namespace, this.key);
+		CompositeKey {
+			Preconditions.notNull(namespace, "namespace must not be null");
+			Preconditions.notNull(key, "key must not be null");
 		}
 
 	}
 
-	private static class StoredValue {
+	private record StoredValue(int order, Supplier<@Nullable Object> supplier) {
 
-		private final int order;
-		private final Supplier<Object> supplier;
-
-		StoredValue(int order, Supplier<Object> supplier) {
-			this.order = order;
-			this.supplier = supplier;
-		}
-
-		private <N> EvaluatedValue<N> evaluateSafely(CompositeKey<N> compositeKey) {
+		private <N> @Nullable EvaluatedValue<N> evaluateSafely(CompositeKey<N> compositeKey) {
 			try {
 				return new EvaluatedValue<>(compositeKey, this.order, evaluate());
 			}
@@ -368,33 +348,25 @@ private <N> EvaluatedValue<N> evaluateSafely(CompositeKey<N> compositeKey) {
 			}
 		}
 
-		private Object evaluate() {
+		private @Nullable Object evaluate() {
 			return this.supplier.get();
 		}
 
-		static Object evaluateIfNotNull(StoredValue value) {
+		static @Nullable Object evaluateIfNotNull(@Nullable StoredValue value) {
 			return value != null ? value.evaluate() : null;
 		}
 
 	}
 
-	private static class EvaluatedValue<N> {
+	private record EvaluatedValue<N>(CompositeKey<N> compositeKey, int order, @Nullable Object value) {
 
 		private static final Comparator<EvaluatedValue<?>> REVERSE_INSERT_ORDER = comparing(
 			(EvaluatedValue<?> it) -> it.order).reversed();
 
-		private final CompositeKey<N> compositeKey;
-		private final int order;
-		private final Object value;
-
-		private EvaluatedValue(CompositeKey<N> compositeKey, int order, Object value) {
-			this.compositeKey = compositeKey;
-			this.order = order;
-			this.value = value;
-		}
-
 		private void close(CloseAction<N> closeAction) throws Throwable {
-			closeAction.close(this.compositeKey.namespace, this.compositeKey.key, this.value);
+			if (this.value != null) {
+				closeAction.close(this.compositeKey.namespace, this.compositeKey.key, this.value);
+			}
 		}
 
 	}
@@ -408,24 +380,26 @@ private void close(CloseAction<N> closeAction) throws Throwable {
 	 *
 	 * @see StoredValue
 	 */
-	private static class MemoizingSupplier implements Supplier<Object> {
+	private static class MemoizingSupplier implements Supplier<@Nullable Object> {
 
 		private static final Object NO_VALUE_SET = new Object();
 
-		private final Supplier<Object> delegate;
+		private final Supplier<@Nullable Object> delegate;
+
+		@Nullable
 		private volatile Object value = NO_VALUE_SET;
 
-		private MemoizingSupplier(Supplier<Object> delegate) {
+		private MemoizingSupplier(Supplier<@Nullable Object> delegate) {
 			this.delegate = delegate;
 		}
 
 		@Override
-		public Object get() {
+		public @Nullable Object get() {
 			if (this.value == NO_VALUE_SET) {
 				computeValue();
 			}
-			if (this.value instanceof Failure) {
-				throw ExceptionUtils.throwAsUncheckedException(((Failure) this.value).throwable);
+			if (this.value instanceof Failure failure) {
+				throw ExceptionUtils.throwAsUncheckedException(failure.throwable);
 			}
 			return this.value;
 		}
@@ -442,13 +416,7 @@ private synchronized void computeValue() {
 			}
 		}
 
-		private static class Failure {
-
-			private final Throwable throwable;
-
-			public Failure(Throwable throwable) {
-				this.throwable = throwable;
-			}
+		private record Failure(Throwable throwable) {
 		}
 
 	}
@@ -461,11 +429,11 @@ public Failure(Throwable throwable) {
 	@FunctionalInterface
 	public interface CloseAction<N> {
 
-		@API(status = EXPERIMENTAL, since = "1.13")
+		@API(status = EXPERIMENTAL, since = "6.0")
 		static <N> CloseAction<N> closeAutoCloseables() {
 			return (__, ___, value) -> {
-				if (value instanceof AutoCloseable) {
-					((AutoCloseable) value).close();
+				if (value instanceof AutoCloseable closeable) {
+					closeable.close();
 				}
 			};
 		}
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/store/NamespacedHierarchicalStoreException.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/store/NamespacedHierarchicalStoreException.java
index 2e67f3d203f4..7b8144739f8a 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/store/NamespacedHierarchicalStoreException.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/store/NamespacedHierarchicalStoreException.java
@@ -10,7 +10,9 @@
 
 package org.junit.platform.engine.support.store;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
+
+import java.io.Serial;
 
 import org.apiguardian.api.API;
 import org.junit.platform.commons.JUnitException;
@@ -20,9 +22,10 @@
  *
  * @since 1.10
  */
-@API(status = EXPERIMENTAL, since = "1.10")
+@API(status = MAINTAINED, since = "1.13.3")
 public class NamespacedHierarchicalStoreException extends JUnitException {
 
+	@Serial
 	private static final long serialVersionUID = 1L;
 
 	public NamespacedHierarchicalStoreException(String message) {
diff --git a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/store/package-info.java b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/store/package-info.java
index d40e1e88e974..e754a7b508de 100644
--- a/junit-platform-engine/src/main/java/org/junit/platform/engine/support/store/package-info.java
+++ b/junit-platform-engine/src/main/java/org/junit/platform/engine/support/store/package-info.java
@@ -2,4 +2,7 @@
  * Reusable data structures for test engines and their extensions.
  */
 
+@NullMarked
 package org.junit.platform.engine.support.store;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-platform-engine/src/testFixtures/java/org/junit/platform/engine/support/hierarchical/DemoEngineExecutionContext.java b/junit-platform-engine/src/testFixtures/java/org/junit/platform/engine/support/hierarchical/DemoEngineExecutionContext.java
index 2bb72762e96d..eb6f00ff5ec3 100644
--- a/junit-platform-engine/src/testFixtures/java/org/junit/platform/engine/support/hierarchical/DemoEngineExecutionContext.java
+++ b/junit-platform-engine/src/testFixtures/java/org/junit/platform/engine/support/hierarchical/DemoEngineExecutionContext.java
@@ -15,12 +15,5 @@
 /**
  * @since 1.0
  */
-public class DemoEngineExecutionContext implements EngineExecutionContext {
-
-	public final ExecutionRequest request;
-
-	public DemoEngineExecutionContext(ExecutionRequest request) {
-		this.request = request;
-	}
-
+public record DemoEngineExecutionContext(ExecutionRequest request) implements EngineExecutionContext {
 }
diff --git a/junit-platform-engine/src/testFixtures/java/org/junit/platform/engine/support/hierarchical/DemoHierarchicalContainerDescriptor.java b/junit-platform-engine/src/testFixtures/java/org/junit/platform/engine/support/hierarchical/DemoHierarchicalContainerDescriptor.java
index 00ead8e16784..1a5b9c20c7ac 100644
--- a/junit-platform-engine/src/testFixtures/java/org/junit/platform/engine/support/hierarchical/DemoHierarchicalContainerDescriptor.java
+++ b/junit-platform-engine/src/testFixtures/java/org/junit/platform/engine/support/hierarchical/DemoHierarchicalContainerDescriptor.java
@@ -12,6 +12,7 @@
 
 import static org.junit.platform.engine.support.hierarchical.Node.SkipResult.doNotSkip;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.engine.TestSource;
 import org.junit.platform.engine.UniqueId;
 import org.junit.platform.engine.support.descriptor.AbstractTestDescriptor;
@@ -22,10 +23,10 @@
 public class DemoHierarchicalContainerDescriptor extends AbstractTestDescriptor
 		implements Node<DemoEngineExecutionContext> {
 
-	private final Runnable beforeBlock;
+	private final @Nullable Runnable beforeBlock;
 
-	public DemoHierarchicalContainerDescriptor(UniqueId uniqueId, String displayName, TestSource source,
-			Runnable beforeBlock) {
+	public DemoHierarchicalContainerDescriptor(UniqueId uniqueId, String displayName, @Nullable TestSource source,
+			@Nullable Runnable beforeBlock) {
 		super(uniqueId, displayName, source);
 		this.beforeBlock = beforeBlock;
 	}
diff --git a/junit-platform-engine/src/testFixtures/java/org/junit/platform/engine/support/hierarchical/DemoHierarchicalEngineDescriptor.java b/junit-platform-engine/src/testFixtures/java/org/junit/platform/engine/support/hierarchical/DemoHierarchicalEngineDescriptor.java
index 5dd40c886bbb..519128ce7459 100644
--- a/junit-platform-engine/src/testFixtures/java/org/junit/platform/engine/support/hierarchical/DemoHierarchicalEngineDescriptor.java
+++ b/junit-platform-engine/src/testFixtures/java/org/junit/platform/engine/support/hierarchical/DemoHierarchicalEngineDescriptor.java
@@ -13,6 +13,7 @@
 import static org.junit.platform.engine.support.hierarchical.Node.SkipResult.doNotSkip;
 import static org.junit.platform.engine.support.hierarchical.Node.SkipResult.skip;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.engine.UniqueId;
 import org.junit.platform.engine.support.descriptor.EngineDescriptor;
 
@@ -21,7 +22,8 @@
  */
 public class DemoHierarchicalEngineDescriptor extends EngineDescriptor implements Node<DemoEngineExecutionContext> {
 
-	private String skippedReason;
+	private @Nullable String skippedReason;
+
 	private boolean skipped;
 	private Runnable beforeAllBehavior = () -> {
 	};
diff --git a/junit-platform-engine/src/testFixtures/java/org/junit/platform/engine/support/hierarchical/DemoHierarchicalTestDescriptor.java b/junit-platform-engine/src/testFixtures/java/org/junit/platform/engine/support/hierarchical/DemoHierarchicalTestDescriptor.java
index 29b57733512a..8cb70bd68d0c 100644
--- a/junit-platform-engine/src/testFixtures/java/org/junit/platform/engine/support/hierarchical/DemoHierarchicalTestDescriptor.java
+++ b/junit-platform-engine/src/testFixtures/java/org/junit/platform/engine/support/hierarchical/DemoHierarchicalTestDescriptor.java
@@ -15,6 +15,7 @@
 
 import java.util.function.BiConsumer;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.engine.TestDescriptor;
 import org.junit.platform.engine.TestSource;
 import org.junit.platform.engine.UniqueId;
@@ -25,17 +26,19 @@
  */
 public class DemoHierarchicalTestDescriptor extends AbstractTestDescriptor implements Node<DemoEngineExecutionContext> {
 
-	private final BiConsumer<DemoEngineExecutionContext, TestDescriptor> executeBlock;
-	private String skippedReason;
+	private final @Nullable BiConsumer<DemoEngineExecutionContext, TestDescriptor> executeBlock;
+
+	private @Nullable String skippedReason;
+
 	private boolean skipped;
 
 	public DemoHierarchicalTestDescriptor(UniqueId uniqueId, String displayName,
-			BiConsumer<DemoEngineExecutionContext, TestDescriptor> executeBlock) {
+			@Nullable BiConsumer<DemoEngineExecutionContext, TestDescriptor> executeBlock) {
 		this(uniqueId, displayName, null, executeBlock);
 	}
 
-	public DemoHierarchicalTestDescriptor(UniqueId uniqueId, String displayName, TestSource source,
-			BiConsumer<DemoEngineExecutionContext, TestDescriptor> executeBlock) {
+	public DemoHierarchicalTestDescriptor(UniqueId uniqueId, String displayName, @Nullable TestSource source,
+			@Nullable BiConsumer<DemoEngineExecutionContext, TestDescriptor> executeBlock) {
 		super(uniqueId, displayName, source);
 		this.executeBlock = executeBlock;
 	}
diff --git a/junit-platform-engine/src/testFixtures/java/org/junit/platform/engine/support/hierarchical/DemoHierarchicalTestEngine.java b/junit-platform-engine/src/testFixtures/java/org/junit/platform/engine/support/hierarchical/DemoHierarchicalTestEngine.java
index ff5e32299dde..e381e3504380 100644
--- a/junit-platform-engine/src/testFixtures/java/org/junit/platform/engine/support/hierarchical/DemoHierarchicalTestEngine.java
+++ b/junit-platform-engine/src/testFixtures/java/org/junit/platform/engine/support/hierarchical/DemoHierarchicalTestEngine.java
@@ -13,6 +13,7 @@
 import java.util.function.BiConsumer;
 import java.util.function.Function;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.engine.EngineDiscoveryRequest;
 import org.junit.platform.engine.ExecutionRequest;
 import org.junit.platform.engine.TestDescriptor;
@@ -61,7 +62,8 @@ public DemoHierarchicalTestDescriptor addTest(String uniqueName, String displayN
 			"test");
 	}
 
-	public DemoHierarchicalContainerDescriptor addContainer(String uniqueName, String displayName, TestSource source) {
+	public DemoHierarchicalContainerDescriptor addContainer(String uniqueName, String displayName,
+			@Nullable TestSource source) {
 		return addContainer(uniqueName, displayName, source, null);
 	}
 
@@ -69,8 +71,8 @@ public DemoHierarchicalContainerDescriptor addContainer(String uniqueName, Runna
 		return addContainer(uniqueName, uniqueName, null, beforeBlock);
 	}
 
-	public DemoHierarchicalContainerDescriptor addContainer(String uniqueName, String displayName, TestSource source,
-			Runnable beforeBlock) {
+	public DemoHierarchicalContainerDescriptor addContainer(String uniqueName, String displayName,
+			@Nullable TestSource source, @Nullable Runnable beforeBlock) {
 
 		return addChild(uniqueName,
 			uniqueId -> new DemoHierarchicalContainerDescriptor(uniqueId, displayName, source, beforeBlock),
diff --git a/junit-platform-engine/src/testFixtures/java/org/junit/platform/fakes/TestEngineSpy.java b/junit-platform-engine/src/testFixtures/java/org/junit/platform/fakes/TestEngineSpy.java
index 7754c75f411b..67a1c34a99d2 100644
--- a/junit-platform-engine/src/testFixtures/java/org/junit/platform/fakes/TestEngineSpy.java
+++ b/junit-platform-engine/src/testFixtures/java/org/junit/platform/fakes/TestEngineSpy.java
@@ -10,6 +10,7 @@
 
 package org.junit.platform.fakes;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.engine.EngineDiscoveryRequest;
 import org.junit.platform.engine.ExecutionRequest;
 import org.junit.platform.engine.TestDescriptor;
@@ -23,7 +24,7 @@ public class TestEngineSpy implements TestEngine {
 
 	private final String id;
 
-	public ExecutionRequest requestForExecution;
+	public @Nullable ExecutionRequest requestForExecution;
 
 	public TestEngineSpy() {
 		this(TestEngineSpy.class.getSimpleName());
diff --git a/junit-platform-engine/src/testFixtures/java/org/junit/platform/fakes/package-info.java b/junit-platform-engine/src/testFixtures/java/org/junit/platform/fakes/package-info.java
new file mode 100644
index 000000000000..fae5df1a599a
--- /dev/null
+++ b/junit-platform-engine/src/testFixtures/java/org/junit/platform/fakes/package-info.java
@@ -0,0 +1,5 @@
+
+@NullMarked
+package org.junit.platform.fakes;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-platform-jfr/junit-platform-jfr.gradle.kts b/junit-platform-jfr/junit-platform-jfr.gradle.kts
deleted file mode 100644
index 0f03e2b99f86..000000000000
--- a/junit-platform-jfr/junit-platform-jfr.gradle.kts
+++ /dev/null
@@ -1,37 +0,0 @@
-plugins {
-	id("junitbuild.java-library-conventions")
-}
-
-description = "JUnit Platform Flight Recorder Support"
-
-dependencies {
-	api(platform(projects.junitBom))
-	api(projects.junitPlatformLauncher)
-
-	compileOnlyApi(libs.apiguardian)
-
-	if (java.toolchain.implementation.orNull == JvmImplementation.J9) {
-		compileOnly(libs.jfrPolyfill) {
-			because("OpenJ9 does not include JFR")
-		}
-	}
-
-	osgiVerification(projects.junitJupiterEngine)
-	osgiVerification(projects.junitPlatformLauncher)
-}
-
-javaLibrary {
-	// --release 8 does not support jdk.jfr even though it was backported
-	configureRelease = false
-}
-
-tasks {
-	compileJava {
-		javaCompiler = project.javaToolchains.compilerFor {
-			languageVersion = JavaLanguageVersion.of(8)
-		}
-	}
-	compileModule {
-		options.release = 11
-	}
-}
diff --git a/junit-platform-jfr/src/main/java/org/junit/platform/jfr/package-info.java b/junit-platform-jfr/src/main/java/org/junit/platform/jfr/package-info.java
deleted file mode 100644
index 0a8c981374f7..000000000000
--- a/junit-platform-jfr/src/main/java/org/junit/platform/jfr/package-info.java
+++ /dev/null
@@ -1,5 +0,0 @@
-/**
- * Java Flight Recorder support package.
- */
-
-package org.junit.platform.jfr;
diff --git a/junit-platform-jfr/src/main/resources/META-INF/services/org.junit.platform.launcher.LauncherDiscoveryListener b/junit-platform-jfr/src/main/resources/META-INF/services/org.junit.platform.launcher.LauncherDiscoveryListener
deleted file mode 100644
index de4e472c48e7..000000000000
--- a/junit-platform-jfr/src/main/resources/META-INF/services/org.junit.platform.launcher.LauncherDiscoveryListener
+++ /dev/null
@@ -1 +0,0 @@
-org.junit.platform.jfr.FlightRecordingDiscoveryListener
diff --git a/junit-platform-jfr/src/main/resources/META-INF/services/org.junit.platform.launcher.TestExecutionListener b/junit-platform-jfr/src/main/resources/META-INF/services/org.junit.platform.launcher.TestExecutionListener
deleted file mode 100644
index 35571863ed87..000000000000
--- a/junit-platform-jfr/src/main/resources/META-INF/services/org.junit.platform.launcher.TestExecutionListener
+++ /dev/null
@@ -1 +0,0 @@
-org.junit.platform.jfr.FlightRecordingExecutionListener
diff --git a/junit-platform-jfr/src/module/org.junit.platform.jfr/module-info.java b/junit-platform-jfr/src/module/org.junit.platform.jfr/module-info.java
deleted file mode 100644
index 6f38bf063cf7..000000000000
--- a/junit-platform-jfr/src/module/org.junit.platform.jfr/module-info.java
+++ /dev/null
@@ -1,32 +0,0 @@
-/*
- * Copyright 2015-2025 the original author or authors.
- *
- * All rights reserved. This program and the accompanying materials are
- * made available under the terms of the Eclipse Public License v2.0 which
- * accompanies this distribution and is available at
- *
- * https://www.eclipse.org/legal/epl-v20.html
- */
-
-/**
- * Provides Java Flight Recorder events for the JUnit Platform.
- *
- * <p>The Flight Recording Listener module implements a
- * {@link org.junit.platform.launcher.LauncherDiscoveryListener} and a
- * {@link org.junit.platform.launcher.TestExecutionListener} that generate Java
- * Flight Recorder (JFR) events.
- *
- * @see <a href="https://openjdk.java.net/jeps/328">JEP 328: Flight Recorder</a>
- * @since 1.7
- */
-module org.junit.platform.jfr {
-	requires jdk.jfr;
-	requires static org.apiguardian.api;
-	requires org.junit.platform.engine;
-	requires org.junit.platform.launcher;
-
-	provides org.junit.platform.launcher.LauncherDiscoveryListener
-			with org.junit.platform.jfr.FlightRecordingDiscoveryListener;
-	provides org.junit.platform.launcher.TestExecutionListener
-			with org.junit.platform.jfr.FlightRecordingExecutionListener;
-}
diff --git a/junit-platform-jfr/src/test/README.md b/junit-platform-jfr/src/test/README.md
deleted file mode 100644
index 6e2fd0b363f0..000000000000
--- a/junit-platform-jfr/src/test/README.md
+++ /dev/null
@@ -1 +0,0 @@
-For compatibility with the Eclipse IDE, the test for this module are in the `platform-tests` project.
diff --git a/junit-platform-launcher/junit-platform-launcher.gradle.kts b/junit-platform-launcher/junit-platform-launcher.gradle.kts
index a9b3630762c8..dd6a9ff2a991 100644
--- a/junit-platform-launcher/junit-platform-launcher.gradle.kts
+++ b/junit-platform-launcher/junit-platform-launcher.gradle.kts
@@ -1,5 +1,6 @@
 plugins {
 	id("junitbuild.java-library-conventions")
+	id("junitbuild.java-nullability-conventions")
 	`java-test-fixtures`
 }
 
@@ -10,6 +11,7 @@ dependencies {
 	api(projects.junitPlatformEngine)
 
 	compileOnlyApi(libs.apiguardian)
+	compileOnly(libs.jspecify)
 
 	osgiVerification(projects.junitJupiterEngine)
 }
diff --git a/junit-platform-launcher/src/module/org.junit.platform.launcher/module-info.java b/junit-platform-launcher/src/main/java/module-info.java
similarity index 96%
rename from junit-platform-launcher/src/module/org.junit.platform.launcher/module-info.java
rename to junit-platform-launcher/src/main/java/module-info.java
index e4e492183f5a..d449031ae040 100644
--- a/junit-platform-launcher/src/module/org.junit.platform.launcher/module-info.java
+++ b/junit-platform-launcher/src/main/java/module-info.java
@@ -22,8 +22,12 @@
  * @uses org.junit.platform.launcher.TestExecutionListener
  */
 module org.junit.platform.launcher {
-	requires transitive java.logging;
+
 	requires static transitive org.apiguardian.api;
+	requires static org.jspecify;
+	requires static jdk.jfr;
+
+	requires transitive java.logging;
 	requires transitive org.junit.platform.commons;
 	requires transitive org.junit.platform.engine;
 
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/AbstractMethodFilter.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/AbstractMethodFilter.java
index 9ac17deea90c..74792aa35e86 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/AbstractMethodFilter.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/AbstractMethodFilter.java
@@ -11,13 +11,13 @@
 package org.junit.platform.launcher;
 
 import static java.util.stream.Collectors.joining;
-import static java.util.stream.Collectors.toList;
 
 import java.util.Arrays;
 import java.util.List;
 import java.util.Optional;
 import java.util.regex.Pattern;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.util.Preconditions;
 import org.junit.platform.commons.util.ReflectionUtils;
 import org.junit.platform.engine.TestDescriptor;
@@ -38,20 +38,20 @@ abstract class AbstractMethodFilter implements MethodFilter {
 	AbstractMethodFilter(String... patterns) {
 		Preconditions.notEmpty(patterns, "patterns array must not be null or empty");
 		Preconditions.containsNoNullElements(patterns, "patterns array must not contain null elements");
-		this.patterns = Arrays.stream(patterns).map(Pattern::compile).collect(toList());
+		this.patterns = Arrays.stream(patterns).map(Pattern::compile).toList();
 		this.patternDescription = Arrays.stream(patterns).collect(joining("' OR '", "'", "'"));
 	}
 
-	protected Optional<Pattern> findMatchingPattern(String methodName) {
+	protected Optional<Pattern> findMatchingPattern(@Nullable String methodName) {
 		if (methodName == null) {
 			return Optional.empty();
 		}
 		return this.patterns.stream().filter(pattern -> pattern.matcher(methodName).matches()).findAny();
 	}
 
-	protected String getFullyQualifiedMethodNameFromDescriptor(TestDescriptor descriptor) {
+	protected @Nullable String getFullyQualifiedMethodNameFromDescriptor(TestDescriptor descriptor) {
 		return descriptor.getSource() //
-				.filter(source -> source instanceof MethodSource) //
+				.filter(MethodSource.class::isInstance) //
 				.map(methodSource -> getFullyQualifiedMethodNameWithoutParameters(((MethodSource) methodSource))) //
 				.orElse(null);
 	}
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/EngineDiscoveryResult.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/EngineDiscoveryResult.java
index b3c104b57fa2..5625715ad0dd 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/EngineDiscoveryResult.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/EngineDiscoveryResult.java
@@ -15,6 +15,7 @@
 import java.util.Optional;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.util.ToStringBuilder;
 
 /**
@@ -66,14 +67,15 @@ public static EngineDiscoveryResult successful() {
 	 * {@code null}
 	 * @return the {@code EngineDiscoveryResult}; never {@code null}
 	 */
-	public static EngineDiscoveryResult failed(Throwable throwable) {
+	public static EngineDiscoveryResult failed(@Nullable Throwable throwable) {
 		return new EngineDiscoveryResult(Status.FAILED, throwable);
 	}
 
 	private final Status status;
-	private final Throwable throwable;
 
-	private EngineDiscoveryResult(Status status, Throwable throwable) {
+	private final @Nullable Throwable throwable;
+
+	private EngineDiscoveryResult(Status status, @Nullable Throwable throwable) {
 		this.status = status;
 		this.throwable = throwable;
 	}
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/EngineFilter.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/EngineFilter.java
index 8dd34af794aa..6c8c7363fb86 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/EngineFilter.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/EngineFilter.java
@@ -10,7 +10,6 @@
 
 package org.junit.platform.launcher;
 
-import static java.util.stream.Collectors.toList;
 import static org.apiguardian.api.API.Status.INTERNAL;
 import static org.apiguardian.api.API.Status.STABLE;
 import static org.junit.platform.engine.FilterResult.includedIf;
@@ -128,20 +127,19 @@ public FilterResult apply(TestEngine testEngine) {
 
 		if (this.type == Type.INCLUDE) {
 			return includedIf(this.engineIds.stream().anyMatch(engineId::equals), //
-				() -> String.format("Engine ID [%s] is in included list [%s]", engineId, this.engineIds), //
-				() -> String.format("Engine ID [%s] is not in included list [%s]", engineId, this.engineIds));
+				() -> "Engine ID [%s] is in included list [%s]".formatted(engineId, this.engineIds), //
+				() -> "Engine ID [%s] is not in included list [%s]".formatted(engineId, this.engineIds));
 		}
 		else {
 			return includedIf(this.engineIds.stream().noneMatch(engineId::equals), //
-				() -> String.format("Engine ID [%s] is not in excluded list [%s]", engineId, this.engineIds), //
-				() -> String.format("Engine ID [%s] is in excluded list [%s]", engineId, this.engineIds));
+				() -> "Engine ID [%s] is not in excluded list [%s]".formatted(engineId, this.engineIds), //
+				() -> "Engine ID [%s] is in excluded list [%s]".formatted(engineId, this.engineIds));
 		}
 	}
 
 	@Override
 	public String toString() {
-		return String.format("%s that %s engines with IDs %s", getClass().getSimpleName(), this.type.verb,
-			this.engineIds);
+		return "%s that %s engines with IDs %s".formatted(getClass().getSimpleName(), this.type.verb, this.engineIds);
 	}
 
 	private static List<String> validateAndTrim(List<String> engineIds) {
@@ -151,7 +149,7 @@ private static List<String> validateAndTrim(List<String> engineIds) {
 		return engineIds.stream()
 				.map(id -> Preconditions.notBlank(id, "engine ID must not be null or blank").trim())
 				.distinct()
-				.collect(toList());
+				.toList();
 		// @formatter:on
 	}
 
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/ExcludeMethodFilter.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/ExcludeMethodFilter.java
index b9b46d764a2e..0466277e0894 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/ExcludeMethodFilter.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/ExcludeMethodFilter.java
@@ -15,6 +15,7 @@
 
 import java.util.regex.Pattern;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.engine.FilterResult;
 import org.junit.platform.engine.TestDescriptor;
 
@@ -41,18 +42,17 @@ public FilterResult apply(TestDescriptor descriptor) {
 				.orElseGet(() -> included(formatInclusionReason(methodName)));
 	}
 
-	private String formatInclusionReason(String methodName) {
-		return String.format("Method name [%s] does not match any excluded pattern: %s", methodName,
-			patternDescription);
+	private String formatInclusionReason(@Nullable String methodName) {
+		return "Method name [%s] does not match any excluded pattern: %s".formatted(methodName, patternDescription);
 	}
 
-	private String formatExclusionReason(String methodName, Pattern pattern) {
-		return String.format("Method name [%s] matches excluded pattern: '%s'", methodName, pattern);
+	private String formatExclusionReason(@Nullable String methodName, Pattern pattern) {
+		return "Method name [%s] matches excluded pattern: '%s'".formatted(methodName, pattern);
 	}
 
 	@Override
 	public String toString() {
-		return String.format("%s that excludes method names that match one of the following regular expressions: %s",
+		return "%s that excludes method names that match one of the following regular expressions: %s".formatted(
 			getClass().getSimpleName(), patternDescription);
 	}
 }
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/IncludeMethodFilter.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/IncludeMethodFilter.java
index 30d943bfcf94..ff0c979f53a4 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/IncludeMethodFilter.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/IncludeMethodFilter.java
@@ -15,6 +15,7 @@
 
 import java.util.regex.Pattern;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.engine.FilterResult;
 import org.junit.platform.engine.TestDescriptor;
 
@@ -41,18 +42,17 @@ public FilterResult apply(TestDescriptor descriptor) {
 				.orElseGet(() -> excluded(formatExclusionReason(methodName)));
 	}
 
-	private String formatInclusionReason(String methodName, Pattern pattern) {
-		return String.format("Method name [%s] matches included pattern: '%s'", methodName, pattern);
+	private String formatInclusionReason(@Nullable String methodName, Pattern pattern) {
+		return "Method name [%s] matches included pattern: '%s'".formatted(methodName, pattern);
 	}
 
-	private String formatExclusionReason(String methodName) {
-		return String.format("Method name [%s] does not match any included pattern: %s", methodName,
-			patternDescription);
+	private String formatExclusionReason(@Nullable String methodName) {
+		return "Method name [%s] does not match any included pattern: %s".formatted(methodName, patternDescription);
 	}
 
 	@Override
 	public String toString() {
-		return String.format("%s that includes method names that match one of the following regular expressions: %s",
+		return "%s that includes method names that match one of the following regular expressions: %s".formatted(
 			getClass().getSimpleName(), patternDescription);
 	}
 }
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/LauncherConstants.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/LauncherConstants.java
index a18a71b45c74..b13d4abd13a0 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/LauncherConstants.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/LauncherConstants.java
@@ -11,6 +11,7 @@
 package org.junit.platform.launcher;
 
 import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
 
 import org.apiguardian.api.API;
@@ -162,7 +163,7 @@ public class LauncherConstants {
 	 *
 	 * @see LauncherInterceptor
 	 */
-	@API(status = EXPERIMENTAL, since = "1.10")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public static final String ENABLE_LAUNCHER_INTERCEPTORS = "junit.platform.launcher.interceptors.enabled";
 
 	/**
@@ -178,7 +179,7 @@ public class LauncherConstants {
 	 *
 	 * <p>Value must be either {@code true} or {@code false}; defaults to {@code false}.
 	 */
-	@API(status = EXPERIMENTAL, since = "1.10")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public static final String DRY_RUN_PROPERTY_NAME = "junit.platform.execution.dryRun.enabled";
 
 	/**
@@ -188,7 +189,7 @@ public class LauncherConstants {
 	 *
 	 * @see org.junit.platform.launcher.core.EngineExecutionOrchestrator
 	 */
-	@API(status = EXPERIMENTAL, since = "1.10")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public static final String STACKTRACE_PRUNING_ENABLED_PROPERTY_NAME = "junit.platform.stacktrace.pruning.enabled";
 
 	/**
@@ -202,7 +203,7 @@ public class LauncherConstants {
 	 * @see #OUTPUT_DIR_UNIQUE_NUMBER_PLACEHOLDER
 	 * @see org.junit.platform.engine.reporting.OutputDirectoryProvider
 	 */
-	@API(status = EXPERIMENTAL, since = "1.12")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public static final String OUTPUT_DIR_PROPERTY_NAME = "junit.platform.reporting.output.dir";
 
 	/**
@@ -216,7 +217,7 @@ public class LauncherConstants {
 	 * @since 1.12
 	 * @see #OUTPUT_DIR_PROPERTY_NAME
 	 */
-	@API(status = EXPERIMENTAL, since = "1.12")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public static final String OUTPUT_DIR_UNIQUE_NUMBER_PLACEHOLDER = "{uniqueNumber}";
 
 	/**
@@ -242,7 +243,7 @@ public class LauncherConstants {
 	 * @since 1.13
 	 * @see org.junit.platform.engine.DiscoveryIssue.Severity
 	 */
-	@API(status = EXPERIMENTAL, since = "1.13")
+	@API(status = EXPERIMENTAL, since = "6.0")
 	public static final String CRITICAL_DISCOVERY_ISSUE_SEVERITY_PROPERTY_NAME = "junit.platform.discovery.issue.severity.critical";
 
 	/**
@@ -263,7 +264,7 @@ public class LauncherConstants {
 	 * @since 1.13
 	 * @see #CRITICAL_DISCOVERY_ISSUE_SEVERITY_PROPERTY_NAME
 	 */
-	@API(status = EXPERIMENTAL, since = "1.13")
+	@API(status = EXPERIMENTAL, since = "6.0")
 	public static final String DISCOVERY_ISSUE_FAILURE_PHASE_PROPERTY_NAME = "junit.platform.discovery.issue.failure.phase";
 
 	private LauncherConstants() {
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/LauncherInterceptor.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/LauncherInterceptor.java
index 490ac65483a2..30746a6d052f 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/LauncherInterceptor.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/LauncherInterceptor.java
@@ -10,9 +10,10 @@
 
 package org.junit.platform.launcher;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 
 /**
  * Interceptor for test discovery and execution by a {@link Launcher} in the
@@ -52,7 +53,7 @@
  * @see LauncherSession
  * @see LauncherConstants#ENABLE_LAUNCHER_INTERCEPTORS
  */
-@API(status = EXPERIMENTAL, since = "1.10")
+@API(status = MAINTAINED, since = "1.13.3")
 public interface LauncherInterceptor {
 
 	/**
@@ -63,7 +64,7 @@ public interface LauncherInterceptor {
 	 * @param invocation the intercepted invocation; never {@code null}
 	 * @return the result of the invocation
 	 */
-	<T> T intercept(Invocation<T> invocation);
+	<T extends @Nullable Object> T intercept(Invocation<T> invocation);
 
 	/**
 	 * Closes this interceptor.
@@ -78,7 +79,7 @@ public interface LauncherInterceptor {
 	 *
 	 * <p>This interface is not intended to be implemented by clients.
 	 */
-	interface Invocation<T> {
+	interface Invocation<T extends @Nullable Object> {
 		T proceed();
 	}
 
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/LauncherSession.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/LauncherSession.java
index 285621b59812..9deea873387b 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/LauncherSession.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/LauncherSession.java
@@ -10,7 +10,7 @@
 
 package org.junit.platform.launcher;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
 
 import org.apiguardian.api.API;
@@ -62,7 +62,7 @@ public interface LauncherSession extends AutoCloseable {
 	 * @since 1.13
 	 * @see NamespacedHierarchicalStore
 	 */
-	@API(status = EXPERIMENTAL, since = "1.13")
+	@API(status = MAINTAINED, since = "1.13.3")
 	NamespacedHierarchicalStore<Namespace> getStore();
 
 }
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/MethodFilter.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/MethodFilter.java
index cff14852ed79..91d1b1f0baae 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/MethodFilter.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/MethodFilter.java
@@ -10,7 +10,7 @@
 
 package org.junit.platform.launcher;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import java.lang.reflect.Method;
 import java.util.List;
@@ -25,7 +25,7 @@
  * @see #includeMethodNamePatterns(String...)
  * @see #excludeMethodNamePatterns(String...)
  */
-@API(status = EXPERIMENTAL, since = "1.12")
+@API(status = MAINTAINED, since = "1.13.3")
 public interface MethodFilter extends PostDiscoveryFilter {
 
 	/**
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/TagFilter.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/TagFilter.java
index 2de149079747..68ccfc8be28b 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/TagFilter.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/TagFilter.java
@@ -12,7 +12,6 @@
 
 import static java.util.Arrays.asList;
 import static org.apiguardian.api.API.Status.STABLE;
-import static org.junit.platform.commons.util.CollectionUtils.toUnmodifiableList;
 
 import java.util.List;
 import java.util.Set;
@@ -20,6 +19,7 @@
 import java.util.stream.Collectors;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.PreconditionViolationException;
 import org.junit.platform.commons.util.Preconditions;
 import org.junit.platform.engine.FilterResult;
@@ -33,7 +33,7 @@
  * <p>Tag expressions are boolean expressions with the following allowed
  * operators: {@code !} (not), {@code &} (and), and {@code |} (or). Parentheses
  * can be used to adjust for operator precedence. Please refer to the
- * <a href="https://junit.org/junit5/docs/current/user-guide/#running-tests-tag-expressions">JUnit 5 User Guide</a>
+ * <a href="https://docs.junit.org/current/user-guide/#running-tests-tag-expressions">JUnit User Guide</a>
  * for usage examples.
  *
  * <p>Please note that a tag name is a valid tag expression. Thus, wherever a tag
@@ -128,8 +128,8 @@ public static PostDiscoveryFilter excludeTags(List<String> tagExpressions) throw
 	}
 
 	private static PostDiscoveryFilter includeMatching(List<String> tagExpressions) {
-		Supplier<String> inclusionReason = () -> inclusionReasonExpressionSatisfy(tagExpressions);
-		Supplier<String> exclusionReason = () -> exclusionReasonExpressionNotSatisfy(tagExpressions);
+		Supplier<@Nullable String> inclusionReason = () -> inclusionReasonExpressionSatisfy(tagExpressions);
+		Supplier<@Nullable String> exclusionReason = () -> exclusionReasonExpressionNotSatisfy(tagExpressions);
 		List<TagExpression> parsedTagExpressions = parseAll(tagExpressions);
 		return descriptor -> {
 			Set<TestTag> tags = descriptor.getTags();
@@ -140,17 +140,16 @@ private static PostDiscoveryFilter includeMatching(List<String> tagExpressions)
 	}
 
 	private static String inclusionReasonExpressionSatisfy(List<String> tagExpressions) {
-		return String.format("included because tags match expression(s): [%s]", formatToString(tagExpressions));
+		return "included because tags match expression(s): [%s]".formatted(formatToString(tagExpressions));
 	}
 
 	private static String exclusionReasonExpressionNotSatisfy(List<String> tagExpressions) {
-		return String.format("excluded because tags do not match tag expression(s): [%s]",
-			formatToString(tagExpressions));
+		return "excluded because tags do not match tag expression(s): [%s]".formatted(formatToString(tagExpressions));
 	}
 
 	private static PostDiscoveryFilter excludeMatching(List<String> tagExpressions) {
-		Supplier<String> inclusionReason = () -> inclusionReasonExpressionNotSatisfy(tagExpressions);
-		Supplier<String> exclusionReason = () -> exclusionReasonExpressionSatisfy(tagExpressions);
+		Supplier<@Nullable String> inclusionReason = () -> inclusionReasonExpressionNotSatisfy(tagExpressions);
+		Supplier<@Nullable String> exclusionReason = () -> exclusionReasonExpressionSatisfy(tagExpressions);
 		List<TagExpression> parsedTagExpressions = parseAll(tagExpressions);
 		return descriptor -> {
 			Set<TestTag> tags = descriptor.getTags();
@@ -161,11 +160,11 @@ private static PostDiscoveryFilter excludeMatching(List<String> tagExpressions)
 	}
 
 	private static String inclusionReasonExpressionNotSatisfy(List<String> tagExpressions) {
-		return String.format("included because tags do not match expression(s): [%s]", formatToString(tagExpressions));
+		return "included because tags do not match expression(s): [%s]".formatted(formatToString(tagExpressions));
 	}
 
 	private static String exclusionReasonExpressionSatisfy(List<String> tagExpressions) {
-		return String.format("excluded because tags match tag expression(s): [%s]", formatToString(tagExpressions));
+		return "excluded because tags match tag expression(s): [%s]".formatted(formatToString(tagExpressions));
 	}
 
 	private static String formatToString(List<String> tagExpressions) {
@@ -173,10 +172,10 @@ private static String formatToString(List<String> tagExpressions) {
 	}
 
 	private static List<TagExpression> parseAll(List<String> tagExpressions) {
-		return tagExpressions.stream().map(TagFilter::parse).collect(toUnmodifiableList());
+		return tagExpressions.stream().map(TagFilter::parse).toList();
 	}
 
-	private static TagExpression parse(String tagExpression) {
+	private static TagExpression parse(@Nullable String tagExpression) {
 		return TagExpression.parseFrom(tagExpression).tagExpressionOrThrow(
 			message -> new PreconditionViolationException(
 				"Unable to parse tag expression \"" + tagExpression + "\": " + message));
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/TestExecutionListener.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/TestExecutionListener.java
index 10f6327a4a76..016de421e3c1 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/TestExecutionListener.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/TestExecutionListener.java
@@ -10,7 +10,7 @@
 
 package org.junit.platform.launcher;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
 
 import org.apiguardian.api.API;
@@ -195,7 +195,7 @@ default void reportingEntryPublished(TestIdentifier testIdentifier, ReportEntry
 	 * @param testIdentifier describes the test or container to which the entry pertains
 	 * @param file the published {@code FileEntry}
 	 */
-	@API(status = EXPERIMENTAL, since = "1.12")
+	@API(status = MAINTAINED, since = "1.13.3")
 	default void fileEntryPublished(TestIdentifier testIdentifier, FileEntry file) {
 	}
 }
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/TestIdentifier.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/TestIdentifier.java
index 80e7cd3b76ec..6cc56a0dd9af 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/TestIdentifier.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/TestIdentifier.java
@@ -22,6 +22,7 @@
 import java.io.ObjectOutputStream;
 import java.io.ObjectStreamClass;
 import java.io.ObjectStreamField;
+import java.io.Serial;
 import java.io.Serializable;
 import java.util.LinkedHashSet;
 import java.util.Objects;
@@ -29,6 +30,7 @@
 import java.util.Set;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.util.Preconditions;
 import org.junit.platform.commons.util.ToStringBuilder;
 import org.junit.platform.engine.TestDescriptor;
@@ -47,16 +49,21 @@
 @API(status = STABLE, since = "1.0")
 public final class TestIdentifier implements Serializable {
 
+	@Serial
 	private static final long serialVersionUID = 1L;
+	@Serial
 	private static final ObjectStreamField[] serialPersistentFields = ObjectStreamClass.lookup(
 		SerializedForm.class).getFields();
 
 	// These are effectively final but not technically due to late initialization when deserializing
 	private /* final */ UniqueId uniqueId;
-	private /* final */ UniqueId parentId;
+
+	private /* final */ @Nullable UniqueId parentId;
+
 	private /* final */ String displayName;
 	private /* final */ String legacyReportingName;
-	private /* final */ TestSource source;
+
+	private /* final */ @Nullable TestSource source;
 	private /* final */ Set<TestTag> tags;
 	private /* final */ Type type;
 
@@ -76,8 +83,8 @@ public static TestIdentifier from(TestDescriptor testDescriptor) {
 		return new TestIdentifier(uniqueId, displayName, source, tags, type, parentId, legacyReportingName);
 	}
 
-	private TestIdentifier(UniqueId uniqueId, String displayName, TestSource source, Set<TestTag> tags, Type type,
-			UniqueId parentId, String legacyReportingName) {
+	private TestIdentifier(UniqueId uniqueId, String displayName, @Nullable TestSource source, Set<TestTag> tags,
+			Type type, @Nullable UniqueId parentId, String legacyReportingName) {
 		Preconditions.notNull(type, "TestDescriptor.Type must not be null");
 		this.uniqueId = uniqueId;
 		this.parentId = parentId;
@@ -89,14 +96,11 @@ private TestIdentifier(UniqueId uniqueId, String displayName, TestSource source,
 	}
 
 	private Set<TestTag> copyOf(Set<TestTag> tags) {
-		switch (tags.size()) {
-			case 0:
-				return emptySet();
-			case 1:
-				return singleton(getOnlyElement(tags));
-			default:
-				return new LinkedHashSet<>(tags);
-		}
+		return switch (tags.size()) {
+			case 0 -> emptySet();
+			case 1 -> singleton(getOnlyElement(tags));
+			default -> new LinkedHashSet<>(tags);
+		};
 	}
 
 	/**
@@ -245,11 +249,7 @@ public Set<TestTag> getTags() {
 
 	@Override
 	public boolean equals(Object obj) {
-		if (obj instanceof TestIdentifier) {
-			TestIdentifier that = (TestIdentifier) obj;
-			return Objects.equals(this.uniqueId, that.uniqueId);
-		}
-		return false;
+		return (obj instanceof TestIdentifier that && Objects.equals(this.uniqueId, that.uniqueId));
 	}
 
 	@Override
@@ -272,11 +272,13 @@ public String toString() {
 		// @formatter:on
 	}
 
+	@Serial
 	private void writeObject(ObjectOutputStream s) throws IOException {
 		SerializedForm serializedForm = new SerializedForm(this);
 		serializedForm.serialize(s);
 	}
 
+	@Serial
 	private void readObject(ObjectInputStream s) throws ClassNotFoundException, IOException {
 		SerializedForm serializedForm = SerializedForm.deserialize(s);
 		uniqueId = UniqueId.parse(serializedForm.uniqueId);
@@ -295,13 +297,20 @@ private void readObject(ObjectInputStream s) throws ClassNotFoundException, IOEx
 	 */
 	private static class SerializedForm implements Serializable {
 
+		@Serial
 		private static final long serialVersionUID = 1L;
 
 		private final String uniqueId;
+
+		@Nullable
 		private final String parentId;
+
 		private final String displayName;
 		private final String legacyReportingName;
+
+		@Nullable
 		private final TestSource source;
+
 		@SuppressWarnings({ "serial", "RedundantSuppression" }) // always used with serializable implementation (see TestIdentifier#copyOf())
 		private final Set<TestTag> tags;
 		private final Type type;
@@ -318,7 +327,7 @@ private static class SerializedForm implements Serializable {
 		}
 
 		@SuppressWarnings("unchecked")
-		private SerializedForm(ObjectInputStream.GetField fields) throws IOException {
+		private SerializedForm(ObjectInputStream.GetField fields) throws IOException, ClassNotFoundException {
 			this.uniqueId = (String) fields.get("uniqueId", null);
 			this.parentId = (String) fields.get("parentId", null);
 			this.displayName = (String) fields.get("displayName", null);
@@ -340,7 +349,7 @@ void serialize(ObjectOutputStream s) throws IOException {
 			s.writeFields();
 		}
 
-		static SerializedForm deserialize(ObjectInputStream s) throws ClassNotFoundException, IOException {
+		static SerializedForm deserialize(ObjectInputStream s) throws IOException, ClassNotFoundException {
 			ObjectInputStream.GetField fields = s.readFields();
 			return new SerializedForm(fields);
 		}
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/TestPlan.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/TestPlan.java
index 522c715a1efe..9ece4d94c9df 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/TestPlan.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/TestPlan.java
@@ -14,7 +14,6 @@
 import static java.util.Collections.synchronizedSet;
 import static java.util.Collections.unmodifiableSet;
 import static org.apiguardian.api.API.Status.DEPRECATED;
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
 import static org.apiguardian.api.API.Status.INTERNAL;
 import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
@@ -28,7 +27,6 @@
 import java.util.function.Predicate;
 
 import org.apiguardian.api.API;
-import org.junit.platform.commons.JUnitException;
 import org.junit.platform.commons.PreconditionViolationException;
 import org.junit.platform.commons.util.Preconditions;
 import org.junit.platform.engine.ConfigurationParameters;
@@ -105,28 +103,13 @@ protected TestPlan(boolean containsTests, ConfigurationParameters configurationP
 		this.outputDirectoryProvider = outputDirectoryProvider;
 	}
 
-	/**
-	 * Add the supplied {@link TestIdentifier} to this test plan.
-	 *
-	 * @param testIdentifier the identifier to add; never {@code null}
-	 * @deprecated Calling this method is no longer supported and will throw an
-	 * exception.
-	 * @throws JUnitException always
-	 */
-	@Deprecated
-	@API(status = DEPRECATED, since = "1.4")
-	public void add(@SuppressWarnings("unused") TestIdentifier testIdentifier) {
-		throw new JUnitException("Unsupported attempt to modify the TestPlan was detected. "
-				+ "Please contact your IDE/tool vendor and request a fix or downgrade to JUnit 5.7.x (see https://github.com/junit-team/junit5/issues/1732 for details).");
-	}
-
 	@API(status = INTERNAL, since = "1.8")
 	public void addInternal(TestIdentifier testIdentifier) {
 		Preconditions.notNull(testIdentifier, "testIdentifier must not be null");
 		allIdentifiers.put(testIdentifier.getUniqueIdObject(), testIdentifier);
 
 		// Root identifiers. Typically, a test engine.
-		if (!testIdentifier.getParentIdObject().isPresent()) {
+		if (testIdentifier.getParentIdObject().isEmpty()) {
 			roots.add(testIdentifier);
 			return;
 		}
@@ -176,22 +159,6 @@ public Set<TestIdentifier> getChildren(TestIdentifier parent) {
 		return getChildren(parent.getUniqueIdObject());
 	}
 
-	/**
-	 * Get the children of the supplied unique ID.
-	 *
-	 * @param parentId the unique ID to look up the children for; never
-	 * {@code null} or blank
-	 * @return an unmodifiable set of the parent's children, potentially empty
-	 * @see #getChildren(TestIdentifier)
-	 * @deprecated Use {@link #getChildren(UniqueId)}
-	 */
-	@API(status = DEPRECATED, since = "1.10")
-	@Deprecated
-	public Set<TestIdentifier> getChildren(String parentId) {
-		Preconditions.notBlank(parentId, "parent ID must not be null or blank");
-		return getChildren(UniqueId.parse(parentId));
-	}
-
 	/**
 	 * Get the children of the supplied unique ID.
 	 *
@@ -215,7 +182,7 @@ public Set<TestIdentifier> getChildren(UniqueId parentId) {
 	 * with the supplied unique ID is present in this test plan
 	 * @deprecated Use {@link #getTestIdentifier(UniqueId)}
 	 */
-	@API(status = DEPRECATED, since = "1.10")
+	@API(status = DEPRECATED, since = "1.10", consumers = "Gradle")
 	@Deprecated
 	public TestIdentifier getTestIdentifier(String uniqueId) throws PreconditionViolationException {
 		Preconditions.notBlank(uniqueId, "unique ID must not be null or blank");
@@ -300,7 +267,7 @@ public ConfigurationParameters getConfigurationParameters() {
 	 * @return the output directory provider; never {@code null}
 	 * @since 1.12
 	 */
-	@API(status = EXPERIMENTAL, since = "1.12")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public OutputDirectoryProvider getOutputDirectoryProvider() {
 		return this.outputDirectoryProvider;
 	}
@@ -312,7 +279,7 @@ public OutputDirectoryProvider getOutputDirectoryProvider() {
 	 * @param visitor the visitor to accept; never {@code null}
 	 * @since 1.10
 	 */
-	@API(status = EXPERIMENTAL, since = "1.10")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public void accept(Visitor visitor) {
 		getRoots().forEach(it -> accept(visitor, it));
 	}
@@ -333,7 +300,7 @@ private void accept(Visitor visitor, TestIdentifier testIdentifier) {
 	 *
 	 * @since 1.10
 	 */
-	@API(status = EXPERIMENTAL, since = "1.10")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public interface Visitor {
 
 		/**
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/ClasspathAlignmentChecker.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/ClasspathAlignmentChecker.java
index 3b95f7153e6a..312fe2519ad7 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/ClasspathAlignmentChecker.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/ClasspathAlignmentChecker.java
@@ -10,11 +10,9 @@
 
 package org.junit.platform.launcher.core;
 
-import static java.util.Collections.unmodifiableList;
 import static java.util.Comparator.comparing;
 
 import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -22,8 +20,8 @@
 import java.util.Optional;
 import java.util.function.Function;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.JUnitException;
-import org.junit.platform.commons.support.ReflectionSupport;
 import org.junit.platform.commons.util.ClassLoaderUtils;
 
 /**
@@ -32,7 +30,7 @@
 class ClasspathAlignmentChecker {
 
 	// VisibleForTesting
-	static final List<String> WELL_KNOWN_PACKAGES = unmodifiableList(Arrays.asList( //
+	static final List<String> WELL_KNOWN_PACKAGES = List.of( //
 		"org.junit.jupiter.api", //
 		"org.junit.jupiter.engine", //
 		"org.junit.jupiter.migrationsupport", //
@@ -40,28 +38,22 @@ class ClasspathAlignmentChecker {
 		"org.junit.platform.commons", //
 		"org.junit.platform.console", //
 		"org.junit.platform.engine", //
-		"org.junit.platform.jfr", //
 		"org.junit.platform.launcher", //
 		"org.junit.platform.reporting", //
-		"org.junit.platform.runner", //
 		"org.junit.platform.suite.api", //
 		"org.junit.platform.suite.commons", //
 		"org.junit.platform.suite.engine", //
 		"org.junit.platform.testkit", //
 		"org.junit.vintage.engine" //
-	));
+	);
 
 	static Optional<JUnitException> check(LinkageError error) {
 		ClassLoader classLoader = ClassLoaderUtils.getClassLoader(ClasspathAlignmentChecker.class);
-		Function<String, Package> packageLookup = name -> ReflectionSupport.findMethod(ClassLoader.class,
-			"getDefinedPackage", String.class) //
-				.map(m -> (Package) ReflectionSupport.invokeMethod(m, classLoader, name)) //
-				.orElseGet(() -> getPackage(name));
-		return check(error, packageLookup);
+		return check(error, classLoader::getDefinedPackage);
 	}
 
 	// VisibleForTesting
-	static Optional<JUnitException> check(LinkageError error, Function<String, Package> packageLookup) {
+	static Optional<JUnitException> check(LinkageError error, Function<String, @Nullable Package> packageLookup) {
 		Map<String, List<Package>> packagesByVersions = new HashMap<>();
 		WELL_KNOWN_PACKAGES.stream() //
 				.map(packageLookup) //
@@ -69,9 +61,6 @@ static Optional<JUnitException> check(LinkageError error, Function<String, Packa
 				.forEach(pkg -> {
 					String version = pkg.getImplementationVersion();
 					if (version != null) {
-						if (pkg.getName().startsWith("org.junit.platform") && version.contains(".")) {
-							version = platformToJupiterVersion(version);
-						}
 						packagesByVersions.computeIfAbsent(version, __ -> new ArrayList<>()).add(pkg);
 					}
 				});
@@ -82,29 +71,19 @@ static Optional<JUnitException> check(LinkageError error, Function<String, Packa
 					.append(" is likely caused by the versions of JUnit jars on the classpath/module path ") //
 					.append("not being properly aligned. ") //
 					.append(lineBreak) //
-					.append("Please ensure consistent versions are used (see https://junit.org/junit5/docs/") //
-					.append(platformToJupiterVersion(
-						ClasspathAlignmentChecker.class.getPackage().getImplementationVersion())) //
+					.append("Please ensure consistent versions are used (see https://docs.junit.org/") //
+					.append(ClasspathAlignmentChecker.class.getPackage().getImplementationVersion()) //
 					.append("/user-guide/#dependency-metadata).") //
 					.append(lineBreak) //
 					.append("The following conflicting versions were detected:").append(lineBreak);
 			packagesByVersions.values().stream() //
 					.flatMap(List::stream) //
 					.sorted(comparing(Package::getName)) //
-					.map(pkg -> String.format("- %s: %s%n", pkg.getName(), pkg.getImplementationVersion())) //
+					.map(pkg -> "- %s: %s%n".formatted(pkg.getName(), pkg.getImplementationVersion())) //
 					.forEach(message::append);
 			return Optional.of(new JUnitException(message.toString(), error));
 		}
 		return Optional.empty();
 	}
 
-	private static String platformToJupiterVersion(String version) {
-		int majorVersion = Integer.parseInt(version.substring(0, version.indexOf("."))) + 4;
-		return majorVersion + version.substring(version.indexOf("."));
-	}
-
-	@SuppressWarnings({ "deprecation", "RedundantSuppression" }) // only called when running on JDK 8
-	private static Package getPackage(String name) {
-		return Package.getPackage(name);
-	}
 }
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/CompositeEngineExecutionListener.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/CompositeEngineExecutionListener.java
index dac24275f15f..142f1f6a1ea3 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/CompositeEngineExecutionListener.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/CompositeEngineExecutionListener.java
@@ -83,9 +83,8 @@ private static <T extends EngineExecutionListener> void notifyEach(List<T> liste
 			}
 			catch (Throwable throwable) {
 				UnrecoverableExceptions.rethrowIfUnrecoverable(throwable);
-				logger.warn(throwable,
-					() -> String.format("EngineExecutionListener [%s] threw exception for method: %s",
-						listener.getClass().getName(), description.get()));
+				logger.warn(throwable, () -> "EngineExecutionListener [%s] threw exception for method: %s".formatted(
+					listener.getClass().getName(), description.get()));
 			}
 		});
 	}
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/CompositeTestExecutionListener.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/CompositeTestExecutionListener.java
index e9e823fed1a7..f514df6da9a2 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/CompositeTestExecutionListener.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/CompositeTestExecutionListener.java
@@ -10,8 +10,6 @@
 
 package org.junit.platform.launcher.core;
 
-import static java.util.stream.Collectors.toList;
-
 import java.util.ArrayList;
 import java.util.List;
 import java.util.function.Consumer;
@@ -39,7 +37,7 @@ class CompositeTestExecutionListener implements TestExecutionListener {
 		this.eagerTestExecutionListeners = this.testExecutionListeners.stream() //
 				.filter(EagerTestExecutionListener.class::isInstance) //
 				.map(EagerTestExecutionListener.class::cast) //
-				.collect(toList());
+				.toList();
 	}
 
 	@Override
@@ -111,7 +109,7 @@ private static <T extends TestExecutionListener> void notifyEach(List<T> listene
 			}
 			catch (Throwable throwable) {
 				UnrecoverableExceptions.rethrowIfUnrecoverable(throwable);
-				logger.warn(throwable, () -> String.format("TestExecutionListener [%s] threw exception for method: %s",
+				logger.warn(throwable, () -> "TestExecutionListener [%s] threw exception for method: %s".formatted(
 					listener.getClass().getName(), description.get()));
 			}
 		});
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/DefaultDiscoveryRequest.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/DefaultDiscoveryRequest.java
index 70106c48fb72..2951e31764f3 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/DefaultDiscoveryRequest.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/DefaultDiscoveryRequest.java
@@ -10,9 +10,6 @@
 
 package org.junit.platform.launcher.core;
 
-import static java.util.Collections.unmodifiableList;
-import static java.util.stream.Collectors.toList;
-
 import java.util.List;
 
 import org.junit.platform.commons.util.Preconditions;
@@ -58,10 +55,10 @@ final class DefaultDiscoveryRequest implements LauncherDiscoveryRequest {
 			List<DiscoveryFilter<?>> discoveryFilters, List<PostDiscoveryFilter> postDiscoveryFilters,
 			LauncherConfigurationParameters configurationParameters, LauncherDiscoveryListener discoveryListener,
 			OutputDirectoryProvider outputDirectoryProvider) {
-		this.selectors = selectors;
-		this.engineFilters = engineFilters;
-		this.discoveryFilters = discoveryFilters;
-		this.postDiscoveryFilters = postDiscoveryFilters;
+		this.selectors = List.copyOf(selectors);
+		this.engineFilters = List.copyOf(engineFilters);
+		this.discoveryFilters = List.copyOf(discoveryFilters);
+		this.postDiscoveryFilters = List.copyOf(postDiscoveryFilters);
 		this.configurationParameters = configurationParameters;
 		this.discoveryListener = discoveryListener;
 		this.outputDirectoryProvider = outputDirectoryProvider;
@@ -70,23 +67,23 @@ final class DefaultDiscoveryRequest implements LauncherDiscoveryRequest {
 	@Override
 	public <T extends DiscoverySelector> List<T> getSelectorsByType(Class<T> selectorType) {
 		Preconditions.notNull(selectorType, "selectorType must not be null");
-		return this.selectors.stream().filter(selectorType::isInstance).map(selectorType::cast).collect(toList());
+		return this.selectors.stream().filter(selectorType::isInstance).map(selectorType::cast).toList();
 	}
 
 	@Override
 	public List<EngineFilter> getEngineFilters() {
-		return unmodifiableList(this.engineFilters);
+		return this.engineFilters;
 	}
 
 	@Override
 	public <T extends DiscoveryFilter<?>> List<T> getFiltersByType(Class<T> filterType) {
 		Preconditions.notNull(filterType, "filterType must not be null");
-		return this.discoveryFilters.stream().filter(filterType::isInstance).map(filterType::cast).collect(toList());
+		return this.discoveryFilters.stream().filter(filterType::isInstance).map(filterType::cast).toList();
 	}
 
 	@Override
 	public List<PostDiscoveryFilter> getPostDiscoveryFilters() {
-		return unmodifiableList(this.postDiscoveryFilters);
+		return this.postDiscoveryFilters;
 	}
 
 	@Override
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/DefaultLauncher.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/DefaultLauncher.java
index c4691503ba1f..509467bf108a 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/DefaultLauncher.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/DefaultLauncher.java
@@ -56,7 +56,7 @@ class DefaultLauncher implements Launcher {
 	 */
 	DefaultLauncher(Iterable<TestEngine> testEngines, Collection<PostDiscoveryFilter> postDiscoveryFilters,
 			NamespacedHierarchicalStore<Namespace> sessionLevelStore) {
-		Preconditions.condition(testEngines != null && testEngines.iterator().hasNext(),
+		Preconditions.condition(testEngines.iterator().hasNext(),
 			() -> "Cannot create Launcher without at least one TestEngine; "
 					+ "consider adding an engine implementation JAR to the classpath");
 		Preconditions.notNull(postDiscoveryFilters, "PostDiscoveryFilter array must not be null");
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/DelegatingLauncherDiscoveryRequest.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/DelegatingLauncherDiscoveryRequest.java
index 4a8c8d5cad97..55d2ba094df2 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/DelegatingLauncherDiscoveryRequest.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/DelegatingLauncherDiscoveryRequest.java
@@ -32,30 +32,37 @@ class DelegatingLauncherDiscoveryRequest implements LauncherDiscoveryRequest {
 		this.request = request;
 	}
 
+	@Override
 	public List<EngineFilter> getEngineFilters() {
 		return this.request.getEngineFilters();
 	}
 
+	@Override
 	public List<PostDiscoveryFilter> getPostDiscoveryFilters() {
 		return this.request.getPostDiscoveryFilters();
 	}
 
+	@Override
 	public LauncherDiscoveryListener getDiscoveryListener() {
 		return this.request.getDiscoveryListener();
 	}
 
+	@Override
 	public <T extends DiscoverySelector> List<T> getSelectorsByType(Class<T> selectorType) {
 		return this.request.getSelectorsByType(selectorType);
 	}
 
+	@Override
 	public <T extends DiscoveryFilter<?>> List<T> getFiltersByType(Class<T> filterType) {
 		return this.request.getFiltersByType(filterType);
 	}
 
+	@Override
 	public ConfigurationParameters getConfigurationParameters() {
 		return this.request.getConfigurationParameters();
 	}
 
+	@Override
 	public OutputDirectoryProvider getOutputDirectoryProvider() {
 		return this.request.getOutputDirectoryProvider();
 	}
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/DiscoveryIssueCollector.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/DiscoveryIssueCollector.java
index 2b19b1e92f81..7714d3fb7618 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/DiscoveryIssueCollector.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/DiscoveryIssueCollector.java
@@ -17,6 +17,7 @@
 import java.util.List;
 import java.util.Locale;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.logging.Logger;
 import org.junit.platform.commons.logging.LoggerFactory;
 import org.junit.platform.engine.ConfigurationParameters;
@@ -69,46 +70,43 @@ public void selectorProcessed(UniqueId engineId, DiscoverySelector selector, Sel
 					.source(toSource(selector)) //
 					.build());
 		}
-		else if (result.getStatus() == UNRESOLVED && selector instanceof UniqueIdSelector) {
-			UniqueId uniqueId = ((UniqueIdSelector) selector).getUniqueId();
+		else if (result.getStatus() == UNRESOLVED && selector instanceof UniqueIdSelector uniqueIdSelector) {
+			UniqueId uniqueId = uniqueIdSelector.getUniqueId();
 			if (uniqueId.hasPrefix(engineId)) {
 				this.issues.add(DiscoveryIssue.create(Severity.ERROR, selector + " could not be resolved"));
 			}
 		}
 	}
 
-	static TestSource toSource(DiscoverySelector selector) {
-		if (selector instanceof ClassSelector) {
-			return ClassSource.from(((ClassSelector) selector).getClassName());
+	static @Nullable TestSource toSource(DiscoverySelector selector) {
+		if (selector instanceof ClassSelector classSelector) {
+			return ClassSource.from(classSelector.getClassName());
 		}
-		if (selector instanceof MethodSelector) {
-			MethodSelector methodSelector = (MethodSelector) selector;
+		if (selector instanceof MethodSelector methodSelector) {
 			return MethodSource.from(methodSelector.getClassName(), methodSelector.getMethodName(),
 				methodSelector.getParameterTypeNames());
 		}
-		if (selector instanceof ClasspathResourceSelector) {
-			ClasspathResourceSelector resourceSelector = (ClasspathResourceSelector) selector;
+		if (selector instanceof ClasspathResourceSelector resourceSelector) {
 			String resourceName = resourceSelector.getClasspathResourceName();
 			return resourceSelector.getPosition() //
 					.map(DiscoveryIssueCollector::convert) //
 					.map(position -> ClasspathResourceSource.from(resourceName, position)) //
 					.orElseGet(() -> ClasspathResourceSource.from(resourceName));
 		}
-		if (selector instanceof PackageSelector) {
-			return PackageSource.from(((PackageSelector) selector).getPackageName());
+		if (selector instanceof PackageSelector packageSelector) {
+			return PackageSource.from(packageSelector.getPackageName());
 		}
-		if (selector instanceof FileSelector) {
-			FileSelector fileSelector = (FileSelector) selector;
+		if (selector instanceof FileSelector fileSelector) {
 			return fileSelector.getPosition() //
 					.map(DiscoveryIssueCollector::convert) //
 					.map(position -> FileSource.from(fileSelector.getFile(), position)) //
 					.orElseGet(() -> FileSource.from(fileSelector.getFile()));
 		}
-		if (selector instanceof DirectorySelector) {
-			return DirectorySource.from(((DirectorySelector) selector).getDirectory());
+		if (selector instanceof DirectorySelector directorySelector) {
+			return DirectorySource.from(directorySelector.getDirectory());
 		}
-		if (selector instanceof UriSelector) {
-			return UriSource.from(((UriSelector) selector).getUri());
+		if (selector instanceof UriSelector uriSelector) {
+			return UriSource.from(uriSelector.getUri());
 		}
 		return null;
 	}
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/DiscoveryIssueException.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/DiscoveryIssueException.java
index 563e3a33629b..b96e93a09da3 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/DiscoveryIssueException.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/DiscoveryIssueException.java
@@ -12,6 +12,8 @@
 
 import static org.apiguardian.api.API.Status.EXPERIMENTAL;
 
+import java.io.Serial;
+
 import org.apiguardian.api.API;
 import org.junit.platform.commons.JUnitException;
 
@@ -21,9 +23,10 @@
  *
  * @since 1.13
  */
-@API(status = EXPERIMENTAL, since = "1.13")
+@API(status = EXPERIMENTAL, since = "6.0")
 public class DiscoveryIssueException extends JUnitException {
 
+	@Serial
 	private static final long serialVersionUID = 1L;
 
 	DiscoveryIssueException(String message) {
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/DiscoveryIssueNotifier.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/DiscoveryIssueNotifier.java
index 592af7bd866b..1e515657ce9b 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/DiscoveryIssueNotifier.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/DiscoveryIssueNotifier.java
@@ -10,17 +10,17 @@
 
 package org.junit.platform.launcher.core;
 
-import static java.util.Collections.emptyList;
 import static java.util.Comparator.comparing;
 import static java.util.stream.Collectors.partitioningBy;
+import static java.util.stream.Collectors.toUnmodifiableList;
 import static org.junit.platform.commons.util.ExceptionUtils.readStackTrace;
 
-import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
 import java.util.function.Consumer;
 import java.util.function.Supplier;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.logging.Logger;
 import org.junit.platform.commons.logging.LoggerFactory;
 import org.junit.platform.commons.util.Preconditions;
@@ -35,27 +35,34 @@
  */
 class DiscoveryIssueNotifier {
 
-	static final DiscoveryIssueNotifier NO_ISSUES = new DiscoveryIssueNotifier(emptyList(), emptyList(), emptyList());
+	static final DiscoveryIssueNotifier NO_ISSUES = new DiscoveryIssueNotifier(List.of(), List.of(), List.of());
 	private static final Logger logger = LoggerFactory.getLogger(DiscoveryIssueNotifier.class);
 
 	private final List<DiscoveryIssue> allIssues;
 	private final List<DiscoveryIssue> criticalIssues;
 	private final List<DiscoveryIssue> nonCriticalIssues;
 
+	@SuppressWarnings("NullAway")
 	static DiscoveryIssueNotifier from(Severity criticalSeverity, List<DiscoveryIssue> issues) {
-		Map<Boolean, List<DiscoveryIssue>> issuesByCriticality = issues.stream() //
-				.sorted(comparing(DiscoveryIssue::severity).reversed()) //
-				.collect(partitioningBy(issue -> issue.severity().compareTo(criticalSeverity) >= 0));
+		var issuesByCriticality = partitionByCriticality(criticalSeverity, issues);
 		List<DiscoveryIssue> criticalIssues = issuesByCriticality.get(true);
 		List<DiscoveryIssue> nonCriticalIssues = issuesByCriticality.get(false);
-		return new DiscoveryIssueNotifier(new ArrayList<>(issues), criticalIssues, nonCriticalIssues);
+		return new DiscoveryIssueNotifier(issues, criticalIssues, nonCriticalIssues);
+	}
+
+	private static Map<Boolean, List<DiscoveryIssue>> partitionByCriticality(Severity criticalSeverity,
+			List<DiscoveryIssue> issues) {
+		return issues.stream() //
+				.sorted(comparing(DiscoveryIssue::severity).reversed()) //
+				.collect(
+					partitioningBy(issue -> issue.severity().compareTo(criticalSeverity) >= 0, toUnmodifiableList()));
 	}
 
 	private DiscoveryIssueNotifier(List<DiscoveryIssue> allIssues, List<DiscoveryIssue> criticalIssues,
 			List<DiscoveryIssue> nonCriticalIssues) {
-		this.allIssues = allIssues;
-		this.criticalIssues = criticalIssues;
-		this.nonCriticalIssues = nonCriticalIssues;
+		this.allIssues = List.copyOf(allIssues);
+		this.criticalIssues = List.copyOf(criticalIssues);
+		this.nonCriticalIssues = List.copyOf(nonCriticalIssues);
 	}
 
 	List<DiscoveryIssue> getAllIssues() {
@@ -74,6 +81,7 @@ void logNonCriticalIssues(TestEngine testEngine) {
 		logIssues(testEngine, nonCriticalIssues, "non-critical");
 	}
 
+	@Nullable
 	DiscoveryIssueException createExceptionForCriticalIssues(TestEngine testEngine) {
 		if (criticalIssues.isEmpty()) {
 			return null;
@@ -90,17 +98,11 @@ private void logIssues(TestEngine testEngine, List<DiscoveryIssue> issues, Strin
 	}
 
 	private static Consumer<Supplier<String>> logger(Severity severity) {
-		// TODO [#4246] Use switch expression
-		switch (severity) {
-			case INFO:
-				return logger::info;
-			case WARNING:
-				return logger::warn;
-			case ERROR:
-				return logger::error;
-			default:
-				throw new IllegalArgumentException("Unknown severity: " + severity);
-		}
+		return switch (severity) {
+			case INFO -> logger::info;
+			case WARNING -> logger::warn;
+			case ERROR -> logger::error;
+		};
 	}
 
 	private static String formatMessage(TestEngine testEngine, List<DiscoveryIssue> issues, String adjective) {
@@ -123,12 +125,10 @@ private static String formatMessage(TestEngine testEngine, List<DiscoveryIssue>
 				issue.message());
 			issue.source().ifPresent(source -> {
 				message.append("\n    Source: ").append(source);
-				if (source instanceof MethodSource) {
-					MethodSource methodSource = (MethodSource) source;
+				if (source instanceof MethodSource methodSource) {
 					appendIdeCompatibleLink(message, methodSource.getClassName(), methodSource.getMethodName());
 				}
-				else if (source instanceof ClassSource) {
-					ClassSource classSource = (ClassSource) source;
+				else if (source instanceof ClassSource classSource) {
 					appendIdeCompatibleLink(message, classSource.getClassName(), "<no-method>");
 				}
 			});
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/EngineDiscoveryOrchestrator.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/EngineDiscoveryOrchestrator.java
index 5c989b32d79a..7d2e7c529d4e 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/EngineDiscoveryOrchestrator.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/EngineDiscoveryOrchestrator.java
@@ -163,13 +163,13 @@ private Map<TestEngine, EngineResultInfo> discoverSafely(LauncherDiscoveryReques
 			boolean engineIsExcluded = engineFilterer.isExcluded(testEngine);
 
 			if (engineIsExcluded) {
-				logger.debug(() -> String.format("Test discovery for engine '%s' was skipped due to an EngineFilter%s.",
-					testEngine.getId(), phase.map(it -> String.format(" in %s phase", it)).orElse("")));
+				logger.debug(() -> "Test discovery for engine '%s' was skipped due to an EngineFilter%s.".formatted(
+					testEngine.getId(), phase.map(" in %s phase"::formatted).orElse("")));
 				continue;
 			}
 
-			logger.debug(() -> String.format("Discovering tests%s in engine '%s'.",
-				phase.map(it -> String.format(" during Launcher %s phase", it)).orElse(""), testEngine.getId()));
+			logger.debug(() -> "Discovering tests%s in engine '%s'.".formatted(
+				phase.map(" during Launcher %s phase"::formatted).orElse(""), testEngine.getId()));
 
 			EngineResultInfo engineResult = discoverEngineRoot(testEngine, request, issueCollector, uniqueIdCreator);
 			testEngineDescriptors.put(testEngine, engineResult);
@@ -200,11 +200,11 @@ private EngineResultInfo discoverEngineRoot(TestEngine testEngine, LauncherDisco
 		catch (Throwable throwable) {
 			UnrecoverableExceptions.rethrowIfUnrecoverable(throwable);
 			JUnitException cause = null;
-			if (throwable instanceof LinkageError) {
-				cause = ClasspathAlignmentChecker.check((LinkageError) throwable).orElse(null);
+			if (throwable instanceof LinkageError error) {
+				cause = ClasspathAlignmentChecker.check(error).orElse(null);
 			}
 			if (cause == null) {
-				String message = String.format("TestEngine with ID '%s' failed to discover tests", testEngine.getId());
+				String message = "TestEngine with ID '%s' failed to discover tests".formatted(testEngine.getId());
 				cause = new JUnitException(message, throwable);
 			}
 			listener.engineDiscoveryFinished(uniqueEngineId, EngineDiscoveryResult.failed(cause));
@@ -247,10 +247,10 @@ private void logTestDescriptorExclusionReasons(Map<String, List<TestDescriptor>>
 			String displayNames = testDescriptors.stream().map(TestDescriptor::getDisplayName).collect(joining(", "));
 			long containerCount = testDescriptors.stream().filter(TestDescriptor::isContainer).count();
 			long methodCount = testDescriptors.stream().filter(TestDescriptor::isTest).count();
-			logger.config(() -> String.format("%d containers and %d tests were %s", containerCount, methodCount,
-				exclusionReason));
+			logger.config(
+				() -> "%d containers and %d tests were %s".formatted(containerCount, methodCount, exclusionReason));
 			logger.debug(
-				() -> String.format("The following containers and tests were %s: %s", exclusionReason, displayNames));
+				() -> "The following containers and tests were %s: %s".formatted(exclusionReason, displayNames));
 		});
 	}
 
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/EngineDiscoveryResultValidator.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/EngineDiscoveryResultValidator.java
index 61b57a24b67b..85d417df85e0 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/EngineDiscoveryResultValidator.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/EngineDiscoveryResultValidator.java
@@ -39,12 +39,11 @@ class EngineDiscoveryResultValidator {
 	 */
 	void validate(TestEngine testEngine, TestDescriptor root) {
 		Preconditions.notNull(root,
-			() -> String.format(
-				"The discover() method for TestEngine with ID '%s' must return a non-null root TestDescriptor.",
+			() -> "The discover() method for TestEngine with ID '%s' must return a non-null root TestDescriptor.".formatted(
 				testEngine.getId()));
 		Optional<String> cyclicGraphInfo = getCyclicGraphInfo(root);
-		Preconditions.condition(!cyclicGraphInfo.isPresent(),
-			() -> String.format("The discover() method for TestEngine with ID '%s' returned a cyclic graph; %s",
+		Preconditions.condition(cyclicGraphInfo.isEmpty(),
+			() -> "The discover() method for TestEngine with ID '%s' returned a cyclic graph; %s".formatted(
 				testEngine.getId(), cyclicGraphInfo.get()));
 	}
 
@@ -69,7 +68,7 @@ private Optional<String> getCyclicGraphInfo(TestDescriptor root) {
 					List<UniqueId> path2 = findPath(visited, parent.getUniqueId());
 					path2.add(uid);
 
-					return Optional.of(String.format("%s exists in at least two paths:\n(1) %s\n(2) %s", uid,
+					return Optional.of("%s exists in at least two paths:\n(1) %s\n(2) %s".formatted(uid,
 						formatted(path1), formatted(path2)));
 				}
 				else {
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/EngineExecutionOrchestrator.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/EngineExecutionOrchestrator.java
index 1cf63758f3aa..0536b5134736 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/EngineExecutionOrchestrator.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/EngineExecutionOrchestrator.java
@@ -235,11 +235,11 @@ private void executeEngine(TestDescriptor engineDescriptor, EngineExecutionListe
 		catch (Throwable throwable) {
 			UnrecoverableExceptions.rethrowIfUnrecoverable(throwable);
 			JUnitException cause = null;
-			if (throwable instanceof LinkageError) {
-				cause = ClasspathAlignmentChecker.check((LinkageError) throwable).orElse(null);
+			if (throwable instanceof LinkageError error) {
+				cause = ClasspathAlignmentChecker.check(error).orElse(null);
 			}
 			if (cause == null) {
-				String message = String.format("TestEngine with ID '%s' failed to execute tests", testEngine.getId());
+				String message = "TestEngine with ID '%s' failed to execute tests".formatted(testEngine.getId());
 				cause = new JUnitException(message, throwable);
 			}
 			delayingListener.reportEngineStartIfNecessary();
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/EngineIdValidator.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/EngineIdValidator.java
index 878df7d3c207..bc7944be4fd2 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/EngineIdValidator.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/EngineIdValidator.java
@@ -32,15 +32,15 @@ static Iterable<TestEngine> validate(Iterable<TestEngine> testEngines) {
 		for (TestEngine testEngine : testEngines) {
 			// check usage of reserved ID prefix
 			if (!validateReservedIds(testEngine)) {
-				getLogger().warn(() -> String.format(
-					"Third-party TestEngine implementations are forbidden to use the reserved 'junit-' prefix for their ID: '%s'",
-					testEngine.getId()));
+				getLogger().warn(
+					() -> "Third-party TestEngine implementations are forbidden to use the reserved 'junit-' prefix for their ID: '%s'".formatted(
+						testEngine.getId()));
 			}
 
 			// check uniqueness
 			if (!ids.add(testEngine.getId())) {
-				throw new JUnitException(String.format(
-					"Cannot create Launcher for multiple engines with the same ID '%s'.", testEngine.getId()));
+				throw new JUnitException(
+					"Cannot create Launcher for multiple engines with the same ID '%s'.".formatted(testEngine.getId()));
 			}
 		}
 		return testEngines;
@@ -51,29 +51,28 @@ private static Logger getLogger() {
 		return LoggerFactory.getLogger(EngineIdValidator.class);
 	}
 
-	// https://github.com/junit-team/junit5/issues/1557
+	// https://github.com/junit-team/junit-framework/issues/1557
 	private static boolean validateReservedIds(TestEngine testEngine) {
 		String engineId = Preconditions.notBlank(testEngine.getId(),
-			() -> String.format("ID for TestEngine [%s] must not be null or blank", testEngine.getClass().getName()));
+			() -> "ID for TestEngine [%s] must not be null or blank".formatted(testEngine.getClass().getName()));
 		if (!engineId.startsWith("junit-")) {
 			return true;
 		}
-		switch (engineId) {
-			case "junit-jupiter": {
+		return switch (engineId) {
+			case "junit-jupiter" -> {
 				validateWellKnownClassName(testEngine, "org.junit.jupiter.engine.JupiterTestEngine");
-				return true;
+				yield true;
 			}
-			case "junit-vintage": {
+			case "junit-vintage" -> {
 				validateWellKnownClassName(testEngine, "org.junit.vintage.engine.VintageTestEngine");
-				return true;
+				yield true;
 			}
-			case "junit-platform-suite": {
+			case "junit-platform-suite" -> {
 				validateWellKnownClassName(testEngine, "org.junit.platform.suite.engine.SuiteTestEngine");
-				return true;
+				yield true;
 			}
-			default:
-				return false;
-		}
+			default -> false;
+		};
 	}
 
 	private static void validateWellKnownClassName(TestEngine testEngine, String expectedClassName) {
@@ -82,7 +81,7 @@ private static void validateWellKnownClassName(TestEngine testEngine, String exp
 			return;
 		}
 		throw new JUnitException(
-			String.format("Third-party TestEngine '%s' is forbidden to use the reserved '%s' TestEngine ID.",
+			"Third-party TestEngine '%s' is forbidden to use the reserved '%s' TestEngine ID.".formatted(
 				actualClassName, testEngine.getId()));
 	}
 
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/HierarchicalOutputDirectoryProvider.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/HierarchicalOutputDirectoryProvider.java
index b85d3176668a..3be48cf03a3e 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/HierarchicalOutputDirectoryProvider.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/HierarchicalOutputDirectoryProvider.java
@@ -13,11 +13,11 @@
 import java.io.IOException;
 import java.nio.file.Files;
 import java.nio.file.Path;
-import java.nio.file.Paths;
 import java.util.List;
 import java.util.function.Supplier;
 import java.util.regex.Pattern;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.util.Preconditions;
 import org.junit.platform.engine.TestDescriptor;
 import org.junit.platform.engine.UniqueId.Segment;
@@ -35,7 +35,8 @@ class HierarchicalOutputDirectoryProvider implements OutputDirectoryProvider {
 	private static final String REPLACEMENT = "_";
 
 	private final Supplier<Path> rootDirSupplier;
-	private volatile Path rootDir;
+
+	private volatile @Nullable Path rootDir;
 
 	HierarchicalOutputDirectoryProvider(Supplier<Path> rootDirSupplier) {
 		this.rootDirSupplier = rootDirSupplier;
@@ -55,14 +56,16 @@ public Path createOutputDirectory(TestDescriptor testDescriptor) throws IOExcept
 
 	@Override
 	public synchronized Path getRootDirectory() {
-		if (rootDir == null) {
-			rootDir = rootDirSupplier.get();
+		var currentRootDir = rootDir;
+		if (currentRootDir == null) {
+			currentRootDir = rootDirSupplier.get();
+			rootDir = currentRootDir;
 		}
-		return rootDir;
+		return currentRootDir;
 	}
 
 	private static Path toSanitizedPath(Segment segment) {
-		return Paths.get(sanitizeName(segment.getValue()));
+		return Path.of(sanitizeName(segment.getValue()));
 	}
 
 	private static String sanitizeName(String value) {
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/InterceptingLauncher.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/InterceptingLauncher.java
index 44656ff04a51..30178e808414 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/InterceptingLauncher.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/InterceptingLauncher.java
@@ -10,6 +10,7 @@
 
 package org.junit.platform.launcher.core;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.launcher.Launcher;
 import org.junit.platform.launcher.LauncherDiscoveryRequest;
 import org.junit.platform.launcher.LauncherInterceptor;
@@ -35,7 +36,7 @@ public TestPlan discover(LauncherDiscoveryRequest launcherDiscoveryRequest) {
 
 	@Override
 	public void execute(LauncherDiscoveryRequest launcherDiscoveryRequest, TestExecutionListener... listeners) {
-		interceptor.intercept(() -> {
+		interceptor.<@Nullable Object> intercept(() -> {
 			super.execute(launcherDiscoveryRequest, listeners);
 			return null;
 		});
@@ -43,7 +44,7 @@ public void execute(LauncherDiscoveryRequest launcherDiscoveryRequest, TestExecu
 
 	@Override
 	public void execute(TestPlan testPlan, TestExecutionListener... listeners) {
-		interceptor.intercept(() -> {
+		interceptor.<@Nullable Object> intercept(() -> {
 			super.execute(testPlan, listeners);
 			return null;
 		});
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/InternalTestPlan.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/InternalTestPlan.java
index 4440a6209801..d2c7d2c98254 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/InternalTestPlan.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/InternalTestPlan.java
@@ -56,12 +56,6 @@ public TestPlan getDelegate() {
 		return delegate;
 	}
 
-	@Override
-	@SuppressWarnings("deprecation")
-	public void add(TestIdentifier testIdentifier) {
-		delegate.add(testIdentifier);
-	}
-
 	@Override
 	public void addInternal(TestIdentifier testIdentifier) {
 		delegate.addInternal(testIdentifier);
@@ -82,23 +76,11 @@ public Set<TestIdentifier> getChildren(TestIdentifier parent) {
 		return delegate.getChildren(parent);
 	}
 
-	@SuppressWarnings("deprecation")
-	@Override
-	public Set<TestIdentifier> getChildren(String parentId) {
-		return delegate.getChildren(parentId);
-	}
-
 	@Override
 	public Set<TestIdentifier> getChildren(UniqueId parentId) {
 		return delegate.getChildren(parentId);
 	}
 
-	@SuppressWarnings("deprecation")
-	@Override
-	public TestIdentifier getTestIdentifier(String uniqueId) throws PreconditionViolationException {
-		return delegate.getTestIdentifier(uniqueId);
-	}
-
 	@Override
 	public TestIdentifier getTestIdentifier(UniqueId uniqueId) {
 		return delegate.getTestIdentifier(uniqueId);
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/LauncherConfigurationParameters.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/LauncherConfigurationParameters.java
index a33793a346e9..cfea8896710d 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/LauncherConfigurationParameters.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/LauncherConfigurationParameters.java
@@ -29,6 +29,7 @@
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.logging.Logger;
 import org.junit.platform.commons.logging.LoggerFactory;
 import org.junit.platform.commons.util.ClassLoaderUtils;
@@ -64,21 +65,13 @@ public Optional<Boolean> getBoolean(String key) {
 		return get(key).map(Boolean::parseBoolean);
 	}
 
-	@Override
-	@SuppressWarnings("deprecation")
-	public int size() {
-		return providers.stream() //
-				.mapToInt(ParameterProvider::size) //
-				.sum();
-	}
-
 	@Override
 	public Set<String> keySet() {
 		return providers.stream().map(ParameterProvider::keySet).flatMap(Collection::stream).collect(
 			Collectors.toSet());
 	}
 
-	private String getProperty(String key) {
+	private @Nullable String getProperty(String key) {
 		Preconditions.notBlank(key, "key must not be null or blank");
 		return providers.stream() //
 				.map(parameterProvider -> parameterProvider.getValue(key)) //
@@ -100,6 +93,8 @@ static final class Builder {
 		private final List<String> configResources = new ArrayList<>();
 		private boolean implicitProvidersEnabled = true;
 		private String configFileName = ConfigurationParameters.CONFIG_FILE_NAME;
+
+		@Nullable
 		private ConfigurationParameters parentConfigurationParameters;
 
 		private Builder() {
@@ -157,26 +152,18 @@ LauncherConfigurationParameters build() {
 
 	private interface ParameterProvider {
 
+		@Nullable
 		String getValue(String key);
 
-		default int size() {
-			return 0;
-		}
-
 		Set<String> keySet();
 
 		static ParameterProvider explicit(Map<String, String> configParams) {
 			return new ParameterProvider() {
 				@Override
-				public String getValue(String key) {
+				public @Nullable String getValue(String key) {
 					return configParams.get(key);
 				}
 
-				@Override
-				public int size() {
-					return configParams.size();
-				}
-
 				@Override
 				public Set<String> keySet() {
 					return configParams.keySet();
@@ -194,7 +181,7 @@ public String toString() {
 		static ParameterProvider systemProperties() {
 			return new ParameterProvider() {
 				@Override
-				public String getValue(String key) {
+				public @Nullable String getValue(String key) {
 					try {
 						return System.getProperty(key);
 					}
@@ -241,16 +228,10 @@ public String toString() {
 		static ParameterProvider inherited(ConfigurationParameters configParams) {
 			return new ParameterProvider() {
 				@Override
-				public String getValue(String key) {
+				public @Nullable String getValue(String key) {
 					return configParams.get(key).orElse(null);
 				}
 
-				@Override
-				@SuppressWarnings("deprecation")
-				public int size() {
-					return configParams.size();
-				}
-
 				@Override
 				public Set<String> keySet() {
 					return configParams.keySet();
@@ -284,14 +265,14 @@ private static Properties loadClasspathResource(String configFileName) {
 							Stream.of(configFileUrl + " (*)"), //
 							resources.stream().skip(1).map(URL::toString) //
 						).collect(joining("\n- ", "\n- ", ""));
-						return String.format(
-							"Discovered %d '%s' configuration files on the classpath (see below); only the first (*) will be used.%s",
+						return "Discovered %d '%s' configuration files on the classpath (see below); only the first (*) will be used.%s".formatted(
 							resources.size(), configFileName, formattedResourceList);
 					});
 				}
 
-				logger.config(() -> String.format(
-					"Loading JUnit Platform configuration parameters from classpath resource [%s].", configFileUrl));
+				logger.config(
+					() -> "Loading JUnit Platform configuration parameters from classpath resource [%s].".formatted(
+						configFileUrl));
 				URLConnection urlConnection = configFileUrl.openConnection();
 				urlConnection.setUseCaches(false);
 				try (InputStream inputStream = urlConnection.getInputStream()) {
@@ -301,8 +282,7 @@ private static Properties loadClasspathResource(String configFileName) {
 		}
 		catch (Exception ex) {
 			logger.warn(ex,
-				() -> String.format(
-					"Failed to load JUnit Platform configuration parameters from classpath resource [%s].",
+				() -> "Failed to load JUnit Platform configuration parameters from classpath resource [%s].".formatted(
 					configFileName));
 		}
 
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/LauncherDiscoveryRequestBuilder.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/LauncherDiscoveryRequestBuilder.java
index d1fa66711079..7ca99cb6c28b 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/LauncherDiscoveryRequestBuilder.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/LauncherDiscoveryRequestBuilder.java
@@ -10,8 +10,7 @@
 
 package org.junit.platform.launcher.core;
 
-import static org.apiguardian.api.API.Status.DEPRECATED;
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
 import static org.junit.platform.launcher.LauncherConstants.OUTPUT_DIR_PROPERTY_NAME;
 
@@ -23,6 +22,7 @@
 import java.util.Map;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.PreconditionViolationException;
 import org.junit.platform.commons.util.Preconditions;
 import org.junit.platform.engine.ConfigurationParameters;
@@ -110,8 +110,10 @@ public final class LauncherDiscoveryRequestBuilder {
 	private final List<String> configurationParametersResources = new ArrayList<>();
 	private final List<LauncherDiscoveryListener> discoveryListeners = new ArrayList<>();
 	private boolean implicitConfigurationParametersEnabled = true;
-	private ConfigurationParameters parentConfigurationParameters;
-	private OutputDirectoryProvider outputDirectoryProvider;
+
+	private @Nullable ConfigurationParameters parentConfigurationParameters;
+
+	private @Nullable OutputDirectoryProvider outputDirectoryProvider;
 
 	/**
 	 * Create a new {@code LauncherDiscoveryRequestBuilder}.
@@ -122,12 +124,7 @@ public static LauncherDiscoveryRequestBuilder request() {
 		return new LauncherDiscoveryRequestBuilder();
 	}
 
-	/**
-	 * @deprecated Use {@link #request()}
-	 */
-	@API(status = DEPRECATED, since = "1.8")
-	@Deprecated
-	public LauncherDiscoveryRequestBuilder() {
+	private LauncherDiscoveryRequestBuilder() {
 	}
 
 	/**
@@ -302,7 +299,7 @@ public LauncherDiscoveryRequestBuilder listeners(LauncherDiscoveryListener... li
 	 * @see OutputDirectoryProvider
 	 * @see LauncherConstants#OUTPUT_DIR_PROPERTY_NAME
 	 */
-	@API(status = EXPERIMENTAL, since = "1.12")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public LauncherDiscoveryRequestBuilder outputDirectoryProvider(OutputDirectoryProvider outputDirectoryProvider) {
 		this.outputDirectoryProvider = Preconditions.notNull(outputDirectoryProvider,
 			"outputDirectoryProvider must not be null");
@@ -310,18 +307,18 @@ public LauncherDiscoveryRequestBuilder outputDirectoryProvider(OutputDirectoryPr
 	}
 
 	private void storeFilter(Filter<?> filter) {
-		if (filter instanceof EngineFilter) {
-			this.engineFilters.add((EngineFilter) filter);
+		if (filter instanceof EngineFilter engineFilter) {
+			this.engineFilters.add(engineFilter);
 		}
-		else if (filter instanceof PostDiscoveryFilter) {
-			this.postDiscoveryFilters.add((PostDiscoveryFilter) filter);
+		else if (filter instanceof PostDiscoveryFilter postDiscoveryFilter) {
+			this.postDiscoveryFilters.add(postDiscoveryFilter);
 		}
-		else if (filter instanceof DiscoveryFilter<?>) {
-			this.discoveryFilters.add((DiscoveryFilter<?>) filter);
+		else if (filter instanceof DiscoveryFilter<?> discoveryFilter) {
+			this.discoveryFilters.add(discoveryFilter);
 		}
 		else {
 			throw new PreconditionViolationException(
-				String.format("Filter [%s] must implement %s, %s, or %s.", filter, EngineFilter.class.getSimpleName(),
+				"Filter [%s] must implement %s, %s, or %s.".formatted(filter, EngineFilter.class.getSimpleName(),
 					PostDiscoveryFilter.class.getSimpleName(), DiscoveryFilter.class.getSimpleName()));
 		}
 	}
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/LauncherDiscoveryResult.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/LauncherDiscoveryResult.java
index 7b3db9368915..6827cd0246a0 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/LauncherDiscoveryResult.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/LauncherDiscoveryResult.java
@@ -11,6 +11,7 @@
 package org.junit.platform.launcher.core;
 
 import static java.util.Collections.unmodifiableMap;
+import static java.util.Objects.requireNonNull;
 import static java.util.stream.Collectors.toMap;
 import static org.apiguardian.api.API.Status.INTERNAL;
 
@@ -20,9 +21,9 @@
 import java.util.Map;
 import java.util.Optional;
 import java.util.function.Predicate;
-import java.util.stream.Collectors;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.engine.ConfigurationParameters;
 import org.junit.platform.engine.DiscoveryIssue;
 import org.junit.platform.engine.TestDescriptor;
@@ -59,7 +60,7 @@ public List<DiscoveryIssue> getDiscoveryIssues(TestEngine testEngine) {
 	}
 
 	EngineResultInfo getEngineResult(TestEngine testEngine) {
-		return this.testEngineResults.get(testEngine);
+		return requireNonNull(this.testEngineResults.get(testEngine));
 	}
 
 	ConfigurationParameters getConfigurationParameters() {
@@ -82,7 +83,7 @@ boolean containsCriticalIssuesOrContainsTests() {
 	Collection<TestDescriptor> getEngineTestDescriptors() {
 		return this.testEngineResults.values().stream() //
 				.map(EngineResultInfo::getRootDescriptor) //
-				.collect(Collectors.toList());
+				.toList();
 	}
 
 	public LauncherDiscoveryResult withRetainedEngines(Predicate<? super TestDescriptor> predicate) {
@@ -116,11 +117,14 @@ static EngineResultInfo errored(TestDescriptor rootDescriptor, DiscoveryIssueNot
 		}
 
 		private final TestDescriptor rootDescriptor;
+
+		@Nullable
 		private final Throwable cause;
+
 		private final DiscoveryIssueNotifier discoveryIssueNotifier;
 
 		EngineResultInfo(TestDescriptor rootDescriptor, DiscoveryIssueNotifier discoveryIssueNotifier,
-				Throwable cause) {
+				@Nullable Throwable cause) {
 			this.rootDescriptor = rootDescriptor;
 			this.discoveryIssueNotifier = discoveryIssueNotifier;
 			this.cause = cause;
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/LauncherFactory.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/LauncherFactory.java
index b3d6ab2613a0..719319efc946 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/LauncherFactory.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/LauncherFactory.java
@@ -35,6 +35,7 @@
 import org.junit.platform.launcher.LauncherSessionListener;
 import org.junit.platform.launcher.PostDiscoveryFilter;
 import org.junit.platform.launcher.TestExecutionListener;
+import org.junit.platform.launcher.jfr.JfrUtils;
 
 /**
  * Factory for creating {@link Launcher} instances by invoking {@link #create()}
@@ -139,6 +140,7 @@ private static DefaultLauncher createDefaultLauncher(LauncherConfig config,
 		Set<TestEngine> engines = collectTestEngines(config);
 		List<PostDiscoveryFilter> filters = collectPostDiscoveryFilters(config);
 		DefaultLauncher launcher = new DefaultLauncher(engines, filters, sessionLevelStore);
+		JfrUtils.registerListeners(launcher);
 		registerLauncherDiscoveryListeners(config, launcher);
 		registerTestExecutionListeners(config, launcher, configurationParameters);
 
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/LauncherPhase.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/LauncherPhase.java
index 107bcf971c94..33d612d7a26e 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/LauncherPhase.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/LauncherPhase.java
@@ -14,7 +14,9 @@
 
 import java.util.Locale;
 import java.util.Optional;
+import java.util.function.Function;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.logging.Logger;
 import org.junit.platform.commons.logging.LoggerFactory;
 import org.junit.platform.engine.ConfigurationParameters;
@@ -31,17 +33,18 @@ enum LauncherPhase {
 	private static final Logger logger = LoggerFactory.getLogger(LauncherPhase.class);
 
 	static Optional<LauncherPhase> getDiscoveryIssueFailurePhase(ConfigurationParameters configurationParameters) {
-		return configurationParameters.get(DISCOVERY_ISSUE_FAILURE_PHASE_PROPERTY_NAME, value -> {
+		Function<String, @Nullable LauncherPhase> stringLauncherPhaseFunction = value -> {
 			try {
 				return LauncherPhase.valueOf(value.toUpperCase(Locale.ROOT));
 			}
 			catch (Exception e) {
 				logger.warn(
-					() -> String.format("Ignoring invalid LauncherPhase '%s' set via the '%s' configuration parameter.",
+					() -> "Ignoring invalid LauncherPhase '%s' set via the '%s' configuration parameter.".formatted(
 						value, DISCOVERY_ISSUE_FAILURE_PHASE_PROPERTY_NAME));
 				return null;
 			}
-		});
+		};
+		return configurationParameters.get(DISCOVERY_ISSUE_FAILURE_PHASE_PROPERTY_NAME, stringLauncherPhaseFunction);
 	}
 
 	@Override
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/OutcomeDelayingEngineExecutionListener.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/OutcomeDelayingEngineExecutionListener.java
index 7bdfe458e03f..239044bc95e3 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/OutcomeDelayingEngineExecutionListener.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/OutcomeDelayingEngineExecutionListener.java
@@ -10,6 +10,11 @@
 
 package org.junit.platform.launcher.core;
 
+import static java.util.Objects.requireNonNull;
+
+import java.util.Optional;
+
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.engine.EngineExecutionListener;
 import org.junit.platform.engine.TestDescriptor;
 import org.junit.platform.engine.TestExecutionResult;
@@ -25,9 +30,12 @@ class OutcomeDelayingEngineExecutionListener extends DelegatingEngineExecutionLi
 	private final TestDescriptor engineDescriptor;
 
 	private volatile boolean engineStarted;
-	private volatile Outcome outcome;
-	private volatile String skipReason;
-	private volatile TestExecutionResult executionResult;
+
+	private volatile @Nullable Outcome outcome;
+
+	private volatile @Nullable String skipReason;
+
+	private volatile @Nullable TestExecutionResult executionResult;
 
 	OutcomeDelayingEngineExecutionListener(EngineExecutionListener delegate, TestDescriptor engineDescriptor) {
 		super(delegate);
@@ -66,10 +74,10 @@ public void executionFinished(TestDescriptor testDescriptor, TestExecutionResult
 
 	void reportEngineOutcome() {
 		if (outcome == Outcome.FINISHED) {
-			super.executionFinished(engineDescriptor, executionResult);
+			super.executionFinished(engineDescriptor, requireNonNull(executionResult));
 		}
 		else if (outcome == Outcome.SKIPPED) {
-			super.executionSkipped(engineDescriptor, skipReason);
+			super.executionSkipped(engineDescriptor, requireNonNull(skipReason));
 		}
 	}
 
@@ -80,9 +88,9 @@ void reportEngineStartIfNecessary() {
 	}
 
 	void reportEngineFailure(Throwable throwable) {
-		if (executionResult != null && executionResult.getThrowable().isPresent()) {
-			throwable.addSuppressed(executionResult.getThrowable().get());
-		}
+		Optional.ofNullable(this.executionResult) //
+				.flatMap(TestExecutionResult::getThrowable) //
+				.ifPresent(throwable::addSuppressed);
 		super.executionFinished(engineDescriptor, TestExecutionResult.failed(throwable));
 	}
 
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/ServiceLoaderRegistry.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/ServiceLoaderRegistry.java
index f06339619841..eebd6de021f7 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/ServiceLoaderRegistry.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/ServiceLoaderRegistry.java
@@ -10,14 +10,13 @@
 
 package org.junit.platform.launcher.core;
 
-import static java.util.stream.Collectors.toList;
-
 import java.util.ArrayList;
 import java.util.List;
 import java.util.ServiceLoader;
 import java.util.function.Function;
 import java.util.function.Predicate;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.logging.Logger;
 import org.junit.platform.commons.logging.LoggerFactory;
 import org.junit.platform.commons.util.ClassLoaderUtils;
@@ -45,19 +44,19 @@ static <T> Iterable<T> load(@SuppressWarnings("SameParameterValue") Class<T> typ
 		return load(type, collectingClassNameFilter, instances -> logLoadedInstances(type, instances, exclusions));
 	}
 
-	private static <T> String logLoadedInstances(Class<T> type, List<T> instances, List<String> exclusions) {
+	private static <T> String logLoadedInstances(Class<T> type, List<T> instances, @Nullable List<String> exclusions) {
 		String typeName = type.getSimpleName();
 		if (exclusions == null) {
-			return String.format("Loaded %s instances: %s", typeName, instances);
+			return "Loaded %s instances: %s".formatted(typeName, instances);
 		}
-		return String.format("Loaded %s instances: %s (excluded classes: %s)", typeName, instances, exclusions);
+		return "Loaded %s instances: %s (excluded classes: %s)".formatted(typeName, instances, exclusions);
 	}
 
 	private static <T> List<T> load(Class<T> type, Predicate<String> classNameFilter,
 			Function<List<T>, String> logMessageSupplier) {
 		ServiceLoader<T> serviceLoader = ServiceLoader.load(type, ClassLoaderUtils.getDefaultClassLoader());
 		Predicate<Class<? extends T>> providerPredicate = clazz -> classNameFilter.test(clazz.getName());
-		List<T> instances = ServiceLoaderUtils.filter(serviceLoader, providerPredicate).collect(toList());
+		List<T> instances = ServiceLoaderUtils.filter(serviceLoader, providerPredicate).toList();
 		getLogger().config(() -> logMessageSupplier.apply(instances));
 		return instances;
 	}
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/StackTracePruningEngineExecutionListener.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/StackTracePruningEngineExecutionListener.java
index 6a6193337d89..835a272e0af9 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/StackTracePruningEngineExecutionListener.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/StackTracePruningEngineExecutionListener.java
@@ -13,7 +13,6 @@
 import java.util.List;
 import java.util.Objects;
 import java.util.Optional;
-import java.util.stream.Collectors;
 
 import org.junit.platform.commons.util.ExceptionUtils;
 import org.junit.platform.engine.EngineExecutionListener;
@@ -50,21 +49,20 @@ private static List<String> getTestClassNames(TestDescriptor testDescriptor) {
 		return testDescriptor.getAncestors() //
 				.stream() //
 				.map(TestDescriptor::getSource) //
-				.filter(Optional::isPresent) //
-				.map(Optional::get) //
+				.flatMap(Optional::stream) //
 				.map(source -> {
-					if (source instanceof ClassSource) {
-						return ((ClassSource) source).getClassName();
+					if (source instanceof ClassSource classSource) {
+						return classSource.getClassName();
 					}
-					else if (source instanceof MethodSource) {
-						return ((MethodSource) source).getClassName();
+					else if (source instanceof MethodSource methodSource) {
+						return methodSource.getClassName();
 					}
 					else {
 						return null;
 					}
 				}) //
 				.filter(Objects::nonNull) //
-				.collect(Collectors.toList());
+				.toList();
 	}
 
 }
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/StreamInterceptingTestExecutionListener.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/StreamInterceptingTestExecutionListener.java
index 65a5f8ba453c..1a337082620e 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/StreamInterceptingTestExecutionListener.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/StreamInterceptingTestExecutionListener.java
@@ -55,7 +55,7 @@ static Optional<StreamInterceptingTestExecutionListener> create(ConfigurationPar
 		Optional<StreamInterceptor> stderrInterceptor = captureStderr ? StreamInterceptor.registerStderr(maxSize)
 				: Optional.empty();
 
-		if ((!stdoutInterceptor.isPresent() && captureStdout) || (!stderrInterceptor.isPresent() && captureStderr)) {
+		if ((stdoutInterceptor.isEmpty() && captureStdout) || (stderrInterceptor.isEmpty() && captureStderr)) {
 			stdoutInterceptor.ifPresent(StreamInterceptor::unregister);
 			stderrInterceptor.ifPresent(StreamInterceptor::unregister);
 			return Optional.empty();
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/StreamInterceptor.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/StreamInterceptor.java
index 85b69f64bb26..60a3d6a8cc9a 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/StreamInterceptor.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/StreamInterceptor.java
@@ -18,6 +18,8 @@
 import java.util.concurrent.ConcurrentLinkedDeque;
 import java.util.function.Consumer;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * @since 1.3
  */
@@ -112,7 +114,7 @@ private void pushToTop(RewindableByteArrayOutputStream out) {
 		}
 	}
 
-	private RewindableByteArrayOutputStream getOutput() {
+	private @Nullable RewindableByteArrayOutputStream getOutput() {
 		RewindableByteArrayOutputStream out = output.get();
 		return out.isMarked() ? out : mostRecentOutputs.peek();
 	}
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/TestEngineFormatter.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/TestEngineFormatter.java
index 558e6824fbe0..3ebd9f109783 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/TestEngineFormatter.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/TestEngineFormatter.java
@@ -33,7 +33,7 @@ static String format(String title, Iterable<TestEngine> testEngines) {
 
 	private static String format(String title, Stream<TestEngine> testEngines) {
 		String details = testEngines //
-				.map(engine -> String.format("- %s (%s)", engine.getId(), join(", ", computeAttributes(engine)))) //
+				.map(engine -> "- %s (%s)".formatted(engine.getId(), join(", ", computeAttributes(engine)))) //
 				.collect(joining("\n"));
 		return title + ":" + (details.isEmpty() ? " <none>" : "\n" + details);
 	}
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/package-info.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/package-info.java
index 779b81d67b93..fca61aab1372 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/package-info.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/package-info.java
@@ -5,4 +5,7 @@
  * LauncherDiscoveryRequestBuilder}.
  */
 
+@NullMarked
 package org.junit.platform.launcher.core;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-platform-jfr/src/main/java/org/junit/platform/jfr/FlightRecordingDiscoveryListener.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/jfr/FlightRecordingDiscoveryListener.java
similarity index 60%
rename from junit-platform-jfr/src/main/java/org/junit/platform/jfr/FlightRecordingDiscoveryListener.java
rename to junit-platform-launcher/src/main/java/org/junit/platform/launcher/jfr/FlightRecordingDiscoveryListener.java
index ed34f1289360..4f036f153283 100644
--- a/junit-platform-jfr/src/main/java/org/junit/platform/jfr/FlightRecordingDiscoveryListener.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/jfr/FlightRecordingDiscoveryListener.java
@@ -8,13 +8,12 @@
  * https://www.eclipse.org/legal/epl-v20.html
  */
 
-package org.junit.platform.jfr;
+package org.junit.platform.launcher.jfr;
 
-import static org.apiguardian.api.API.Status.STABLE;
+import static org.apiguardian.api.API.Status.INTERNAL;
 
+import java.util.HashMap;
 import java.util.Map;
-import java.util.concurrent.ConcurrentHashMap;
-import java.util.concurrent.atomic.AtomicReference;
 
 import jdk.jfr.Category;
 import jdk.jfr.Event;
@@ -23,6 +22,7 @@
 import jdk.jfr.StackTrace;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.util.ExceptionUtils;
 import org.junit.platform.engine.DiscoveryFilter;
 import org.junit.platform.engine.DiscoveryIssue;
@@ -38,50 +38,62 @@
  * @since 1.8
  * @see <a href="https://openjdk.java.net/jeps/328">JEP 328: Flight Recorder</a>
  */
-@API(status = STABLE, since = "1.11")
-public class FlightRecordingDiscoveryListener implements LauncherDiscoveryListener {
+@API(status = INTERNAL, since = "6.0")
+class FlightRecordingDiscoveryListener implements LauncherDiscoveryListener {
 
-	private final AtomicReference<LauncherDiscoveryEvent> launcherDiscoveryEvent = new AtomicReference<>();
-	private final Map<org.junit.platform.engine.UniqueId, EngineDiscoveryEvent> engineDiscoveryEvents = new ConcurrentHashMap<>();
+	private final Map<org.junit.platform.engine.UniqueId, EngineDiscoveryEvent> engineDiscoveryEvents = new HashMap<>();
+	private @Nullable LauncherDiscoveryEvent launcherDiscoveryEvent;
 
 	@Override
 	public void launcherDiscoveryStarted(LauncherDiscoveryRequest request) {
-		LauncherDiscoveryEvent event = new LauncherDiscoveryEvent();
-		event.selectors = request.getSelectorsByType(DiscoverySelector.class).size();
-		event.filters = request.getFiltersByType(DiscoveryFilter.class).size();
-		event.begin();
-		launcherDiscoveryEvent.set(event);
+		var event = new LauncherDiscoveryEvent();
+		if (event.isEnabled()) {
+			event.begin();
+			this.launcherDiscoveryEvent = event;
+		}
 	}
 
 	@Override
 	public void launcherDiscoveryFinished(LauncherDiscoveryRequest request) {
-		launcherDiscoveryEvent.getAndSet(null).commit();
+		LauncherDiscoveryEvent event = this.launcherDiscoveryEvent;
+		this.launcherDiscoveryEvent = null;
+		if (event != null && event.shouldCommit()) {
+			event.selectors = request.getSelectorsByType(DiscoverySelector.class).size();
+			event.filters = request.getFiltersByType(DiscoveryFilter.class).size();
+			event.commit();
+		}
 	}
 
 	@Override
 	public void engineDiscoveryStarted(org.junit.platform.engine.UniqueId engineId) {
-		EngineDiscoveryEvent event = new EngineDiscoveryEvent();
-		event.uniqueId = engineId.toString();
-		event.begin();
-		engineDiscoveryEvents.put(engineId, event);
+		var event = new EngineDiscoveryEvent();
+		if (event.isEnabled()) {
+			event.begin();
+			this.engineDiscoveryEvents.put(engineId, event);
+		}
 	}
 
 	@Override
 	public void engineDiscoveryFinished(org.junit.platform.engine.UniqueId engineId, EngineDiscoveryResult result) {
-		EngineDiscoveryEvent event = engineDiscoveryEvents.remove(engineId);
-		event.result = result.getStatus().toString();
-		event.commit();
+		EngineDiscoveryEvent event = this.engineDiscoveryEvents.remove(engineId);
+		if (event != null && event.shouldCommit()) {
+			event.uniqueId = engineId.toString();
+			event.result = result.getStatus().toString();
+			event.commit();
+		}
 	}
 
 	@Override
 	public void issueEncountered(org.junit.platform.engine.UniqueId engineId, DiscoveryIssue issue) {
-		DiscoveryIssueEvent event = new DiscoveryIssueEvent();
-		event.engineId = engineId.toString();
-		event.severity = issue.severity().name();
-		event.message = issue.message();
-		event.source = issue.source().map(Object::toString).orElse(null);
-		event.cause = issue.cause().map(ExceptionUtils::readStackTrace).orElse(null);
-		event.commit();
+		var event = new DiscoveryIssueEvent();
+		if (event.shouldCommit()) {
+			event.engineId = engineId.toString();
+			event.severity = issue.severity().name();
+			event.message = issue.message();
+			event.source = issue.source().map(Object::toString).orElse(null);
+			event.cause = issue.cause().map(ExceptionUtils::readStackTrace).orElse(null);
+			event.commit();
+		}
 	}
 
 	@Category({ "JUnit", "Discovery" })
@@ -106,9 +118,11 @@ static class EngineDiscoveryEvent extends DiscoveryEvent {
 
 		@UniqueId
 		@Label("Unique Id")
+		@Nullable
 		String uniqueId;
 
 		@Label("Result")
+		@Nullable
 		String result;
 	}
 
@@ -117,18 +131,23 @@ static class EngineDiscoveryEvent extends DiscoveryEvent {
 	static class DiscoveryIssueEvent extends DiscoveryEvent {
 
 		@Label("Engine Id")
+		@Nullable
 		String engineId;
 
 		@Label("Severity")
+		@Nullable
 		String severity;
 
 		@Label("Message")
+		@Nullable
 		String message;
 
 		@Label("Source")
+		@Nullable
 		String source;
 
 		@Label("Cause")
+		@Nullable
 		String cause;
 	}
 }
diff --git a/junit-platform-jfr/src/main/java/org/junit/platform/jfr/FlightRecordingExecutionListener.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/jfr/FlightRecordingExecutionListener.java
similarity index 61%
rename from junit-platform-jfr/src/main/java/org/junit/platform/jfr/FlightRecordingExecutionListener.java
rename to junit-platform-launcher/src/main/java/org/junit/platform/launcher/jfr/FlightRecordingExecutionListener.java
index a854b81d98ec..07ce9562af30 100644
--- a/junit-platform-jfr/src/main/java/org/junit/platform/jfr/FlightRecordingExecutionListener.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/jfr/FlightRecordingExecutionListener.java
@@ -8,14 +8,13 @@
  * https://www.eclipse.org/legal/epl-v20.html
  */
 
-package org.junit.platform.jfr;
+package org.junit.platform.launcher.jfr;
 
-import static org.apiguardian.api.API.Status.STABLE;
+import static org.apiguardian.api.API.Status.INTERNAL;
 
 import java.util.Map;
 import java.util.Optional;
 import java.util.concurrent.ConcurrentHashMap;
-import java.util.concurrent.atomic.AtomicReference;
 import java.util.stream.Collectors;
 
 import jdk.jfr.Category;
@@ -25,6 +24,7 @@
 import jdk.jfr.StackTrace;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.engine.TestExecutionResult;
 import org.junit.platform.engine.reporting.FileEntry;
 import org.junit.platform.engine.reporting.ReportEntry;
@@ -39,71 +39,87 @@
  * @since 1.8
  * @see <a href="https://openjdk.java.net/jeps/328">JEP 328: Flight Recorder</a>
  */
-@API(status = STABLE, since = "1.11")
-public class FlightRecordingExecutionListener implements TestExecutionListener {
+@API(status = INTERNAL, since = "6.0")
+class FlightRecordingExecutionListener implements TestExecutionListener {
 
-	private final AtomicReference<TestPlanExecutionEvent> testPlanExecutionEvent = new AtomicReference<>();
 	private final Map<org.junit.platform.engine.UniqueId, TestExecutionEvent> testExecutionEvents = new ConcurrentHashMap<>();
+	private @Nullable TestPlanExecutionEvent testPlanExecutionEvent;
 
 	@Override
 	public void testPlanExecutionStarted(TestPlan plan) {
-		TestPlanExecutionEvent event = new TestPlanExecutionEvent();
-		event.containsTests = plan.containsTests();
-		event.engineNames = plan.getRoots().stream().map(TestIdentifier::getDisplayName).collect(
-			Collectors.joining(", "));
-		testPlanExecutionEvent.set(event);
-		event.begin();
+		var event = new TestPlanExecutionEvent();
+		if (event.isEnabled()) {
+			event.begin();
+			this.testPlanExecutionEvent = event;
+		}
 	}
 
 	@Override
 	public void testPlanExecutionFinished(TestPlan plan) {
-		testPlanExecutionEvent.getAndSet(null).commit();
+		var event = this.testPlanExecutionEvent;
+		this.testPlanExecutionEvent = null;
+		if (event != null && event.shouldCommit()) {
+			event.containsTests = plan.containsTests();
+			event.engineNames = plan.getRoots().stream().map(TestIdentifier::getDisplayName).collect(
+				Collectors.joining(", "));
+			event.commit();
+		}
 	}
 
 	@Override
 	public void executionSkipped(TestIdentifier test, String reason) {
-		SkippedTestEvent event = new SkippedTestEvent();
-		event.initialize(test);
-		event.reason = reason;
-		event.commit();
+		var event = new SkippedTestEvent();
+		if (event.shouldCommit()) {
+			event.initialize(test);
+			event.reason = reason;
+			event.commit();
+		}
 	}
 
 	@Override
 	public void executionStarted(TestIdentifier test) {
-		TestExecutionEvent event = new TestExecutionEvent();
-		testExecutionEvents.put(test.getUniqueIdObject(), event);
-		event.initialize(test);
-		event.begin();
+		var event = new TestExecutionEvent();
+		if (event.isEnabled()) {
+			event.begin();
+			this.testExecutionEvents.put(test.getUniqueIdObject(), event);
+		}
 	}
 
 	@Override
 	public void executionFinished(TestIdentifier test, TestExecutionResult result) {
-		Optional<Throwable> throwable = result.getThrowable();
-		TestExecutionEvent event = testExecutionEvents.remove(test.getUniqueIdObject());
-		event.end();
-		event.result = result.getStatus().toString();
-		event.exceptionClass = throwable.map(Throwable::getClass).orElse(null);
-		event.exceptionMessage = throwable.map(Throwable::getMessage).orElse(null);
-		event.commit();
+		TestExecutionEvent event = this.testExecutionEvents.remove(test.getUniqueIdObject());
+		if (event != null && event.shouldCommit()) {
+			event.end();
+			event.initialize(test);
+			event.result = result.getStatus().toString();
+			Optional<Throwable> throwable = result.getThrowable();
+			event.exceptionClass = throwable.map(Throwable::getClass).orElse(null);
+			event.exceptionMessage = throwable.map(Throwable::getMessage).orElse(null);
+			event.commit();
+		}
 	}
 
 	@Override
 	public void reportingEntryPublished(TestIdentifier test, ReportEntry reportEntry) {
-		for (Map.Entry<String, String> entry : reportEntry.getKeyValuePairs().entrySet()) {
-			ReportEntryEvent event = new ReportEntryEvent();
-			event.uniqueId = test.getUniqueId();
-			event.key = entry.getKey();
-			event.value = entry.getValue();
-			event.commit();
+		for (var entry : reportEntry.getKeyValuePairs().entrySet()) {
+			var event = new ReportEntryEvent();
+			if (event.shouldCommit()) {
+				event.uniqueId = test.getUniqueId();
+				event.key = entry.getKey();
+				event.value = entry.getValue();
+				event.commit();
+			}
 		}
 	}
 
 	@Override
 	public void fileEntryPublished(TestIdentifier testIdentifier, FileEntry file) {
-		FileEntryEvent event = new FileEntryEvent();
-		event.uniqueId = testIdentifier.getUniqueId();
-		event.path = file.getPath().toAbsolutePath().toString();
-		event.commit();
+		var event = new FileEntryEvent();
+		if (event.shouldCommit()) {
+			event.uniqueId = testIdentifier.getUniqueId();
+			event.path = file.getPath().toAbsolutePath().toString();
+			event.commit();
+		}
 	}
 
 	@Category({ "JUnit", "Execution" })
@@ -114,21 +130,32 @@ abstract static class ExecutionEvent extends Event {
 	@Label("Test Execution")
 	@Name("org.junit.TestPlanExecution")
 	static class TestPlanExecutionEvent extends ExecutionEvent {
+
 		@Label("Contains Tests")
 		boolean containsTests;
+
 		@Label("Engine Names")
+		@Nullable
 		String engineNames;
 	}
 
 	abstract static class TestEvent extends ExecutionEvent {
+
 		@UniqueId
 		@Label("Unique Id")
+		@Nullable
 		String uniqueId;
+
 		@Label("Display Name")
+		@Nullable
 		String displayName;
+
 		@Label("Tags")
+		@Nullable
 		String tags;
+
 		@Label("Type")
+		@Nullable
 		String type;
 
 		void initialize(TestIdentifier test) {
@@ -143,39 +170,56 @@ void initialize(TestIdentifier test) {
 	@Name("org.junit.SkippedTest")
 	static class SkippedTestEvent extends TestEvent {
 		@Label("Reason")
+		@Nullable
 		String reason;
 	}
 
 	@Label("Test")
 	@Name("org.junit.TestExecution")
 	static class TestExecutionEvent extends TestEvent {
+
 		@Label("Result")
+		@Nullable
 		String result;
+
 		@Label("Exception Class")
+		@Nullable
 		Class<?> exceptionClass;
+
 		@Label("Exception Message")
+		@Nullable
 		String exceptionMessage;
 	}
 
 	@Label("Report Entry")
 	@Name("org.junit.ReportEntry")
 	static class ReportEntryEvent extends ExecutionEvent {
+
 		@UniqueId
 		@Label("Unique Id")
+		@Nullable
 		String uniqueId;
+
 		@Label("Key")
+		@Nullable
 		String key;
+
 		@Label("Value")
+		@Nullable
 		String value;
 	}
 
 	@Label("File Entry")
 	@Name("org.junit.FileEntry")
 	static class FileEntryEvent extends ExecutionEvent {
+
 		@UniqueId
 		@Label("Unique Id")
+		@Nullable
 		String uniqueId;
+
 		@Label("Path")
+		@Nullable
 		String path;
 	}
 }
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/jfr/JfrUtils.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/jfr/JfrUtils.java
new file mode 100644
index 000000000000..7ec83dd91fbb
--- /dev/null
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/jfr/JfrUtils.java
@@ -0,0 +1,38 @@
+/*
+ * Copyright 2015-2025 the original author or authors.
+ *
+ * All rights reserved. This program and the accompanying materials are
+ * made available under the terms of the Eclipse Public License v2.0 which
+ * accompanies this distribution and is available at
+ *
+ * https://www.eclipse.org/legal/epl-v20.html
+ */
+
+package org.junit.platform.launcher.jfr;
+
+import static org.apiguardian.api.API.Status.INTERNAL;
+
+import org.apiguardian.api.API;
+import org.junit.platform.commons.support.ReflectionSupport;
+import org.junit.platform.launcher.Launcher;
+
+/**
+ * Internal utility for Java Flight Recorder (JFR) support.
+ *
+ * @since 6.0
+ */
+@API(status = INTERNAL, since = "6.0")
+public class JfrUtils {
+
+	public static void registerListeners(Launcher launcher) {
+		if (isJfrAvailable()) {
+			launcher.registerLauncherDiscoveryListeners(new FlightRecordingDiscoveryListener());
+			launcher.registerTestExecutionListeners(new FlightRecordingExecutionListener());
+		}
+	}
+
+	private static boolean isJfrAvailable() {
+		return System.getProperty("org.graalvm.nativeimage.imagecode") == null //
+				&& ReflectionSupport.tryToLoadClass("jdk.jfr.FlightRecorder").toOptional().isPresent();
+	}
+}
diff --git a/junit-platform-jfr/src/main/java/org/junit/platform/jfr/UniqueId.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/jfr/UniqueId.java
similarity index 94%
rename from junit-platform-jfr/src/main/java/org/junit/platform/jfr/UniqueId.java
rename to junit-platform-launcher/src/main/java/org/junit/platform/launcher/jfr/UniqueId.java
index 21ced50f0e42..c13b0e3d1bb7 100644
--- a/junit-platform-jfr/src/main/java/org/junit/platform/jfr/UniqueId.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/jfr/UniqueId.java
@@ -8,7 +8,7 @@
  * https://www.eclipse.org/legal/epl-v20.html
  */
 
-package org.junit.platform.jfr;
+package org.junit.platform.launcher.jfr;
 
 import java.lang.annotation.ElementType;
 import java.lang.annotation.Retention;
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/jfr/package-info.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/jfr/package-info.java
new file mode 100644
index 000000000000..0045dfb23da8
--- /dev/null
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/jfr/package-info.java
@@ -0,0 +1,8 @@
+/**
+ * Java Flight Recorder (JFR) support package.
+ */
+
+@NullMarked
+package org.junit.platform.launcher.jfr;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/LegacyReportingUtils.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/LegacyReportingUtils.java
deleted file mode 100644
index 9417a1482856..000000000000
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/LegacyReportingUtils.java
+++ /dev/null
@@ -1,86 +0,0 @@
-/*
- * Copyright 2015-2025 the original author or authors.
- *
- * All rights reserved. This program and the accompanying materials are
- * made available under the terms of the Eclipse Public License v2.0 which
- * accompanies this distribution and is available at
- *
- * https://www.eclipse.org/legal/epl-v20.html
- */
-
-package org.junit.platform.launcher.listeners;
-
-import static org.apiguardian.api.API.Status.DEPRECATED;
-
-import org.apiguardian.api.API;
-import org.junit.platform.commons.util.Preconditions;
-import org.junit.platform.engine.support.descriptor.ClassSource;
-import org.junit.platform.launcher.TestIdentifier;
-import org.junit.platform.launcher.TestPlan;
-
-/**
- * Utility methods for dealing with legacy reporting infrastructure, such as
- * reporting systems built on the Ant-based XML reporting format for JUnit 4.
- *
- * @since 1.0.3
- * @deprecated Use {@link org.junit.platform.reporting.legacy.LegacyReportingUtils}
- * instead.
- */
-@Deprecated
-@SuppressWarnings("JavadocReference")
-@API(status = DEPRECATED, since = "1.6")
-public class LegacyReportingUtils {
-
-	private LegacyReportingUtils() {
-		/* no-op */
-	}
-
-	/**
-	 * Get the class name for the supplied {@link TestIdentifier} using the
-	 * supplied {@link TestPlan}.
-	 *
-	 * <p>This implementation attempts to find the closest test identifier with
-	 * a {@link ClassSource} by traversing the hierarchy upwards towards the
-	 * root starting with the supplied test identifier. In case no such source
-	 * is found, it falls back to using the parent's
-	 * {@linkplain TestIdentifier#getLegacyReportingName legacy reporting name}.
-	 *
-	 * @param testPlan the test plan that contains the {@code TestIdentifier};
-	 * never {@code null}
-	 * @param testIdentifier the identifier to determine the class name for;
-	 * never {@code null}
-	 * @see TestIdentifier#getLegacyReportingName
-	 */
-	public static String getClassName(TestPlan testPlan, TestIdentifier testIdentifier) {
-		Preconditions.notNull(testPlan, "testPlan must not be null");
-		Preconditions.notNull(testIdentifier, "testIdentifier must not be null");
-		for (TestIdentifier current = testIdentifier; current != null; current = getParent(testPlan, current)) {
-			ClassSource source = getClassSource(current);
-			if (source != null) {
-				return source.getClassName();
-			}
-		}
-		return getParentLegacyReportingName(testPlan, testIdentifier);
-	}
-
-	private static TestIdentifier getParent(TestPlan testPlan, TestIdentifier testIdentifier) {
-		return testPlan.getParent(testIdentifier).orElse(null);
-	}
-
-	private static ClassSource getClassSource(TestIdentifier current) {
-		// @formatter:off
-		return current.getSource()
-				.filter(ClassSource.class::isInstance)
-				.map(ClassSource.class::cast)
-				.orElse(null);
-		// @formatter:on
-	}
-
-	private static String getParentLegacyReportingName(TestPlan testPlan, TestIdentifier testIdentifier) {
-		// @formatter:off
-		return testPlan.getParent(testIdentifier)
-				.map(TestIdentifier::getLegacyReportingName)
-				.orElse("<unrooted>");
-		// @formatter:on
-	}
-}
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/LoggingListener.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/LoggingListener.java
index 3b6e37907565..14ded1f6b141 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/LoggingListener.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/LoggingListener.java
@@ -18,6 +18,7 @@
 import java.util.logging.Logger;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.util.Preconditions;
 import org.junit.platform.engine.TestExecutionResult;
 import org.junit.platform.launcher.TestExecutionListener;
@@ -78,14 +79,15 @@ public static LoggingListener forJavaUtilLogging(Level logLevel) {
 	 * @see #forJavaUtilLogging()
 	 * @see #forJavaUtilLogging(Level)
 	 */
-	public static LoggingListener forBiConsumer(BiConsumer<Throwable, Supplier<String>> logger) {
+	public static LoggingListener forBiConsumer(BiConsumer<@Nullable Throwable, Supplier<String>> logger) {
 		return new LoggingListener(logger);
 	}
 
-	private final BiConsumer<Throwable, Supplier<String>> logger;
+	private final BiConsumer<@Nullable Throwable, Supplier<String>> logger;
 
-	private LoggingListener(BiConsumer<Throwable, Supplier<String>> logger) {
-		this.logger = Preconditions.notNull(logger, "logger must not be null");
+	private LoggingListener(BiConsumer<@Nullable Throwable, Supplier<String>> logger) {
+		Preconditions.notNull(logger, "logger must not be null");
+		this.logger = logger;
 	}
 
 	@Override
@@ -123,8 +125,8 @@ private void log(String message, Object... args) {
 		logWithThrowable(message, null, args);
 	}
 
-	private void logWithThrowable(String message, Throwable t, Object... args) {
-		this.logger.accept(t, () -> String.format(message, args));
+	private void logWithThrowable(String message, @Nullable Throwable t, Object... args) {
+		this.logger.accept(t, () -> message.formatted(args));
 	}
 
 }
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/MutableTestExecutionSummary.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/MutableTestExecutionSummary.java
index 0ef6826b016b..483e67293da9 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/MutableTestExecutionSummary.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/MutableTestExecutionSummary.java
@@ -14,6 +14,7 @@
 import static java.util.Collections.synchronizedList;
 
 import java.io.PrintWriter;
+import java.io.Serial;
 import java.time.Duration;
 import java.util.ArrayList;
 import java.util.Collections;
@@ -250,7 +251,7 @@ private void printStackTrace(PrintWriter writer, StackTraceElement[] parentTrace
 		seenThrowables.add(throwable);
 
 		StackTraceElement[] trace = throwable.getStackTrace();
-		if (parentTrace != null && parentTrace.length > 0) {
+		if (parentTrace.length > 0) {
 			writer.printf("%s%s%s%n", indentation, caption, throwable);
 		}
 		int duplicates = numberOfCommonFrames(trace, parentTrace);
@@ -282,18 +283,11 @@ private int numberOfCommonFrames(StackTraceElement[] currentTrace, StackTraceEle
 		return currentTrace.length - 1 - currentIndex;
 	}
 
-	private static class DefaultFailure implements Failure {
+	private record DefaultFailure(TestIdentifier testIdentifier, Throwable exception) implements Failure {
 
+		@Serial
 		private static final long serialVersionUID = 1L;
 
-		private final TestIdentifier testIdentifier;
-		private final Throwable exception;
-
-		DefaultFailure(TestIdentifier testIdentifier, Throwable exception) {
-			this.testIdentifier = testIdentifier;
-			this.exception = exception;
-		}
-
 		@Override
 		public TestIdentifier getTestIdentifier() {
 			return testIdentifier;
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/OutputDir.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/OutputDir.java
index acff49f57a9d..34be95e19c12 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/OutputDir.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/OutputDir.java
@@ -17,7 +17,6 @@
 import java.io.UncheckedIOException;
 import java.nio.file.Files;
 import java.nio.file.Path;
-import java.nio.file.Paths;
 import java.nio.file.attribute.BasicFileAttributes;
 import java.security.SecureRandom;
 import java.util.Optional;
@@ -36,7 +35,7 @@ public class OutputDir {
 		Pattern.quote(OUTPUT_DIR_UNIQUE_NUMBER_PLACEHOLDER));
 
 	public static OutputDir create(Optional<String> customDir) {
-		return create(customDir, () -> Paths.get("."));
+		return create(customDir, () -> Path.of("."));
 	}
 
 	static OutputDir create(Optional<String> customDir, Supplier<Path> currentWorkingDir) {
@@ -98,7 +97,7 @@ public Path toPath() {
 	}
 
 	public Path createFile(String prefix, String extension) throws UncheckedIOException {
-		String filename = String.format("%s-%d.%s", prefix, Math.abs(random.nextLong()), extension);
+		String filename = "%s-%d.%s".formatted(prefix, Math.abs(random.nextLong()), extension);
 		Path outputFile = path.resolve(filename);
 
 		try {
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/SummaryGeneratingListener.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/SummaryGeneratingListener.java
index 751888b2ae86..e404a7457c1a 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/SummaryGeneratingListener.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/SummaryGeneratingListener.java
@@ -10,13 +10,16 @@
 
 package org.junit.platform.launcher.listeners;
 
+import static java.util.Objects.requireNonNull;
 import static java.util.stream.Stream.concat;
 import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import java.util.stream.Stream;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.PreconditionViolationException;
+import org.junit.platform.commons.util.Preconditions;
 import org.junit.platform.engine.TestExecutionResult;
 import org.junit.platform.launcher.TestExecutionListener;
 import org.junit.platform.launcher.TestIdentifier;
@@ -32,8 +35,9 @@
 @API(status = MAINTAINED, since = "1.0")
 public class SummaryGeneratingListener implements TestExecutionListener {
 
-	private TestPlan testPlan;
-	private MutableTestExecutionSummary summary;
+	private @Nullable TestPlan testPlan;
+
+	private @Nullable MutableTestExecutionSummary summary;
 
 	public SummaryGeneratingListener() {
 
@@ -43,7 +47,11 @@ public SummaryGeneratingListener() {
 	 * Get the summary generated by this listener.
 	 */
 	public TestExecutionSummary getSummary() {
-		return this.summary;
+		return getMutableSummary();
+	}
+
+	private MutableTestExecutionSummary getMutableSummary() {
+		return Preconditions.notNull(this.summary, "No tests have yet been executed");
 	}
 
 	@Override
@@ -54,22 +62,25 @@ public void testPlanExecutionStarted(TestPlan testPlan) {
 
 	@Override
 	public void testPlanExecutionFinished(TestPlan testPlan) {
-		this.summary.timeFinished = System.currentTimeMillis();
-		this.summary.timeFinishedNanos = System.nanoTime();
+		var summary = getMutableSummary();
+		summary.timeFinished = System.currentTimeMillis();
+		summary.timeFinishedNanos = System.nanoTime();
 	}
 
 	@Override
 	public void dynamicTestRegistered(TestIdentifier testIdentifier) {
+		var summary = getMutableSummary();
 		if (testIdentifier.isContainer()) {
-			this.summary.containersFound.incrementAndGet();
+			summary.containersFound.incrementAndGet();
 		}
 		if (testIdentifier.isTest()) {
-			this.summary.testsFound.incrementAndGet();
+			summary.testsFound.incrementAndGet();
 		}
 	}
 
 	@Override
 	public void executionSkipped(TestIdentifier testIdentifier, String reason) {
+		var testPlan = requireNonNull(this.testPlan);
 		// @formatter:off
 		long skippedContainers = concat(Stream.of(testIdentifier), testPlan.getDescendants(testIdentifier).stream())
 				.filter(TestIdentifier::isContainer)
@@ -78,60 +89,59 @@ public void executionSkipped(TestIdentifier testIdentifier, String reason) {
 				.filter(TestIdentifier::isTest)
 				.count();
 		// @formatter:on
-		this.summary.containersSkipped.addAndGet(skippedContainers);
-		this.summary.testsSkipped.addAndGet(skippedTests);
+		var summary = getMutableSummary();
+		summary.containersSkipped.addAndGet(skippedContainers);
+		summary.testsSkipped.addAndGet(skippedTests);
 	}
 
 	@Override
 	public void executionStarted(TestIdentifier testIdentifier) {
+		var summary = getMutableSummary();
 		if (testIdentifier.isContainer()) {
-			this.summary.containersStarted.incrementAndGet();
+			summary.containersStarted.incrementAndGet();
 		}
 		if (testIdentifier.isTest()) {
-			this.summary.testsStarted.incrementAndGet();
+			summary.testsStarted.incrementAndGet();
 		}
 	}
 
 	@Override
 	public void executionFinished(TestIdentifier testIdentifier, TestExecutionResult testExecutionResult) {
+		var summary = getMutableSummary();
 
 		switch (testExecutionResult.getStatus()) {
 
-			case SUCCESSFUL: {
+			case SUCCESSFUL -> {
 				if (testIdentifier.isContainer()) {
-					this.summary.containersSucceeded.incrementAndGet();
+					summary.containersSucceeded.incrementAndGet();
 				}
 				if (testIdentifier.isTest()) {
-					this.summary.testsSucceeded.incrementAndGet();
+					summary.testsSucceeded.incrementAndGet();
 				}
-				break;
 			}
 
-			case ABORTED: {
+			case ABORTED -> {
 				if (testIdentifier.isContainer()) {
-					this.summary.containersAborted.incrementAndGet();
+					summary.containersAborted.incrementAndGet();
 				}
 				if (testIdentifier.isTest()) {
-					this.summary.testsAborted.incrementAndGet();
+					summary.testsAborted.incrementAndGet();
 				}
-				break;
 			}
 
-			case FAILED: {
+			case FAILED -> {
 				if (testIdentifier.isContainer()) {
-					this.summary.containersFailed.incrementAndGet();
+					summary.containersFailed.incrementAndGet();
 				}
 				if (testIdentifier.isTest()) {
-					this.summary.testsFailed.incrementAndGet();
+					summary.testsFailed.incrementAndGet();
 				}
 				testExecutionResult.getThrowable().ifPresent(
-					throwable -> this.summary.addFailure(testIdentifier, throwable));
-				break;
+					throwable -> summary.addFailure(testIdentifier, throwable));
 			}
 
-			default:
-				throw new PreconditionViolationException(
-					"Unsupported execution status:" + testExecutionResult.getStatus());
+			default -> throw new PreconditionViolationException(
+				"Unsupported execution status:" + testExecutionResult.getStatus());
 		}
 	}
 
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/UniqueIdTrackingListener.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/UniqueIdTrackingListener.java
index 8b8b8d51f274..802168bb5267 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/UniqueIdTrackingListener.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/UniqueIdTrackingListener.java
@@ -10,6 +10,7 @@
 
 package org.junit.platform.launcher.listeners;
 
+import static java.util.Objects.requireNonNull;
 import static org.apiguardian.api.API.Status.STABLE;
 
 import java.io.IOException;
@@ -23,6 +24,7 @@
 import java.util.function.Supplier;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.logging.Logger;
 import org.junit.platform.commons.logging.LoggerFactory;
 import org.junit.platform.engine.ConfigurationParameters;
@@ -134,7 +136,8 @@ public class UniqueIdTrackingListener implements TestExecutionListener {
 	private final List<String> uniqueIds = new ArrayList<>();
 
 	private boolean enabled;
-	private TestPlan testPlan;
+
+	private @Nullable TestPlan testPlan;
 
 	public UniqueIdTrackingListener() {
 		// to avoid missing-explicit-ctor warning
@@ -165,7 +168,7 @@ public void executionFinished(TestIdentifier testIdentifier, TestExecutionResult
 	private void trackTestUidRecursively(TestIdentifier testIdentifier) {
 		boolean tracked = trackTestUid(testIdentifier);
 		if (!tracked) {
-			this.testPlan.getChildren(testIdentifier).forEach(this::trackTestUidRecursively);
+			requireNonNull(this.testPlan).getChildren(testIdentifier).forEach(this::trackTestUidRecursively);
 		}
 	}
 
@@ -206,7 +209,7 @@ private Path createOutputFile(ConfigurationParameters configurationParameters) {
 		String prefix = configurationParameters.get(OUTPUT_FILE_PREFIX_PROPERTY_NAME) //
 				.orElse(DEFAULT_OUTPUT_FILE_PREFIX);
 		Supplier<Path> workingDirSupplier = () -> configurationParameters.get(WORKING_DIR_PROPERTY_NAME).map(
-			Paths::get).orElseGet(() -> Paths.get("."));
+			Paths::get).orElseGet(() -> Path.of("."));
 		return OutputDir.create(configurationParameters.get(OUTPUT_DIR_PROPERTY_NAME), workingDirSupplier) //
 				.createFile(prefix, "txt");
 	}
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/discovery/CompositeLauncherDiscoveryListener.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/discovery/CompositeLauncherDiscoveryListener.java
index a9ba957786e4..f8695a9fc09d 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/discovery/CompositeLauncherDiscoveryListener.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/discovery/CompositeLauncherDiscoveryListener.java
@@ -12,8 +12,6 @@
 
 import static org.junit.platform.commons.util.CollectionUtils.forEachInReverseOrder;
 
-import java.util.ArrayList;
-import java.util.Collections;
 import java.util.List;
 
 import org.junit.platform.engine.DiscoveryIssue;
@@ -33,7 +31,7 @@ class CompositeLauncherDiscoveryListener implements LauncherDiscoveryListener {
 	private final List<LauncherDiscoveryListener> listeners;
 
 	CompositeLauncherDiscoveryListener(List<LauncherDiscoveryListener> listeners) {
-		this.listeners = Collections.unmodifiableList(new ArrayList<>(listeners));
+		this.listeners = List.copyOf(listeners);
 	}
 
 	@Override
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/discovery/LoggingLauncherDiscoveryListener.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/discovery/LoggingLauncherDiscoveryListener.java
index b57289f8dab0..922b9068b2e4 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/discovery/LoggingLauncherDiscoveryListener.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/discovery/LoggingLauncherDiscoveryListener.java
@@ -69,23 +69,19 @@ public void engineDiscoveryFinished(UniqueId engineId, EngineDiscoveryResult res
 	@Override
 	public void selectorProcessed(UniqueId engineId, DiscoverySelector selector, SelectorResolutionResult result) {
 		switch (result.getStatus()) {
-			case RESOLVED:
-				logger.debug(() -> selector + " was resolved by " + engineId);
-				break;
-			case FAILED:
-				logger.error(result.getThrowable().orElse(null),
-					() -> "Resolution of " + selector + " by " + engineId + " failed");
-				break;
-			case UNRESOLVED:
+			case RESOLVED -> logger.debug(() -> selector + " was resolved by " + engineId);
+			case FAILED -> logger.error(result.getThrowable().orElse(null),
+				() -> "Resolution of " + selector + " by " + engineId + " failed");
+			case UNRESOLVED -> {
 				Consumer<Supplier<String>> loggingConsumer = logger::debug;
-				if (selector instanceof UniqueIdSelector) {
-					UniqueId uniqueId = ((UniqueIdSelector) selector).getUniqueId();
+				if (selector instanceof UniqueIdSelector uniqueIdSelector) {
+					UniqueId uniqueId = uniqueIdSelector.getUniqueId();
 					if (uniqueId.hasPrefix(engineId)) {
 						loggingConsumer = logger::warn;
 					}
 				}
 				loggingConsumer.accept(() -> selector + " could not be resolved by " + engineId);
-				break;
+			}
 		}
 	}
 
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/discovery/package-info.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/discovery/package-info.java
index 371df34d4fb3..de2821f42f91 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/discovery/package-info.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/discovery/package-info.java
@@ -6,4 +6,7 @@
  * @since 1.6
  */
 
+@NullMarked
 package org.junit.platform.launcher.listeners.discovery;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/package-info.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/package-info.java
index d8a0a06ea0a9..e662ea8e912e 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/package-info.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/package-info.java
@@ -4,4 +4,7 @@
  * the {@link org.junit.platform.launcher.Launcher Launcher}.
  */
 
+@NullMarked
 package org.junit.platform.launcher.listeners;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/session/CompositeLauncherSessionListener.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/session/CompositeLauncherSessionListener.java
index c1c13327652c..e03a6940f237 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/session/CompositeLauncherSessionListener.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/session/CompositeLauncherSessionListener.java
@@ -12,8 +12,6 @@
 
 import static org.junit.platform.commons.util.CollectionUtils.forEachInReverseOrder;
 
-import java.util.ArrayList;
-import java.util.Collections;
 import java.util.List;
 
 import org.junit.platform.launcher.LauncherSession;
@@ -28,7 +26,7 @@ class CompositeLauncherSessionListener implements LauncherSessionListener {
 	private final List<LauncherSessionListener> listeners;
 
 	CompositeLauncherSessionListener(List<LauncherSessionListener> listeners) {
-		this.listeners = Collections.unmodifiableList(new ArrayList<>(listeners));
+		this.listeners = List.copyOf(listeners);
 	}
 
 	@Override
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/session/package-info.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/session/package-info.java
index 97541a153cba..7c6f4f5167ac 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/session/package-info.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/listeners/session/package-info.java
@@ -6,4 +6,7 @@
  * @since 1.8
  */
 
+@NullMarked
 package org.junit.platform.launcher.listeners.session;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/package-info.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/package-info.java
index 4005a8426267..4101c31e89d5 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/package-info.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/package-info.java
@@ -4,4 +4,7 @@
  * <p>This API is typically used by IDEs and build tools.
  */
 
+@NullMarked
 package org.junit.platform.launcher;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/DequeStack.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/DequeStack.java
index 4d3899199cee..6cff93dd5af6 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/DequeStack.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/DequeStack.java
@@ -13,6 +13,8 @@
 import java.util.ArrayDeque;
 import java.util.Deque;
 
+import org.junit.platform.commons.util.Preconditions;
+
 /**
  * @since 1.1
  */
@@ -27,12 +29,12 @@ public void push(T t) {
 
 	@Override
 	public T peek() {
-		return deque.peek();
+		return Preconditions.notNull(deque.peek(), () -> "stack is empty");
 	}
 
 	@Override
 	public T pop() {
-		return deque.pollFirst();
+		return Preconditions.notNull(deque.pollFirst(), () -> "stack is empty");
 	}
 
 	@Override
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/Operator.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/Operator.java
index 7adc69050a06..4f09bb92c59b 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/Operator.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/Operator.java
@@ -10,6 +10,7 @@
 
 package org.junit.platform.launcher.tagexpression;
 
+import static java.util.Objects.requireNonNull;
 import static org.junit.platform.launcher.tagexpression.Operator.Associativity.Left;
 import static org.junit.platform.launcher.tagexpression.ParseStatus.missingOperatorBetween;
 import static org.junit.platform.launcher.tagexpression.ParseStatus.missingRhsOperand;
@@ -19,6 +20,8 @@
 import java.util.function.BiFunction;
 import java.util.function.Function;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * @since 1.1
  */
@@ -36,33 +39,35 @@ static Operator nullaryOperator(String representation, int precedence) {
 		return new Operator(representation, precedence, 0, null, (expressions, operatorToken) -> success());
 	}
 
+	@SuppressWarnings("SameParameterValue")
 	static Operator unaryOperator(String representation, int precedence, Associativity associativity,
 			Function<TagExpression, TagExpression> unaryExpression) {
 
 		return new Operator(representation, precedence, 1, associativity, (expressions, operatorToken) -> {
 			TokenWith<TagExpression> rhs = expressions.pop();
-			if (operatorToken.isLeftOf(rhs.token)) {
-				Token combinedToken = operatorToken.concatenate(rhs.token);
-				expressions.push(new TokenWith<>(combinedToken, unaryExpression.apply(rhs.element)));
+			if (operatorToken.isLeftOf(rhs.token())) {
+				Token combinedToken = operatorToken.concatenate(rhs.token());
+				expressions.push(new TokenWith<>(combinedToken, unaryExpression.apply(rhs.element())));
 				return success();
 			}
 			return missingRhsOperand(operatorToken, representation);
 		});
 	}
 
+	@SuppressWarnings("SameParameterValue")
 	static Operator binaryOperator(String representation, int precedence, Associativity associativity,
 			BiFunction<TagExpression, TagExpression, TagExpression> binaryExpression) {
 
 		return new Operator(representation, precedence, 2, associativity, (expressions, operatorToken) -> {
 			TokenWith<TagExpression> rhs = expressions.pop();
 			TokenWith<TagExpression> lhs = expressions.pop();
-			Token lhsToken = lhs.token;
-			if (lhsToken.isLeftOf(operatorToken) && operatorToken.isLeftOf(rhs.token)) {
-				Token combinedToken = lhsToken.concatenate(operatorToken).concatenate(rhs.token);
-				expressions.push(new TokenWith<>(combinedToken, binaryExpression.apply(lhs.element, rhs.element)));
+			Token lhsToken = lhs.token();
+			if (lhsToken.isLeftOf(operatorToken) && operatorToken.isLeftOf(rhs.token())) {
+				Token combinedToken = lhsToken.concatenate(operatorToken).concatenate(rhs.token());
+				expressions.push(new TokenWith<>(combinedToken, binaryExpression.apply(lhs.element(), rhs.element())));
 				return success();
 			}
-			if (rhs.token.isLeftOf(operatorToken)) {
+			if (rhs.token().isLeftOf(operatorToken)) {
 				return missingRhsOperand(operatorToken, representation);
 			}
 			if (operatorToken.isLeftOf(lhsToken)) {
@@ -75,10 +80,12 @@ static Operator binaryOperator(String representation, int precedence, Associativ
 	private final String representation;
 	private final int precedence;
 	private final int arity;
-	private final Associativity associativity;
+
+	private final @Nullable Associativity associativity;
+
 	private final TagExpressionCreator tagExpressionCreator;
 
-	private Operator(String representation, int precedence, int arity, Associativity associativity,
+	private Operator(String representation, int precedence, int arity, @Nullable Associativity associativity,
 			TagExpressionCreator tagExpressionCreator) {
 
 		this.representation = representation;
@@ -126,7 +133,8 @@ private String createMissingOperandMessage(Stack<TokenWith<TagExpression>> expre
 			if (2 == mismatch) {
 				return "missing lhs and rhs operand";
 			}
-			return missingOneOperand(operatorToken.isLeftOf(expressions.peek().token) ? "lhs" : "rhs");
+			return missingOneOperand(
+				operatorToken.isLeftOf(requireNonNull(expressions.peek()).token()) ? "lhs" : "rhs");
 		}
 		return "missing operand";
 	}
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/Operators.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/Operators.java
index 541ceb976bb1..3ea407374d4c 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/Operators.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/Operators.java
@@ -18,6 +18,8 @@
 import java.util.Map;
 import java.util.stream.Stream;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * @since 1.1
  */
@@ -30,10 +32,7 @@ class Operators {
 	private final Map<String, Operator> representationToOperator = Stream.of(Not, And, Or).collect(
 		toMap(Operator::representation, identity()));
 
-	boolean isOperator(String token) {
-		return representationToOperator.containsKey(token);
-	}
-
+	@Nullable
 	Operator operatorFor(String token) {
 		return representationToOperator.get(token);
 	}
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/ParseResult.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/ParseResult.java
index 0882acda8ede..befc5227eaaa 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/ParseResult.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/ParseResult.java
@@ -41,7 +41,7 @@ default TagExpression tagExpressionOrThrow(Function<String, RuntimeException> ex
 		if (errorMessage().isPresent()) {
 			throw exceptionCreator.apply(errorMessage().get());
 		}
-		return tagExpression().get();
+		return tagExpression().orElseThrow();
 	}
 
 	/**
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/ParseStatus.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/ParseStatus.java
index 695ef20c70ac..de4bbd374d12 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/ParseStatus.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/ParseStatus.java
@@ -12,6 +12,8 @@
 
 import java.util.function.Supplier;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * @since 1.1
  */
@@ -43,8 +45,8 @@ static ParseStatus errorAt(Token token, String operatorRepresentation, String me
 	}
 
 	static ParseStatus missingOperatorBetween(TokenWith<TagExpression> lhs, TokenWith<TagExpression> rhs) {
-		String lhsString = "'" + lhs.element.toString() + "' at index " + format(lhs.token.lastCharacterIndex());
-		String rhsString = "'" + rhs.element.toString() + "' at index " + format(rhs.token.trimmedTokenStartIndex());
+		String lhsString = "'" + lhs.element() + "' at index " + format(lhs.token().lastCharacterIndex());
+		String rhsString = "'" + rhs.element() + "' at index " + format(rhs.token().trimmedTokenStartIndex());
 		return error("missing operator between " + lhsString + " and " + rhsString);
 	}
 
@@ -56,13 +58,13 @@ private static String format(int indexInTagExpression) {
 		return "<" + indexInTagExpression + ">";
 	}
 
-	private static ParseStatus error(String errorMessage) {
+	private static ParseStatus error(@Nullable String errorMessage) {
 		return new ParseStatus(errorMessage);
 	}
 
-	final String errorMessage;
+	final @Nullable String errorMessage;
 
-	private ParseStatus(String errorMessage) {
+	private ParseStatus(@Nullable String errorMessage) {
 		this.errorMessage = errorMessage;
 	}
 
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/Parser.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/Parser.java
index 417cf3e52aad..5605ba4ac3a2 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/Parser.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/Parser.java
@@ -12,6 +12,8 @@
 
 import java.util.List;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * @since 1.1
  */
@@ -19,11 +21,11 @@ class Parser {
 
 	private final Tokenizer tokenizer = new Tokenizer();
 
-	ParseResult parse(String infixTagExpression) {
+	ParseResult parse(@Nullable String infixTagExpression) {
 		return constructExpressionFrom(tokensDerivedFrom(infixTagExpression));
 	}
 
-	private List<Token> tokensDerivedFrom(String infixTagExpression) {
+	private List<Token> tokensDerivedFrom(@Nullable String infixTagExpression) {
 		return tokenizer.tokenize(infixTagExpression);
 	}
 
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/ShuntingYard.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/ShuntingYard.java
index b54d40f5b6a9..8a1922012d2d 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/ShuntingYard.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/ShuntingYard.java
@@ -11,6 +11,7 @@
 package org.junit.platform.launcher.tagexpression;
 
 import static java.lang.Integer.MIN_VALUE;
+import static java.util.Objects.requireNonNull;
 import static org.junit.platform.launcher.tagexpression.Operator.nullaryOperator;
 import static org.junit.platform.launcher.tagexpression.ParseStatus.emptyTagExpression;
 import static org.junit.platform.launcher.tagexpression.ParseStatus.missingClosingParenthesis;
@@ -53,9 +54,9 @@ public ParseResult execute() {
 				.process(this::ensureOnlySingleExpressionRemains);
 		// @formatter:on
 		if (parseStatus.isError()) {
-			return ParseResults.error(parseStatus.errorMessage);
+			return ParseResults.error(requireNonNull(parseStatus.errorMessage));
 		}
-		return ParseResults.success(expressions.pop().element);
+		return ParseResults.success(expressions.pop().element());
 	}
 
 	private ParseStatus processTokens() {
@@ -75,8 +76,8 @@ private ParseStatus process(Token token) {
 		if (RightParenthesis.represents(trimmed)) {
 			return findMatchingLeftParenthesis(token);
 		}
-		if (validOperators.isOperator(trimmed)) {
-			Operator operator = validOperators.operatorFor(trimmed);
+		var operator = validOperators.operatorFor(trimmed);
+		if (operator != null) {
 			return findOperands(token, operator);
 		}
 		pushExpressionAt(token, convertLeafTokenToExpression(trimmed));
@@ -96,11 +97,11 @@ private TagExpression convertLeafTokenToExpression(String trimmed) {
 	private ParseStatus findMatchingLeftParenthesis(Token token) {
 		while (!operators.isEmpty()) {
 			TokenWith<Operator> tokenWithWithOperator = operators.pop();
-			Operator operator = tokenWithWithOperator.element;
+			Operator operator = tokenWithWithOperator.element();
 			if (LeftParenthesis.equals(operator)) {
 				return success();
 			}
-			ParseStatus parseStatus = operator.createAndAddExpressionTo(expressions, tokenWithWithOperator.token);
+			ParseStatus parseStatus = operator.createAndAddExpressionTo(expressions, tokenWithWithOperator.token());
 			if (parseStatus.isError()) {
 				return parseStatus;
 			}
@@ -112,8 +113,8 @@ private ParseStatus findOperands(Token token, Operator currentOperator) {
 		while (currentOperator.hasLowerPrecedenceThan(previousOperator())
 				|| currentOperator.hasSamePrecedenceAs(previousOperator()) && currentOperator.isLeftAssociative()) {
 			TokenWith<Operator> tokenWithWithOperator = operators.pop();
-			ParseStatus parseStatus = tokenWithWithOperator.element.createAndAddExpressionTo(expressions,
-				tokenWithWithOperator.token);
+			ParseStatus parseStatus = tokenWithWithOperator.element().createAndAddExpressionTo(expressions,
+				tokenWithWithOperator.token());
 			if (parseStatus.isError()) {
 				return parseStatus;
 			}
@@ -123,7 +124,7 @@ private ParseStatus findOperands(Token token, Operator currentOperator) {
 	}
 
 	private Operator previousOperator() {
-		return operators.peek().element;
+		return operators.peek().element();
 	}
 
 	private void pushExpressionAt(Token token, TagExpression tagExpression) {
@@ -137,11 +138,11 @@ private void pushOperatorAt(Token token, Operator operator) {
 	private ParseStatus consumeRemainingOperators() {
 		while (!operators.isEmpty()) {
 			TokenWith<Operator> tokenWithWithOperator = operators.pop();
-			Operator operator = tokenWithWithOperator.element;
+			Operator operator = tokenWithWithOperator.element();
 			if (LeftParenthesis.equals(operator)) {
-				return missingClosingParenthesis(tokenWithWithOperator.token, operator.representation());
+				return missingClosingParenthesis(tokenWithWithOperator.token(), operator.representation());
 			}
-			ParseStatus parseStatus = operator.createAndAddExpressionTo(expressions, tokenWithWithOperator.token);
+			ParseStatus parseStatus = operator.createAndAddExpressionTo(expressions, tokenWithWithOperator.token());
 			if (parseStatus.isError()) {
 				return parseStatus;
 			}
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/TagExpression.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/TagExpression.java
index ac101b2a6810..46f04acee8d1 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/TagExpression.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/TagExpression.java
@@ -15,6 +15,7 @@
 import java.util.Collection;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.engine.TestTag;
 
 /**
@@ -30,11 +31,12 @@ public interface TagExpression {
 	 * Attempt to parse a {@link TagExpression} from the supplied <em>tag
 	 * expression string</em>.
 	 *
-	 * @param infixTagExpression the tag expression string to parse; never {@code null}.
+	 * @param infixTagExpression the tag expression string to parse; may be
+	 * {@code null}.
 	 * @see ParseResult
 	 */
 	@API(status = INTERNAL, since = "1.1")
-	static ParseResult parseFrom(String infixTagExpression) {
+	static ParseResult parseFrom(@Nullable String infixTagExpression) {
 		return new Parser().parse(infixTagExpression);
 	}
 
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/Token.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/Token.java
index 4b90dd72c915..b239179f68e2 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/Token.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/Token.java
@@ -13,15 +13,7 @@
 /**
  * @since 1.1
  */
-class Token {
-
-	final int startIndex;
-	final String rawString;
-
-	Token(int startIndex, String rawString) {
-		this.startIndex = startIndex;
-		this.rawString = rawString;
-	}
+record Token(int startIndex, String rawString) {
 
 	String string() {
 		return rawString.trim();
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/TokenWith.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/TokenWith.java
index 161cb229f6e7..1e387dd83eaa 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/TokenWith.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/TokenWith.java
@@ -13,14 +13,5 @@
 /**
  * @since 1.1
  */
-class TokenWith<T> {
-
-	final Token token;
-	final T element;
-
-	TokenWith(Token token, T element) {
-		this.token = token;
-		this.element = element;
-	}
-
+record TokenWith<T>(Token token, T element) {
 }
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/Tokenizer.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/Tokenizer.java
index f21dd73aa332..57a5e6cbe687 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/Tokenizer.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/Tokenizer.java
@@ -18,15 +18,17 @@
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * @since 1.1
  */
 class Tokenizer {
 
-	private static final Pattern PATTERN = Pattern.compile("\\s*(?:(?:(?:any|none)\\(\\))|[()!|&]|(?:[^\\s()!|&]+))",
+	private static final Pattern PATTERN = Pattern.compile("\\s*(?:(?:any|none)\\(\\)|[()!|&]|[^\\s()!|&]+)",
 		CASE_INSENSITIVE);
 
-	List<Token> tokenize(String infixTagExpression) {
+	List<Token> tokenize(@Nullable String infixTagExpression) {
 		if (infixTagExpression == null) {
 			return emptyList();
 		}
diff --git a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/package-info.java b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/package-info.java
index 53e2a7fac56d..efab367f98dc 100644
--- a/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/package-info.java
+++ b/junit-platform-launcher/src/main/java/org/junit/platform/launcher/tagexpression/package-info.java
@@ -2,4 +2,7 @@
  * The tag expression language parser and related support classes.
  */
 
+@NullMarked
 package org.junit.platform.launcher.tagexpression;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-platform-reporting/junit-platform-reporting.gradle.kts b/junit-platform-reporting/junit-platform-reporting.gradle.kts
index 5f11aab2adf9..5bc26173b981 100644
--- a/junit-platform-reporting/junit-platform-reporting.gradle.kts
+++ b/junit-platform-reporting/junit-platform-reporting.gradle.kts
@@ -2,6 +2,7 @@ import junitbuild.extensions.javaModuleName
 
 plugins {
 	id("junitbuild.java-library-conventions")
+	id("junitbuild.java-nullability-conventions")
 	id("junitbuild.shadow-conventions")
 	`java-test-fixtures`
 }
@@ -12,8 +13,10 @@ dependencies {
 	api(platform(projects.junitBom))
 	api(projects.junitPlatformLauncher)
 
+	implementation(libs.openTestReporting.tooling.spi)
+
 	compileOnlyApi(libs.apiguardian)
-	compileOnlyApi(libs.openTestReporting.tooling.spi)
+	compileOnly(libs.jspecify)
 
 	shadowed(libs.openTestReporting.events)
 
@@ -35,10 +38,16 @@ tasks {
 			into("META-INF")
 		}
 	}
-	compileModule {
+	compileJava {
 		options.compilerArgs.addAll(listOf(
 			"--add-modules", "org.opentest4j.reporting.events",
 			"--add-reads", "${javaModuleName}=org.opentest4j.reporting.events"
 		))
 	}
+	javadoc {
+		(options as StandardJavadocDocletOptions).apply {
+			addStringOption("-add-modules", "org.opentest4j.reporting.events")
+			addStringOption("-add-reads", "${javaModuleName}=org.opentest4j.reporting.events")
+		}
+	}
 }
diff --git a/junit-platform-reporting/src/module/org.junit.platform.reporting/module-info.java b/junit-platform-reporting/src/main/java/module-info.java
similarity index 97%
rename from junit-platform-reporting/src/module/org.junit.platform.reporting/module-info.java
rename to junit-platform-reporting/src/main/java/module-info.java
index f1fe8cd51dca..11202c5829c3 100644
--- a/junit-platform-reporting/src/module/org.junit.platform.reporting/module-info.java
+++ b/junit-platform-reporting/src/main/java/module-info.java
@@ -14,8 +14,11 @@
  * @since 1.4
  */
 module org.junit.platform.reporting {
-	requires java.xml;
+
 	requires static transitive org.apiguardian.api;
+	requires static org.jspecify;
+
+	requires java.xml;
 	requires org.junit.platform.commons;
 	requires transitive org.junit.platform.engine;
 	requires transitive org.junit.platform.launcher;
diff --git a/junit-platform-reporting/src/main/java/org/junit/platform/reporting/legacy/LegacyReportingUtils.java b/junit-platform-reporting/src/main/java/org/junit/platform/reporting/legacy/LegacyReportingUtils.java
index 318a6b5351ed..b82ac7c9f1a8 100644
--- a/junit-platform-reporting/src/main/java/org/junit/platform/reporting/legacy/LegacyReportingUtils.java
+++ b/junit-platform-reporting/src/main/java/org/junit/platform/reporting/legacy/LegacyReportingUtils.java
@@ -13,6 +13,8 @@
 import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
+import org.junit.platform.commons.util.Preconditions;
 import org.junit.platform.engine.support.descriptor.ClassSource;
 import org.junit.platform.launcher.TestIdentifier;
 import org.junit.platform.launcher.TestPlan;
@@ -49,9 +51,37 @@ private LegacyReportingUtils() {
 	 * never {@code null}
 	 * @see TestIdentifier#getLegacyReportingName
 	 */
-	@SuppressWarnings("deprecation")
 	public static String getClassName(TestPlan testPlan, TestIdentifier testIdentifier) {
-		return org.junit.platform.launcher.listeners.LegacyReportingUtils.getClassName(testPlan, testIdentifier);
+		Preconditions.notNull(testPlan, "testPlan must not be null");
+		Preconditions.notNull(testIdentifier, "testIdentifier must not be null");
+		for (TestIdentifier current = testIdentifier; current != null; current = getParent(testPlan, current)) {
+			ClassSource source = getClassSource(current);
+			if (source != null) {
+				return source.getClassName();
+			}
+		}
+		return getParentLegacyReportingName(testPlan, testIdentifier);
+	}
+
+	private static @Nullable TestIdentifier getParent(TestPlan testPlan, TestIdentifier testIdentifier) {
+		return testPlan.getParent(testIdentifier).orElse(null);
+	}
+
+	private static @Nullable ClassSource getClassSource(TestIdentifier current) {
+		// @formatter:off
+		return current.getSource()
+				.filter(ClassSource.class::isInstance)
+				.map(ClassSource.class::cast)
+				.orElse(null);
+		// @formatter:on
+	}
+
+	private static String getParentLegacyReportingName(TestPlan testPlan, TestIdentifier testIdentifier) {
+		// @formatter:off
+		return testPlan.getParent(testIdentifier)
+				.map(TestIdentifier::getLegacyReportingName)
+				.orElse("<unrooted>");
+		// @formatter:on
 	}
 
 }
diff --git a/junit-platform-reporting/src/main/java/org/junit/platform/reporting/legacy/package-info.java b/junit-platform-reporting/src/main/java/org/junit/platform/reporting/legacy/package-info.java
index f7a50ee115f0..af41a0a5efbe 100644
--- a/junit-platform-reporting/src/main/java/org/junit/platform/reporting/legacy/package-info.java
+++ b/junit-platform-reporting/src/main/java/org/junit/platform/reporting/legacy/package-info.java
@@ -2,4 +2,7 @@
  * Support for legacy reporting formats.
  */
 
+@NullMarked
 package org.junit.platform.reporting.legacy;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-platform-reporting/src/main/java/org/junit/platform/reporting/legacy/xml/LegacyXmlReportGeneratingListener.java b/junit-platform-reporting/src/main/java/org/junit/platform/reporting/legacy/xml/LegacyXmlReportGeneratingListener.java
index 06bd0ecfc7a0..cf96452b202d 100644
--- a/junit-platform-reporting/src/main/java/org/junit/platform/reporting/legacy/xml/LegacyXmlReportGeneratingListener.java
+++ b/junit-platform-reporting/src/main/java/org/junit/platform/reporting/legacy/xml/LegacyXmlReportGeneratingListener.java
@@ -10,6 +10,7 @@
 
 package org.junit.platform.reporting.legacy.xml;
 
+import static java.util.Objects.requireNonNull;
 import static org.apiguardian.api.API.Status.STABLE;
 
 import java.io.IOException;
@@ -17,12 +18,12 @@
 import java.io.Writer;
 import java.nio.file.Files;
 import java.nio.file.Path;
-import java.nio.file.Paths;
 import java.time.Clock;
 
 import javax.xml.stream.XMLStreamException;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.engine.TestExecutionResult;
 import org.junit.platform.engine.reporting.ReportEntry;
 import org.junit.platform.launcher.TestExecutionListener;
@@ -49,7 +50,7 @@ public class LegacyXmlReportGeneratingListener implements TestExecutionListener
 	private final PrintWriter out;
 	private final Clock clock;
 
-	private XmlReportData reportData;
+	private @Nullable XmlReportData reportData;
 
 	public LegacyXmlReportGeneratingListener(Path reportsDir, PrintWriter out) {
 		this(reportsDir, out, Clock.systemDefaultZone());
@@ -57,7 +58,7 @@ public LegacyXmlReportGeneratingListener(Path reportsDir, PrintWriter out) {
 
 	// For tests only
 	LegacyXmlReportGeneratingListener(String reportsDir, PrintWriter out, Clock clock) {
-		this(Paths.get(reportsDir), out, clock);
+		this(Path.of(reportsDir), out, clock);
 	}
 
 	private LegacyXmlReportGeneratingListener(Path reportsDir, PrintWriter out, Clock clock) {
@@ -84,23 +85,23 @@ public void testPlanExecutionFinished(TestPlan testPlan) {
 
 	@Override
 	public void executionSkipped(TestIdentifier testIdentifier, String reason) {
-		this.reportData.markSkipped(testIdentifier, reason);
+		requiredReportData().markSkipped(testIdentifier, reason);
 		writeXmlReportInCaseOfRoot(testIdentifier);
 	}
 
 	@Override
 	public void executionStarted(TestIdentifier testIdentifier) {
-		this.reportData.markStarted(testIdentifier);
+		requiredReportData().markStarted(testIdentifier);
 	}
 
 	@Override
 	public void reportingEntryPublished(TestIdentifier testIdentifier, ReportEntry entry) {
-		this.reportData.addReportEntry(testIdentifier, entry);
+		requiredReportData().addReportEntry(testIdentifier, entry);
 	}
 
 	@Override
 	public void executionFinished(TestIdentifier testIdentifier, TestExecutionResult result) {
-		this.reportData.markFinished(testIdentifier, result);
+		requiredReportData().markFinished(testIdentifier, result);
 		writeXmlReportInCaseOfRoot(testIdentifier);
 	}
 
@@ -114,15 +115,19 @@ private void writeXmlReportInCaseOfRoot(TestIdentifier testIdentifier) {
 	private void writeXmlReportSafely(TestIdentifier testIdentifier, String rootName) {
 		Path xmlFile = this.reportsDir.resolve("TEST-" + rootName + ".xml");
 		try (Writer fileWriter = Files.newBufferedWriter(xmlFile)) {
-			new XmlReportWriter(this.reportData).writeXmlReport(testIdentifier, fileWriter);
+			new XmlReportWriter(requiredReportData()).writeXmlReport(testIdentifier, fileWriter);
 		}
 		catch (XMLStreamException | IOException e) {
 			printException("Could not write XML report: " + xmlFile, e);
 		}
 	}
 
+	private XmlReportData requiredReportData() {
+		return requireNonNull(this.reportData);
+	}
+
 	private boolean isRoot(TestIdentifier testIdentifier) {
-		return !testIdentifier.getParentIdObject().isPresent();
+		return testIdentifier.getParentIdObject().isEmpty();
 	}
 
 	private void printException(String message, Exception exception) {
diff --git a/junit-platform-reporting/src/main/java/org/junit/platform/reporting/legacy/xml/XmlReportData.java b/junit-platform-reporting/src/main/java/org/junit/platform/reporting/legacy/xml/XmlReportData.java
index f1ce85be73cb..cf78931aca0d 100644
--- a/junit-platform-reporting/src/main/java/org/junit/platform/reporting/legacy/xml/XmlReportData.java
+++ b/junit-platform-reporting/src/main/java/org/junit/platform/reporting/legacy/xml/XmlReportData.java
@@ -11,7 +11,6 @@
 package org.junit.platform.reporting.legacy.xml;
 
 import static java.util.Collections.emptyList;
-import static java.util.stream.Collectors.toList;
 import static org.junit.platform.engine.TestExecutionResult.Status.ABORTED;
 
 import java.time.Clock;
@@ -25,6 +24,7 @@
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.function.Predicate;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.util.ExceptionUtils;
 import org.junit.platform.engine.TestExecutionResult;
 import org.junit.platform.engine.reporting.ReportEntry;
@@ -60,7 +60,7 @@ Clock getClock() {
 		return this.clock;
 	}
 
-	void markSkipped(TestIdentifier testIdentifier, String reason) {
+	void markSkipped(TestIdentifier testIdentifier, @Nullable String reason) {
 		this.skippedTests.put(testIdentifier, reason == null ? "" : reason);
 	}
 
@@ -94,6 +94,7 @@ boolean wasSkipped(TestIdentifier testIdentifier) {
 		return Duration.between(startInstant, endInstant).toMillis() / (double) MILLIS_PER_SECOND;
 	}
 
+	@Nullable
 	String getSkipReason(TestIdentifier testIdentifier) {
 		return findSkippedAncestor(testIdentifier).map(skippedTestIdentifier -> {
 			String reason = this.skippedTests.get(skippedTestIdentifier);
@@ -108,7 +109,7 @@ List<TestExecutionResult> getResults(TestIdentifier testIdentifier) {
 		return getAncestors(testIdentifier).stream() //
 				.map(this.finishedTests::get) //
 				.filter(Objects::nonNull) //
-				.collect(toList());
+				.toList();
 	}
 
 	List<ReportEntry> getReportEntries(TestIdentifier testIdentifier) {
diff --git a/junit-platform-reporting/src/main/java/org/junit/platform/reporting/legacy/xml/XmlReportWriter.java b/junit-platform-reporting/src/main/java/org/junit/platform/reporting/legacy/xml/XmlReportWriter.java
index d3ae6b008bd9..5847b73cbb7c 100644
--- a/junit-platform-reporting/src/main/java/org/junit/platform/reporting/legacy/xml/XmlReportWriter.java
+++ b/junit-platform-reporting/src/main/java/org/junit/platform/reporting/legacy/xml/XmlReportWriter.java
@@ -13,8 +13,8 @@
 import static java.text.MessageFormat.format;
 import static java.time.format.DateTimeFormatter.ISO_LOCAL_DATE_TIME;
 import static java.util.Collections.emptyList;
-import static java.util.Collections.unmodifiableMap;
 import static java.util.Comparator.naturalOrder;
+import static java.util.Objects.requireNonNull;
 import static java.util.function.Function.identity;
 import static java.util.stream.Collectors.counting;
 import static java.util.stream.Collectors.groupingBy;
@@ -40,7 +40,6 @@
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.EnumSet;
-import java.util.HashMap;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Locale;
@@ -55,6 +54,7 @@
 import javax.xml.stream.XMLStreamException;
 import javax.xml.stream.XMLStreamWriter;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.engine.TestExecutionResult;
 import org.junit.platform.engine.reporting.ReportEntry;
 import org.junit.platform.launcher.TestIdentifier;
@@ -73,14 +73,11 @@ class XmlReportWriter {
 
 	static final char ILLEGAL_CHARACTER_REPLACEMENT = '\uFFFD';
 
-	private static final Map<Character, String> REPLACEMENTS_IN_ATTRIBUTE_VALUES;
-	static {
-		Map<Character, String> tmp = new HashMap<>(3);
-		tmp.put('\n', "&#10;");
-		tmp.put('\r', "&#13;");
-		tmp.put('\t', "&#9;");
-		REPLACEMENTS_IN_ATTRIBUTE_VALUES = unmodifiableMap(tmp);
-	}
+	private static final Map<Character, String> REPLACEMENTS_IN_ATTRIBUTE_VALUES = Map.of( //
+		'\n', "&#10;", //
+		'\r', "&#13;", //
+		'\t', "&#9;" //
+	);
 
 	// Using zero-width assertions in the split pattern simplifies the splitting process: All split parts
 	// (including the first and last one) can be used directly, without having to re-add separator characters.
@@ -244,10 +241,10 @@ private void writeSkippedOrErrorOrFailureElement(TestIdentifier testIdentifier,
 			}
 		}
 
-		private void writeSkippedElement(String reason, XMLStreamWriter writer) throws XMLStreamException {
+		private void writeSkippedElement(@Nullable String reason, XMLStreamWriter writer) throws XMLStreamException {
 			if (isNotBlank(reason)) {
 				writer.writeStartElement("skipped");
-				writeCDataSafely(reason);
+				writeCDataSafely(requireNonNull(reason));
 				writer.writeEndElement();
 			}
 			else {
@@ -256,7 +253,7 @@ private void writeSkippedElement(String reason, XMLStreamWriter writer) throws X
 			newLine();
 		}
 
-		private void writeErrorOrFailureElement(Type type, Throwable throwable, XMLStreamWriter writer)
+		private void writeErrorOrFailureElement(Type type, @Nullable Throwable throwable, XMLStreamWriter writer)
 				throws XMLStreamException {
 
 			String elementName = type == FAILURE ? "failure" : "error";
diff --git a/junit-platform-reporting/src/main/java/org/junit/platform/reporting/legacy/xml/package-info.java b/junit-platform-reporting/src/main/java/org/junit/platform/reporting/legacy/xml/package-info.java
index d41e891b296a..bdec16594877 100644
--- a/junit-platform-reporting/src/main/java/org/junit/platform/reporting/legacy/xml/package-info.java
+++ b/junit-platform-reporting/src/main/java/org/junit/platform/reporting/legacy/xml/package-info.java
@@ -4,4 +4,7 @@
  * by the Ant build system.
  */
 
+@NullMarked
 package org.junit.platform.reporting.legacy.xml;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-platform-reporting/src/main/java/org/junit/platform/reporting/open/xml/GitInfoCollector.java b/junit-platform-reporting/src/main/java/org/junit/platform/reporting/open/xml/GitInfoCollector.java
new file mode 100644
index 000000000000..1bd95732f2d4
--- /dev/null
+++ b/junit-platform-reporting/src/main/java/org/junit/platform/reporting/open/xml/GitInfoCollector.java
@@ -0,0 +1,209 @@
+/*
+ * Copyright 2015-2025 the original author or authors.
+ *
+ * All rights reserved. This program and the accompanying materials are
+ * made available under the terms of the Eclipse Public License v2.0 which
+ * accompanies this distribution and is available at
+ *
+ * https://www.eclipse.org/legal/epl-v20.html
+ */
+
+package org.junit.platform.reporting.open.xml;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.io.Reader;
+import java.io.UncheckedIOException;
+import java.net.URI;
+import java.net.URISyntaxException;
+import java.nio.charset.Charset;
+import java.nio.file.Path;
+import java.util.Optional;
+import java.util.concurrent.TimeUnit;
+import java.util.function.BiConsumer;
+
+import org.junit.platform.commons.util.ExceptionUtils;
+import org.junit.platform.commons.util.StringUtils;
+
+/**
+ * @since 5.13.2
+ */
+interface GitInfoCollector {
+
+	static Optional<GitInfoCollector> get(Path workingDir) {
+		ProcessExecutor executor = new ProcessExecutor(workingDir);
+		boolean gitInstalled = executor.exec("git", "--version").isPresent();
+		return gitInstalled ? Optional.of(new CliGitInfoCollector(executor)) : Optional.empty();
+	}
+
+	Optional<String> getOriginUrl();
+
+	Optional<String> getBranch();
+
+	Optional<String> getCommitHash();
+
+	Optional<String> getStatus();
+
+	class CliGitInfoCollector implements GitInfoCollector {
+
+		private static final String ALLOWED_USERNAME = "git";
+		private static final String USER_INFO_REPLACEMENT = "***";
+		private static final String USER_INFO_SEPARATOR = "@";
+
+		private final ProcessExecutor executor;
+
+		public CliGitInfoCollector(ProcessExecutor executor) {
+			this.executor = executor;
+		}
+
+		@Override
+		public Optional<String> getOriginUrl() {
+			return executor.exec("git", "config", "--get", "remote.origin.url") //
+					.filter(StringUtils::isNotBlank) //
+					.flatMap(this::toGitUrl) //
+					.flatMap(this::obfuscateUserInfo);
+		}
+
+		@Override
+		public Optional<String> getBranch() {
+			return executor.exec("git", "rev-parse", "--abbrev-ref", "HEAD") //
+					.filter(StringUtils::isNotBlank);
+		}
+
+		@Override
+		public Optional<String> getCommitHash() {
+			return executor.exec("git", "rev-parse", "--verify", "HEAD") //
+					.filter(StringUtils::isNotBlank);
+		}
+
+		@Override
+		public Optional<String> getStatus() {
+			return executor.exec("git", "status", "--porcelain");
+		}
+
+		private Optional<String> obfuscateUserInfo(GitUrl gitUrl) {
+			try {
+				if (gitUrl.uri.getUserInfo() != null) {
+					URI newUri = new URI(gitUrl.uri.getScheme(), USER_INFO_REPLACEMENT, gitUrl.uri.getHost(),
+						gitUrl.uri.getPort(), gitUrl.uri.getPath(), gitUrl.uri.getQuery(), gitUrl.uri.getFragment());
+					return Optional.of(newUri.toString().substring(gitUrl.addedPrefix.length()));
+				}
+				if (gitUrl.uri.getAuthority() != null && gitUrl.uri.getAuthority().contains(USER_INFO_SEPARATOR)) {
+					String oldAuthority = gitUrl.uri.getAuthority();
+					String[] parts = oldAuthority.split(USER_INFO_SEPARATOR, 2);
+					if (!ALLOWED_USERNAME.equals(parts[0])) {
+						String newAuthority = USER_INFO_REPLACEMENT + USER_INFO_SEPARATOR + parts[1];
+						URI newUri = new URI(gitUrl.uri.getScheme(), newAuthority, gitUrl.uri.getPath(),
+							gitUrl.uri.getQuery(), gitUrl.uri.getFragment());
+						return Optional.of(newUri.toString().substring(gitUrl.addedPrefix.length()));
+					}
+				}
+				return Optional.of(gitUrl.rawValue);
+			}
+			catch (URISyntaxException e) {
+				return Optional.empty();
+			}
+		}
+
+		private Optional<GitUrl> toGitUrl(String remoteUrl) {
+			try {
+				return Optional.of(new GitUrl(remoteUrl, new URI(remoteUrl), ""));
+			}
+			catch (URISyntaxException ex) {
+				try {
+					return Optional.of(new GitUrl(remoteUrl, new URI("ssh://" + remoteUrl), "ssh://"));
+				}
+				catch (URISyntaxException ignore) {
+					return Optional.empty();
+				}
+			}
+		}
+	}
+
+	class ProcessExecutor {
+
+		private final Path workingDir;
+
+		ProcessExecutor(Path workingDir) {
+			this.workingDir = workingDir;
+		}
+
+		Optional<String> exec(String... args) {
+
+			Process process = startProcess(args);
+
+			try (Reader out = newBufferedReader(process.getInputStream());
+					Reader err = newBufferedReader(process.getErrorStream())) {
+
+				StringBuilder output = new StringBuilder();
+				readAllChars(out, (chars, numChars) -> output.append(chars, 0, numChars));
+
+				readAllChars(err, (__, ___) -> {
+					// ignore
+				});
+
+				boolean terminated = process.waitFor(10, TimeUnit.SECONDS);
+				return terminated && process.exitValue() == 0 ? Optional.of(trimAtEnd(output)) : Optional.empty();
+			}
+			catch (InterruptedException e) {
+				throw ExceptionUtils.throwAsUncheckedException(e);
+			}
+			catch (IOException ignore) {
+				return Optional.empty();
+			}
+			finally {
+				process.destroyForcibly();
+			}
+		}
+
+		private static BufferedReader newBufferedReader(InputStream stream) {
+			return new BufferedReader(new InputStreamReader(stream, Charset.defaultCharset()));
+		}
+
+		private Process startProcess(String[] command) {
+			Process process;
+			try {
+				process = new ProcessBuilder().directory(workingDir.toFile()).command(command).start();
+			}
+			catch (IOException e) {
+				throw new UncheckedIOException("Failed to start process", e);
+			}
+			return process;
+		}
+
+		private static void readAllChars(Reader reader, BiConsumer<char[], Integer> consumer) throws IOException {
+			char[] buffer = new char[1024];
+			int numChars;
+			while ((numChars = reader.read(buffer)) != -1) {
+				consumer.accept(buffer, numChars);
+			}
+		}
+
+		private static String trimAtEnd(StringBuilder value) {
+			int endIndex = value.length();
+			for (int i = value.length() - 1; i >= 0; i--) {
+				if (Character.isWhitespace(value.charAt(i))) {
+					endIndex--;
+					break;
+				}
+			}
+			return value.substring(0, endIndex);
+		}
+	}
+
+	class GitUrl {
+
+		private final String rawValue;
+		private final URI uri;
+		private final String addedPrefix;
+
+		GitUrl(String rawValue, URI uri, String addedPrefix) {
+			this.rawValue = rawValue;
+			this.uri = uri;
+			this.addedPrefix = addedPrefix;
+		}
+	}
+
+}
diff --git a/junit-platform-reporting/src/main/java/org/junit/platform/reporting/open/xml/OpenTestReportGeneratingListener.java b/junit-platform-reporting/src/main/java/org/junit/platform/reporting/open/xml/OpenTestReportGeneratingListener.java
index 954cdc334fc5..94c1a128c57e 100644
--- a/junit-platform-reporting/src/main/java/org/junit/platform/reporting/open/xml/OpenTestReportGeneratingListener.java
+++ b/junit-platform-reporting/src/main/java/org/junit/platform/reporting/open/xml/OpenTestReportGeneratingListener.java
@@ -10,7 +10,8 @@
 
 package org.junit.platform.reporting.open.xml;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static java.util.Objects.requireNonNull;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.junit.platform.commons.util.StringUtils.isNotBlank;
 import static org.junit.platform.launcher.LauncherConstants.STDERR_REPORT_ENTRY_KEY;
 import static org.junit.platform.launcher.LauncherConstants.STDOUT_REPORT_ENTRY_KEY;
@@ -51,30 +52,20 @@
 import static org.opentest4j.reporting.events.root.RootFactory.reported;
 import static org.opentest4j.reporting.events.root.RootFactory.started;
 
-import java.io.BufferedReader;
 import java.io.IOException;
-import java.io.InputStream;
-import java.io.InputStreamReader;
-import java.io.Reader;
 import java.io.UncheckedIOException;
 import java.net.InetAddress;
 import java.net.UnknownHostException;
-import java.nio.charset.Charset;
 import java.nio.file.Path;
-import java.nio.file.Paths;
 import java.time.Instant;
 import java.time.LocalDateTime;
 import java.util.Map;
-import java.util.Optional;
 import java.util.concurrent.ConcurrentHashMap;
-import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicInteger;
-import java.util.function.BiConsumer;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.JUnitException;
-import org.junit.platform.commons.util.ExceptionUtils;
-import org.junit.platform.commons.util.StringUtils;
 import org.junit.platform.engine.ConfigurationParameters;
 import org.junit.platform.engine.TestExecutionResult;
 import org.junit.platform.engine.TestSource;
@@ -106,20 +97,22 @@
  *
  * @since 1.9
  */
-@API(status = EXPERIMENTAL, since = "1.9")
+@API(status = MAINTAINED, since = "1.13.3")
 public class OpenTestReportGeneratingListener implements TestExecutionListener {
 
 	static final String ENABLED_PROPERTY_NAME = "junit.platform.reporting.open.xml.enabled";
+	static final String GIT_ENABLED_PROPERTY_NAME = "junit.platform.reporting.open.xml.git.enabled";
 
 	private final AtomicInteger idCounter = new AtomicInteger();
 	private final Map<UniqueId, String> inProgressIds = new ConcurrentHashMap<>();
 	private DocumentWriter<Events> eventsFileWriter = DocumentWriter.noop();
 	private final Path workingDir;
-	private Path outputDir;
+
+	private @Nullable Path outputDir;
 
 	@SuppressWarnings("unused") // Used via ServiceLoader
 	public OpenTestReportGeneratingListener() {
-		this(Paths.get(".").toAbsolutePath());
+		this(Path.of(".").toAbsolutePath());
 	}
 
 	OpenTestReportGeneratingListener(Path workingDir) {
@@ -134,14 +127,13 @@ public void testPlanExecutionStarted(TestPlan testPlan) {
 					.add("e", Namespace.REPORTING_EVENTS) //
 					.add("git", Namespace.REPORTING_GIT) //
 					.add("java", Namespace.REPORTING_JAVA) //
-					.add("junit", JUnitFactory.NAMESPACE,
-						"https://junit.org/junit5/schemas/open-test-reporting/junit-1.9.xsd") //
+					.add("junit", JUnitFactory.NAMESPACE, "https://schemas.junit.org/open-test-reporting/junit-1.9.xsd") //
 					.build();
 			outputDir = testPlan.getOutputDirectoryProvider().getRootDirectory();
 			Path eventsXml = outputDir.resolve("open-test-report.xml");
 			try {
 				eventsFileWriter = Events.createDocumentWriter(namespaceRegistry, eventsXml);
-				reportInfrastructure();
+				reportInfrastructure(config);
 			}
 			catch (Exception e) {
 				throw new JUnitException("Failed to initialize XML events file: " + eventsXml, e);
@@ -149,11 +141,15 @@ public void testPlanExecutionStarted(TestPlan testPlan) {
 		}
 	}
 
-	private Boolean isEnabled(ConfigurationParameters config) {
+	private boolean isEnabled(ConfigurationParameters config) {
 		return config.getBoolean(ENABLED_PROPERTY_NAME).orElse(false);
 	}
 
-	private void reportInfrastructure() {
+	private boolean isGitEnabled(ConfigurationParameters config) {
+		return config.getBoolean(GIT_ENABLED_PROPERTY_NAME).orElse(false);
+	}
+
+	private void reportInfrastructure(ConfigurationParameters config) {
 		eventsFileWriter.append(infrastructure(), infrastructure -> {
 			try {
 				String hostName = InetAddress.getLocalHost().getHostName();
@@ -169,89 +165,23 @@ private void reportInfrastructure() {
 					.append(fileEncoding(System.getProperty("file.encoding"))) //
 					.append(heapSize(), heapSize -> heapSize.withMax(Runtime.getRuntime().maxMemory()));
 
-			addGitInfo(infrastructure);
+			if (isGitEnabled(config)) {
+				GitInfoCollector.get(workingDir).ifPresent(git -> addGitInfo(infrastructure, git));
+			}
 		});
 	}
 
-	private void addGitInfo(Infrastructure infrastructure) {
-		boolean gitInstalled = exec("git", "--version").isPresent();
-		if (gitInstalled) {
-			exec("git", "config", "--get", "remote.origin.url") //
-					.filter(StringUtils::isNotBlank) //
-					.ifPresent(
-						gitUrl -> infrastructure.append(repository(), repository -> repository.withOriginUrl(gitUrl)));
-			exec("git", "rev-parse", "--abbrev-ref", "HEAD") //
-					.filter(StringUtils::isNotBlank) //
-					.ifPresent(branch -> infrastructure.append(branch(branch)));
-			exec("git", "rev-parse", "--verify", "HEAD") //
-					.filter(StringUtils::isNotBlank) //
-					.ifPresent(gitCommitHash -> infrastructure.append(commit(gitCommitHash)));
-			exec("git", "status", "--porcelain") //
-					.ifPresent(statusOutput -> infrastructure.append(status(statusOutput),
-						status -> status.withClean(statusOutput.isEmpty())));
-		}
-	}
-
-	Optional<String> exec(String... args) {
-
-		Process process = startProcess(args);
-
-		try (Reader out = newBufferedReader(process.getInputStream());
-				Reader err = newBufferedReader(process.getErrorStream())) {
-
-			StringBuilder output = new StringBuilder();
-			readAllChars(out, (chars, numChars) -> output.append(chars, 0, numChars));
-
-			readAllChars(err, (__, ___) -> {
-				// ignore
-			});
-
-			boolean terminated = process.waitFor(10, TimeUnit.SECONDS);
-			return terminated && process.exitValue() == 0 ? Optional.of(trimAtEnd(output)) : Optional.empty();
-		}
-		catch (InterruptedException e) {
-			throw ExceptionUtils.throwAsUncheckedException(e);
-		}
-		catch (IOException ignore) {
-			return Optional.empty();
-		}
-		finally {
-			process.destroyForcibly();
-		}
-	}
-
-	private static BufferedReader newBufferedReader(InputStream stream) {
-		return new BufferedReader(new InputStreamReader(stream, Charset.defaultCharset()));
-	}
-
-	private Process startProcess(String[] command) {
-		Process process;
-		try {
-			process = new ProcessBuilder().directory(workingDir.toFile()).command(command).start();
-		}
-		catch (IOException e) {
-			throw new UncheckedIOException("Failed to start process", e);
-		}
-		return process;
-	}
-
-	private static void readAllChars(Reader reader, BiConsumer<char[], Integer> consumer) throws IOException {
-		char[] buffer = new char[1024];
-		int numChars;
-		while ((numChars = reader.read(buffer)) != -1) {
-			consumer.accept(buffer, numChars);
-		}
-	}
-
-	private static String trimAtEnd(StringBuilder value) {
-		int endIndex = value.length();
-		for (int i = value.length() - 1; i >= 0; i--) {
-			if (Character.isWhitespace(value.charAt(i))) {
-				endIndex--;
-				break;
-			}
-		}
-		return value.substring(0, endIndex);
+	private void addGitInfo(Infrastructure infrastructure, GitInfoCollector git) {
+		git.getOriginUrl() //
+				.ifPresent(
+					gitUrl -> infrastructure.append(repository(), repository -> repository.withOriginUrl(gitUrl)));
+		git.getBranch() //
+				.ifPresent(branch -> infrastructure.append(branch(branch)));
+		git.getCommitHash() //
+				.ifPresent(gitCommitHash -> infrastructure.append(commit(gitCommitHash)));
+		git.getStatus() //
+				.ifPresent(statusOutput -> infrastructure.append(status(statusOutput),
+					status -> status.withClean(statusOutput.isEmpty())));
 	}
 
 	@Override
@@ -304,17 +234,15 @@ private void reportStarted(TestIdentifier testIdentifier, String id) {
 	}
 
 	private void addTestSource(TestSource source, Sources sources) {
-		if (source instanceof CompositeTestSource) {
-			((CompositeTestSource) source).getSources().forEach(it -> addTestSource(it, sources));
+		if (source instanceof CompositeTestSource compositeSource) {
+			compositeSource.getSources().forEach(it -> addTestSource(it, sources));
 		}
-		else if (source instanceof ClassSource) {
-			ClassSource classSource = (ClassSource) source;
+		else if (source instanceof ClassSource classSource) {
 			sources.append(classSource(classSource.getClassName()), //
 				element -> classSource.getPosition().ifPresent(
 					filePosition -> element.addFilePosition(filePosition.getLine(), filePosition.getColumn())));
 		}
-		else if (source instanceof MethodSource) {
-			MethodSource methodSource = (MethodSource) source;
+		else if (source instanceof MethodSource methodSource) {
 			sources.append(methodSource(methodSource.getClassName(), methodSource.getMethodName()), element -> {
 				String methodParameterTypes = methodSource.getMethodParameterTypes();
 				if (methodParameterTypes != null) {
@@ -322,26 +250,24 @@ else if (source instanceof MethodSource) {
 				}
 			});
 		}
-		else if (source instanceof ClasspathResourceSource) {
-			ClasspathResourceSource classpathResourceSource = (ClasspathResourceSource) source;
+		else if (source instanceof ClasspathResourceSource classpathResourceSource) {
 			sources.append(classpathResourceSource(classpathResourceSource.getClasspathResourceName()), //
 				element -> classpathResourceSource.getPosition().ifPresent(
 					filePosition -> element.addFilePosition(filePosition.getLine(), filePosition.getColumn())));
 		}
-		else if (source instanceof PackageSource) {
-			sources.append(packageSource(((PackageSource) source).getPackageName()));
+		else if (source instanceof PackageSource packageSource) {
+			sources.append(packageSource(packageSource.getPackageName()));
 		}
-		else if (source instanceof FileSource) {
-			FileSource fileSource = (FileSource) source;
+		else if (source instanceof FileSource fileSource) {
 			sources.append(fileSource(fileSource.getFile()), //
 				element -> fileSource.getPosition().ifPresent(
 					filePosition -> element.addFilePosition(filePosition.getLine(), filePosition.getColumn())));
 		}
-		else if (source instanceof DirectorySource) {
-			sources.append(directorySource(((DirectorySource) source).getFile()));
+		else if (source instanceof DirectorySource directorySource) {
+			sources.append(directorySource(directorySource.getFile()));
 		}
-		else if (source instanceof UriSource) {
-			sources.append(uriSource(((UriSource) source).getUri()));
+		else if (source instanceof UriSource uriSource) {
+			sources.append(uriSource(uriSource.getUri()));
 		}
 	}
 
@@ -366,7 +292,8 @@ public void reportingEntryPublished(TestIdentifier testIdentifier, ReportEntry e
 				}));
 	}
 
-	private static void attachOutput(Attachments attachments, LocalDateTime timestamp, String content, String source) {
+	private static void attachOutput(Attachments attachments, LocalDateTime timestamp, @Nullable String content,
+			String source) {
 		if (content != null) {
 			attachments.append(output(timestamp), output -> output.withSource(source).withContent(content));
 		}
@@ -378,7 +305,7 @@ public void fileEntryPublished(TestIdentifier testIdentifier, FileEntry entry) {
 		eventsFileWriter.append(reported(id, Instant.now()), //
 			reported -> reported.append(attachments(), attachments -> attachments.append(file(entry.getTimestamp()), //
 				file -> {
-					file.withPath(outputDir.relativize(entry.getPath()).toString());
+					file.withPath(requireNonNull(outputDir).relativize(entry.getPath()).toString());
 					entry.getMediaType().ifPresent(file::withMediaType);
 				})));
 	}
@@ -393,15 +320,11 @@ public void executionFinished(TestIdentifier testIdentifier, TestExecutionResult
 	}
 
 	private Result.Status convertStatus(TestExecutionResult.Status status) {
-		switch (status) {
-			case FAILED:
-				return Result.Status.FAILED;
-			case SUCCESSFUL:
-				return Result.Status.SUCCESSFUL;
-			case ABORTED:
-				return Result.Status.ABORTED;
-		}
-		throw new JUnitException("Unhandled status: " + status);
+		return switch (status) {
+			case FAILED -> Result.Status.FAILED;
+			case SUCCESSFUL -> Result.Status.SUCCESSFUL;
+			case ABORTED -> Result.Status.ABORTED;
+		};
 	}
 
 }
diff --git a/junit-platform-reporting/src/main/java/org/junit/platform/reporting/open/xml/package-info.java b/junit-platform-reporting/src/main/java/org/junit/platform/reporting/open/xml/package-info.java
index 5befd7af7b57..15a76f02d2c6 100644
--- a/junit-platform-reporting/src/main/java/org/junit/platform/reporting/open/xml/package-info.java
+++ b/junit-platform-reporting/src/main/java/org/junit/platform/reporting/open/xml/package-info.java
@@ -2,4 +2,7 @@
  * Support for generating Open Test Reporting compatible XML event reports.
  */
 
+@NullMarked
 package org.junit.platform.reporting.open.xml;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-platform-reporting/src/main/java/org/junit/platform/reporting/package-info.java b/junit-platform-reporting/src/main/java/org/junit/platform/reporting/package-info.java
index d7c603241d19..09fb2bd2538e 100644
--- a/junit-platform-reporting/src/main/java/org/junit/platform/reporting/package-info.java
+++ b/junit-platform-reporting/src/main/java/org/junit/platform/reporting/package-info.java
@@ -2,4 +2,7 @@
  * JUnit Platform Reporting.
  */
 
+@NullMarked
 package org.junit.platform.reporting;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-platform-reporting/src/main/resources/org/junit/platform/reporting/open/xml/catalog.xml b/junit-platform-reporting/src/main/resources/org/junit/platform/reporting/open/xml/catalog.xml
index 057d295ac832..d3c5a0eda66d 100644
--- a/junit-platform-reporting/src/main/resources/org/junit/platform/reporting/open/xml/catalog.xml
+++ b/junit-platform-reporting/src/main/resources/org/junit/platform/reporting/open/xml/catalog.xml
@@ -1,4 +1,4 @@
 <?xml version="1.0"?>
 <catalog xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog">
-    <system systemId="https://junit.org/junit5/schemas/open-test-reporting/junit-1.9.xsd" uri="junit.xsd"/>
+    <system systemId="https://schemas.junit.org/open-test-reporting/junit-1.9.xsd" uri="junit.xsd"/>
 </catalog>
diff --git a/junit-platform-runner/junit-platform-runner.gradle.kts b/junit-platform-runner/junit-platform-runner.gradle.kts
deleted file mode 100644
index bbc2ae9d95be..000000000000
--- a/junit-platform-runner/junit-platform-runner.gradle.kts
+++ /dev/null
@@ -1,37 +0,0 @@
-plugins {
-	id("junitbuild.java-library-conventions")
-	id("junitbuild.junit4-compatibility")
-}
-
-description = "JUnit Platform Runner"
-
-dependencies {
-	api(platform(projects.junitBom))
-	api(libs.junit4)
-	api(projects.junitPlatformLauncher)
-	api(projects.junitPlatformSuiteApi)
-
-	compileOnlyApi(libs.apiguardian)
-
-	implementation(projects.junitPlatformSuiteCommons)
-
-	testImplementation(testFixtures(projects.junitPlatformEngine))
-	testImplementation(testFixtures(projects.junitPlatformLauncher))
-
-	osgiVerification(projects.junitJupiterEngine)
-	osgiVerification(projects.junitPlatformLauncher)
-}
-
-tasks.jar {
-	bundle {
-		val importAPIGuardian: String by extra
-		bnd("""
-			# Import JUnit4 packages with a version
-			Import-Package: \
-				$importAPIGuardian,\
-				org.junit.platform.commons.logging;status=INTERNAL,\
-				org.junit.runner.*;version="[${libs.versions.junit4Min.get()},5)",\
-				*
-		""")
-	}
-}
diff --git a/junit-platform-runner/src/main/java/org/junit/platform/runner/JUnitPlatform.java b/junit-platform-runner/src/main/java/org/junit/platform/runner/JUnitPlatform.java
deleted file mode 100644
index 0df3bbb19ef3..000000000000
--- a/junit-platform-runner/src/main/java/org/junit/platform/runner/JUnitPlatform.java
+++ /dev/null
@@ -1,206 +0,0 @@
-/*
- * Copyright 2015-2025 the original author or authors.
- *
- * All rights reserved. This program and the accompanying materials are
- * made available under the terms of the Eclipse Public License v2.0 which
- * accompanies this distribution and is available at
- *
- * https://www.eclipse.org/legal/epl-v20.html
- */
-
-package org.junit.platform.runner;
-
-import static java.util.stream.Collectors.toList;
-import static org.apiguardian.api.API.Status.DEPRECATED;
-import static org.junit.platform.commons.support.AnnotationSupport.isAnnotated;
-import static org.junit.platform.engine.discovery.DiscoverySelectors.selectClass;
-import static org.junit.platform.suite.commons.SuiteLauncherDiscoveryRequestBuilder.request;
-
-import java.lang.annotation.Annotation;
-import java.util.Arrays;
-import java.util.List;
-import java.util.Set;
-
-import org.apiguardian.api.API;
-import org.junit.platform.engine.DiscoverySelector;
-import org.junit.platform.engine.discovery.DiscoverySelectors;
-import org.junit.platform.launcher.Launcher;
-import org.junit.platform.launcher.LauncherDiscoveryRequest;
-import org.junit.platform.launcher.TestIdentifier;
-import org.junit.platform.launcher.TestPlan;
-import org.junit.platform.launcher.core.LauncherFactory;
-import org.junit.platform.suite.api.ConfigurationParameter;
-import org.junit.platform.suite.api.ConfigurationParametersResource;
-import org.junit.platform.suite.api.ExcludeClassNamePatterns;
-import org.junit.platform.suite.api.ExcludeEngines;
-import org.junit.platform.suite.api.ExcludePackages;
-import org.junit.platform.suite.api.ExcludeTags;
-import org.junit.platform.suite.api.IncludeClassNamePatterns;
-import org.junit.platform.suite.api.IncludeEngines;
-import org.junit.platform.suite.api.IncludePackages;
-import org.junit.platform.suite.api.IncludeTags;
-import org.junit.platform.suite.api.Select;
-import org.junit.platform.suite.api.SelectClasses;
-import org.junit.platform.suite.api.SelectClasspathResource;
-import org.junit.platform.suite.api.SelectDirectories;
-import org.junit.platform.suite.api.SelectFile;
-import org.junit.platform.suite.api.SelectModules;
-import org.junit.platform.suite.api.SelectPackages;
-import org.junit.platform.suite.api.SelectUris;
-import org.junit.platform.suite.api.Suite;
-import org.junit.platform.suite.api.SuiteDisplayName;
-import org.junit.platform.suite.commons.SuiteLauncherDiscoveryRequestBuilder;
-import org.junit.runner.Description;
-import org.junit.runner.Runner;
-import org.junit.runner.manipulation.Filter;
-import org.junit.runner.manipulation.Filterable;
-import org.junit.runner.manipulation.NoTestsRemainException;
-import org.junit.runner.notification.RunNotifier;
-
-/**
- * JUnit 4 based {@link Runner} which runs tests on the JUnit Platform in a
- * JUnit 4 environment.
- *
- * <p>Annotating a class with {@code @RunWith(JUnitPlatform.class)} allows it
- * to be run with IDEs and build systems that support JUnit 4 but do not yet
- * support the JUnit Platform directly.
- *
- * <p>Please note that test classes and suites annotated with
- * {@code @RunWith(JUnitPlatform.class)} <em>cannot</em> be executed directly on
- * the JUnit Platform (or as a "JUnit 5" test as documented in some IDEs). Such
- * classes and suites can only be executed using JUnit 4 infrastructure.
- *
- * <p>Consult the various annotations in the {@code org.junit.platform.suite.api}
- * package for configuration options.
- *
- * <p>If you do not use any configuration annotations from the
- * {@code org.junit.platform.suite.api} package, you can use this runner on a
- * test class whose programming model is supported on the JUnit Platform &mdash;
- * for example, a JUnit Jupiter test class. Note, however, that any test class
- * run with this runner must be {@code public} in order to be picked up by IDEs
- * and build tools.
- *
- * <p>When used on a class that serves as a test suite and the
- * {@link IncludeClassNamePatterns @IncludeClassNamePatterns} annotation is not
- * present, the default include pattern
- * {@value org.junit.platform.engine.discovery.ClassNameFilter#STANDARD_INCLUDE_PATTERN}
- * will be used in order to avoid loading classes unnecessarily (see {@link
- * org.junit.platform.engine.discovery.ClassNameFilter#STANDARD_INCLUDE_PATTERN
- * ClassNameFilter#STANDARD_INCLUDE_PATTERN}).
- *
- * @since 1.0
- * @see Select
- * @see SelectClasses
- * @see SelectClasspathResource
- * @see SelectDirectories
- * @see SelectFile
- * @see SelectModules
- * @see SelectPackages
- * @see SelectUris
- * @see IncludeClassNamePatterns
- * @see ExcludeClassNamePatterns
- * @see IncludeEngines
- * @see ExcludeEngines
- * @see IncludePackages
- * @see ExcludePackages
- * @see IncludeTags
- * @see ExcludeTags
- * @see SuiteDisplayName
- * @see org.junit.platform.suite.api.UseTechnicalNames UseTechnicalNames
- * @see ConfigurationParameter
- * @see ConfigurationParametersResource
- * @deprecated since 1.8, in favor of the {@link Suite @Suite} support provided by
- * the {@code junit-platform-suite-engine} module; to be removed in JUnit Platform 2.0
- */
-@API(status = DEPRECATED, since = "1.8")
-@Deprecated
-public class JUnitPlatform extends Runner implements Filterable {
-
-	// @formatter:off
-	private static final List<Class<? extends Annotation>> IMPLICIT_SUITE_ANNOTATIONS = Arrays.asList(
-			SelectClasses.class,
-			SelectClasspathResource.class,
-			SelectDirectories.class,
-			SelectFile.class,
-			SelectFile.class,
-			SelectModules.class,
-			SelectPackages.class,
-			SelectUris.class
-	);
-	// @formatter:on
-
-	private final Class<?> testClass;
-	private final Launcher launcher;
-
-	private JUnitPlatformTestTree testTree;
-
-	public JUnitPlatform(Class<?> testClass) {
-		this(testClass, LauncherFactory.create());
-	}
-
-	// For testing only
-	JUnitPlatform(Class<?> testClass, Launcher launcher) {
-		this.launcher = launcher;
-		this.testClass = testClass;
-		this.testTree = generateTestTree(createDiscoveryRequest());
-	}
-
-	@Override
-	public Description getDescription() {
-		return this.testTree.getSuiteDescription();
-	}
-
-	@Override
-	public void run(RunNotifier notifier) {
-		this.launcher.execute(this.testTree.getTestPlan(), new JUnitPlatformRunnerListener(this.testTree, notifier));
-	}
-
-	private JUnitPlatformTestTree generateTestTree(LauncherDiscoveryRequest discoveryRequest) {
-		TestPlan testPlan = this.launcher.discover(discoveryRequest);
-		return new JUnitPlatformTestTree(testPlan, this.testClass);
-	}
-
-	@SuppressWarnings("deprecation")
-	private LauncherDiscoveryRequest createDiscoveryRequest() {
-		SuiteLauncherDiscoveryRequestBuilder requestBuilder = request();
-		// Allows @RunWith(JUnitPlatform.class) to be added to any test case
-		boolean isSuite = isSuite();
-		if (!isSuite) {
-			requestBuilder.selectors(selectClass(this.testClass));
-		}
-
-		// @formatter:off
-		return requestBuilder
-				.filterStandardClassNamePatterns(isSuite)
-				.suite(this.testClass)
-				.build();
-		// @formatter:on
-	}
-
-	private boolean isSuite() {
-		// @formatter:off
-		return IMPLICIT_SUITE_ANNOTATIONS.stream()
-				.anyMatch(annotation -> isAnnotated(this.testClass, annotation));
-		// @formatter:on
-	}
-
-	@Override
-	public void filter(Filter filter) throws NoTestsRemainException {
-		Set<TestIdentifier> filteredIdentifiers = this.testTree.getFilteredLeaves(filter);
-		if (filteredIdentifiers.isEmpty()) {
-			throw new NoTestsRemainException();
-		}
-		this.testTree = generateTestTree(createDiscoveryRequestForUniqueIds(filteredIdentifiers));
-	}
-
-	private LauncherDiscoveryRequest createDiscoveryRequestForUniqueIds(Set<TestIdentifier> testIdentifiers) {
-		// @formatter:off
-		List<DiscoverySelector> selectors = testIdentifiers.stream()
-				.map(TestIdentifier::getUniqueIdObject)
-				.map(DiscoverySelectors::selectUniqueId)
-				.collect(toList());
-		// @formatter:on
-		return request().selectors(selectors).build();
-	}
-
-}
diff --git a/junit-platform-runner/src/main/java/org/junit/platform/runner/JUnitPlatformRunnerListener.java b/junit-platform-runner/src/main/java/org/junit/platform/runner/JUnitPlatformRunnerListener.java
deleted file mode 100644
index 180472e20bb6..000000000000
--- a/junit-platform-runner/src/main/java/org/junit/platform/runner/JUnitPlatformRunnerListener.java
+++ /dev/null
@@ -1,102 +0,0 @@
-/*
- * Copyright 2015-2025 the original author or authors.
- *
- * All rights reserved. This program and the accompanying materials are
- * made available under the terms of the Eclipse Public License v2.0 which
- * accompanies this distribution and is available at
- *
- * https://www.eclipse.org/legal/epl-v20.html
- */
-
-package org.junit.platform.runner;
-
-import static org.junit.platform.engine.TestExecutionResult.Status.ABORTED;
-import static org.junit.platform.engine.TestExecutionResult.Status.FAILED;
-
-import org.junit.platform.engine.TestExecutionResult;
-import org.junit.platform.engine.TestExecutionResult.Status;
-import org.junit.platform.engine.UniqueId;
-import org.junit.platform.engine.reporting.FileEntry;
-import org.junit.platform.engine.reporting.ReportEntry;
-import org.junit.platform.launcher.TestExecutionListener;
-import org.junit.platform.launcher.TestIdentifier;
-import org.junit.runner.Description;
-import org.junit.runner.notification.Failure;
-import org.junit.runner.notification.RunNotifier;
-
-/**
- * @since 1.0
- */
-class JUnitPlatformRunnerListener implements TestExecutionListener {
-
-	private final JUnitPlatformTestTree testTree;
-	private final RunNotifier notifier;
-
-	JUnitPlatformRunnerListener(JUnitPlatformTestTree testTree, RunNotifier notifier) {
-		this.testTree = testTree;
-		this.notifier = notifier;
-	}
-
-	@Override
-	public void dynamicTestRegistered(TestIdentifier testIdentifier) {
-		UniqueId parentId = testIdentifier.getParentIdObject().get();
-		testTree.addDynamicDescription(testIdentifier, parentId);
-	}
-
-	@Override
-	public void executionSkipped(TestIdentifier testIdentifier, String reason) {
-		if (testIdentifier.isTest()) {
-			fireTestIgnored(testIdentifier);
-		}
-		else {
-			testTree.getTestsInSubtree(testIdentifier).forEach(this::fireTestIgnored);
-		}
-	}
-
-	private void fireTestIgnored(TestIdentifier testIdentifier) {
-		Description description = findJUnit4Description(testIdentifier);
-		this.notifier.fireTestIgnored(description);
-	}
-
-	@Override
-	public void executionStarted(TestIdentifier testIdentifier) {
-		Description description = findJUnit4Description(testIdentifier);
-		if (description.isTest()) {
-			this.notifier.fireTestStarted(description);
-		}
-	}
-
-	@Override
-	public void executionFinished(TestIdentifier testIdentifier, TestExecutionResult testExecutionResult) {
-		Description description = findJUnit4Description(testIdentifier);
-		Status status = testExecutionResult.getStatus();
-		if (status == ABORTED) {
-			this.notifier.fireTestAssumptionFailed(toFailure(testExecutionResult, description));
-		}
-		else if (status == FAILED) {
-			this.notifier.fireTestFailure(toFailure(testExecutionResult, description));
-		}
-		if (description.isTest()) {
-			this.notifier.fireTestFinished(description);
-		}
-	}
-
-	@Override
-	public void reportingEntryPublished(TestIdentifier testIdentifier, ReportEntry entry) {
-		System.out.println(entry);
-	}
-
-	@Override
-	public void fileEntryPublished(TestIdentifier testIdentifier, FileEntry file) {
-		System.out.println(file);
-	}
-
-	private Failure toFailure(TestExecutionResult testExecutionResult, Description description) {
-		return new Failure(description, testExecutionResult.getThrowable().orElse(null));
-	}
-
-	private Description findJUnit4Description(TestIdentifier testIdentifier) {
-		return this.testTree.getDescription(testIdentifier);
-	}
-
-}
diff --git a/junit-platform-runner/src/main/java/org/junit/platform/runner/JUnitPlatformTestTree.java b/junit-platform-runner/src/main/java/org/junit/platform/runner/JUnitPlatformTestTree.java
deleted file mode 100644
index e76f2d56a9be..000000000000
--- a/junit-platform-runner/src/main/java/org/junit/platform/runner/JUnitPlatformTestTree.java
+++ /dev/null
@@ -1,167 +0,0 @@
-/*
- * Copyright 2015-2025 the original author or authors.
- *
- * All rights reserved. This program and the accompanying materials are
- * made available under the terms of the Eclipse Public License v2.0 which
- * accompanies this distribution and is available at
- *
- * https://www.eclipse.org/legal/epl-v20.html
- */
-
-package org.junit.platform.runner;
-
-import static java.util.stream.Collectors.toCollection;
-import static java.util.stream.Collectors.toSet;
-
-import java.util.HashMap;
-import java.util.LinkedHashSet;
-import java.util.Map;
-import java.util.Map.Entry;
-import java.util.Optional;
-import java.util.Set;
-import java.util.function.Function;
-import java.util.function.Predicate;
-
-import org.junit.platform.commons.support.AnnotationSupport;
-import org.junit.platform.commons.util.StringUtils;
-import org.junit.platform.engine.TestSource;
-import org.junit.platform.engine.UniqueId;
-import org.junit.platform.engine.support.descriptor.ClassSource;
-import org.junit.platform.engine.support.descriptor.MethodSource;
-import org.junit.platform.launcher.TestIdentifier;
-import org.junit.platform.launcher.TestPlan;
-import org.junit.platform.suite.api.SuiteDisplayName;
-import org.junit.runner.Description;
-import org.junit.runner.manipulation.Filter;
-
-/**
- * @since 1.0
- */
-class JUnitPlatformTestTree {
-
-	private final Map<TestIdentifier, Description> descriptions = new HashMap<>();
-	private final TestPlan testPlan;
-	private final Function<TestIdentifier, String> nameExtractor;
-	private final Description suiteDescription;
-
-	JUnitPlatformTestTree(TestPlan testPlan, Class<?> testClass) {
-		this.testPlan = testPlan;
-		this.nameExtractor = useTechnicalNames(testClass) ? this::getTechnicalName : TestIdentifier::getDisplayName;
-		this.suiteDescription = generateSuiteDescription(testPlan, testClass);
-	}
-
-	public TestPlan getTestPlan() {
-		return testPlan;
-	}
-
-	@SuppressWarnings("deprecation")
-	private static boolean useTechnicalNames(Class<?> testClass) {
-		return testClass.isAnnotationPresent(org.junit.platform.suite.api.UseTechnicalNames.class);
-	}
-
-	Description getSuiteDescription() {
-		return this.suiteDescription;
-	}
-
-	Description getDescription(TestIdentifier identifier) {
-		return this.descriptions.get(identifier);
-	}
-
-	private Description generateSuiteDescription(TestPlan testPlan, Class<?> testClass) {
-		String displayName = useTechnicalNames(testClass) ? testClass.getName() : getSuiteDisplayName(testClass);
-		Description suiteDescription = Description.createSuiteDescription(displayName);
-		buildDescriptionTree(suiteDescription, testPlan);
-		return suiteDescription;
-	}
-
-	private String getSuiteDisplayName(Class<?> testClass) {
-		// @formatter:off
-		return AnnotationSupport.findAnnotation(testClass, SuiteDisplayName.class)
-				.map(SuiteDisplayName::value)
-				.filter(StringUtils::isNotBlank)
-				.orElse(testClass.getName());
-		// @formatter:on
-	}
-
-	private void buildDescriptionTree(Description suiteDescription, TestPlan testPlan) {
-		testPlan.getRoots().forEach(testIdentifier -> buildDescription(testIdentifier, suiteDescription, testPlan));
-	}
-
-	void addDynamicDescription(TestIdentifier newIdentifier, UniqueId parentId) {
-		Description parent = getDescription(this.testPlan.getTestIdentifier(parentId));
-		buildDescription(newIdentifier, parent, this.testPlan);
-	}
-
-	private void buildDescription(TestIdentifier identifier, Description parent, TestPlan testPlan) {
-		Description newDescription = createJUnit4Description(identifier, testPlan);
-		parent.addChild(newDescription);
-		this.descriptions.put(identifier, newDescription);
-		testPlan.getChildren(identifier).forEach(
-			testIdentifier -> buildDescription(testIdentifier, newDescription, testPlan));
-	}
-
-	private Description createJUnit4Description(TestIdentifier identifier, TestPlan testPlan) {
-		String name = nameExtractor.apply(identifier);
-		if (identifier.isTest()) {
-			String containerName = testPlan.getParent(identifier).map(nameExtractor).orElse("<unrooted>");
-			return Description.createTestDescription(containerName, name, identifier.getUniqueIdObject());
-		}
-		return Description.createSuiteDescription(name, identifier.getUniqueIdObject());
-	}
-
-	private String getTechnicalName(TestIdentifier testIdentifier) {
-		Optional<TestSource> optionalSource = testIdentifier.getSource();
-		if (optionalSource.isPresent()) {
-			TestSource source = optionalSource.get();
-			if (source instanceof ClassSource) {
-				return ((ClassSource) source).getJavaClass().getName();
-			}
-			else if (source instanceof MethodSource) {
-				MethodSource methodSource = (MethodSource) source;
-				String methodParameterTypes = methodSource.getMethodParameterTypes();
-				if (StringUtils.isBlank(methodParameterTypes)) {
-					return methodSource.getMethodName();
-				}
-				return String.format("%s(%s)", methodSource.getMethodName(), methodParameterTypes);
-			}
-		}
-
-		// Else fall back to display name
-		return testIdentifier.getDisplayName();
-	}
-
-	Set<TestIdentifier> getTestsInSubtree(TestIdentifier ancestor) {
-		// @formatter:off
-		return testPlan.getDescendants(ancestor).stream()
-				.filter(TestIdentifier::isTest)
-				.collect(toCollection(LinkedHashSet::new));
-		// @formatter:on
-	}
-
-	Set<TestIdentifier> getFilteredLeaves(Filter filter) {
-		Set<TestIdentifier> identifiers = applyFilterToDescriptions(filter);
-		return removeNonLeafIdentifiers(identifiers);
-	}
-
-	private Set<TestIdentifier> removeNonLeafIdentifiers(Set<TestIdentifier> identifiers) {
-		return identifiers.stream().filter(isALeaf(identifiers)).collect(toSet());
-	}
-
-	private Predicate<? super TestIdentifier> isALeaf(Set<TestIdentifier> identifiers) {
-		return testIdentifier -> {
-			Set<TestIdentifier> descendants = testPlan.getDescendants(testIdentifier);
-			return identifiers.stream().noneMatch(descendants::contains);
-		};
-	}
-
-	private Set<TestIdentifier> applyFilterToDescriptions(Filter filter) {
-		// @formatter:off
-		return descriptions.entrySet()
-				.stream()
-				.filter(entry -> filter.shouldRun(entry.getValue()))
-				.map(Entry::getKey)
-				.collect(toSet());
-		// @formatter:on
-	}
-
-}
diff --git a/junit-platform-runner/src/main/java/org/junit/platform/runner/package-info.java b/junit-platform-runner/src/main/java/org/junit/platform/runner/package-info.java
deleted file mode 100644
index ef778ce20957..000000000000
--- a/junit-platform-runner/src/main/java/org/junit/platform/runner/package-info.java
+++ /dev/null
@@ -1,6 +0,0 @@
-/**
- * {@code Runner} and annotations for configuring and executing tests on the
- * JUnit Platform in a JUnit 4 environment.
- */
-
-package org.junit.platform.runner;
diff --git a/junit-platform-runner/src/module/org.junit.platform.runner/module-info.java b/junit-platform-runner/src/module/org.junit.platform.runner/module-info.java
deleted file mode 100644
index e9dc34ed78d1..000000000000
--- a/junit-platform-runner/src/module/org.junit.platform.runner/module-info.java
+++ /dev/null
@@ -1,25 +0,0 @@
-/*
- * Copyright 2015-2025 the original author or authors.
- *
- * All rights reserved. This program and the accompanying materials are
- * made available under the terms of the Eclipse Public License v2.0 which
- * accompanies this distribution and is available at
- *
- * https://www.eclipse.org/legal/epl-v20.html
- */
-
-/**
- * {@code Runner} and annotations for configuring and executing tests on the
- * JUnit Platform in a JUnit 4 environment.
- *
- * @since 1.0
- */
-module org.junit.platform.runner {
-	requires transitive junit; // 4
-	requires static transitive org.apiguardian.api;
-	requires transitive org.junit.platform.launcher;
-	requires transitive org.junit.platform.suite.api;
-	requires org.junit.platform.suite.commons;
-
-	exports org.junit.platform.runner;
-}
diff --git a/junit-platform-runner/src/test/README.md b/junit-platform-runner/src/test/README.md
deleted file mode 100644
index 6e2fd0b363f0..000000000000
--- a/junit-platform-runner/src/test/README.md
+++ /dev/null
@@ -1 +0,0 @@
-For compatibility with the Eclipse IDE, the test for this module are in the `platform-tests` project.
diff --git a/junit-platform-suite-api/junit-platform-suite-api.gradle.kts b/junit-platform-suite-api/junit-platform-suite-api.gradle.kts
index cc5eb1d08bb7..a5f73150fae6 100644
--- a/junit-platform-suite-api/junit-platform-suite-api.gradle.kts
+++ b/junit-platform-suite-api/junit-platform-suite-api.gradle.kts
@@ -1,5 +1,6 @@
 plugins {
 	id("junitbuild.java-library-conventions")
+	id("junitbuild.java-nullability-conventions")
 }
 
 description = "JUnit Platform Suite API"
@@ -9,6 +10,7 @@ dependencies {
 	api(projects.junitPlatformCommons)
 
 	compileOnlyApi(libs.apiguardian)
+	compileOnly(libs.jspecify)
 
 	osgiVerification(projects.junitJupiterEngine)
 	osgiVerification(projects.junitPlatformLauncher)
diff --git a/junit-platform-suite-api/src/module/org.junit.platform.suite.api/module-info.java b/junit-platform-suite-api/src/main/java/module-info.java
similarity index 94%
rename from junit-platform-suite-api/src/module/org.junit.platform.suite.api/module-info.java
rename to junit-platform-suite-api/src/main/java/module-info.java
index 9d8df8da3cf0..690db0fe2d21 100644
--- a/junit-platform-suite-api/src/module/org.junit.platform.suite.api/module-info.java
+++ b/junit-platform-suite-api/src/main/java/module-info.java
@@ -14,7 +14,10 @@
  * @since 1.0
  */
 module org.junit.platform.suite.api {
+
 	requires static transitive org.apiguardian.api;
+	requires static org.jspecify;
+
 	requires transitive org.junit.platform.commons;
 
 	exports org.junit.platform.suite.api;
diff --git a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/AfterSuite.java b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/AfterSuite.java
index 77ff31333f1a..97a93f7f7758 100644
--- a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/AfterSuite.java
+++ b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/AfterSuite.java
@@ -10,7 +10,7 @@
 
 package org.junit.platform.suite.api;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import java.lang.annotation.Documented;
 import java.lang.annotation.ElementType;
@@ -70,6 +70,6 @@
 @Target(ElementType.METHOD)
 @Retention(RetentionPolicy.RUNTIME)
 @Documented
-@API(status = EXPERIMENTAL, since = "1.11")
+@API(status = MAINTAINED, since = "1.13.3")
 public @interface AfterSuite {
 }
diff --git a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/BeforeSuite.java b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/BeforeSuite.java
index c62d9ccdc040..1b0f89ac181a 100644
--- a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/BeforeSuite.java
+++ b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/BeforeSuite.java
@@ -10,7 +10,7 @@
 
 package org.junit.platform.suite.api;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import java.lang.annotation.Documented;
 import java.lang.annotation.ElementType;
@@ -70,6 +70,6 @@
 @Target(ElementType.METHOD)
 @Retention(RetentionPolicy.RUNTIME)
 @Documented
-@API(status = EXPERIMENTAL, since = "1.11")
+@API(status = MAINTAINED, since = "1.13.3")
 public @interface BeforeSuite {
 }
diff --git a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/ConfigurationParameter.java b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/ConfigurationParameter.java
index 0a8d010a3624..a12e45674789 100644
--- a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/ConfigurationParameter.java
+++ b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/ConfigurationParameter.java
@@ -32,7 +32,6 @@
  * @see ConfigurationParametersResource
  * @see DisableParentConfigurationParameters
  * @see Suite
- * @see org.junit.platform.runner.JUnitPlatform
  * @see org.junit.platform.launcher.core.LauncherDiscoveryRequestBuilder#configurationParameter(String, String)
  */
 @Retention(RetentionPolicy.RUNTIME)
diff --git a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/ConfigurationParametersResource.java b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/ConfigurationParametersResource.java
index 6e370f69ff4c..926efdf4353d 100644
--- a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/ConfigurationParametersResource.java
+++ b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/ConfigurationParametersResource.java
@@ -10,7 +10,7 @@
 
 package org.junit.platform.suite.api;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import java.lang.annotation.Documented;
 import java.lang.annotation.ElementType;
@@ -32,14 +32,13 @@
  * @see ConfigurationParameter
  * @see DisableParentConfigurationParameters
  * @see Suite
- * @see org.junit.platform.runner.JUnitPlatform
  * @see org.junit.platform.launcher.core.LauncherDiscoveryRequestBuilder#configurationParametersResources(String...)
  */
 @Retention(RetentionPolicy.RUNTIME)
 @Target(ElementType.TYPE)
 @Inherited
 @Documented
-@API(status = EXPERIMENTAL, since = "1.11")
+@API(status = MAINTAINED, since = "1.13.3")
 @Repeatable(ConfigurationParametersResources.class)
 public @interface ConfigurationParametersResource {
 
diff --git a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/ConfigurationParametersResources.java b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/ConfigurationParametersResources.java
index 0897e77b4622..8726fd4f3f83 100644
--- a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/ConfigurationParametersResources.java
+++ b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/ConfigurationParametersResources.java
@@ -10,7 +10,7 @@
 
 package org.junit.platform.suite.api;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import java.lang.annotation.Documented;
 import java.lang.annotation.ElementType;
@@ -36,7 +36,7 @@
 @Target(ElementType.TYPE)
 @Inherited
 @Documented
-@API(status = EXPERIMENTAL, since = "1.11")
+@API(status = MAINTAINED, since = "1.13.3")
 public @interface ConfigurationParametersResources {
 
 	/**
diff --git a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/ExcludeClassNamePatterns.java b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/ExcludeClassNamePatterns.java
index 9e8ee74c28ef..76c2e74ae2ab 100644
--- a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/ExcludeClassNamePatterns.java
+++ b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/ExcludeClassNamePatterns.java
@@ -32,7 +32,6 @@
  *
  * @since 1.0
  * @see Suite
- * @see org.junit.platform.runner.JUnitPlatform
  * @see org.junit.platform.engine.discovery.ClassNameFilter#excludeClassNamePatterns
  */
 @Retention(RetentionPolicy.RUNTIME)
diff --git a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/ExcludeEngines.java b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/ExcludeEngines.java
index f6c2ac53f4dc..f77714c1c9fd 100644
--- a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/ExcludeEngines.java
+++ b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/ExcludeEngines.java
@@ -28,7 +28,6 @@
  *
  * @since 1.0
  * @see Suite
- * @see org.junit.platform.runner.JUnitPlatform
  * @see org.junit.platform.launcher.EngineFilter#excludeEngines
  */
 @Retention(RetentionPolicy.RUNTIME)
diff --git a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/ExcludePackages.java b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/ExcludePackages.java
index 5335f7c0e844..4df7bc43a353 100644
--- a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/ExcludePackages.java
+++ b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/ExcludePackages.java
@@ -27,7 +27,6 @@
 
  * @since 1.0
  * @see Suite
- * @see org.junit.platform.runner.JUnitPlatform
  * @see org.junit.platform.engine.discovery.PackageNameFilter#excludePackageNames(String...)
  */
 @Retention(RetentionPolicy.RUNTIME)
diff --git a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/ExcludeTags.java b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/ExcludeTags.java
index f24bc12ae6e7..fe3e43c88903 100644
--- a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/ExcludeTags.java
+++ b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/ExcludeTags.java
@@ -31,7 +31,7 @@
  * <p>Tag expressions are boolean expressions with the following allowed
  * operators: {@code !} (not), {@code &} (and) and {@code |} (or). Parentheses
  * can be used to adjust for operator precedence. Please refer to the
- * <a href="https://junit.org/junit5/docs/current/user-guide/#running-tests-tag-expressions">JUnit 5 User Guide</a>
+ * <a href="https://docs.junit.org/current/user-guide/#running-tests-tag-expressions">JUnit User Guide</a>
  * for usage examples.
  *
  * <h2>Syntax Rules for Tags</h2>
@@ -55,7 +55,6 @@
  *
  * @since 1.0
  * @see Suite
- * @see org.junit.platform.runner.JUnitPlatform
  * @see org.junit.platform.launcher.TagFilter#excludeTags
  */
 @Retention(RetentionPolicy.RUNTIME)
diff --git a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/IncludeClassNamePatterns.java b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/IncludeClassNamePatterns.java
index 313f52c9d371..4f638b868db5 100644
--- a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/IncludeClassNamePatterns.java
+++ b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/IncludeClassNamePatterns.java
@@ -32,7 +32,6 @@
  *
  * @since 1.0
  * @see Suite
- * @see org.junit.platform.runner.JUnitPlatform
  * @see org.junit.platform.engine.discovery.ClassNameFilter#STANDARD_INCLUDE_PATTERN
  * @see org.junit.platform.engine.discovery.ClassNameFilter#includeClassNamePatterns
  */
diff --git a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/IncludeEngines.java b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/IncludeEngines.java
index f35461d438fd..3b953bef831f 100644
--- a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/IncludeEngines.java
+++ b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/IncludeEngines.java
@@ -28,7 +28,6 @@
  *
  * @since 1.0
  * @see Suite
- * @see org.junit.platform.runner.JUnitPlatform
  * @see org.junit.platform.launcher.EngineFilter#includeEngines
  */
 @Retention(RetentionPolicy.RUNTIME)
diff --git a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/IncludePackages.java b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/IncludePackages.java
index f634544a7b84..06d8a02f79d6 100644
--- a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/IncludePackages.java
+++ b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/IncludePackages.java
@@ -27,7 +27,6 @@
  *
  * @since 1.0
  * @see Suite
- * @see org.junit.platform.runner.JUnitPlatform
  * @see org.junit.platform.engine.discovery.PackageNameFilter#includePackageNames(String...)
  */
 @Retention(RetentionPolicy.RUNTIME)
diff --git a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/IncludeTags.java b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/IncludeTags.java
index 12110bee9bfc..2efb0137d11b 100644
--- a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/IncludeTags.java
+++ b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/IncludeTags.java
@@ -31,7 +31,7 @@
  * <p>Tag expressions are boolean expressions with the following allowed
  * operators: {@code !} (not), {@code &} (and) and {@code |} (or). Parentheses
  * can be used to adjust for operator precedence. Please refer to the
- * <a href="https://junit.org/junit5/docs/current/user-guide/#running-tests-tag-expressions">JUnit 5 User Guide</a>
+ * <a href="https://docs.junit.org/current/user-guide/#running-tests-tag-expressions">JUnit User Guide</a>
  * for usage examples.
  *
  * <h2>Syntax Rules for Tags</h2>
@@ -55,7 +55,6 @@
  *
  * @since 1.0
  * @see Suite
- * @see org.junit.platform.runner.JUnitPlatform
  * @see org.junit.platform.launcher.TagFilter#includeTags
  */
 @Retention(RetentionPolicy.RUNTIME)
diff --git a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/Select.java b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/Select.java
index f2fd4a47a370..e8de03805ddf 100644
--- a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/Select.java
+++ b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/Select.java
@@ -10,7 +10,7 @@
 
 package org.junit.platform.suite.api;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import java.lang.annotation.Documented;
 import java.lang.annotation.ElementType;
@@ -35,7 +35,7 @@
 @Target(ElementType.TYPE)
 @Inherited
 @Documented
-@API(status = EXPERIMENTAL, since = "1.11")
+@API(status = MAINTAINED, since = "1.13.3")
 @Repeatable(Selects.class)
 public @interface Select {
 
diff --git a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/SelectClasses.java b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/SelectClasses.java
index 9964f7b68b68..1abfb8d10262 100644
--- a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/SelectClasses.java
+++ b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/SelectClasses.java
@@ -10,7 +10,6 @@
 
 package org.junit.platform.suite.api;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
 import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import java.lang.annotation.Documented;
@@ -28,7 +27,6 @@
  *
  * @since 1.0
  * @see Suite
- * @see org.junit.platform.runner.JUnitPlatform
  * @see org.junit.platform.engine.discovery.DiscoverySelectors#selectClass(Class)
  * @see org.junit.platform.engine.discovery.DiscoverySelectors#selectClass(String)
  */
@@ -57,7 +55,7 @@
 	 *
 	 * @since 1.10
 	 */
-	@API(status = EXPERIMENTAL, since = "1.10")
+	@API(status = MAINTAINED, since = "1.13.3")
 	String[] names() default {};
 
 }
diff --git a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/SelectClasspathResource.java b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/SelectClasspathResource.java
index c3255f501c39..5099cc27aef7 100644
--- a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/SelectClasspathResource.java
+++ b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/SelectClasspathResource.java
@@ -29,7 +29,6 @@
  *
  * @since 1.8
  * @see Suite
- * @see org.junit.platform.runner.JUnitPlatform
  * @see org.junit.platform.engine.discovery.DiscoverySelectors#selectClasspathResource(String, org.junit.platform.engine.discovery.FilePosition)
  */
 @Retention(RetentionPolicy.RUNTIME)
diff --git a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/SelectDirectories.java b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/SelectDirectories.java
index 57ea6bdbbe39..21ae13e9f564 100644
--- a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/SelectDirectories.java
+++ b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/SelectDirectories.java
@@ -27,7 +27,6 @@
  *
  * @since 1.8
  * @see Suite
- * @see org.junit.platform.runner.JUnitPlatform
  * @see org.junit.platform.engine.discovery.DiscoverySelectors#selectDirectory(String)
  */
 @Retention(RetentionPolicy.RUNTIME)
diff --git a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/SelectFile.java b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/SelectFile.java
index 7359febbda84..4ee43d25114c 100644
--- a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/SelectFile.java
+++ b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/SelectFile.java
@@ -29,7 +29,6 @@
  *
  * @since 1.8
  * @see Suite
- * @see org.junit.platform.runner.JUnitPlatform
  * @see org.junit.platform.engine.discovery.DiscoverySelectors#selectFile(String, org.junit.platform.engine.discovery.FilePosition)
  */
 @Retention(RetentionPolicy.RUNTIME)
diff --git a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/SelectMethod.java b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/SelectMethod.java
index c1fa0f6dc40d..f8a81e4f9aa0 100644
--- a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/SelectMethod.java
+++ b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/SelectMethod.java
@@ -10,7 +10,7 @@
 
 package org.junit.platform.suite.api;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import java.lang.annotation.Documented;
 import java.lang.annotation.ElementType;
@@ -29,7 +29,6 @@
  *
  * @since 1.10
  * @see Suite
- * @see org.junit.platform.runner.JUnitPlatform
  * @see org.junit.platform.engine.discovery.DiscoverySelectors#selectMethod(String)
  * @see org.junit.platform.engine.discovery.DiscoverySelectors#selectMethod(String, String, String)
  * @see org.junit.platform.engine.discovery.DiscoverySelectors#selectMethod(String, String, Class...)
@@ -40,7 +39,7 @@
 @Target(ElementType.TYPE)
 @Inherited
 @Documented
-@API(status = EXPERIMENTAL, since = "1.10")
+@API(status = MAINTAINED, since = "1.13.3")
 @Repeatable(SelectMethods.class)
 public @interface SelectMethod {
 
diff --git a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/SelectMethods.java b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/SelectMethods.java
index f3583156f325..6454363e95df 100644
--- a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/SelectMethods.java
+++ b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/SelectMethods.java
@@ -10,7 +10,7 @@
 
 package org.junit.platform.suite.api;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import java.lang.annotation.Documented;
 import java.lang.annotation.ElementType;
@@ -36,7 +36,7 @@
 @Target(ElementType.TYPE)
 @Inherited
 @Documented
-@API(status = EXPERIMENTAL, since = "1.10")
+@API(status = MAINTAINED, since = "1.13.3")
 public @interface SelectMethods {
 
 	/**
diff --git a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/SelectModules.java b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/SelectModules.java
index e0dccf332c18..9c3ba49a4e81 100644
--- a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/SelectModules.java
+++ b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/SelectModules.java
@@ -28,7 +28,6 @@
  *
  * @since 1.8
  * @see Suite
- * @see org.junit.platform.runner.JUnitPlatform
  * @see org.junit.platform.engine.discovery.DiscoverySelectors#selectModules(Set)
  */
 @Retention(RetentionPolicy.RUNTIME)
diff --git a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/SelectPackages.java b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/SelectPackages.java
index bba47a24c2d9..6b78cd0769b6 100644
--- a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/SelectPackages.java
+++ b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/SelectPackages.java
@@ -27,7 +27,6 @@
  *
  * @since 1.0
  * @see Suite
- * @see org.junit.platform.runner.JUnitPlatform
  * @see org.junit.platform.engine.discovery.DiscoverySelectors#selectPackage(String)
  */
 @Retention(RetentionPolicy.RUNTIME)
diff --git a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/SelectUris.java b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/SelectUris.java
index a281678df0a2..e55ebe1f8043 100644
--- a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/SelectUris.java
+++ b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/SelectUris.java
@@ -27,7 +27,6 @@
  *
  * @since 1.8
  * @see Suite
- * @see org.junit.platform.runner.JUnitPlatform
  * @see org.junit.platform.engine.discovery.DiscoverySelectors#selectUri(String)
  */
 @Retention(RetentionPolicy.RUNTIME)
diff --git a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/Selects.java b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/Selects.java
index 63f52143916b..6215c409b7fc 100644
--- a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/Selects.java
+++ b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/Selects.java
@@ -10,7 +10,7 @@
 
 package org.junit.platform.suite.api;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import java.lang.annotation.Documented;
 import java.lang.annotation.ElementType;
@@ -36,7 +36,7 @@
 @Target(ElementType.TYPE)
 @Inherited
 @Documented
-@API(status = EXPERIMENTAL, since = "1.11")
+@API(status = MAINTAINED, since = "1.13.3")
 public @interface Selects {
 
 	/**
diff --git a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/SuiteDisplayName.java b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/SuiteDisplayName.java
index 0113b1827b44..8a632fd72ac6 100644
--- a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/SuiteDisplayName.java
+++ b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/SuiteDisplayName.java
@@ -28,17 +28,12 @@
  * <p>Display names are typically used for test reporting in IDEs and build
  * tools and may contain spaces, special characters, and even emoji.
  *
- * <h2>JUnit 4 Suite Support</h2>
- * <p>Test suites can be run on the JUnit Platform in a JUnit 4 environment via
- * {@code @RunWith(JUnitPlatform.class)}.
- *
- * <h2>JUnit 5 Suite Support</h2>
- * <p>Test suites can be run on the JUnit Platform in a JUnit 5 environment via
- * the {@code junit-platform-suite-engine} module.
+ * <h2>Execution</h2>
+ * <p>Test suites can be run on the JUnit Platform the
+ * {@code junit-platform-suite-engine} module.
  *
  * @since 1.1
  * @see Suite
- * @see org.junit.platform.runner.JUnitPlatform
  */
 @Retention(RUNTIME)
 @Target(TYPE)
diff --git a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/UseTechnicalNames.java b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/UseTechnicalNames.java
deleted file mode 100644
index 749fcdb13a9f..000000000000
--- a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/UseTechnicalNames.java
+++ /dev/null
@@ -1,56 +0,0 @@
-/*
- * Copyright 2015-2025 the original author or authors.
- *
- * All rights reserved. This program and the accompanying materials are
- * made available under the terms of the Eclipse Public License v2.0 which
- * accompanies this distribution and is available at
- *
- * https://www.eclipse.org/legal/epl-v20.html
- */
-
-package org.junit.platform.suite.api;
-
-import static org.apiguardian.api.API.Status.DEPRECATED;
-
-import java.lang.annotation.Documented;
-import java.lang.annotation.ElementType;
-import java.lang.annotation.Inherited;
-import java.lang.annotation.Retention;
-import java.lang.annotation.RetentionPolicy;
-import java.lang.annotation.Target;
-
-import org.apiguardian.api.API;
-
-/**
- * {@code @UseTechnicalNames} specifies that <em>technical names</em> should be
- * used instead of <em>display names</em> when running a test suite on the
- * JUnit Platform.
- *
- * <p>By default, <em>display names</em> will be used for test artifacts in
- * reports and graphical displays in IDEs; however, when a JUnit Platform test
- * suite is executed with a build tool such as Gradle or Maven, the generated
- * test report may need to include the <em>technical names</em> of test
- * artifacts &mdash; for example, fully qualified class names &mdash; instead
- * of shorter <em>display names</em> like the simple name of a test class or a
- * custom display name containing special characters.
- *
- * <p>Note that the presence of {@code @UseTechnicalNames} overrides any custom
- * display name configured for the suite via {@link SuiteDisplayName @SuiteDisplayName}.
- *
- * <h2>JUnit 4 Suite Support</h2>
- * <p>Test suites can be run on the JUnit Platform in a JUnit 4 environment via
- * {@code @RunWith(JUnitPlatform.class)}.
- *
- * @since 1.0
- * @see org.junit.platform.runner.JUnitPlatform
- * @deprecated since 1.8, in favor of the {@link Suite @Suite} support provided by
- * the {@code junit-platform-suite-engine} module; to be removed in JUnit Platform 2.0
- */
-@Retention(RetentionPolicy.RUNTIME)
-@Target(ElementType.TYPE)
-@Inherited
-@Documented
-@API(status = DEPRECATED, since = "1.8")
-@Deprecated
-public @interface UseTechnicalNames {
-}
diff --git a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/package-info.java b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/package-info.java
index f5cd9bc50756..7463a9aa06e8 100644
--- a/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/package-info.java
+++ b/junit-platform-suite-api/src/main/java/org/junit/platform/suite/api/package-info.java
@@ -1,13 +1,12 @@
 /**
  * Annotations for configuring a <em>test suite</em> on the JUnit Platform.
  *
- * <h2>JUnit 4 Suite Support</h2>
- * <p>Test suites can be run on the JUnit Platform in a JUnit 4 environment via
- * {@code @RunWith(JUnitPlatform.class)} with the {@code junit-platform-runner}.
- *
- * <h2>JUnit 5 Suite Support</h2>
- * <p>Test suites can be run on the JUnit Platform in a JUnit 5 environment via
- * {@link Suite @Suite} with the {@code junit-platform-suite-engine}.
+ * <h2>Execution</h2>
+ * <p>Test suites can be run on the JUnit Platform the
+ * {@code junit-platform-suite-engine} module.
  */
 
+@NullMarked
 package org.junit.platform.suite.api;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-platform-suite-commons/junit-platform-suite-commons.gradle.kts b/junit-platform-suite-commons/junit-platform-suite-commons.gradle.kts
index f65b677db193..cb43e5d6963c 100644
--- a/junit-platform-suite-commons/junit-platform-suite-commons.gradle.kts
+++ b/junit-platform-suite-commons/junit-platform-suite-commons.gradle.kts
@@ -1,5 +1,6 @@
 plugins {
 	id("junitbuild.java-library-conventions")
+	id("junitbuild.java-nullability-conventions")
 }
 
 description = "JUnit Platform Suite Commons"
@@ -9,6 +10,7 @@ dependencies {
 	api(projects.junitPlatformLauncher)
 
 	compileOnlyApi(libs.apiguardian)
+	compileOnly(libs.jspecify)
 
 	implementation(projects.junitPlatformEngine)
 	implementation(projects.junitPlatformSuiteApi)
@@ -16,3 +18,7 @@ dependencies {
 	osgiVerification(projects.junitJupiterEngine)
 	osgiVerification(projects.junitPlatformLauncher)
 }
+
+tasks.compileJava {
+	options.compilerArgs.add("-Xlint:-module") // due to qualified exports
+}
diff --git a/junit-platform-suite-commons/src/module/org.junit.platform.suite.commons/module-info.java b/junit-platform-suite-commons/src/main/java/module-info.java
similarity index 91%
rename from junit-platform-suite-commons/src/module/org.junit.platform.suite.commons/module-info.java
rename to junit-platform-suite-commons/src/main/java/module-info.java
index 62c6732235d3..f0514a14064d 100644
--- a/junit-platform-suite-commons/src/module/org.junit.platform.suite.commons/module-info.java
+++ b/junit-platform-suite-commons/src/main/java/module-info.java
@@ -14,13 +14,15 @@
  * @since 1.8
  */
 module org.junit.platform.suite.commons {
+
 	requires static transitive org.apiguardian.api;
+	requires static org.jspecify;
+
 	requires org.junit.platform.suite.api;
 	requires org.junit.platform.commons;
 	requires org.junit.platform.engine;
 	requires transitive org.junit.platform.launcher;
 
 	exports org.junit.platform.suite.commons to
-			org.junit.platform.suite.engine,
-			org.junit.platform.runner;
+			org.junit.platform.suite.engine;
 }
diff --git a/junit-platform-suite-commons/src/main/java/org/junit/platform/suite/commons/AdditionalDiscoverySelectors.java b/junit-platform-suite-commons/src/main/java/org/junit/platform/suite/commons/AdditionalDiscoverySelectors.java
index 969fe04e9376..bbfe6aa026ac 100644
--- a/junit-platform-suite-commons/src/main/java/org/junit/platform/suite/commons/AdditionalDiscoverySelectors.java
+++ b/junit-platform-suite-commons/src/main/java/org/junit/platform/suite/commons/AdditionalDiscoverySelectors.java
@@ -41,7 +41,7 @@ static List<UriSelector> selectUris(String... uris) {
 		return uniqueStreamOf(uris)
 				.filter(StringUtils::isNotBlank)
 				.map(DiscoverySelectors::selectUri)
-				.collect(Collectors.toList());
+				.toList();
 		// @formatter:on
 	}
 
@@ -53,7 +53,7 @@ static List<DirectorySelector> selectDirectories(String... paths) {
 		return uniqueStreamOf(paths)
 				.filter(StringUtils::isNotBlank)
 				.map(DiscoverySelectors::selectDirectory)
-				.collect(Collectors.toList());
+				.toList();
 		// @formatter:on
 	}
 
@@ -64,7 +64,7 @@ static List<PackageSelector> selectPackages(String... packageNames) {
 		// @formatter:off
 		return uniqueStreamOf(packageNames)
 				.map(DiscoverySelectors::selectPackage)
-				.collect(Collectors.toList());
+				.toList();
 		// @formatter:on
 	}
 
@@ -113,9 +113,9 @@ static ClasspathResourceSelector selectClasspathResource(String classpathResourc
 		return DiscoverySelectors.selectClasspathResource(classpathResourceName, FilePosition.from(line, column));
 	}
 
-	static List<DiscoverySelector> parseIdentifiers(String[] identifiers) {
+	static List<? extends DiscoverySelector> parseIdentifiers(String[] identifiers) {
 		return DiscoverySelectors.parseAll(identifiers) //
-				.collect(Collectors.toList());
+				.toList();
 	}
 
 	private static <T> Stream<T> uniqueStreamOf(T[] elements) {
diff --git a/junit-platform-suite-commons/src/main/java/org/junit/platform/suite/commons/SuiteLauncherDiscoveryRequestBuilder.java b/junit-platform-suite-commons/src/main/java/org/junit/platform/suite/commons/SuiteLauncherDiscoveryRequestBuilder.java
index 44985338fd1b..d0a4464f23ed 100644
--- a/junit-platform-suite-commons/src/main/java/org/junit/platform/suite/commons/SuiteLauncherDiscoveryRequestBuilder.java
+++ b/junit-platform-suite-commons/src/main/java/org/junit/platform/suite/commons/SuiteLauncherDiscoveryRequestBuilder.java
@@ -10,7 +10,6 @@
 
 package org.junit.platform.suite.commons;
 
-import static java.util.stream.Collectors.toList;
 import static org.apiguardian.api.API.Status.DEPRECATED;
 import static org.apiguardian.api.API.Status.INTERNAL;
 import static org.junit.platform.commons.support.AnnotationSupport.findAnnotation;
@@ -32,6 +31,7 @@
 import java.util.stream.Stream;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.util.Preconditions;
 import org.junit.platform.commons.util.StringUtils;
 import org.junit.platform.engine.ConfigurationParameters;
@@ -113,14 +113,16 @@
  * @see org.junit.platform.launcher.EngineFilter
  * @see org.junit.platform.launcher.TagFilter
  */
-@API(status = INTERNAL, since = "1.8", consumers = { "org.junit.platform.suite.engine", "org.junit.platform.runner" })
+@API(status = INTERNAL, since = "1.8", consumers = "org.junit.platform.suite.engine")
 public final class SuiteLauncherDiscoveryRequestBuilder {
 
 	private final LauncherDiscoveryRequestBuilder delegate = LauncherDiscoveryRequestBuilder.request();
 	private final Set<String> selectedClassNames = new LinkedHashSet<>();
 	private boolean includeClassNamePatternsUsed;
 	private boolean filterStandardClassNamePatterns = false;
-	private ConfigurationParameters parentConfigurationParameters;
+
+	private @Nullable ConfigurationParameters parentConfigurationParameters;
+
 	private boolean enableParentConfigurationParameters = true;
 
 	private SuiteLauncherDiscoveryRequestBuilder() {
@@ -458,12 +460,12 @@ private List<ClassSelector> selectClasses(Class<?> suiteClass, SelectClasses ann
 		return toClassSelectors(suiteClass, annotation) //
 				.distinct() //
 				.peek(selector -> this.selectedClassNames.add(selector.getClassName())) //
-				.collect(toList());
+				.toList();
 	}
 
 	private static Stream<ClassSelector> toClassSelectors(Class<?> suiteClass, SelectClasses annotation) {
 		Preconditions.condition(annotation.value().length > 0 || annotation.names().length > 0,
-			() -> String.format("@SelectClasses on class [%s] must declare at least one class reference or name",
+			() -> "@SelectClasses on class [%s] must declare at least one class reference or name".formatted(
 				suiteClass.getName()));
 		return Stream.concat(//
 			AdditionalDiscoverySelectors.selectClasses(annotation.value()), //
@@ -516,14 +518,16 @@ private static MethodSelector toMethodSelectorFromFQMN(Class<?> suiteClass, Sele
 		return DiscoverySelectors.selectMethod(annotation.value());
 	}
 
-	private static MethodSelector toMethodSelector(Class<?> suiteClass, Class<?> type, String typeName,
-			Class<?>[] parameterTypes, String methodName, String parameterTypeNames) {
+	private static MethodSelector toMethodSelector(Class<?> suiteClass, @Nullable Class<?> type,
+			@Nullable String typeName, Class<?> @Nullable [] parameterTypes, String methodName,
+			String parameterTypeNames) {
 		if (type == null) {
-			Preconditions.notBlank(typeName, () -> prefixErrorMessageForInvalidSelectMethodUsage(suiteClass,
-				"type must be set or type name must not be blank"));
+			String nonBlankTypeName = Preconditions.notBlank(typeName,
+				() -> prefixErrorMessageForInvalidSelectMethodUsage(suiteClass,
+					"type must be set or type name must not be blank"));
 			return parameterTypes == null //
-					? DiscoverySelectors.selectMethod(typeName, methodName, parameterTypeNames) //
-					: DiscoverySelectors.selectMethod(typeName, methodName, parameterTypes);
+					? DiscoverySelectors.selectMethod(nonBlankTypeName, methodName, parameterTypeNames) //
+					: DiscoverySelectors.selectMethod(nonBlankTypeName, methodName, parameterTypes);
 		}
 		else {
 			Preconditions.condition(typeName == null, () -> prefixErrorMessageForInvalidSelectMethodUsage(suiteClass,
@@ -535,7 +539,7 @@ private static MethodSelector toMethodSelector(Class<?> suiteClass, Class<?> typ
 	}
 
 	private static String prefixErrorMessageForInvalidSelectMethodUsage(Class<?> suiteClass, String detailMessage) {
-		return String.format("@SelectMethod on class [%s]: %s", suiteClass.getName(), detailMessage);
+		return "@SelectMethod on class [%s]: %s".formatted(suiteClass.getName(), detailMessage);
 	}
 
 	private ClassNameFilter createIncludeClassNameFilter(String... patterns) {
diff --git a/junit-platform-suite-commons/src/main/java/org/junit/platform/suite/commons/package-info.java b/junit-platform-suite-commons/src/main/java/org/junit/platform/suite/commons/package-info.java
index 3eeb635013aa..422ebf466472 100644
--- a/junit-platform-suite-commons/src/main/java/org/junit/platform/suite/commons/package-info.java
+++ b/junit-platform-suite-commons/src/main/java/org/junit/platform/suite/commons/package-info.java
@@ -8,4 +8,7 @@
  * APIs by external parties is not supported!</strong>
  */
 
+@NullMarked
 package org.junit.platform.suite.commons;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-platform-suite-engine/junit-platform-suite-engine.gradle.kts b/junit-platform-suite-engine/junit-platform-suite-engine.gradle.kts
index 36abcdbc088d..7e777400ca8b 100644
--- a/junit-platform-suite-engine/junit-platform-suite-engine.gradle.kts
+++ b/junit-platform-suite-engine/junit-platform-suite-engine.gradle.kts
@@ -1,5 +1,6 @@
 plugins {
 	id("junitbuild.java-library-conventions")
+	id("junitbuild.java-nullability-conventions")
 }
 
 description = "JUnit Platform Suite Engine"
@@ -10,6 +11,7 @@ dependencies {
 	api(projects.junitPlatformSuiteApi)
 
 	compileOnlyApi(libs.apiguardian)
+	compileOnly(libs.jspecify)
 
 	implementation(projects.junitPlatformSuiteCommons)
 
diff --git a/junit-platform-suite-engine/src/module/org.junit.platform.suite.engine/module-info.java b/junit-platform-suite-engine/src/main/java/module-info.java
similarity index 96%
rename from junit-platform-suite-engine/src/module/org.junit.platform.suite.engine/module-info.java
rename to junit-platform-suite-engine/src/main/java/module-info.java
index e8a43bf80e1c..e7e15543dba2 100644
--- a/junit-platform-suite-engine/src/module/org.junit.platform.suite.engine/module-info.java
+++ b/junit-platform-suite-engine/src/main/java/module-info.java
@@ -16,7 +16,10 @@
  * @provides org.junit.platform.engine.TestEngine
  */
 module org.junit.platform.suite.engine {
+
 	requires static org.apiguardian.api;
+	requires static org.jspecify;
+
 	requires org.junit.platform.suite.api;
 	requires org.junit.platform.suite.commons;
 	requires org.junit.platform.commons;
diff --git a/junit-platform-suite-engine/src/main/java/org/junit/platform/suite/engine/ClassSelectorResolver.java b/junit-platform-suite-engine/src/main/java/org/junit/platform/suite/engine/ClassSelectorResolver.java
index 9694f15c9860..764841e4b052 100644
--- a/junit-platform-suite-engine/src/main/java/org/junit/platform/suite/engine/ClassSelectorResolver.java
+++ b/junit-platform-suite-engine/src/main/java/org/junit/platform/suite/engine/ClassSelectorResolver.java
@@ -133,8 +133,7 @@ private static boolean containsCycle(UniqueId id) {
 	}
 
 	private static String createConfigContainsCycleMessage(Class<?> suiteClass, UniqueId suiteId) {
-		return String.format(
-			"The suite configuration of [%s] resulted in a cycle [%s] and will not be discovered a second time.",
+		return "The suite configuration of [%s] resulted in a cycle [%s] and will not be discovered a second time.".formatted(
 			suiteClass.getName(), suiteId);
 	}
 
diff --git a/junit-platform-suite-engine/src/main/java/org/junit/platform/suite/engine/IsSuiteClass.java b/junit-platform-suite-engine/src/main/java/org/junit/platform/suite/engine/IsSuiteClass.java
index 6d9fcbe98ffa..277ac34edcd7 100644
--- a/junit-platform-suite-engine/src/main/java/org/junit/platform/suite/engine/IsSuiteClass.java
+++ b/junit-platform-suite-engine/src/main/java/org/junit/platform/suite/engine/IsSuiteClass.java
@@ -65,8 +65,7 @@ private static Condition<Class<?>> isNotInner(DiscoveryIssueReporter issueReport
 	}
 
 	private static DiscoveryIssue createIssue(Class<?> testClass, String detailMessage) {
-		String message = String.format("@Suite class '%s' %s It will not be executed.", testClass.getName(),
-			detailMessage);
+		String message = "@Suite class '%s' %s It will not be executed.".formatted(testClass.getName(), detailMessage);
 		return DiscoveryIssue.builder(DiscoveryIssue.Severity.WARNING, message) //
 				.source(ClassSource.from(testClass)) //
 				.build();
diff --git a/junit-platform-suite-engine/src/main/java/org/junit/platform/suite/engine/LifecycleMethodUtils.java b/junit-platform-suite-engine/src/main/java/org/junit/platform/suite/engine/LifecycleMethodUtils.java
index df8d894c3444..214d036a35d5 100644
--- a/junit-platform-suite-engine/src/main/java/org/junit/platform/suite/engine/LifecycleMethodUtils.java
+++ b/junit-platform-suite-engine/src/main/java/org/junit/platform/suite/engine/LifecycleMethodUtils.java
@@ -11,7 +11,6 @@
 package org.junit.platform.suite.engine;
 
 import static org.junit.platform.commons.support.AnnotationSupport.findAnnotatedMethods;
-import static org.junit.platform.commons.util.CollectionUtils.toUnmodifiableList;
 
 import java.lang.annotation.Annotation;
 import java.lang.reflect.Method;
@@ -59,13 +58,13 @@ private static List<Method> findMethodsAndCheckStaticAndNonPrivate(Class<?> test
 							.and(isNotPrivate(annotationType, issueReporter)) //
 							.and(hasNoParameters(annotationType, issueReporter)) //
 							.toPredicate()) //
-				.collect(toUnmodifiableList());
+				.toList();
 	}
 
 	private static DiscoveryIssueReporter.Condition<Method> isStatic(Class<? extends Annotation> annotationType,
 			DiscoveryIssueReporter issueReporter) {
 		return issueReporter.createReportingCondition(ModifierSupport::isStatic, method -> {
-			String message = String.format("@%s method '%s' must be static.", annotationType.getSimpleName(),
+			String message = "@%s method '%s' must be static.".formatted(annotationType.getSimpleName(),
 				method.toGenericString());
 			return createError(message, method);
 		});
@@ -74,7 +73,7 @@ private static DiscoveryIssueReporter.Condition<Method> isStatic(Class<? extends
 	private static DiscoveryIssueReporter.Condition<Method> isNotPrivate(Class<? extends Annotation> annotationType,
 			DiscoveryIssueReporter issueReporter) {
 		return issueReporter.createReportingCondition(ModifierSupport::isNotPrivate, method -> {
-			String message = String.format("@%s method '%s' must not be private.", annotationType.getSimpleName(),
+			String message = "@%s method '%s' must not be private.".formatted(annotationType.getSimpleName(),
 				method.toGenericString());
 			return createError(message, method);
 		});
@@ -83,7 +82,7 @@ private static DiscoveryIssueReporter.Condition<Method> isNotPrivate(Class<? ext
 	private static DiscoveryIssueReporter.Condition<Method> returnsPrimitiveVoid(
 			Class<? extends Annotation> annotationType, DiscoveryIssueReporter issueReporter) {
 		return issueReporter.createReportingCondition(ReflectionUtils::returnsPrimitiveVoid, method -> {
-			String message = String.format("@%s method '%s' must not return a value.", annotationType.getSimpleName(),
+			String message = "@%s method '%s' must not return a value.".formatted(annotationType.getSimpleName(),
 				method.toGenericString());
 			return createError(message, method);
 		});
@@ -92,8 +91,8 @@ private static DiscoveryIssueReporter.Condition<Method> returnsPrimitiveVoid(
 	private static DiscoveryIssueReporter.Condition<Method> hasNoParameters(Class<? extends Annotation> annotationType,
 			DiscoveryIssueReporter issueReporter) {
 		return issueReporter.createReportingCondition(method -> method.getParameterCount() == 0, method -> {
-			String message = String.format("@%s method '%s' must not accept parameters.",
-				annotationType.getSimpleName(), method.toGenericString());
+			String message = "@%s method '%s' must not accept parameters.".formatted(annotationType.getSimpleName(),
+				method.toGenericString());
 			return createError(message, method);
 		});
 	}
diff --git a/junit-platform-suite-engine/src/main/java/org/junit/platform/suite/engine/NoTestsDiscoveredException.java b/junit-platform-suite-engine/src/main/java/org/junit/platform/suite/engine/NoTestsDiscoveredException.java
index e0f22d8fa257..6283e63c27aa 100644
--- a/junit-platform-suite-engine/src/main/java/org/junit/platform/suite/engine/NoTestsDiscoveredException.java
+++ b/junit-platform-suite-engine/src/main/java/org/junit/platform/suite/engine/NoTestsDiscoveredException.java
@@ -10,14 +10,17 @@
 
 package org.junit.platform.suite.engine;
 
+import java.io.Serial;
+
 import org.junit.platform.commons.JUnitException;
 
 class NoTestsDiscoveredException extends JUnitException {
 
+	@Serial
 	private static final long serialVersionUID = 1L;
 
 	NoTestsDiscoveredException(Class<?> suiteClass) {
-		super(String.format("Suite [%s] did not discover any tests", suiteClass.getName()));
+		super("Suite [%s] did not discover any tests".formatted(suiteClass.getName()));
 	}
 
 }
diff --git a/junit-platform-suite-engine/src/main/java/org/junit/platform/suite/engine/SuiteTestDescriptor.java b/junit-platform-suite-engine/src/main/java/org/junit/platform/suite/engine/SuiteTestDescriptor.java
index d9837a6a2319..161c5189aa91 100644
--- a/junit-platform-suite-engine/src/main/java/org/junit/platform/suite/engine/SuiteTestDescriptor.java
+++ b/junit-platform-suite-engine/src/main/java/org/junit/platform/suite/engine/SuiteTestDescriptor.java
@@ -10,6 +10,7 @@
 
 package org.junit.platform.suite.engine;
 
+import static java.util.Objects.requireNonNull;
 import static java.util.function.Predicate.isEqual;
 import static java.util.stream.Collectors.joining;
 import static org.junit.platform.commons.support.AnnotationSupport.findAnnotation;
@@ -21,6 +22,7 @@
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.JUnitException;
 import org.junit.platform.commons.support.ReflectionSupport;
 import org.junit.platform.commons.util.Preconditions;
@@ -71,8 +73,9 @@ final class SuiteTestDescriptor extends AbstractTestDescriptor {
 	private final Class<?> suiteClass;
 	private final LifecycleMethods lifecycleMethods;
 
-	private LauncherDiscoveryResult launcherDiscoveryResult;
-	private SuiteLauncher launcher;
+	private @Nullable LauncherDiscoveryResult launcherDiscoveryResult;
+
+	private @Nullable SuiteLauncher launcher;
 
 	SuiteTestDescriptor(UniqueId id, Class<?> suiteClass, ConfigurationParameters configurationParameters,
 			OutputDirectoryProvider outputDirectoryProvider, EngineDiscoveryListener discoveryListener,
@@ -90,7 +93,7 @@ private static Boolean getFailIfNoTests(Class<?> suiteClass) {
 		// @formatter:off
 		return findAnnotation(suiteClass, Suite.class)
 				.map(Suite::failIfNoTests)
-				.orElseThrow(() -> new JUnitException(String.format("Suite [%s] was not annotated with @Suite", suiteClass.getName())));
+				.orElseThrow(() -> new JUnitException("Suite [%s] was not annotated with @Suite".formatted(suiteClass.getName())));
 		// @formatter:on
 	}
 
@@ -174,7 +177,7 @@ private void executeBeforeSuiteMethods(ThrowableCollector throwableCollector) {
 		}
 	}
 
-	private TestExecutionSummary executeTests(EngineExecutionListener parentEngineExecutionListener,
+	private @Nullable TestExecutionSummary executeTests(EngineExecutionListener parentEngineExecutionListener,
 			NamespacedHierarchicalStore<Namespace> requestLevelStore, ThrowableCollector throwableCollector) {
 		if (throwableCollector.isNotEmpty()) {
 			return null;
@@ -183,9 +186,9 @@ private TestExecutionSummary executeTests(EngineExecutionListener parentEngineEx
 		// #2838: The discovery result from a suite may have been filtered by
 		// post discovery filters from the launcher. The discovery result should
 		// be pruned accordingly.
-		LauncherDiscoveryResult discoveryResult = this.launcherDiscoveryResult.withRetainedEngines(
+		LauncherDiscoveryResult discoveryResult = requireNonNull(this.launcherDiscoveryResult).withRetainedEngines(
 			getChildren()::contains);
-		return launcher.execute(discoveryResult, parentEngineExecutionListener, requestLevelStore);
+		return requireNonNull(launcher).execute(discoveryResult, parentEngineExecutionListener, requestLevelStore);
 	}
 
 	private void executeAfterSuiteMethods(ThrowableCollector throwableCollector) {
@@ -194,12 +197,13 @@ private void executeAfterSuiteMethods(ThrowableCollector throwableCollector) {
 		}
 	}
 
-	private TestExecutionResult computeTestExecutionResult(TestExecutionSummary summary,
+	private TestExecutionResult computeTestExecutionResult(@Nullable TestExecutionSummary summary,
 			ThrowableCollector throwableCollector) {
-		if (throwableCollector.isNotEmpty()) {
-			return TestExecutionResult.failed(throwableCollector.getThrowable());
+		var throwable = throwableCollector.getThrowable();
+		if (throwable != null) {
+			return TestExecutionResult.failed(throwable);
 		}
-		if (failIfNoTests && summary.getTestsFoundCount() == 0) {
+		if (failIfNoTests && requireNonNull(summary).getTestsFoundCount() == 0) {
 			return TestExecutionResult.failed(new NoTestsDiscoveredException(suiteClass));
 		}
 		return TestExecutionResult.successful();
@@ -224,7 +228,9 @@ private static class LifecycleMethods {
 		}
 	}
 
-	private static class DiscoveryIssueForwardingListener implements LauncherDiscoveryListener {
+	private record DiscoveryIssueForwardingListener(EngineDiscoveryListener discoveryListener,
+			BiFunction<UniqueId, DiscoveryIssue, DiscoveryIssue> issueTransformer)
+			implements LauncherDiscoveryListener {
 
 		private static final Predicate<Segment> SUITE_SEGMENTS = where(Segment::getType, isEqual(SEGMENT_TYPE));
 
@@ -246,19 +252,10 @@ static DiscoveryIssueForwardingListener create(UniqueId id, EngineDiscoveryListe
 					if (message.endsWith(".")) {
 						message = message.substring(0, message.length() - 1);
 					}
-					return String.format("[%s] %s (via @Suite %s).", engineId, message, suitePath);
+					return "[%s] %s (via @Suite %s).".formatted(engineId, message, suitePath);
 				}));
 		}
 
-		private final EngineDiscoveryListener discoveryListener;
-		private final BiFunction<UniqueId, DiscoveryIssue, DiscoveryIssue> issueTransformer;
-
-		private DiscoveryIssueForwardingListener(EngineDiscoveryListener discoveryListener,
-				BiFunction<UniqueId, DiscoveryIssue, DiscoveryIssue> issueTransformer) {
-			this.discoveryListener = discoveryListener;
-			this.issueTransformer = issueTransformer;
-		}
-
 		@Override
 		public void issueEncountered(UniqueId engineUniqueId, DiscoveryIssue issue) {
 			DiscoveryIssue transformedIssue = this.issueTransformer.apply(engineUniqueId, issue);
diff --git a/junit-platform-suite-engine/src/main/java/org/junit/platform/suite/engine/package-info.java b/junit-platform-suite-engine/src/main/java/org/junit/platform/suite/engine/package-info.java
index fa4237d3cec4..09748becae7e 100644
--- a/junit-platform-suite-engine/src/main/java/org/junit/platform/suite/engine/package-info.java
+++ b/junit-platform-suite-engine/src/main/java/org/junit/platform/suite/engine/package-info.java
@@ -2,4 +2,7 @@
  * Core package for the JUnit Platform Suite test engine.
  */
 
+@NullMarked
 package org.junit.platform.suite.engine;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-platform-suite/junit-platform-suite.gradle.kts b/junit-platform-suite/junit-platform-suite.gradle.kts
index 83e475a2a689..8bce8504e7d8 100644
--- a/junit-platform-suite/junit-platform-suite.gradle.kts
+++ b/junit-platform-suite/junit-platform-suite.gradle.kts
@@ -1,5 +1,5 @@
 plugins {
-	id("junitbuild.java-library-conventions")
+	id("junitbuild.java-aggregator-conventions")
 }
 
 description = "JUnit Platform Suite (Aggregator)"
diff --git a/junit-platform-suite/src/module/org.junit.platform.suite/module-info.java b/junit-platform-suite/src/main/java/module-info.java
similarity index 100%
rename from junit-platform-suite/src/module/org.junit.platform.suite/module-info.java
rename to junit-platform-suite/src/main/java/module-info.java
diff --git a/junit-platform-testkit/junit-platform-testkit.gradle.kts b/junit-platform-testkit/junit-platform-testkit.gradle.kts
index 38e89344db34..7cb29ac6f662 100644
--- a/junit-platform-testkit/junit-platform-testkit.gradle.kts
+++ b/junit-platform-testkit/junit-platform-testkit.gradle.kts
@@ -1,5 +1,6 @@
 plugins {
 	id("junitbuild.java-library-conventions")
+	id("junitbuild.java-nullability-conventions")
 }
 
 description = "JUnit Platform Test Kit"
@@ -11,6 +12,7 @@ dependencies {
 	api(projects.junitPlatformLauncher)
 
 	compileOnlyApi(libs.apiguardian)
+	compileOnly(libs.jspecify)
 
 	osgiVerification(projects.junitJupiterEngine)
 	osgiVerification(projects.junitPlatformLauncher)
diff --git a/junit-platform-testkit/src/module/org.junit.platform.testkit/module-info.java b/junit-platform-testkit/src/main/java/module-info.java
similarity index 96%
rename from junit-platform-testkit/src/module/org.junit.platform.testkit/module-info.java
rename to junit-platform-testkit/src/main/java/module-info.java
index 58f2033bcf62..cbfbd2a41393 100644
--- a/junit-platform-testkit/src/module/org.junit.platform.testkit/module-info.java
+++ b/junit-platform-testkit/src/main/java/module-info.java
@@ -15,7 +15,10 @@
  * @uses org.junit.platform.engine.TestEngine
  */
 module org.junit.platform.testkit {
+
 	requires static transitive org.apiguardian.api;
+	requires static org.jspecify;
+
 	requires transitive org.assertj.core;
 	requires org.junit.platform.commons;
 	requires transitive org.junit.platform.engine;
diff --git a/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/Assertions.java b/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/Assertions.java
index 3e01ed7a9f0d..2f7d3e157304 100644
--- a/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/Assertions.java
+++ b/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/Assertions.java
@@ -12,7 +12,6 @@
 
 import java.util.List;
 import java.util.Objects;
-import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
 import org.junit.platform.commons.util.Preconditions;
@@ -50,7 +49,7 @@ static void assertAll(String heading, Stream<Executable> executables) {
 					}
 				}) //
 				.filter(Objects::nonNull) //
-				.collect(Collectors.toList());
+				.toList();
 
 		if (!failures.isEmpty()) {
 			MultipleFailuresError multipleFailuresError = new MultipleFailuresError(heading, failures);
@@ -82,7 +81,7 @@ private static String buildPrefix(String message) {
 	}
 
 	private static String formatValues(long expected, long actual) {
-		return String.format("expected: <%d> but was: <%d>", expected, actual);
+		return "expected: <%d> but was: <%d>".formatted(expected, actual);
 	}
 
 }
diff --git a/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/EngineDiscoveryResults.java b/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/EngineDiscoveryResults.java
index 901462794d31..53bb2e671db6 100644
--- a/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/EngineDiscoveryResults.java
+++ b/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/EngineDiscoveryResults.java
@@ -10,7 +10,6 @@
 
 package org.junit.platform.testkit.engine;
 
-import static java.util.Collections.unmodifiableList;
 import static org.apiguardian.api.API.Status.EXPERIMENTAL;
 
 import java.util.List;
@@ -28,7 +27,7 @@
  *
  * @since 1.13
  */
-@API(status = EXPERIMENTAL, since = "1.13")
+@API(status = EXPERIMENTAL, since = "6.0")
 public class EngineDiscoveryResults {
 
 	private final TestDescriptor engineDescriptor;
@@ -36,7 +35,7 @@ public class EngineDiscoveryResults {
 
 	EngineDiscoveryResults(TestDescriptor engineDescriptor, List<DiscoveryIssue> discoveryIssues) {
 		this.engineDescriptor = Preconditions.notNull(engineDescriptor, "Engine descriptor must not be null");
-		this.discoveryIssues = unmodifiableList(
+		this.discoveryIssues = List.copyOf(
 			Preconditions.notNull(discoveryIssues, "Discovery issues list must not be null"));
 		Preconditions.containsNoNullElements(discoveryIssues, "Discovery issues list must not contain null elements");
 	}
diff --git a/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/EngineTestKit.java b/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/EngineTestKit.java
index 37398b4efd3e..192163ab7d05 100644
--- a/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/EngineTestKit.java
+++ b/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/EngineTestKit.java
@@ -12,7 +12,6 @@
 
 import static java.util.Collections.emptySet;
 import static java.util.Collections.singleton;
-import static org.apiguardian.api.API.Status.DEPRECATED;
 import static org.apiguardian.api.API.Status.EXPERIMENTAL;
 import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
@@ -26,6 +25,7 @@
 import java.util.stream.Stream;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.JUnitException;
 import org.junit.platform.commons.PreconditionViolationException;
 import org.junit.platform.commons.util.CollectionUtils;
@@ -33,13 +33,10 @@
 import org.junit.platform.engine.DiscoveryFilter;
 import org.junit.platform.engine.DiscoveryIssue;
 import org.junit.platform.engine.DiscoverySelector;
-import org.junit.platform.engine.EngineDiscoveryRequest;
 import org.junit.platform.engine.EngineExecutionListener;
-import org.junit.platform.engine.ExecutionRequest;
 import org.junit.platform.engine.Filter;
 import org.junit.platform.engine.TestDescriptor;
 import org.junit.platform.engine.TestEngine;
-import org.junit.platform.engine.UniqueId;
 import org.junit.platform.engine.reporting.OutputDirectoryProvider;
 import org.junit.platform.engine.support.store.Namespace;
 import org.junit.platform.engine.support.store.NamespacedHierarchicalStore;
@@ -159,7 +156,7 @@ public static Builder engine(TestEngine testEngine) {
 	 * @see #engine(String)
 	 * @see #engine(TestEngine)
 	 */
-	@API(status = EXPERIMENTAL, since = "1.13")
+	@API(status = EXPERIMENTAL, since = "6.0")
 	public static EngineDiscoveryResults discover(String engineId, LauncherDiscoveryRequest discoveryRequest) {
 		Preconditions.notBlank(engineId, "TestEngine ID must not be null or blank");
 		return discover(loadTestEngine(engineId.trim()), discoveryRequest);
@@ -184,7 +181,7 @@ public static EngineDiscoveryResults discover(String engineId, LauncherDiscovery
 	 * @see #engine(String)
 	 * @see #engine(TestEngine)
 	 */
-	@API(status = EXPERIMENTAL, since = "1.13")
+	@API(status = EXPERIMENTAL, since = "6.0")
 	public static EngineDiscoveryResults discover(TestEngine testEngine, LauncherDiscoveryRequest discoveryRequest) {
 		Preconditions.notNull(testEngine, "TestEngine must not be null");
 		Preconditions.notNull(discoveryRequest, "EngineDiscoveryRequest must not be null");
@@ -194,42 +191,6 @@ public static EngineDiscoveryResults discover(TestEngine testEngine, LauncherDis
 		return new EngineDiscoveryResults(engineDescriptor, discoveryIssues);
 	}
 
-	/**
-	 * Execute tests for the given {@link EngineDiscoveryRequest} using the
-	 * {@link TestEngine} with the supplied ID.
-	 *
-	 * <p>The {@code TestEngine} will be loaded via Java's {@link ServiceLoader}
-	 * mechanism, analogous to the manner in which test engines are loaded in
-	 * the JUnit Platform Launcher API.
-	 *
-	 * <p>Note that {@link org.junit.platform.launcher.LauncherDiscoveryRequest}
-	 * from the {@code junit-platform-launcher} module is a subtype of
-	 * {@code EngineDiscoveryRequest}. It is therefore quite convenient to make
-	 * use of the DSL provided in
-	 * {@link org.junit.platform.launcher.core.LauncherDiscoveryRequestBuilder}
-	 * to build an appropriate discovery request to supply to this method. As
-	 * an alternative, consider using {@link #engine(String)} for a more fluent
-	 * API.
-	 *
-	 * @param engineId the ID of the {@code TestEngine} to use; must not be
-	 * {@code null} or <em>blank</em>
-	 * @param discoveryRequest the {@code EngineDiscoveryRequest} to use
-	 * @return the results of the execution
-	 * @throws PreconditionViolationException for invalid arguments or if the
-	 * {@code TestEngine} with the supplied ID cannot be loaded
-	 * @see #execute(String, LauncherDiscoveryRequest)
-	 * @see #engine(String)
-	 * @see #engine(TestEngine)
-	 * @deprecated Please use {@link #execute(String, LauncherDiscoveryRequest)}
-	 * instead.
-	 */
-	@Deprecated
-	@API(status = DEPRECATED, since = "1.7")
-	public static EngineExecutionResults execute(String engineId, EngineDiscoveryRequest discoveryRequest) {
-		Preconditions.notBlank(engineId, "TestEngine ID must not be null or blank");
-		return execute(loadTestEngine(engineId.trim()), discoveryRequest);
-	}
-
 	/**
 	 * Execute tests for the given {@link LauncherDiscoveryRequest} using the
 	 * {@link TestEngine} with the supplied ID.
@@ -259,41 +220,6 @@ public static EngineExecutionResults execute(String engineId, LauncherDiscoveryR
 		return execute(loadTestEngine(engineId.trim()), discoveryRequest);
 	}
 
-	/**
-	 * Execute tests for the given {@link EngineDiscoveryRequest} using the
-	 * supplied {@link TestEngine}.
-	 *
-	 * <p>Note that {@link org.junit.platform.launcher.LauncherDiscoveryRequest}
-	 * from the {@code junit-platform-launcher} module is a subtype of
-	 * {@code EngineDiscoveryRequest}. It is therefore quite convenient to make
-	 * use of the DSL provided in
-	 * {@link org.junit.platform.launcher.core.LauncherDiscoveryRequestBuilder}
-	 * to build an appropriate discovery request to supply to this method. As
-	 * an alternative, consider using {@link #engine(TestEngine)} for a more fluent
-	 * API.
-	 *
-	 * @param testEngine the {@code TestEngine} to use; must not be {@code null}
-	 * @param discoveryRequest the {@code EngineDiscoveryRequest} to use; must
-	 * not be {@code null}
-	 * @return the recorded {@code EngineExecutionResults}
-	 * @throws PreconditionViolationException for invalid arguments
-	 * @see #execute(TestEngine, LauncherDiscoveryRequest)
-	 * @see #engine(String)
-	 * @see #engine(TestEngine)
-	 * @deprecated Please use {@link #execute(TestEngine, LauncherDiscoveryRequest)}
-	 * instead.
-	 */
-	@Deprecated
-	@API(status = DEPRECATED, since = "1.7")
-	public static EngineExecutionResults execute(TestEngine testEngine, EngineDiscoveryRequest discoveryRequest) {
-		Preconditions.notNull(testEngine, "TestEngine must not be null");
-		Preconditions.notNull(discoveryRequest, "EngineDiscoveryRequest must not be null");
-
-		ExecutionRecorder executionRecorder = new ExecutionRecorder();
-		executeDirectly(testEngine, discoveryRequest, executionRecorder);
-		return executionRecorder.getExecutionResults();
-	}
-
 	/**
 	 * Execute tests for the given {@link LauncherDiscoveryRequest} using the
 	 * supplied {@link TestEngine}.
@@ -322,17 +248,6 @@ public static EngineExecutionResults execute(TestEngine testEngine, LauncherDisc
 		return executionRecorder.getExecutionResults();
 	}
 
-	private static void executeDirectly(TestEngine testEngine, EngineDiscoveryRequest discoveryRequest,
-			EngineExecutionListener listener) {
-		UniqueId engineUniqueId = UniqueId.forEngine(testEngine.getId());
-		TestDescriptor engineTestDescriptor = testEngine.discover(discoveryRequest, engineUniqueId);
-		withRequestLevelStore(store -> {
-			ExecutionRequest request = ExecutionRequest.create(engineTestDescriptor, listener,
-				discoveryRequest.getConfigurationParameters(), discoveryRequest.getOutputDirectoryProvider(), store);
-			testEngine.execute(request);
-		});
-	}
-
 	private static void executeUsingLauncherOrchestration(TestEngine testEngine,
 			LauncherDiscoveryRequest discoveryRequest, EngineExecutionListener listener) {
 		LauncherDiscoveryResult discoveryResult = discoverUsingOrchestrator(testEngine, discoveryRequest);
@@ -348,7 +263,8 @@ private static void withRequestLevelStore(Consumer<NamespacedHierarchicalStore<N
 		}
 	}
 
-	private static NamespacedHierarchicalStore<Namespace> newStore(NamespacedHierarchicalStore<Namespace> parentStore) {
+	private static NamespacedHierarchicalStore<Namespace> newStore(
+			@Nullable NamespacedHierarchicalStore<Namespace> parentStore) {
 		return new NamespacedHierarchicalStore<>(parentStore, closeAutoCloseables());
 	}
 
@@ -365,7 +281,7 @@ private static TestEngine loadTestEngine(String engineId) {
 				.filter((TestEngine engine) -> engineId.equals(engine.getId()))//
 				.findFirst()//
 				.orElseThrow(() -> new PreconditionViolationException(
-					String.format("Failed to load TestEngine with ID [%s]", engineId)));
+					"Failed to load TestEngine with ID [%s]".formatted(engineId)));
 	}
 
 	private EngineTestKit() {
@@ -416,29 +332,6 @@ public Builder selectors(DiscoverySelector... selectors) {
 			return this;
 		}
 
-		/**
-		 * Add all of the supplied {@linkplain DiscoveryFilter discovery filters}.
-		 *
-		 * <p>Built-in discovery filters can be created via the static factory
-		 * methods in {@link org.junit.platform.engine.discovery.ClassNameFilter}
-		 * and {@link org.junit.platform.engine.discovery.PackageNameFilter}.
-		 *
-		 * @param filters the discovery filters to add; never {@code null}
-		 * @return this builder for method chaining
-		 * @see #filters(Filter...)
-		 * @see #selectors(DiscoverySelector...)
-		 * @see #configurationParameter(String, String)
-		 * @see #configurationParameters(Map)
-		 * @see #execute()
-		 * @deprecated Please use {@link #filters(Filter...)} instead.
-		 */
-		@Deprecated
-		@API(status = DEPRECATED, since = "1.7")
-		public Builder filters(DiscoveryFilter<?>... filters) {
-			this.requestBuilder.filters(filters);
-			return this;
-		}
-
 		/**
 		 * Add all of the supplied {@linkplain Filter filters}.
 		 *
@@ -531,7 +424,7 @@ public Builder enableImplicitConfigurationParameters(boolean enabled) {
 		 * @since 1.12
 		 * @see OutputDirectoryProvider
 		 */
-		@API(status = EXPERIMENTAL, since = "1.12")
+		@API(status = MAINTAINED, since = "1.13.3")
 		public Builder outputDirectoryProvider(OutputDirectoryProvider outputDirectoryProvider) {
 			this.requestBuilder.outputDirectoryProvider(outputDirectoryProvider);
 			return this;
@@ -550,7 +443,7 @@ public Builder outputDirectoryProvider(OutputDirectoryProvider outputDirectoryPr
 		 * @see #configurationParameter(String, String)
 		 * @see #configurationParameters(Map)
 		 */
-		@API(status = EXPERIMENTAL, since = "1.13")
+		@API(status = EXPERIMENTAL, since = "6.0")
 		public EngineDiscoveryResults discover() {
 			LauncherDiscoveryRequest request = this.requestBuilder.build();
 			return EngineTestKit.discover(this.testEngine, request);
diff --git a/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/Event.java b/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/Event.java
index 9d6187e5ccc1..0d12c06e0498 100644
--- a/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/Event.java
+++ b/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/Event.java
@@ -10,7 +10,6 @@
 
 package org.junit.platform.testkit.engine;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
 import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.junit.platform.commons.util.FunctionUtils.where;
 
@@ -19,6 +18,7 @@
 import java.util.function.Predicate;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.util.Preconditions;
 import org.junit.platform.commons.util.ToStringBuilder;
 import org.junit.platform.engine.TestDescriptor;
@@ -64,7 +64,7 @@ public static Event reportingEntryPublished(TestDescriptor testDescriptor, Repor
 	 * @since 1.12
 	 * @see EventType#FILE_ENTRY_PUBLISHED
 	 */
-	@API(status = EXPERIMENTAL, since = "1.12")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public static Event fileEntryPublished(TestDescriptor testDescriptor, FileEntry file) {
 		Preconditions.notNull(file, "FileEntry must not be null");
 		return new Event(EventType.FILE_ENTRY_PUBLISHED, testDescriptor, file);
@@ -93,7 +93,7 @@ public static Event dynamicTestRegistered(TestDescriptor testDescriptor) {
 	 * @return the newly created {@code Event}
 	 * @see EventType#SKIPPED
 	 */
-	public static Event executionSkipped(TestDescriptor testDescriptor, String reason) {
+	public static Event executionSkipped(TestDescriptor testDescriptor, @Nullable String reason) {
 		return new Event(EventType.SKIPPED, testDescriptor, reason);
 	}
 
@@ -170,7 +170,8 @@ public static Predicate<Event> byTestDescriptor(Predicate<? super TestDescriptor
 	private final Instant timestamp = Instant.now();
 	private final EventType type;
 	private final TestDescriptor testDescriptor;
-	private final Object payload;
+
+	private final @Nullable Object payload;
 
 	/**
 	 * Construct an {@code Event} with the supplied arguments.
@@ -180,7 +181,7 @@ public static Predicate<Event> byTestDescriptor(Predicate<? super TestDescriptor
 	 * never {@code null}
 	 * @param payload the generic payload associated with the event; may be {@code null}
 	 */
-	private Event(EventType type, TestDescriptor testDescriptor, Object payload) {
+	private Event(EventType type, TestDescriptor testDescriptor, @Nullable Object payload) {
 		this.type = Preconditions.notNull(type, "EventType must not be null");
 		this.testDescriptor = Preconditions.notNull(testDescriptor, "TestDescriptor must not be null");
 		this.payload = payload;
diff --git a/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/EventConditions.java b/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/EventConditions.java
index 4be237c109e0..e99f92ff8d56 100644
--- a/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/EventConditions.java
+++ b/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/EventConditions.java
@@ -11,7 +11,6 @@
 package org.junit.platform.testkit.engine;
 
 import static java.util.function.Predicate.isEqual;
-import static java.util.stream.Collectors.toList;
 import static org.apiguardian.api.API.Status.EXPERIMENTAL;
 import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.apiguardian.api.API.Status.STABLE;
@@ -62,7 +61,7 @@ private EventConditions() {
 
 	/**
 	 * Create a new {@link Condition} that matches if and only if an
-	 * {@link Event} matches all of the supplied conditions.
+	 * {@link Event} matches all the supplied conditions.
 	 */
 	@SafeVarargs
 	@SuppressWarnings("varargs")
@@ -257,7 +256,7 @@ public static Condition<Event> dynamicTestRegistered(Condition<Event> condition)
 	 *
 	 * @since 1.13
 	 */
-	@API(status = EXPERIMENTAL, since = "1.13")
+	@API(status = EXPERIMENTAL, since = "6.0")
 	public static Condition<Event> uniqueId(String uniqueId) {
 		return uniqueId(UniqueId.parse(uniqueId));
 	}
@@ -270,7 +269,7 @@ public static Condition<Event> uniqueId(String uniqueId) {
 	 *
 	 * @since 1.13
 	 */
-	@API(status = EXPERIMENTAL, since = "1.13")
+	@API(status = EXPERIMENTAL, since = "6.0")
 	public static Condition<Event> uniqueId(UniqueId uniqueId) {
 		return uniqueId(new Condition<>(isEqual(uniqueId), "equal to '%s'", uniqueId));
 	}
@@ -298,7 +297,7 @@ public static Condition<Event> uniqueIdSubstring(String uniqueIdSubstring) {
 	 *
 	 * @since 1.13
 	 */
-	@API(status = EXPERIMENTAL, since = "1.13")
+	@API(status = EXPERIMENTAL, since = "6.0")
 	public static Condition<Event> uniqueId(Condition<? super UniqueId> condition) {
 		return new Condition<>(byTestDescriptor(where(TestDescriptor::getUniqueId, condition::matches)),
 			"descriptor with uniqueId %s", condition.description().value());
@@ -326,7 +325,7 @@ public static Condition<Event> uniqueIdSubstrings(String... uniqueIdSubstrings)
 	 */
 	public static Condition<Event> uniqueIdSubstrings(List<String> uniqueIdSubstrings) {
 		// The following worked with AssertJ 3.13.2
-		// return allOf(uniqueIdSubstrings.stream().map(EventConditions::uniqueIdSubstring).collect(toList()));
+		// return allOf(uniqueIdSubstrings.stream().map(EventConditions::uniqueIdSubstring).toList());
 
 		// Workaround for a regression in AssertJ 3.14.0 that loses the individual descriptions
 		// when multiple conditions are supplied as an Iterable instead of as an array.
@@ -336,8 +335,8 @@ public static Condition<Event> uniqueIdSubstrings(List<String> uniqueIdSubstring
 		// does not track all descriptions.
 		List<Condition<Event>> conditions = uniqueIdSubstrings.stream()//
 				.map(EventConditions::uniqueIdSubstring)//
-				.collect(toList());
-		List<Description> descriptions = conditions.stream().map(Condition::description).collect(toList());
+				.toList();
+		List<Description> descriptions = conditions.stream().map(Condition::description).toList();
 		return allOf(conditions).describedAs(new JoinDescription("all of :[", "]", descriptions));
 	}
 
@@ -360,7 +359,7 @@ public static Condition<Event> displayName(String displayName) {
 	 *
 	 * @since 1.13
 	 */
-	@API(status = EXPERIMENTAL, since = "1.13")
+	@API(status = EXPERIMENTAL, since = "6.0")
 	public static Condition<Event> legacyReportingName(String legacyReportingName) {
 		return new Condition<>(
 			byTestDescriptor(where(TestDescriptor::getLegacyReportingName, isEqual(legacyReportingName))),
@@ -532,7 +531,7 @@ public static Condition<Event> reportEntry(Map<String, String> keyValuePairs) {
 	 *
 	 * @since 1.12
 	 */
-	@API(status = EXPERIMENTAL, since = "1.12")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public static Condition<Event> fileEntry(Predicate<FileEntry> predicate) {
 		return new Condition<>(byPayload(FileEntry.class, predicate), "event for file entry with custom predicate");
 	}
diff --git a/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/EventStatistics.java b/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/EventStatistics.java
index a0e38754ca61..19c34329a605 100644
--- a/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/EventStatistics.java
+++ b/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/EventStatistics.java
@@ -10,7 +10,6 @@
 
 package org.junit.platform.testkit.engine;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
 import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.junit.platform.testkit.engine.Assertions.assertEquals;
 
@@ -135,7 +134,7 @@ public EventStatistics reportingEntryPublished(long expected) {
 	 * @return this {@code EventStatistics} for method chaining
 	 * @since 1.12
 	 */
-	@API(status = EXPERIMENTAL, since = "1.12")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public EventStatistics fileEntryPublished(long expected) {
 		this.executables.add(
 			() -> assertEquals(expected, this.events.fileEntryPublished().count(), "file entry published"));
diff --git a/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/EventType.java b/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/EventType.java
index 9cef63ee24f9..25b23fef3f1b 100644
--- a/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/EventType.java
+++ b/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/EventType.java
@@ -10,7 +10,6 @@
 
 package org.junit.platform.testkit.engine;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
 import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import org.apiguardian.api.API;
@@ -70,7 +69,7 @@ public enum EventType {
 	 * @since 1.12
 	 * @see org.junit.platform.engine.EngineExecutionListener#fileEntryPublished(TestDescriptor, FileEntry)
 	 */
-	@API(status = EXPERIMENTAL, since = "1.12")
+	@API(status = MAINTAINED, since = "1.13.3")
 	FILE_ENTRY_PUBLISHED
 
 }
diff --git a/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/Events.java b/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/Events.java
index 6866116f3ff2..744ff5a3aed3 100644
--- a/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/Events.java
+++ b/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/Events.java
@@ -12,8 +12,6 @@
 
 import static java.util.Collections.sort;
 import static java.util.function.Predicate.isEqual;
-import static java.util.stream.Collectors.toList;
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
 import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.junit.platform.commons.util.FunctionUtils.where;
 import static org.junit.platform.testkit.engine.Event.byPayload;
@@ -24,7 +22,6 @@
 import java.io.Writer;
 import java.util.ArrayList;
 import java.util.Arrays;
-import java.util.Collections;
 import java.util.List;
 import java.util.Objects;
 import java.util.Optional;
@@ -39,6 +36,7 @@
 import org.assertj.core.api.ListAssert;
 import org.assertj.core.api.SoftAssertions;
 import org.assertj.core.data.Index;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.util.Preconditions;
 import org.junit.platform.engine.TestExecutionResult;
 import org.junit.platform.engine.TestExecutionResult.Status;
@@ -57,14 +55,14 @@ public final class Events {
 	private final String category;
 
 	Events(Stream<Event> events, String category) {
-		this(Preconditions.notNull(events, "Event stream must not be null").collect(toList()), category);
+		this(Preconditions.notNull(events, "Event stream must not be null").toList(), category);
 	}
 
 	Events(List<Event> events, String category) {
 		Preconditions.notNull(events, "Event list must not be null");
 		Preconditions.containsNoNullElements(events, "Event list must not contain null elements");
 
-		this.events = Collections.unmodifiableList(events);
+		this.events = List.copyOf(events);
 		this.category = category;
 	}
 
@@ -215,7 +213,7 @@ public Events reportingEntryPublished() {
 	 * @return the filtered {@code Events}; never {@code null}
 	 * @since 1.12
 	 */
-	@API(status = EXPERIMENTAL, since = "1.12")
+	@API(status = MAINTAINED, since = "1.13.3")
 	public Events fileEntryPublished() {
 		return new Events(eventsByType(EventType.FILE_ENTRY_PUBLISHED), this.category + " File Entry Published");
 	}
@@ -446,7 +444,7 @@ private static void assertEventsMatchLooselyInOrder(List<Event> events, Conditio
 				.map(condition -> findEvent(events, softly, condition))
 				.filter(Objects::nonNull)
 				.map(events::indexOf)
-				.collect(toList());
+				.toList();
 		// @formatter:on
 
 		if (isNotInIncreasingOrder(indices)) {
@@ -469,14 +467,15 @@ private static void checkCondition(List<Event> events, SoftAssertions softly, Co
 		}
 	}
 
-	private static Event findEvent(List<Event> events, SoftAssertions softly, Condition<? super Event> condition) {
+	private static @Nullable Event findEvent(List<Event> events, SoftAssertions softly,
+			Condition<? super Event> condition) {
 		// @formatter:off
 		Optional<Event> matchedEvent = events.stream()
 				.filter(condition::matches)
 				.findFirst();
 		// @formatter:on
 
-		if (!matchedEvent.isPresent()) {
+		if (matchedEvent.isEmpty()) {
 			softly.fail("Condition did not match any event: " + condition);
 		}
 
diff --git a/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/ExecutionRecorder.java b/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/ExecutionRecorder.java
index d27b058160da..fd904b7e2ca1 100644
--- a/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/ExecutionRecorder.java
+++ b/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/ExecutionRecorder.java
@@ -10,7 +10,6 @@
 
 package org.junit.platform.testkit.engine;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
 import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import java.util.List;
@@ -89,7 +88,7 @@ public void reportingEntryPublished(TestDescriptor testDescriptor, ReportEntry e
 	 *
 	 * @since 1.12
 	 */
-	@API(status = EXPERIMENTAL, since = "1.12")
+	@API(status = MAINTAINED, since = "1.13.3")
 	@Override
 	public void fileEntryPublished(TestDescriptor testDescriptor, FileEntry file) {
 		this.events.add(Event.fileEntryPublished(testDescriptor, file));
diff --git a/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/Executions.java b/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/Executions.java
index fae09e861905..edfd4311fd67 100644
--- a/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/Executions.java
+++ b/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/Executions.java
@@ -10,7 +10,6 @@
 
 package org.junit.platform.testkit.engine;
 
-import static java.util.stream.Collectors.toList;
 import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import java.io.OutputStream;
@@ -18,7 +17,6 @@
 import java.io.Writer;
 import java.time.Instant;
 import java.util.ArrayList;
-import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -48,7 +46,7 @@ public final class Executions {
 	private Executions(Stream<Execution> executions, String category) {
 		Preconditions.notNull(executions, "Execution stream must not be null");
 
-		this.executions = Collections.unmodifiableList(executions.collect(toList()));
+		this.executions = executions.toList();
 		this.category = category;
 	}
 
@@ -56,7 +54,7 @@ private Executions(Stream<Execution> executions, String category) {
 		Preconditions.notNull(events, "Event list must not be null");
 		Preconditions.containsNoNullElements(events, "Event list must not contain null elements");
 
-		this.executions = Collections.unmodifiableList(createExecutions(events));
+		this.executions = List.copyOf(createExecutions(events));
 		this.category = category;
 	}
 
@@ -256,11 +254,8 @@ private static List<Execution> createExecutions(List<Event> events) {
 
 		for (Event event : events) {
 			switch (event.getType()) {
-				case STARTED: {
-					executionStarts.put(event.getTestDescriptor(), event.getTimestamp());
-					break;
-				}
-				case SKIPPED: {
+				case STARTED -> executionStarts.put(event.getTestDescriptor(), event.getTimestamp());
+				case SKIPPED -> {
 					// Based on the Javadoc for EngineExecutionListener.executionSkipped(...),
 					// a skipped descriptor must never be reported as started or finished,
 					// but just in case a TestEngine does not adhere to that contract, we
@@ -273,9 +268,8 @@ private static List<Execution> createExecutions(List<Event> events) {
 					Execution skippedEvent = Execution.skipped(event.getTestDescriptor(), timestamp, timestamp,
 						event.getRequiredPayload(String.class));
 					executions.add(skippedEvent);
-					break;
 				}
-				case FINISHED: {
+				case FINISHED -> {
 					Instant startInstant = executionStarts.remove(event.getTestDescriptor());
 					Instant endInstant = event.getTimestamp();
 
@@ -287,11 +281,9 @@ private static List<Execution> createExecutions(List<Event> events) {
 							endInstant, event.getRequiredPayload(TestExecutionResult.class));
 						executions.add(finishedEvent);
 					}
-					break;
 				}
-				default: {
+				default -> {
 					// Ignore other events
-					break;
 				}
 			}
 		}
diff --git a/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/TerminationInfo.java b/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/TerminationInfo.java
index 092c10fe1440..8c7a03a54472 100644
--- a/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/TerminationInfo.java
+++ b/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/TerminationInfo.java
@@ -13,6 +13,7 @@
 import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.util.Preconditions;
 import org.junit.platform.commons.util.ToStringBuilder;
 import org.junit.platform.engine.TestExecutionResult;
@@ -38,7 +39,7 @@ public class TerminationInfo {
 	 * @return the created {@code TerminationInfo}; never {@code null}
 	 * @see #executed(TestExecutionResult)
 	 */
-	public static TerminationInfo skipped(String reason) {
+	public static TerminationInfo skipped(@Nullable String reason) {
 		return new TerminationInfo(true, reason, null);
 	}
 
@@ -58,10 +59,13 @@ public static TerminationInfo executed(TestExecutionResult testExecutionResult)
 	// -------------------------------------------------------------------------
 
 	private final boolean skipped;
-	private final String skipReason;
-	private final TestExecutionResult testExecutionResult;
 
-	private TerminationInfo(boolean skipped, String skipReason, TestExecutionResult testExecutionResult) {
+	private final @Nullable String skipReason;
+
+	private final @Nullable TestExecutionResult testExecutionResult;
+
+	private TerminationInfo(boolean skipped, @Nullable String skipReason,
+			@Nullable TestExecutionResult testExecutionResult) {
 		boolean executed = (testExecutionResult != null);
 		Preconditions.condition((skipped ^ executed),
 			"TerminationInfo must represent either a skipped execution or a TestExecutionResult but not both");
@@ -109,7 +113,7 @@ public boolean executed() {
 	 * @throws UnsupportedOperationException if this {@code TerminationInfo}
 	 * does not represent a skipped execution
 	 */
-	public String getSkipReason() throws UnsupportedOperationException {
+	public @Nullable String getSkipReason() throws UnsupportedOperationException {
 		if (skipped()) {
 			return this.skipReason;
 		}
@@ -125,7 +129,7 @@ public String getSkipReason() throws UnsupportedOperationException {
 	 * does not represent a completed execution
 	 */
 	public TestExecutionResult getExecutionResult() throws UnsupportedOperationException {
-		if (executed()) {
+		if (this.testExecutionResult != null) {
 			return this.testExecutionResult;
 		}
 		// else
diff --git a/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/TestExecutionResultConditions.java b/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/TestExecutionResultConditions.java
index f9b1b1f9c53c..b75b58245202 100644
--- a/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/TestExecutionResultConditions.java
+++ b/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/TestExecutionResultConditions.java
@@ -11,8 +11,6 @@
 package org.junit.platform.testkit.engine;
 
 import static java.util.function.Predicate.isEqual;
-import static java.util.stream.Collectors.toList;
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
 import static org.apiguardian.api.API.Status.MAINTAINED;
 import static org.junit.platform.commons.util.FunctionUtils.where;
 
@@ -24,6 +22,8 @@
 import org.apiguardian.api.API;
 import org.assertj.core.api.Assertions;
 import org.assertj.core.api.Condition;
+import org.jspecify.annotations.Nullable;
+import org.junit.platform.commons.util.FunctionUtils;
 import org.junit.platform.commons.util.Preconditions;
 import org.junit.platform.engine.TestExecutionResult;
 import org.junit.platform.engine.TestExecutionResult.Status;
@@ -63,7 +63,7 @@ public static Condition<TestExecutionResult> status(Status expectedStatus) {
 	public static Condition<TestExecutionResult> throwable(Condition<Throwable>... conditions) {
 		List<Condition<TestExecutionResult>> list = Arrays.stream(conditions)//
 				.map(TestExecutionResultConditions::throwable)//
-				.collect(toList());
+				.toList();
 
 		return Assertions.allOf(list);
 	}
@@ -81,7 +81,7 @@ public static Condition<TestExecutionResult> throwable(Condition<Throwable>... c
 	public static Condition<Throwable> cause(Condition<Throwable>... conditions) {
 		List<Condition<Throwable>> list = Arrays.stream(conditions)//
 				.map(TestExecutionResultConditions::cause)//
-				.collect(toList());
+				.toList();
 
 		return Assertions.allOf(list);
 	}
@@ -95,13 +95,13 @@ public static Condition<Throwable> cause(Condition<Throwable>... conditions) {
 	 * @see #cause(Condition...)
 	 * @see #suppressed(int, Condition...)
 	 */
-	@API(status = EXPERIMENTAL, since = "1.11")
+	@API(status = MAINTAINED, since = "1.13.3")
 	@SafeVarargs
 	@SuppressWarnings("varargs")
 	public static Condition<Throwable> rootCause(Condition<Throwable>... conditions) {
 		List<Condition<Throwable>> list = Arrays.stream(conditions)//
 				.map(TestExecutionResultConditions::rootCause)//
-				.collect(toList());
+				.toList();
 
 		return Assertions.allOf(list);
 	}
@@ -119,7 +119,7 @@ public static Condition<Throwable> rootCause(Condition<Throwable>... conditions)
 	public static Condition<Throwable> suppressed(int index, Condition<Throwable>... conditions) {
 		List<Condition<Throwable>> list = Arrays.stream(conditions)//
 				.map(condition -> suppressed(index, condition))//
-				.collect(toList());
+				.toList();
 
 		return Assertions.allOf(list);
 	}
@@ -139,8 +139,9 @@ public static Condition<Throwable> instanceOf(Class<? extends Throwable> expecte
 	 * to the supplied {@link String}.
 	 */
 	public static Condition<Throwable> message(String expectedMessage) {
-		return new Condition<>(where(Throwable::getMessage, isEqual(expectedMessage)), "message is '%s'",
-			expectedMessage);
+		return new Condition<>(
+			FunctionUtils.<Throwable, @Nullable String> where(Throwable::getMessage, isEqual(expectedMessage)),
+			"message is '%s'", expectedMessage);
 	}
 
 	/**
@@ -149,7 +150,9 @@ public static Condition<Throwable> message(String expectedMessage) {
 	 * the supplied {@link Predicate}.
 	 */
 	public static Condition<Throwable> message(Predicate<String> expectedMessagePredicate) {
-		return new Condition<>(where(Throwable::getMessage, expectedMessagePredicate), "message matches predicate");
+		return new Condition<>(
+			FunctionUtils.<Throwable, @Nullable String> where(Throwable::getMessage, expectedMessagePredicate),
+			"message matches predicate");
 	}
 
 	private static Condition<TestExecutionResult> throwable(Condition<? super Throwable> condition) {
diff --git a/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/package-info.java b/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/package-info.java
index c50fec3e29c1..808c8a16ef53 100644
--- a/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/package-info.java
+++ b/junit-platform-testkit/src/main/java/org/junit/platform/testkit/engine/package-info.java
@@ -3,4 +3,7 @@
  * running on the JUnit Platform.
  */
 
+@NullMarked
 package org.junit.platform.testkit.engine;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-platform-testkit/src/main/java/org/junit/platform/testkit/package-info.java b/junit-platform-testkit/src/main/java/org/junit/platform/testkit/package-info.java
index 7a10b625264b..3a5c5b1062d3 100644
--- a/junit-platform-testkit/src/main/java/org/junit/platform/testkit/package-info.java
+++ b/junit-platform-testkit/src/main/java/org/junit/platform/testkit/package-info.java
@@ -2,4 +2,7 @@
  * Test Kit for the JUnit Platform.
  */
 
+@NullMarked
 package org.junit.platform.testkit;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-vintage-engine/junit-vintage-engine.gradle.kts b/junit-vintage-engine/junit-vintage-engine.gradle.kts
index 54d444b43c81..73fb5b3ffa45 100644
--- a/junit-vintage-engine/junit-vintage-engine.gradle.kts
+++ b/junit-vintage-engine/junit-vintage-engine.gradle.kts
@@ -1,5 +1,6 @@
 plugins {
 	id("junitbuild.java-library-conventions")
+	id("junitbuild.java-nullability-conventions")
 	id("junitbuild.junit4-compatibility")
 	id("junitbuild.testing-conventions")
 	`java-test-fixtures`
@@ -14,14 +15,16 @@ dependencies {
 	api(libs.junit4)
 
 	compileOnlyApi(libs.apiguardian)
+	compileOnly(libs.jspecify)
 
 	testFixturesApi(platform(libs.groovy2.bom))
 	testFixturesApi(libs.spock1)
-	testFixturesImplementation(projects.junitPlatformRunner)
+	testFixturesImplementation(projects.junitPlatformSuiteApi)
 
 	testImplementation(projects.junitPlatformLauncher)
 	testImplementation(projects.junitPlatformSuiteEngine)
 	testImplementation(projects.junitPlatformTestkit)
+	testImplementation(testFixtures(projects.junitPlatformCommons))
 	testImplementation(testFixtures(projects.junitJupiterApi))
 	testImplementation(testFixtures(projects.junitPlatformLauncher))
 	testImplementation(testFixtures(projects.junitPlatformReporting))
@@ -30,6 +33,9 @@ dependencies {
 }
 
 tasks {
+	compileJava {
+		options.compilerArgs.add("-Xlint:-requires-automatic") // JUnit 4
+	}
 	compileTestFixturesGroovy {
 		javaLauncher = project.javaToolchains.launcherFor {
 			// Groovy 2.x (used for Spock tests) does not support current JDKs
@@ -39,12 +45,14 @@ tasks {
 	jar {
 		bundle {
 			val junit4Min = libs.versions.junit4Min.get()
-			val platformVersion: String by rootProject.extra
 			val version = project.version
+			val importAPIGuardian: String by extra
+			val importJSpecify: String by extra
 			bnd("""
 				# Import JUnit4 packages with a version
 				Import-Package: \
-					${extra["importAPIGuardian"]},\
+					${importAPIGuardian},\
+					${importJSpecify},\
 					junit.runner;version="[${junit4Min},5)",\
 					org.junit;version="[${junit4Min},5)",\
 					org.junit.experimental.categories;version="[${junit4Min},5)",\
@@ -60,7 +68,7 @@ tasks {
 						version:Version="${'$'}{version_cleanup;$version}"
 				Require-Capability:\
 					org.junit.platform.launcher;\
-						filter:='(&(org.junit.platform.launcher=junit-platform-launcher)(version>=${'$'}{version_cleanup;$platformVersion})(!(version>=${'$'}{versionmask;+;${'$'}{version_cleanup;$platformVersion}})))';\
+						filter:='(&(org.junit.platform.launcher=junit-platform-launcher)(version>=${'$'}{version_cleanup;$version})(!(version>=${'$'}{versionmask;+;${'$'}{version_cleanup;$version}})))';\
 						effective:=active
 			""")
 		}
@@ -96,4 +104,9 @@ eclipse {
 		// Avoid exposing test resources to dependent projects
 		containsTestFixtures = false
 	}
+	project {
+		// Remove Groovy Nature, since we don't require a Groovy plugin for Eclipse
+		// in order for developers to work with the code base.
+		natures.removeAll { it == "org.eclipse.jdt.groovy.core.groovyNature" }
+	}
 }
diff --git a/junit-vintage-engine/src/module/org.junit.vintage.engine/module-info.java b/junit-vintage-engine/src/main/java/module-info.java
similarity index 92%
rename from junit-vintage-engine/src/module/org.junit.vintage.engine/module-info.java
rename to junit-vintage-engine/src/main/java/module-info.java
index 6880a39df91d..c6e3e02fe161 100644
--- a/junit-vintage-engine/src/module/org.junit.vintage.engine/module-info.java
+++ b/junit-vintage-engine/src/main/java/module-info.java
@@ -16,9 +16,13 @@
  * @provides org.junit.platform.engine.TestEngine The {@code VintageTestEngine}
  * runs JUnit 3 and 4 based tests on the platform.
  */
+@SuppressWarnings("deprecation")
 module org.junit.vintage.engine {
-	requires junit; // 4
+
 	requires static org.apiguardian.api;
+	requires static org.jspecify;
+
+	requires junit; // 4
 	requires org.junit.platform.engine;
 
 	provides org.junit.platform.engine.TestEngine
diff --git a/junit-vintage-engine/src/main/java/org/junit/vintage/engine/Constants.java b/junit-vintage-engine/src/main/java/org/junit/vintage/engine/Constants.java
index 3d97979d2276..97838f336ab4 100644
--- a/junit-vintage-engine/src/main/java/org/junit/vintage/engine/Constants.java
+++ b/junit-vintage-engine/src/main/java/org/junit/vintage/engine/Constants.java
@@ -10,17 +10,19 @@
 
 package org.junit.vintage.engine;
 
-import static org.apiguardian.api.API.Status.EXPERIMENTAL;
-import static org.apiguardian.api.API.Status.STABLE;
+import static org.apiguardian.api.API.Status.DEPRECATED;
+import static org.apiguardian.api.API.Status.MAINTAINED;
 
 import org.apiguardian.api.API;
 
 /**
  * Collection of constants related to the {@link VintageTestEngine}.
  *
- * @since 5.12
+ * @deprecated Should only be used temporarily while migrating tests to JUnit
+ * Jupiter or another testing framework with native JUnit Platform support
  */
-@API(status = STABLE, since = "5.12")
+@Deprecated(since = "6.0")
+@API(status = DEPRECATED, since = "6.0")
 public final class Constants {
 
 	/**
@@ -31,7 +33,7 @@ public final class Constants {
 	 *
 	 * @since 5.12
 	 */
-	@API(status = EXPERIMENTAL, since = "5.12")
+	@API(status = MAINTAINED, since = "5.13.3")
 	public static final String PARALLEL_EXECUTION_ENABLED = "junit.vintage.execution.parallel.enabled";
 
 	/**
@@ -43,7 +45,7 @@ public final class Constants {
 	 *
 	 * @since 5.12
 	 */
-	@API(status = EXPERIMENTAL, since = "5.12")
+	@API(status = MAINTAINED, since = "5.13.3")
 	public static final String PARALLEL_POOL_SIZE = "junit.vintage.execution.parallel.pool-size";
 
 	/**
@@ -55,7 +57,7 @@ public final class Constants {
 	 *
 	 * @since 5.12
 	 */
-	@API(status = EXPERIMENTAL, since = "5.12")
+	@API(status = MAINTAINED, since = "5.13.3")
 	public static final String PARALLEL_CLASS_EXECUTION = "junit.vintage.execution.parallel.classes";
 
 	/**
@@ -67,7 +69,7 @@ public final class Constants {
 	 *
 	 * @since 5.12
 	 */
-	@API(status = EXPERIMENTAL, since = "5.12")
+	@API(status = MAINTAINED, since = "5.13.3")
 	public static final String PARALLEL_METHOD_EXECUTION = "junit.vintage.execution.parallel.methods";
 
 	private Constants() {
diff --git a/junit-vintage-engine/src/main/java/org/junit/vintage/engine/VintageTestEngine.java b/junit-vintage-engine/src/main/java/org/junit/vintage/engine/VintageTestEngine.java
index 8d9279ae108e..fdb8e4c8c2de 100644
--- a/junit-vintage-engine/src/main/java/org/junit/vintage/engine/VintageTestEngine.java
+++ b/junit-vintage-engine/src/main/java/org/junit/vintage/engine/VintageTestEngine.java
@@ -10,7 +10,7 @@
 
 package org.junit.vintage.engine;
 
-import static org.apiguardian.api.API.Status.INTERNAL;
+import static org.apiguardian.api.API.Status.DEPRECATED;
 import static org.junit.platform.engine.TestExecutionResult.successful;
 import static org.junit.vintage.engine.descriptor.VintageTestDescriptor.ENGINE_ID;
 
@@ -31,8 +31,11 @@
  * The JUnit Vintage {@link TestEngine}.
  *
  * @since 4.12
+ * @deprecated Should only be used temporarily while migrating tests to JUnit
+ * Jupiter or another testing framework with native JUnit Platform support
  */
-@API(status = INTERNAL, since = "4.12")
+@Deprecated(since = "6.0")
+@API(status = DEPRECATED, since = "6.0")
 public final class VintageTestEngine implements TestEngine {
 
 	@Override
diff --git a/junit-vintage-engine/src/main/java/org/junit/vintage/engine/descriptor/DescriptionUtils.java b/junit-vintage-engine/src/main/java/org/junit/vintage/engine/descriptor/DescriptionUtils.java
index a55ffd3c572f..915e3c18d713 100644
--- a/junit-vintage-engine/src/main/java/org/junit/vintage/engine/descriptor/DescriptionUtils.java
+++ b/junit-vintage-engine/src/main/java/org/junit/vintage/engine/descriptor/DescriptionUtils.java
@@ -11,6 +11,7 @@
 package org.junit.vintage.engine.descriptor;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.runner.Description;
 
 @API(status = API.Status.INTERNAL, since = "5.8")
@@ -19,7 +20,7 @@ public class DescriptionUtils {
 	private DescriptionUtils() {
 	}
 
-	public static String getMethodName(Description description) {
+	public static @Nullable String getMethodName(Description description) {
 		String displayName = description.getDisplayName();
 		int i = displayName.indexOf('(');
 		if (i >= 0) {
diff --git a/junit-vintage-engine/src/main/java/org/junit/vintage/engine/descriptor/RunnerTestDescriptor.java b/junit-vintage-engine/src/main/java/org/junit/vintage/engine/descriptor/RunnerTestDescriptor.java
index 05eb8ebfb046..2fa6af237698 100644
--- a/junit-vintage-engine/src/main/java/org/junit/vintage/engine/descriptor/RunnerTestDescriptor.java
+++ b/junit-vintage-engine/src/main/java/org/junit/vintage/engine/descriptor/RunnerTestDescriptor.java
@@ -26,6 +26,7 @@
 import java.util.function.Consumer;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.JUnitException;
 import org.junit.platform.commons.logging.Logger;
 import org.junit.platform.commons.logging.LoggerFactory;
@@ -54,7 +55,8 @@ public class RunnerTestDescriptor extends VintageTestDescriptor {
 	private Runner runner;
 	private final boolean ignored;
 	private boolean wasFiltered;
-	private List<Filter> filters = new ArrayList<>();
+
+	private @Nullable List<Filter> filters = new ArrayList<>();
 
 	public RunnerTestDescriptor(UniqueId uniqueId, Class<?> testClass, Runner runner, boolean ignored) {
 		super(uniqueId, runner.getDescription(), testClass.getSimpleName(), ClassSource.from(testClass));
@@ -85,10 +87,10 @@ protected boolean tryToExcludeFromRunner(Description description) {
 	}
 
 	private boolean tryToFilterRunner(Description description) {
-		if (runner instanceof Filterable) {
+		if (runner instanceof Filterable filterable) {
 			ExcludeDescriptionFilter filter = new ExcludeDescriptionFilter(description);
 			try {
-				((Filterable) runner).filter(filter);
+				filterable.filter(filter);
 			}
 			catch (NoTestsRemainException ignore) {
 				// it's safe to ignore this exception because childless TestDescriptors will get pruned
@@ -163,7 +165,7 @@ public void applyFilters(Consumer<RunnerTestDescriptor> childrenCreator) {
 	}
 
 	private Runner getRunnerToReport() {
-		return (runner instanceof RunnerDecorator) ? ((RunnerDecorator) runner).getDecoratedRunner() : runner;
+		return (runner instanceof RunnerDecorator decorator) ? decorator.getDecoratedRunner() : runner;
 	}
 
 	public boolean isIgnored() {
@@ -172,8 +174,8 @@ public boolean isIgnored() {
 
 	public void setExecutorService(ExecutorService executorService) {
 		Runner runner = getRunnerToReport();
-		if (runner instanceof ParentRunner) {
-			((ParentRunner<?>) runner).setScheduler(new RunnerScheduler() {
+		if (runner instanceof ParentRunner<?> parentRunner) {
+			parentRunner.setScheduler(new RunnerScheduler() {
 
 				private final List<Future<?>> futures = new CopyOnWriteArrayList<>();
 
diff --git a/junit-vintage-engine/src/main/java/org/junit/vintage/engine/descriptor/TestSourceProvider.java b/junit-vintage-engine/src/main/java/org/junit/vintage/engine/descriptor/TestSourceProvider.java
index 2037f7aeb8d8..65a748aa89ec 100644
--- a/junit-vintage-engine/src/main/java/org/junit/vintage/engine/descriptor/TestSourceProvider.java
+++ b/junit-vintage-engine/src/main/java/org/junit/vintage/engine/descriptor/TestSourceProvider.java
@@ -12,7 +12,6 @@
 
 import static java.util.Collections.synchronizedMap;
 import static java.util.function.Predicate.isEqual;
-import static java.util.stream.Collectors.toList;
 import static org.apiguardian.api.API.Status.INTERNAL;
 import static org.junit.platform.commons.support.HierarchyTraversalMode.TOP_DOWN;
 import static org.junit.platform.commons.support.ReflectionSupport.findMethods;
@@ -24,6 +23,7 @@
 import java.util.concurrent.ConcurrentHashMap;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.support.ModifierSupport;
 import org.junit.platform.commons.util.LruCache;
 import org.junit.platform.engine.TestSource;
@@ -44,7 +44,7 @@ public class TestSourceProvider {
 	private final Map<Description, TestSource> testSourceCache = new ConcurrentHashMap<>();
 	private final Map<Class<?>, List<Method>> methodsCache = synchronizedMap(new LruCache<>(31));
 
-	public TestSource findTestSource(Description description) {
+	public @Nullable TestSource findTestSource(Description description) {
 		TestSource testSource = testSourceCache.computeIfAbsent(description, this::computeTestSource);
 		return testSource == NULL_SOURCE ? null : testSource;
 	}
@@ -72,18 +72,18 @@ private String sanitizeMethodName(String methodName) {
 		return methodName;
 	}
 
-	private Method findMethod(Class<?> testClass, String methodName) {
+	private @Nullable Method findMethod(Class<?> testClass, String methodName) {
 		List<Method> methods = methodsCache.computeIfAbsent(testClass,
 			clazz -> findMethods(clazz, m -> true, TOP_DOWN)).stream() //
 				.filter(where(Method::getName, isEqual(methodName))) //
-				.collect(toList());
+				.toList();
 		if (methods.isEmpty()) {
 			return null;
 		}
 		if (methods.size() == 1) {
 			return methods.get(0);
 		}
-		methods = methods.stream().filter(ModifierSupport::isPublic).collect(toList());
+		methods = methods.stream().filter(ModifierSupport::isPublic).toList();
 		if (methods.size() == 1) {
 			return methods.get(0);
 		}
diff --git a/junit-vintage-engine/src/main/java/org/junit/vintage/engine/descriptor/VintageTestDescriptor.java b/junit-vintage-engine/src/main/java/org/junit/vintage/engine/descriptor/VintageTestDescriptor.java
index 47319da6e3b6..d9ad9ea0ac73 100644
--- a/junit-vintage-engine/src/main/java/org/junit/vintage/engine/descriptor/VintageTestDescriptor.java
+++ b/junit-vintage-engine/src/main/java/org/junit/vintage/engine/descriptor/VintageTestDescriptor.java
@@ -23,6 +23,7 @@
 import java.util.Set;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.experimental.categories.Category;
 import org.junit.platform.commons.util.ReflectionUtils;
 import org.junit.platform.engine.TestDescriptor;
@@ -45,15 +46,16 @@ public class VintageTestDescriptor extends AbstractTestDescriptor {
 
 	protected Description description;
 
-	public VintageTestDescriptor(UniqueId uniqueId, Description description, TestSource source) {
+	public VintageTestDescriptor(UniqueId uniqueId, Description description, @Nullable TestSource source) {
 		this(uniqueId, description, generateDisplayName(description), source);
 	}
 
-	VintageTestDescriptor(UniqueId uniqueId, Description description, String displayName, TestSource source) {
+	VintageTestDescriptor(UniqueId uniqueId, Description description, String displayName, @Nullable TestSource source) {
 		super(uniqueId, displayName, source);
 		this.description = description;
 	}
 
+	@SuppressWarnings("NullAway")
 	private static String generateDisplayName(Description description) {
 		String methodName = DescriptionUtils.getMethodName(description);
 		return isNotBlank(methodName) ? methodName : description.getDisplayName();
diff --git a/junit-vintage-engine/src/main/java/org/junit/vintage/engine/descriptor/package-info.java b/junit-vintage-engine/src/main/java/org/junit/vintage/engine/descriptor/package-info.java
index bef751cbdc9f..7743a7448580 100644
--- a/junit-vintage-engine/src/main/java/org/junit/vintage/engine/descriptor/package-info.java
+++ b/junit-vintage-engine/src/main/java/org/junit/vintage/engine/descriptor/package-info.java
@@ -2,4 +2,7 @@
  * Test descriptors used within the JUnit Vintage test engine.
  */
 
+@NullMarked
 package org.junit.vintage.engine.descriptor;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-vintage-engine/src/main/java/org/junit/vintage/engine/discovery/ClassSelectorResolver.java b/junit-vintage-engine/src/main/java/org/junit/vintage/engine/discovery/ClassSelectorResolver.java
index e8a005591a40..5a2741d42ecc 100644
--- a/junit-vintage-engine/src/main/java/org/junit/vintage/engine/discovery/ClassSelectorResolver.java
+++ b/junit-vintage-engine/src/main/java/org/junit/vintage/engine/discovery/ClassSelectorResolver.java
@@ -56,7 +56,7 @@ public Resolution resolve(UniqueIdSelector selector, Context context) {
 			String testClassName = lastSegment.getValue();
 			if (classFilter.match(testClassName)) {
 				Class<?> testClass = ReflectionSupport.tryToLoadClass(testClassName)//
-						.getOrThrow(cause -> new JUnitException("Unknown class: " + testClassName, cause));
+						.getNonNullOrThrow(cause -> new JUnitException("Unknown class: " + testClassName, cause));
 				return resolveTestClassThatPassedNameFilter(testClass, context);
 			}
 		}
diff --git a/junit-vintage-engine/src/main/java/org/junit/vintage/engine/discovery/DefensiveAllDefaultPossibilitiesBuilder.java b/junit-vintage-engine/src/main/java/org/junit/vintage/engine/discovery/DefensiveAllDefaultPossibilitiesBuilder.java
index db80b987d897..c858e3c06b5e 100644
--- a/junit-vintage-engine/src/main/java/org/junit/vintage/engine/discovery/DefensiveAllDefaultPossibilitiesBuilder.java
+++ b/junit-vintage-engine/src/main/java/org/junit/vintage/engine/discovery/DefensiveAllDefaultPossibilitiesBuilder.java
@@ -13,6 +13,7 @@
 import java.lang.reflect.Method;
 import java.util.function.Predicate;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.Ignore;
 import org.junit.internal.builders.AllDefaultPossibilitiesBuilder;
 import org.junit.internal.builders.AnnotatedBuilder;
@@ -109,7 +110,7 @@ private static class DefensiveAnnotatedBuilder extends AnnotatedBuilder {
 		}
 
 		@Override
-		public Runner buildRunner(Class<? extends Runner> runnerClass, Class<?> testClass) throws Exception {
+		public @Nullable Runner buildRunner(Class<? extends Runner> runnerClass, Class<?> testClass) throws Exception {
 			// Referenced by name because it might not be available at runtime.
 			if ("org.junit.platform.runner.JUnitPlatform".equals(runnerClass.getName())) {
 				logger.warn(() -> "Ignoring test class using JUnitPlatform runner: " + testClass.getName());
@@ -128,7 +129,7 @@ private static class DefensiveJUnit4Builder extends JUnit4Builder {
 		private static final Predicate<Method> isPotentialJUnit4TestMethod = new IsPotentialJUnit4TestMethod();
 
 		@Override
-		public Runner runnerForClass(Class<?> testClass) throws Throwable {
+		public @Nullable Runner runnerForClass(Class<?> testClass) throws Throwable {
 			if (containsTestMethods(testClass)) {
 				return super.runnerForClass(testClass);
 			}
@@ -147,7 +148,7 @@ private boolean containsTestMethods(Class<?> testClass) {
 	 */
 	private static class NullIgnoredBuilder extends IgnoredBuilder {
 		@Override
-		public Runner runnerForClass(Class<?> testClass) {
+		public @Nullable Runner runnerForClass(Class<?> testClass) {
 			// don't ignore entire test classes just yet
 			return null;
 		}
diff --git a/junit-vintage-engine/src/main/java/org/junit/vintage/engine/discovery/MethodSelectorResolver.java b/junit-vintage-engine/src/main/java/org/junit/vintage/engine/discovery/MethodSelectorResolver.java
index 6511fe8c5af8..1e14ea908c7c 100644
--- a/junit-vintage-engine/src/main/java/org/junit/vintage/engine/discovery/MethodSelectorResolver.java
+++ b/junit-vintage-engine/src/main/java/org/junit/vintage/engine/discovery/MethodSelectorResolver.java
@@ -59,8 +59,7 @@ private Resolution resolveParentAndAddFilter(Context context, DiscoverySelector
 
 	private Optional<RunnerTestDescriptor> addFilter(TestDescriptor parent,
 			Function<RunnerTestDescriptor, Filter> filterCreator) {
-		if (parent instanceof RunnerTestDescriptor) {
-			RunnerTestDescriptor runnerTestDescriptor = (RunnerTestDescriptor) parent;
+		if (parent instanceof RunnerTestDescriptor runnerTestDescriptor) {
 			runnerTestDescriptor.getFilters().ifPresent(
 				filters -> filters.add(filterCreator.apply(runnerTestDescriptor)));
 			return Optional.of(runnerTestDescriptor);
@@ -108,12 +107,12 @@ public boolean shouldRun(Description description) {
 
 			private boolean isParameterizedMethod(Description description) {
 				String methodName = DescriptionUtils.getMethodName(description);
-				return methodName.startsWith(desiredMethodName + "[");
+				return methodName != null && methodName.startsWith(desiredMethodName + "[");
 			}
 
 			@Override
 			public String describe() {
-				return String.format("Method %s", desiredDescription.getDisplayName());
+				return "Method %s".formatted(desiredDescription.getDisplayName());
 			}
 		};
 	}
diff --git a/junit-vintage-engine/src/main/java/org/junit/vintage/engine/discovery/UniqueIdFilter.java b/junit-vintage-engine/src/main/java/org/junit/vintage/engine/discovery/UniqueIdFilter.java
index a6d15af76b80..14ec702d97fd 100644
--- a/junit-vintage-engine/src/main/java/org/junit/vintage/engine/discovery/UniqueIdFilter.java
+++ b/junit-vintage-engine/src/main/java/org/junit/vintage/engine/discovery/UniqueIdFilter.java
@@ -33,7 +33,10 @@ class UniqueIdFilter extends Filter {
 	private final RunnerTestDescriptor runnerTestDescriptor;
 	private final UniqueId uniqueId;
 
+	@SuppressWarnings({ "NullAway.Init", "NotNullFieldNotInitialized" })
 	private Deque<Description> path;
+
+	@SuppressWarnings({ "NullAway.Init", "NotNullFieldNotInitialized" })
 	private Set<Description> descendants;
 
 	UniqueIdFilter(RunnerTestDescriptor runnerTestDescriptor, UniqueId uniqueId) {
@@ -41,6 +44,7 @@ class UniqueIdFilter extends Filter {
 		this.uniqueId = uniqueId;
 	}
 
+	@SuppressWarnings("ConstantValue")
 	private void ensureInitialized() {
 		if (descendants == null) {
 			Optional<? extends TestDescriptor> identifiedTestDescriptor = runnerTestDescriptor.findByUniqueId(uniqueId);
diff --git a/junit-vintage-engine/src/main/java/org/junit/vintage/engine/discovery/VintageDiscoverer.java b/junit-vintage-engine/src/main/java/org/junit/vintage/engine/discovery/VintageDiscoverer.java
index 5f50c2c439f0..df0e99c50462 100644
--- a/junit-vintage-engine/src/main/java/org/junit/vintage/engine/discovery/VintageDiscoverer.java
+++ b/junit-vintage-engine/src/main/java/org/junit/vintage/engine/discovery/VintageDiscoverer.java
@@ -14,6 +14,7 @@
 
 import org.apiguardian.api.API;
 import org.junit.platform.commons.support.scanning.ClassFilter;
+import org.junit.platform.engine.DiscoveryIssue;
 import org.junit.platform.engine.EngineDiscoveryRequest;
 import org.junit.platform.engine.TestDescriptor;
 import org.junit.platform.engine.UniqueId;
@@ -45,6 +46,13 @@ public VintageEngineDescriptor discover(EngineDiscoveryRequest discoveryRequest,
 			RunnerTestDescriptor runnerTestDescriptor = (RunnerTestDescriptor) testDescriptor;
 			postProcessor.applyFiltersAndCreateDescendants(runnerTestDescriptor);
 		}
+		if (!engineDescriptor.getChildren().isEmpty()) {
+			var issue = DiscoveryIssue.create(DiscoveryIssue.Severity.INFO, //
+				"The JUnit Vintage engine is deprecated and should only be " //
+						+ "used temporarily while migrating tests to JUnit Jupiter or another testing " //
+						+ "framework with native JUnit Platform support.");
+			discoveryRequest.getDiscoveryListener().issueEncountered(uniqueId, issue);
+		}
 		return engineDescriptor;
 	}
 
diff --git a/junit-vintage-engine/src/main/java/org/junit/vintage/engine/discovery/package-info.java b/junit-vintage-engine/src/main/java/org/junit/vintage/engine/discovery/package-info.java
index a22ae3939187..4e99c954b753 100644
--- a/junit-vintage-engine/src/main/java/org/junit/vintage/engine/discovery/package-info.java
+++ b/junit-vintage-engine/src/main/java/org/junit/vintage/engine/discovery/package-info.java
@@ -2,4 +2,7 @@
  * Internal classes for test discovery within the JUnit Vintage test engine.
  */
 
+@NullMarked
 package org.junit.vintage.engine.discovery;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-vintage-engine/src/main/java/org/junit/vintage/engine/execution/RunListenerAdapter.java b/junit-vintage-engine/src/main/java/org/junit/vintage/engine/execution/RunListenerAdapter.java
index ae0aab651df9..6a0b4756f7fd 100644
--- a/junit-vintage-engine/src/main/java/org/junit/vintage/engine/execution/RunListenerAdapter.java
+++ b/junit-vintage-engine/src/main/java/org/junit/vintage/engine/execution/RunListenerAdapter.java
@@ -15,6 +15,7 @@
 import java.util.Optional;
 import java.util.function.Function;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.Ignore;
 import org.junit.platform.engine.EngineExecutionListener;
 import org.junit.platform.engine.TestDescriptor;
@@ -192,7 +193,7 @@ private Optional<String> determineReasonForIgnoredTest(TestDescriptor testDescri
 				.flatMap(testClass -> getReason(testClass.getAnnotation(Ignore.class)));
 	}
 
-	private static Optional<String> getReason(Ignore annotation) {
+	private static Optional<String> getReason(@Nullable Ignore annotation) {
 		return Optional.ofNullable(annotation).map(Ignore::value);
 	}
 
@@ -216,7 +217,7 @@ private void fireExecutionFinishedForInProgressNonAncestorTestDescriptorsWithSyn
 
 	private boolean isAncestor(TestDescriptor candidate, TestDescriptor testDescriptor) {
 		Optional<TestDescriptor> parent = testDescriptor.getParent();
-		if (!parent.isPresent()) {
+		if (parent.isEmpty()) {
 			return false;
 		}
 		if (parent.get().equals(candidate)) {
diff --git a/junit-vintage-engine/src/main/java/org/junit/vintage/engine/execution/TestRun.java b/junit-vintage-engine/src/main/java/org/junit/vintage/engine/execution/TestRun.java
index 0e1a4e0ec2e7..1b7814a8a106 100644
--- a/junit-vintage-engine/src/main/java/org/junit/vintage/engine/execution/TestRun.java
+++ b/junit-vintage-engine/src/main/java/org/junit/vintage/engine/execution/TestRun.java
@@ -11,8 +11,8 @@
 package org.junit.vintage.engine.execution;
 
 import static java.util.Collections.emptyList;
+import static java.util.Objects.requireNonNull;
 import static java.util.stream.Collectors.toCollection;
-import static java.util.stream.Collectors.toList;
 import static java.util.stream.Collectors.toMap;
 import static java.util.stream.Stream.concat;
 import static org.junit.platform.engine.TestExecutionResult.failed;
@@ -114,7 +114,7 @@ private Optional<VintageTestDescriptor> lookupUnambiguouslyOrApplyFallback(Descr
 		VintageDescriptors vintageDescriptors = descriptionToDescriptors.getOrDefault(description,
 			VintageDescriptors.NONE);
 		Optional<VintageTestDescriptor> result = vintageDescriptors.getUnambiguously(description);
-		if (!result.isPresent()) {
+		if (result.isEmpty()) {
 			result = fallback.apply(vintageDescriptors);
 		}
 		return result;
@@ -122,9 +122,8 @@ private Optional<VintageTestDescriptor> lookupUnambiguouslyOrApplyFallback(Descr
 
 	void markSkipped(TestDescriptor testDescriptor) {
 		skippedDescriptors.add(testDescriptor);
-		if (testDescriptor instanceof VintageTestDescriptor) {
-			VintageTestDescriptor vintageDescriptor = (VintageTestDescriptor) testDescriptor;
-			descriptionToDescriptors.get(vintageDescriptor.getDescription()).incrementSkippedOrStarted();
+		if (testDescriptor instanceof VintageTestDescriptor vintageDescriptor) {
+			getVintageDescriptors(vintageDescriptor).incrementSkippedOrStarted();
 		}
 	}
 
@@ -139,13 +138,17 @@ boolean isSkipped(TestDescriptor testDescriptor) {
 	void markStarted(TestDescriptor testDescriptor, EventType eventType) {
 		inProgressDescriptors.put(testDescriptor, eventType);
 		startedDescriptors.add(testDescriptor);
-		if (testDescriptor instanceof VintageTestDescriptor) {
-			VintageTestDescriptor vintageDescriptor = (VintageTestDescriptor) testDescriptor;
+		if (testDescriptor instanceof VintageTestDescriptor vintageDescriptor) {
 			inProgressDescriptorsByStartingThread.get().addLast(vintageDescriptor);
-			descriptionToDescriptors.get(vintageDescriptor.getDescription()).incrementSkippedOrStarted();
+			getVintageDescriptors(vintageDescriptor).incrementSkippedOrStarted();
 		}
 	}
 
+	private VintageDescriptors getVintageDescriptors(VintageTestDescriptor vintageDescriptor) {
+		return requireNonNull(descriptionToDescriptors.get(vintageDescriptor.getDescription()),
+			() -> "No descriptors for " + vintageDescriptor);
+	}
+
 	boolean isNotStarted(TestDescriptor testDescriptor) {
 		return !startedDescriptors.contains(testDescriptor);
 	}
@@ -153,8 +156,7 @@ boolean isNotStarted(TestDescriptor testDescriptor) {
 	void markFinished(TestDescriptor testDescriptor) {
 		inProgressDescriptors.remove(testDescriptor);
 		finishedDescriptors.add(testDescriptor);
-		if (testDescriptor instanceof VintageTestDescriptor) {
-			VintageTestDescriptor descriptor = (VintageTestDescriptor) testDescriptor;
+		if (testDescriptor instanceof VintageTestDescriptor descriptor) {
 			inProgressDescriptorsByStartingThread.get().removeLastOccurrence(descriptor);
 		}
 	}
@@ -194,8 +196,8 @@ TestExecutionResult getStoredResultOrSuccessful(TestDescriptor testDescriptor) {
 		List<Throwable> failures = testExecutionResults
 				.stream()
 				.map(TestExecutionResult::getThrowable)
-				.map(Optional::get)
-				.collect(toList());
+				.map(Optional::orElseThrow)
+				.toList();
 		// @formatter:on
 		MultipleFailuresError multipleFailuresError = new MultipleFailuresError("", failures);
 		failures.forEach(multipleFailuresError::addSuppressed);
diff --git a/junit-vintage-engine/src/main/java/org/junit/vintage/engine/execution/VintageExecutor.java b/junit-vintage-engine/src/main/java/org/junit/vintage/engine/execution/VintageExecutor.java
index 0ca61c6655fe..450dc4fde4dd 100644
--- a/junit-vintage-engine/src/main/java/org/junit/vintage/engine/execution/VintageExecutor.java
+++ b/junit-vintage-engine/src/main/java/org/junit/vintage/engine/execution/VintageExecutor.java
@@ -10,12 +10,8 @@
 
 package org.junit.vintage.engine.execution;
 
-import static java.util.stream.Collectors.toList;
+import static java.util.Objects.requireNonNullElse;
 import static org.apiguardian.api.API.Status.INTERNAL;
-import static org.junit.vintage.engine.Constants.PARALLEL_CLASS_EXECUTION;
-import static org.junit.vintage.engine.Constants.PARALLEL_EXECUTION_ENABLED;
-import static org.junit.vintage.engine.Constants.PARALLEL_METHOD_EXECUTION;
-import static org.junit.vintage.engine.Constants.PARALLEL_POOL_SIZE;
 
 import java.util.ArrayList;
 import java.util.Iterator;
@@ -34,12 +30,14 @@
 import org.junit.platform.engine.EngineExecutionListener;
 import org.junit.platform.engine.ExecutionRequest;
 import org.junit.platform.engine.TestDescriptor;
+import org.junit.vintage.engine.Constants;
 import org.junit.vintage.engine.descriptor.RunnerTestDescriptor;
 import org.junit.vintage.engine.descriptor.VintageEngineDescriptor;
 
 /**
  * @since 5.12
  */
+@SuppressWarnings({ "deprecation", "RedundantSuppression" })
 @API(status = INTERNAL, since = "5.12")
 public class VintageExecutor {
 
@@ -62,9 +60,11 @@ public VintageExecutor(VintageEngineDescriptor engineDescriptor, EngineExecution
 		this.engineExecutionListener = engineExecutionListener;
 		this.request = request;
 		this.parallelExecutionEnabled = request.getConfigurationParameters().getBoolean(
-			PARALLEL_EXECUTION_ENABLED).orElse(false);
-		this.classes = request.getConfigurationParameters().getBoolean(PARALLEL_CLASS_EXECUTION).orElse(false);
-		this.methods = request.getConfigurationParameters().getBoolean(PARALLEL_METHOD_EXECUTION).orElse(false);
+			Constants.PARALLEL_EXECUTION_ENABLED).orElse(false);
+		this.classes = request.getConfigurationParameters().getBoolean(Constants.PARALLEL_CLASS_EXECUTION).orElse(
+			false);
+		this.methods = request.getConfigurationParameters().getBoolean(Constants.PARALLEL_METHOD_EXECUTION).orElse(
+			false);
 	}
 
 	public void executeAllChildren() {
@@ -110,7 +110,7 @@ private boolean executeInParallel() {
 	}
 
 	private int getThreadPoolSize() {
-		Optional<String> optionalPoolSize = request.getConfigurationParameters().get(PARALLEL_POOL_SIZE);
+		Optional<String> optionalPoolSize = request.getConfigurationParameters().get(Constants.PARALLEL_POOL_SIZE);
 		if (optionalPoolSize.isPresent()) {
 			try {
 				int poolSize = Integer.parseInt(optionalPoolSize.get());
@@ -130,7 +130,7 @@ private List<RunnerTestDescriptor> collectRunnerTestDescriptors(ExecutorService
 		return engineDescriptor.getModifiableChildren().stream() //
 				.map(RunnerTestDescriptor.class::cast) //
 				.map(it -> methods ? parallelMethodExecutor(it, executorService) : it) //
-				.collect(toList());
+				.toList();
 	}
 
 	private RunnerTestDescriptor parallelMethodExecutor(RunnerTestDescriptor runnerTestDescriptor,
@@ -165,7 +165,7 @@ private boolean executeClassesInParallel(List<RunnerTestDescriptor> runnerTestDe
 			wasInterrupted = true;
 		}
 		catch (ExecutionException e) {
-			throw ExceptionUtils.throwAsUncheckedException(e.getCause());
+			throw ExceptionUtils.throwAsUncheckedException(requireNonNullElse(e.getCause(), e));
 		}
 		finally {
 			shutdownExecutorService(executorService);
diff --git a/junit-vintage-engine/src/main/java/org/junit/vintage/engine/execution/package-info.java b/junit-vintage-engine/src/main/java/org/junit/vintage/engine/execution/package-info.java
index 43e48e1d4ad6..3749427c181f 100644
--- a/junit-vintage-engine/src/main/java/org/junit/vintage/engine/execution/package-info.java
+++ b/junit-vintage-engine/src/main/java/org/junit/vintage/engine/execution/package-info.java
@@ -2,4 +2,7 @@
  * Internal classes for test execution within the JUnit Vintage test engine.
  */
 
+@NullMarked
 package org.junit.vintage.engine.execution;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-vintage-engine/src/main/java/org/junit/vintage/engine/package-info.java b/junit-vintage-engine/src/main/java/org/junit/vintage/engine/package-info.java
index af7d60d30f7e..05e48ea8ece3 100644
--- a/junit-vintage-engine/src/main/java/org/junit/vintage/engine/package-info.java
+++ b/junit-vintage-engine/src/main/java/org/junit/vintage/engine/package-info.java
@@ -2,4 +2,7 @@
  * Core package for the JUnit Vintage test engine.
  */
 
+@NullMarked
 package org.junit.vintage.engine;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-vintage-engine/src/main/java/org/junit/vintage/engine/support/UniqueIdReader.java b/junit-vintage-engine/src/main/java/org/junit/vintage/engine/support/UniqueIdReader.java
index d9cae90a119a..3973c1c6b1bd 100644
--- a/junit-vintage-engine/src/main/java/org/junit/vintage/engine/support/UniqueIdReader.java
+++ b/junit-vintage-engine/src/main/java/org/junit/vintage/engine/support/UniqueIdReader.java
@@ -10,7 +10,6 @@
 
 package org.junit.vintage.engine.support;
 
-import static java.lang.String.format;
 import static org.apiguardian.api.API.Status.INTERNAL;
 import static org.junit.platform.commons.util.ReflectionUtils.tryToReadFieldValue;
 
@@ -47,7 +46,7 @@ public Serializable apply(Description description) {
 		return tryToReadFieldValue(Description.class, fieldName, description)
 				.andThenTry(Serializable.class::cast)
 				.ifFailure(cause -> logger.warn(cause, () ->
-						format("Could not read unique ID for Description; using display name instead: %s", description)))
+						"Could not read unique ID for Description; using display name instead: %s".formatted(description)))
 				.toOptional()
 				.orElseGet(description::getDisplayName);
 		// @formatter:on
diff --git a/junit-vintage-engine/src/main/java/org/junit/vintage/engine/support/package-info.java b/junit-vintage-engine/src/main/java/org/junit/vintage/engine/support/package-info.java
index bb5a291af76f..35401fcf225c 100644
--- a/junit-vintage-engine/src/main/java/org/junit/vintage/engine/support/package-info.java
+++ b/junit-vintage-engine/src/main/java/org/junit/vintage/engine/support/package-info.java
@@ -3,4 +3,7 @@
  * Vintage test engine.
  */
 
+@NullMarked
 package org.junit.vintage.engine.support;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/junit-vintage-engine/src/test/java/org/junit/vintage/engine/JUnit4ParameterizedTests.java b/junit-vintage-engine/src/test/java/org/junit/vintage/engine/JUnit4ParameterizedTests.java
index 5ac12b0a1f26..99253ff128c4 100644
--- a/junit-vintage-engine/src/test/java/org/junit/vintage/engine/JUnit4ParameterizedTests.java
+++ b/junit-vintage-engine/src/test/java/org/junit/vintage/engine/JUnit4ParameterizedTests.java
@@ -63,6 +63,7 @@ private void executeTests(DiscoverySelector selector) {
 			request()
 				.selectors(selector)
 				.filters(includeEngines("junit-vintage"))
+				.enableImplicitConfigurationParameters(false)
 				.build()
 		);
 		// @formatter:on
diff --git a/junit-vintage-engine/src/test/java/org/junit/vintage/engine/JUnit4VersionCheckTests.java b/junit-vintage-engine/src/test/java/org/junit/vintage/engine/JUnit4VersionCheckTests.java
index fc3416f404af..cc5a828928ed 100644
--- a/junit-vintage-engine/src/test/java/org/junit/vintage/engine/JUnit4VersionCheckTests.java
+++ b/junit-vintage-engine/src/test/java/org/junit/vintage/engine/JUnit4VersionCheckTests.java
@@ -84,4 +84,5 @@ void handlesMissingJUnit() {
 				+ "an excludeEngines(\"junit-vintage\") filter.",
 			exception.getMessage());
 	}
+
 }
diff --git a/junit-vintage-engine/src/test/java/org/junit/vintage/engine/VintageLauncherIntegrationTests.java b/junit-vintage-engine/src/test/java/org/junit/vintage/engine/VintageLauncherIntegrationTests.java
index 975752edee61..9b6e3bb4811b 100644
--- a/junit-vintage-engine/src/test/java/org/junit/vintage/engine/VintageLauncherIntegrationTests.java
+++ b/junit-vintage-engine/src/test/java/org/junit/vintage/engine/VintageLauncherIntegrationTests.java
@@ -280,7 +280,9 @@ public void executionFinished(TestIdentifier testIdentifier, TestExecutionResult
 	}
 
 	private LauncherDiscoveryRequest toRequest(LauncherDiscoveryRequestBuilder requestBuilder) {
-		return requestBuilder.filters(includeEngines(ENGINE_ID)).build();
+		return requestBuilder.filters(includeEngines(ENGINE_ID)) //
+				.enableImplicitConfigurationParameters(false) //
+				.build();
 	}
 
 }
diff --git a/junit-vintage-engine/src/test/java/org/junit/vintage/engine/VintageTestEngineBasicTests.java b/junit-vintage-engine/src/test/java/org/junit/vintage/engine/VintageTestEngineBasicTests.java
index 3f6fa7b5e5d7..1a1efcdb0bd1 100644
--- a/junit-vintage-engine/src/test/java/org/junit/vintage/engine/VintageTestEngineBasicTests.java
+++ b/junit-vintage-engine/src/test/java/org/junit/vintage/engine/VintageTestEngineBasicTests.java
@@ -20,6 +20,7 @@
  *
  * @since 4.12
  */
+@SuppressWarnings("deprecation")
 class VintageTestEngineBasicTests {
 
 	private final VintageTestEngine vintage = new VintageTestEngine();
diff --git a/junit-vintage-engine/src/test/java/org/junit/vintage/engine/VintageTestEngineDiscoveryTests.java b/junit-vintage-engine/src/test/java/org/junit/vintage/engine/VintageTestEngineDiscoveryTests.java
index 8947aeae6212..26b6eeb12d63 100644
--- a/junit-vintage-engine/src/test/java/org/junit/vintage/engine/VintageTestEngineDiscoveryTests.java
+++ b/junit-vintage-engine/src/test/java/org/junit/vintage/engine/VintageTestEngineDiscoveryTests.java
@@ -33,7 +33,6 @@
 import java.net.URLClassLoader;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.Path;
-import java.nio.file.Paths;
 import java.util.ArrayList;
 import java.util.Base64;
 import java.util.List;
@@ -41,12 +40,15 @@
 
 import org.junit.jupiter.api.Test;
 import org.junit.platform.commons.util.ClassUtils;
+import org.junit.platform.engine.DiscoveryIssue.Severity;
 import org.junit.platform.engine.TestDescriptor;
 import org.junit.platform.engine.TestTag;
 import org.junit.platform.engine.UniqueId;
 import org.junit.platform.engine.support.descriptor.ClassSource;
 import org.junit.platform.engine.support.descriptor.MethodSource;
 import org.junit.platform.launcher.LauncherDiscoveryRequest;
+import org.junit.platform.testkit.engine.EngineDiscoveryResults;
+import org.junit.platform.testkit.engine.EngineTestKit;
 import org.junit.runner.manipulation.Filter;
 import org.junit.vintage.engine.samples.PlainOldJavaClassWithoutAnyTestsTestCase;
 import org.junit.vintage.engine.samples.junit3.JUnit3SuiteWithSingleTestCaseWithSingleTestWhichFails;
@@ -77,8 +79,6 @@
  */
 class VintageTestEngineDiscoveryTests {
 
-	VintageTestEngine engine = new VintageTestEngine();
-
 	@Test
 	void resolvesSimpleJUnit4TestClass() throws Exception {
 		Class<?> testClass = PlainJUnit4TestCaseWithSingleTestWhichFails.class;
@@ -271,7 +271,7 @@ void resolvesClasspathSelector() throws Exception {
 	@Test
 	void resolvesClasspathSelectorForJarFile() throws Exception {
 		var jarUrl = getClass().getResource("/vintage-testjar.jar");
-		var jarFile = Paths.get(jarUrl.toURI());
+		var jarFile = Path.of(jarUrl.toURI());
 
 		var originalClassLoader = Thread.currentThread().getContextClassLoader();
 		try (var classLoader = new URLClassLoader(new URL[] { jarUrl })) {
@@ -703,6 +703,28 @@ void resolvesTestSourceForParameterizedTests() throws Exception {
 		assertMethodSource(testClass.getMethod("test"), testMethodDescriptor);
 	}
 
+	@Test
+	void reportsNoDiscoveryIssuesWhenNoTestsAreFound() {
+		var request = discoveryRequestForClass(PlainOldJavaClassWithoutAnyTestsTestCase.class);
+
+		var results = discover(request);
+
+		assertThat(results.getDiscoveryIssues()).isEmpty();
+	}
+
+	@Test
+	void reportDiscoveryIssueWhenTestsAreFound() {
+		var request = discoveryRequestForClass(PlainJUnit4TestCaseWithSingleTestWhichFails.class);
+
+		var results = discover(request);
+
+		assertThat(results.getDiscoveryIssues()).hasSize(1);
+
+		var issue = results.getDiscoveryIssues().getFirst();
+		assertThat(issue.severity()).isEqualTo(Severity.INFO);
+		assertThat(issue.message()).contains("JUnit Vintage engine is deprecated");
+	}
+
 	private TestDescriptor findChildByDisplayName(TestDescriptor runnerDescriptor, String displayName) {
 		// @formatter:off
 		var children = runnerDescriptor.getChildren();
@@ -716,12 +738,17 @@ private TestDescriptor findChildByDisplayName(TestDescriptor runnerDescriptor, S
 	}
 
 	private TestDescriptor discoverTests(LauncherDiscoveryRequest discoveryRequest) {
-		return engine.discover(discoveryRequest, UniqueId.forEngine(engine.getId()));
+		return discover(discoveryRequest).getEngineDescriptor();
+	}
+
+	@SuppressWarnings("deprecation")
+	private static EngineDiscoveryResults discover(LauncherDiscoveryRequest discoveryRequest) {
+		return EngineTestKit.discover(new VintageTestEngine(), discoveryRequest);
 	}
 
 	private Path getClasspathRoot(Class<?> testClass) throws Exception {
 		var location = testClass.getProtectionDomain().getCodeSource().getLocation();
-		return Paths.get(location.toURI());
+		return Path.of(location.toURI());
 	}
 
 	private void assertYieldsNoDescriptors(Class<?> testClass) {
diff --git a/junit-vintage-engine/src/test/java/org/junit/vintage/engine/VintageTestEngineExecutionTests.java b/junit-vintage-engine/src/test/java/org/junit/vintage/engine/VintageTestEngineExecutionTests.java
index 8811f97d404d..356b2b95bf30 100644
--- a/junit-vintage-engine/src/test/java/org/junit/vintage/engine/VintageTestEngineExecutionTests.java
+++ b/junit-vintage-engine/src/test/java/org/junit/vintage/engine/VintageTestEngineExecutionTests.java
@@ -42,6 +42,8 @@
 import org.assertj.core.api.Condition;
 import org.junit.AssumptionViolatedException;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.condition.DisabledIf;
+import org.junit.platform.commons.util.ReflectionUtils;
 import org.junit.platform.engine.EngineExecutionListener;
 import org.junit.platform.engine.ExecutionRequest;
 import org.junit.platform.engine.TestDescriptor;
@@ -98,7 +100,6 @@
 import org.junit.vintage.engine.samples.junit4.PlainJUnit4TestCaseWithSingleTestWhichFails;
 import org.junit.vintage.engine.samples.junit4.PlainJUnit4TestCaseWithSingleTestWhichIsIgnored;
 import org.junit.vintage.engine.samples.junit4.PlainJUnit4TestCaseWithTwoTestMethods;
-import org.junit.vintage.engine.samples.spock.SpockTestCaseWithUnrolledAndRegularFeatureMethods;
 import org.opentest4j.MultipleFailuresError;
 
 /**
@@ -786,8 +787,10 @@ void executesJUnit4SuiteWithJUnit4TestCaseWithFailingDescriptionThatIsNotReporte
 	@Test
 	void executesCompletelyDynamicTestCaseDiscoveredByUniqueId() {
 		Class<?> testClass = CompletelyDynamicTestCase.class;
-		var request = LauncherDiscoveryRequestBuilder.request().selectors(
-			selectUniqueId(VintageUniqueIdBuilder.uniqueIdForClass(testClass))).build();
+		var request = LauncherDiscoveryRequestBuilder.request() //
+				.selectors(selectUniqueId(VintageUniqueIdBuilder.uniqueIdForClass(testClass))) //
+				.enableImplicitConfigurationParameters(false) //
+				.build();
 
 		execute(request).allEvents().assertEventsMatchExactly( //
 			event(engine(), started()), //
@@ -862,13 +865,18 @@ void executesJUnit4TestCaseWithRunnerWithDuplicateChangingChildDescriptions() {
 	}
 
 	@Test
+	@DisabledIf("org.junit.platform.commons.test.IdeUtils#runningInEclipse()")
 	void executesUnrolledSpockFeatureMethod() {
-		Class<?> testClass = SpockTestCaseWithUnrolledAndRegularFeatureMethods.class;
-		var request = LauncherDiscoveryRequestBuilder.request().selectors(
-			selectMethod(testClass, "unrolled feature for #input")).build();
+		// Load Groovy class via reflection to avoid compilation errors in Eclipse IDE.
+		String testClassName = "org.junit.vintage.engine.samples.spock.SpockTestCaseWithUnrolledAndRegularFeatureMethods";
+		Class<?> testClass = ReflectionUtils.loadRequiredClass(testClassName, getClass().getClassLoader());
+		var request = LauncherDiscoveryRequestBuilder.request() //
+				.selectors(selectMethod(testClass, "unrolled feature for #input"))//
+				.enableImplicitConfigurationParameters(false) //
+				.build();
 		execute(request).allEvents().assertEventsMatchExactly( //
 			event(engine(), started()), //
-			event(uniqueIdSubstring(testClass.getName()), started()), //
+			event(uniqueIdSubstring(testClassName), started()), //
 			event(dynamicTestRegistered("unrolled feature for 23")), //
 			event(test("unrolled feature for 23"), started()), //
 			event(test("unrolled feature for 23"), finishedWithFailure()), //
@@ -880,9 +888,15 @@ void executesUnrolledSpockFeatureMethod() {
 	}
 
 	@Test
+	@DisabledIf("org.junit.platform.commons.test.IdeUtils#runningInEclipse()")
 	void executesRegularSpockFeatureMethod() {
-		Class<?> testClass = SpockTestCaseWithUnrolledAndRegularFeatureMethods.class;
-		var request = LauncherDiscoveryRequestBuilder.request().selectors(selectMethod(testClass, "regular")).build();
+		// Load Groovy class via reflection to avoid compilation errors in Eclipse IDE.
+		String testClassName = "org.junit.vintage.engine.samples.spock.SpockTestCaseWithUnrolledAndRegularFeatureMethods";
+		Class<?> testClass = ReflectionUtils.loadRequiredClass(testClassName, getClass().getClassLoader());
+		var request = LauncherDiscoveryRequestBuilder.request() //
+				.selectors(selectMethod(testClass, "regular")) //
+				.enableImplicitConfigurationParameters(false) //
+				.build();
 		execute(request).allEvents().assertEventsMatchExactly( //
 			event(engine(), started()), //
 			event(container(testClass), started()), //
@@ -917,10 +931,12 @@ private static EngineExecutionResults execute(Class<?> testClass) {
 		return execute(request(testClass));
 	}
 
+	@SuppressWarnings("deprecation")
 	private static EngineExecutionResults execute(LauncherDiscoveryRequest request) {
 		return EngineTestKit.execute(new VintageTestEngine(), request);
 	}
 
+	@SuppressWarnings("deprecation")
 	private static void execute(Class<?> testClass, EngineExecutionListener listener) {
 		TestEngine testEngine = new VintageTestEngine();
 		var discoveryRequest = request(testClass);
@@ -931,7 +947,10 @@ private static void execute(Class<?> testClass, EngineExecutionListener listener
 	}
 
 	private static LauncherDiscoveryRequest request(Class<?> testClass) {
-		return LauncherDiscoveryRequestBuilder.request().selectors(selectClass(testClass)).build();
+		return LauncherDiscoveryRequestBuilder.request() //
+				.selectors(selectClass(testClass)) //
+				.enableImplicitConfigurationParameters(false) //
+				.build();
 	}
 
 	private static boolean atLeastJUnit4_13() {
diff --git a/junit-vintage-engine/src/test/java/org/junit/vintage/engine/VintageTestEngineTestSuite.java b/junit-vintage-engine/src/test/java/org/junit/vintage/engine/VintageTestEngineTestSuite.java
index d45ca3b2139b..12f94fae817b 100644
--- a/junit-vintage-engine/src/test/java/org/junit/vintage/engine/VintageTestEngineTestSuite.java
+++ b/junit-vintage-engine/src/test/java/org/junit/vintage/engine/VintageTestEngineTestSuite.java
@@ -10,6 +10,7 @@
 
 package org.junit.vintage.engine;
 
+import org.junit.platform.suite.api.ExcludeTags;
 import org.junit.platform.suite.api.IncludeClassNamePatterns;
 import org.junit.platform.suite.api.IncludeEngines;
 import org.junit.platform.suite.api.SelectPackages;
@@ -34,5 +35,6 @@
 @SelectPackages("org.junit.vintage.engine")
 @IncludeClassNamePatterns(".*Tests?")
 @IncludeEngines("junit-jupiter")
+@ExcludeTags("missing-junit4")
 class VintageTestEngineTestSuite {
 }
diff --git a/junit-vintage-engine/src/test/java/org/junit/vintage/engine/execution/ParallelExecutionIntegrationTests.java b/junit-vintage-engine/src/test/java/org/junit/vintage/engine/execution/ParallelExecutionIntegrationTests.java
index 41b96da2c5cb..ce3efd137e42 100644
--- a/junit-vintage-engine/src/test/java/org/junit/vintage/engine/execution/ParallelExecutionIntegrationTests.java
+++ b/junit-vintage-engine/src/test/java/org/junit/vintage/engine/execution/ParallelExecutionIntegrationTests.java
@@ -17,10 +17,6 @@
 import static org.junit.platform.testkit.engine.EventConditions.finishedSuccessfully;
 import static org.junit.platform.testkit.engine.EventConditions.started;
 import static org.junit.platform.testkit.engine.EventConditions.test;
-import static org.junit.vintage.engine.Constants.PARALLEL_CLASS_EXECUTION;
-import static org.junit.vintage.engine.Constants.PARALLEL_EXECUTION_ENABLED;
-import static org.junit.vintage.engine.Constants.PARALLEL_METHOD_EXECUTION;
-import static org.junit.vintage.engine.Constants.PARALLEL_POOL_SIZE;
 import static org.junit.vintage.engine.descriptor.VintageTestDescriptor.SEGMENT_TYPE_RUNNER;
 import static org.junit.vintage.engine.descriptor.VintageTestDescriptor.SEGMENT_TYPE_TEST;
 import static org.junit.vintage.engine.samples.junit4.JUnit4ParallelClassesTestCase.FirstClassTestCase;
@@ -51,6 +47,7 @@
 import org.junit.platform.testkit.engine.EngineTestKit;
 import org.junit.platform.testkit.engine.Event;
 import org.junit.platform.testkit.engine.Events;
+import org.junit.vintage.engine.Constants;
 import org.junit.vintage.engine.VintageTestEngine;
 import org.junit.vintage.engine.samples.junit4.JUnit4ParallelClassesTestCase;
 import org.junit.vintage.engine.samples.junit4.JUnit4ParallelMethodsTestCase;
@@ -180,12 +177,14 @@ private Events executeInParallelSuccessfully(int poolSize, boolean parallelClass
 		}
 	}
 
+	@SuppressWarnings("deprecation")
 	private static EngineExecutionResults execute(int poolSize, boolean parallelClasses, boolean parallelMethods,
 			Class<?>... testClass) {
 		return EngineTestKit.execute(new VintageTestEngine(),
 			request(poolSize, parallelClasses, parallelMethods, testClass));
 	}
 
+	@SuppressWarnings("deprecation")
 	private static LauncherDiscoveryRequest request(int poolSize, boolean parallelClasses, boolean parallelMethods,
 			Class<?>... testClasses) {
 		var classSelectors = Arrays.stream(testClasses) //
@@ -194,10 +193,11 @@ private static LauncherDiscoveryRequest request(int poolSize, boolean parallelCl
 
 		return LauncherDiscoveryRequestBuilder.request() //
 				.selectors(classSelectors) //
-				.configurationParameter(PARALLEL_EXECUTION_ENABLED, String.valueOf(true)) //
-				.configurationParameter(PARALLEL_POOL_SIZE, String.valueOf(poolSize)) //
-				.configurationParameter(PARALLEL_CLASS_EXECUTION, String.valueOf(parallelClasses)) //
-				.configurationParameter(PARALLEL_METHOD_EXECUTION, String.valueOf(parallelMethods)) //
+				.configurationParameter(Constants.PARALLEL_EXECUTION_ENABLED, String.valueOf(true)) //
+				.configurationParameter(Constants.PARALLEL_POOL_SIZE, String.valueOf(poolSize)) //
+				.configurationParameter(Constants.PARALLEL_CLASS_EXECUTION, String.valueOf(parallelClasses)) //
+				.configurationParameter(Constants.PARALLEL_METHOD_EXECUTION, String.valueOf(parallelMethods)) //
+				.enableImplicitConfigurationParameters(false) //
 				.build();
 	}
 
diff --git a/junit-vintage-engine/src/test/java/org/junit/vintage/engine/support/UniqueIdStringifierTests.java b/junit-vintage-engine/src/test/java/org/junit/vintage/engine/support/UniqueIdStringifierTests.java
index d8859b1e1c31..b2a5d0482872 100644
--- a/junit-vintage-engine/src/test/java/org/junit/vintage/engine/support/UniqueIdStringifierTests.java
+++ b/junit-vintage-engine/src/test/java/org/junit/vintage/engine/support/UniqueIdStringifierTests.java
@@ -17,6 +17,7 @@
 import java.io.InvalidObjectException;
 import java.io.ObjectInputStream;
 import java.io.ObjectStreamException;
+import java.io.Serial;
 import java.io.Serializable;
 import java.util.Base64;
 
@@ -45,7 +46,7 @@ void serializesUnknownTypes() throws Exception {
 
 		var deserializedObject = deserialize(decodeBase64(serialized));
 		assertThat(deserializedObject).isInstanceOf(MyCustomId.class);
-		assertEquals(42, ((MyCustomId) deserializedObject).getValue());
+		assertEquals(42, ((MyCustomId) deserializedObject).value());
 	}
 
 	@Test
@@ -68,26 +69,19 @@ private Object deserialize(byte[] bytes) throws Exception {
 		}
 	}
 
-	private static class MyCustomId implements Serializable {
+	private record MyCustomId(int value) implements Serializable {
 
+		@Serial
 		private static final long serialVersionUID = 1L;
 
-		private final int value;
-
-		MyCustomId(int value) {
-			this.value = value;
-		}
-
-		int getValue() {
-			return value;
-		}
-
 	}
 
 	private static class ClassWithErroneousSerialization implements Serializable {
 
+		@Serial
 		private static final long serialVersionUID = 1L;
 
+		@Serial
 		Object writeReplace() throws ObjectStreamException {
 			throw new InvalidObjectException("failed on purpose");
 		}
diff --git a/junit-vintage-engine/src/testFixtures/java/org/junit/platform/runner/JUnitPlatform.java b/junit-vintage-engine/src/testFixtures/java/org/junit/platform/runner/JUnitPlatform.java
new file mode 100644
index 000000000000..02f7102aa886
--- /dev/null
+++ b/junit-vintage-engine/src/testFixtures/java/org/junit/platform/runner/JUnitPlatform.java
@@ -0,0 +1,44 @@
+/*
+ * Copyright 2015-2025 the original author or authors.
+ *
+ * All rights reserved. This program and the accompanying materials are
+ * made available under the terms of the Eclipse Public License v2.0 which
+ * accompanies this distribution and is available at
+ *
+ * https://www.eclipse.org/legal/epl-v20.html
+ */
+
+package org.junit.platform.runner;
+
+import java.util.List;
+
+import org.junit.runner.Description;
+import org.junit.runner.notification.RunNotifier;
+import org.junit.runners.ParentRunner;
+import org.junit.runners.model.InitializationError;
+
+/**
+ * Dummy Runner class mimicking the one from the discontinued
+ * {@code junit-platform-runner} module.
+ */
+public class JUnitPlatform extends ParentRunner<Void> {
+
+	public JUnitPlatform(Class<?> testClass) throws InitializationError {
+		super(testClass);
+	}
+
+	@Override
+	protected List<Void> getChildren() {
+		return List.of();
+	}
+
+	@Override
+	protected Description describeChild(Void child) {
+		throw new UnsupportedOperationException();
+	}
+
+	@Override
+	protected void runChild(Void child, RunNotifier notifier) {
+		throw new UnsupportedOperationException();
+	}
+}
diff --git a/junit-vintage-engine/src/testFixtures/java/org/junit/vintage/engine/samples/junit4/EnclosedWithParameterizedChildrenJUnit4TestCase.java b/junit-vintage-engine/src/testFixtures/java/org/junit/vintage/engine/samples/junit4/EnclosedWithParameterizedChildrenJUnit4TestCase.java
index c4e24e94ca41..188806ca23c6 100644
--- a/junit-vintage-engine/src/testFixtures/java/org/junit/vintage/engine/samples/junit4/EnclosedWithParameterizedChildrenJUnit4TestCase.java
+++ b/junit-vintage-engine/src/testFixtures/java/org/junit/vintage/engine/samples/junit4/EnclosedWithParameterizedChildrenJUnit4TestCase.java
@@ -19,7 +19,7 @@
 import org.junit.runners.Parameterized;
 import org.junit.runners.Parameterized.Parameters;
 
-// Source: https://github.com/junit-team/junit5/issues/3083
+// Source: https://github.com/junit-team/junit-framework/issues/3083
 @RunWith(Enclosed.class)
 public class EnclosedWithParameterizedChildrenJUnit4TestCase {
 
diff --git a/junit-vintage-engine/src/testFixtures/java/org/junit/vintage/engine/samples/junit4/JUnit4TestCaseWithRunnerWithCustomUniqueIdsAndDisplayNames.java b/junit-vintage-engine/src/testFixtures/java/org/junit/vintage/engine/samples/junit4/JUnit4TestCaseWithRunnerWithCustomUniqueIdsAndDisplayNames.java
index 07dab7575284..b8a91e6d2a2d 100644
--- a/junit-vintage-engine/src/testFixtures/java/org/junit/vintage/engine/samples/junit4/JUnit4TestCaseWithRunnerWithCustomUniqueIdsAndDisplayNames.java
+++ b/junit-vintage-engine/src/testFixtures/java/org/junit/vintage/engine/samples/junit4/JUnit4TestCaseWithRunnerWithCustomUniqueIdsAndDisplayNames.java
@@ -10,10 +10,6 @@
 
 package org.junit.vintage.engine.samples.junit4;
 
-import static java.lang.annotation.RetentionPolicy.RUNTIME;
-
-import java.lang.annotation.Retention;
-
 import org.junit.Assert;
 import org.junit.Test;
 import org.junit.runner.RunWith;
@@ -32,8 +28,3 @@ public void test() {
 	}
 
 }
-
-@Retention(RUNTIME)
-@interface Label {
-	String value();
-}
diff --git a/junit-vintage-engine/src/testFixtures/java/org/junit/vintage/engine/samples/junit4/Label.java b/junit-vintage-engine/src/testFixtures/java/org/junit/vintage/engine/samples/junit4/Label.java
new file mode 100644
index 000000000000..5450edc8bb8c
--- /dev/null
+++ b/junit-vintage-engine/src/testFixtures/java/org/junit/vintage/engine/samples/junit4/Label.java
@@ -0,0 +1,20 @@
+/*
+ * Copyright 2015-2025 the original author or authors.
+ *
+ * All rights reserved. This program and the accompanying materials are
+ * made available under the terms of the Eclipse Public License v2.0 which
+ * accompanies this distribution and is available at
+ *
+ * https://www.eclipse.org/legal/epl-v20.html
+ */
+
+package org.junit.vintage.engine.samples.junit4;
+
+import static java.lang.annotation.RetentionPolicy.RUNTIME;
+
+import java.lang.annotation.Retention;
+
+@Retention(RUNTIME)
+@interface Label {
+	String value();
+}
diff --git a/junit-vintage-engine/src/testFixtures/java/org/junit/vintage/engine/samples/junit4/RunnerWithCustomUniqueIdsAndDisplayNames.java b/junit-vintage-engine/src/testFixtures/java/org/junit/vintage/engine/samples/junit4/RunnerWithCustomUniqueIdsAndDisplayNames.java
index f3af1814485d..e449e256ec4d 100644
--- a/junit-vintage-engine/src/testFixtures/java/org/junit/vintage/engine/samples/junit4/RunnerWithCustomUniqueIdsAndDisplayNames.java
+++ b/junit-vintage-engine/src/testFixtures/java/org/junit/vintage/engine/samples/junit4/RunnerWithCustomUniqueIdsAndDisplayNames.java
@@ -53,28 +53,18 @@ private String getLabel(Annotatable element, Supplier<String> fallback) {
 		return label == null ? fallback.get() : label.value();
 	}
 
-	private static class CustomUniqueId implements Serializable {
+	private record CustomUniqueId(String testName) implements Serializable {
 
 		@Serial
 		private static final long serialVersionUID = 1L;
 
-		private final String testName;
-
-		public CustomUniqueId(String testName) {
-			this.testName = testName;
-		}
-
 		@Override
 		public boolean equals(Object obj) {
-			if (obj instanceof CustomUniqueId that) {
-				return Objects.equals(this.testName, that.testName);
+			if (obj instanceof CustomUniqueId(String name)) {
+				return Objects.equals(this.testName, name);
 			}
 			return false;
 		}
 
-		@Override
-		public int hashCode() {
-			return testName.hashCode();
-		}
 	}
 }
diff --git a/junit-vintage-engine/src/testFixtures/java/org/junit/vintage/engine/samples/junit4/TestCaseRunWithJUnitPlatformRunner.java b/junit-vintage-engine/src/testFixtures/java/org/junit/vintage/engine/samples/junit4/TestCaseRunWithJUnitPlatformRunner.java
index fe1011fac50e..189dc2ee7ea2 100644
--- a/junit-vintage-engine/src/testFixtures/java/org/junit/vintage/engine/samples/junit4/TestCaseRunWithJUnitPlatformRunner.java
+++ b/junit-vintage-engine/src/testFixtures/java/org/junit/vintage/engine/samples/junit4/TestCaseRunWithJUnitPlatformRunner.java
@@ -17,7 +17,6 @@
 /**
  * @since 4.12
  */
-@SuppressWarnings("deprecation")
 @RunWith(JUnitPlatform.class)
 @SelectClasses(PlainJUnit4TestCaseWithSingleTestWhichFails.class)
 public class TestCaseRunWithJUnitPlatformRunner {
diff --git a/junit-vintage-engine/src/testFixtures/java/org/junit/vintage/engine/samples/junit4/package-info.java b/junit-vintage-engine/src/testFixtures/java/org/junit/vintage/engine/samples/junit4/package-info.java
new file mode 100644
index 000000000000..678ca9e2e64c
--- /dev/null
+++ b/junit-vintage-engine/src/testFixtures/java/org/junit/vintage/engine/samples/junit4/package-info.java
@@ -0,0 +1,5 @@
+
+@NullUnmarked
+package org.junit.vintage.engine.samples.junit4;
+
+import org.jspecify.annotations.NullUnmarked;
diff --git a/jupiter-tests/jupiter-tests.gradle.kts b/jupiter-tests/jupiter-tests.gradle.kts
index 061920f4d96d..9b1baaf781a7 100644
--- a/jupiter-tests/jupiter-tests.gradle.kts
+++ b/jupiter-tests/jupiter-tests.gradle.kts
@@ -1,7 +1,10 @@
 import org.gradle.api.tasks.PathSensitivity.RELATIVE
+import org.gradle.plugins.ide.eclipse.model.Classpath
+import org.gradle.plugins.ide.eclipse.model.SourceFolder
 
 plugins {
 	id("junitbuild.code-generator")
+	id("junitbuild.java-nullability-conventions")
 	id("junitbuild.kotlin-library-conventions")
 	id("junitbuild.junit4-compatibility")
 	id("junitbuild.testing-conventions")
@@ -25,6 +28,8 @@ dependencies {
 	testImplementation(testFixtures(projects.junitJupiterEngine))
 	testImplementation(testFixtures(projects.junitPlatformLauncher))
 	testImplementation(testFixtures(projects.junitPlatformReporting))
+
+	testRuntimeOnly(kotlin("reflect"))
 }
 
 tasks {
@@ -38,3 +43,21 @@ tasks {
 		}
 	}
 }
+
+eclipse {
+	classpath.file.whenMerged {
+		this as Classpath
+		entries.filterIsInstance<SourceFolder>().forEach {
+			if (it.path == "src/test/java") {
+				// Exclude test classes that depend on compiled Kotlin code.
+				it.excludes.add("**/AtypicalJvmMethodNameTests.java")
+				it.excludes.add("**/TestInstanceLifecycleKotlinTests.java")
+			}
+		}
+	}
+	project {
+		// Remove Groovy Nature, since we don't require a Groovy plugin for Eclipse
+		// in order for developers to work with the code base.
+		natures.removeAll { it == "org.eclipse.jdt.groovy.core.groovyNature" }
+	}
+}
diff --git a/jupiter-tests/src/templates/resources/test/org/junit/jupiter/api/condition/DisabledOnJreConditionTests.java.jte b/jupiter-tests/src/templates/resources/test/org/junit/jupiter/api/condition/DisabledOnJreConditionTests.java.jte
index b6ce05e15fa6..67d8d3978950 100644
--- a/jupiter-tests/src/templates/resources/test/org/junit/jupiter/api/condition/DisabledOnJreConditionTests.java.jte
+++ b/jupiter-tests/src/templates/resources/test/org/junit/jupiter/api/condition/DisabledOnJreConditionTests.java.jte
@@ -1,14 +1,14 @@
 @import java.util.List
 @import junitbuild.generator.model.JRE
 
-@param List<JRE> jres
-@param List<JRE> jresSortedByStringValue
+@param List<JRE> supportedJres
+@param List<JRE> supportedJresSortedByStringValue
 @param String licenseHeader
 ${licenseHeader}
 package org.junit.jupiter.api.condition;
 
 import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
-@for(var jre : jresSortedByStringValue)<%--
+@for(var jre : supportedJresSortedByStringValue)<%--
 --%>import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava${jre.getVersion()};
 @endfor<%--
 --%>import static org.junit.jupiter.api.condition.JavaVersionPredicates.onKnownVersion;
@@ -89,7 +89,7 @@ class DisabledOnJreConditionTests extends AbstractExecutionConditionTests {
 		assertDisabledOnCurrentJreIf(true);
 		assertCustomDisabledReasonIs("Disabled on every JRE");
 	}
-@for(var jre : jres)
+@for(var jre : supportedJres)
 	/**
 	 * @see DisabledOnJreIntegrationTests#jre${jre.getVersion()}()
 	 */
@@ -99,7 +99,7 @@ class DisabledOnJreConditionTests extends AbstractExecutionConditionTests {
 		assertDisabledOnCurrentJreIf(onJava${jre.getVersion()}());
 	}
 @endfor<%--
---%>@for(var jre : jres)
+--%>@for(var jre : supportedJres)
 	/**
 	 * @see DisabledOnJreIntegrationTests#version${jre.getVersion()}()
 	 */
diff --git a/jupiter-tests/src/templates/resources/test/org/junit/jupiter/api/condition/DisabledOnJreIntegrationTests.java.jte b/jupiter-tests/src/templates/resources/test/org/junit/jupiter/api/condition/DisabledOnJreIntegrationTests.java.jte
index 509b5d47fa48..429d9d3f90ef 100644
--- a/jupiter-tests/src/templates/resources/test/org/junit/jupiter/api/condition/DisabledOnJreIntegrationTests.java.jte
+++ b/jupiter-tests/src/templates/resources/test/org/junit/jupiter/api/condition/DisabledOnJreIntegrationTests.java.jte
@@ -1,8 +1,9 @@
 @import java.util.List
 @import junitbuild.generator.model.JRE
 
-@param List<JRE> jres
-@param List<JRE> jresSortedByStringValue
+@param List<JRE> allJres
+@param List<JRE> supportedJres
+@param List<JRE> supportedJresSortedByStringValue
 @param String licenseHeader
 ${licenseHeader}
 package org.junit.jupiter.api.condition;
@@ -10,12 +11,7 @@ package org.junit.jupiter.api.condition;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 import static org.junit.jupiter.api.Assertions.fail;
-@for(var jre : jresSortedByStringValue)<%--
---%>import static org.junit.jupiter.api.condition.JRE.JAVA_${jre.getVersion()};
-@endfor<%--
---%>import static org.junit.jupiter.api.condition.JRE.OTHER;
-import static org.junit.jupiter.api.condition.JRE.UNDEFINED;
-@for(var jre : jresSortedByStringValue)<%--
+@for(var jre : supportedJresSortedByStringValue)<%--
 --%>import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava${jre.getVersion()};
 @endfor<%--
 --%>import static org.junit.jupiter.api.condition.JavaVersionPredicates.onKnownVersion;
@@ -38,40 +34,41 @@ class DisabledOnJreIntegrationTests {
 
 	@Test
 	@Disabled("Only used in a unit test via reflection")
-	@DisabledOnJre({})
+	@DisabledOnJre
 	void missingVersionDeclaration() {
 	}
 
 	@Test
 	@Disabled("Only used in a unit test via reflection")
-	@DisabledOnJre(UNDEFINED)
+	@DisabledOnJre(JRE.UNDEFINED)
 	void jreUndefined() {
 	}
 
 	@Test
 	@Disabled("Only used in a unit test via reflection")
-	@DisabledOnJre(value = JAVA_17, versions = { 21, 7 })
+	@DisabledOnJre(value = JRE.JAVA_17, versions = { 21, 7 })
 	void version7() {
 	}
 
+	@SuppressWarnings("removal")
 	@Test
 	@DisabledOnJre(disabledReason = "Disabled on every JRE", value = { //
-@for(var jre : jres)<%--
---%>			JAVA_${jre.getVersion()}, //
+@for(var jre : allJres)<%--
+--%>			JRE.JAVA_${jre.getVersion()}, //
 @endfor<%--
---%>			OTHER //
+--%>			JRE.OTHER //
 	})
 	void disabledOnAllJavaVersions() {
 		fail("should be disabled");
 	}
-@for(var jre : jres)
+@for(var jre : supportedJres)
 	@Test
-	@DisabledOnJre(JAVA_${jre.getVersion()})
+	@DisabledOnJre(JRE.JAVA_${jre.getVersion()})
 	void jre${jre.getVersion()}() {
 		assertFalse(onJava${jre.getVersion()}());
 	}
 @endfor<%--
---%>@for(var jre : jres)
+--%>@for(var jre : supportedJres)
 	@Test
 	@DisabledOnJre(versions = ${jre.getVersion()})
 	void version${jre.getVersion()}() {
@@ -79,7 +76,7 @@ class DisabledOnJreIntegrationTests {
 	}
 @endfor
 	@Test
-	@DisabledOnJre(OTHER)
+	@DisabledOnJre(JRE.OTHER)
 	void other() {
 		assertTrue(onKnownVersion());
 	}
diff --git a/jupiter-tests/src/templates/resources/test/org/junit/jupiter/api/condition/EnabledOnJreConditionTests.java.jte b/jupiter-tests/src/templates/resources/test/org/junit/jupiter/api/condition/EnabledOnJreConditionTests.java.jte
index 9d6a1ee02021..7319b74ce364 100644
--- a/jupiter-tests/src/templates/resources/test/org/junit/jupiter/api/condition/EnabledOnJreConditionTests.java.jte
+++ b/jupiter-tests/src/templates/resources/test/org/junit/jupiter/api/condition/EnabledOnJreConditionTests.java.jte
@@ -1,14 +1,14 @@
 @import java.util.List
 @import junitbuild.generator.model.JRE
 
-@param List<JRE> jres
-@param List<JRE> jresSortedByStringValue
+@param List<JRE> supportedJres
+@param List<JRE> supportedJresSortedByStringValue
 @param String licenseHeader
 ${licenseHeader}
 package org.junit.jupiter.api.condition;
 
 import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
-@for(var jre : jresSortedByStringValue)<%--
+@for(var jre : supportedJresSortedByStringValue)<%--
 --%>import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava${jre.getVersion()};
 @endfor<%--
 --%>import static org.junit.jupiter.api.condition.JavaVersionPredicates.onKnownVersion;
@@ -88,7 +88,7 @@ class EnabledOnJreConditionTests extends AbstractExecutionConditionTests {
 		evaluateCondition();
 		assertEnabledOnCurrentJreIf(true);
 	}
-@for(var jre : jres)
+@for(var jre : supportedJres)
 	/**
 	 * @see EnabledOnJreIntegrationTests#jre${jre.getVersion()}()
 	 */
@@ -98,7 +98,7 @@ class EnabledOnJreConditionTests extends AbstractExecutionConditionTests {
 		assertEnabledOnCurrentJreIf(onJava${jre.getVersion()}());
 	}
 @endfor<%--
---%>@for(var jre : jres)
+--%>@for(var jre : supportedJres)
 	/**
 	 * @see EnabledOnJreIntegrationTests#version${jre.getVersion()}()
 	 */
diff --git a/jupiter-tests/src/templates/resources/test/org/junit/jupiter/api/condition/EnabledOnJreIntegrationTests.java.jte b/jupiter-tests/src/templates/resources/test/org/junit/jupiter/api/condition/EnabledOnJreIntegrationTests.java.jte
index 651345ea02b3..a1217d687b71 100644
--- a/jupiter-tests/src/templates/resources/test/org/junit/jupiter/api/condition/EnabledOnJreIntegrationTests.java.jte
+++ b/jupiter-tests/src/templates/resources/test/org/junit/jupiter/api/condition/EnabledOnJreIntegrationTests.java.jte
@@ -1,20 +1,16 @@
 @import java.util.List
 @import junitbuild.generator.model.JRE
 
-@param List<JRE> jres
-@param List<JRE> jresSortedByStringValue
+@param List<JRE> allJres
+@param List<JRE> supportedJres
+@param List<JRE> supportedJresSortedByStringValue
 @param String licenseHeader
 ${licenseHeader}
 package org.junit.jupiter.api.condition;
 
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertTrue;
-@for(var jre : jresSortedByStringValue)<%--
---%>import static org.junit.jupiter.api.condition.JRE.JAVA_${jre.getVersion()};
-@endfor<%--
---%>import static org.junit.jupiter.api.condition.JRE.OTHER;
-import static org.junit.jupiter.api.condition.JRE.UNDEFINED;
-@for(var jre : jresSortedByStringValue)<%--
+@for(var jre : supportedJresSortedByStringValue)<%--
 --%>import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava${jre.getVersion()};
 @endfor<%--
 --%>import static org.junit.jupiter.api.condition.JavaVersionPredicates.onKnownVersion;
@@ -37,39 +33,40 @@ class EnabledOnJreIntegrationTests {
 
 	@Test
 	@Disabled("Only used in a unit test via reflection")
-	@EnabledOnJre({})
+	@EnabledOnJre
 	void missingVersionDeclaration() {
 	}
 
 	@Test
 	@Disabled("Only used in a unit test via reflection")
-	@EnabledOnJre(UNDEFINED)
+	@EnabledOnJre(JRE.UNDEFINED)
 	void jreUndefined() {
 	}
 
 	@Test
 	@Disabled("Only used in a unit test via reflection")
-	@EnabledOnJre(value = JAVA_17, versions = { 21, 7 })
+	@EnabledOnJre(value = JRE.JAVA_17, versions = { 21, 7 })
 	void version7() {
 	}
 
+	@SuppressWarnings("removal")
 	@Test
 	@EnabledOnJre({ //
-@for(var jre : jres)<%--
---%>			JAVA_${jre.getVersion()}, //
+@for(var jre : allJres)<%--
+--%>			JRE.JAVA_${jre.getVersion()}, //
 @endfor<%--
---%>			OTHER //
+--%>			JRE.OTHER //
 	})
 	void enabledOnAllJavaVersions() {
 	}
-@for(var jre : jres)
+@for(var jre : supportedJres)
 	@Test
-	@EnabledOnJre(JAVA_${jre.getVersion()})
+	@EnabledOnJre(JRE.JAVA_${jre.getVersion()})
 	void jre${jre.getVersion()}() {
 		assertTrue(onJava${jre.getVersion()}());
 	}
 @endfor<%--
---%>@for(var jre : jres)
+--%>@for(var jre : supportedJres)
 	@Test
 	@EnabledOnJre(versions = ${jre.getVersion()})
 	void version${jre.getVersion()}() {
@@ -77,7 +74,7 @@ class EnabledOnJreIntegrationTests {
 	}
 @endfor
 	@Test
-	@EnabledOnJre(value = OTHER, disabledReason = "Disabled on almost every JRE")
+	@EnabledOnJre(value = JRE.OTHER, disabledReason = "Disabled on almost every JRE")
 	void other() {
 		assertFalse(onKnownVersion());
 	}
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/api/AssertAllAssertionsTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/api/AssertAllAssertionsTests.java
index dac3a628fb17..08fdcdd65e1c 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/api/AssertAllAssertionsTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/api/AssertAllAssertionsTests.java
@@ -19,7 +19,6 @@
 import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
-import static org.junit.jupiter.api.Assertions.fail;
 
 import java.io.IOException;
 import java.util.Collection;
@@ -38,21 +37,25 @@
  */
 class AssertAllAssertionsTests {
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void assertAllWithNullExecutableArray() {
 		assertPrecondition("executables array must not be null or empty", () -> assertAll((Executable[]) null));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void assertAllWithNullExecutableCollection() {
 		assertPrecondition("executables collection must not be null", () -> assertAll((Collection<Executable>) null));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void assertAllWithNullExecutableStream() {
 		assertPrecondition("executables stream must not be null", () -> assertAll((Stream<Executable>) null));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void assertAllWithNullInExecutableArray() {
 		assertPrecondition("individual executables must not be null", () -> assertAll((Executable) null));
@@ -63,6 +66,7 @@ void assertAllWithNullInExecutableCollection() {
 		assertPrecondition("individual executables must not be null", () -> assertAll(asList((Executable) null)));
 	}
 
+	@SuppressWarnings("DataFlowIssue")
 	@Test
 	void assertAllWithNullInExecutableStream() {
 		assertPrecondition("individual executables must not be null", () -> assertAll(Stream.of((Executable) null)));
@@ -103,8 +107,8 @@ void assertAllWithExecutablesThatThrowAssertionErrors() {
 		// @formatter:off
 		MultipleFailuresError multipleFailuresError = assertThrows(MultipleFailuresError.class, () ->
 			assertAll(
-				() -> fail(),
-				() -> fail()
+				Assertions::fail,
+				Assertions::fail
 			)
 		);
 		// @formatter:on
@@ -117,8 +121,8 @@ void assertAllWithCollectionOfExecutablesThatThrowAssertionErrors() {
 		// @formatter:off
 		MultipleFailuresError multipleFailuresError = assertThrows(MultipleFailuresError.class, () ->
 			assertAll(asList(
-				() -> fail(),
-				() -> fail()
+				Assertions::fail,
+				Assertions::fail
 			))
 		);
 		// @formatter:on
@@ -131,8 +135,8 @@ void assertAllWithStreamOfExecutablesThatThrowAssertionErrors() {
 		// @formatter:off
 		MultipleFailuresError multipleFailuresError = assertThrows(MultipleFailuresError.class, () ->
 			assertAll(Stream.of(
-				() -> fail(),
-				() -> fail()
+				Assertions::fail,
+				Assertions::fail
 			))
 		);
 		// @formatter:on
@@ -208,7 +212,7 @@ static void assertExpectedExceptionTypes(MultipleFailuresError multipleFailuresE
 		assertEquals(exceptionTypes.length, failures.size(), "number of failures");
 
 		// Verify that exceptions are also present as suppressed exceptions.
-		// https://github.com/junit-team/junit5/issues/1602
+		// https://github.com/junit-team/junit-framework/issues/1602
 		Throwable[] suppressed = multipleFailuresError.getSuppressed();
 		assertEquals(exceptionTypes.length, suppressed.length, "number of suppressed exceptions");
 
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/api/AssertDoesNotThrowAssertionsTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/api/AssertDoesNotThrowAssertionsTests.java
index 260be584308a..90eafaf27f87 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/api/AssertDoesNotThrowAssertionsTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/api/AssertDoesNotThrowAssertionsTests.java
@@ -36,9 +36,7 @@ class AssertDoesNotThrowAssertionsTests {
 
 	@Test
 	void assertDoesNotThrowWithMethodReferenceForNonVoidReturnType() {
-		FutureTask<String> future = new FutureTask<>(() -> {
-			return "foo";
-		});
+		FutureTask<String> future = new FutureTask<>(() -> "foo");
 		future.run();
 
 		String result;
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/api/AssertInstanceOfAssertionsTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/api/AssertInstanceOfAssertionsTests.java
index b5bfd62438eb..1e3fa189b858 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/api/AssertInstanceOfAssertionsTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/api/AssertInstanceOfAssertionsTests.java
@@ -17,6 +17,7 @@
 
 import java.io.IOException;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.function.Executable;
 import org.opentest4j.AssertionFailedError;
 
@@ -91,9 +92,9 @@ private <T> void assertInstanceOfSucceeds(Class<T> expectedType, Object actualVa
 		assertSame(res, actualValue);
 	}
 
-	private void assertInstanceOfFails(Class<?> expectedType, Object actualValue, String unexpectedSort) {
+	private void assertInstanceOfFails(Class<?> expectedType, @Nullable Object actualValue, String unexpectedSort) {
 		String valueType = actualValue == null ? "null" : actualValue.getClass().getCanonicalName();
-		String expectedMessage = String.format("Unexpected %s, expected: <%s> but was: <%s>", unexpectedSort,
+		String expectedMessage = "Unexpected %s, expected: <%s> but was: <%s>".formatted(unexpectedSort,
 			expectedType.getCanonicalName(), valueType);
 
 		assertThrowsWithMessage(expectedMessage, () -> assertInstanceOf(expectedType, actualValue));
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/api/AssertIterableEqualsAssertionsTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/api/AssertIterableEqualsAssertionsTests.java
index e09823ddd89d..ca53fc023c3d 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/api/AssertIterableEqualsAssertionsTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/api/AssertIterableEqualsAssertionsTests.java
@@ -445,7 +445,7 @@ void assertIterableEqualsDifferentNestedIterablesAndMessageSupplier() {
 	}
 
 	@Test
-	// https://github.com/junit-team/junit5/issues/2157
+	// https://github.com/junit-team/junit-framework/issues/2157
 	void assertIterableEqualsWithListOfPath() {
 		var expected = listOf(Path.of("1"));
 		var actual = listOf(Path.of("1"));
@@ -462,7 +462,7 @@ void assertIterableEqualsThrowsStackOverflowErrorForInterlockedRecursiveStructur
 	}
 
 	@Test
-	// https://github.com/junit-team/junit5/issues/2915
+	// https://github.com/junit-team/junit-framework/issues/2915
 	void assertIterableEqualsWithDifferentListOfPath() {
 		try {
 			var expected = listOf(Path.of("1").resolve("2"));
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/api/AssertLinesMatchAssertionsTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/api/AssertLinesMatchAssertionsTests.java
index 273b75d11276..4bc5f0c57765 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/api/AssertLinesMatchAssertionsTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/api/AssertLinesMatchAssertionsTests.java
@@ -27,10 +27,10 @@
 import java.util.List;
 import java.util.Random;
 import java.util.function.Supplier;
-import java.util.stream.Collectors;
 import java.util.stream.IntStream;
 import java.util.stream.Stream;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.commons.PreconditionViolationException;
 import org.opentest4j.AssertionFailedError;
 
@@ -95,7 +95,7 @@ void assertLinesMatchUsingFastForwardMarkerWithLimit3() {
 	}
 
 	@Test
-	@SuppressWarnings({ "unchecked", "rawtypes" })
+	@SuppressWarnings({ "unchecked", "rawtypes", "DataFlowIssue", "NullAway" })
 	void assertLinesMatchWithNullFails() {
 		assertThrows(PreconditionViolationException.class, () -> assertLinesMatch(null, (List) null));
 		assertThrows(PreconditionViolationException.class, () -> assertLinesMatch(null, Collections.emptyList()));
@@ -242,8 +242,8 @@ void assertLinesMatchMatches() {
 
 	@Test
 	void largeListsThatDoNotMatchAreTruncated() {
-		var expected = IntStream.range(1, 999).boxed().map(Object::toString).collect(Collectors.toList());
-		var actual = IntStream.range(0, 1000).boxed().map(Object::toString).collect(Collectors.toList());
+		var expected = IntStream.range(1, 999).boxed().map(Object::toString).toList();
+		var actual = IntStream.range(0, 1000).boxed().map(Object::toString).toList();
 		var error = assertThrows(AssertionFailedError.class,
 			() -> assertLinesMatch(expected, actual, "custom message"));
 		var expectedMessage = String.join(System.lineSeparator(), List.of( //
@@ -274,7 +274,7 @@ void simpleStringMessage() {
 		@Test
 		void stringSupplierWithMultiLineMessage() {
 			var message = "XXX\nYYY";
-			Supplier<String> supplier = () -> message;
+			Supplier<@Nullable String> supplier = () -> message;
 			var expected = List.of("a", "b", "c");
 			var actual = List.of("a", "d", "c");
 			var error = assertThrows(AssertionFailedError.class, () -> assertLinesMatch(expected, actual, supplier));
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/api/AssertNullAssertionsTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/api/AssertNullAssertionsTests.java
index e960d250a993..bab28bfee9e4 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/api/AssertNullAssertionsTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/api/AssertNullAssertionsTests.java
@@ -18,6 +18,8 @@
 
 import java.util.function.Supplier;
 
+import org.jspecify.annotations.NullUnmarked;
+import org.jspecify.annotations.Nullable;
 import org.opentest4j.AssertionFailedError;
 
 /**
@@ -63,7 +65,8 @@ void assertNullWithNonNullObjectWithNullStringReturnedFromToStringAndMessageSupp
 	}
 
 	@SuppressWarnings("unused")
-	private void assertNullWithNonNullObjectWithNullStringReturnedFromToString(Supplier<String> messageSupplier) {
+	private void assertNullWithNonNullObjectWithNullStringReturnedFromToString(
+			@Nullable Supplier<@Nullable String> messageSupplier) {
 		String actual = "null";
 		try {
 			if (messageSupplier == null) {
@@ -94,7 +97,8 @@ void assertNullWithNonNullObjectWithNullReferenceReturnedFromToStringAndMessageS
 	}
 
 	@SuppressWarnings("unused")
-	private void assertNullWithNonNullObjectWithNullReferenceReturnedFromToString(Supplier<String> messageSupplier) {
+	private void assertNullWithNonNullObjectWithNullReferenceReturnedFromToString(
+			@Nullable Supplier<@Nullable String> messageSupplier) {
 		Object actual = new NullToString();
 		try {
 			if (messageSupplier == null) {
@@ -141,6 +145,7 @@ void assertNullWithNonNullObjectAndMessageSupplier() {
 		}
 	}
 
+	@NullUnmarked
 	private static class NullToString {
 
 		@Override
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/api/AssertThrowsAssertionsTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/api/AssertThrowsAssertionsTests.java
index c1f5a003cbc4..9f9e3edf4131 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/api/AssertThrowsAssertionsTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/api/AssertThrowsAssertionsTests.java
@@ -47,6 +47,7 @@ void assertThrowsWithMethodReferenceForNonVoidReturnType() {
 		future.run();
 
 		ExecutionException exception = assertThrows(ExecutionException.class, future::get);
+		assertNotNull(exception.getCause());
 		assertEquals("boom", exception.getCause().getMessage());
 	}
 
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/api/AssertThrowsExactlyAssertionsTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/api/AssertThrowsExactlyAssertionsTests.java
index d167f4f08e43..ea683191e03e 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/api/AssertThrowsExactlyAssertionsTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/api/AssertThrowsExactlyAssertionsTests.java
@@ -87,6 +87,7 @@ void assertThrowsWithMethodReferenceForNonVoidReturnType() {
 		future.run();
 
 		ExecutionException exception = assertThrowsExactly(ExecutionException.class, future::get);
+		assertNotNull(exception.getCause());
 		assertEquals("boom", exception.getCause().getMessage());
 	}
 
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/api/AssertTimeoutPreemptivelyAssertionsTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/api/AssertTimeoutPreemptivelyAssertionsTests.java
index 303bbb3124fe..b7fb03847676 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/api/AssertTimeoutPreemptivelyAssertionsTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/api/AssertTimeoutPreemptivelyAssertionsTests.java
@@ -18,7 +18,6 @@
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTimeoutPreemptively;
-import static org.junit.jupiter.api.Assertions.assertTrue;
 import static org.junit.jupiter.api.Assertions.fail;
 import static org.junit.jupiter.api.condition.OS.WINDOWS;
 
@@ -28,6 +27,7 @@
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicReference;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.function.Executable;
 import org.junit.platform.commons.util.ExceptionUtils;
 import org.opentest4j.AssertionFailedError;
@@ -81,7 +81,7 @@ void assertTimeoutPreemptivelyForExecutableThatCompletesAfterTheTimeout() {
 			() -> assertTimeoutPreemptively(PREEMPTIVE_TIMEOUT, this::waitForInterrupt));
 		assertMessageEquals(error, "execution timed out after " + PREEMPTIVE_TIMEOUT.toMillis() + " ms");
 		assertMessageStartsWith(error.getCause(), "Execution timed out in ");
-		assertStackTraceContains(error.getCause().getStackTrace(), "CountDownLatch", "await");
+		assertStackTraceContains(error.getCause(), "CountDownLatch", "await");
 	}
 
 	@Test
@@ -91,7 +91,7 @@ void assertTimeoutPreemptivelyWithMessageForExecutableThatCompletesAfterTheTimeo
 		assertMessageEquals(error,
 			"Tempus Fugit ==> execution timed out after " + PREEMPTIVE_TIMEOUT.toMillis() + " ms");
 		assertMessageStartsWith(error.getCause(), "Execution timed out in ");
-		assertStackTraceContains(error.getCause().getStackTrace(), "CountDownLatch", "await");
+		assertStackTraceContains(error.getCause(), "CountDownLatch", "await");
 	}
 
 	@Test
@@ -102,7 +102,7 @@ void assertTimeoutPreemptivelyWithMessageSupplierForExecutableThatCompletesAfter
 		assertMessageEquals(error,
 			"Tempus Fugit ==> execution timed out after " + PREEMPTIVE_TIMEOUT.toMillis() + " ms");
 		assertMessageStartsWith(error.getCause(), "Execution timed out in ");
-		assertStackTraceContains(error.getCause().getStackTrace(), "CountDownLatch", "await");
+		assertStackTraceContains(error.getCause(), "CountDownLatch", "await");
 	}
 
 	@Test
@@ -156,7 +156,7 @@ void assertTimeoutPreemptivelyForSupplierThatCompletesAfterTheTimeout() {
 
 		assertMessageEquals(error, "execution timed out after " + PREEMPTIVE_TIMEOUT.toMillis() + " ms");
 		assertMessageStartsWith(error.getCause(), "Execution timed out in ");
-		assertStackTraceContains(error.getCause().getStackTrace(), "CountDownLatch", "await");
+		assertStackTraceContains(error.getCause(), "CountDownLatch", "await");
 	}
 
 	@Test
@@ -171,7 +171,7 @@ void assertTimeoutPreemptivelyWithMessageForSupplierThatCompletesAfterTheTimeout
 		assertMessageEquals(error,
 			"Tempus Fugit ==> execution timed out after " + PREEMPTIVE_TIMEOUT.toMillis() + " ms");
 		assertMessageStartsWith(error.getCause(), "Execution timed out in ");
-		assertStackTraceContains(error.getCause().getStackTrace(), "CountDownLatch", "await");
+		assertStackTraceContains(error.getCause(), "CountDownLatch", "await");
 	}
 
 	@Test
@@ -186,15 +186,16 @@ void assertTimeoutPreemptivelyWithMessageSupplierForSupplierThatCompletesAfterTh
 		assertMessageEquals(error,
 			"Tempus Fugit ==> execution timed out after " + PREEMPTIVE_TIMEOUT.toMillis() + " ms");
 		assertMessageStartsWith(error.getCause(), "Execution timed out in ");
-		assertStackTraceContains(error.getCause().getStackTrace(), "CountDownLatch", "await");
+		assertStackTraceContains(error.getCause(), "CountDownLatch", "await");
 	}
 
 	@Test
 	void assertTimeoutPreemptivelyUsesThreadsWithSpecificNamePrefix() {
 		AtomicReference<String> threadName = new AtomicReference<>("");
 		assertTimeoutPreemptively(ofMillis(1000), () -> threadName.set(Thread.currentThread().getName()));
-		assertTrue(threadName.get().startsWith("junit-timeout-thread-"),
-			"Thread name does not match the expected prefix");
+		assertThat(threadName.get()) //
+				.withFailMessage("Thread name does not match the expected prefix") //
+				.startsWith("junit-timeout-thread-");
 	}
 
 	@Test
@@ -244,8 +245,9 @@ private void waitForInterrupt() {
 	/**
 	 * Assert the given stack trace elements contain an element with the given class name and method name.
 	 */
-	private static void assertStackTraceContains(StackTraceElement[] stackTrace, String className, String methodName) {
-		assertThat(stackTrace).anySatisfy(element -> {
+	private static void assertStackTraceContains(@Nullable Throwable throwable, String className, String methodName) {
+		assertThat(throwable).isNotNull();
+		assertThat(throwable.getStackTrace()).anySatisfy(element -> {
 			assertThat(element.getClassName()).endsWith(className);
 			assertThat(element.getMethodName()).isEqualTo(methodName);
 		});
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/api/AssertionTestUtils.java b/jupiter-tests/src/test/java/org/junit/jupiter/api/AssertionTestUtils.java
index d961acd53496..a5bb7c0886a0 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/api/AssertionTestUtils.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/api/AssertionTestUtils.java
@@ -13,6 +13,8 @@
 import java.io.Serializable;
 import java.util.Objects;
 
+import org.apache.groovy.parser.antlr4.util.StringUtils;
+import org.jspecify.annotations.Nullable;
 import org.opentest4j.AssertionFailedError;
 import org.opentest4j.ValueWrapper;
 
@@ -27,7 +29,7 @@ static void expectAssertionFailedError() {
 	}
 
 	static void assertEmptyMessage(Throwable ex) throws AssertionError {
-		if (!ex.getMessage().isEmpty()) {
+		if (!StringUtils.isEmpty(ex.getMessage())) {
 			throw new AssertionError("Exception message should be empty, but was [" + ex.getMessage() + "].");
 		}
 	}
@@ -39,35 +41,41 @@ static void assertMessageEquals(Throwable ex, String msg) throws AssertionError
 	}
 
 	static void assertMessageMatches(Throwable ex, String regex) throws AssertionError {
-		if (!ex.getMessage().matches(regex)) {
+		if (ex.getMessage() == null || !ex.getMessage().matches(regex)) {
 			throw new AssertionError("Exception message should match regular expression [" + regex + "], but was ["
 					+ ex.getMessage() + "].");
 		}
 	}
 
-	static void assertMessageStartsWith(Throwable ex, String msg) throws AssertionError {
-		if (!ex.getMessage().startsWith(msg)) {
+	static void assertMessageStartsWith(@Nullable Throwable ex, String msg) throws AssertionError {
+		if (ex == null) {
+			throw new AssertionError("Cause should not have been null");
+		}
+		if (ex.getMessage() == null || !ex.getMessage().startsWith(msg)) {
 			throw new AssertionError(
 				"Exception message should start with [" + msg + "], but was [" + ex.getMessage() + "].");
 		}
 	}
 
 	static void assertMessageEndsWith(Throwable ex, String msg) throws AssertionError {
-		if (!ex.getMessage().endsWith(msg)) {
+		if (ex.getMessage() == null || !ex.getMessage().endsWith(msg)) {
 			throw new AssertionError(
 				"Exception message should end with [" + msg + "], but was [" + ex.getMessage() + "].");
 		}
 	}
 
-	static void assertMessageContains(Throwable ex, String msg) throws AssertionError {
-		if (!ex.getMessage().contains(msg)) {
+	static void assertMessageContains(@Nullable Throwable ex, String msg) throws AssertionError {
+		if (ex == null) {
+			throw new AssertionError("Cause should not have been null");
+		}
+		if (ex.getMessage() == null || !ex.getMessage().contains(msg)) {
 			throw new AssertionError(
 				"Exception message should contain [" + msg + "], but was [" + ex.getMessage() + "].");
 		}
 	}
 
-	static void assertExpectedAndActualValues(AssertionFailedError ex, Object expected, Object actual)
-			throws AssertionError {
+	static void assertExpectedAndActualValues(AssertionFailedError ex, @Nullable Object expected,
+			@Nullable Object actual) throws AssertionError {
 		if (!wrapsEqualValue(ex.getExpected(), expected)) {
 			throw new AssertionError("Expected value in AssertionFailedError should equal ["
 					+ ValueWrapper.create(expected) + "], but was [" + ex.getExpected() + "].");
@@ -78,7 +86,7 @@ static void assertExpectedAndActualValues(AssertionFailedError ex, Object expect
 		}
 	}
 
-	static boolean wrapsEqualValue(ValueWrapper wrapper, Object value) {
+	static boolean wrapsEqualValue(ValueWrapper wrapper, @Nullable Object value) {
 		if (value == null || value instanceof Serializable) {
 			return Objects.equals(value, wrapper.getValue());
 		}
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/api/AssumptionsTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/api/AssumptionsTests.java
index 7aa35c56b634..499704bf6604 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/api/AssumptionsTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/api/AssumptionsTests.java
@@ -23,6 +23,7 @@
 import java.util.List;
 import java.util.Objects;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.function.Executable;
 import org.opentest4j.TestAbortedException;
 
@@ -216,11 +217,11 @@ void abortWithStringSupplier() {
 
 	// -------------------------------------------------------------------
 
-	private static void assertAssumptionFailure(String msg, Executable executable) {
+	private static void assertAssumptionFailure(@Nullable String msg, Executable executable) {
 		assertTestAbortedException(msg == null ? "Assumption failed" : "Assumption failed: " + msg, executable);
 	}
 
-	private static void assertTestAbortedException(String expectedMessage, Executable executable) {
+	private static void assertTestAbortedException(@Nullable String expectedMessage, Executable executable) {
 		try {
 			executable.execute();
 			expectTestAbortedException();
@@ -235,7 +236,7 @@ private static void expectTestAbortedException() {
 		throw new AssertionError("Should have thrown a " + TestAbortedException.class.getName());
 	}
 
-	private static void assertMessageEquals(Throwable t, String expectedMessage) throws AssertionError {
+	private static void assertMessageEquals(Throwable t, @Nullable String expectedMessage) throws AssertionError {
 		if (!Objects.equals(expectedMessage, t.getMessage())) {
 			throw new AssertionError("Message in TestAbortedException should be [" + expectedMessage + "], but was ["
 					+ t.getMessage() + "].");
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/api/DisplayNameGenerationTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/api/DisplayNameGenerationTests.java
index 323470e59556..bf356db5d3ca 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/api/DisplayNameGenerationTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/api/DisplayNameGenerationTests.java
@@ -397,8 +397,6 @@ static class UnderscoreStyleInheritedFromSuperClassTestCase extends UnderscoreSt
 	@DisplayNameGeneration(DisplayNameGenerator.ReplaceUnderscores.class)
 	static class StackTestCase {
 
-		Stack<Object> stack;
-
 		@Test
 		void is_instantiated_using_its_noarg_constructor() {
 			new Stack<>();
@@ -407,6 +405,8 @@ void is_instantiated_using_its_noarg_constructor() {
 		@Nested
 		class A_new_stack {
 
+			Stack<Object> stack;
+
 			@BeforeEach
 			void createNewStack() {
 				stack = new Stack<>();
@@ -464,8 +464,6 @@ void peek_returns_that_element_without_removing_it_from_the_stack() {
 	@IndicativeSentencesGeneration(generator = DisplayNameGenerator.ReplaceUnderscores.class)
 	static class IndicativeGeneratorTestCase {
 
-		Stack<Object> stack;
-
 		@Test
 		void is_instantiated_with_its_constructor() {
 			new Stack<>();
@@ -474,6 +472,8 @@ void is_instantiated_with_its_constructor() {
 		@Nested
 		class when_new {
 
+			Stack<Object> stack;
+
 			@BeforeEach
 			void create_with_new_stack() {
 				stack = new Stack<>();
@@ -509,8 +509,6 @@ void is_no_longer_empty() {
 	@IndicativeSentencesGeneration(separator = " >> ", generator = DisplayNameGenerator.ReplaceUnderscores.class)
 	static class IndicativeGeneratorWithCustomSeparatorTestCase {
 
-		Stack<Object> stack;
-
 		@Test
 		void is_instantiated_with_its_constructor() {
 			new Stack<>();
@@ -519,6 +517,8 @@ void is_instantiated_with_its_constructor() {
 		@Nested
 		class when_new {
 
+			Stack<Object> stack;
+
 			@BeforeEach
 			void create_with_new_stack() {
 				stack = new Stack<>();
@@ -554,8 +554,6 @@ void is_no_longer_empty() {
 	@IndicativeSentencesGeneration
 	static class IndicativeGeneratorWithCustomSentenceFragmentsTestCase {
 
-		Stack<Object> stack;
-
 		@SentenceFragment("is instantiated with its constructor")
 		@Test
 		void instantiateViaConstructor() {
@@ -566,6 +564,8 @@ void instantiateViaConstructor() {
 		@Nested
 		class NewStackTestCase {
 
+			Stack<Object> stack;
+
 			@BeforeEach
 			void createNewStack() {
 				stack = new Stack<>();
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/api/DynamicTestTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/api/DynamicTestTests.java
index 073678ad4088..409940b6212d 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/api/DynamicTestTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/api/DynamicTestTests.java
@@ -24,9 +24,9 @@
 import java.util.List;
 import java.util.Locale;
 import java.util.function.Function;
-import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.function.Executable;
 import org.junit.jupiter.api.function.ThrowingConsumer;
 import org.junit.platform.commons.PreconditionViolationException;
@@ -41,8 +41,9 @@ class DynamicTestTests {
 	private static final Executable nix = () -> {
 	};
 
-	private final List<String> assertedValues = new ArrayList<>();
+	private final List<@Nullable String> assertedValues = new ArrayList<>();
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void streamFromStreamPreconditions() {
 		ThrowingConsumer<Object> testExecutor = input -> {
@@ -57,6 +58,7 @@ void streamFromStreamPreconditions() {
 			() -> DynamicTest.stream(Stream.empty(), displayNameGenerator, null));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void streamFromIteratorPreconditions() {
 		ThrowingConsumer<Object> testExecutor = input -> {
@@ -71,6 +73,7 @@ void streamFromIteratorPreconditions() {
 			() -> DynamicTest.stream(emptyIterator(), displayNameGenerator, null));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void streamFromStreamWithNamesPreconditions() {
 		ThrowingConsumer<Object> testExecutor = input -> {
@@ -81,6 +84,7 @@ void streamFromStreamWithNamesPreconditions() {
 		assertThrows(PreconditionViolationException.class, () -> DynamicTest.stream(Stream.empty(), null));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void streamFromIteratorWithNamesPreconditions() {
 		ThrowingConsumer<Object> testExecutor = input -> {
@@ -91,12 +95,14 @@ void streamFromIteratorWithNamesPreconditions() {
 		assertThrows(PreconditionViolationException.class, () -> DynamicTest.stream(emptyIterator(), null));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void streamFromStreamWithNamedExecutablesPreconditions() {
 		assertThrows(PreconditionViolationException.class,
 			() -> DynamicTest.stream((Stream<DummyNamedExecutableForTests>) null));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void streamFromIteratorWithNamedExecutablesPreconditions() {
 		assertThrows(PreconditionViolationException.class,
@@ -153,7 +159,7 @@ void streamFromIteratorWithNamedExecutables() throws Throwable {
 	}
 
 	private void assertStream(Stream<DynamicTest> stream) throws Throwable {
-		List<DynamicTest> dynamicTests = stream.collect(Collectors.toList());
+		List<DynamicTest> dynamicTests = stream.toList();
 
 		assertThat(dynamicTests).extracting(DynamicTest::getDisplayName).containsExactly("FOO", "BAR", "BAZ");
 
@@ -170,7 +176,7 @@ private void assertStream(Stream<DynamicTest> stream) throws Throwable {
 		assertThat(assertedValues).containsExactly("foo", "bar");
 	}
 
-	private void throwingConsumer(String str) throws Throwable {
+	private void throwingConsumer(@Nullable String str) throws Throwable {
 		if ("baz".equals(str)) {
 			throw new Throwable("Baz!");
 		}
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/api/FailAssertionsTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/api/FailAssertionsTests.java
index d549bbbed364..fff673f1bd56 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/api/FailAssertionsTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/api/FailAssertionsTests.java
@@ -20,6 +20,7 @@
 import java.util.function.Supplier;
 import java.util.stream.Stream;
 
+import org.jspecify.annotations.Nullable;
 import org.opentest4j.AssertionFailedError;
 
 /**
@@ -73,10 +74,11 @@ void failWithNullString() {
 		}
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void failWithNullMessageSupplier() {
 		try {
-			fail((Supplier<String>) null);
+			fail((Supplier<@Nullable String>) null);
 			expectAssertionFailedError();
 		}
 		catch (AssertionFailedError ex) {
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/api/IterableFactory.java b/jupiter-tests/src/test/java/org/junit/jupiter/api/IterableFactory.java
index 0dcb9c312037..ae363fe49c04 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/api/IterableFactory.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/api/IterableFactory.java
@@ -15,13 +15,16 @@
 import java.util.List;
 import java.util.Set;
 
+import org.jspecify.annotations.Nullable;
+
 final class IterableFactory {
 
-	static List<Object> listOf(Object... objects) {
+	@SuppressWarnings("NullableProblems")
+	static List<Object> listOf(@Nullable Object... objects) {
 		return Arrays.asList(objects);
 	}
 
-	static Set<Object> setOf(Object... objects) {
+	static Set<Object> setOf(@Nullable Object... objects) {
 		return new LinkedHashSet<>(listOf(objects));
 	}
 
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/api/condition/AbstractExecutionConditionTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/api/condition/AbstractExecutionConditionTests.java
index bff8050468de..9345aec1591d 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/api/condition/AbstractExecutionConditionTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/api/condition/AbstractExecutionConditionTests.java
@@ -12,6 +12,7 @@
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 import static org.junit.platform.commons.support.HierarchyTraversalMode.TOP_DOWN;
 import static org.junit.platform.commons.support.ReflectionSupport.findMethod;
@@ -27,6 +28,7 @@
 import java.util.Optional;
 import java.util.function.Predicate;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.BeforeAll;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
@@ -53,7 +55,7 @@ abstract class AbstractExecutionConditionTests {
 
 	private final ExtensionContext context = mock();
 
-	private ConditionEvaluationResult result;
+	private @Nullable ConditionEvaluationResult result;
 
 	@BeforeAll
 	void ensureAllTestMethodsAreCovered() {
@@ -84,18 +86,22 @@ protected void evaluateCondition() {
 	}
 
 	protected void assertEnabled() {
+		assertNotNull(this.result);
 		assertFalse(this.result.isDisabled(), "Should be enabled");
 	}
 
 	protected void assertDisabled() {
+		assertNotNull(this.result);
 		assertTrue(this.result.isDisabled(), "Should be disabled");
 	}
 
 	protected void assertReasonContains(String text) {
+		assertNotNull(this.result);
 		assertThat(this.result.getReason()).hasValueSatisfying(reason -> assertThat(reason).contains(text));
 	}
 
 	protected void assertCustomDisabledReasonIs(String text) {
+		assertNotNull(this.result);
 		if (this.result.isDisabled()) {
 			assertThat(this.result.getReason()).hasValueSatisfying(
 				reason -> assertThat(reason).contains(" ==> " + text));
@@ -103,11 +109,11 @@ protected void assertCustomDisabledReasonIs(String text) {
 	}
 
 	private Optional<AnnotatedElement> method(TestInfo testInfo) {
-		return method(getTestClass(), testInfo.getTestMethod().get().getName());
+		return method(getTestClass(), testInfo.getTestMethod().orElseThrow().getName());
 	}
 
 	private Optional<AnnotatedElement> method(Class<?> testClass, String methodName) {
-		return Optional.of(findMethod(testClass, methodName).get());
+		return Optional.of(findMethod(testClass, methodName).orElseThrow());
 	}
 
 }
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/api/condition/DisabledForJreRangeConditionTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/api/condition/DisabledForJreRangeConditionTests.java
index 8703958019ed..db7a64095fd8 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/api/condition/DisabledForJreRangeConditionTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/api/condition/DisabledForJreRangeConditionTests.java
@@ -11,18 +11,9 @@
 package org.junit.jupiter.api.condition;
 
 import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
-import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava10;
-import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava11;
-import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava12;
-import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava13;
-import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava14;
-import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava15;
-import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava16;
 import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava17;
 import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava18;
 import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava19;
-import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava8;
-import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava9;
 import static org.junit.jupiter.api.condition.JavaVersionPredicates.onKnownVersion;
 
 import org.junit.jupiter.api.Test;
@@ -89,18 +80,18 @@ void effectiveVersionDefaultValues() {
 	}
 
 	/**
-	 * @see DisabledForJreRangeIntegrationTests#min8()
+	 * @see DisabledForJreRangeIntegrationTests#min17()
 	 */
 	@Test
-	void min8() {
+	void min17() {
 		defaultValues();
 	}
 
 	/**
-	 * @see DisabledForJreRangeIntegrationTests#minVersion8()
+	 * @see DisabledForJreRangeIntegrationTests#minVersion17()
 	 */
 	@Test
-	void minVersion8() {
+	void minVersion17() {
 		defaultValues();
 	}
 
@@ -131,13 +122,14 @@ void minVersion7() {
 	}
 
 	/**
-	 * @see DisabledForJreRangeIntegrationTests#maxVersion7()
+	 * @see DisabledForJreRangeIntegrationTests#maxVersion16()
 	 */
 	@Test
-	void maxVersion7() {
+	void maxVersion16() {
 		assertThatExceptionOfType(PreconditionViolationException.class)//
 				.isThrownBy(this::evaluateCondition)//
-				.withMessage("@DisabledForJreRange's maxVersion [7] must be greater than or equal to 8");
+				.withMessage(
+					"@DisabledForJreRange's minimum value [17] must be less than or equal to its maximum value [16]");
 	}
 
 	/**
@@ -170,7 +162,7 @@ void minGreaterThanMax() {
 		assertThatExceptionOfType(PreconditionViolationException.class)//
 				.isThrownBy(this::evaluateCondition)//
 				.withMessage(
-					"@DisabledForJreRange's minimum value [21] must be less than or equal to its maximum value [11]");
+					"@DisabledForJreRange's minimum value [21] must be less than or equal to its maximum value [17]");
 	}
 
 	/**
@@ -220,8 +212,7 @@ void minVersion18() {
 	@Test
 	void max18() {
 		evaluateCondition();
-		assertDisabledOnCurrentJreIf(onJava8() || onJava9() || onJava10() || onJava11() || onJava12() || onJava13()
-				|| onJava14() || onJava15() || onJava16() || onJava17() || onJava18());
+		assertDisabledOnCurrentJreIf(onJava17() || onJava18());
 	}
 
 	/**
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/api/condition/DisabledForJreRangeIntegrationTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/api/condition/DisabledForJreRangeIntegrationTests.java
index 7d043196079f..73e974b600a8 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/api/condition/DisabledForJreRangeIntegrationTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/api/condition/DisabledForJreRangeIntegrationTests.java
@@ -13,25 +13,14 @@
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 import static org.junit.jupiter.api.Assertions.fail;
-import static org.junit.jupiter.api.condition.JRE.JAVA_11;
 import static org.junit.jupiter.api.condition.JRE.JAVA_17;
 import static org.junit.jupiter.api.condition.JRE.JAVA_18;
 import static org.junit.jupiter.api.condition.JRE.JAVA_19;
 import static org.junit.jupiter.api.condition.JRE.JAVA_21;
-import static org.junit.jupiter.api.condition.JRE.JAVA_8;
 import static org.junit.jupiter.api.condition.JRE.OTHER;
-import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava10;
-import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava11;
-import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava12;
-import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava13;
-import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava14;
-import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava15;
-import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava16;
 import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava17;
 import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava18;
 import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava19;
-import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava8;
-import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava9;
 import static org.junit.jupiter.api.condition.JavaVersionPredicates.onKnownVersion;
 
 import org.junit.jupiter.api.Disabled;
@@ -57,29 +46,29 @@ void defaultValues() {
 
 	@Test
 	@Disabled("Only used in a unit test via reflection")
-	@DisabledForJreRange(min = JAVA_8, max = OTHER)
+	@DisabledForJreRange(min = JAVA_17, max = OTHER)
 	void effectiveJreDefaultValues() {
 		fail("should result in a configuration exception");
 	}
 
 	@Test
 	@Disabled("Only used in a unit test via reflection")
-	@DisabledForJreRange(minVersion = 8, maxVersion = Integer.MAX_VALUE)
+	@DisabledForJreRange(minVersion = 17, maxVersion = Integer.MAX_VALUE)
 	void effectiveVersionDefaultValues() {
 		fail("should result in a configuration exception");
 	}
 
 	@Test
 	@Disabled("Only used in a unit test via reflection")
-	@DisabledForJreRange(min = JAVA_8)
-	void min8() {
+	@DisabledForJreRange(min = JAVA_17)
+	void min17() {
 		fail("should result in a configuration exception");
 	}
 
 	@Test
 	@Disabled("Only used in a unit test via reflection")
-	@DisabledForJreRange(minVersion = 8)
-	void minVersion8() {
+	@DisabledForJreRange(minVersion = 17)
+	void minVersion17() {
 		fail("should result in a configuration exception");
 	}
 
@@ -106,8 +95,8 @@ void minVersion7() {
 
 	@Test
 	@Disabled("Only used in a unit test via reflection")
-	@DisabledForJreRange(maxVersion = 7)
-	void maxVersion7() {
+	@DisabledForJreRange(maxVersion = 16)
+	void maxVersion16() {
 		fail("should result in a configuration exception");
 	}
 
@@ -127,28 +116,28 @@ void maxAndMaxVersion() {
 
 	@Test
 	@Disabled("Only used in a unit test via reflection")
-	@DisabledForJreRange(min = JAVA_21, max = JAVA_11)
+	@DisabledForJreRange(min = JAVA_21, max = JAVA_17)
 	void minGreaterThanMax() {
 		fail("should result in a configuration exception");
 	}
 
 	@Test
 	@Disabled("Only used in a unit test via reflection")
-	@DisabledForJreRange(min = JAVA_21, maxVersion = 11)
+	@DisabledForJreRange(min = JAVA_21, maxVersion = 17)
 	void minGreaterThanMaxVersion() {
 		fail("should result in a configuration exception");
 	}
 
 	@Test
 	@Disabled("Only used in a unit test via reflection")
-	@DisabledForJreRange(minVersion = 21, maxVersion = 11)
+	@DisabledForJreRange(minVersion = 21, maxVersion = 17)
 	void minVersionGreaterThanMaxVersion() {
 		fail("should result in a configuration exception");
 	}
 
 	@Test
 	@Disabled("Only used in a unit test via reflection")
-	@DisabledForJreRange(minVersion = 21, max = JAVA_11)
+	@DisabledForJreRange(minVersion = 21, max = JAVA_17)
 	void minVersionGreaterThanMax() {
 		fail("should result in a configuration exception");
 	}
@@ -169,8 +158,7 @@ void minVersion18() {
 	@Test
 	@DisabledForJreRange(max = JAVA_18)
 	void max18() {
-		assertFalse(onJava8() || onJava9() || onJava10() || onJava11() || onJava12() || onJava13() || onJava14()
-				|| onJava15() || onJava16() || onJava17() || onJava18());
+		assertFalse(onJava17() || onJava18());
 	}
 
 	@Test
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/api/condition/DisabledIfEnvironmentVariableConditionTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/api/condition/DisabledIfEnvironmentVariableConditionTests.java
index c9c7434a5bea..921f5d173e4e 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/api/condition/DisabledIfEnvironmentVariableConditionTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/api/condition/DisabledIfEnvironmentVariableConditionTests.java
@@ -16,6 +16,7 @@
 import static org.junit.jupiter.api.condition.DisabledIfEnvironmentVariableIntegrationTests.KEY1;
 import static org.junit.jupiter.api.condition.DisabledIfEnvironmentVariableIntegrationTests.KEY2;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExecutionCondition;
 import org.junit.platform.commons.PreconditionViolationException;
@@ -36,7 +37,7 @@ class DisabledIfEnvironmentVariableConditionTests extends AbstractExecutionCondi
 	private ExecutionCondition condition = new DisabledIfEnvironmentVariableCondition() {
 
 		@Override
-		protected String getEnvironmentVariable(String name) {
+		protected @Nullable String getEnvironmentVariable(String name) {
 			return KEY1.equals(name) ? ENIGMA : null;
 		}
 	};
@@ -99,7 +100,7 @@ void disabledBecauseEnvironmentVariableForComposedAnnotationMatchesExactly() {
 		this.condition = new DisabledIfEnvironmentVariableCondition() {
 
 			@Override
-			protected String getEnvironmentVariable(String name) {
+			protected @Nullable String getEnvironmentVariable(String name) {
 				return KEY1.equals(name) || KEY2.equals(name) ? ENIGMA : null;
 			}
 		};
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/api/condition/DisabledOnOsConditionTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/api/condition/DisabledOnOsConditionTests.java
index 8a098c8a7e04..2f16d47e4d77 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/api/condition/DisabledOnOsConditionTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/api/condition/DisabledOnOsConditionTests.java
@@ -74,7 +74,7 @@ void missingOsAndArchitectureDeclaration() {
 	void disabledOnEveryOs() {
 		evaluateCondition();
 		assertDisabled();
-		assertReasonContains(String.format("Disabled on operating system: %s ==> Disabled on every OS", OS_NAME));
+		assertReasonContains("Disabled on operating system: %s ==> Disabled on every OS".formatted(OS_NAME));
 	}
 
 	/**
@@ -234,33 +234,33 @@ void aarch64WithLinux() {
 	private void assertDisabledOnCurrentOsIf(boolean condition) {
 		if (condition) {
 			assertDisabled();
-			assertReasonContains(String.format("Disabled on operating system: %s", OS_NAME));
+			assertReasonContains("Disabled on operating system: %s".formatted(OS_NAME));
 		}
 		else {
 			assertEnabled();
-			assertReasonContains(String.format("Enabled on operating system: %s", OS_NAME));
+			assertReasonContains("Enabled on operating system: %s".formatted(OS_NAME));
 		}
 	}
 
 	private void assertDisabledOnCurrentArchitectureIf(boolean condition) {
 		if (condition) {
 			assertDisabled();
-			assertReasonContains(String.format("Disabled on architecture: %s", ARCH));
+			assertReasonContains("Disabled on architecture: %s".formatted(ARCH));
 		}
 		else {
 			assertEnabled();
-			assertReasonContains(String.format("Enabled on architecture: %s", ARCH));
+			assertReasonContains("Enabled on architecture: %s".formatted(ARCH));
 		}
 	}
 
 	private void assertDisabledOnCurrentOsAndArchitectureIf(boolean condition) {
 		if (condition) {
 			assertDisabled();
-			assertReasonContains(String.format("Disabled on operating system: %s (%s)", OS_NAME, ARCH));
+			assertReasonContains("Disabled on operating system: %s (%s)".formatted(OS_NAME, ARCH));
 		}
 		else {
 			assertEnabled();
-			assertReasonContains(String.format("Enabled on operating system: %s (%s)", OS_NAME, ARCH));
+			assertReasonContains("Enabled on operating system: %s (%s)".formatted(OS_NAME, ARCH));
 		}
 	}
 
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/api/condition/EnabledForJreRangeConditionTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/api/condition/EnabledForJreRangeConditionTests.java
index 886af0b8e309..d142586050ef 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/api/condition/EnabledForJreRangeConditionTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/api/condition/EnabledForJreRangeConditionTests.java
@@ -11,13 +11,6 @@
 package org.junit.jupiter.api.condition;
 
 import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
-import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava10;
-import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava11;
-import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava12;
-import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava13;
-import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava14;
-import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava15;
-import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava16;
 import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava17;
 import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava18;
 import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava19;
@@ -27,8 +20,7 @@
 import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava23;
 import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava24;
 import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava25;
-import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava8;
-import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava9;
+import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava26;
 import static org.junit.jupiter.api.condition.JavaVersionPredicates.onKnownVersion;
 
 import org.junit.jupiter.api.Test;
@@ -95,18 +87,18 @@ void effectiveVersionDefaultValues() {
 	}
 
 	/**
-	 * @see EnabledForJreRangeIntegrationTests#min8()
+	 * @see EnabledForJreRangeIntegrationTests#min17()
 	 */
 	@Test
-	void min8() {
+	void min17() {
 		defaultValues();
 	}
 
 	/**
-	 * @see EnabledForJreRangeIntegrationTests#minVersion8()
+	 * @see EnabledForJreRangeIntegrationTests#minVersion17()
 	 */
 	@Test
-	void minVersion8() {
+	void minVersion17() {
 		defaultValues();
 	}
 
@@ -137,13 +129,14 @@ void minVersion7() {
 	}
 
 	/**
-	 * @see EnabledForJreRangeIntegrationTests#maxVersion7()
+	 * @see EnabledForJreRangeIntegrationTests#maxVersion16()
 	 */
 	@Test
-	void maxVersion7() {
+	void maxVersion16() {
 		assertThatExceptionOfType(PreconditionViolationException.class)//
 				.isThrownBy(this::evaluateCondition)//
-				.withMessage("@EnabledForJreRange's maxVersion [7] must be greater than or equal to 8");
+				.withMessage(
+					"@EnabledForJreRange's minimum value [17] must be less than or equal to its maximum value [16]");
 	}
 
 	/**
@@ -176,7 +169,7 @@ void minGreaterThanMax() {
 		assertThatExceptionOfType(PreconditionViolationException.class)//
 				.isThrownBy(this::evaluateCondition)//
 				.withMessage(
-					"@EnabledForJreRange's minimum value [21] must be less than or equal to its maximum value [11]");
+					"@EnabledForJreRange's minimum value [21] must be less than or equal to its maximum value [17]");
 	}
 
 	/**
@@ -209,7 +202,8 @@ void minVersionGreaterThanMax() {
 	@Test
 	void min20() {
 		evaluateCondition();
-		assertEnabledOnCurrentJreIf(onJava20() || onJava21() || onJava22() || onJava23() || onJava24() || onJava25());
+		assertEnabledOnCurrentJreIf(
+			onJava20() || onJava21() || onJava22() || onJava23() || onJava24() || onJava25() || onJava26());
 	}
 
 	/**
@@ -226,9 +220,7 @@ void minVersion20() {
 	@Test
 	void max21() {
 		evaluateCondition();
-		assertEnabledOnCurrentJreIf(
-			onJava8() || onJava9() || onJava10() || onJava11() || onJava12() || onJava13() || onJava14() || onJava15()
-					|| onJava16() || onJava17() || onJava18() || onJava19() || onJava20() || onJava21());
+		assertEnabledOnCurrentJreIf(onJava17() || onJava18() || onJava19() || onJava20() || onJava21());
 	}
 
 	/**
@@ -240,10 +232,10 @@ void maxVersion21() {
 	}
 
 	/**
-	 * @see EnabledForJreRangeIntegrationTests#min8Max21()
+	 * @see EnabledForJreRangeIntegrationTests#min17Max21()
 	 */
 	@Test
-	void min8Max21() {
+	void min17Max21() {
 		max21();
 	}
 
@@ -314,13 +306,12 @@ void minVersion20MaxVersion21() {
 	}
 
 	/**
-	 * @see EnabledForJreRangeIntegrationTests#minVersion17MaxVersionMaxInteger()
+	 * @see EnabledForJreRangeIntegrationTests#minVersion21MaxVersionMaxInteger()
 	 */
 	@Test
-	void minVersion17MaxVersionMaxInteger() {
+	void minVersion21MaxVersionMaxInteger() {
 		evaluateCondition();
-		assertEnabledOnCurrentJreIf(onJava17() || onJava18() || onJava19() || onJava20() || onJava21() || onJava22()
-				|| onJava23() || onJava24() || onJava25());
+		assertEnabledOnCurrentJreIf(onJava21() || onJava22() || onJava23() || onJava24() || onJava25() || onJava26());
 	}
 
 	/**
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/api/condition/EnabledForJreRangeIntegrationTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/api/condition/EnabledForJreRangeIntegrationTests.java
index 03d33d1e2632..f075bd2cd886 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/api/condition/EnabledForJreRangeIntegrationTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/api/condition/EnabledForJreRangeIntegrationTests.java
@@ -13,20 +13,11 @@
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 import static org.junit.jupiter.api.Assertions.fail;
-import static org.junit.jupiter.api.condition.JRE.JAVA_11;
 import static org.junit.jupiter.api.condition.JRE.JAVA_17;
 import static org.junit.jupiter.api.condition.JRE.JAVA_18;
 import static org.junit.jupiter.api.condition.JRE.JAVA_20;
 import static org.junit.jupiter.api.condition.JRE.JAVA_21;
-import static org.junit.jupiter.api.condition.JRE.JAVA_8;
 import static org.junit.jupiter.api.condition.JRE.OTHER;
-import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava10;
-import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava11;
-import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava12;
-import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava13;
-import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava14;
-import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava15;
-import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava16;
 import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava17;
 import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava18;
 import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava19;
@@ -34,8 +25,6 @@
 import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava21;
 import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava22;
 import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava23;
-import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava8;
-import static org.junit.jupiter.api.condition.JavaVersionPredicates.onJava9;
 import static org.junit.jupiter.api.condition.JavaVersionPredicates.onKnownVersion;
 
 import org.junit.jupiter.api.Disabled;
@@ -64,29 +53,29 @@ void defaultValues() {
 
 	@Test
 	@Disabled("Only used in a unit test via reflection")
-	@EnabledForJreRange(min = JAVA_8, max = OTHER)
+	@EnabledForJreRange(min = JAVA_17, max = OTHER)
 	void effectiveJreDefaultValues() {
 		fail("should result in a configuration exception");
 	}
 
 	@Test
 	@Disabled("Only used in a unit test via reflection")
-	@EnabledForJreRange(minVersion = 8, maxVersion = Integer.MAX_VALUE)
+	@EnabledForJreRange(minVersion = 17, maxVersion = Integer.MAX_VALUE)
 	void effectiveVersionDefaultValues() {
 		fail("should result in a configuration exception");
 	}
 
 	@Test
 	@Disabled("Only used in a unit test via reflection")
-	@EnabledForJreRange(min = JAVA_8)
-	void min8() {
+	@EnabledForJreRange(min = JAVA_17)
+	void min17() {
 		fail("should result in a configuration exception");
 	}
 
 	@Test
 	@Disabled("Only used in a unit test via reflection")
-	@EnabledForJreRange(minVersion = 8)
-	void minVersion8() {
+	@EnabledForJreRange(minVersion = 17)
+	void minVersion17() {
 		fail("should result in a configuration exception");
 	}
 
@@ -113,8 +102,8 @@ void minVersion7() {
 
 	@Test
 	@Disabled("Only used in a unit test via reflection")
-	@EnabledForJreRange(maxVersion = 7)
-	void maxVersion7() {
+	@EnabledForJreRange(maxVersion = 16)
+	void maxVersion16() {
 		fail("should result in a configuration exception");
 	}
 
@@ -134,28 +123,28 @@ void maxAndMaxVersion() {
 
 	@Test
 	@Disabled("Only used in a unit test via reflection")
-	@EnabledForJreRange(min = JAVA_21, max = JAVA_11)
+	@EnabledForJreRange(min = JAVA_21, max = JAVA_17)
 	void minGreaterThanMax() {
 		fail("should result in a configuration exception");
 	}
 
 	@Test
 	@Disabled("Only used in a unit test via reflection")
-	@EnabledForJreRange(min = JAVA_21, maxVersion = 11)
+	@EnabledForJreRange(min = JAVA_21, maxVersion = 17)
 	void minGreaterThanMaxVersion() {
 		fail("should result in a configuration exception");
 	}
 
 	@Test
 	@Disabled("Only used in a unit test via reflection")
-	@EnabledForJreRange(minVersion = 21, maxVersion = 11)
+	@EnabledForJreRange(minVersion = 21, maxVersion = 17)
 	void minVersionGreaterThanMaxVersion() {
 		fail("should result in a configuration exception");
 	}
 
 	@Test
 	@Disabled("Only used in a unit test via reflection")
-	@EnabledForJreRange(minVersion = 21, max = JAVA_11)
+	@EnabledForJreRange(minVersion = 21, max = JAVA_17)
 	void minVersionGreaterThanMax() {
 		fail("should result in a configuration exception");
 	}
@@ -184,8 +173,7 @@ void max21() {
 		assertTrue(CURRENT_JRE.compareTo(JAVA_21) <= 0);
 		assertTrue(CURRENT_JRE.version() <= 21);
 
-		assertTrue(onJava8() || onJava9() || onJava10() || onJava11() || onJava12() || onJava13() || onJava14()
-				|| onJava15() || onJava16() || onJava17() || onJava18() || onJava19() || onJava20() || onJava21());
+		assertTrue(onJava17() || onJava18() || onJava19() || onJava20() || onJava21());
 		assertFalse(onJava22());
 	}
 
@@ -196,8 +184,8 @@ void maxVersion21() {
 	}
 
 	@Test
-	@EnabledForJreRange(min = JAVA_8, max = JAVA_21)
-	void min8Max21() {
+	@EnabledForJreRange(min = JAVA_17, max = JAVA_21)
+	void min17Max21() {
 		max21();
 	}
 
@@ -251,10 +239,10 @@ void minVersion20MaxVersion21() {
 	}
 
 	@Test
-	@EnabledForJreRange(minVersion = 17, maxVersion = Integer.MAX_VALUE)
-	void minVersion17MaxVersionMaxInteger() {
+	@EnabledForJreRange(minVersion = 21, maxVersion = Integer.MAX_VALUE)
+	void minVersion21MaxVersionMaxInteger() {
 		assertTrue(onKnownVersion());
-		assertTrue(JRE.currentVersionNumber() >= 17);
+		assertTrue(JRE.currentVersionNumber() >= 21);
 	}
 
 	@Test
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/api/condition/EnabledIfEnvironmentVariableConditionTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/api/condition/EnabledIfEnvironmentVariableConditionTests.java
index db0116e38695..7410b433c1eb 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/api/condition/EnabledIfEnvironmentVariableConditionTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/api/condition/EnabledIfEnvironmentVariableConditionTests.java
@@ -17,6 +17,7 @@
 import static org.junit.jupiter.api.condition.EnabledIfEnvironmentVariableIntegrationTests.KEY1;
 import static org.junit.jupiter.api.condition.EnabledIfEnvironmentVariableIntegrationTests.KEY2;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExecutionCondition;
 import org.junit.platform.commons.PreconditionViolationException;
@@ -37,7 +38,7 @@ class EnabledIfEnvironmentVariableConditionTests extends AbstractExecutionCondit
 	private ExecutionCondition condition = new EnabledIfEnvironmentVariableCondition() {
 
 		@Override
-		protected String getEnvironmentVariable(String name) {
+		protected @Nullable String getEnvironmentVariable(String name) {
 			return KEY1.equals(name) ? ENIGMA : null;
 		}
 	};
@@ -100,7 +101,7 @@ void enabledBecauseBothEnvironmentVariablesMatchExactly() {
 		this.condition = new EnabledIfEnvironmentVariableCondition() {
 
 			@Override
-			protected String getEnvironmentVariable(String name) {
+			protected @Nullable String getEnvironmentVariable(String name) {
 				return KEY1.equals(name) || KEY2.equals(name) ? ENIGMA : null;
 			}
 		};
@@ -141,7 +142,7 @@ void disabledBecauseEnvironmentVariableForComposedAnnotationDoesNotMatch() {
 		this.condition = new EnabledIfEnvironmentVariableCondition() {
 
 			@Override
-			protected String getEnvironmentVariable(String name) {
+			protected @Nullable String getEnvironmentVariable(String name) {
 				return KEY1.equals(name) ? ENIGMA : KEY2.equals(name) ? BOGUS : null;
 			}
 		};
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/api/condition/EnabledOnOsConditionTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/api/condition/EnabledOnOsConditionTests.java
index 56c3f0431a37..57ca8a41b69a 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/api/condition/EnabledOnOsConditionTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/api/condition/EnabledOnOsConditionTests.java
@@ -234,33 +234,33 @@ void aarch64WithLinux() {
 	private void assertEnabledOnCurrentOsIf(boolean condition) {
 		if (condition) {
 			assertEnabled();
-			assertReasonContains(String.format("Enabled on operating system: %s", OS_NAME));
+			assertReasonContains("Enabled on operating system: %s".formatted(OS_NAME));
 		}
 		else {
 			assertDisabled();
-			assertReasonContains(String.format("Disabled on operating system: %s", OS_NAME));
+			assertReasonContains("Disabled on operating system: %s".formatted(OS_NAME));
 		}
 	}
 
 	private void assertEnabledOnCurrentArchitectureIf(boolean condition) {
 		if (condition) {
 			assertEnabled();
-			assertReasonContains(String.format("Enabled on architecture: %s", ARCH));
+			assertReasonContains("Enabled on architecture: %s".formatted(ARCH));
 		}
 		else {
 			assertDisabled();
-			assertReasonContains(String.format("Disabled on architecture: %s", ARCH));
+			assertReasonContains("Disabled on architecture: %s".formatted(ARCH));
 		}
 	}
 
 	private void assertEnabledOnCurrentOsAndArchitectureIf(boolean condition) {
 		if (condition) {
 			assertEnabled();
-			assertReasonContains(String.format("Enabled on operating system: %s (%s)", OS_NAME, ARCH));
+			assertReasonContains("Enabled on operating system: %s (%s)".formatted(OS_NAME, ARCH));
 		}
 		else {
 			assertDisabled();
-			assertReasonContains(String.format("Disabled on operating system: %s (%s)", OS_NAME, ARCH));
+			assertReasonContains("Disabled on operating system: %s (%s)".formatted(OS_NAME, ARCH));
 		}
 	}
 
diff --git a/platform-tests/src/test/java/org/junit/jupiter/api/condition/OSTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/api/condition/OSTests.java
similarity index 99%
rename from platform-tests/src/test/java/org/junit/jupiter/api/condition/OSTests.java
rename to jupiter-tests/src/test/java/org/junit/jupiter/api/condition/OSTests.java
index 70a0c42350e1..6a0c582fb354 100644
--- a/platform-tests/src/test/java/org/junit/jupiter/api/condition/OSTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/api/condition/OSTests.java
@@ -19,6 +19,7 @@
 import org.junit.jupiter.params.provider.ValueSource;
 
 class OSTests {
+
 	@ParameterizedTest
 	@NullAndEmptySource
 	@ValueSource(strings = { " ", "\t" })
@@ -76,4 +77,5 @@ void windows(String name) {
 			assertEquals(OS.WINDOWS, OS.parse(name));
 		}
 	}
+
 }
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/api/extension/ExtensionComposabilityTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/api/extension/ExtensionComposabilityTests.java
index 9fb7a9efa9dd..8d8c7c7e9339 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/api/extension/ExtensionComposabilityTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/api/extension/ExtensionComposabilityTests.java
@@ -150,7 +150,7 @@ private boolean isExtensionApi(Class<?> candidate) {
 	}
 
 	private String methodSignature(Method method) {
-		return String.format("%s(%s)", method.getName(),
+		return "%s(%s)".formatted(method.getName(),
 			ClassUtils.nullSafeToString(Class::getSimpleName, method.getParameterTypes()));
 	}
 
diff --git a/platform-tests/src/test/java/org/junit/jupiter/extensions/Heavyweight.java b/jupiter-tests/src/test/java/org/junit/jupiter/api/extension/Heavyweight.java
similarity index 85%
rename from platform-tests/src/test/java/org/junit/jupiter/extensions/Heavyweight.java
rename to jupiter-tests/src/test/java/org/junit/jupiter/api/extension/Heavyweight.java
index ab9207301eff..a7552d2787f2 100644
--- a/platform-tests/src/test/java/org/junit/jupiter/extensions/Heavyweight.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/api/extension/Heavyweight.java
@@ -8,20 +8,16 @@
  * https://www.eclipse.org/legal/epl-v20.html
  */
 
-package org.junit.jupiter.extensions;
+package org.junit.jupiter.api.extension;
 
+import static java.util.Objects.requireNonNull;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicInteger;
 
-import org.junit.jupiter.api.extension.BeforeEachCallback;
-import org.junit.jupiter.api.extension.ExtensionContext;
-import org.junit.jupiter.api.extension.ParameterContext;
-import org.junit.jupiter.api.extension.ParameterResolver;
-
-public class Heavyweight implements ParameterResolver, BeforeEachCallback {
+class Heavyweight implements ParameterResolver, BeforeEachCallback {
 
 	@Override
 	public void beforeEach(ExtensionContext context) {
@@ -37,7 +33,7 @@ public boolean supportsParameter(ParameterContext parameterContext, ExtensionCon
 	public Object resolveParameter(ParameterContext parameterContext, ExtensionContext context) {
 		var engineContext = context.getRoot();
 		var store = engineContext.getStore(ExtensionContext.Namespace.GLOBAL);
-		var resource = store.getOrComputeIfAbsent(ResourceValue.class);
+		var resource = requireNonNull(store.getOrComputeIfAbsent(ResourceValue.class));
 		resource.usages.incrementAndGet();
 		return resource;
 	}
diff --git a/platform-tests/src/test/java/org/junit/jupiter/extensions/HeavyweightTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/api/extension/HeavyweightTests.java
similarity index 96%
rename from platform-tests/src/test/java/org/junit/jupiter/extensions/HeavyweightTests.java
rename to jupiter-tests/src/test/java/org/junit/jupiter/api/extension/HeavyweightTests.java
index 6c278c9ae8c2..872a00f44d81 100644
--- a/platform-tests/src/test/java/org/junit/jupiter/extensions/HeavyweightTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/api/extension/HeavyweightTests.java
@@ -8,7 +8,7 @@
  * https://www.eclipse.org/legal/epl-v20.html
  */
 
-package org.junit.jupiter.extensions;
+package org.junit.jupiter.api.extension;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertTrue;
@@ -25,7 +25,6 @@
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.TestFactory;
 import org.junit.jupiter.api.TestInstance;
-import org.junit.jupiter.api.extension.ExtendWith;
 import org.junit.jupiter.api.parallel.ResourceLock;
 
 /**
@@ -107,4 +106,5 @@ void afterAll(Heavyweight.Resource resource) {
 		}
 
 	}
+
 }
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/api/extension/KitchenSinkExtension.java b/jupiter-tests/src/test/java/org/junit/jupiter/api/extension/KitchenSinkExtension.java
index 45dfd821661a..e7b9dbb478d8 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/api/extension/KitchenSinkExtension.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/api/extension/KitchenSinkExtension.java
@@ -15,6 +15,8 @@
 import java.util.Optional;
 import java.util.stream.Stream;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * <em>Kitchen Sink</em> extension that implements every extension API
  * supported by JUnit Jupiter.
@@ -140,7 +142,7 @@ public void preConstructTestInstance(TestInstanceFactoryContext factoryContext,
 
 	@Override
 	public Object createTestInstance(TestInstanceFactoryContext factoryContext, ExtensionContext extensionContext) {
-		return null;
+		throw new UnsupportedOperationException();
 	}
 
 	@Override
@@ -157,7 +159,7 @@ public boolean supportsParameter(ParameterContext parameterContext, ExtensionCon
 	}
 
 	@Override
-	public Object resolveParameter(ParameterContext parameterContext, ExtensionContext extensionContext) {
+	public @Nullable Object resolveParameter(ParameterContext parameterContext, ExtensionContext extensionContext) {
 		return null;
 	}
 
@@ -165,7 +167,7 @@ public Object resolveParameter(ParameterContext parameterContext, ExtensionConte
 
 	@Override
 	public ConditionEvaluationResult evaluateExecutionCondition(ExtensionContext context) {
-		return null;
+		throw new UnsupportedOperationException();
 	}
 
 	// --- @TestTemplate -------------------------------------------------------
@@ -177,7 +179,7 @@ public boolean supportsTestTemplate(ExtensionContext context) {
 
 	@Override
 	public Stream<TestTemplateInvocationContext> provideTestTemplateInvocationContexts(ExtensionContext context) {
-		return null;
+		throw new UnsupportedOperationException();
 	}
 
 	@Override
@@ -194,7 +196,7 @@ public boolean supportsClassTemplate(ExtensionContext context) {
 
 	@Override
 	public Stream<ClassTemplateInvocationContext> provideClassTemplateInvocationContexts(ExtensionContext context) {
-		return null;
+		throw new UnsupportedOperationException();
 	}
 
 	@Override
@@ -213,11 +215,11 @@ public void testSuccessful(ExtensionContext context) {
 	}
 
 	@Override
-	public void testAborted(ExtensionContext context, Throwable cause) {
+	public void testAborted(ExtensionContext context, @Nullable Throwable cause) {
 	}
 
 	@Override
-	public void testFailed(ExtensionContext context, Throwable cause) {
+	public void testFailed(ExtensionContext context, @Nullable Throwable cause) {
 	}
 
 	// --- InvocationInterceptor -----------------------------------------------
@@ -231,20 +233,20 @@ public <T> T interceptTestClassConstructor(Invocation<T> invocation,
 	}
 
 	@Override
-	public void interceptBeforeAllMethod(Invocation<Void> invocation,
+	public void interceptBeforeAllMethod(Invocation<@Nullable Void> invocation,
 			ReflectiveInvocationContext<Method> invocationContext, ExtensionContext extensionContext) throws Throwable {
 		InvocationInterceptor.super.interceptBeforeAllMethod(invocation, invocationContext, extensionContext);
 	}
 
 	@Override
-	public void interceptBeforeEachMethod(Invocation<Void> invocation,
+	public void interceptBeforeEachMethod(Invocation<@Nullable Void> invocation,
 			ReflectiveInvocationContext<Method> invocationContext, ExtensionContext extensionContext) throws Throwable {
 		InvocationInterceptor.super.interceptBeforeEachMethod(invocation, invocationContext, extensionContext);
 	}
 
 	@Override
-	public void interceptTestMethod(Invocation<Void> invocation, ReflectiveInvocationContext<Method> invocationContext,
-			ExtensionContext extensionContext) throws Throwable {
+	public void interceptTestMethod(Invocation<@Nullable Void> invocation,
+			ReflectiveInvocationContext<Method> invocationContext, ExtensionContext extensionContext) throws Throwable {
 		InvocationInterceptor.super.interceptTestMethod(invocation, invocationContext, extensionContext);
 	}
 
@@ -255,31 +257,25 @@ public <T> T interceptTestFactoryMethod(Invocation<T> invocation,
 	}
 
 	@Override
-	public void interceptTestTemplateMethod(Invocation<Void> invocation,
+	public void interceptTestTemplateMethod(Invocation<@Nullable Void> invocation,
 			ReflectiveInvocationContext<Method> invocationContext, ExtensionContext extensionContext) throws Throwable {
 		InvocationInterceptor.super.interceptTestTemplateMethod(invocation, invocationContext, extensionContext);
 	}
 
-	@SuppressWarnings("deprecation")
-	@Override
-	public void interceptDynamicTest(Invocation<Void> invocation, ExtensionContext extensionContext) throws Throwable {
-		InvocationInterceptor.super.interceptDynamicTest(invocation, extensionContext);
-	}
-
 	@Override
-	public void interceptDynamicTest(Invocation<Void> invocation, DynamicTestInvocationContext invocationContext,
-			ExtensionContext extensionContext) throws Throwable {
+	public void interceptDynamicTest(Invocation<@Nullable Void> invocation,
+			DynamicTestInvocationContext invocationContext, ExtensionContext extensionContext) throws Throwable {
 		InvocationInterceptor.super.interceptDynamicTest(invocation, invocationContext, extensionContext);
 	}
 
 	@Override
-	public void interceptAfterEachMethod(Invocation<Void> invocation,
+	public void interceptAfterEachMethod(Invocation<@Nullable Void> invocation,
 			ReflectiveInvocationContext<Method> invocationContext, ExtensionContext extensionContext) throws Throwable {
 		InvocationInterceptor.super.interceptAfterEachMethod(invocation, invocationContext, extensionContext);
 	}
 
 	@Override
-	public void interceptAfterAllMethod(Invocation<Void> invocation,
+	public void interceptAfterAllMethod(Invocation<@Nullable Void> invocation,
 			ReflectiveInvocationContext<Method> invocationContext, ExtensionContext extensionContext) throws Throwable {
 		InvocationInterceptor.super.interceptAfterAllMethod(invocation, invocationContext, extensionContext);
 	}
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/api/extension/MediaTypeTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/api/extension/MediaTypeTests.java
index b1d06036b6fc..7e1bea151e7c 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/api/extension/MediaTypeTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/api/extension/MediaTypeTests.java
@@ -45,6 +45,7 @@ void parseWithInvalidMediaType() {
 		assertEquals("Invalid media type: 'invalid'", exception.getMessage());
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void parseWithNullMediaType() {
 		var exception = assertThrows(PreconditionViolationException.class, () -> MediaType.parse(null));
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/api/extension/support/TypeBasedParameterResolverTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/api/extension/support/TypeBasedParameterResolverTests.java
index eec416474611..a8b06d75f34b 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/api/extension/support/TypeBasedParameterResolverTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/api/extension/support/TypeBasedParameterResolverTests.java
@@ -56,20 +56,20 @@ void missingTypeTypeBasedParameterResolver() {
 	@Test
 	void supportsParameterForBasicTypes() {
 		Parameter parameter1 = findParameterOfMethod("methodWithBasicTypeParameter", String.class);
-		assertTrue(basicTypeBasedParameterResolver.supportsParameter(parameterContext(parameter1), null));
-		assertTrue(subClassedBasicTypeBasedParameterResolver.supportsParameter(parameterContext(parameter1), null));
+		assertTrue(basicTypeBasedParameterResolver.supportsParameter(parameterContext(parameter1), mock()));
+		assertTrue(subClassedBasicTypeBasedParameterResolver.supportsParameter(parameterContext(parameter1), mock()));
 
 		Parameter parameter2 = findParameterOfMethod("methodWithObjectParameter", Object.class);
-		assertFalse(basicTypeBasedParameterResolver.supportsParameter(parameterContext(parameter2), null));
+		assertFalse(basicTypeBasedParameterResolver.supportsParameter(parameterContext(parameter2), mock()));
 	}
 
 	@Test
 	void supportsParameterForParameterizedTypes() {
 		Parameter parameter1 = findParameterOfMethod("methodWithParameterizedTypeParameter", Map.class);
-		assertTrue(parametrizedTypeBasedParameterResolver.supportsParameter(parameterContext(parameter1), null));
+		assertTrue(parametrizedTypeBasedParameterResolver.supportsParameter(parameterContext(parameter1), mock()));
 
 		Parameter parameter3 = findParameterOfMethod("methodWithAnotherParameterizedTypeParameter", Map.class);
-		assertFalse(parametrizedTypeBasedParameterResolver.supportsParameter(parameterContext(parameter3), null));
+		assertFalse(parametrizedTypeBasedParameterResolver.supportsParameter(parameterContext(parameter3), mock()));
 	}
 
 	@Test
@@ -98,7 +98,7 @@ private static ExtensionContext extensionContext() {
 	}
 
 	private Parameter findParameterOfMethod(String methodName, Class<?>... parameterTypes) {
-		Method method = ReflectionSupport.findMethod(Sample.class, methodName, parameterTypes).get();
+		Method method = ReflectionSupport.findMethod(Sample.class, methodName, parameterTypes).orElseThrow();
 		return method.getParameters()[0];
 	}
 
@@ -119,7 +119,7 @@ static class BasicTypeBasedParameterResolver extends TypeBasedParameterResolver<
 		public String resolveParameter(ParameterContext parameterContext, ExtensionContext extensionContext)
 				throws ParameterResolutionException {
 			Class<?> parameterAnnotation = parameterContext.getParameter().getAnnotations()[0].annotationType();
-			return String.format("%s %s", extensionContext.getDisplayName(), parameterAnnotation.getSimpleName());
+			return "%s %s".formatted(extensionContext.getDisplayName(), parameterAnnotation.getSimpleName());
 		}
 	}
 
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/api/parallel/LockTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/api/parallel/LockTests.java
index f0e54f73424f..a311d83bd702 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/api/parallel/LockTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/api/parallel/LockTests.java
@@ -14,9 +14,9 @@
 import static org.junit.jupiter.api.EqualsAndHashCodeAssertions.assertEqualsAndHashCode;
 import static org.junit.jupiter.api.parallel.ResourceAccessMode.READ;
 import static org.junit.jupiter.api.parallel.ResourceAccessMode.READ_WRITE;
-import static org.junit.jupiter.api.parallel.ResourceLocksProvider.Lock;
 
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.parallel.ResourceLocksProvider.Lock;
 
 /**
  * Unit tests for {@link Lock}.
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/api/parallel/ResourceLockAnnotationTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/api/parallel/ResourceLockAnnotationTests.java
index cc300beee64e..73c01e8ec3e3 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/api/parallel/ResourceLockAnnotationTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/api/parallel/ResourceLockAnnotationTests.java
@@ -16,7 +16,6 @@
 import static org.junit.platform.engine.discovery.DiscoverySelectors.selectClass;
 import static org.junit.platform.engine.discovery.DiscoverySelectors.selectIteration;
 import static org.junit.platform.engine.discovery.DiscoverySelectors.selectMethod;
-import static org.junit.platform.engine.support.hierarchical.ExclusiveResource.LockMode;
 import static org.junit.platform.testkit.engine.EventConditions.finishedWithFailure;
 import static org.junit.platform.testkit.engine.TestExecutionResultConditions.instanceOf;
 import static org.junit.platform.testkit.engine.TestExecutionResultConditions.message;
@@ -50,6 +49,7 @@
 import org.junit.platform.engine.TestExecutionResult;
 import org.junit.platform.engine.UniqueId;
 import org.junit.platform.engine.support.hierarchical.ExclusiveResource;
+import org.junit.platform.engine.support.hierarchical.ExclusiveResource.LockMode;
 import org.junit.platform.testkit.engine.Event;
 
 /**
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/api/parallel/ResourceLocksProviderTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/api/parallel/ResourceLocksProviderTests.java
index f5bc7a17b77b..750c886f429c 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/api/parallel/ResourceLocksProviderTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/api/parallel/ResourceLocksProviderTests.java
@@ -11,6 +11,7 @@
 package org.junit.jupiter.api.parallel;
 
 import static java.util.Collections.emptySet;
+import static java.util.Objects.requireNonNull;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertTrue;
@@ -24,6 +25,7 @@
 import java.util.Set;
 import java.util.stream.Stream;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.AfterAll;
 import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Test;
@@ -115,6 +117,7 @@ static class Provider implements ResourceLocksProvider {
 			private static boolean isProvideForNestedClassCalled = false;
 			private static boolean isProvideForNestedTestMethodCalled = false;
 
+			@Nullable
 			private Class<?> testClass;
 
 			@Override
@@ -128,7 +131,7 @@ public Set<Lock> provideForClass(Class<?> testClass) {
 			@Override
 			public Set<Lock> provideForNestedClass(List<Class<?>> enclosingInstanceTypes, Class<?> testClass) {
 				isProvideForNestedClassCalled = true;
-				assertEquals(List.of(this.testClass), enclosingInstanceTypes);
+				assertEquals(List.of(requireNonNull(this.testClass)), enclosingInstanceTypes);
 				assertEquals(ClassLevelProviderTestCase.NestedClass.class, testClass);
 				return emptySet();
 			}
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/AbstractJupiterTestEngineTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/AbstractJupiterTestEngineTests.java
index 0dcd074d74f8..8b6b7c5ae009 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/AbstractJupiterTestEngineTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/AbstractJupiterTestEngineTests.java
@@ -10,6 +10,8 @@
 
 package org.junit.jupiter.engine;
 
+import static kotlin.jvm.JvmClassMappingKt.getJavaClass;
+import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.jupiter.api.Assertions.fail;
 import static org.junit.platform.engine.discovery.DiscoverySelectors.selectClass;
 import static org.junit.platform.engine.discovery.DiscoverySelectors.selectMethod;
@@ -22,6 +24,7 @@
 
 import org.junit.platform.engine.DiscoveryIssue.Severity;
 import org.junit.platform.engine.DiscoverySelector;
+import org.junit.platform.engine.TestDescriptor;
 import org.junit.platform.engine.UniqueId;
 import org.junit.platform.launcher.LauncherDiscoveryRequest;
 import org.junit.platform.launcher.core.LauncherDiscoveryRequestBuilder;
@@ -29,6 +32,8 @@
 import org.junit.platform.testkit.engine.EngineExecutionResults;
 import org.junit.platform.testkit.engine.EngineTestKit;
 
+import kotlin.reflect.KClass;
+
 /**
  * Abstract base class for tests involving the {@link JupiterTestEngine}.
  *
@@ -38,6 +43,10 @@ public abstract class AbstractJupiterTestEngineTests {
 
 	private final JupiterTestEngine engine = new JupiterTestEngine();
 
+	protected EngineExecutionResults executeTestsForClass(KClass<?> testClass) {
+		return executeTestsForClass(getJavaClass(testClass));
+	}
+
 	protected EngineExecutionResults executeTestsForClass(Class<?> testClass) {
 		return executeTests(selectClass(testClass));
 	}
@@ -60,6 +69,12 @@ protected EngineExecutionResults executeTests(LauncherDiscoveryRequest request)
 		return EngineTestKit.execute(this.engine, request);
 	}
 
+	protected TestDescriptor discoverTestsWithoutIssues(LauncherDiscoveryRequest request) {
+		var results = discoverTests(request);
+		assertThat(results.getDiscoveryIssues()).isEmpty();
+		return results.getEngineDescriptor();
+	}
+
 	protected EngineDiscoveryResults discoverTestsForClass(Class<?> testClass) {
 		return discoverTests(selectClass(testClass));
 	}
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/ClassTemplateInvocationTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/ClassTemplateInvocationTests.java
index cd15da225011..8be2bab63816 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/ClassTemplateInvocationTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/ClassTemplateInvocationTests.java
@@ -50,6 +50,7 @@
 import java.util.stream.IntStream;
 import java.util.stream.Stream;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.AfterAll;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeAll;
@@ -87,6 +88,7 @@
 import org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor;
 import org.junit.jupiter.engine.descriptor.TestTemplateInvocationTestDescriptor;
 import org.junit.jupiter.engine.descriptor.TestTemplateTestDescriptor;
+import org.junit.jupiter.params.ParameterizedClass;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.ValueSource;
 import org.junit.platform.engine.TestTag;
@@ -978,8 +980,10 @@ void templateWithPreparations() {
 
 	@Test
 	void propagatesTagsFromEnclosingClassesToNestedClassTemplates() {
-		var engineDescriptor = discoverTestsForClass(
-			NestedClassTemplateWithTagOnEnclosingClassTestCase.class).getEngineDescriptor();
+		var request = defaultRequest() //
+				.selectors(selectClass(NestedClassTemplateWithTagOnEnclosingClassTestCase.class)) //
+				.build();
+		var engineDescriptor = discoverTestsWithoutIssues(request);
 		var classDescriptor = getOnlyElement(engineDescriptor.getChildren());
 		var nestedClassTemplateDescriptor = getOnlyElement(classDescriptor.getChildren());
 
@@ -989,6 +993,17 @@ void propagatesTagsFromEnclosingClassesToNestedClassTemplates() {
 				.containsExactlyInAnyOrder("top-level", "nested");
 	}
 
+	@Test
+	void ignoresComposedAnnotations() {
+		var request = defaultRequest() //
+				.selectors(selectClass(ParameterizedClass.class)) //
+				.build();
+
+		var engineDescriptor = discoverTestsWithoutIssues(request);
+
+		assertThat(engineDescriptor.getDescendants()).isEmpty();
+	}
+
 	// -------------------------------------------------------------------
 
 	private static Stream<String> allReportEntryValues(EngineExecutionResults results) {
@@ -1168,8 +1183,8 @@ public boolean supportsParameter(ParameterContext parameterContext, ExtensionCon
 			}
 
 			@Override
-			public Object resolveParameter(ParameterContext parameterContext, ExtensionContext extensionContext)
-					throws ParameterResolutionException {
+			public @Nullable Object resolveParameter(ParameterContext parameterContext,
+					ExtensionContext extensionContext) throws ParameterResolutionException {
 				return extensionContext.getStore(Namespace.GLOBAL).get("someResource");
 			}
 		}
@@ -1431,7 +1446,7 @@ public boolean supportsParameter(ParameterContext parameterContext, ExtensionCon
 		}
 
 		@Override
-		public Object resolveParameter(ParameterContext parameterContext, ExtensionContext extensionContext)
+		public @Nullable Object resolveParameter(ParameterContext parameterContext, ExtensionContext extensionContext)
 				throws ParameterResolutionException {
 			return extensionContext.getStore(PreparingClassTemplateInvocationContextProvider.NAMESPACE).get("resource");
 		}
@@ -1492,7 +1507,7 @@ static class ClassTemplateInvocationCallbacks
 			implements BeforeClassTemplateInvocationCallback, AfterClassTemplateInvocationCallback {
 
 		private final String prefix;
-		private final Function<String, Throwable> exceptionFactory;
+		private final Function<String, @Nullable Throwable> exceptionFactory;
 
 		@SuppressWarnings("unused")
 		ClassTemplateInvocationCallbacks() {
@@ -1503,7 +1518,7 @@ static class ClassTemplateInvocationCallbacks
 			this(prefix, __ -> null);
 		}
 
-		ClassTemplateInvocationCallbacks(String prefix, Function<String, Throwable> exceptionFactory) {
+		ClassTemplateInvocationCallbacks(String prefix, Function<String, @Nullable Throwable> exceptionFactory) {
 			this.prefix = prefix;
 			this.exceptionFactory = exceptionFactory;
 		}
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/DefaultExecutionModeTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/DefaultExecutionModeTests.java
index c67182cd7283..4857345b6cef 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/DefaultExecutionModeTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/DefaultExecutionModeTests.java
@@ -19,6 +19,7 @@
 import static org.junit.platform.engine.support.hierarchical.Node.ExecutionMode.SAME_THREAD;
 import static org.junit.platform.launcher.core.LauncherDiscoveryRequestBuilder.request;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.TestInstance;
@@ -41,7 +42,7 @@ void defaultExecutionModeIsReadFromConfigurationParameter() {
 		assertUsesExpectedExecutionMode(CONCURRENT, CONCURRENT);
 	}
 
-	private void assertUsesExpectedExecutionMode(ExecutionMode defaultExecutionMode,
+	private void assertUsesExpectedExecutionMode(@Nullable ExecutionMode defaultExecutionMode,
 			ExecutionMode expectedExecutionMode) {
 		var engineDescriptor = discoverTestsWithDefaultExecutionMode(TestCase.class, defaultExecutionMode);
 		assertExecutionModeRecursively(engineDescriptor, expectedExecutionMode);
@@ -63,7 +64,7 @@ void annotationOverridesDefaultExecutionModeToSameThreadForAllDescendants() {
 	}
 
 	private void assertUsesExpectedExecutionModeForTestClassAndItsDescendants(Class<?> testClass,
-			ExecutionMode defaultExecutionMode, ExecutionMode expectedExecutionMode) {
+			@Nullable ExecutionMode defaultExecutionMode, ExecutionMode expectedExecutionMode) {
 		var engineDescriptor = discoverTestsWithDefaultExecutionMode(testClass, defaultExecutionMode);
 		engineDescriptor.getChildren().forEach(child -> assertExecutionModeRecursively(child, expectedExecutionMode));
 	}
@@ -104,7 +105,7 @@ void methodsInNestedTestClassesWithInstancePerClassInHierarchyHaveExecutionModeS
 	}
 
 	private JupiterEngineDescriptor discoverTestsWithDefaultExecutionMode(Class<?> testClass,
-			ExecutionMode executionMode) {
+			@Nullable ExecutionMode executionMode) {
 		LauncherDiscoveryRequestBuilder request = request().selectors(selectClass(testClass));
 		if (executionMode != null) {
 			request.configurationParameter(Constants.DEFAULT_PARALLEL_EXECUTION_MODE, executionMode.name());
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/NestedTestClassesTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/NestedTestClassesTests.java
index 2fe8352f41b8..68bd39c89366 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/NestedTestClassesTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/NestedTestClassesTests.java
@@ -13,28 +13,40 @@
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.jupiter.api.Assertions.assertAll;
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.platform.engine.discovery.ClassNameFilter.includeClassNamePatterns;
 import static org.junit.platform.engine.discovery.DiscoverySelectors.selectClass;
 import static org.junit.platform.engine.discovery.DiscoverySelectors.selectMethod;
+import static org.junit.platform.engine.discovery.DiscoverySelectors.selectPackage;
 import static org.junit.platform.engine.discovery.DiscoverySelectors.selectUniqueId;
 import static org.junit.platform.launcher.LauncherConstants.CRITICAL_DISCOVERY_ISSUE_SEVERITY_PROPERTY_NAME;
-import static org.junit.platform.launcher.core.LauncherDiscoveryRequestBuilder.request;
 import static org.junit.platform.testkit.engine.EventConditions.finishedWithFailure;
 import static org.junit.platform.testkit.engine.TestExecutionResultConditions.message;
 
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
 import java.util.List;
+import java.util.function.Consumer;
+import java.util.regex.Pattern;
 
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Named;
 import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.engine.NestedTestClassesTests.OuterClass.NestedClass;
 import org.junit.jupiter.engine.NestedTestClassesTests.OuterClass.NestedClass.RecursiveNestedClass;
 import org.junit.jupiter.engine.NestedTestClassesTests.OuterClass.NestedClass.RecursiveNestedSiblingClass;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.MethodSource;
+import org.junit.jupiter.params.provider.ValueSource;
 import org.junit.platform.engine.DiscoveryIssue.Severity;
 import org.junit.platform.engine.TestDescriptor;
 import org.junit.platform.engine.support.descriptor.ClassSource;
 import org.junit.platform.launcher.LauncherDiscoveryRequest;
+import org.junit.platform.launcher.core.LauncherDiscoveryRequestBuilder;
 import org.junit.platform.testkit.engine.EngineExecutionResults;
 import org.junit.platform.testkit.engine.Events;
 
@@ -48,29 +60,46 @@ class NestedTestClassesTests extends AbstractJupiterTestEngineTests {
 
 	@Test
 	void nestedTestsAreCorrectlyDiscovered() {
-		LauncherDiscoveryRequest request = request().selectors(selectClass(TestCaseWithNesting.class)).build();
-		TestDescriptor engineDescriptor = discoverTests(request).getEngineDescriptor();
+		LauncherDiscoveryRequest request = defaultRequest().selectors(selectClass(TestCaseWithNesting.class)).build();
+		TestDescriptor engineDescriptor = discoverTestsWithoutIssues(request);
 		assertEquals(5, engineDescriptor.getDescendants().size(), "# resolved test descriptors");
 	}
 
-	@Test
-	void nestedTestsAreExecuted() {
-		EngineExecutionResults executionResults = executeTestsForClass(TestCaseWithNesting.class);
-		Events containers = executionResults.containerEvents();
-		Events tests = executionResults.testEvents();
+	@ParameterizedTest(name = "{0}")
+	@MethodSource
+	void nestedTestsAreExecutedInTheRightOrder(Consumer<LauncherDiscoveryRequestBuilder> configurer) {
+		EngineExecutionResults executionResults = executeTests(configurer);
 
+		Events tests = executionResults.testEvents();
 		assertEquals(3, tests.started().count(), "# tests started");
 		assertEquals(2, tests.succeeded().count(), "# tests succeeded");
 		assertEquals(1, tests.failed().count(), "# tests failed");
 
+		assertThat(tests.started().map(it -> it.getTestDescriptor().getDisplayName())) //
+				.containsExactlyInAnyOrder("someTest()", "successful()", "failing()") //
+				.containsSubsequence("someTest()", "successful()") //
+				.containsSubsequence("someTest()", "failing()");
+
+		Events containers = executionResults.containerEvents();
 		assertEquals(3, containers.started().count(), "# containers started");
 		assertEquals(3, containers.finished().count(), "# containers finished");
 	}
 
+	static List<Named<Consumer<LauncherDiscoveryRequestBuilder>>> nestedTestsAreExecutedInTheRightOrder() {
+		return List.of( //
+			Named.of("class selector", request -> request //
+					.selectors(selectClass(TestCaseWithNesting.class))),
+			Named.of("package selector", request -> request //
+					.selectors(selectPackage(TestCaseWithNesting.class.getPackageName())) //
+					.filters(includeClassNamePatterns(Pattern.quote(TestCaseWithNesting.class.getName()) + ".*"))) //
+		);
+	}
+
 	@Test
 	void doublyNestedTestsAreCorrectlyDiscovered() {
-		LauncherDiscoveryRequest request = request().selectors(selectClass(TestCaseWithDoubleNesting.class)).build();
-		TestDescriptor engineDescriptor = discoverTests(request).getEngineDescriptor();
+		LauncherDiscoveryRequest request = defaultRequest().selectors(
+			selectClass(TestCaseWithDoubleNesting.class)).build();
+		TestDescriptor engineDescriptor = discoverTestsWithoutIssues(request);
 		assertEquals(8, engineDescriptor.getDescendants().size(), "# resolved test descriptors");
 	}
 
@@ -206,10 +235,40 @@ void individualMethodsWithinRecursiveNestedTestClassHierarchiesAreExecuted() {
 		executionResults.testEvents().assertStatistics(stats -> stats.started(1).succeeded(1));
 	}
 
+	@Test
+	void doesNotReportDiscoveryIssueForClassWithAbstractInnerClass() {
+		var discoveryIssues = discoverTestsForClass(ConcreteWithExtendedInnerClassTestCase.class).getDiscoveryIssues();
+
+		assertThat(discoveryIssues).isEmpty();
+	}
+
+	@Test
+	void doesNotReportDiscoveryIssueForAbstractInnerClass() {
+		var discoveryIssues = discoverTestsForClass(
+			AbstractBaseWithInnerClassTestCase.AbstractInnerClass.class).getDiscoveryIssues();
+
+		assertThat(discoveryIssues).isEmpty();
+	}
+
+	@Test
+	void nestedTestsWithCustomAnnotationAreCorrectlyDiscovered() {
+		LauncherDiscoveryRequest request = defaultRequest().selectors(
+			selectClass(CustomAnnotationTestCase.class)).build();
+		TestDescriptor engineDescriptor = discoverTestsWithoutIssues(request);
+		assertEquals(3, engineDescriptor.getDescendants().size(), "# resolved test descriptors");
+	}
+
+	@ParameterizedTest
+	@ValueSource(classes = { TopLevelComposedNested.class, CustomAnnotationTestCase.MyNested.class })
+	void ignoresComposedAnnotations(Class<?> annotationType) {
+		LauncherDiscoveryRequest request = defaultRequest().selectors(selectClass(annotationType)).build();
+		TestDescriptor engineDescriptor = discoverTestsWithoutIssues(request);
+		assertEquals(0, engineDescriptor.getDescendants().size(), "# resolved test descriptors");
+	}
+
 	private void assertNestedCycle(Class<?> start, Class<?> from, Class<?> to) {
 		var results = executeTestsForClass(start);
-		var expectedMessage = String.format(
-			"Cause: org.junit.platform.commons.JUnitException: Detected cycle in inner class hierarchy between %s and %s",
+		var expectedMessage = "Cause: org.junit.platform.commons.JUnitException: Detected cycle in inner class hierarchy between %s and %s".formatted(
 			from.getName(), to.getName());
 		results.containerEvents().assertThatEvents() //
 				.haveExactly(1, finishedWithFailure(message(it -> it.contains(expectedMessage))));
@@ -397,4 +456,38 @@ void nested() {
 		}
 	}
 
+	static class AbstractBaseWithInnerClassTestCase {
+		@SuppressWarnings("InnerClassMayBeStatic")
+		abstract class AbstractInnerClass {
+			@Test
+			void test() {
+			}
+		}
+	}
+
+	static class ConcreteWithExtendedInnerClassTestCase extends AbstractBaseWithInnerClassTestCase {
+		@Nested
+		class NestedTests extends AbstractInnerClass {
+		}
+	}
+
+	static class CustomAnnotationTestCase {
+
+		@Nested
+		@Retention(RetentionPolicy.RUNTIME)
+		@Target(ElementType.TYPE)
+		@interface MyNested {
+		}
+
+		@SuppressWarnings({ "JUnitMalformedDeclaration", "InnerClassMayBeStatic" })
+		@MyNested
+		class Inner {
+
+			@Test
+			void test() {
+
+			}
+		}
+	}
+
 }
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/NestedWithInheritanceTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/NestedWithInheritanceTests.java
index 3b3602e09fb8..64a75e51e58f 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/NestedWithInheritanceTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/NestedWithInheritanceTests.java
@@ -15,11 +15,13 @@
 import java.util.ArrayList;
 import java.util.List;
 
+import org.jspecify.annotations.NullUnmarked;
 import org.junit.jupiter.api.BeforeAll;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Test;
 
+@NullUnmarked
 class NestedWithInheritanceTests extends SuperClass {
 
 	static List<String> lifecycleInvokingClassNames;
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/NestedWithSeparateInheritanceTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/NestedWithSeparateInheritanceTests.java
index b73cee268861..c79080613a0c 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/NestedWithSeparateInheritanceTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/NestedWithSeparateInheritanceTests.java
@@ -10,11 +10,13 @@
 
 package org.junit.jupiter.engine;
 
+import static java.util.Objects.requireNonNull;
 import static org.assertj.core.api.Assertions.assertThat;
 
 import java.util.ArrayList;
 import java.util.List;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.BeforeAll;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Nested;
@@ -22,7 +24,7 @@
 
 class NestedWithSeparateInheritanceTests extends SuperClass1 {
 
-	static List<String> lifecycleInvokingClassNames;
+	static @Nullable List<String> lifecycleInvokingClassNames;
 
 	static String OUTER = NestedWithSeparateInheritanceTests.class.getSimpleName();
 	static String NESTED = NestedClass.class.getSimpleName();
@@ -59,7 +61,7 @@ static void setup() {
 	@BeforeEach
 	public void beforeEach() {
 		String invokingClass = this.getClass().getSimpleName();
-		NestedWithSeparateInheritanceTests.lifecycleInvokingClassNames.add(invokingClass);
+		requireNonNull(NestedWithSeparateInheritanceTests.lifecycleInvokingClassNames).add(invokingClass);
 	}
 
 }
@@ -74,7 +76,7 @@ static void setup() {
 	@BeforeEach
 	public void beforeEach() {
 		String invokingClass = this.getClass().getSimpleName();
-		NestedWithSeparateInheritanceTests.lifecycleInvokingClassNames.add(invokingClass);
+		requireNonNull(NestedWithSeparateInheritanceTests.lifecycleInvokingClassNames).add(invokingClass);
 	}
 
 }
@@ -89,7 +91,7 @@ static void setup() {
 	@BeforeEach
 	public void beforeEach() {
 		String invokingClass = this.getClass().getSimpleName();
-		NestedWithSeparateInheritanceTests.lifecycleInvokingClassNames.add(invokingClass);
+		requireNonNull(NestedWithSeparateInheritanceTests.lifecycleInvokingClassNames).add(invokingClass);
 	}
 
 }
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/OverloadedTestMethodTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/OverloadedTestMethodTests.java
index d0669f81cbe4..c84e974f89ff 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/OverloadedTestMethodTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/OverloadedTestMethodTests.java
@@ -53,7 +53,7 @@ void executeTestCaseWithOverloadedMethodsAndThenRerunOnlyOneOfTheMethodsSelected
 	}
 
 	@Test
-	void executeTestCaseWithOverloadedMethodsWithSingleMethodThatAcceptsArgumentsSelectedByFullyQualifedMethodName() {
+	void executeTestCaseWithOverloadedMethodsWithSingleMethodThatAcceptsArgumentsSelectedByFullyQualifiedMethodName() {
 		String fqmn = TestCase.class.getName() + "#test(" + TestInfo.class.getName() + ")";
 		Events tests = executeTests(selectMethod(fqmn)).testEvents();
 
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/ReportingTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/ReportingTests.java
index 7d69e5d8c932..7c9f0f9d035f 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/ReportingTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/ReportingTests.java
@@ -115,6 +115,7 @@ void succeedingTest(TestReporter reporter) {
 				file -> Files.writeString(file, "succeedingTest"));
 		}
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void invalidReportData(TestReporter reporter) {
 
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/TestInstanceLifecycleTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/TestInstanceLifecycleTests.java
index a360f0c8306e..185f903dc785 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/TestInstanceLifecycleTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/TestInstanceLifecycleTests.java
@@ -34,6 +34,7 @@
 import java.util.Objects;
 import java.util.stream.Stream;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.AfterAll;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeAll;
@@ -96,6 +97,7 @@ void init() {
 		afterEachCount = 0;
 	}
 
+	@SuppressWarnings("NullAway")
 	@Test
 	void instancePerMethod() {
 		Class<?> testClass = InstancePerMethodTestCase.class;
@@ -181,6 +183,7 @@ void instancePerClassWithInheritedLifecycleMode() {
 			instanceCounts(entry(SubInstancePerClassTestCase.class, 1)));
 	}
 
+	@SuppressWarnings("NullAway")
 	private void instancePerClass(Class<?> testClass, Map.Entry<Class<?>, Integer>[] instances) {
 		int containers = 3;
 		int tests = 3;
@@ -248,6 +251,7 @@ private void instancePerClass(Class<?> testClass, Map.Entry<Class<?>, Integer>[]
 		assertThat(lifecyclesMap.get(testClass).stream()).allMatch(Lifecycle.PER_CLASS::equals);
 	}
 
+	@SuppressWarnings("NullAway")
 	@Test
 	void instancePerMethodWithNestedTestClass() {
 		Class<?> testClass = InstancePerMethodOuterTestCase.class;
@@ -370,6 +374,7 @@ void instancePerMethodWithNestedTestClass() {
 		assertThat(lifecyclesMap.get(nestedTestClass).stream()).allMatch(Lifecycle.PER_METHOD::equals);
 	}
 
+	@SuppressWarnings("NullAway")
 	@Test
 	void instancePerClassWithNestedTestClass() {
 		Class<?> testClass = InstancePerClassOuterTestCase.class;
@@ -490,6 +495,7 @@ void instancePerClassWithNestedTestClass() {
 		assertThat(lifecyclesMap.get(nestedTestClass).stream()).allMatch(Lifecycle.PER_CLASS::equals);
 	}
 
+	@SuppressWarnings("NullAway")
 	@Test
 	void instancePerMethodOnOuterTestClassWithInstancePerClassOnNestedTestClass() {
 		Class<?> testClass = MixedLifecyclesOuterTestCase.class;
@@ -676,7 +682,7 @@ private static void incrementInstanceCount(Class<?> testClass) {
 		instanceCount.compute(testClass, (key, value) -> value == null ? 1 : value + 1);
 	}
 
-	private static String executionConditionKey(Class<?> testClass, String testMethod) {
+	private static String executionConditionKey(Class<?> testClass, @Nullable String testMethod) {
 		return concat(ExecutionCondition.class, testClass, testMethod);
 	}
 
@@ -708,7 +714,7 @@ private static String testTemplateKey(Class<?> testClass, String testMethod) {
 		return concat(TestTemplateInvocationContextProvider.class, testClass, testMethod);
 	}
 
-	private static String concat(Class<?> c1, Class<?> c2, String str) {
+	private static String concat(Class<?> c1, Class<?> c2, @Nullable String str) {
 		return concat(c1.getSimpleName(), c2.getSimpleName(), str);
 	}
 
@@ -716,7 +722,7 @@ private static String concat(Class<?> c1, Class<?> c2) {
 		return concat(c1.getSimpleName(), c2.getSimpleName());
 	}
 
-	private static String concat(String... args) {
+	private static String concat(@Nullable String... args) {
 		return join(".", args);
 	}
 
@@ -814,6 +820,7 @@ static void beforeAll(TestInfo testInfo) {
 			beforeAllCount++;
 		}
 
+		@SuppressWarnings("NullAway")
 		@Test
 		void outerTest() {
 			assertSame(this, instanceMap.get(postProcessTestInstanceKey(getClass())).getInnermostInstance());
@@ -839,18 +846,21 @@ void beforeEach() {
 				beforeEachCount++;
 			}
 
+			@SuppressWarnings("NullAway")
 			@Test
 			void test1(TestInfo testInfo) {
 				assertSame(this, instanceMap.get(postProcessTestInstanceKey(getClass())).getInnermostInstance());
 				testsInvoked.add(testInfo.getTestMethod().get().getName());
 			}
 
+			@SuppressWarnings("NullAway")
 			@Test
 			void test2(TestInfo testInfo) {
 				assertSame(this, instanceMap.get(postProcessTestInstanceKey(getClass())).getInnermostInstance());
 				testsInvoked.add(testInfo.getTestMethod().get().getName());
 			}
 
+			@SuppressWarnings("NullAway")
 			@SingletonTest
 			void singletonTest(TestInfo testInfo) {
 				assertSame(this, instanceMap.get(postProcessTestInstanceKey(getClass())).getInnermostInstance());
@@ -879,6 +889,7 @@ static void beforeAll(TestInfo testInfo) {
 			beforeAllCount++;
 		}
 
+		@SuppressWarnings("NullAway")
 		@Test
 		void outerTest() {
 			assertSame(this, instanceMap.get(postProcessTestInstanceKey(getClass())).getInnermostInstance());
@@ -909,18 +920,21 @@ void beforeEach() {
 				beforeEachCount++;
 			}
 
+			@SuppressWarnings("NullAway")
 			@Test
 			void test1(TestInfo testInfo) {
 				assertSame(this, instanceMap.get(postProcessTestInstanceKey(getClass())).getInnermostInstance());
 				testsInvoked.add(testInfo.getTestMethod().get().getName());
 			}
 
+			@SuppressWarnings("NullAway")
 			@Test
 			void test2(TestInfo testInfo) {
 				assertSame(this, instanceMap.get(postProcessTestInstanceKey(getClass())).getInnermostInstance());
 				testsInvoked.add(testInfo.getTestMethod().get().getName());
 			}
 
+			@SuppressWarnings("NullAway")
 			@SingletonTest
 			void singletonTest(TestInfo testInfo) {
 				assertSame(this, instanceMap.get(postProcessTestInstanceKey(getClass())).getInnermostInstance());
@@ -955,6 +969,7 @@ void beforeEach() {
 			beforeEachCount++;
 		}
 
+		@SuppressWarnings("NullAway")
 		@Test
 		void outerTest() {
 			assertSame(this, instanceMap.get(postProcessTestInstanceKey(getClass())).getInnermostInstance());
@@ -984,18 +999,21 @@ void beforeEach() {
 				beforeEachCount++;
 			}
 
+			@SuppressWarnings("NullAway")
 			@Test
 			void test1(TestInfo testInfo) {
 				assertSame(this, instanceMap.get(postProcessTestInstanceKey(getClass())).getInnermostInstance());
 				testsInvoked.add(testInfo.getTestMethod().get().getName());
 			}
 
+			@SuppressWarnings("NullAway")
 			@Test
 			void test2(TestInfo testInfo) {
 				assertSame(this, instanceMap.get(postProcessTestInstanceKey(getClass())).getInnermostInstance());
 				testsInvoked.add(testInfo.getTestMethod().get().getName());
 			}
 
+			@SuppressWarnings("NullAway")
 			@SingletonTest
 			void singletonTest(TestInfo testInfo) {
 				assertSame(this, instanceMap.get(postProcessTestInstanceKey(getClass())).getInnermostInstance());
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/TestTemplateInvocationTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/TestTemplateInvocationTests.java
index 5cb6dba4dd82..9e5a7f9fe050 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/TestTemplateInvocationTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/TestTemplateInvocationTests.java
@@ -44,6 +44,7 @@
 import java.util.stream.Stream;
 
 import org.assertj.core.api.Condition;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.AfterAll;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeAll;
@@ -499,6 +500,7 @@ void templateWithWrongParameterType(int parameter) {
 			fail("never called: " + parameter);
 		}
 
+		@Nullable
 		String parameterInstanceVariable;
 
 		@ExtendWith(StringParameterInjectingInvocationContextProvider.class)
@@ -549,7 +551,7 @@ void template(String parameter) {
 
 	static class TestTemplateTestClassWithBeforeAndAfterEach {
 
-		private static List<String> lifecycleEvents = new ArrayList<>();
+		private static final List<String> lifecycleEvents = new ArrayList<>();
 
 		@BeforeAll
 		static void beforeAll(TestInfo testInfo) {
@@ -916,7 +918,7 @@ public boolean supportsParameter(ParameterContext parameterContext, ExtensionCon
 		}
 
 		@Override
-		public Object resolveParameter(ParameterContext parameterContext, ExtensionContext extensionContext)
+		public @Nullable Object resolveParameter(ParameterContext parameterContext, ExtensionContext extensionContext)
 				throws ParameterResolutionException {
 			return extensionContext.getStore(PreparingTestTemplateInvocationContextProvider.NAMESPACE).get("resource");
 		}
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/TopLevelComposedNested.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/TopLevelComposedNested.java
new file mode 100644
index 000000000000..7f711f8cb4dc
--- /dev/null
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/TopLevelComposedNested.java
@@ -0,0 +1,24 @@
+/*
+ * Copyright 2015-2025 the original author or authors.
+ *
+ * All rights reserved. This program and the accompanying materials are
+ * made available under the terms of the Eclipse Public License v2.0 which
+ * accompanies this distribution and is available at
+ *
+ * https://www.eclipse.org/legal/epl-v20.html
+ */
+
+package org.junit.jupiter.engine;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+import org.junit.jupiter.api.Nested;
+
+@Nested
+@Retention(RetentionPolicy.RUNTIME)
+@Target(ElementType.TYPE)
+public @interface TopLevelComposedNested {
+}
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/config/DefaultJupiterConfigurationTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/config/DefaultJupiterConfigurationTests.java
index ba7daa0fe4bb..af5fc8088059 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/config/DefaultJupiterConfigurationTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/config/DefaultJupiterConfigurationTests.java
@@ -25,6 +25,7 @@
 import java.util.Optional;
 import java.util.function.Supplier;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.DisplayNameGenerator;
 import org.junit.jupiter.api.MethodOrderer;
 import org.junit.jupiter.api.Test;
@@ -42,23 +43,26 @@ class DefaultJupiterConfigurationTests {
 
 	private static final String KEY = DEFAULT_TEST_INSTANCE_LIFECYCLE_PROPERTY_NAME;
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void getDefaultTestInstanceLifecyclePreconditions() {
 		PreconditionViolationException exception = assertThrows(PreconditionViolationException.class,
-			() -> new DefaultJupiterConfiguration(null, dummyOutputDirectoryProvider()));
+			() -> new DefaultJupiterConfiguration(null, dummyOutputDirectoryProvider(), mock()));
 		assertThat(exception).hasMessage("ConfigurationParameters must not be null");
 	}
 
 	@Test
 	void getDefaultTestInstanceLifecycleWithNoConfigParamSet() {
-		JupiterConfiguration configuration = new DefaultJupiterConfiguration(mock(), dummyOutputDirectoryProvider());
+		JupiterConfiguration configuration = new DefaultJupiterConfiguration(mock(), dummyOutputDirectoryProvider(),
+			mock());
 		Lifecycle lifecycle = configuration.getDefaultTestInstanceLifecycle();
 		assertThat(lifecycle).isEqualTo(PER_METHOD);
 	}
 
 	@Test
 	void getDefaultTempDirCleanupModeWithNoConfigParamSet() {
-		JupiterConfiguration configuration = new DefaultJupiterConfiguration(mock(), dummyOutputDirectoryProvider());
+		JupiterConfiguration configuration = new DefaultJupiterConfiguration(mock(), dummyOutputDirectoryProvider(),
+			mock());
 		CleanupMode cleanupMode = configuration.getDefaultTempDirCleanupMode();
 		assertThat(cleanupMode).isEqualTo(ALWAYS);
 	}
@@ -83,8 +87,8 @@ void shouldGetDefaultDisplayNameGeneratorWithConfigParamSet() {
 		ConfigurationParameters parameters = mock();
 		String key = Constants.DEFAULT_DISPLAY_NAME_GENERATOR_PROPERTY_NAME;
 		when(parameters.get(key)).thenReturn(Optional.of(CustomDisplayNameGenerator.class.getName()));
-		JupiterConfiguration configuration = new DefaultJupiterConfiguration(parameters,
-			dummyOutputDirectoryProvider());
+		JupiterConfiguration configuration = new DefaultJupiterConfiguration(parameters, dummyOutputDirectoryProvider(),
+			mock());
 
 		DisplayNameGenerator defaultDisplayNameGenerator = configuration.getDefaultDisplayNameGenerator();
 
@@ -96,8 +100,8 @@ void shouldGetStandardAsDefaultDisplayNameGeneratorWithoutConfigParamSet() {
 		ConfigurationParameters parameters = mock();
 		String key = Constants.DEFAULT_DISPLAY_NAME_GENERATOR_PROPERTY_NAME;
 		when(parameters.get(key)).thenReturn(Optional.empty());
-		JupiterConfiguration configuration = new DefaultJupiterConfiguration(parameters,
-			dummyOutputDirectoryProvider());
+		JupiterConfiguration configuration = new DefaultJupiterConfiguration(parameters, dummyOutputDirectoryProvider(),
+			mock());
 
 		DisplayNameGenerator defaultDisplayNameGenerator = configuration.getDefaultDisplayNameGenerator();
 
@@ -109,8 +113,8 @@ void shouldGetNothingAsDefaultTestMethodOrderWithoutConfigParamSet() {
 		ConfigurationParameters parameters = mock();
 		String key = Constants.DEFAULT_TEST_METHOD_ORDER_PROPERTY_NAME;
 		when(parameters.get(key)).thenReturn(Optional.empty());
-		JupiterConfiguration configuration = new DefaultJupiterConfiguration(parameters,
-			dummyOutputDirectoryProvider());
+		JupiterConfiguration configuration = new DefaultJupiterConfiguration(parameters, dummyOutputDirectoryProvider(),
+			mock());
 
 		final Optional<MethodOrderer> defaultTestMethodOrder = configuration.getDefaultTestMethodOrderer();
 
@@ -122,8 +126,8 @@ void shouldGetDefaultTempDirFactorySupplierWithConfigParamSet() {
 		ConfigurationParameters parameters = mock();
 		String key = Constants.DEFAULT_TEMP_DIR_FACTORY_PROPERTY_NAME;
 		when(parameters.get(key)).thenReturn(Optional.of(CustomFactory.class.getName()));
-		JupiterConfiguration configuration = new DefaultJupiterConfiguration(parameters,
-			dummyOutputDirectoryProvider());
+		JupiterConfiguration configuration = new DefaultJupiterConfiguration(parameters, dummyOutputDirectoryProvider(),
+			mock());
 
 		Supplier<TempDirFactory> supplier = configuration.getDefaultTempDirFactorySupplier();
 
@@ -143,19 +147,19 @@ void shouldGetStandardAsDefaultTempDirFactorySupplierWithoutConfigParamSet() {
 		ConfigurationParameters parameters = mock();
 		String key = Constants.DEFAULT_TEMP_DIR_FACTORY_PROPERTY_NAME;
 		when(parameters.get(key)).thenReturn(Optional.empty());
-		JupiterConfiguration configuration = new DefaultJupiterConfiguration(parameters,
-			dummyOutputDirectoryProvider());
+		JupiterConfiguration configuration = new DefaultJupiterConfiguration(parameters, dummyOutputDirectoryProvider(),
+			mock());
 
 		Supplier<TempDirFactory> supplier = configuration.getDefaultTempDirFactorySupplier();
 
 		assertThat(supplier.get()).isSameAs(TempDirFactory.Standard.INSTANCE);
 	}
 
-	private void assertDefaultConfigParam(String configValue, Lifecycle expected) {
+	private void assertDefaultConfigParam(@Nullable String configValue, Lifecycle expected) {
 		ConfigurationParameters configParams = mock();
 		when(configParams.get(KEY)).thenReturn(Optional.ofNullable(configValue));
-		Lifecycle lifecycle = new DefaultJupiterConfiguration(configParams,
-			dummyOutputDirectoryProvider()).getDefaultTestInstanceLifecycle();
+		Lifecycle lifecycle = new DefaultJupiterConfiguration(configParams, dummyOutputDirectoryProvider(),
+			mock()).getDefaultTestInstanceLifecycle();
 		assertThat(lifecycle).isEqualTo(expected);
 	}
 
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/descriptor/DisplayNameUtilsTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/descriptor/DisplayNameUtilsTests.java
index ee7aa76cd0cd..40fddf7fbd78 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/descriptor/DisplayNameUtilsTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/descriptor/DisplayNameUtilsTests.java
@@ -17,8 +17,6 @@
 import java.lang.reflect.Method;
 import java.util.List;
 import java.util.function.Supplier;
-import java.util.logging.Level;
-import java.util.logging.LogRecord;
 
 import org.junit.jupiter.api.DisplayName;
 import org.junit.jupiter.api.DisplayNameGeneration;
@@ -26,7 +24,6 @@
 import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.engine.config.JupiterConfiguration;
-import org.junit.platform.commons.logging.LogRecordListener;
 
 /**
  * Unit tests for {@link DisplayNameUtils}.
@@ -180,18 +177,12 @@ void shouldFallbackOnDefaultDisplayNameGeneratorWhenNullIsGenerated() throws Exc
 		}
 	}
 
-	private LogRecord firstWarningLogRecord(LogRecordListener listener) throws AssertionError {
-		return listener.stream(DisplayNameUtils.class, Level.WARNING).findFirst().orElseThrow(
-			() -> new AssertionError("Failed to find warning log record"));
-	}
-
 	@DisplayName("my-test-case\t")
 	@DisplayNameGeneration(value = CustomDisplayNameGenerator.class)
 	static class MyTestCase {
 
 		void test1() {
 		}
-
 	}
 
 	@DisplayName("")
@@ -227,6 +218,7 @@ class NestedTestCase {
 
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	static class NullDisplayNameGenerator implements DisplayNameGenerator {
 
 		@Override
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/descriptor/ExtensionContextTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/descriptor/ExtensionContextTests.java
index 2417b145c380..2599244c739c 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/descriptor/ExtensionContextTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/descriptor/ExtensionContextTests.java
@@ -37,6 +37,7 @@
 import java.util.Set;
 import java.util.function.Function;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.DisplayNameGenerator;
 import org.junit.jupiter.api.Named;
@@ -94,7 +95,7 @@ void setUp() {
 	void fromJupiterEngineDescriptor() {
 		var engineTestDescriptor = new JupiterEngineDescriptor(UniqueId.root("engine", "junit-jupiter"), configuration);
 
-		try (var engineContext = new JupiterEngineExtensionContext(null, engineTestDescriptor, configuration,
+		try (var engineContext = new JupiterEngineExtensionContext(mock(), engineTestDescriptor, configuration,
 			extensionRegistry, launcherStoreFacade)) {
 			// @formatter:off
 			assertAll("engineContext",
@@ -125,8 +126,10 @@ void fromClassTestDescriptor() {
 		nestedClassDescriptor.addChild(doublyNestedClassDescriptor);
 		nestedClassDescriptor.addChild(methodTestDescriptor);
 
-		var outerExtensionContext = new ClassExtensionContext(null, null, outerClassDescriptor, PER_METHOD,
-			configuration, extensionRegistry, launcherStoreFacade, null);
+		var parentExtensionContext = mock(AbstractExtensionContext.class);
+
+		var outerExtensionContext = new ClassExtensionContext(parentExtensionContext, mock(), outerClassDescriptor,
+			PER_METHOD, configuration, extensionRegistry, launcherStoreFacade, mock());
 
 		// @formatter:off
 		assertAll("outerContext",
@@ -138,15 +141,15 @@ void fromClassTestDescriptor() {
 			() -> assertThrows(PreconditionViolationException.class, outerExtensionContext::getRequiredTestInstance),
 			() -> assertThrows(PreconditionViolationException.class, outerExtensionContext::getRequiredTestMethod),
 			() -> assertThat(outerExtensionContext.getDisplayName()).isEqualTo(outerClassDescriptor.getDisplayName()),
-			() -> assertThat(outerExtensionContext.getParent()).isEmpty(),
+			() -> assertThat(outerExtensionContext.getParent()).containsSame(parentExtensionContext),
 			() -> assertThat(outerExtensionContext.getExecutionMode()).isEqualTo(ExecutionMode.SAME_THREAD),
 			() -> assertThat(outerExtensionContext.getExtensions(PreInterruptCallback.class)).isEmpty(),
 			() -> assertThat(outerExtensionContext.getEnclosingTestClasses()).isEmpty()
 		);
 		// @formatter:on
 
-		var nestedExtensionContext = new ClassExtensionContext(outerExtensionContext, null, nestedClassDescriptor,
-			PER_METHOD, configuration, extensionRegistry, launcherStoreFacade, null);
+		var nestedExtensionContext = new ClassExtensionContext(outerExtensionContext, mock(), nestedClassDescriptor,
+			PER_METHOD, configuration, extensionRegistry, launcherStoreFacade, mock());
 		// @formatter:off
 		assertAll("nestedContext",
 			() -> assertThat(nestedExtensionContext.getParent()).containsSame(outerExtensionContext),
@@ -155,8 +158,8 @@ void fromClassTestDescriptor() {
 		);
 		// @formatter:on
 
-		var doublyNestedExtensionContext = new ClassExtensionContext(nestedExtensionContext, null,
-			doublyNestedClassDescriptor, PER_METHOD, configuration, extensionRegistry, launcherStoreFacade, null);
+		var doublyNestedExtensionContext = new ClassExtensionContext(nestedExtensionContext, mock(),
+			doublyNestedClassDescriptor, PER_METHOD, configuration, extensionRegistry, launcherStoreFacade, mock());
 		// @formatter:off
 		assertAll("doublyNestedContext",
 				() -> assertThat(doublyNestedExtensionContext.getParent()).containsSame(nestedExtensionContext),
@@ -165,7 +168,7 @@ void fromClassTestDescriptor() {
 		);
 		// @formatter:on
 
-		var methodExtensionContext = new MethodExtensionContext(nestedExtensionContext, null, methodTestDescriptor,
+		var methodExtensionContext = new MethodExtensionContext(nestedExtensionContext, mock(), methodTestDescriptor,
 			configuration, extensionRegistry, launcherStoreFacade, new OpenTest4JAwareThrowableCollector());
 		// @formatter:off
 		assertAll("methodContext",
@@ -179,8 +182,8 @@ void fromClassTestDescriptor() {
 	@Test
 	void ExtensionContext_With_ExtensionRegistry_getExtensions() {
 		var classTestDescriptor = nestedClassDescriptor();
-		try (var ctx = new ClassExtensionContext(null, null, classTestDescriptor, PER_METHOD, configuration,
-			extensionRegistry, launcherStoreFacade, null)) {
+		try (var ctx = new ClassExtensionContext(mock(AbstractExtensionContext.class), mock(), classTestDescriptor,
+			PER_METHOD, configuration, extensionRegistry, launcherStoreFacade, mock())) {
 
 			Extension ext = mock();
 			when(extensionRegistry.getExtensions(Extension.class)).thenReturn(List.of(ext));
@@ -197,22 +200,26 @@ void tagsCanBeRetrievedInExtensionContext() {
 		var methodTestDescriptor = methodDescriptor();
 		outerClassDescriptor.addChild(methodTestDescriptor);
 
-		var outerExtensionContext = new ClassExtensionContext(null, null, outerClassDescriptor, PER_METHOD,
-			configuration, extensionRegistry, launcherStoreFacade, null);
+		var rootExtensionContext = new JupiterEngineExtensionContext(mock(), mock(), configuration, extensionRegistry,
+			launcherStoreFacade);
+		assertThat(rootExtensionContext.getRoot()).isSameAs(rootExtensionContext);
+
+		var outerExtensionContext = new ClassExtensionContext(rootExtensionContext, mock(), outerClassDescriptor,
+			PER_METHOD, configuration, extensionRegistry, launcherStoreFacade, mock());
 
 		assertThat(outerExtensionContext.getTags()).containsExactly("outer-tag");
-		assertThat(outerExtensionContext.getRoot()).isSameAs(outerExtensionContext);
+		assertThat(outerExtensionContext.getRoot()).isSameAs(rootExtensionContext);
 
-		var nestedExtensionContext = new ClassExtensionContext(outerExtensionContext, null, nestedClassDescriptor,
-			PER_METHOD, configuration, extensionRegistry, launcherStoreFacade, null);
+		var nestedExtensionContext = new ClassExtensionContext(outerExtensionContext, mock(), nestedClassDescriptor,
+			PER_METHOD, configuration, extensionRegistry, launcherStoreFacade, mock());
 		assertThat(nestedExtensionContext.getTags()).containsExactlyInAnyOrder("outer-tag", "nested-tag");
-		assertThat(nestedExtensionContext.getRoot()).isSameAs(outerExtensionContext);
+		assertThat(nestedExtensionContext.getRoot()).isSameAs(rootExtensionContext);
 
-		var methodExtensionContext = new MethodExtensionContext(outerExtensionContext, null, methodTestDescriptor,
+		var methodExtensionContext = new MethodExtensionContext(outerExtensionContext, mock(), methodTestDescriptor,
 			configuration, extensionRegistry, launcherStoreFacade, new OpenTest4JAwareThrowableCollector());
 		methodExtensionContext.setTestInstances(DefaultTestInstances.of(new OuterClassTestCase()));
 		assertThat(methodExtensionContext.getTags()).containsExactlyInAnyOrder("outer-tag", "method-tag");
-		assertThat(methodExtensionContext.getRoot()).isSameAs(outerExtensionContext);
+		assertThat(methodExtensionContext.getRoot()).isSameAs(rootExtensionContext);
 	}
 
 	@Test
@@ -226,11 +233,11 @@ void fromMethodTestDescriptor() {
 		Object testInstance = new OuterClassTestCase();
 		var testMethod = methodTestDescriptor.getTestMethod();
 
-		var engineExtensionContext = new JupiterEngineExtensionContext(null, engineDescriptor, configuration,
+		var engineExtensionContext = new JupiterEngineExtensionContext(mock(), engineDescriptor, configuration,
 			extensionRegistry, launcherStoreFacade);
-		var classExtensionContext = new ClassExtensionContext(engineExtensionContext, null, classTestDescriptor,
-			PER_METHOD, configuration, extensionRegistry, launcherStoreFacade, null);
-		var methodExtensionContext = new MethodExtensionContext(classExtensionContext, null, methodTestDescriptor,
+		var classExtensionContext = new ClassExtensionContext(engineExtensionContext, mock(), classTestDescriptor,
+			PER_METHOD, configuration, extensionRegistry, launcherStoreFacade, mock());
+		var methodExtensionContext = new MethodExtensionContext(classExtensionContext, mock(), methodTestDescriptor,
 			configuration, extensionRegistry, launcherStoreFacade, new OpenTest4JAwareThrowableCollector());
 		methodExtensionContext.setTestInstances(DefaultTestInstances.of(testInstance));
 
@@ -255,10 +262,11 @@ void fromMethodTestDescriptor() {
 	@Test
 	@SuppressWarnings("resource")
 	void reportEntriesArePublishedToExecutionListener() {
-		var classTestDescriptor = outerClassDescriptor(null);
+		var classTestDescriptor = outerClassDescriptor(mock());
 		var engineExecutionListener = spy(EngineExecutionListener.class);
-		ExtensionContext extensionContext = new ClassExtensionContext(null, engineExecutionListener,
-			classTestDescriptor, PER_METHOD, configuration, extensionRegistry, launcherStoreFacade, null);
+		ExtensionContext extensionContext = new ClassExtensionContext(mock(AbstractExtensionContext.class),
+			engineExecutionListener, classTestDescriptor, PER_METHOD, configuration, extensionRegistry,
+			launcherStoreFacade, mock());
 
 		var map1 = Collections.singletonMap("key", "value");
 		var map2 = Collections.singletonMap("other key", "other value");
@@ -374,6 +382,19 @@ void failsWhenAttemptingToPublishRegularFilesAsDirectories(@TempDir Path tempDir
 			"Published path must be a directory: " + tempDir.resolve("OuterClass").resolve("test"));
 	}
 
+	@Test
+	void allowsPublishingToTheSameDirectoryTwice(@TempDir Path tempDir) {
+		var extensionContext = createExtensionContextForFilePublishing(tempDir);
+
+		extensionContext.publishDirectory("test",
+			dir -> Files.writeString(dir.resolve("nested1.txt"), "Nested content 1"));
+		extensionContext.publishDirectory("test",
+			dir -> Files.writeString(dir.resolve("nested2.txt"), "Nested content 2"));
+
+		assertThat(tempDir.resolve("OuterClass/test/nested1.txt")).hasContent("Nested content 1");
+		assertThat(tempDir.resolve("OuterClass/test/nested2.txt")).hasContent("Nested content 2");
+	}
+
 	private ExtensionContext createExtensionContextForFilePublishing(Path tempDir) {
 		return createExtensionContextForFilePublishing(tempDir, mock(EngineExecutionListener.class),
 			outerClassDescriptor(null));
@@ -383,8 +404,8 @@ private ExtensionContext createExtensionContextForFilePublishing(Path tempDir,
 			EngineExecutionListener engineExecutionListener, ClassTestDescriptor classTestDescriptor) {
 		when(configuration.getOutputDirectoryProvider()) //
 				.thenReturn(hierarchicalOutputDirectoryProvider(tempDir));
-		return new ClassExtensionContext(null, engineExecutionListener, classTestDescriptor, PER_METHOD, configuration,
-			extensionRegistry, launcherStoreFacade, null);
+		return new ClassExtensionContext(mock(AbstractExtensionContext.class), engineExecutionListener,
+			classTestDescriptor, PER_METHOD, configuration, extensionRegistry, launcherStoreFacade, mock());
 	}
 
 	@Test
@@ -392,9 +413,9 @@ private ExtensionContext createExtensionContextForFilePublishing(Path tempDir,
 	void usingStore() {
 		var methodTestDescriptor = methodDescriptor();
 		var classTestDescriptor = outerClassDescriptor(methodTestDescriptor);
-		ExtensionContext parentContext = new ClassExtensionContext(null, null, classTestDescriptor, PER_METHOD,
-			configuration, extensionRegistry, launcherStoreFacade, null);
-		var childContext = new MethodExtensionContext(parentContext, null, methodTestDescriptor, configuration,
+		ExtensionContext parentContext = new ClassExtensionContext(mock(AbstractExtensionContext.class), mock(),
+			classTestDescriptor, PER_METHOD, configuration, extensionRegistry, launcherStoreFacade, mock());
+		var childContext = new MethodExtensionContext(parentContext, mock(), methodTestDescriptor, configuration,
 			extensionRegistry, launcherStoreFacade, new OpenTest4JAwareThrowableCollector());
 		childContext.setTestInstances(DefaultTestInstances.of(new OuterClassTestCase()));
 
@@ -431,7 +452,7 @@ void usingStore() {
 	@MethodSource("extensionContextFactories")
 	void configurationParameter(Function<JupiterConfiguration, ? extends ExtensionContext> extensionContextFactory) {
 		JupiterConfiguration echo = new DefaultJupiterConfiguration(new EchoParameters(),
-			dummyOutputDirectoryProvider());
+			dummyOutputDirectoryProvider(), mock());
 		var key = "123";
 		var expected = Optional.of(key);
 
@@ -448,22 +469,22 @@ void configurationParameter(Function<JupiterConfiguration, ? extends ExtensionCo
 			named("engine", (JupiterConfiguration configuration) -> {
 				var engineUniqueId = UniqueId.parse("[engine:junit-jupiter]");
 				var engineDescriptor = new JupiterEngineDescriptor(engineUniqueId, configuration);
-				return new JupiterEngineExtensionContext(null, engineDescriptor, configuration, extensionRegistry,
+				return new JupiterEngineExtensionContext(mock(), engineDescriptor, configuration, extensionRegistry,
 					launcherStoreFacade);
 			}), //
 			named("class", (JupiterConfiguration configuration) -> {
 				var classUniqueId = UniqueId.parse("[engine:junit-jupiter]/[class:MyClass]");
 				var classTestDescriptor = new ClassTestDescriptor(classUniqueId, testClass, configuration);
-				return new ClassExtensionContext(null, null, classTestDescriptor, PER_METHOD, configuration,
-					extensionRegistry, launcherStoreFacade, null);
+				return new ClassExtensionContext(mock(AbstractExtensionContext.class), mock(), classTestDescriptor,
+					PER_METHOD, configuration, extensionRegistry, launcherStoreFacade, mock());
 			}), //
 			named("method", (JupiterConfiguration configuration) -> {
 				var method = ReflectionSupport.findMethod(testClass, "extensionContextFactories").orElseThrow();
 				var methodUniqueId = UniqueId.parse("[engine:junit-jupiter]/[class:MyClass]/[method:myMethod]");
 				var methodTestDescriptor = new TestMethodTestDescriptor(methodUniqueId, testClass, method, List::of,
 					configuration);
-				return new MethodExtensionContext(null, null, methodTestDescriptor, configuration, extensionRegistry,
-					launcherStoreFacade, null);
+				return new MethodExtensionContext(mock(AbstractExtensionContext.class), mock(), methodTestDescriptor,
+					configuration, extensionRegistry, launcherStoreFacade, mock());
 			}) //
 		);
 	}
@@ -478,7 +499,7 @@ private NestedClassTestDescriptor doublyNestedClassDescriptor() {
 			OuterClassTestCase.NestedClass.DoublyNestedClass.class, List::of, configuration);
 	}
 
-	private ClassTestDescriptor outerClassDescriptor(TestDescriptor child) {
+	private ClassTestDescriptor outerClassDescriptor(@Nullable TestDescriptor child) {
 		var classTestDescriptor = new ClassTestDescriptor(UniqueId.root("class", "OuterClass"),
 			OuterClassTestCase.class, configuration);
 		if (child != null) {
@@ -543,12 +564,6 @@ public Optional<Boolean> getBoolean(String key) {
 			throw new UnsupportedOperationException("getBoolean(String) should not be called");
 		}
 
-		@SuppressWarnings({ "deprecation", "RedundantSuppression" })
-		@Override
-		public int size() {
-			throw new UnsupportedOperationException("size() should not be called");
-		}
-
 		@Override
 		public Set<String> keySet() {
 			throw new UnsupportedOperationException("keySet() should not be called");
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/descriptor/LauncherStoreFacadeTest.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/descriptor/LauncherStoreFacadeTest.java
index e140cb7329d5..ae6d12135362 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/descriptor/LauncherStoreFacadeTest.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/descriptor/LauncherStoreFacadeTest.java
@@ -79,6 +79,7 @@ void returnsNamespaceAwareStore() {
 		assertNotNull(adapter);
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void throwsExceptionWhenNamespaceIsNull() {
 		LauncherStoreFacade facade = new LauncherStoreFacade(requestLevelStore);
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/descriptor/LifecycleMethodUtilsTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/descriptor/LifecycleMethodUtilsTests.java
index d4f56b9b684f..44f67c95609f 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/descriptor/LifecycleMethodUtilsTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/descriptor/LifecycleMethodUtilsTests.java
@@ -22,6 +22,7 @@
 import java.util.ArrayList;
 import java.util.List;
 
+import org.jspecify.annotations.NullUnmarked;
 import org.junit.jupiter.api.AfterAll;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeAll;
@@ -251,6 +252,7 @@ void eight() {
 }
 
 @SuppressWarnings("JUnitMalformedDeclaration")
+@NullUnmarked
 class TestCaseWithInvalidLifecycleMethods {
 
 	@BeforeEach
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/descriptor/ResourceAutoClosingTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/descriptor/ResourceAutoClosingTests.java
index ce217f3b838f..86bc5ffa08f3 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/descriptor/ResourceAutoClosingTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/descriptor/ResourceAutoClosingTests.java
@@ -35,11 +35,12 @@ class ResourceAutoClosingTests {
 		NamespacedHierarchicalStoreProviders.dummyNamespacedHierarchicalStore());
 
 	@Test
+	@SuppressWarnings("resource")
 	void shouldCloseAutoCloseableWhenIsClosingStoredAutoCloseablesEnabledIsTrue() throws Exception {
 		AutoCloseableResource resource = new AutoCloseableResource();
 		when(configuration.isClosingStoredAutoCloseablesEnabled()).thenReturn(true);
 
-		ExtensionContext extensionContext = new JupiterEngineExtensionContext(null, testDescriptor, configuration,
+		ExtensionContext extensionContext = new JupiterEngineExtensionContext(mock(), testDescriptor, configuration,
 			extensionRegistry, launcherStoreFacade);
 		ExtensionContext.Store store = extensionContext.getStore(ExtensionContext.Namespace.GLOBAL);
 		store.put("resource", resource);
@@ -50,11 +51,12 @@ void shouldCloseAutoCloseableWhenIsClosingStoredAutoCloseablesEnabledIsTrue() th
 	}
 
 	@Test
+	@SuppressWarnings("resource")
 	void shouldNotCloseAutoCloseableWhenIsClosingStoredAutoCloseablesEnabledIsFalse() throws Exception {
 		AutoCloseableResource resource = new AutoCloseableResource();
 		when(configuration.isClosingStoredAutoCloseablesEnabled()).thenReturn(false);
 
-		ExtensionContext extensionContext = new JupiterEngineExtensionContext(null, testDescriptor, configuration,
+		ExtensionContext extensionContext = new JupiterEngineExtensionContext(mock(), testDescriptor, configuration,
 			extensionRegistry, launcherStoreFacade);
 		ExtensionContext.Store store = extensionContext.getStore(ExtensionContext.Namespace.GLOBAL);
 		store.put("resource", resource);
@@ -65,6 +67,7 @@ void shouldNotCloseAutoCloseableWhenIsClosingStoredAutoCloseablesEnabledIsFalse(
 	}
 
 	@Test
+	@SuppressWarnings("resource")
 	void shouldLogWarningWhenResourceImplementsCloseableResourceButNotAutoCloseableAndConfigIsTrue(
 			@TrackLogRecords LogRecordListener listener) throws Exception {
 		ExecutionRecorder executionRecorder = new ExecutionRecorder();
@@ -84,6 +87,7 @@ void shouldLogWarningWhenResourceImplementsCloseableResourceButNotAutoCloseableA
 	}
 
 	@Test
+	@SuppressWarnings("resource")
 	void shouldNotLogWarningWhenResourceImplementsCloseableResourceAndAutoCloseableAndConfigIsFalse(
 			@TrackLogRecords LogRecordListener listener) throws Exception {
 		ExecutionRecorder executionRecorder = new ExecutionRecorder();
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/descriptor/TestFactoryTestDescriptorTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/descriptor/TestFactoryTestDescriptorTests.java
index d072738824d9..287dcb25c0d9 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/descriptor/TestFactoryTestDescriptorTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/descriptor/TestFactoryTestDescriptorTests.java
@@ -163,7 +163,7 @@ void before() throws Exception {
 			extensionContext = mock();
 			isClosed = false;
 
-			context = new JupiterEngineExecutionContext(null, null, null) //
+			context = new JupiterEngineExecutionContext(mock(), mock(), mock()) //
 					.extend() //
 					.withThrowableCollector(new OpenTest4JAwareThrowableCollector()) //
 					.withExtensionContext(extensionContext) //
@@ -203,13 +203,7 @@ private void prepareMockForTestInstanceWithCustomStream(Stream<?> stream) {
 
 	}
 
-	private static class CustomStreamTestCase {
-
-		private final Stream<?> mockStream;
-
-		CustomStreamTestCase(Stream<?> mockStream) {
-			this.mockStream = mockStream;
-		}
+	private record CustomStreamTestCase(Stream<?> mockStream) {
 
 		@TestFactory
 		Stream<?> customStream() {
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/descriptor/TestInstanceLifecycleUtilsTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/descriptor/TestInstanceLifecycleUtilsTests.java
index 186604bc98a9..2617a5153215 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/descriptor/TestInstanceLifecycleUtilsTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/descriptor/TestInstanceLifecycleUtilsTests.java
@@ -48,11 +48,12 @@ class TestInstanceLifecycleUtilsTests {
 
 	private static final String KEY = DEFAULT_TEST_INSTANCE_LIFECYCLE_PROPERTY_NAME;
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void getTestInstanceLifecyclePreconditions() {
 		PreconditionViolationException exception = assertThrows(PreconditionViolationException.class,
 			() -> getTestInstanceLifecycle(null,
-				new DefaultJupiterConfiguration(mock(), dummyOutputDirectoryProvider())));
+				new DefaultJupiterConfiguration(mock(), dummyOutputDirectoryProvider(), mock())));
 		assertThat(exception).hasMessage("testClass must not be null");
 
 		exception = assertThrows(PreconditionViolationException.class,
@@ -63,7 +64,7 @@ void getTestInstanceLifecyclePreconditions() {
 	@Test
 	void getTestInstanceLifecycleWithNoConfigParamSet() {
 		Lifecycle lifecycle = getTestInstanceLifecycle(getClass(),
-			new DefaultJupiterConfiguration(mock(), dummyOutputDirectoryProvider()));
+			new DefaultJupiterConfiguration(mock(), dummyOutputDirectoryProvider(), mock()));
 		assertThat(lifecycle).isEqualTo(PER_METHOD);
 	}
 
@@ -72,7 +73,7 @@ void getTestInstanceLifecycleWithConfigParamSet() {
 		ConfigurationParameters configParams = mock();
 		when(configParams.get(KEY)).thenReturn(Optional.of(PER_CLASS.name().toLowerCase()));
 		Lifecycle lifecycle = getTestInstanceLifecycle(getClass(),
-			new DefaultJupiterConfiguration(configParams, dummyOutputDirectoryProvider()));
+			new DefaultJupiterConfiguration(configParams, dummyOutputDirectoryProvider(), mock()));
 		assertThat(lifecycle).isEqualTo(PER_CLASS);
 	}
 
@@ -81,7 +82,7 @@ void getTestInstanceLifecycleWithLocalConfigThatOverridesCustomDefaultSetViaConf
 		ConfigurationParameters configParams = mock();
 		when(configParams.get(KEY)).thenReturn(Optional.of(PER_CLASS.name().toLowerCase()));
 		Lifecycle lifecycle = getTestInstanceLifecycle(TestCase.class,
-			new DefaultJupiterConfiguration(configParams, dummyOutputDirectoryProvider()));
+			new DefaultJupiterConfiguration(configParams, dummyOutputDirectoryProvider(), mock()));
 		assertThat(lifecycle).isEqualTo(PER_METHOD);
 	}
 
@@ -89,7 +90,7 @@ void getTestInstanceLifecycleWithLocalConfigThatOverridesCustomDefaultSetViaConf
 	void getTestInstanceLifecycleFromMetaAnnotationWithNoConfigParamSet() {
 		Class<?> testClass = BaseMetaAnnotatedTestCase.class;
 		Lifecycle lifecycle = getTestInstanceLifecycle(testClass,
-			new DefaultJupiterConfiguration(mock(), dummyOutputDirectoryProvider()));
+			new DefaultJupiterConfiguration(mock(), dummyOutputDirectoryProvider(), mock()));
 		assertThat(lifecycle).isEqualTo(PER_CLASS);
 	}
 
@@ -97,7 +98,7 @@ void getTestInstanceLifecycleFromMetaAnnotationWithNoConfigParamSet() {
 	void getTestInstanceLifecycleFromSpecializedClassWithNoConfigParamSet() {
 		Class<?> testClass = SpecializedTestCase.class;
 		Lifecycle lifecycle = getTestInstanceLifecycle(testClass,
-			new DefaultJupiterConfiguration(mock(), dummyOutputDirectoryProvider()));
+			new DefaultJupiterConfiguration(mock(), dummyOutputDirectoryProvider(), mock()));
 		assertThat(lifecycle).isEqualTo(PER_CLASS);
 	}
 
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/discovery/DiscoverySelectorResolverTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/discovery/DiscoverySelectorResolverTests.java
index f607f28e15b9..3a58eda73c6b 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/discovery/DiscoverySelectorResolverTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/discovery/DiscoverySelectorResolverTests.java
@@ -49,12 +49,12 @@
 import java.net.URL;
 import java.net.URLClassLoader;
 import java.nio.file.Path;
-import java.nio.file.Paths;
 import java.util.List;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.function.Predicate;
 import java.util.stream.Stream;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.ClassTemplate;
 import org.junit.jupiter.api.DisplayNameGenerator;
@@ -99,7 +99,8 @@ class DiscoverySelectorResolverTests extends AbstractJupiterTestEngineTests {
 
 	private final JupiterConfiguration configuration = mock();
 	private final LauncherDiscoveryListener discoveryListener = mock();
-	private TestDescriptor engineDescriptor;
+
+	private @Nullable TestDescriptor engineDescriptor;
 
 	@BeforeEach
 	void setUp() {
@@ -112,7 +113,7 @@ void setUp() {
 	void nonTestClassResolution() {
 		resolve(request().selectors(selectClass(NonTestClass.class)));
 
-		assertTrue(engineDescriptor.getDescendants().isEmpty());
+		assertTrue(requireNonNull(engineDescriptor).getDescendants().isEmpty());
 	}
 
 	@Test
@@ -120,7 +121,7 @@ void doesNotAttemptToResolveMethodsForNonTestClasses() {
 		var methodSelector = selectMethod(NonTestClass.class, "doesNotExist");
 		resolve(request().selectors(methodSelector));
 
-		assertTrue(engineDescriptor.getDescendants().isEmpty());
+		assertTrue(requireNonNull(engineDescriptor).getDescendants().isEmpty());
 		assertUnresolved(methodSelector);
 	}
 
@@ -128,7 +129,7 @@ void doesNotAttemptToResolveMethodsForNonTestClasses() {
 	void abstractClassResolution() {
 		resolve(request().selectors(selectClass(AbstractTestClass.class)));
 
-		assertTrue(engineDescriptor.getDescendants().isEmpty());
+		assertTrue(requireNonNull(engineDescriptor).getDescendants().isEmpty());
 		assertUnresolved(selectClass(AbstractTestClass.class));
 	}
 
@@ -138,7 +139,7 @@ void singleClassResolution() {
 
 		resolve(request().selectors(selector));
 
-		assertEquals(4, engineDescriptor.getDescendants().size());
+		assertEquals(4, requireNonNull(engineDescriptor).getDescendants().size());
 		assertUniqueIdsForMyTestClass(uniqueIds());
 	}
 
@@ -148,7 +149,7 @@ void classResolutionForNonexistentClass() {
 
 		resolve(request().selectors(selector));
 
-		assertTrue(engineDescriptor.getDescendants().isEmpty());
+		assertTrue(requireNonNull(engineDescriptor).getDescendants().isEmpty());
 		var result = verifySelectorProcessed(selector);
 		assertThat(result.getStatus()).isEqualTo(FAILED);
 		assertThat(result.getThrowable().orElseThrow()).hasMessageContaining("Could not load class with name");
@@ -161,7 +162,7 @@ void duplicateClassSelectorOnlyResolvesOnce() {
 			selectClass(MyTestClass.class) //
 		));
 
-		assertEquals(4, engineDescriptor.getDescendants().size());
+		assertEquals(4, requireNonNull(engineDescriptor).getDescendants().size());
 		assertUniqueIdsForMyTestClass(uniqueIds());
 	}
 
@@ -172,7 +173,7 @@ void twoClassesResolution() {
 
 		resolve(request().selectors(selector1, selector2));
 
-		assertEquals(7, engineDescriptor.getDescendants().size());
+		assertEquals(7, requireNonNull(engineDescriptor).getDescendants().size());
 		List<UniqueId> uniqueIds = uniqueIds();
 		assertUniqueIdsForMyTestClass(uniqueIds);
 		assertThat(uniqueIds).contains(uniqueIdForClass(YourTestClass.class));
@@ -193,7 +194,7 @@ void classResolutionOfStaticNestedClass() {
 
 		resolve(request().selectors(selector));
 
-		assertEquals(3, engineDescriptor.getDescendants().size());
+		assertEquals(3, requireNonNull(engineDescriptor).getDescendants().size());
 		List<UniqueId> uniqueIds = uniqueIds();
 		assertThat(uniqueIds).contains(uniqueIdForClass(OtherTestClass.NestedTestClass.class));
 		assertThat(uniqueIds).contains(uniqueIdForMethod(OtherTestClass.NestedTestClass.class, "test5()"));
@@ -218,7 +219,7 @@ void classResolutionOfClassTemplate() {
 
 		assertThat(verified.get()).describedAs("filter can see descendants").isTrue();
 
-		TestDescriptor classTemplateDescriptor = getOnlyElement(engineDescriptor.getChildren());
+		TestDescriptor classTemplateDescriptor = getOnlyElement(requireNonNull(engineDescriptor).getChildren());
 		assertThat(classTemplateDescriptor.mayRegisterTests()).isTrue();
 		assertThat(classTemplateDescriptor.getDescendants()).isEmpty();
 
@@ -234,17 +235,17 @@ void uniqueIdResolutionOfClassTemplateInvocation() {
 
 		resolve(request().selectors(selector));
 
-		assertThat(engineDescriptor.getChildren()).hasSize(1);
+		assertThat(requireNonNull(engineDescriptor).getChildren()).hasSize(1);
 
-		TestDescriptor classTemplateDescriptor = getOnlyElement(engineDescriptor.getChildren());
+		TestDescriptor classTemplateDescriptor = getOnlyElement(requireNonNull(engineDescriptor).getChildren());
 
 		classTemplateDescriptor.prune();
-		assertThat(engineDescriptor.getChildren()).hasSize(1);
+		assertThat(requireNonNull(engineDescriptor).getChildren()).hasSize(1);
 		assertThat(classTemplateDescriptor.mayRegisterTests()).isTrue();
 		assertThat(classTemplateDescriptor.getDescendants()).isEmpty();
 
 		classTemplateDescriptor.prune();
-		assertThat(engineDescriptor.getChildren()).hasSize(1);
+		assertThat(requireNonNull(engineDescriptor).getChildren()).hasSize(1);
 		assertThat(classTemplateDescriptor.mayRegisterTests()).isTrue();
 		assertThat(classTemplateDescriptor.getDescendants()).isEmpty();
 	}
@@ -256,7 +257,7 @@ void methodResolution() throws NoSuchMethodException {
 
 		resolve(request().selectors(selector));
 
-		assertEquals(2, engineDescriptor.getDescendants().size());
+		assertEquals(2, requireNonNull(engineDescriptor).getDescendants().size());
 		List<UniqueId> uniqueIds = uniqueIds();
 		assertThat(uniqueIds).contains(uniqueIdForClass(MyTestClass.class));
 		assertThat(uniqueIds).contains(uniqueIdForMethod(MyTestClass.class, "test1()"));
@@ -268,7 +269,7 @@ void methodResolutionFromInheritedMethod() throws NoSuchMethodException {
 
 		resolve(request().selectors(selector));
 
-		assertEquals(2, engineDescriptor.getDescendants().size());
+		assertEquals(2, requireNonNull(engineDescriptor).getDescendants().size());
 		List<UniqueId> uniqueIds = uniqueIds();
 		assertThat(uniqueIds).contains(uniqueIdForClass(HerTestClass.class));
 		assertThat(uniqueIds).contains(uniqueIdForMethod(HerTestClass.class, "test1()"));
@@ -281,7 +282,7 @@ void resolvingSelectorOfNonTestMethodResolvesNothing() throws NoSuchMethodExcept
 
 		resolve(request().selectors(selector));
 
-		assertTrue(engineDescriptor.getDescendants().isEmpty());
+		assertTrue(requireNonNull(engineDescriptor).getDescendants().isEmpty());
 	}
 
 	@Test
@@ -292,7 +293,7 @@ void methodResolutionForNonexistentClass() {
 
 		resolve(request().selectors(selector));
 
-		assertTrue(engineDescriptor.getDescendants().isEmpty());
+		assertTrue(requireNonNull(engineDescriptor).getDescendants().isEmpty());
 		var result = verifySelectorProcessed(selector);
 		assertThat(result.getStatus()).isEqualTo(FAILED);
 		assertThat(result.getThrowable().orElseThrow())//
@@ -306,7 +307,7 @@ void methodResolutionForNonexistentMethod() {
 
 		resolve(request().selectors(selector));
 
-		assertTrue(engineDescriptor.getDescendants().isEmpty());
+		assertTrue(requireNonNull(engineDescriptor).getDescendants().isEmpty());
 		var result = verifySelectorProcessed(selector);
 		assertThat(result.getStatus()).isEqualTo(FAILED);
 		assertThat(result.getThrowable().orElseThrow()).hasMessageContaining("Could not find method");
@@ -318,7 +319,7 @@ void classResolutionByUniqueId() {
 
 		resolve(request().selectors(selector));
 
-		assertEquals(4, engineDescriptor.getDescendants().size());
+		assertEquals(4, requireNonNull(engineDescriptor).getDescendants().size());
 		List<UniqueId> uniqueIds = uniqueIds();
 		assertUniqueIdsForMyTestClass(uniqueIds);
 	}
@@ -329,7 +330,7 @@ void staticNestedClassResolutionByUniqueId() {
 
 		resolve(request().selectors(selector));
 
-		assertEquals(3, engineDescriptor.getDescendants().size());
+		assertEquals(3, requireNonNull(engineDescriptor).getDescendants().size());
 		List<UniqueId> uniqueIds = uniqueIds();
 		assertThat(uniqueIds).contains(uniqueIdForClass(OtherTestClass.NestedTestClass.class));
 		assertThat(uniqueIds).contains(uniqueIdForMethod(OtherTestClass.NestedTestClass.class, "test5()"));
@@ -343,7 +344,7 @@ void methodOfInnerClassByUniqueId() {
 
 		resolve(request().selectors(selector));
 
-		assertEquals(2, engineDescriptor.getDescendants().size());
+		assertEquals(2, requireNonNull(engineDescriptor).getDescendants().size());
 		List<UniqueId> uniqueIds = uniqueIds();
 		assertThat(uniqueIds).contains(uniqueIdForClass(OtherTestClass.NestedTestClass.class));
 		assertThat(uniqueIds).contains(uniqueIdForMethod(OtherTestClass.NestedTestClass.class, "test5()"));
@@ -356,7 +357,7 @@ void resolvingUniqueIdWithUnknownSegmentTypeResolvesNothing() {
 
 		resolve(request().selectors(selector));
 
-		assertTrue(engineDescriptor.getDescendants().isEmpty());
+		assertTrue(requireNonNull(engineDescriptor).getDescendants().isEmpty());
 		assertUnresolved(selector);
 	}
 
@@ -366,7 +367,7 @@ void resolvingUniqueIdOfNonTestMethodResolvesNothing() {
 
 		resolve(request().selectors(selector));
 
-		assertThat(engineDescriptor.getDescendants()).isEmpty();
+		assertThat(requireNonNull(engineDescriptor).getDescendants()).isEmpty();
 		assertUnresolved(selector);
 	}
 
@@ -376,7 +377,7 @@ void methodResolutionByUniqueIdWithMissingMethodName() {
 
 		resolve(request().selectors(selectUniqueId(uniqueId)));
 
-		assertTrue(engineDescriptor.getDescendants().isEmpty());
+		assertTrue(requireNonNull(engineDescriptor).getDescendants().isEmpty());
 		var result = verifySelectorProcessed(selectUniqueId(uniqueId));
 		assertThat(result.getStatus()).isEqualTo(FAILED);
 		assertThat(result.getThrowable().orElseThrow())//
@@ -390,7 +391,7 @@ void methodResolutionByUniqueIdWithMissingParameters() {
 
 		resolve(request().selectors(selectUniqueId(uniqueId)));
 
-		assertThat(engineDescriptor.getDescendants()).isEmpty();
+		assertThat(requireNonNull(engineDescriptor).getDescendants()).isEmpty();
 		var result = verifySelectorProcessed(selectUniqueId(uniqueId));
 		assertThat(result.getStatus()).isEqualTo(FAILED);
 		assertThat(result.getThrowable().orElseThrow())//
@@ -404,7 +405,7 @@ void methodResolutionByUniqueIdWithBogusParameters() {
 
 		resolve(request().selectors(selectUniqueId(uniqueId)));
 
-		assertTrue(engineDescriptor.getDescendants().isEmpty());
+		assertTrue(requireNonNull(engineDescriptor).getDescendants().isEmpty());
 		var result = verifySelectorProcessed(selectUniqueId(uniqueId));
 		assertThat(result.getStatus()).isEqualTo(FAILED);
 		assertThat(result.getThrowable().orElseThrow())//
@@ -419,7 +420,7 @@ void methodResolutionByUniqueId() {
 
 		resolve(request().selectors(selector));
 
-		assertEquals(2, engineDescriptor.getDescendants().size());
+		assertEquals(2, requireNonNull(engineDescriptor).getDescendants().size());
 		List<UniqueId> uniqueIds = uniqueIds();
 		assertThat(uniqueIds).contains(uniqueIdForClass(MyTestClass.class));
 		assertThat(uniqueIds).contains(uniqueIdForMethod(MyTestClass.class, "test1()"));
@@ -431,7 +432,7 @@ void methodResolutionByUniqueIdFromInheritedClass() {
 
 		resolve(request().selectors(selector));
 
-		assertEquals(2, engineDescriptor.getDescendants().size());
+		assertEquals(2, requireNonNull(engineDescriptor).getDescendants().size());
 		List<UniqueId> uniqueIds = uniqueIds();
 
 		assertThat(uniqueIds).contains(uniqueIdForClass(HerTestClass.class));
@@ -445,7 +446,7 @@ void methodResolutionByUniqueIdWithParams() {
 
 		resolve(request().selectors(selector));
 
-		assertEquals(2, engineDescriptor.getDescendants().size());
+		assertEquals(2, requireNonNull(engineDescriptor).getDescendants().size());
 		List<UniqueId> uniqueIds = uniqueIds();
 		assertThat(uniqueIds).contains(uniqueIdForClass(HerTestClass.class));
 		assertThat(uniqueIds).contains(uniqueIdForMethod(HerTestClass.class, "test7(java.lang.String)"));
@@ -458,7 +459,7 @@ void resolvingUniqueIdWithWrongParamsResolvesNothing() {
 
 		resolve(request().selectors(selectUniqueId(uniqueId)));
 
-		assertTrue(engineDescriptor.getDescendants().isEmpty());
+		assertTrue(requireNonNull(engineDescriptor).getDescendants().isEmpty());
 		assertUnresolved(selectUniqueId(uniqueId));
 	}
 
@@ -470,7 +471,7 @@ void twoMethodResolutionsByUniqueId() {
 		// adding same selector twice should have no effect
 		resolve(request().selectors(selector1, selector2, selector2));
 
-		assertEquals(3, engineDescriptor.getDescendants().size());
+		assertEquals(3, requireNonNull(engineDescriptor).getDescendants().size());
 		List<UniqueId> uniqueIds = uniqueIds();
 		assertThat(uniqueIds).contains(uniqueIdForClass(MyTestClass.class));
 		assertThat(uniqueIds).contains(uniqueIdForMethod(MyTestClass.class, "test1()"));
@@ -491,7 +492,7 @@ void packageResolutionUsingExplicitBasePackage() {
 
 		resolve(request().selectors(selector));
 
-		assertEquals(6, engineDescriptor.getDescendants().size());
+		assertEquals(6, requireNonNull(engineDescriptor).getDescendants().size());
 		List<UniqueId> uniqueIds = uniqueIds();
 		assertThat(uniqueIds).contains(uniqueIdForClass(Class1WithTestCases.class));
 		assertThat(uniqueIds).contains(uniqueIdForMethod(Class1WithTestCases.class, "test1()"));
@@ -506,7 +507,7 @@ void packageResolutionUsingDefaultPackage() throws Exception {
 		resolve(request().selectors(selectPackage("")));
 
 		// 150 is completely arbitrary. The actual number is likely much higher.
-		assertThat(engineDescriptor.getDescendants())//
+		assertThat(requireNonNull(engineDescriptor).getDescendants())//
 				.describedAs("Too few test descriptors in classpath")//
 				.hasSizeGreaterThan(150);
 
@@ -522,7 +523,7 @@ void packageResolutionUsingDefaultPackage() throws Exception {
 
 	@Test
 	void classpathResolution() throws Exception {
-		Path classpath = Paths.get(
+		Path classpath = Path.of(
 			DiscoverySelectorResolverTests.class.getProtectionDomain().getCodeSource().getLocation().toURI());
 
 		List<ClasspathRootSelector> selectors = selectClasspathRoots(singleton(classpath));
@@ -530,14 +531,14 @@ void classpathResolution() throws Exception {
 		resolve(request().selectors(selectors));
 
 		// 150 is completely arbitrary. The actual number is likely much higher.
-		assertThat(engineDescriptor.getDescendants())//
+		assertThat(requireNonNull(engineDescriptor).getDescendants())//
 				.describedAs("Too few test descriptors in classpath")//
 				.hasSizeGreaterThan(150);
 
 		List<UniqueId> uniqueIds = uniqueIds();
 		assertThat(uniqueIds)//
 				.describedAs("Failed to pick up DefaultPackageTestCase via classpath scanning")//
-				.contains(uniqueIdForClass(ReflectionSupport.tryToLoadClass("DefaultPackageTestCase").get()));
+				.contains(uniqueIdForClass(ReflectionSupport.tryToLoadClass("DefaultPackageTestCase").getNonNull()));
 		assertThat(uniqueIds).contains(uniqueIdForClass(Class1WithTestCases.class));
 		assertThat(uniqueIds).contains(uniqueIdForMethod(Class1WithTestCases.class, "test1()"));
 		assertThat(uniqueIds).contains(uniqueIdForClass(Class2WithTestCases.class));
@@ -549,7 +550,7 @@ void classpathResolution() throws Exception {
 	@Test
 	void classpathResolutionForJarFiles() throws Exception {
 		URL jarUrl = requireNonNull(getClass().getResource("/jupiter-testjar.jar"));
-		Path path = Paths.get(jarUrl.toURI());
+		Path path = Path.of(jarUrl.toURI());
 		List<ClasspathRootSelector> selectors = selectClasspathRoots(singleton(path));
 
 		ClassLoader originalClassLoader = Thread.currentThread().getContextClassLoader();
@@ -642,7 +643,7 @@ void methodResolutionInDoubleNestedTestClass() throws NoSuchMethodException {
 
 		resolve(request().selectors(selector));
 
-		assertEquals(4, engineDescriptor.getDescendants().size());
+		assertEquals(4, requireNonNull(engineDescriptor).getDescendants().size());
 		List<UniqueId> uniqueIds = uniqueIds();
 		assertThat(uniqueIds).contains(uniqueIdForClass(TestCaseWithNesting.class));
 		assertThat(uniqueIds).contains(uniqueIdForClass(TestCaseWithNesting.NestedTestCase.class));
@@ -672,7 +673,7 @@ void testFactoryMethodResolutionByUniqueId() {
 
 		resolve(request().selectors(selectUniqueId(factoryUid)));
 
-		assertThat(engineDescriptor.getDescendants()).hasSize(2);
+		assertThat(requireNonNull(engineDescriptor).getDescendants()).hasSize(2);
 		assertThat(uniqueIds()).containsSequence(uniqueIdForClass(clazz), factoryUid);
 	}
 
@@ -683,7 +684,7 @@ void testTemplateMethodResolutionByUniqueId() {
 
 		resolve(request().selectors(selectUniqueId(templateUid)));
 
-		assertThat(engineDescriptor.getDescendants()).hasSize(2);
+		assertThat(requireNonNull(engineDescriptor).getDescendants()).hasSize(2);
 		assertThat(uniqueIds()).containsSequence(uniqueIdForClass(clazz), templateUid);
 	}
 
@@ -696,9 +697,9 @@ void resolvingDynamicTestByUniqueIdResolvesUpToParentTestFactory() {
 
 		resolve(request().selectors(selectUniqueId(dynamicTestUid)));
 
-		assertThat(engineDescriptor.getDescendants()).hasSize(2);
+		assertThat(requireNonNull(engineDescriptor).getDescendants()).hasSize(2);
 		assertThat(uniqueIds()).containsSequence(uniqueIdForClass(clazz), factoryUid);
-		TestDescriptor testClassDescriptor = getOnlyElement(engineDescriptor.getChildren());
+		TestDescriptor testClassDescriptor = getOnlyElement(requireNonNull(engineDescriptor).getChildren());
 
 		TestDescriptor testFactoryDescriptor = getOnlyElement(testClassDescriptor.getChildren());
 		DynamicDescendantFilter dynamicDescendantFilter = getDynamicDescendantFilter(testFactoryDescriptor);
@@ -719,9 +720,9 @@ void resolvingDynamicContainerByUniqueIdResolvesUpToParentTestFactory() {
 
 		resolve(request().selectors(selectUniqueId(dynamicTestUid)));
 
-		assertThat(engineDescriptor.getDescendants()).hasSize(2);
+		assertThat(requireNonNull(engineDescriptor).getDescendants()).hasSize(2);
 		assertThat(uniqueIds()).containsSequence(uniqueIdForClass(clazz), factoryUid);
-		TestDescriptor testClassDescriptor = getOnlyElement(engineDescriptor.getChildren());
+		TestDescriptor testClassDescriptor = getOnlyElement(requireNonNull(engineDescriptor).getChildren());
 
 		TestDescriptor testFactoryDescriptor = getOnlyElement(testClassDescriptor.getChildren());
 		DynamicDescendantFilter dynamicDescendantFilter = getDynamicDescendantFilter(testFactoryDescriptor);
@@ -740,9 +741,9 @@ void resolvingDynamicTestByUniqueIdAndTestFactoryByMethodSelectorResolvesTestFac
 
 		resolve(request().selectors(selectUniqueId(dynamicTestUid), selectMethod(clazz, "dynamicTest")));
 
-		assertThat(engineDescriptor.getDescendants()).hasSize(2);
+		assertThat(requireNonNull(engineDescriptor).getDescendants()).hasSize(2);
 		assertThat(uniqueIds()).containsSequence(uniqueIdForClass(clazz), factoryUid);
-		TestDescriptor testClassDescriptor = getOnlyElement(engineDescriptor.getChildren());
+		TestDescriptor testClassDescriptor = getOnlyElement(requireNonNull(engineDescriptor).getChildren());
 		TestDescriptor testFactoryDescriptor = getOnlyElement(testClassDescriptor.getChildren());
 		DynamicDescendantFilter dynamicDescendantFilter = getDynamicDescendantFilter(testFactoryDescriptor);
 		assertThat(dynamicDescendantFilter.test(UniqueId.root("foo", "bar"), 42)).isTrue();
@@ -761,7 +762,7 @@ void resolvingTestTemplateInvocationByUniqueIdResolvesOnlyUpToParentTestTemplate
 
 		resolve(request().selectors(selectUniqueId(invocationUid)));
 
-		assertThat(engineDescriptor.getDescendants()).hasSize(2);
+		assertThat(requireNonNull(engineDescriptor).getDescendants()).hasSize(2);
 		assertThat(uniqueIds()).containsSequence(uniqueIdForClass(clazz), templateUid);
 	}
 
@@ -770,7 +771,7 @@ void includingPackageNameFilterExcludesClassesInNonMatchingPackages() {
 		resolve(request().selectors(selectClass(MatchingClass.class)).filters(
 			includePackageNames("org.junit.jupiter.engine.unknown")));
 
-		assertThat(engineDescriptor.getDescendants()).isEmpty();
+		assertThat(requireNonNull(engineDescriptor).getDescendants()).isEmpty();
 	}
 
 	@Test
@@ -778,7 +779,7 @@ void includingPackageNameFilterIncludesClassesInMatchingPackages() {
 		resolve(request().selectors(selectClass(MatchingClass.class)).filters(
 			includePackageNames("org.junit.jupiter.engine")));
 
-		assertThat(engineDescriptor.getDescendants()).hasSize(3);
+		assertThat(requireNonNull(engineDescriptor).getDescendants()).hasSize(3);
 	}
 
 	@Test
@@ -786,7 +787,7 @@ void excludingPackageNameFilterExcludesClassesInMatchingPackages() {
 		resolve(request().selectors(selectClass(MatchingClass.class)).filters(
 			excludePackageNames("org.junit.jupiter.engine")));
 
-		assertThat(engineDescriptor.getDescendants()).isEmpty();
+		assertThat(requireNonNull(engineDescriptor).getDescendants()).isEmpty();
 	}
 
 	@Test
@@ -794,7 +795,7 @@ void excludingPackageNameFilterIncludesClassesInNonMatchingPackages() {
 		resolve(request().selectors(selectClass(MatchingClass.class)).filters(
 			excludePackageNames("org.junit.jupiter.engine.unknown")));
 
-		assertThat(engineDescriptor.getDescendants()).hasSize(3);
+		assertThat(requireNonNull(engineDescriptor).getDescendants()).hasSize(3);
 	}
 
 	@Test
@@ -802,7 +803,7 @@ void classNamePatternFilterExcludesNonMatchingClasses() {
 		resolve(request().selectors(selectClass(MatchingClass.class), selectClass(OtherClass.class)).filters(
 			includeClassNamePatterns(".*MatchingClass")));
 
-		assertThat(engineDescriptor.getDescendants()).hasSize(3);
+		assertThat(requireNonNull(engineDescriptor).getDescendants()).hasSize(3);
 	}
 
 	private void resolve(LauncherDiscoveryRequestBuilder builder) {
@@ -810,12 +811,12 @@ private void resolve(LauncherDiscoveryRequestBuilder builder) {
 	}
 
 	private TestDescriptor descriptorByUniqueId(UniqueId uniqueId) {
-		return engineDescriptor.getDescendants().stream().filter(
+		return requireNonNull(engineDescriptor).getDescendants().stream().filter(
 			d -> d.getUniqueId().equals(uniqueId)).findFirst().orElseThrow();
 	}
 
 	private List<UniqueId> uniqueIds() {
-		return engineDescriptor.getDescendants().stream().map(TestDescriptor::getUniqueId).toList();
+		return requireNonNull(engineDescriptor).getDescendants().stream().map(TestDescriptor::getUniqueId).toList();
 	}
 
 	private LauncherDiscoveryRequestBuilder request() {
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/discovery/DiscoveryTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/discovery/DiscoveryTests.java
index 26db9306abb9..2cb8532f3cef 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/discovery/DiscoveryTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/discovery/DiscoveryTests.java
@@ -48,6 +48,7 @@
 import org.junit.jupiter.params.provider.Arguments;
 import org.junit.jupiter.params.provider.MethodSource;
 import org.junit.platform.engine.DiscoveryIssue;
+import org.junit.platform.engine.DiscoveryIssue.Severity;
 import org.junit.platform.engine.TestDescriptor;
 import org.junit.platform.engine.support.descriptor.ClassSource;
 import org.junit.platform.launcher.LauncherDiscoveryRequest;
@@ -62,14 +63,14 @@ class DiscoveryTests extends AbstractJupiterTestEngineTests {
 	@Test
 	void discoverTestClass() {
 		LauncherDiscoveryRequest request = defaultRequest().selectors(selectClass(LocalTestCase.class)).build();
-		TestDescriptor engineDescriptor = discoverTests(request).getEngineDescriptor();
+		TestDescriptor engineDescriptor = discoverTestsWithoutIssues(request);
 		assertEquals(7, engineDescriptor.getDescendants().size(), "# resolved test descriptors");
 	}
 
 	@Test
 	void doNotDiscoverAbstractTestClass() {
 		LauncherDiscoveryRequest request = defaultRequest().selectors(selectClass(AbstractTestCase.class)).build();
-		TestDescriptor engineDescriptor = discoverTests(request).getEngineDescriptor();
+		TestDescriptor engineDescriptor = discoverTestsWithoutIssues(request);
 		assertEquals(0, engineDescriptor.getDescendants().size(), "# resolved test descriptors");
 	}
 
@@ -77,7 +78,7 @@ void doNotDiscoverAbstractTestClass() {
 	void discoverMethodByUniqueId() {
 		LauncherDiscoveryRequest request = defaultRequest().selectors(
 			selectUniqueId(JupiterUniqueIdBuilder.uniqueIdForMethod(LocalTestCase.class, "test1()"))).build();
-		TestDescriptor engineDescriptor = discoverTests(request).getEngineDescriptor();
+		TestDescriptor engineDescriptor = discoverTestsWithoutIssues(request);
 		assertEquals(2, engineDescriptor.getDescendants().size(), "# resolved test descriptors");
 	}
 
@@ -85,7 +86,7 @@ void discoverMethodByUniqueId() {
 	void discoverMethodByUniqueIdForOverloadedMethod() {
 		LauncherDiscoveryRequest request = defaultRequest().selectors(
 			selectUniqueId(JupiterUniqueIdBuilder.uniqueIdForMethod(LocalTestCase.class, "test4()"))).build();
-		TestDescriptor engineDescriptor = discoverTests(request).getEngineDescriptor();
+		TestDescriptor engineDescriptor = discoverTestsWithoutIssues(request);
 		assertEquals(2, engineDescriptor.getDescendants().size(), "# resolved test descriptors");
 	}
 
@@ -94,7 +95,7 @@ void discoverMethodByUniqueIdForOverloadedMethodVariantThatAcceptsArguments() {
 		LauncherDiscoveryRequest request = defaultRequest().selectors(
 			selectUniqueId(JupiterUniqueIdBuilder.uniqueIdForMethod(LocalTestCase.class,
 				"test4(" + TestInfo.class.getName() + ")"))).build();
-		TestDescriptor engineDescriptor = discoverTests(request).getEngineDescriptor();
+		TestDescriptor engineDescriptor = discoverTestsWithoutIssues(request);
 		assertEquals(2, engineDescriptor.getDescendants().size(), "# resolved test descriptors");
 	}
 
@@ -104,7 +105,7 @@ void discoverMethodByMethodReference() throws NoSuchMethodException {
 
 		LauncherDiscoveryRequest request = defaultRequest().selectors(
 			selectMethod(LocalTestCase.class, testMethod)).build();
-		TestDescriptor engineDescriptor = discoverTests(request).getEngineDescriptor();
+		TestDescriptor engineDescriptor = discoverTestsWithoutIssues(request);
 		assertEquals(2, engineDescriptor.getDescendants().size(), "# resolved test descriptors");
 	}
 
@@ -113,7 +114,7 @@ void discoverMultipleMethodsOfSameClass() {
 		LauncherDiscoveryRequest request = defaultRequest().selectors(selectMethod(LocalTestCase.class, "test1"),
 			selectMethod(LocalTestCase.class, "test2")).build();
 
-		TestDescriptor engineDescriptor = discoverTests(request).getEngineDescriptor();
+		TestDescriptor engineDescriptor = discoverTestsWithoutIssues(request);
 
 		assertThat(engineDescriptor.getChildren()).hasSize(1);
 		TestDescriptor classDescriptor = getOnlyElement(engineDescriptor.getChildren());
@@ -289,7 +290,35 @@ void reportsWarningForTestClassWithPotentialNestedTestClasses() {
 	}
 
 	@Test
-	void reportsWarningsForInvalidTags() throws NoSuchMethodException {
+	void ignoresUnrelatedClassDefinitionCycles() {
+		var results = discoverTestsForClass(UnrelatedRecursiveHierarchyTestCase.class);
+
+		assertThat(results.getDiscoveryIssues()).isEmpty();
+	}
+
+	@Test
+	void ignoresRecursiveNonTestHierarchyCycles() {
+		var results = discoverTestsForClass(NonTestRecursiveHierarchyTestCase.class);
+
+		assertThat(results.getDiscoveryIssues()).isEmpty();
+	}
+
+	@Test
+	void reportsMissingNestedAnnotationOnRecursiveHierarchy() {
+		var results = discoverTestsForClass(RecursiveHierarchyWithoutNestedTestCase.class);
+
+		var discoveryIssues = results.getDiscoveryIssues();
+		assertThat(discoveryIssues).hasSize(1);
+		assertThat(discoveryIssues.getFirst().severity()) //
+				.isEqualTo(Severity.WARNING);
+		assertThat(discoveryIssues.getFirst().message()) //
+				.isEqualTo(
+					"Inner class '%s' looks like it was intended to be a test class but will not be executed. It must be static or annotated with @Nested.",
+					RecursiveHierarchyWithoutNestedTestCase.Inner.class.getName());
+	}
+
+	@Test
+	void reportsWarningsForInvalidTags() throws Exception {
 
 		var results = discoverTestsForClass(InvalidTagsTestCase.class);
 
@@ -311,7 +340,7 @@ void reportsWarningsForInvalidTags() throws NoSuchMethodException {
 	}
 
 	@Test
-	void reportsWarningsForBlankDisplayNames() throws NoSuchMethodException {
+	void reportsWarningsForBlankDisplayNames() throws Exception {
 
 		var results = discoverTestsForClass(BlankDisplayNamesTestCase.class);
 
@@ -335,11 +364,14 @@ void reportsWarningsForBlankDisplayNames() throws NoSuchMethodException {
 	// -------------------------------------------------------------------
 
 	@SuppressWarnings("unused")
-	private static abstract class AbstractTestCase {
+	static abstract class AbstractTestCase {
 
 		@Test
-		void abstractTest() {
+		void test() {
 		}
+
+		@Test
+		abstract void abstractTest();
 	}
 
 	@SuppressWarnings("JUnitMalformedDeclaration")
@@ -441,6 +473,39 @@ private class InvalidTestClassSubclassTestCase extends InvalidTestClassTestCase
 
 	}
 
+	@SuppressWarnings("JUnitMalformedDeclaration")
+	static class UnrelatedRecursiveHierarchyTestCase {
+
+		@Test
+		void test() {
+		}
+
+		@SuppressWarnings({ "InnerClassMayBeStatic", "unused" })
+		class Inner {
+			class Recursive extends Inner {
+			}
+		}
+	}
+
+	@SuppressWarnings("JUnitMalformedDeclaration")
+	static class RecursiveHierarchyWithoutNestedTestCase {
+
+		@Test
+		void test() {
+		}
+
+		@SuppressWarnings({ "InnerClassMayBeStatic", "unused" })
+		class Inner extends RecursiveHierarchyWithoutNestedTestCase {
+		}
+	}
+
+	@SuppressWarnings("unused")
+	static class NonTestRecursiveHierarchyTestCase {
+		@SuppressWarnings("InnerClassMayBeStatic")
+		class Inner extends NonTestRecursiveHierarchyTestCase {
+		}
+	}
+
 	@SuppressWarnings("JUnitMalformedDeclaration")
 	@Tag("")
 	static class InvalidTagsTestCase {
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/discovery/predicates/IsTestMethodTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/discovery/predicates/IsTestMethodTests.java
index b5d4bc5aa89c..73373a4999d2 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/discovery/predicates/IsTestMethodTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/discovery/predicates/IsTestMethodTests.java
@@ -72,12 +72,7 @@ void bogusAbstractTestMethod() {
 		var method = abstractMethod("bogusAbstractTestMethod");
 
 		assertThat(isTestMethod).rejects(method);
-
-		var issue = getOnlyElement(discoveryIssues);
-		assertThat(issue.severity()).isEqualTo(Severity.WARNING);
-		assertThat(issue.message()).isEqualTo("@Test method '%s' must not be abstract. It will not be executed.",
-			method.toGenericString());
-		assertThat(issue.source()).contains(MethodSource.from(method));
+		assertThat(discoveryIssues).isEmpty();
 	}
 
 	@Test
@@ -86,12 +81,8 @@ void bogusAbstractNonVoidTestMethod() {
 
 		assertThat(isTestMethod).rejects(method);
 
-		assertThat(discoveryIssues).hasSize(2);
-		discoveryIssues.sort(comparing(DiscoveryIssue::message));
-		assertThat(discoveryIssues.getFirst().message()) //
-				.isEqualTo("@Test method '%s' must not be abstract. It will not be executed.",
-					method.toGenericString());
-		assertThat(discoveryIssues.getLast().message()) //
+		var issue = getOnlyElement(discoveryIssues);
+		assertThat(issue.message()) //
 				.isEqualTo("@Test method '%s' must not return a value. It will not be executed.",
 					method.toGenericString());
 	}
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/discovery/predicates/TestClassPredicatesTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/discovery/predicates/TestClassPredicatesTests.java
index 757d4a8cfa6c..bacd663d33df 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/discovery/predicates/TestClassPredicatesTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/discovery/predicates/TestClassPredicatesTests.java
@@ -12,7 +12,6 @@
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.jupiter.api.Assertions.assertFalse;
-import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import java.util.ArrayList;
@@ -24,7 +23,6 @@
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.TestFactory;
 import org.junit.jupiter.api.TestTemplate;
-import org.junit.platform.commons.JUnitException;
 import org.junit.platform.engine.DiscoveryIssue;
 import org.junit.platform.engine.DiscoveryIssue.Severity;
 import org.junit.platform.engine.support.descriptor.ClassSource;
@@ -214,11 +212,11 @@ void privateStaticTestClassEvaluatesToFalse() {
 		}
 
 		/*
-		 * see https://github.com/junit-team/junit5/issues/2249
+		 * see https://github.com/junit-team/junit-framework/issues/2249
 		 */
 		@Test
 		void recursiveHierarchies() {
-			assertThrows(JUnitException.class, () -> predicates.looksLikeIntendedTestClass(TestCases.OuterClass.class));
+			assertTrue(predicates.looksLikeIntendedTestClass(TestCases.OuterClass.class));
 			assertTrue(predicates.isValidStandaloneTestClass(TestCases.OuterClass.class));
 			assertThat(discoveryIssues).isEmpty();
 
@@ -404,6 +402,7 @@ void test() {
 			@SuppressWarnings("InnerClassMayBeStatic")
 			class RecursiveInnerClass extends OuterClass {
 			}
+
 		}
 
 		private static class NestedClassesTestCase {
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/execution/AbstractExecutableInvokerTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/execution/AbstractExecutableInvokerTests.java
index c054f3ec1220..bec4c4141d21 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/execution/AbstractExecutableInvokerTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/execution/AbstractExecutableInvokerTests.java
@@ -12,21 +12,22 @@
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
-import static org.junit.jupiter.engine.execution.ParameterResolutionUtilsTests.ConfigurableParameterResolver;
-import static org.junit.jupiter.engine.execution.ParameterResolutionUtilsTests.ConstructorInjectionTestCase;
-import static org.junit.jupiter.engine.execution.ParameterResolutionUtilsTests.MethodSource;
-import static org.junit.jupiter.engine.execution.ParameterResolutionUtilsTests.NumberParameterResolver;
-import static org.junit.jupiter.engine.execution.ParameterResolutionUtilsTests.StringParameterResolver;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.verify;
 
 import java.lang.reflect.Constructor;
 import java.lang.reflect.Method;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExtensionContext;
 import org.junit.jupiter.api.extension.ParameterResolver;
 import org.junit.jupiter.engine.config.JupiterConfiguration;
+import org.junit.jupiter.engine.execution.ParameterResolutionUtilsTests.ConfigurableParameterResolver;
+import org.junit.jupiter.engine.execution.ParameterResolutionUtilsTests.ConstructorInjectionTestCase;
+import org.junit.jupiter.engine.execution.ParameterResolutionUtilsTests.MethodSource;
+import org.junit.jupiter.engine.execution.ParameterResolutionUtilsTests.NumberParameterResolver;
+import org.junit.jupiter.engine.execution.ParameterResolutionUtilsTests.StringParameterResolver;
 import org.junit.jupiter.engine.extension.MutableExtensionRegistry;
 import org.junit.platform.commons.support.ReflectionSupport;
 import org.junit.platform.commons.util.ReflectionUtils;
@@ -39,7 +40,8 @@ abstract class AbstractExecutableInvokerTests {
 	private static final String ENIGMA = "enigma";
 
 	protected final MethodSource instance = mock();
-	protected Method method;
+
+	protected @Nullable Method method;
 
 	protected final ExtensionContext extensionContext = mock();
 
@@ -84,7 +86,7 @@ private void thereIsAParameterResolverThatResolvesTheParameterTo(Object argument
 
 	private void testMethodWithASingleStringParameter() {
 		this.method = ReflectionSupport.findMethod(this.instance.getClass(), "singleStringParameter",
-			String.class).get();
+			String.class).orElseThrow();
 	}
 
 	private void register(ParameterResolver... resolvers) {
@@ -95,6 +97,6 @@ private void register(ParameterResolver... resolvers) {
 
 	abstract void invokeMethod();
 
-	abstract <T> T invokeConstructor(Constructor<T> constructor, Object outerInstance);
+	abstract <T> T invokeConstructor(Constructor<T> constructor, @Nullable Object outerInstance);
 
 }
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/execution/DefaultExecutableInvokerTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/execution/DefaultExecutableInvokerTests.java
index c9db82e0dd9c..27cc736eb43d 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/execution/DefaultExecutableInvokerTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/execution/DefaultExecutableInvokerTests.java
@@ -10,8 +10,12 @@
 
 package org.junit.jupiter.engine.execution;
 
+import static java.util.Objects.requireNonNull;
+
 import java.lang.reflect.Constructor;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * Unit tests for {@link DefaultExecutableInvoker}.
  *
@@ -21,11 +25,11 @@ class DefaultExecutableInvokerTests extends AbstractExecutableInvokerTests {
 
 	@Override
 	void invokeMethod() {
-		newInvoker().invoke(this.method, this.instance);
+		newInvoker().invoke(requireNonNull(this.method), this.instance);
 	}
 
 	@Override
-	<T> T invokeConstructor(Constructor<T> constructor, Object outerInstance) {
+	<T> T invokeConstructor(Constructor<T> constructor, @Nullable Object outerInstance) {
 		return newInvoker().invoke(constructor, outerInstance);
 	}
 
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/execution/DynamicTestIntegrationTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/execution/DynamicTestIntegrationTests.java
index f9f666cbda76..591690b5c5c8 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/execution/DynamicTestIntegrationTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/execution/DynamicTestIntegrationTests.java
@@ -32,7 +32,7 @@ class DynamicTestIntegrationTests {
 	 * {@code -mx200m} VM argument will cause an {@link OutOfMemoryError} before
 	 * the 200 limit is reached.
 	 *
-	 * @see <a href="https://github.com/junit-team/junit5/issues/1865">Issue 1865</a>
+	 * @see <a href="https://github.com/junit-team/junit-framework/issues/1865">Issue 1865</a>
 	 */
 	@TestFactory
 	Stream<DynamicTest> generateDynamicTestsThatReferenceLargeAmountsOfMemory() {
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/execution/InterceptingExecutableInvokerTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/execution/InterceptingExecutableInvokerTests.java
index 58d96e0ecce1..a3abef9708e2 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/execution/InterceptingExecutableInvokerTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/execution/InterceptingExecutableInvokerTests.java
@@ -10,10 +10,13 @@
 
 package org.junit.jupiter.engine.execution;
 
+import static java.util.Objects.requireNonNull;
+
 import java.lang.reflect.Constructor;
 import java.lang.reflect.Executable;
 import java.util.Optional;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.engine.execution.InterceptingExecutableInvoker.ReflectiveInterceptorCall;
 
 /**
@@ -25,12 +28,12 @@ class InterceptingExecutableInvokerTests extends AbstractExecutableInvokerTests
 
 	@Override
 	void invokeMethod() {
-		newInvoker().invoke(this.method, this.instance, this.extensionContext, this.extensionRegistry,
+		newInvoker().invoke(requireNonNull(this.method), this.instance, this.extensionContext, this.extensionRegistry,
 			passthroughInterceptor());
 	}
 
 	@Override
-	<T> T invokeConstructor(Constructor<T> constructor, Object outerInstance) {
+	<T> T invokeConstructor(Constructor<T> constructor, @Nullable Object outerInstance) {
 		return newInvoker().invoke(constructor, Optional.ofNullable(outerInstance), __ -> extensionContext,
 			extensionRegistry, passthroughInterceptor());
 	}
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/execution/ParameterResolutionUtilsTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/execution/ParameterResolutionUtilsTests.java
index 54e175b8bc6f..3e2f0e297d6f 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/execution/ParameterResolutionUtilsTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/execution/ParameterResolutionUtilsTests.java
@@ -10,6 +10,7 @@
 
 package org.junit.jupiter.engine.execution;
 
+import static java.util.Objects.requireNonNull;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNull;
@@ -25,6 +26,7 @@
 import java.util.function.Predicate;
 import java.util.regex.Pattern;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExtensionContext;
 import org.junit.jupiter.api.extension.ParameterContext;
@@ -45,7 +47,8 @@ class ParameterResolutionUtilsTests {
 	private static final String ENIGMA = "enigma";
 
 	private final MethodSource instance = mock();
-	private Method method;
+
+	private @Nullable Method method;
 
 	private final ExtensionContext extensionContext = mock();
 
@@ -59,6 +62,7 @@ void resolveConstructorArguments() {
 		register(new StringParameterResolver());
 
 		Class<ConstructorInjectionTestCase> topLevelClass = ConstructorInjectionTestCase.class;
+		@Nullable
 		Object[] arguments = resolveConstructorParameters(topLevelClass, null);
 
 		assertThat(arguments).containsExactly(ENIGMA);
@@ -72,6 +76,7 @@ void resolveNestedConstructorArguments() {
 		ConstructorInjectionTestCase outer = ReflectionSupport.newInstance(outerClass, "str");
 
 		Class<ConstructorInjectionTestCase.NestedTestCase> innerClass = ConstructorInjectionTestCase.NestedTestCase.class;
+		@Nullable
 		Object[] arguments = resolveConstructorParameters(innerClass, outer);
 
 		assertThat(arguments).containsExactly(outer, 42);
@@ -97,6 +102,7 @@ void resolvingArgumentsForMethodsWithoutParameterDoesNotDependOnParameterResolve
 		testMethodWithNoParameters();
 		throwDuringParameterResolution(new RuntimeException("boom!"));
 
+		@Nullable
 		Object[] arguments = resolveMethodParameters();
 
 		assertThat(arguments).isEmpty();
@@ -107,6 +113,7 @@ void resolveArgumentsViaParameterResolver() {
 		testMethodWithASingleStringParameter();
 		thereIsAParameterResolverThatResolvesTheParameterTo("argument");
 
+		@Nullable
 		Object[] arguments = resolveMethodParameters();
 
 		assertThat(arguments).containsExactly("argument");
@@ -116,16 +123,14 @@ void resolveArgumentsViaParameterResolver() {
 	void resolveMultipleArguments() {
 		testMethodWith("multipleParameters", String.class, Integer.class, Double.class);
 		register(ConfigurableParameterResolver.supportsAndResolvesTo(parameterContext -> {
-			switch (parameterContext.getIndex()) {
-				case 0:
-					return "0";
-				case 1:
-					return 1;
-				default:
-					return 2.0;
-			}
+			return switch (parameterContext.getIndex()) {
+				case 0 -> "0";
+				case 1 -> 1;
+				default -> 2.0;
+			};
 		}));
 
+		@Nullable
 		Object[] arguments = resolveMethodParameters();
 
 		assertThat(arguments).containsExactly("0", 1, 2.0);
@@ -137,11 +142,13 @@ void onlyConsiderParameterResolversThatSupportAParticularParameter() {
 		thereIsAParameterResolverThatDoesNotSupportThisParameter();
 		thereIsAParameterResolverThatResolvesTheParameterTo("something");
 
+		@Nullable
 		Object[] arguments = resolveMethodParameters();
 
 		assertThat(arguments).containsExactly("something");
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void passContextInformationToParameterResolverMethods() {
 		anyTestMethodWithAtLeastOneParameter();
@@ -152,10 +159,10 @@ void passContextInformationToParameterResolverMethods() {
 
 		assertSame(extensionContext, extension.supportsArguments.extensionContext);
 		assertEquals(0, extension.supportsArguments.parameterContext.getIndex());
-		assertSame(instance, extension.supportsArguments.parameterContext.getTarget().get());
+		assertSame(instance, extension.supportsArguments.parameterContext.getTarget().orElseThrow());
 		assertSame(extensionContext, extension.resolveArguments.extensionContext);
 		assertEquals(0, extension.resolveArguments.parameterContext.getIndex());
-		assertSame(instance, extension.resolveArguments.parameterContext.getTarget().get());
+		assertSame(instance, extension.resolveArguments.parameterContext.getTarget().orElseThrow());
 		assertThat(extension.resolveArguments.parameterContext.toString())//
 				.contains("parameter", String.class.getTypeName(), "index", "0", "target", "Mock");
 	}
@@ -165,6 +172,7 @@ void resolvingArgumentsForMethodsWithPrimitiveTypesIsSupported() {
 		testMethodWithASinglePrimitiveIntParameter();
 		thereIsAParameterResolverThatResolvesTheParameterTo(42);
 
+		@Nullable
 		Object[] arguments = resolveMethodParameters();
 
 		assertThat(arguments).containsExactly(42);
@@ -175,6 +183,7 @@ void nullIsAViableArgumentIfAReferenceTypeParameterIsExpected() {
 		testMethodWithASingleStringParameter();
 		thereIsAParameterResolverThatResolvesTheParameterTo(null);
 
+		@Nullable
 		Object[] arguments = resolveMethodParameters();
 
 		assertThat(arguments).hasSize(1);
@@ -289,7 +298,7 @@ private void throwDuringParameterResolution(RuntimeException parameterResolution
 		register(ConfigurableParameterResolver.onAnyCallThrow(parameterResolutionException));
 	}
 
-	private void thereIsAParameterResolverThatResolvesTheParameterTo(Object argument) {
+	private void thereIsAParameterResolverThatResolvesTheParameterTo(@Nullable Object argument) {
 		register(ConfigurableParameterResolver.supportsAndResolvesTo(parameterContext -> argument));
 	}
 
@@ -323,14 +332,14 @@ private void register(ParameterResolver... resolvers) {
 		}
 	}
 
-	private <T> Object[] resolveConstructorParameters(Class<T> clazz, Object outerInstance) {
+	private <T> @Nullable Object[] resolveConstructorParameters(Class<T> clazz, @Nullable Object outerInstance) {
 		Constructor<T> constructor = ReflectionUtils.getDeclaredConstructor(clazz);
 		return ParameterResolutionUtils.resolveParameters(constructor, Optional.empty(),
 			Optional.ofNullable(outerInstance), extensionContext, extensionRegistry);
 	}
 
-	private Object[] resolveMethodParameters() {
-		return ParameterResolutionUtils.resolveParameters(this.method, Optional.of(this.instance),
+	private @Nullable Object[] resolveMethodParameters() {
+		return ParameterResolutionUtils.resolveParameters(requireNonNull(this.method), Optional.of(this.instance),
 			this.extensionContext, this.extensionRegistry);
 	}
 
@@ -338,18 +347,10 @@ private Object[] resolveMethodParameters() {
 
 	static class ArgumentRecordingParameterResolver implements ParameterResolver {
 
-		ArgumentRecordingParameterResolver.Arguments supportsArguments;
-		ArgumentRecordingParameterResolver.Arguments resolveArguments;
-
-		static class Arguments {
-
-			final ParameterContext parameterContext;
-			final ExtensionContext extensionContext;
+		ArgumentRecordingParameterResolver.@Nullable Arguments supportsArguments;
+		ArgumentRecordingParameterResolver.@Nullable Arguments resolveArguments;
 
-			Arguments(ParameterContext parameterContext, ExtensionContext extensionContext) {
-				this.parameterContext = parameterContext;
-				this.extensionContext = extensionContext;
-			}
+		record Arguments(ParameterContext parameterContext, ExtensionContext extensionContext) {
 		}
 
 		@Override
@@ -359,7 +360,7 @@ public boolean supportsParameter(ParameterContext parameterContext, ExtensionCon
 		}
 
 		@Override
-		public Object resolveParameter(ParameterContext parameterContext, ExtensionContext extensionContext) {
+		public @Nullable Object resolveParameter(ParameterContext parameterContext, ExtensionContext extensionContext) {
 			resolveArguments = new ArgumentRecordingParameterResolver.Arguments(parameterContext, extensionContext);
 			return null;
 		}
@@ -375,7 +376,7 @@ static ParameterResolver onAnyCallThrow(RuntimeException runtimeException) {
 			});
 		}
 
-		static ParameterResolver supportsAndResolvesTo(Function<ParameterContext, Object> resolve) {
+		static ParameterResolver supportsAndResolvesTo(Function<ParameterContext, @Nullable Object> resolve) {
 			return new ConfigurableParameterResolver(parameterContext -> true, resolve);
 		}
 
@@ -386,10 +387,10 @@ static ParameterResolver withoutSupport() {
 		}
 
 		private final Predicate<ParameterContext> supports;
-		private final Function<ParameterContext, Object> resolve;
+		private final Function<ParameterContext, @Nullable Object> resolve;
 
 		private ConfigurableParameterResolver(Predicate<ParameterContext> supports,
-				Function<ParameterContext, Object> resolve) {
+				Function<ParameterContext, @Nullable Object> resolve) {
 			this.supports = supports;
 			this.resolve = resolve;
 		}
@@ -400,7 +401,7 @@ public boolean supportsParameter(ParameterContext parameterContext, ExtensionCon
 		}
 
 		@Override
-		public Object resolveParameter(ParameterContext parameterContext, ExtensionContext extensionContext) {
+		public @Nullable Object resolveParameter(ParameterContext parameterContext, ExtensionContext extensionContext) {
 			return resolve.apply(parameterContext);
 		}
 	}
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/execution/UniqueIdParsingForArrayParameterIntegrationTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/execution/UniqueIdParsingForArrayParameterIntegrationTests.java
index 71035953ee13..d6f43d850341 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/execution/UniqueIdParsingForArrayParameterIntegrationTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/execution/UniqueIdParsingForArrayParameterIntegrationTests.java
@@ -27,7 +27,7 @@
  * Integration tests for {@link UniqueId#parse(String)} for methods
  * with array type parameters.
  *
- * @see <a href="https://github.com/junit-team/junit5/issues/810">#810</a>
+ * @see <a href="https://github.com/junit-team/junit-framework/issues/810">#810</a>
  * @see org.junit.platform.engine.UniqueIdTests
  *
  * @since 5.0
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/execution/injection/sample/LongParameterResolver.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/execution/injection/sample/LongParameterResolver.java
index b668e8fc9609..661ee3178b49 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/execution/injection/sample/LongParameterResolver.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/execution/injection/sample/LongParameterResolver.java
@@ -43,8 +43,8 @@ public boolean supportsParameter(ParameterContext parameterContext, ExtensionCon
 		for (TypeVariable<?> typeVariable : parameterContext.getDeclaringExecutable().getDeclaringClass().getTypeParameters()) {
 			boolean namesMatch = typeInMethod.getTypeName().equals(typeVariable.getName());
 			boolean typesAreCompatible = typeVariable.getBounds().length == 1 && //
-					typeVariable.getBounds()[0] instanceof Class && //
-					((Class<?>) typeVariable.getBounds()[0]).isAssignableFrom(Long.class);
+					typeVariable.getBounds()[0] instanceof Class<?> clazz && //
+					clazz.isAssignableFrom(Long.class);
 
 			if (namesMatch && typesAreCompatible) {
 				return true;
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/execution/injection/sample/MapOfStringsParameterResolver.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/execution/injection/sample/MapOfStringsParameterResolver.java
index e669fe26b07b..d0e2ddf96462 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/execution/injection/sample/MapOfStringsParameterResolver.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/execution/injection/sample/MapOfStringsParameterResolver.java
@@ -29,10 +29,10 @@ public class MapOfStringsParameterResolver implements ParameterResolver {
 	@Override
 	public boolean supportsParameter(ParameterContext parameterContext, ExtensionContext extensionContext) {
 		Type type = parameterContext.getParameter().getParameterizedType();
-		if (!(type instanceof ParameterizedType)) {
+		if (!(type instanceof ParameterizedType parameterizedType)) {
 			return false;
 		}
-		Type[] actualTypeArguments = ((ParameterizedType) type).getActualTypeArguments();
+		Type[] actualTypeArguments = parameterizedType.getActualTypeArguments();
 		if (actualTypeArguments.length != 2) {
 			return false;
 		}
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/AutoCloseTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/AutoCloseTests.java
index c1fc0ed4cfa1..736bff1d25a6 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/AutoCloseTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/AutoCloseTests.java
@@ -28,6 +28,7 @@
 import java.util.logging.Level;
 import java.util.logging.LogRecord;
 
+import org.jspecify.annotations.NullUnmarked;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.AutoClose;
 import org.junit.jupiter.api.BeforeAll;
@@ -61,8 +62,7 @@ void resetTracking() {
 	@Test
 	void blankCloseMethodName() {
 		Class<?> testClass = BlankCloseMethodNameTestCase.class;
-		String msg = String.format("@AutoClose on field %s.field must specify a method name.",
-			testClass.getCanonicalName());
+		String msg = "@AutoClose on field %s.field must specify a method name.".formatted(testClass.getCanonicalName());
 		Events tests = executeTestsForClass(testClass).testEvents();
 		assertFailingWithMessage(tests, msg);
 	}
@@ -70,8 +70,7 @@ void blankCloseMethodName() {
 	@Test
 	void primitiveTypeCannotBeClosed() {
 		Class<?> testClass = PrimitiveFieldTestCase.class;
-		String msg = String.format("@AutoClose is not supported on primitive field %s.x.",
-			testClass.getCanonicalName());
+		String msg = "@AutoClose is not supported on primitive field %s.x.".formatted(testClass.getCanonicalName());
 		Events tests = executeTestsForClass(testClass).testEvents();
 		assertFailingWithMessage(tests, msg);
 	}
@@ -79,7 +78,7 @@ void primitiveTypeCannotBeClosed() {
 	@Test
 	void arrayCannotBeClosed() {
 		Class<?> testClass = ArrayFieldTestCase.class;
-		String msg = String.format("@AutoClose is not supported on array field %s.x.", testClass.getCanonicalName());
+		String msg = "@AutoClose is not supported on array field %s.x.".formatted(testClass.getCanonicalName());
 		Events tests = executeTestsForClass(testClass).testEvents();
 		assertFailingWithMessage(tests, msg);
 	}
@@ -87,8 +86,7 @@ void arrayCannotBeClosed() {
 	@Test
 	void nullCannotBeClosed(@TrackLogRecords LogRecordListener listener) {
 		Class<?> testClass = NullCloseableFieldTestCase.class;
-		String msg = String.format("Cannot @AutoClose field %s.field because it is null.",
-			testClass.getCanonicalName());
+		String msg = "Cannot @AutoClose field %s.field because it is null.".formatted(testClass.getCanonicalName());
 		Events tests = executeTestsForClass(testClass).testEvents();
 		tests.assertStatistics(stats -> stats.succeeded(1).failed(0));
 		assertThat(listener.stream(Level.WARNING)).map(LogRecord::getMessage).anyMatch(msg::equals);
@@ -120,7 +118,7 @@ void spyPermitsOnlyASingleAction() {
 	}
 
 	/**
-	 * @see <a href="https://github.com/junit-team/junit5/issues/3684">#3684</a>
+	 * @see <a href="https://github.com/junit-team/junit-framework/issues/3684">#3684</a>
 	 */
 	@Test
 	void fieldsAreProperlyClosedViaInterfaceMethods() {
@@ -394,7 +392,7 @@ private static void assertFailingWithMessage(Events testEvents, String msg) {
 	}
 
 	private void assertMissingCloseMethod(Class<?> testClass, String methodName) {
-		String msg = String.format("Cannot @AutoClose field %s.field because %s does not define method %s().",
+		String msg = "Cannot @AutoClose field %s.field because %s does not define method %s().".formatted(
 			testClass.getCanonicalName(), String.class.getName(), methodName);
 		Events tests = executeTestsForClass(testClass).testEvents();
 		assertFailingWithMessage(tests, msg);
@@ -425,6 +423,7 @@ static class ArrayFieldTestCase implements TestInterface {
 		final int[] x = {};
 	}
 
+	@NullUnmarked
 	static class NullCloseableFieldTestCase implements TestInterface {
 
 		@AutoClose
@@ -459,6 +458,7 @@ static class CloseMethodMustBeInvokedViaInterfaceTestCase implements TestInterfa
 
 	@TestInstance(PER_METHOD)
 	@SuppressWarnings("JUnitMalformedDeclaration")
+	@NullUnmarked
 	static class InstancePerMethodTestCase {
 
 		@AutoClose
@@ -697,6 +697,7 @@ void nestedTest() {
 		}
 	}
 
+	@NullUnmarked
 	static class AutoCloseSpy implements AutoCloseable, Runnable {
 
 		private final String prefix;
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/BeforeAndAfterAllTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/BeforeAndAfterAllTests.java
index 34ebef190656..04ae42dd6afd 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/BeforeAndAfterAllTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/BeforeAndAfterAllTests.java
@@ -18,6 +18,7 @@
 import java.util.List;
 import java.util.Optional;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.AfterAll;
 import org.junit.jupiter.api.BeforeAll;
 import org.junit.jupiter.api.Test;
@@ -38,7 +39,7 @@ class BeforeAndAfterAllTests extends AbstractJupiterTestEngineTests {
 
 	private static final List<String> callSequence = new ArrayList<>();
 
-	private static Optional<Throwable> actualExceptionInAfterAllCallback;
+	private static @Nullable Optional<Throwable> actualExceptionInAfterAllCallback;
 
 	@Test
 	void beforeAllAndAfterAllCallbacks() {
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/BeforeAndAfterEachTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/BeforeAndAfterEachTests.java
index 0b320af3dbb4..a5e6b501e1ea 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/BeforeAndAfterEachTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/BeforeAndAfterEachTests.java
@@ -18,6 +18,7 @@
 import java.util.List;
 import java.util.Optional;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Nested;
@@ -42,8 +43,9 @@ class BeforeAndAfterEachTests extends AbstractJupiterTestEngineTests {
 	private static final List<String> callSequence = new ArrayList<>();
 	private static final List<String> beforeEachMethodCallSequence = new ArrayList<>();
 
-	private static Optional<Throwable> actualExceptionInAfterEachCallback;
+	private static @Nullable Optional<Throwable> actualExceptionInAfterEachCallback;
 
+	@SuppressWarnings("OptionalAssignedToNull")
 	@BeforeEach
 	void resetCallSequence() {
 		callSequence.clear();
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/BeforeAndAfterTestExecutionCallbackTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/BeforeAndAfterTestExecutionCallbackTests.java
index 119b2ecb6909..18a981e7dc96 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/BeforeAndAfterTestExecutionCallbackTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/BeforeAndAfterTestExecutionCallbackTests.java
@@ -20,6 +20,7 @@
 import java.util.List;
 import java.util.Optional;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Nested;
@@ -42,10 +43,11 @@
  */
 class BeforeAndAfterTestExecutionCallbackTests extends AbstractJupiterTestEngineTests {
 
-	private static List<String> callSequence = new ArrayList<>();
+	private static final List<String> callSequence = new ArrayList<>();
 
-	private static Optional<Throwable> actualExceptionInAfterTestExecution;
+	private static @Nullable Optional<Throwable> actualExceptionInAfterTestExecution;
 
+	@SuppressWarnings("OptionalAssignedToNull")
 	@BeforeEach
 	void resetCallSequence() {
 		callSequence.clear();
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/CloseablePathTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/CloseablePathTests.java
index 5c66048d03f6..6f4a3bfb427b 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/CloseablePathTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/CloseablePathTests.java
@@ -52,6 +52,8 @@
 import com.google.common.jimfs.Jimfs;
 
 import org.assertj.core.api.ThrowableAssert.ThrowingCallable;
+import org.jspecify.annotations.NullUnmarked;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.DisplayName;
@@ -68,6 +70,7 @@
 import org.junit.jupiter.api.io.TempDirFactory;
 import org.junit.jupiter.engine.AbstractJupiterTestEngineTests;
 import org.junit.jupiter.engine.execution.NamespaceAwareStore;
+import org.junit.jupiter.engine.extension.TempDirectory.CloseablePath;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.ValueSource;
 import org.junit.platform.commons.PreconditionViolationException;
@@ -86,7 +89,7 @@ class CloseablePathTests extends AbstractJupiterTestEngineTests {
 	private final AnnotatedElementContext elementContext = mock();
 	private final ExtensionContext extensionContext = mock();
 
-	private TempDirectory.CloseablePath closeablePath;
+	private @Nullable CloseablePath closeablePath;
 
 	@Target(METHOD)
 	@Retention(RUNTIME)
@@ -164,6 +167,7 @@ void factoryReturnsDirectoryOnNonDefaultFileSystemWithPath() throws IOException
 			delete(closeablePath.get());
 		}
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@DisplayName("fails if the factory returns null")
 		@ParameterizedTest
 		@ElementTypeSource
@@ -276,7 +280,9 @@ class Cleanup {
 
 		@AfterEach
 		void cleanupTempDirectory() throws IOException {
-			deleteIfExists(closeablePath.get());
+			if (closeablePath != null) {
+				deleteIfExists(closeablePath.get());
+			}
 		}
 
 		@DisplayName("is done for a cleanup mode of ALWAYS")
@@ -457,6 +463,7 @@ void deletesSymbolicLinksTargetingDirOutsideTempDir(Class<?> elementType,
 		}
 	}
 
+	@NullUnmarked
 	static class TestCase {
 
 		Path tempDir;
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/ExtensionContextExecutionTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/ExtensionContextExecutionTests.java
index c3214cf18aad..5f3281917664 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/ExtensionContextExecutionTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/ExtensionContextExecutionTests.java
@@ -34,13 +34,13 @@ void extensionContextHierarchy(ExtensionContext methodExtensionContext) {
 
 		Optional<ExtensionContext> classExtensionContext = methodExtensionContext.getParent();
 		assertThat(classExtensionContext).isNotEmpty();
-		assertThat(classExtensionContext.orElse(null).getElement()).contains(ExtensionContextExecutionTests.class);
+		assertThat(classExtensionContext.orElseThrow().getElement()).contains(ExtensionContextExecutionTests.class);
 
-		Optional<ExtensionContext> engineExtensionContext = classExtensionContext.orElse(null).getParent();
+		Optional<ExtensionContext> engineExtensionContext = classExtensionContext.orElseThrow().getParent();
 		assertThat(engineExtensionContext).isNotEmpty();
-		assertThat(engineExtensionContext.orElse(null).getElement()).isEmpty();
+		assertThat(engineExtensionContext.orElseThrow().getElement()).isEmpty();
 
-		assertThat(engineExtensionContext.orElse(null).getParent()).isEmpty();
+		assertThat(engineExtensionContext.orElseThrow().getParent()).isEmpty();
 	}
 
 	@Test
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/ExtensionRegistrationViaParametersAndFieldsTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/ExtensionRegistrationViaParametersAndFieldsTests.java
index c70238d7473e..7be354083dfc 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/ExtensionRegistrationViaParametersAndFieldsTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/ExtensionRegistrationViaParametersAndFieldsTests.java
@@ -40,6 +40,8 @@
 import java.util.stream.IntStream;
 import java.util.stream.Stream;
 
+import org.jspecify.annotations.NullUnmarked;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.AfterAll;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeAll;
@@ -596,6 +598,7 @@ void test(Long number) {
 		}
 	}
 
+	@NullUnmarked
 	static class MultipleExtendWithRegistrationsViaFieldTestCase {
 
 		@SuppressWarnings("unused")
@@ -623,6 +626,7 @@ void test() {
 	/**
 	 * The {@link MagicField.Extension} is registered via a static field.
 	 */
+	@NullUnmarked
 	static class StaticFieldTestCase {
 
 		@SuppressWarnings("unused")
@@ -648,6 +652,7 @@ void test() {
 	/**
 	 * The {@link MagicField.Extension} is registered via an instance field.
 	 */
+	@NullUnmarked
 	static class InstanceFieldTestCase {
 
 		@MagicField
@@ -667,6 +672,7 @@ void test() {
 	 * The {@link MagicField.Extension} is registered via a static field and
 	 * an instance field.
 	 */
+	@NullUnmarked
 	@TestInstance(Lifecycle.PER_CLASS)
 	static class TestInstancePerClassFieldTestCase {
 
@@ -689,6 +695,7 @@ void test() {
 		}
 	}
 
+	@NullUnmarked
 	@TestInstance(Lifecycle.PER_METHOD)
 	static class AllInOneWithTestInstancePerMethodTestCase {
 
@@ -779,6 +786,7 @@ static class AllInOneWithTestInstancePerClassTestCase extends AllInOneWithTestIn
 		}
 	}
 
+	@NullUnmarked
 	static class ProgrammaticTestInstancePostProcessorTestCase {
 
 		@RegisterExtension
@@ -853,7 +861,7 @@ public Object resolveParameter(ParameterContext parameterContext, ExtensionConte
 			String name = declaringExecutable instanceof Constructor
 					? declaringExecutable.getDeclaringClass().getSimpleName()
 					: declaringExecutable.getName();
-			return String.format("%s-%d-%s", name, parameterContext.getIndex(), text);
+			return "%s-%d-%s".formatted(name, parameterContext.getIndex(), text);
 		}
 	}
 }
@@ -954,7 +962,8 @@ public final void postProcessTestInstance(Object testInstance, ExtensionContext
 			ModifierSupport::isNotStatic);
 	}
 
-	private void injectFields(String trigger, Class<?> testClass, Object instance, Predicate<Field> predicate) {
+	private void injectFields(String trigger, Class<?> testClass, @Nullable Object instance,
+			Predicate<Field> predicate) {
 		findAnnotatedFields(testClass, this.annotationType, predicate).forEach(field -> {
 			try {
 				makeAccessible(field).set(instance, trigger + " - " + field.getName());
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/InvocationInterceptorTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/InvocationInterceptorTests.java
index b9b39cecff58..a0138398097e 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/InvocationInterceptorTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/InvocationInterceptorTests.java
@@ -30,6 +30,7 @@
 import java.util.function.UnaryOperator;
 import java.util.stream.Stream;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.AfterAll;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeAll;
@@ -71,7 +72,7 @@ static class InvocationIgnoringInterceptorTestCase {
 		@RegisterExtension
 		Extension interceptor = new InvocationInterceptor() {
 			@Override
-			public void interceptTestMethod(Invocation<Void> invocation,
+			public void interceptTestMethod(Invocation<@Nullable Void> invocation,
 					ReflectiveInvocationContext<Method> invocationContext, ExtensionContext extensionContext) {
 				// do nothing
 			}
@@ -95,7 +96,7 @@ static class InvocationSkippedTestCase {
 		@RegisterExtension
 		Extension interceptor = new InvocationInterceptor() {
 			@Override
-			public void interceptTestMethod(Invocation<Void> invocation,
+			public void interceptTestMethod(Invocation<@Nullable Void> invocation,
 					ReflectiveInvocationContext<Method> invocationContext, ExtensionContext extensionContext) {
 				invocation.skip();
 			}
@@ -122,7 +123,7 @@ static class DoubleInvocationInterceptorTestCase {
 		@RegisterExtension
 		Extension interceptor = new InvocationInterceptor() {
 			@Override
-			public void interceptTestMethod(Invocation<Void> invocation,
+			public void interceptTestMethod(Invocation<@Nullable Void> invocation,
 					ReflectiveInvocationContext<Method> invocationContext, ExtensionContext extensionContext)
 					throws Throwable {
 				invocation.proceed();
@@ -287,7 +288,7 @@ public ExtensionContextScope getTestInstantiationExtensionContextScope(Extension
 		}
 
 		@Override
-		public void interceptBeforeAllMethod(Invocation<Void> invocation,
+		public void interceptBeforeAllMethod(Invocation<@Nullable Void> invocation,
 				ReflectiveInvocationContext<Method> invocationContext, ExtensionContext extensionContext)
 				throws Throwable {
 			assertEquals(testClass, invocationContext.getTargetClass());
@@ -295,7 +296,7 @@ public void interceptBeforeAllMethod(Invocation<Void> invocation,
 			assertEquals(testClass.getDeclaredMethod("beforeAll", TestReporter.class),
 				invocationContext.getExecutable());
 			assertThat(invocationContext.getArguments()).hasSize(1).hasOnlyElementsOfType(TestReporter.class);
-			reportAndProceed(invocation, extensionContext, InvocationType.BEFORE_ALL);
+			this.<@Nullable Void> reportAndProceed(invocation, extensionContext, InvocationType.BEFORE_ALL);
 		}
 
 		@Override
@@ -309,7 +310,7 @@ public <T> T interceptTestClassConstructor(Invocation<T> invocation,
 		}
 
 		@Override
-		public void interceptBeforeEachMethod(Invocation<Void> invocation,
+		public void interceptBeforeEachMethod(Invocation<@Nullable Void> invocation,
 				ReflectiveInvocationContext<Method> invocationContext, ExtensionContext extensionContext)
 				throws Throwable {
 			assertEquals(testClass, invocationContext.getTargetClass());
@@ -317,22 +318,22 @@ public void interceptBeforeEachMethod(Invocation<Void> invocation,
 			assertEquals(testClass.getDeclaredMethod("beforeEach", TestReporter.class),
 				invocationContext.getExecutable());
 			assertThat(invocationContext.getArguments()).hasSize(1).hasOnlyElementsOfType(TestReporter.class);
-			reportAndProceed(invocation, extensionContext, InvocationType.BEFORE_EACH);
+			this.<@Nullable Void> reportAndProceed(invocation, extensionContext, InvocationType.BEFORE_EACH);
 		}
 
 		@Override
-		public void interceptTestMethod(Invocation<Void> invocation,
+		public void interceptTestMethod(Invocation<@Nullable Void> invocation,
 				ReflectiveInvocationContext<Method> invocationContext, ExtensionContext extensionContext)
 				throws Throwable {
 			assertEquals(testClass, invocationContext.getTargetClass());
 			assertThat(invocationContext.getTarget()).containsInstanceOf(testClass);
 			assertEquals(testClass.getDeclaredMethod("test", TestReporter.class), invocationContext.getExecutable());
 			assertThat(invocationContext.getArguments()).hasSize(1).hasOnlyElementsOfType(TestReporter.class);
-			reportAndProceed(invocation, extensionContext, InvocationType.TEST_METHOD);
+			this.<@Nullable Void> reportAndProceed(invocation, extensionContext, InvocationType.TEST_METHOD);
 		}
 
 		@Override
-		public void interceptTestTemplateMethod(Invocation<Void> invocation,
+		public void interceptTestTemplateMethod(Invocation<@Nullable Void> invocation,
 				ReflectiveInvocationContext<Method> invocationContext, ExtensionContext extensionContext)
 				throws Throwable {
 			assertEquals(testClass, invocationContext.getTargetClass());
@@ -340,7 +341,7 @@ public void interceptTestTemplateMethod(Invocation<Void> invocation,
 			assertEquals(testClass.getDeclaredMethod("testTemplate", TestReporter.class),
 				invocationContext.getExecutable());
 			assertThat(invocationContext.getArguments()).hasSize(1).hasOnlyElementsOfType(TestReporter.class);
-			reportAndProceed(invocation, extensionContext, InvocationType.TEST_TEMPLATE_METHOD);
+			this.<@Nullable Void> reportAndProceed(invocation, extensionContext, InvocationType.TEST_TEMPLATE_METHOD);
 		}
 
 		@Override
@@ -356,18 +357,18 @@ public <T> T interceptTestFactoryMethod(Invocation<T> invocation,
 		}
 
 		@Override
-		public void interceptDynamicTest(Invocation<Void> invocation, DynamicTestInvocationContext invocationContext,
-				ExtensionContext extensionContext) throws Throwable {
+		public void interceptDynamicTest(Invocation<@Nullable Void> invocation,
+				DynamicTestInvocationContext invocationContext, ExtensionContext extensionContext) throws Throwable {
 			assertThat(invocationContext.getExecutable()).isNotNull();
 			assertThat(extensionContext.getUniqueId()).isNotBlank();
 			assertThat(extensionContext.getElement()).isEmpty();
 			assertThat(extensionContext.getParent().flatMap(ExtensionContext::getTestMethod)) //
 					.contains(testClass.getDeclaredMethod("testFactory", TestReporter.class));
-			reportAndProceed(invocation, extensionContext, InvocationType.DYNAMIC_TEST);
+			this.<@Nullable Void> reportAndProceed(invocation, extensionContext, InvocationType.DYNAMIC_TEST);
 		}
 
 		@Override
-		public void interceptAfterEachMethod(Invocation<Void> invocation,
+		public void interceptAfterEachMethod(Invocation<@Nullable Void> invocation,
 				ReflectiveInvocationContext<Method> invocationContext, ExtensionContext extensionContext)
 				throws Throwable {
 			assertEquals(testClass, invocationContext.getTargetClass());
@@ -375,11 +376,11 @@ public void interceptAfterEachMethod(Invocation<Void> invocation,
 			assertEquals(testClass.getDeclaredMethod("afterEach", TestReporter.class),
 				invocationContext.getExecutable());
 			assertThat(invocationContext.getArguments()).hasSize(1).hasOnlyElementsOfType(TestReporter.class);
-			reportAndProceed(invocation, extensionContext, InvocationType.AFTER_EACH);
+			this.<@Nullable Void> reportAndProceed(invocation, extensionContext, InvocationType.AFTER_EACH);
 		}
 
 		@Override
-		public void interceptAfterAllMethod(Invocation<Void> invocation,
+		public void interceptAfterAllMethod(Invocation<@Nullable Void> invocation,
 				ReflectiveInvocationContext<Method> invocationContext, ExtensionContext extensionContext)
 				throws Throwable {
 			assertEquals(testClass, invocationContext.getTargetClass());
@@ -387,11 +388,11 @@ public void interceptAfterAllMethod(Invocation<Void> invocation,
 			assertEquals(testClass.getDeclaredMethod("afterAll", TestReporter.class),
 				invocationContext.getExecutable());
 			assertThat(invocationContext.getArguments()).hasSize(1).hasOnlyElementsOfType(TestReporter.class);
-			reportAndProceed(invocation, extensionContext, InvocationType.AFTER_ALL);
+			this.<@Nullable Void> reportAndProceed(invocation, extensionContext, InvocationType.AFTER_ALL);
 		}
 
-		private <T> T reportAndProceed(Invocation<T> invocation, ExtensionContext extensionContext, InvocationType type)
-				throws Throwable {
+		private <T extends @Nullable Object> T reportAndProceed(Invocation<T> invocation,
+				ExtensionContext extensionContext, InvocationType type) throws Throwable {
 			extensionContext.publishReportEntry(type.name(), "before:" + name);
 			try {
 				return invocation.proceed();
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/OrderedClassTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/OrderedClassTests.java
index b1e163d7cfa9..1954b93d35e0 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/OrderedClassTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/OrderedClassTests.java
@@ -23,6 +23,7 @@
 import java.util.logging.LogRecord;
 import java.util.stream.Stream;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.ClassOrderer;
@@ -209,12 +210,12 @@ private static void assertIneffectiveOrderAnnotationIssues(List<DiscoveryIssue>
 				.containsExactlyInAnyOrder(ClassSource.from(A_TestCase.class), ClassSource.from(C_TestCase.class));
 	}
 
-	private Events executeTests(Class<? extends ClassOrderer> classOrderer) {
+	private Events executeTests(@Nullable Class<? extends ClassOrderer> classOrderer) {
 		return executeTests(classOrderer, selectClass(A_TestCase.class), selectClass(B_TestCase.class),
 			selectClass(C_TestCase.class));
 	}
 
-	private Events executeTests(Class<? extends ClassOrderer> classOrderer, DiscoverySelector... selectors) {
+	private Events executeTests(@Nullable Class<? extends ClassOrderer> classOrderer, DiscoverySelector... selectors) {
 		// @formatter:off
 		return testKit(classOrderer, selectors)
 				.execute()
@@ -222,17 +223,17 @@ private Events executeTests(Class<? extends ClassOrderer> classOrderer, Discover
 		// @formatter:on
 	}
 
-	private EngineDiscoveryResults discoverTests(Class<? extends ClassOrderer> classOrderer) {
+	private EngineDiscoveryResults discoverTests(@Nullable Class<? extends ClassOrderer> classOrderer) {
 		return discoverTests(classOrderer, selectClass(A_TestCase.class), selectClass(B_TestCase.class),
 			selectClass(C_TestCase.class));
 	}
 
-	private EngineDiscoveryResults discoverTests(Class<? extends ClassOrderer> classOrderer,
+	private EngineDiscoveryResults discoverTests(@Nullable Class<? extends ClassOrderer> classOrderer,
 			DiscoverySelector... selectors) {
 		return testKit(classOrderer, selectors).discover();
 	}
 
-	private static EngineTestKit.Builder testKit(Class<? extends ClassOrderer> classOrderer,
+	private static EngineTestKit.Builder testKit(@Nullable Class<? extends ClassOrderer> classOrderer,
 			DiscoverySelector[] selectors) {
 
 		var testKit = EngineTestKit.engine("junit-jupiter");
@@ -246,7 +247,7 @@ static abstract class BaseTestCase {
 
 		@BeforeEach
 		void trackInvocations(TestInfo testInfo) {
-			var testClass = testInfo.getTestClass().get();
+			var testClass = testInfo.getTestClass().orElseThrow();
 
 			callSequence.add(testClass.getSimpleName());
 		}
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/OrderedMethodTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/OrderedMethodTests.java
index 0517a6dd026a..0d191dfadd99 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/OrderedMethodTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/OrderedMethodTests.java
@@ -34,6 +34,7 @@
 import java.util.logging.LogRecord;
 import java.util.regex.Pattern;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.DisplayName;
 import org.junit.jupiter.api.DynamicTest;
@@ -83,40 +84,18 @@ void clearCallSequence() {
 		threadNames.clear();
 	}
 
-	@Test
-	void alphanumeric() {
-		Class<?> testClass = AlphanumericTestCase.class;
-
-		// The name of the base class MUST start with a letter alphanumerically
-		// greater than "A" so that BaseTestCase comes after AlphanumericTestCase
-		// if methods are sorted by class name for the fallback ordering if two
-		// methods have the same name but different parameter lists. Note, however,
-		// that Alphanumeric actually does not order methods like that, but we want
-		// this check to remain in place to ensure that the ordering does not rely
-		// on the class names.
-		assertThat(testClass.getSuperclass().getName()).isGreaterThan(testClass.getName());
-
-		var tests = executeTestsInParallel(testClass, Random.class);
-
-		tests.assertStatistics(stats -> stats.succeeded(callSequence.size()));
-
-		assertThat(callSequence).containsExactly("$()", "AAA()", "AAA(org.junit.jupiter.api.TestInfo)",
-			"AAA(org.junit.jupiter.api.TestReporter)", "ZZ_Top()", "___()", "a1()", "a2()", "b()", "c()", "zzz()");
-		assertThat(threadNames).hasSize(1);
-	}
-
 	@Test
 	void methodName() {
-		Class<?> testClass = MethodNameTestCase.class;
+		Class<?> testClass = AMethodNameTestCase.class;
 
 		// The name of the base class MUST start with a letter alphanumerically
-		// greater than "A" so that BaseTestCase comes after AlphanumericTestCase
+		// greater than "A" so that BaseTestCase comes after AMethodNameTestCase
 		// if methods are sorted by class name for the fallback ordering if two
 		// methods have the same name but different parameter lists. Note, however,
-		// that Alphanumeric actually does not order methods like that, but we want
+		// that MethodName actually does not order methods like that, but we want
 		// this check to remain in place to ensure that the ordering does not rely
 		// on the class names.
-		assertThat(testClass.getSuperclass().getName()).isLessThan(testClass.getName());
+		assertThat(testClass.getSuperclass().getName()).isGreaterThan(testClass.getName());
 
 		var tests = executeTestsInParallel(testClass, Random.class);
 
@@ -345,23 +324,24 @@ void misbehavingMethodOrdererThatRemovesElements() {
 				.containsSubsequence("test2()", "test4()");// removed item is re-added before ordered item
 	}
 
-	private EngineDiscoveryResults discoverTests(Class<?> testClass, Class<? extends MethodOrderer> defaultOrderer) {
+	private EngineDiscoveryResults discoverTests(Class<?> testClass,
+			@Nullable Class<? extends MethodOrderer> defaultOrderer) {
 		return testKit(testClass, defaultOrderer, Severity.INFO).discover();
 	}
 
-	private Events executeTestsInParallel(Class<?> testClass, Class<? extends MethodOrderer> defaultOrderer) {
+	private Events executeTestsInParallel(Class<?> testClass, @Nullable Class<? extends MethodOrderer> defaultOrderer) {
 		return executeTestsInParallel(testClass, defaultOrderer, Severity.INFO);
 	}
 
-	private Events executeTestsInParallel(Class<?> testClass, Class<? extends MethodOrderer> defaultOrderer,
+	private Events executeTestsInParallel(Class<?> testClass, @Nullable Class<? extends MethodOrderer> defaultOrderer,
 			Severity criticalSeverity) {
 		return testKit(testClass, defaultOrderer, criticalSeverity) //
 				.execute() //
 				.testEvents();
 	}
 
-	private static EngineTestKit.Builder testKit(Class<?> testClass, Class<? extends MethodOrderer> defaultOrderer,
-			Severity criticalSeverity) {
+	private static EngineTestKit.Builder testKit(Class<?> testClass,
+			@Nullable Class<? extends MethodOrderer> defaultOrderer, Severity criticalSeverity) {
 		var testKit = EngineTestKit.engine("junit-jupiter") //
 				.configurationParameter(PARALLEL_EXECUTION_ENABLED_PROPERTY_NAME, "true") //
 				.configurationParameter(DEFAULT_PARALLEL_EXECUTION_MODE, "concurrent") //
@@ -419,65 +399,12 @@ void c() {
 
 	@SuppressWarnings({ "unused", "JUnitMalformedDeclaration" })
 	@TestMethodOrder(MethodName.class)
-	static class MethodNameTestCase extends BaseTestCase {
-
-		@BeforeEach
-		void trackInvocations(TestInfo testInfo) {
-			var method = testInfo.getTestMethod().orElseThrow(AssertionError::new);
-			var signature = String.format("%s(%s)", method.getName(),
-				ClassUtils.nullSafeToString(method.getParameterTypes()));
-
-			callSequence.add(signature);
-			threadNames.add(Thread.currentThread().getName());
-		}
-
-		@TestFactory
-		DynamicTest b() {
-			return dynamicTest("dynamic", () -> {
-			});
-		}
-
-		@Test
-		void $() {
-		}
-
-		@Test
-		void ___() {
-		}
-
-		@Test
-		void AAA(TestReporter testReporter) {
-		}
-
-		@Test
-		void AAA(TestInfo testInfo) {
-		}
-
-		@Test
-		void ZZ_Top() {
-		}
-
-		@Test
-		void a1() {
-		}
-
-		@Test
-		void a2() {
-		}
-
-		@RepeatedTest(1)
-		void zzz() {
-		}
-	}
-
-	@SuppressWarnings({ "deprecation", "unused", "JUnitMalformedDeclaration" })
-	@TestMethodOrder(org.junit.jupiter.api.MethodOrderer.Alphanumeric.class)
-	static class AlphanumericTestCase extends BaseTestCase {
+	static class AMethodNameTestCase extends BaseTestCase {
 
 		@BeforeEach
 		void trackInvocations(TestInfo testInfo) {
 			var method = testInfo.getTestMethod().orElseThrow(AssertionError::new);
-			var signature = String.format("%s(%s)", method.getName(),
+			var signature = "%s(%s)".formatted(method.getName(),
 				ClassUtils.nullSafeToString(method.getParameterTypes()));
 
 			callSequence.add(signature);
@@ -815,17 +742,17 @@ public void orderMethods(MethodOrdererContext context) {
 			context.getMethodDescriptors().set(1, createMethodDescriptorImpersonator(method2));
 		}
 
-		@SuppressWarnings("unchecked")
+		@SuppressWarnings({ "unchecked", "DataFlowIssue" })
 		static <T> T createMethodDescriptorImpersonator(MethodDescriptor method) {
 			MethodDescriptor stub = new MethodDescriptor() {
 				@Override
 				public Method getMethod() {
-					return null;
+					throw new UnsupportedOperationException();
 				}
 
 				@Override
 				public String getDisplayName() {
-					return null;
+					throw new UnsupportedOperationException();
 				}
 
 				@Override
@@ -835,12 +762,12 @@ public boolean isAnnotated(Class<? extends Annotation> annotationType) {
 
 				@Override
 				public <A extends Annotation> Optional<A> findAnnotation(Class<A> annotationType) {
-					return null;
+					return Optional.empty();
 				}
 
 				@Override
 				public <A extends Annotation> List<A> findRepeatableAnnotations(Class<A> annotationType) {
-					return null;
+					return List.of();
 				}
 
 				@SuppressWarnings("EqualsWhichDoesntCheckParameterClass")
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/OrderedProgrammaticExtensionRegistrationTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/OrderedProgrammaticExtensionRegistrationTests.java
index 1cd4632dc28e..816c505a59da 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/OrderedProgrammaticExtensionRegistrationTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/OrderedProgrammaticExtensionRegistrationTests.java
@@ -106,7 +106,7 @@ void instanceLevelWithDefaultOrderAndExplicitOrder() {
 	 * non-annotated "after" callbacks.
 	 *
 	 * @since 5.6
-	 * @see <a href="https://github.com/junit-team/junit5/issues/1924">gh-1924</a>
+	 * @see <a href="https://github.com/junit-team/junit-framework/issues/1924">gh-1924</a>
 	 */
 	@Test
 	void instanceLevelWithDefaultOrderPlusOneAndDefaultOrder() {
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/ParameterResolverTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/ParameterResolverTests.java
index 500a1fcbd1f3..b0f7e1fe3945 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/ParameterResolverTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/ParameterResolverTests.java
@@ -227,7 +227,7 @@ void executeTestsForTypeBasedParameterResolverTestCaseSelectingByFullyQualifiedM
 	void executeTestsForParameterizedTypesSelectingByFullyQualifiedMethodNameContainingGenericInfo() throws Exception {
 		Method method = ParameterizedTypeTestCase.class.getDeclaredMethod("testMapOfStrings", Map.class);
 		String genericParameterTypeName = method.getGenericParameterTypes()[0].getTypeName();
-		String fqmn = String.format("%s#%s(%s)", ParameterizedTypeTestCase.class.getName(), "testMapOfStrings",
+		String fqmn = "%s#%s(%s)".formatted(ParameterizedTypeTestCase.class.getName(), "testMapOfStrings",
 			genericParameterTypeName);
 
 		assertEventsForParameterizedTypes(executeTests(selectMethod(fqmn)));
@@ -301,7 +301,7 @@ void test() {
 		}
 
 		@Nested
-		// See https://github.com/junit-team/junit5/issues/1345
+		// See https://github.com/junit-team/junit-framework/issues/1345
 		class AnnotatedConstructorParameterNestedTestCase {
 
 			private final TestInfo innerTestInfo;
@@ -471,7 +471,7 @@ static class ExtendWithOnMethodTestCase {
 		 * {@code ExtensionRegistry} as the one used for the corresponding
 		 * {@code @Test} method.
 		 *
-		 * @see <a href="https://github.com/junit-team/junit5/issues/523">#523</a>
+		 * @see <a href="https://github.com/junit-team/junit-framework/issues/523">#523</a>
 		 */
 		@SuppressWarnings("JUnitMalformedDeclaration")
 		@BeforeEach
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/ProgrammaticExtensionRegistrationTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/ProgrammaticExtensionRegistrationTests.java
index e168d58cc974..c871279414ed 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/ProgrammaticExtensionRegistrationTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/ProgrammaticExtensionRegistrationTests.java
@@ -29,6 +29,8 @@
 import java.util.function.Predicate;
 
 import org.assertj.core.api.Condition;
+import org.jspecify.annotations.NullUnmarked;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.AfterAll;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeAll;
@@ -187,7 +189,7 @@ void classLevelWithPrivateField() {
 	void instanceLevelWithNullField() {
 		Class<?> testClass = InstanceLevelExtensionRegistrationWithNullFieldTestCase.class;
 
-		executeTestsForClass(testClass).testEvents().assertThatEvents().haveExactly(1, finishedWithFailure(
+		executeTestsForClass(testClass).testEvents().debug().assertThatEvents().haveExactly(1, finishedWithFailure(
 			instanceOf(PreconditionViolationException.class), message(expectedMessage(testClass, null))));
 	}
 
@@ -221,7 +223,7 @@ void classLevelWithNonExtensionFieldValue() {
 			instanceOf(PreconditionViolationException.class), message(expectedMessage(testClass, String.class))));
 	}
 
-	private String expectedMessage(Class<?> testClass, Class<?> valueType) {
+	private String expectedMessage(Class<?> testClass, @Nullable Class<?> valueType) {
 		return "Failed to register extension via @RegisterExtension field [" + field(testClass)
 				+ "]: field value's type [" + (valueType != null ? valueType.getName() : null) + "] must implement an ["
 				+ Extension.class.getName() + "] API.";
@@ -324,6 +326,7 @@ void afterEach(String wisdom) {
 
 	@SuppressWarnings("JUnitMalformedDeclaration")
 	@ExtendWith(ExtensionInjector.class)
+	@NullUnmarked
 	static class InstanceLevelExtensionRegistrationWithInjectedExtensionTestCase {
 
 		@RegisterExtension
@@ -463,13 +466,7 @@ void test(String wisdom) {
 
 	}
 
-	private static class CrystalBall implements ParameterResolver {
-
-		private final String wisdom;
-
-		public CrystalBall(String wisdom) {
-			this.wisdom = wisdom;
-		}
+	private record CrystalBall(String wisdom) implements ParameterResolver {
 
 		@Override
 		public boolean supportsParameter(ParameterContext parameterContext, ExtensionContext extensionContext) {
@@ -629,6 +626,7 @@ static class ClassLevelExtensionRegistrationWithPrivateFieldTestCase extends Abs
 
 	}
 
+	@NullUnmarked
 	static class InstanceLevelExtensionRegistrationWithNullFieldTestCase extends AbstractTestCase {
 
 		@RegisterExtension
@@ -636,6 +634,7 @@ static class InstanceLevelExtensionRegistrationWithNullFieldTestCase extends Abs
 
 	}
 
+	@NullUnmarked
 	static class ClassLevelExtensionRegistrationWithNullFieldTestCase extends AbstractTestCase {
 
 		@RegisterExtension
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/RepeatedTestTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/RepeatedTestTests.java
index bed689112b13..23750bfc0d4d 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/RepeatedTestTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/RepeatedTestTests.java
@@ -136,15 +136,13 @@ public LifecycleMethodTests(RepetitionInfo repetitionInfo) {
 		@AfterEach
 		void beforeAndAfterEach(TestInfo testInfo, RepetitionInfo repetitionInfo) {
 			switch (testInfo.getTestMethod().get().getName()) {
-				case "repeatedOnce": {
+				case "repeatedOnce" -> {
 					assertThat(repetitionInfo.getCurrentRepetition()).isEqualTo(1);
 					assertThat(repetitionInfo.getTotalRepetitions()).isEqualTo(1);
-					break;
 				}
-				case "repeatedFortyTwoTimes": {
+				case "repeatedFortyTwoTimes" -> {
 					assertThat(repetitionInfo.getCurrentRepetition()).isBetween(1, 42);
 					assertThat(repetitionInfo.getTotalRepetitions()).isEqualTo(42);
-					break;
 				}
 			}
 		}
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/SeparateThreadTimeoutInvocationTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/SeparateThreadTimeoutInvocationTests.java
index 04e2735f4805..7414362b790b 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/SeparateThreadTimeoutInvocationTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/SeparateThreadTimeoutInvocationTests.java
@@ -18,6 +18,7 @@
 import java.util.concurrent.TimeoutException;
 import java.util.concurrent.atomic.AtomicReference;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.DisplayName;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.Timeout.ThreadMode;
@@ -43,7 +44,7 @@ void throwsTimeoutException() {
 		var invocation = aSeparateThreadInvocation(() -> {
 			threadName.set(Thread.currentThread().getName());
 			Thread.sleep(PREEMPTIVE_TIMEOUT_MILLIS * 2);
-			return null;
+			return "ignored";
 		});
 
 		assertThatThrownBy(invocation::proceed) //
@@ -70,7 +71,8 @@ void shouldThrowInvocationException() {
 				.hasMessage("hi!");
 	}
 
-	private static <T> SeparateThreadTimeoutInvocation<T> aSeparateThreadInvocation(Invocation<T> invocation) {
+	private static <T extends @Nullable Object> SeparateThreadTimeoutInvocation<T> aSeparateThreadInvocation(
+			Invocation<T> invocation) {
 		var namespace = ExtensionContext.Namespace.create(SeparateThreadTimeoutInvocationTests.class);
 		var store = new NamespaceAwareStore(new NamespacedHierarchicalStore<>(null),
 			Namespace.create(namespace.getParts()));
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TempDirectoryCleanupTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TempDirectoryCleanupTests.java
index b8d0b90468aa..5619832335ba 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TempDirectoryCleanupTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TempDirectoryCleanupTests.java
@@ -27,6 +27,7 @@
 import java.util.logging.Level;
 import java.util.logging.LogRecord;
 
+import org.jspecify.annotations.NullUnmarked;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.MethodOrderer;
 import org.junit.jupiter.api.Nested;
@@ -53,6 +54,7 @@
 class TempDirectoryCleanupTests extends AbstractJupiterTestEngineTests {
 
 	@Nested
+	@NullUnmarked
 	class TempDirFieldTests {
 
 		private static Path defaultFieldDir;
@@ -315,6 +317,7 @@ void passingTest(@TempDir(cleanup = ON_SUCCESS) Path tempDir) {
 	}
 
 	@Nested
+	@NullUnmarked
 	class TempDirParameterTests {
 
 		private static Path defaultParameterDir;
@@ -539,6 +542,7 @@ void doesNotFollowJunctions(@TempDir Path tempDir, @TrackLogRecords LogRecordLis
 		}
 
 		@SuppressWarnings("JUnitMalformedDeclaration")
+		@NullUnmarked
 		static class JunctionTestCase {
 			public static Path target;
 
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TempDirectoryMetaAnnotationTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TempDirectoryMetaAnnotationTests.java
index 338ba7dd286a..7e93ae45728f 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TempDirectoryMetaAnnotationTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TempDirectoryMetaAnnotationTests.java
@@ -19,6 +19,7 @@
 import java.nio.file.Files;
 import java.nio.file.Path;
 
+import org.jspecify.annotations.NullUnmarked;
 import org.junit.jupiter.api.DisplayName;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.io.TempDir;
@@ -45,6 +46,7 @@ void annotationOnParameter() {
 	}
 
 	@SuppressWarnings("JUnitMalformedDeclaration")
+	@NullUnmarked
 	static class AnnotationOnFieldTestCase {
 
 		@CustomTempDir
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TempDirectoryPerContextTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TempDirectoryPerContextTests.java
deleted file mode 100644
index 6200f2e47645..000000000000
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TempDirectoryPerContextTests.java
+++ /dev/null
@@ -1,1527 +0,0 @@
-/*
- * Copyright 2015-2025 the original author or authors.
- *
- * All rights reserved. This program and the accompanying materials are
- * made available under the terms of the Eclipse Public License v2.0 which
- * accompanies this distribution and is available at
- *
- * https://www.eclipse.org/legal/epl-v20.html
- */
-
-package org.junit.jupiter.engine.extension;
-
-import static org.assertj.core.api.Assertions.assertThat;
-import static org.junit.jupiter.api.Assertions.assertEquals;
-import static org.junit.jupiter.api.Assertions.assertNotEquals;
-import static org.junit.jupiter.api.Assertions.assertNotNull;
-import static org.junit.jupiter.api.Assertions.assertSame;
-import static org.junit.jupiter.api.Assertions.assertTrue;
-import static org.junit.jupiter.api.Assertions.fail;
-import static org.junit.jupiter.api.Assumptions.assumeTrue;
-import static org.junit.jupiter.api.TestInstance.Lifecycle.PER_CLASS;
-import static org.junit.platform.engine.discovery.DiscoverySelectors.selectClass;
-import static org.junit.platform.launcher.core.LauncherDiscoveryRequestBuilder.request;
-import static org.junit.platform.testkit.engine.EventConditions.finishedWithFailure;
-import static org.junit.platform.testkit.engine.TestExecutionResultConditions.cause;
-import static org.junit.platform.testkit.engine.TestExecutionResultConditions.instanceOf;
-import static org.junit.platform.testkit.engine.TestExecutionResultConditions.message;
-
-import java.io.File;
-import java.io.IOException;
-import java.nio.file.Files;
-import java.nio.file.Path;
-import java.nio.file.attribute.DosFileAttributeView;
-import java.util.Deque;
-import java.util.LinkedList;
-import java.util.function.Supplier;
-
-import org.assertj.core.api.Condition;
-import org.junit.jupiter.api.AfterAll;
-import org.junit.jupiter.api.AfterEach;
-import org.junit.jupiter.api.BeforeAll;
-import org.junit.jupiter.api.BeforeEach;
-import org.junit.jupiter.api.DisplayName;
-import org.junit.jupiter.api.MethodOrderer.OrderAnnotation;
-import org.junit.jupiter.api.Nested;
-import org.junit.jupiter.api.Order;
-import org.junit.jupiter.api.Test;
-import org.junit.jupiter.api.TestInfo;
-import org.junit.jupiter.api.TestInstance;
-import org.junit.jupiter.api.TestMethodOrder;
-import org.junit.jupiter.api.extension.AnnotatedElementContext;
-import org.junit.jupiter.api.extension.ExtensionConfigurationException;
-import org.junit.jupiter.api.extension.ExtensionContext;
-import org.junit.jupiter.api.extension.ParameterResolutionException;
-import org.junit.jupiter.api.io.TempDir;
-import org.junit.jupiter.api.io.TempDirFactory;
-import org.junit.jupiter.api.io.TempDirFactory.Standard;
-import org.junit.jupiter.engine.AbstractJupiterTestEngineTests;
-import org.junit.platform.commons.PreconditionViolationException;
-import org.junit.platform.launcher.core.LauncherDiscoveryRequestBuilder;
-import org.junit.platform.testkit.engine.EngineExecutionResults;
-
-/**
- * Integration tests for the legacy behavior of the {@link TempDirectory}
- * extension to create a single temp directory per context, i.e., test class or
- * method.
- *
- * @since 5.4
- */
-@DisplayName("TempDirectory extension (per context)")
-class TempDirectoryPerContextTests extends AbstractJupiterTestEngineTests {
-
-	@Override
-	protected EngineExecutionResults executeTestsForClass(Class<?> testClass) {
-		return executeTests(requestBuilder(testClass).build());
-	}
-
-	private EngineExecutionResults executeTestsForClassWithDefaultFactory(Class<?> testClass,
-			Class<? extends TempDirFactory> factoryClass) {
-		return executeTests(requestBuilder(testClass) //
-				.configurationParameter(TempDir.DEFAULT_FACTORY_PROPERTY_NAME, factoryClass.getName()) //
-				.build());
-	}
-
-	@SuppressWarnings("deprecation")
-	private static LauncherDiscoveryRequestBuilder requestBuilder(Class<?> testClass) {
-		return request() //
-				.selectors(selectClass(testClass)) //
-				.configurationParameter(TempDir.SCOPE_PROPERTY_NAME, TempDirectory.Scope.PER_CONTEXT.name());
-	}
-
-	@BeforeEach
-	@AfterEach
-	void resetStaticVariables() {
-		BaseSharedTempDirFieldInjectionTestCase.staticTempDir = null;
-		BaseSharedTempDirParameterInjectionTestCase.tempDir = null;
-		BaseSeparateTempDirsFieldInjectionTestCase.tempDirs.clear();
-		BaseSeparateTempDirsParameterInjectionTestCase.tempDirs.clear();
-		BaseConstructorInjectionTestCase.tempDirs.clear();
-	}
-
-	@Test
-	@DisplayName("does not prevent constructor parameter resolution")
-	void tempDirectoryDoesNotPreventConstructorParameterResolution() {
-		executeTestsForClass(TempDirectoryDoesNotPreventConstructorParameterResolutionTestCase.class).testEvents()//
-				.assertStatistics(stats -> stats.started(1).succeeded(1));
-	}
-
-	@Test
-	@DisplayName("does not prevent user from deleting the temp dir within a test")
-	void tempDirectoryDoesNotPreventUserFromDeletingTempDir() {
-		executeTestsForClass(UserTempDirectoryDeletionDoesNotCauseFailureTestCase.class).testEvents()//
-				.assertStatistics(stats -> stats.started(1).succeeded(1));
-	}
-
-	@Test
-	@DisplayName("is capable of removing a read-only file")
-	void nonWritableFileDoesNotCauseFailure() {
-		executeTestsForClass(NonWritableFileDoesNotCauseFailureTestCase.class).testEvents()//
-				.assertStatistics(stats -> stats.started(1).succeeded(1));
-	}
-
-	@Test
-	@DisplayName("is capable of removing non-executable, non-writable, or non-readable directories and folders")
-	void nonMintPermissionsContentDoesNotCauseFailure() {
-		executeTestsForClass(NonMintPermissionContentInTempDirectoryDoesNotCauseFailureTestCase.class).testEvents()//
-				.assertStatistics(stats -> stats.started(13).succeeded(13));
-	}
-
-	@Test
-	@DisplayName("is capable of removing a directory when its permissions have been changed")
-	void nonMintPermissionsDoNotCauseFailure() {
-		executeTestsForClass(NonMintTempDirectoryPermissionsDoNotCauseFailureTestCase.class).testEvents()//
-				.assertStatistics(stats -> stats.started(42).succeeded(42));
-	}
-
-	@Test
-	@DisplayName("is capable of removing a read-only file in a read-only dir")
-	void readOnlyFileInReadOnlyDirDoesNotCauseFailure() {
-		executeTestsForClass(ReadOnlyFileInReadOnlyDirDoesNotCauseFailureTestCase.class).testEvents()//
-				.assertStatistics(stats -> stats.started(1).succeeded(1));
-	}
-
-	@Test
-	@DisplayName("is capable of removing a read-only file in a dir in a read-only dir")
-	void readOnlyFileInNestedReadOnlyDirDoesNotCauseFailure() {
-		executeTestsForClass(ReadOnlyFileInDirInReadOnlyDirDoesNotCauseFailureTestCase.class).testEvents()//
-				.assertStatistics(stats -> stats.started(1).succeeded(1));
-	}
-
-	@Test
-	@DisplayName("can be used via instance field inside nested test classes")
-	void canBeUsedViaInstanceFieldInsideNestedTestClasses() {
-		executeTestsForClass(TempDirUsageInsideNestedClassesTestCase.class).testEvents()//
-				.assertStatistics(stats -> stats.started(3).succeeded(3));
-	}
-
-	@Test
-	@DisplayName("can be used via static field inside nested test classes")
-	void canBeUsedViaStaticFieldInsideNestedTestClasses() {
-		executeTestsForClass(StaticTempDirUsageInsideNestedClassTestCase.class).testEvents()//
-				.assertStatistics(stats -> stats.started(2).succeeded(2));
-	}
-
-	@Test
-	@DisplayName("resolves java.io.File injection type")
-	void resolvesFileInstances() {
-		executeTestsForClass(FileInjectionTestCase.class).testEvents()//
-				.assertStatistics(stats -> stats.started(1).succeeded(1));
-	}
-
-	@Nested
-	@DisplayName("resolves shared temp dir")
-	@TestMethodOrder(OrderAnnotation.class)
-	class SharedTempDir {
-
-		@Test
-		@DisplayName("when @TempDir is used on static field")
-		@Order(10)
-		void resolvesSharedTempDirWhenAnnotationIsUsedOnStaticField() {
-			assertSharedTempDirForFieldInjection(AnnotationOnStaticFieldTestCase.class);
-		}
-
-		@Test
-		@DisplayName("when @TempDir is used on static field and @BeforeAll method parameter")
-		@Order(11)
-		void resolvesSharedTempDirWhenAnnotationIsUsedOnStaticFieldAndBeforeAllMethodParameter() {
-			assertSharedTempDirForFieldInjection(AnnotationOnStaticFieldAndBeforeAllMethodParameterTestCase.class);
-		}
-
-		@Test
-		@DisplayName("when @TempDir is used on instance field and @BeforeAll method parameter")
-		@Order(14)
-		void resolvesSharedTempDirWhenAnnotationIsUsedOnInstanceFieldAndBeforeAllMethodParameter() {
-			assertSharedTempDirForFieldInjection(AnnotationOnInstanceFieldAndBeforeAllMethodParameterTestCase.class);
-		}
-
-		@Test
-		@DisplayName("when @TempDir is used on instance field and @BeforeAll method parameter with @TestInstance(PER_CLASS)")
-		@Order(15)
-		void resolvesSharedTempDirWhenAnnotationIsUsedOnInstanceFieldAndBeforeAllMethodParameterWithTestInstancePerClass() {
-			assertSharedTempDirForFieldInjection(
-				AnnotationOnInstanceFieldAndBeforeAllMethodParameterWithTestInstancePerClassTestCase.class);
-		}
-
-		@Test
-		@DisplayName("when @TempDir is used on @BeforeAll method parameter")
-		@Order(23)
-		void resolvesSharedTempDirWhenAnnotationIsUsedOnBeforeAllMethodParameter() {
-			assertSharedTempDirForParameterInjection(AnnotationOnBeforeAllMethodParameterTestCase.class);
-		}
-
-		@Test
-		@DisplayName("when @TempDir is used on @BeforeAll method parameter with @TestInstance(PER_CLASS)")
-		@Order(24)
-		void resolvesSharedTempDirWhenAnnotationIsUsedOnBeforeAllMethodParameterWithTestInstancePerClass() {
-			assertSharedTempDirForParameterInjection(
-				AnnotationOnBeforeAllMethodParameterWithTestInstancePerClassTestCase.class);
-		}
-
-		@Test
-		@DisplayName("when @TempDir is used on constructor parameter with @TestInstance(PER_CLASS)")
-		@Order(25)
-		void resolvesSharedTempDirWhenAnnotationIsUsedOnConstructorWithTestInstancePerClass() {
-			var results = executeTestsForClass(SharedTempDirsConstructorInjectionPerClassTestCase.class);
-
-			results.testEvents().assertStatistics(stats -> stats.started(2).failed(0).succeeded(2));
-			assertThat(BaseConstructorInjectionTestCase.tempDirs.getFirst()).doesNotExist();
-			assertThat(BaseConstructorInjectionTestCase.tempDirs.getLast()).doesNotExist();
-		}
-
-		private void assertSharedTempDirForFieldInjection(
-				Class<? extends BaseSharedTempDirFieldInjectionTestCase> testClass) {
-
-			assertSharedTempDirForParameterInjection(testClass,
-				() -> BaseSharedTempDirFieldInjectionTestCase.staticTempDir);
-		}
-
-		private void assertSharedTempDirForParameterInjection(
-				Class<? extends BaseSharedTempDirParameterInjectionTestCase> testClass) {
-
-			assertSharedTempDirForParameterInjection(testClass,
-				() -> BaseSharedTempDirParameterInjectionTestCase.tempDir);
-		}
-
-		private void assertSharedTempDirForParameterInjection(Class<?> testClass, Supplier<Path> staticTempDir) {
-			var results = executeTestsForClass(testClass);
-
-			results.testEvents().assertStatistics(stats -> stats.started(2).failed(0).succeeded(2));
-			assertThat(staticTempDir.get()).isNotNull().doesNotExist();
-		}
-
-	}
-
-	@Nested
-	@DisplayName("resolves separate temp dirs")
-	@TestMethodOrder(OrderAnnotation.class)
-	class SeparateTempDirs {
-
-		@Test
-		@DisplayName("when @TempDir is used on instance field")
-		@Order(11)
-		void resolvesSeparateTempDirWhenAnnotationIsUsedOnInstanceField() {
-			assertSeparateTempDirsForFieldInjection(
-				SeparateTempDirsWhenUsedOnForEachLifecycleMethodsFieldInjectionTestCase.class);
-			assertThat(BaseSeparateTempDirsFieldInjectionTestCase.tempDirs.getFirst()).doesNotExist();
-			assertThat(BaseSeparateTempDirsFieldInjectionTestCase.tempDirs.getLast()).doesNotExist();
-		}
-
-		@Test
-		@DisplayName("when @TempDir is used on instance field with @TestInstance(PER_CLASS)")
-		@Order(12)
-		void resolvesSeparateTempDirWhenAnnotationIsUsedOnInstanceFieldWithTestInstancePerClass() {
-			assertSeparateTempDirsForFieldInjection(
-				SeparateTempDirsWhenUsedOnForEachLifecycleMethodsWithTestInstancePerClassFieldInjectionTestCase.class);
-			assertThat(BaseSeparateTempDirsFieldInjectionTestCase.tempDirs.getFirst()).doesNotExist();
-			assertThat(BaseSeparateTempDirsFieldInjectionTestCase.tempDirs.getLast()).doesNotExist();
-		}
-
-		@Test
-		@DisplayName("when @TempDir is used on @BeforeEach/@AfterEach method parameters")
-		@Order(21)
-		void resolvesSeparateTempDirsWhenUsedOnForEachLifecycleMethods() {
-			assertSeparateTempDirsForParameterInjection(
-				SeparateTempDirsWhenUsedOnForEachLifecycleMethodsParameterInjectionTestCase.class);
-			assertThat(BaseSeparateTempDirsParameterInjectionTestCase.tempDirs.getFirst()).doesNotExist();
-			assertThat(BaseSeparateTempDirsParameterInjectionTestCase.tempDirs.getLast()).doesNotExist();
-		}
-
-		@Test
-		@DisplayName("when @TempDir is used on @BeforeEach/@AfterEach method parameters with @TestInstance(PER_CLASS)")
-		@Order(22)
-		void resolvesSeparateTempDirsWhenUsedOnForEachLifecycleMethodsWithTestInstancePerClass() {
-			assertSeparateTempDirsForParameterInjection(
-				SeparateTempDirsWhenUsedOnForEachLifecycleMethodsWithTestInstancePerClassParameterInjectionTestCase.class);
-			assertThat(BaseSeparateTempDirsParameterInjectionTestCase.tempDirs.getFirst()).doesNotExist();
-			assertThat(BaseSeparateTempDirsParameterInjectionTestCase.tempDirs.getLast()).doesNotExist();
-		}
-
-		@Test
-		@DisplayName("for @AfterAll method parameter when @TempDir is not used on constructor or @BeforeAll method parameter")
-		@Order(31)
-		void resolvesSeparateTempDirWhenAnnotationIsUsedOnAfterAllMethodParameterOnly() {
-			var results = executeTestsForClass(AnnotationOnAfterAllMethodParameterTestCase.class);
-
-			results.testEvents().assertStatistics(stats -> stats.started(1).failed(0).succeeded(1));
-			assertThat(AnnotationOnAfterAllMethodParameterTestCase.firstTempDir).isNotNull().doesNotExist();
-			assertThat(AnnotationOnAfterAllMethodParameterTestCase.secondTempDir).isNotNull().doesNotExist();
-		}
-
-		@Test
-		@DisplayName("when @TempDir is used on constructor parameter")
-		@Order(32)
-		void resolvesSeparateTempDirsWhenAnnotationIsUsedOnConstructorWithTestInstancePerMethod() {
-			var results = executeTestsForClass(SeparateTempDirsConstructorInjectionPerMethodTestCase.class);
-
-			results.testEvents().assertStatistics(stats -> stats.started(2).failed(0).succeeded(2));
-			assertThat(BaseConstructorInjectionTestCase.tempDirs.getFirst()).doesNotExist();
-			assertThat(BaseConstructorInjectionTestCase.tempDirs.getLast()).doesNotExist();
-		}
-
-	}
-
-	@Nested
-	@DisplayName("supports default factory")
-	@TestMethodOrder(OrderAnnotation.class)
-	class DefaultFactory {
-
-		@Test
-		@DisplayName("set to Jupiter's default")
-		void supportsStandardDefaultFactory() {
-			var results = executeTestsForClassWithDefaultFactory(StandardDefaultFactoryTestCase.class, Standard.class);
-
-			results.testEvents().assertStatistics(stats -> stats.started(1).succeeded(1));
-		}
-
-		@Test
-		@DisplayName("set to custom factory")
-		void supportsCustomDefaultFactory() {
-			var results = executeTestsForClassWithDefaultFactory(CustomDefaultFactoryTestCase.class, Factory.class);
-
-			results.testEvents().assertStatistics(stats -> stats.started(1).succeeded(1));
-		}
-
-		private static class Factory implements TempDirFactory {
-
-			@Override
-			public Path createTempDirectory(AnnotatedElementContext elementContext, ExtensionContext extensionContext)
-					throws Exception {
-				return Files.createTempDirectory("junit");
-			}
-		}
-
-	}
-
-	@Nested
-	@DisplayName("reports failure")
-	@TestMethodOrder(OrderAnnotation.class)
-	class Failures {
-
-		@Test
-		@DisplayName("when @TempDir is used on static field of an unsupported type")
-		@Order(20)
-		void onlySupportsStaticFieldsOfTypePathAndFile() {
-			var results = executeTestsForClass(AnnotationOnStaticFieldWithUnsupportedTypeTestCase.class);
-
-			assertSingleFailedContainer(results, ExtensionConfigurationException.class,
-				"Can only resolve @TempDir field of type java.nio.file.Path or java.io.File");
-		}
-
-		@Test
-		@DisplayName("when @TempDir is used on instance field of an unsupported type")
-		@Order(21)
-		void onlySupportsInstanceFieldsOfTypePathAndFile() {
-			var results = executeTestsForClass(AnnotationOnInstanceFieldWithUnsupportedTypeTestCase.class);
-
-			assertSingleFailedTest(results, ExtensionConfigurationException.class,
-				"Can only resolve @TempDir field of type java.nio.file.Path or java.io.File");
-		}
-
-		@Test
-		@DisplayName("when @TempDir is used on parameter of an unsupported type")
-		@Order(22)
-		void onlySupportsParametersOfTypePathAndFile() {
-			var results = executeTestsForClass(InvalidTestCase.class);
-
-			// @formatter:off
-			assertSingleFailedTest(results, instanceOf(ParameterResolutionException.class),
-				message(m -> m.matches("Failed to resolve parameter \\[java.lang.String .+] in method \\[.+]: .+")),
-				cause(
-					instanceOf(ExtensionConfigurationException.class),
-					message("Can only resolve @TempDir parameter of type java.nio.file.Path or java.io.File but was: java.lang.String")));
-			// @formatter:on
-		}
-
-		@Test
-		@DisplayName("when non-default @TempDir factory is set")
-		@Order(32)
-		void doesNotSupportNonDefaultTempDirFactory() {
-			var results = executeTestsForClass(NonDefaultFactoryTestCase.class);
-
-			// @formatter:off
-			assertSingleFailedTest(results, instanceOf(ParameterResolutionException.class),
-					message(m -> m.matches("Failed to resolve parameter \\[.+] in method \\[.+]: .+")),
-					cause(
-							instanceOf(ExtensionConfigurationException.class),
-							message("Custom @TempDir factory is not supported with junit.jupiter.tempdir.scope=per_context. "
-									+ "Use junit.jupiter.tempdir.factory.default instead.")));
-			// @formatter:on
-		}
-
-		@Test
-		@DisplayName("when default @TempDir factory does not return directory")
-		@Order(33)
-		void doesNotSupportCustomDefaultTempDirFactoryNotReturningDirectory() {
-			var results = executeTestsForClassWithDefaultFactory(
-				CustomDefaultFactoryNotReturningDirectoryTestCase.class, FactoryNotReturningDirectory.class);
-
-			// @formatter:off
-			assertSingleFailedTest(results, instanceOf(ParameterResolutionException.class),
-					message(m -> m.matches("Failed to resolve parameter \\[.+] in method \\[.+]: .+")),
-					cause(
-							instanceOf(ExtensionConfigurationException.class),
-							message("Failed to create default temp directory"),
-							cause(
-									instanceOf(PreconditionViolationException.class),
-									message("temp directory must be a directory")
-							)
-					));
-			// @formatter:on
-		}
-
-		private static class FactoryNotReturningDirectory implements TempDirFactory {
-
-			@Override
-			public Path createTempDirectory(AnnotatedElementContext elementContext, ExtensionContext extensionContext) {
-				return null;
-			}
-		}
-
-	}
-
-	@Nested
-	@DisplayName("supports @TempDir")
-	@TestMethodOrder(OrderAnnotation.class)
-	class PrivateFields {
-
-		@Test
-		@DisplayName("on private static field")
-		@Order(10)
-		void supportsPrivateInstanceFields() {
-			executeTestsForClass(AnnotationOnPrivateStaticFieldTestCase.class).testEvents()//
-					.assertStatistics(stats -> stats.started(1).succeeded(1));
-		}
-
-		@Test
-		@DisplayName("on private instance field")
-		@Order(11)
-		void supportsPrivateStaticFields() {
-			executeTestsForClass(AnnotationOnPrivateInstanceFieldTestCase.class).testEvents()//
-					.assertStatistics(stats -> stats.started(1).succeeded(1));
-		}
-
-	}
-
-	private static void assertSingleFailedContainer(EngineExecutionResults results, Class<? extends Throwable> clazz,
-			String message) {
-
-		assertSingleFailedContainer(results, instanceOf(clazz), message(actual -> actual.contains(message)));
-	}
-
-	@SafeVarargs
-	@SuppressWarnings("varargs")
-	private static void assertSingleFailedContainer(EngineExecutionResults results,
-			Condition<Throwable>... conditions) {
-
-		results.containerEvents()//
-				.assertStatistics(stats -> stats.started(2).failed(1).succeeded(1))//
-				.assertThatEvents().haveExactly(1, finishedWithFailure(conditions));
-	}
-
-	private static void assertSingleFailedTest(EngineExecutionResults results, Class<? extends Throwable> clazz,
-			String message) {
-
-		assertSingleFailedTest(results, instanceOf(clazz), message(actual -> actual.contains(message)));
-	}
-
-	@SafeVarargs
-	@SuppressWarnings("varargs")
-	private static void assertSingleFailedTest(EngineExecutionResults results, Condition<Throwable>... conditions) {
-		results.testEvents().assertStatistics(stats -> stats.started(1).failed(1).succeeded(0));
-		results.testEvents().assertThatEvents().haveExactly(1, finishedWithFailure(conditions));
-	}
-
-	private void assertSeparateTempDirsForFieldInjection(
-			Class<? extends BaseSeparateTempDirsFieldInjectionTestCase> testClass) {
-
-		assertResolvesSeparateTempDirs(testClass, BaseSeparateTempDirsFieldInjectionTestCase.tempDirs);
-	}
-
-	private void assertSeparateTempDirsForParameterInjection(
-			Class<? extends BaseSeparateTempDirsParameterInjectionTestCase> testClass) {
-
-		assertResolvesSeparateTempDirs(testClass, BaseSeparateTempDirsParameterInjectionTestCase.tempDirs);
-	}
-
-	private void assertResolvesSeparateTempDirs(Class<?> testClass, Deque<Path> tempDirs) {
-		var results = executeTestsForClass(testClass);
-
-		results.testEvents().assertStatistics(stats -> stats.started(2).failed(0).succeeded(2));
-		assertThat(tempDirs).hasSize(2);
-	}
-
-	// -------------------------------------------------------------------------
-
-	@SuppressWarnings("JUnitMalformedDeclaration")
-	static class BaseSharedTempDirFieldInjectionTestCase {
-
-		static Path staticTempDir;
-
-		@TempDir
-		Path tempDir;
-
-		@BeforeEach
-		void beforeEach(@TempDir Path tempDir) {
-			if (BaseSharedTempDirFieldInjectionTestCase.staticTempDir != null) {
-				assertSame(BaseSharedTempDirFieldInjectionTestCase.staticTempDir, tempDir);
-			}
-			else {
-				BaseSharedTempDirFieldInjectionTestCase.staticTempDir = tempDir;
-			}
-			check(tempDir);
-		}
-
-		@Test
-		void test1(@TempDir Path tempDir, TestInfo testInfo) throws Exception {
-			check(tempDir);
-			writeFile(tempDir, testInfo);
-		}
-
-		@Test
-		void test2(TestInfo testInfo, @TempDir Path tempDir) throws Exception {
-			check(tempDir);
-			writeFile(tempDir, testInfo);
-		}
-
-		@AfterEach
-		void afterEach(@TempDir Path tempDir) {
-			check(tempDir);
-		}
-
-		void check(Path tempDir) {
-			assertThat(BaseSharedTempDirFieldInjectionTestCase.staticTempDir)//
-					.isNotNull()//
-					.isSameAs(tempDir)//
-					.isSameAs(this.tempDir);
-			assertTrue(Files.exists(tempDir));
-		}
-
-	}
-
-	static class AnnotationOnStaticFieldTestCase extends BaseSharedTempDirFieldInjectionTestCase {
-
-		@TempDir
-		static Path staticTempPath;
-
-		@TempDir
-		static File staticTempFile;
-
-		@Override
-		void check(Path tempDir) {
-			assertThat(BaseSharedTempDirFieldInjectionTestCase.staticTempDir)//
-					.isNotNull()//
-					.isSameAs(AnnotationOnStaticFieldTestCase.staticTempPath)//
-					.isSameAs(tempDir)//
-					.isSameAs(this.tempDir);
-			assertTrue(Files.exists(tempDir));
-		}
-
-	}
-
-	static class AnnotationOnStaticFieldAndBeforeAllMethodParameterTestCase extends AnnotationOnStaticFieldTestCase {
-
-		@BeforeAll
-		static void beforeAll(@TempDir Path tempDir) {
-			assertThat(BaseSharedTempDirFieldInjectionTestCase.staticTempDir).isNull();
-			BaseSharedTempDirFieldInjectionTestCase.staticTempDir = tempDir;
-			assertThat(AnnotationOnStaticFieldTestCase.staticTempFile).isNotNull();
-			assertThat(AnnotationOnStaticFieldTestCase.staticTempPath)//
-					.isNotNull()//
-					.isSameAs(tempDir);
-			assertThat(AnnotationOnStaticFieldTestCase.staticTempFile.toPath().toAbsolutePath())//
-					.isEqualTo(AnnotationOnStaticFieldTestCase.staticTempPath.toAbsolutePath());
-			assertTrue(Files.exists(tempDir));
-		}
-
-	}
-
-	static class AnnotationOnInstanceFieldAndBeforeAllMethodParameterTestCase
-			extends BaseSharedTempDirFieldInjectionTestCase {
-
-		@BeforeAll
-		static void beforeAll(@TempDir Path tempDir) {
-			assertThat(BaseSharedTempDirFieldInjectionTestCase.staticTempDir).isNull();
-			BaseSharedTempDirFieldInjectionTestCase.staticTempDir = tempDir;
-			assertTrue(Files.exists(tempDir));
-		}
-
-	}
-
-	@TestInstance(PER_CLASS)
-	static class AnnotationOnInstanceFieldAndBeforeAllMethodParameterWithTestInstancePerClassTestCase
-			extends AnnotationOnInstanceFieldAndBeforeAllMethodParameterTestCase {
-
-	}
-
-	@SuppressWarnings("JUnitMalformedDeclaration")
-	static class AnnotationOnPrivateInstanceFieldTestCase {
-
-		@SuppressWarnings("unused")
-		@TempDir
-		private Path tempDir;
-
-		@Test
-		void test() {
-			assertTrue(Files.exists(tempDir));
-		}
-
-	}
-
-	@SuppressWarnings("JUnitMalformedDeclaration")
-	static class AnnotationOnPrivateStaticFieldTestCase {
-
-		@SuppressWarnings("unused")
-		@TempDir
-		private static Path tempDir;
-
-		@Test
-		void test() {
-			assertTrue(Files.exists(tempDir));
-		}
-
-	}
-
-	@SuppressWarnings("JUnitMalformedDeclaration")
-	static class AnnotationOnStaticFieldWithUnsupportedTypeTestCase {
-
-		@SuppressWarnings("unused")
-		@TempDir
-		static String tempDir;
-
-		@Test
-		void test1() {
-		}
-
-	}
-
-	@SuppressWarnings("JUnitMalformedDeclaration")
-	static class AnnotationOnInstanceFieldWithUnsupportedTypeTestCase {
-
-		@SuppressWarnings("unused")
-		@TempDir
-		String tempDir;
-
-		@Test
-		void test1() {
-		}
-
-	}
-
-	@SuppressWarnings("JUnitMalformedDeclaration")
-	static class BaseSharedTempDirParameterInjectionTestCase {
-
-		static Path tempDir;
-
-		@BeforeEach
-		void beforeEach(@TempDir Path tempDir) {
-			check(tempDir);
-		}
-
-		@Test
-		void test1(@TempDir Path tempDir, TestInfo testInfo) throws Exception {
-			check(tempDir);
-			writeFile(tempDir, testInfo);
-		}
-
-		@Test
-		void test2(TestInfo testInfo, @TempDir Path tempDir) throws Exception {
-			check(tempDir);
-			writeFile(tempDir, testInfo);
-		}
-
-		@AfterEach
-		void afterEach(@TempDir Path tempDir) {
-			check(tempDir);
-		}
-
-		static void check(Path tempDir) {
-			assertThat(BaseSharedTempDirParameterInjectionTestCase.tempDir).isNotNull().isSameAs(tempDir);
-			assertTrue(Files.exists(tempDir));
-		}
-
-	}
-
-	@SuppressWarnings("JUnitMalformedDeclaration")
-	static class BaseConstructorInjectionTestCase {
-
-		static final Deque<Path> tempDirs = new LinkedList<>();
-
-		private final Path tempDir;
-
-		BaseConstructorInjectionTestCase(Path tempDir) {
-			this.tempDir = tempDir;
-		}
-
-		@Test
-		void test1(@TempDir Path tempDir, TestInfo testInfo) throws Exception {
-			check(tempDir);
-			writeFile(tempDir, testInfo);
-		}
-
-		@Test
-		void test2(TestInfo testInfo, @TempDir Path tempDir) throws Exception {
-			check(tempDir);
-			writeFile(tempDir, testInfo);
-		}
-
-		@AfterEach
-		void afterEach(@TempDir Path tempDir) {
-			check(tempDir);
-		}
-
-		void check(Path tempDir) {
-			assertThat(tempDirs.getLast())//
-					.isNotNull()//
-					.isSameAs(tempDir)//
-					.isSameAs(this.tempDir);
-			assertTrue(Files.exists(tempDir));
-		}
-
-	}
-
-	static class SeparateTempDirsConstructorInjectionPerMethodTestCase extends BaseConstructorInjectionTestCase {
-
-		SeparateTempDirsConstructorInjectionPerMethodTestCase(@TempDir Path tempDir) {
-			super(tempDir);
-		}
-
-		@BeforeEach
-		void beforeEach(@TempDir Path tempDir) {
-			for (Path dir : tempDirs) {
-				assertThat(dir).doesNotExist();
-			}
-			assertThat(tempDirs).doesNotContain(tempDir);
-			tempDirs.add(tempDir);
-			check(tempDir);
-		}
-	}
-
-	@TestInstance(PER_CLASS)
-	static class SharedTempDirsConstructorInjectionPerClassTestCase extends BaseConstructorInjectionTestCase {
-
-		SharedTempDirsConstructorInjectionPerClassTestCase(@TempDir Path tempDir) {
-			super(tempDir);
-		}
-
-		@BeforeEach
-		void beforeEach(@TempDir Path tempDir) {
-			for (Path dir : tempDirs) {
-				assertThat(dir).isSameAs(tempDir).exists();
-			}
-			tempDirs.add(tempDir);
-			check(tempDir);
-		}
-	}
-
-	@SuppressWarnings("JUnitMalformedDeclaration")
-	static class NonDefaultFactoryTestCase {
-
-		@Test
-		void test(@SuppressWarnings("unused") @TempDir(factory = Factory.class) Path tempDir) {
-			// never called
-		}
-
-		private static class Factory implements TempDirFactory {
-
-			@Override
-			public Path createTempDirectory(AnnotatedElementContext elementContext, ExtensionContext extensionContext)
-					throws Exception {
-				return Files.createTempDirectory("junit-");
-			}
-		}
-
-	}
-
-	@SuppressWarnings("JUnitMalformedDeclaration")
-	static class StandardDefaultFactoryTestCase {
-
-		@Test
-		void test(@TempDir Path tempDir1, @TempDir Path tempDir2) {
-			assertSame(tempDir1, tempDir2);
-		}
-
-	}
-
-	@SuppressWarnings("JUnitMalformedDeclaration")
-	static class CustomDefaultFactoryTestCase {
-
-		@Test
-		void test(@TempDir Path tempDir1, @TempDir Path tempDir2) {
-			assertSame(tempDir1, tempDir2);
-		}
-
-	}
-
-	@SuppressWarnings("JUnitMalformedDeclaration")
-	static class CustomDefaultFactoryNotReturningDirectoryTestCase {
-
-		@Test
-		void test(@SuppressWarnings("unused") @TempDir Path tempDir) {
-			// never called
-		}
-
-	}
-
-	static class AnnotationOnBeforeAllMethodParameterTestCase extends BaseSharedTempDirParameterInjectionTestCase {
-
-		@BeforeAll
-		static void beforeAll(@TempDir Path tempDir) {
-			assertThat(BaseSharedTempDirParameterInjectionTestCase.tempDir).isNull();
-			BaseSharedTempDirParameterInjectionTestCase.tempDir = tempDir;
-			check(tempDir);
-		}
-	}
-
-	@TestInstance(PER_CLASS)
-	static class AnnotationOnBeforeAllMethodParameterWithTestInstancePerClassTestCase
-			extends BaseSharedTempDirParameterInjectionTestCase {
-
-		@BeforeAll
-		void beforeAll(@TempDir Path tempDir) {
-			assertThat(BaseSharedTempDirParameterInjectionTestCase.tempDir).isNull();
-			BaseSharedTempDirParameterInjectionTestCase.tempDir = tempDir;
-			check(tempDir);
-		}
-	}
-
-	@SuppressWarnings("JUnitMalformedDeclaration")
-	static class AnnotationOnAfterAllMethodParameterTestCase {
-
-		static Path firstTempDir = null;
-		static Path secondTempDir = null;
-
-		@Test
-		void test(@TempDir Path tempDir, TestInfo testInfo) throws Exception {
-			assertThat(firstTempDir).isNull();
-			firstTempDir = tempDir;
-			writeFile(tempDir, testInfo);
-		}
-
-		@AfterAll
-		static void afterAll(@TempDir Path tempDir) {
-			assertThat(firstTempDir).isNotNull();
-			assertNotEquals(firstTempDir, tempDir);
-			secondTempDir = tempDir;
-		}
-	}
-
-	@SuppressWarnings("JUnitMalformedDeclaration")
-	static class BaseSeparateTempDirsFieldInjectionTestCase {
-
-		static final Deque<Path> tempDirs = new LinkedList<>();
-
-		@TempDir
-		Path tempDir;
-
-		@BeforeEach
-		void beforeEach(@TempDir Path tempDir) {
-			for (Path dir : tempDirs) {
-				assertThat(dir).doesNotExist();
-			}
-			assertThat(tempDirs).doesNotContain(tempDir);
-			tempDirs.add(tempDir);
-			check(tempDir);
-		}
-
-		@Test
-		void test1(@TempDir Path tempDir, TestInfo testInfo) throws Exception {
-			check(tempDir);
-			writeFile(tempDir, testInfo);
-		}
-
-		@Test
-		void test2(TestInfo testInfo, @TempDir Path tempDir) throws Exception {
-			check(tempDir);
-			writeFile(tempDir, testInfo);
-		}
-
-		@AfterEach
-		void afterEach(@TempDir Path tempDir) {
-			check(tempDir);
-		}
-
-		void check(Path tempDir) {
-			assertThat(tempDirs.getLast())//
-					.isNotNull()//
-					.isSameAs(tempDir)//
-					.isSameAs(this.tempDir);
-			assertTrue(Files.exists(tempDir));
-		}
-
-	}
-
-	static class SeparateTempDirsWhenUsedOnForEachLifecycleMethodsFieldInjectionTestCase
-			extends BaseSeparateTempDirsFieldInjectionTestCase {
-	}
-
-	@TestInstance(PER_CLASS)
-	static class SeparateTempDirsWhenUsedOnForEachLifecycleMethodsWithTestInstancePerClassFieldInjectionTestCase
-			extends SeparateTempDirsWhenUsedOnForEachLifecycleMethodsFieldInjectionTestCase {
-	}
-
-	@SuppressWarnings("JUnitMalformedDeclaration")
-	static class BaseSeparateTempDirsParameterInjectionTestCase {
-
-		static final Deque<Path> tempDirs = new LinkedList<>();
-
-		@BeforeEach
-		void beforeEach(@TempDir Path tempDir) {
-			for (Path dir : tempDirs) {
-				assertThat(dir).doesNotExist();
-			}
-			assertThat(tempDirs).doesNotContain(tempDir);
-			tempDirs.add(tempDir);
-			check(tempDir);
-		}
-
-		@Test
-		void test1(@TempDir Path tempDir, TestInfo testInfo) throws Exception {
-			check(tempDir);
-			writeFile(tempDir, testInfo);
-		}
-
-		@Test
-		void test2(TestInfo testInfo, @TempDir Path tempDir) throws Exception {
-			check(tempDir);
-			writeFile(tempDir, testInfo);
-		}
-
-		@AfterEach
-		void afterEach(@TempDir Path tempDir) {
-			check(tempDir);
-		}
-
-		void check(Path tempDir) {
-			assertSame(tempDirs.getLast(), tempDir);
-			assertTrue(Files.exists(tempDir));
-		}
-	}
-
-	static class SeparateTempDirsWhenUsedOnForEachLifecycleMethodsParameterInjectionTestCase
-			extends BaseSeparateTempDirsParameterInjectionTestCase {
-	}
-
-	@TestInstance(PER_CLASS)
-	static class SeparateTempDirsWhenUsedOnForEachLifecycleMethodsWithTestInstancePerClassParameterInjectionTestCase
-			extends SeparateTempDirsWhenUsedOnForEachLifecycleMethodsParameterInjectionTestCase {
-	}
-
-	@SuppressWarnings("JUnitMalformedDeclaration")
-	static class InvalidTestCase {
-
-		@Test
-		void wrongParameterType(@SuppressWarnings("unused") @TempDir String ignored) {
-			fail("this should never be called");
-		}
-	}
-
-	@SuppressWarnings("JUnitMalformedDeclaration")
-	static class FileInjectionTestCase {
-
-		@TempDir
-		File fileTempDir;
-
-		@TempDir
-		Path pathTempDir;
-
-		@Test
-		void checkFile(@TempDir File tempDir, @TempDir Path ref) {
-			assertFileAndPathAreEqual(tempDir, ref);
-			assertFileAndPathAreEqual(this.fileTempDir, this.pathTempDir);
-		}
-
-		private void assertFileAndPathAreEqual(File tempDir, Path ref) {
-			Path path = tempDir.toPath();
-			assertEquals(ref.toAbsolutePath(), path.toAbsolutePath());
-			assertTrue(Files.exists(path));
-		}
-
-	}
-
-	private static void writeFile(Path tempDir, TestInfo testInfo) throws IOException {
-		Path file = tempDir.resolve(testInfo.getTestMethod().orElseThrow().getName() + ".txt");
-		Files.write(file, testInfo.getDisplayName().getBytes());
-	}
-
-	// https://github.com/junit-team/junit5/issues/1748
-	@SuppressWarnings("JUnitMalformedDeclaration")
-	static class TempDirectoryDoesNotPreventConstructorParameterResolutionTestCase {
-
-		TempDirectoryDoesNotPreventConstructorParameterResolutionTestCase(TestInfo testInfo) {
-			assertNotNull(testInfo);
-		}
-
-		@Test
-		void test() {
-		}
-
-	}
-
-	// https://github.com/junit-team/junit5/issues/1801
-	@SuppressWarnings("JUnitMalformedDeclaration")
-	static class UserTempDirectoryDeletionDoesNotCauseFailureTestCase {
-
-		@Test
-		void deleteTempDir(@TempDir Path tempDir) throws IOException {
-			Files.delete(tempDir);
-			assertThat(tempDir).doesNotExist();
-		}
-
-	}
-
-	// https://github.com/junit-team/junit5/issues/2046
-	@SuppressWarnings("JUnitMalformedDeclaration")
-	static class NonWritableFileDoesNotCauseFailureTestCase {
-
-		@Test
-		void createReadonlyFile(@TempDir Path tempDir) throws IOException {
-			// Removal of setWritable(false) files might fail (e.g. for Windows)
-			// The test verifies that @TempDir is capable of removing of such files
-			var path = Files.write(tempDir.resolve("test.txt"), new byte[0]);
-			assumeTrue(path.toFile().setWritable(false),
-				() -> "Unable to set file " + path + " readonly via .toFile().setWritable(false)");
-		}
-
-	}
-
-	// https://github.com/junit-team/junit5/issues/2171
-	@SuppressWarnings("JUnitMalformedDeclaration")
-	static class ReadOnlyFileInReadOnlyDirDoesNotCauseFailureTestCase {
-
-		@Test
-		void createReadOnlyFileInReadOnlyDir(@TempDir File tempDir) throws IOException {
-			File file = tempDir.toPath().resolve("file").toFile();
-			assumeTrue(file.createNewFile());
-			assumeTrue(makeReadOnly(tempDir));
-			assumeTrue(makeReadOnly(file));
-		}
-
-	}
-
-	// https://github.com/junit-team/junit5/issues/2171
-	@SuppressWarnings("JUnitMalformedDeclaration")
-	static class ReadOnlyFileInDirInReadOnlyDirDoesNotCauseFailureTestCase {
-
-		@Test
-		void createReadOnlyFileInReadOnlyDir(@TempDir File tempDir) throws IOException {
-			File file = tempDir.toPath().resolve("dir").resolve("file").toFile();
-			assumeTrue(file.getParentFile().mkdirs());
-			assumeTrue(file.createNewFile());
-			assumeTrue(makeReadOnly(tempDir));
-			assumeTrue(makeReadOnly(file.getParentFile()));
-			assumeTrue(makeReadOnly(file));
-		}
-
-	}
-
-	private static boolean makeReadOnly(File file) throws IOException {
-		var dos = Files.getFileAttributeView(file.toPath(), DosFileAttributeView.class);
-		if (dos != null) {
-			dos.setReadOnly(true);
-			return true;
-		}
-		return file.setReadOnly();
-	}
-
-	// https://github.com/junit-team/junit5/issues/2609
-	@SuppressWarnings({ "ResultOfMethodCallIgnored", "JUnitMalformedDeclaration" })
-	static class NonMintPermissionContentInTempDirectoryDoesNotCauseFailureTestCase {
-
-		@Test
-		void createFile(@TempDir Path tempDir) throws IOException {
-			Files.createFile(tempDir.resolve("test-file.txt")).toFile();
-		}
-
-		@Test
-		void createFolder(@TempDir Path tempDir) throws IOException {
-			Files.createFile(tempDir.resolve("test-file.txt")).toFile();
-		}
-
-		@Test
-		void createNonWritableFile(@TempDir Path tempDir) throws IOException {
-			Files.createFile(tempDir.resolve("test-file.txt")).toFile().setWritable(false);
-		}
-
-		@Test
-		void createNonReadableFile(@TempDir Path tempDir) throws IOException {
-			Files.createFile(tempDir.resolve("test-file.txt")).toFile().setReadable(false);
-		}
-
-		@Test
-		void createNonWritableDirectory(@TempDir Path tempDir) throws IOException {
-			Files.createDirectory(tempDir.resolve("test-sub-dir")).toFile().setWritable(false);
-		}
-
-		@Test
-		void createNonReadableDirectory(@TempDir Path tempDir) throws IOException {
-			Files.createDirectory(tempDir.resolve("test-sub-dir")).toFile().setReadable(false);
-		}
-
-		@Test
-		void createNonExecutableDirectory(@TempDir Path tempDir) throws IOException {
-			Files.createDirectory(tempDir.resolve("test-sub-dir")).toFile().setExecutable(false);
-		}
-
-		@Test
-		void createNonEmptyNonWritableDirectory(@TempDir Path tempDir) throws IOException {
-			Path subDir = Files.createDirectory(tempDir.resolve("test-sub-dir"));
-			Files.createFile(tempDir.resolve("test-sub-dir/test-file.txt"));
-			subDir.toFile().setWritable(false);
-		}
-
-		@Test
-		void createNonEmptyNonReadableDirectory(@TempDir Path tempDir) throws IOException {
-			Path subDir = Files.createDirectory(tempDir.resolve("test-sub-dir"));
-			Files.createFile(tempDir.resolve("test-sub-dir/test-file.txt"));
-			subDir.toFile().setReadable(false);
-		}
-
-		@Test
-		void createNonEmptyNonExecutableDirectory(@TempDir Path tempDir) throws IOException {
-			Path subDir = Files.createDirectory(tempDir.resolve("test-sub-dir"));
-			Files.createFile(tempDir.resolve("test-sub-dir/test-file.txt"));
-			subDir.toFile().setExecutable(false);
-		}
-
-		@Test
-		void createNonEmptyDirectory(@TempDir Path tempDir) throws IOException {
-			Files.createDirectory(tempDir.resolve("test-sub-dir"));
-			Files.createFile(tempDir.resolve("test-sub-dir/test-file.txt"));
-		}
-
-		@Test
-		void createNonEmptyDirectoryWithNonWritableFile(@TempDir Path tempDir) throws IOException {
-			Files.createDirectory(tempDir.resolve("test-sub-dir"));
-			Files.createFile(tempDir.resolve("test-sub-dir/test-file.txt")).toFile().setWritable(false);
-		}
-
-		@Test
-		void createNonEmptyDirectoryWithNonReadableFile(@TempDir Path tempDir) throws IOException {
-			Files.createDirectory(tempDir.resolve("test-sub-dir"));
-			Files.createFile(tempDir.resolve("test-sub-dir/test-file.txt")).toFile().setReadable(false);
-		}
-	}
-
-	// https://github.com/junit-team/junit5/issues/2609
-	@SuppressWarnings("ResultOfMethodCallIgnored")
-	static class NonMintTempDirectoryPermissionsDoNotCauseFailureTestCase {
-
-		@Nested
-		class NonWritable {
-
-			@Test
-			void makeEmptyTempDirectoryNonWritable(@TempDir Path tempDir) {
-				tempDir.toFile().setWritable(false);
-			}
-
-			@Test
-			void makeTempDirectoryWithFileNonWritable(@TempDir Path tempDir) throws IOException {
-				Files.createFile(tempDir.resolve("test-file.txt"));
-				tempDir.toFile().setWritable(false);
-			}
-
-			@Test
-			void makeTempDirectoryWithEmptyFolderNonWritable(@TempDir Path tempDir) throws IOException {
-				Files.createDirectory(tempDir.resolve("test-sub-dir"));
-				tempDir.toFile().setWritable(false);
-			}
-
-			@Test
-			void makeTempDirectoryWithNonWritableFileNonWritable(@TempDir Path tempDir) throws IOException {
-				Files.createFile(tempDir.resolve("test-file.txt")).toFile().setWritable(false);
-				tempDir.toFile().setWritable(false);
-			}
-
-			@Test
-			void makeTempDirectoryWithNonReadableFileNonWritable(@TempDir Path tempDir) throws IOException {
-				Files.createFile(tempDir.resolve("test-file.txt")).toFile().setReadable(false);
-				tempDir.toFile().setWritable(false);
-			}
-
-			@Test
-			void makeTempDirectoryWithNonWritableFolderNonWritable(@TempDir Path tempDir) throws IOException {
-				Files.createDirectory(tempDir.resolve("test-sub-dir")).toFile().setWritable(false);
-				tempDir.toFile().setWritable(false);
-			}
-
-			@Test
-			void makeTempDirectoryWithNonReadableFolderNonWritable(@TempDir Path tempDir) throws IOException {
-				Files.createDirectory(tempDir.resolve("test-sub-dir")).toFile().setReadable(false);
-				tempDir.toFile().setWritable(false);
-			}
-
-			@Test
-			void makeTempDirectoryWithNonExecutableFolderNonWritable(@TempDir Path tempDir) throws IOException {
-				Files.createDirectory(tempDir.resolve("test-sub-dir")).toFile().setExecutable(false);
-				tempDir.toFile().setWritable(false);
-			}
-
-			@Test
-			void makeTempDirectoryWithNonEmptyNonReadableFolderNonWritable(@TempDir Path tempDir) throws IOException {
-				Path subDir = Files.createDirectory(tempDir.resolve("test-sub-dir"));
-				Files.createFile(tempDir.resolve("test-sub-dir/test-file.txt"));
-				subDir.toFile().setReadable(false);
-				tempDir.toFile().setWritable(false);
-			}
-
-			@Test
-			void makeTempDirectoryWithNonEmptyNonWritableFolderNonWritable(@TempDir Path tempDir) throws IOException {
-				Path subDir = Files.createDirectory(tempDir.resolve("test-sub-dir"));
-				Files.createFile(tempDir.resolve("test-sub-dir/test-file.txt"));
-				subDir.toFile().setWritable(false);
-				tempDir.toFile().setWritable(false);
-			}
-
-			@Test
-			void makeTempDirectoryWithNonEmptyNonExecutableFolderNonWritable(@TempDir Path tempDir) throws IOException {
-				Path subDir = Files.createDirectory(tempDir.resolve("test-sub-dir"));
-				Files.createFile(tempDir.resolve("test-sub-dir/test-file.txt"));
-				subDir.toFile().setExecutable(false);
-				tempDir.toFile().setWritable(false);
-			}
-
-			@Test
-			void makeTempDirectoryWithNonEmptyFolderNonWritable(@TempDir Path tempDir) throws IOException {
-				Files.createDirectory(tempDir.resolve("test-sub-dir"));
-				Files.createFile(tempDir.resolve("test-sub-dir/test-file.txt"));
-				tempDir.toFile().setWritable(false);
-			}
-
-			@Test
-			void makeTempDirectoryWithNonEmptyFolderContainingNonWritableFileNonWritable(@TempDir Path tempDir)
-					throws IOException {
-				Files.createDirectory(tempDir.resolve("test-sub-dir"));
-				Files.createFile(tempDir.resolve("test-sub-dir/test-file.txt")).toFile().setWritable(false);
-				tempDir.toFile().setWritable(false);
-			}
-
-			@Test
-			void makeTempDirectoryWithNonEmptyFolderContainingNonReadableFileNonWritable(@TempDir Path tempDir)
-					throws IOException {
-				Files.createDirectory(tempDir.resolve("test-sub-dir"));
-				Files.createFile(tempDir.resolve("test-sub-dir/test-file.txt")).toFile().setReadable(false);
-				tempDir.toFile().setWritable(false);
-			}
-		}
-
-		@Nested
-		class NonReadable {
-
-			@Test
-			void makeEmptyTempDirectoryNonReadable(@TempDir Path tempDir) {
-				tempDir.toFile().setReadable(false);
-			}
-
-			@Test
-			void makeTempDirectoryWithFileNonReadable(@TempDir Path tempDir) throws IOException {
-				Files.createFile(tempDir.resolve("test-file.txt"));
-				tempDir.toFile().setReadable(false);
-			}
-
-			@Test
-			void makeTempDirectoryWithEmptyFolderNonReadable(@TempDir Path tempDir) throws IOException {
-				Files.createDirectory(tempDir.resolve("test-sub-dir"));
-				tempDir.toFile().setReadable(false);
-			}
-
-			@Test
-			void makeTempDirectoryWithNonWritableFileNonReadable(@TempDir Path tempDir) throws IOException {
-				Files.createFile(tempDir.resolve("test-file.txt")).toFile().setWritable(false);
-				tempDir.toFile().setReadable(false);
-			}
-
-			@Test
-			void makeTempDirectoryWithNonReadableFileNonReadable(@TempDir Path tempDir) throws IOException {
-				Files.createFile(tempDir.resolve("test-file.txt")).toFile().setReadable(false);
-				tempDir.toFile().setReadable(false);
-			}
-
-			@Test
-			void makeTempDirectoryWithNonWritableFolderNonReadable(@TempDir Path tempDir) throws IOException {
-				Files.createDirectory(tempDir.resolve("test-sub-dir")).toFile().setWritable(false);
-				tempDir.toFile().setReadable(false);
-			}
-
-			@Test
-			void makeTempDirectoryWithNonReadableFolderNonReadable(@TempDir Path tempDir) throws IOException {
-				Files.createDirectory(tempDir.resolve("test-sub-dir")).toFile().setReadable(false);
-				tempDir.toFile().setReadable(false);
-			}
-
-			@Test
-			void makeTempDirectoryWithNonExecutableFolderNonReadable(@TempDir Path tempDir) throws IOException {
-				Files.createDirectory(tempDir.resolve("test-sub-dir")).toFile().setExecutable(false);
-				tempDir.toFile().setReadable(false);
-			}
-
-			@Test
-			void makeTempDirectoryWithNonEmptyNonWritableFolderNonReadable(@TempDir Path tempDir) throws IOException {
-				Path subDir = Files.createDirectory(tempDir.resolve("test-sub-dir"));
-				Files.createFile(tempDir.resolve("test-sub-dir/test-file.txt"));
-				subDir.toFile().setWritable(false);
-				tempDir.toFile().setReadable(false);
-			}
-
-			@Test
-			void makeTempDirectoryWithNonEmptyNonReadableFolderNonReadable(@TempDir Path tempDir) throws IOException {
-				Path subDir = Files.createDirectory(tempDir.resolve("test-sub-dir"));
-				Files.createFile(tempDir.resolve("test-sub-dir/test-file.txt"));
-				subDir.toFile().setReadable(false);
-				tempDir.toFile().setReadable(false);
-			}
-
-			@Test
-			void makeTempDirectoryWithNonEmptyNonExecutableFolderNonReadable(@TempDir Path tempDir) throws IOException {
-				Path subDir = Files.createDirectory(tempDir.resolve("test-sub-dir"));
-				Files.createFile(tempDir.resolve("test-sub-dir/test-file.txt"));
-				subDir.toFile().setExecutable(false);
-				tempDir.toFile().setReadable(false);
-			}
-
-			@Test
-			void makeTempDirectoryWithNonEmptyFolderNonReadable(@TempDir Path tempDir) throws IOException {
-				Files.createDirectory(tempDir.resolve("test-sub-dir"));
-				Files.createFile(tempDir.resolve("test-sub-dir/test-file.txt"));
-				tempDir.toFile().setReadable(false);
-			}
-
-			@Test
-			void makeTempDirectoryWithNonEmptyFolderContainingNonWritableFileNonReadable(@TempDir Path tempDir)
-					throws IOException {
-				Files.createDirectory(tempDir.resolve("test-sub-dir"));
-				Files.createFile(tempDir.resolve("test-sub-dir/test-file.txt")).toFile().setWritable(false);
-				tempDir.toFile().setReadable(false);
-			}
-
-			@Test
-			void makeTempDirectoryWithNonEmptyFolderContainingNonReadableFileNonReadable(@TempDir Path tempDir)
-					throws IOException {
-				Files.createDirectory(tempDir.resolve("test-sub-dir"));
-				Files.createFile(tempDir.resolve("test-sub-dir/test-file.txt")).toFile().setReadable(false);
-				tempDir.toFile().setReadable(false);
-			}
-		}
-
-		@Nested
-		class NonExecutable {
-
-			@Test
-			void makeEmptyTempDirectoryNonExecutable(@TempDir Path tempDir) {
-				tempDir.toFile().setExecutable(false);
-			}
-
-			@Test
-			void makeTempDirectoryWithFileNonExecutable(@TempDir Path tempDir) throws IOException {
-				Files.createFile(tempDir.resolve("test-file.txt"));
-				tempDir.toFile().setExecutable(false);
-			}
-
-			@Test
-			void makeTempDirectoryWithEmptyFolderNonExecutable(@TempDir Path tempDir) throws IOException {
-				Files.createDirectory(tempDir.resolve("test-sub-dir"));
-				tempDir.toFile().setExecutable(false);
-			}
-
-			@Test
-			void makeTempDirectoryWithNonWritableFileNonExecutable(@TempDir Path tempDir) throws IOException {
-				Files.createFile(tempDir.resolve("test-file.txt")).toFile().setWritable(false);
-				tempDir.toFile().setExecutable(false);
-			}
-
-			@Test
-			void makeTempDirectoryWithNonReadableFileNonExecutable(@TempDir Path tempDir) throws IOException {
-				Files.createFile(tempDir.resolve("test-file.txt")).toFile().setReadable(false);
-				tempDir.toFile().setExecutable(false);
-			}
-
-			@Test
-			void makeTempDirectoryWithNonWritableFolderNonExecutable(@TempDir Path tempDir) throws IOException {
-				Files.createDirectory(tempDir.resolve("test-sub-dir")).toFile().setWritable(false);
-				tempDir.toFile().setExecutable(false);
-			}
-
-			@Test
-			void makeTempDirectoryWithNonReadableFolderNonExecutable(@TempDir Path tempDir) throws IOException {
-				Files.createDirectory(tempDir.resolve("test-sub-dir")).toFile().setReadable(false);
-				tempDir.toFile().setExecutable(false);
-			}
-
-			@Test
-			void makeTempDirectoryWithNonExecutableFolderNonExecutable(@TempDir Path tempDir) throws IOException {
-				Files.createDirectory(tempDir.resolve("test-sub-dir")).toFile().setExecutable(false);
-				tempDir.toFile().setExecutable(false);
-			}
-
-			@Test
-			void makeTempDirectoryWithNonEmptyNonWritableFolderNonExecutable(@TempDir Path tempDir) throws IOException {
-				Path subDir = Files.createDirectory(tempDir.resolve("test-sub-dir"));
-				Files.createFile(tempDir.resolve("test-sub-dir/test-file.txt"));
-				subDir.toFile().setWritable(false);
-				tempDir.toFile().setExecutable(false);
-			}
-
-			@Test
-			void makeTempDirectoryWithNonEmptyNonReadableFolderNonExecutable(@TempDir Path tempDir) throws IOException {
-				Path subDir = Files.createDirectory(tempDir.resolve("test-sub-dir"));
-				Files.createFile(tempDir.resolve("test-sub-dir/test-file.txt"));
-				subDir.toFile().setReadable(false);
-				tempDir.toFile().setExecutable(false);
-			}
-
-			@Test
-			void makeTempDirectoryWithNonEmptyNonExecutableFolderNonExecutable(@TempDir Path tempDir)
-					throws IOException {
-				Path subDir = Files.createDirectory(tempDir.resolve("test-sub-dir"));
-				Files.createFile(tempDir.resolve("test-sub-dir/test-file.txt"));
-				subDir.toFile().setExecutable(false);
-				tempDir.toFile().setExecutable(false);
-			}
-
-			@Test
-			void makeTempDirectoryWithNonEmptyFolderNonExecutable(@TempDir Path tempDir) throws IOException {
-				Files.createDirectory(tempDir.resolve("test-sub-dir"));
-				Files.createFile(tempDir.resolve("test-sub-dir/test-file.txt"));
-				tempDir.toFile().setExecutable(false);
-			}
-
-			@Test
-			void makeTempDirectoryWithNonEmptyFolderContainingNonWritableFileNonExecutable(@TempDir Path tempDir)
-					throws IOException {
-				Files.createDirectory(tempDir.resolve("test-sub-dir"));
-				Files.createFile(tempDir.resolve("test-sub-dir/test-file.txt")).toFile().setWritable(false);
-				tempDir.toFile().setExecutable(false);
-			}
-
-			@Test
-			void makeTempDirectoryWithNonEmptyFolderContainingNonReadableFileNonExecutable(@TempDir Path tempDir)
-					throws IOException {
-				Files.createDirectory(tempDir.resolve("test-sub-dir"));
-				Files.createFile(tempDir.resolve("test-sub-dir/test-file.txt")).toFile().setReadable(false);
-				tempDir.toFile().setExecutable(false);
-			}
-		}
-	}
-
-	// https://github.com/junit-team/junit5/issues/2079
-	@SuppressWarnings("JUnitMalformedDeclaration")
-	static class TempDirUsageInsideNestedClassesTestCase {
-
-		@TempDir
-		File tempDir;
-
-		@Test
-		void topLevel() {
-			assertNotNull(tempDir);
-			assertTrue(tempDir.exists());
-		}
-
-		@Nested
-		class NestedTestClass {
-
-			@Test
-			void nested() {
-				assertNotNull(tempDir);
-				assertTrue(tempDir.exists());
-			}
-
-			@Nested
-			class EvenDeeperNestedTestClass {
-
-				@Test
-				void deeplyNested() {
-					assertNotNull(tempDir);
-					assertTrue(tempDir.exists());
-				}
-			}
-		}
-	}
-
-	@SuppressWarnings("JUnitMalformedDeclaration")
-	static class StaticTempDirUsageInsideNestedClassTestCase {
-
-		@TempDir
-		static File tempDir;
-
-		static File initialTempDir;
-
-		@Test
-		void topLevel() {
-			assertNotNull(tempDir);
-			assertTrue(tempDir.exists());
-			initialTempDir = tempDir;
-		}
-
-		@Nested
-		class NestedTestClass {
-
-			@Test
-			void nested() {
-				assertNotNull(tempDir);
-				assertTrue(tempDir.exists());
-				assertSame(initialTempDir, tempDir);
-			}
-		}
-	}
-
-}
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TempDirectoryPreconditionTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TempDirectoryPreconditionTests.java
index fc3f84f3a146..1312ce42b1b0 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TempDirectoryPreconditionTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TempDirectoryPreconditionTests.java
@@ -20,7 +20,6 @@
 
 import java.io.File;
 import java.nio.file.Path;
-import java.nio.file.Paths;
 
 import org.junit.jupiter.api.DisplayName;
 import org.junit.jupiter.api.Test;
@@ -102,7 +101,7 @@ void invalidTempDirType(@TempDir String text) {
 	@SuppressWarnings("JUnitMalformedDeclaration")
 	static class FinalStaticFieldTestCase {
 
-		static final @TempDir Path path = Paths.get(".");
+		static final @TempDir Path path = Path.of(".");
 
 		@Test
 		void test() {
@@ -112,7 +111,7 @@ void test() {
 	@SuppressWarnings("JUnitMalformedDeclaration")
 	static class FinalInstanceFieldTestCase {
 
-		final @TempDir Path path = Paths.get(".");
+		final @TempDir Path path = Path.of(".");
 
 		@Test
 		void test() {
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TempDirectoryPerDeclarationTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TempDirectoryTests.java
similarity index 96%
rename from jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TempDirectoryPerDeclarationTests.java
rename to jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TempDirectoryTests.java
index 5eddab66bcad..0096a9fcd998 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TempDirectoryPerDeclarationTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TempDirectoryTests.java
@@ -14,6 +14,7 @@
 import static java.lang.annotation.ElementType.FIELD;
 import static java.lang.annotation.ElementType.PARAMETER;
 import static java.lang.annotation.RetentionPolicy.RUNTIME;
+import static java.util.Objects.requireNonNull;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.jupiter.api.Assertions.assertAll;
 import static org.junit.jupiter.api.Assertions.assertNotEquals;
@@ -51,6 +52,8 @@
 import com.google.common.jimfs.Jimfs;
 
 import org.assertj.core.api.Condition;
+import org.jspecify.annotations.NullUnmarked;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.AfterAll;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeAll;
@@ -82,6 +85,8 @@
 import org.junit.jupiter.params.provider.EnumSource;
 import org.junit.jupiter.params.provider.ValueSource;
 import org.junit.platform.commons.PreconditionViolationException;
+import org.junit.platform.engine.DiscoveryIssue;
+import org.junit.platform.engine.DiscoveryIssue.Severity;
 import org.junit.platform.engine.reporting.ReportEntry;
 import org.junit.platform.testkit.engine.EngineExecutionResults;
 
@@ -92,7 +97,7 @@
  * @since 5.8
  */
 @DisplayName("TempDirectory extension (per declaration)")
-class TempDirectoryPerDeclarationTests extends AbstractJupiterTestEngineTests {
+class TempDirectoryTests extends AbstractJupiterTestEngineTests {
 
 	private EngineExecutionResults executeTestsForClassWithDefaultFactory(Class<?> testClass,
 			Class<? extends TempDirFactory> factoryClass) {
@@ -108,6 +113,7 @@ void resetStaticVariables() {
 		AllPossibleDeclarationLocationsTestCase.tempDirs.clear();
 	}
 
+	@SuppressWarnings("NullAway")
 	@ParameterizedTest(name = "{0}")
 	@EnumSource(TestInstance.Lifecycle.class)
 	@DisplayName("resolves separate temp dirs for each annotation declaration")
@@ -256,6 +262,17 @@ void onlyAttemptsToDeleteUndeletablePathsOnce(Class<?> testClass) {
 		);
 	}
 
+	@Test
+	void usingTheRemovedScopeConfigurationParameterProducesWarning() {
+		var results = discoverTests(request() //
+				.selectors(selectClass(AllPossibleDeclarationLocationsTestCase.class)) //
+				.configurationParameter("junit.jupiter.tempdir.scope", "per_context"));
+
+		assertThat(results.getDiscoveryIssues()) //
+				.contains(DiscoveryIssue.create(Severity.WARNING,
+					"The 'junit.jupiter.tempdir.scope' configuration parameter is no longer supported: per_context. Please remove it from your configuration."));
+	}
+
 	@Nested
 	@DisplayName("reports failure")
 	@TestMethodOrder(OrderAnnotation.class)
@@ -339,6 +356,7 @@ void doesNotSupportCustomDefaultTempDirFactoryNotReturningDirectory() {
 
 		private static class FactoryNotReturningDirectory implements TempDirFactory {
 
+			@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 			@Override
 			public Path createTempDirectory(AnnotatedElementContext elementContext, ExtensionContext extensionContext) {
 				return null;
@@ -610,7 +628,7 @@ private static void assertFileAndPathAreNotEqual(File tempDir, Path ref) {
 
 	}
 
-	// https://github.com/junit-team/junit5/issues/1748
+	// https://github.com/junit-team/junit-framework/issues/1748
 	@SuppressWarnings("JUnitMalformedDeclaration")
 	static class TempDirectoryDoesNotPreventConstructorParameterResolutionTestCase {
 
@@ -628,7 +646,7 @@ void test() {
 
 	}
 
-	// https://github.com/junit-team/junit5/issues/1801
+	// https://github.com/junit-team/junit-framework/issues/1801
 	@SuppressWarnings("JUnitMalformedDeclaration")
 	static class UserTempDirectoryDeletionDoesNotCauseFailureTestCase {
 
@@ -640,7 +658,7 @@ void deleteTempDir(@TempDir Path tempDir) throws IOException {
 
 	}
 
-	// https://github.com/junit-team/junit5/issues/2046
+	// https://github.com/junit-team/junit-framework/issues/2046
 	@SuppressWarnings("JUnitMalformedDeclaration")
 	static class NonWritableFileDoesNotCauseFailureTestCase {
 
@@ -655,7 +673,7 @@ void createReadonlyFile(@TempDir Path tempDir) throws IOException {
 
 	}
 
-	// https://github.com/junit-team/junit5/issues/2171
+	// https://github.com/junit-team/junit-framework/issues/2171
 	@SuppressWarnings("JUnitMalformedDeclaration")
 	static class ReadOnlyFileInReadOnlyDirDoesNotCauseFailureTestCase {
 
@@ -669,7 +687,7 @@ void createReadOnlyFileInReadOnlyDir(@TempDir File tempDir) throws IOException {
 
 	}
 
-	// https://github.com/junit-team/junit5/issues/2171
+	// https://github.com/junit-team/junit-framework/issues/2171
 	@SuppressWarnings("JUnitMalformedDeclaration")
 	static class ReadOnlyFileInDirInReadOnlyDirDoesNotCauseFailureTestCase {
 
@@ -685,7 +703,7 @@ void createReadOnlyFileInReadOnlyDir(@TempDir File tempDir) throws IOException {
 
 	}
 
-	// https://github.com/junit-team/junit5/issues/2609
+	// https://github.com/junit-team/junit-framework/issues/2609
 	@SuppressWarnings({ "ResultOfMethodCallIgnored", "JUnitMalformedDeclaration" })
 	static class NonMintPermissionContentInTempDirectoryDoesNotCauseFailureTestCase {
 
@@ -764,7 +782,7 @@ void createNonEmptyDirectoryWithNonReadableFile(@TempDir Path tempDir) throws IO
 		}
 	}
 
-	// https://github.com/junit-team/junit5/issues/2609
+	// https://github.com/junit-team/junit-framework/issues/2609
 	@SuppressWarnings("ResultOfMethodCallIgnored")
 	static class NonMintTempDirectoryPermissionsDoNotCauseFailureTestCase {
 
@@ -1064,7 +1082,7 @@ void makeTempDirectoryWithNonEmptyFolderContainingNonReadableFileNonExecutable(@
 		}
 	}
 
-	// https://github.com/junit-team/junit5/issues/2079
+	// https://github.com/junit-team/junit-framework/issues/2079
 	@SuppressWarnings("JUnitMalformedDeclaration")
 	static class TempDirUsageInsideNestedClassesTestCase {
 
@@ -1099,6 +1117,7 @@ void deeplyNested() {
 	}
 
 	@SuppressWarnings("JUnitMalformedDeclaration")
+	@NullUnmarked
 	static class StaticTempDirUsageInsideNestedClassTestCase {
 
 		@TempDir
@@ -1283,7 +1302,7 @@ public Path createTempDirectory(AnnotatedElementContext elementContext, Extensio
 
 	}
 
-	// https://github.com/junit-team/junit5/issues/2088
+	// https://github.com/junit-team/junit-framework/issues/2088
 	@SuppressWarnings("JUnitMalformedDeclaration")
 	static class FactoryWithCustomParentDirectoryTestCase {
 
@@ -1295,6 +1314,7 @@ void test(@TempDir(factory = Factory.class) Path tempDir) {
 
 		private static class Factory implements TempDirFactory {
 
+			@Nullable
 			private static Path parent;
 
 			private Factory() throws IOException {
@@ -1304,7 +1324,7 @@ private Factory() throws IOException {
 			@Override
 			public Path createTempDirectory(AnnotatedElementContext elementContext, ExtensionContext extensionContext)
 					throws Exception {
-				return Files.createTempDirectory(parent, "prefix");
+				return Files.createTempDirectory(requireNonNull(parent), "prefix");
 			}
 		}
 
@@ -1321,6 +1341,7 @@ void test(@TempDir(factory = Factory.class) Path tempDir) {
 
 		private static class Factory implements TempDirFactory {
 
+			@Nullable
 			private static FileSystem fileSystem;
 
 			@Override
@@ -1332,7 +1353,7 @@ public Path createTempDirectory(AnnotatedElementContext elementContext, Extensio
 
 			@Override
 			public void close() throws IOException {
-				fileSystem.close();
+				requireNonNull(fileSystem).close();
 				fileSystem = null;
 			}
 		}
@@ -1350,6 +1371,7 @@ void test(@TempDir(factory = Factory.class) Path tempDir) {
 
 		private static class Factory implements TempDirFactory {
 
+			@Nullable
 			private static FileSystem fileSystem;
 
 			@Override
@@ -1361,7 +1383,7 @@ public Path createTempDirectory(AnnotatedElementContext elementContext, Extensio
 
 			@Override
 			public void close() throws IOException {
-				fileSystem.close();
+				requireNonNull(fileSystem).close();
 				fileSystem = null;
 			}
 		}
@@ -1389,7 +1411,7 @@ public Path createTempDirectory(AnnotatedElementContext elementContext, Extensio
 			}
 
 			private static String getName(AnnotatedElement element) {
-				return element instanceof Field ? ((Field) element).getName() : ((Parameter) element).getName();
+				return element instanceof Field field ? field.getName() : ((Parameter) element).getName();
 			}
 
 		}
@@ -1397,6 +1419,7 @@ private static String getName(AnnotatedElement element) {
 	}
 
 	@SuppressWarnings("JUnitMalformedDeclaration")
+	@NullUnmarked
 	static class FactoryWithCustomMetaAnnotationTestCase {
 
 		@TempDirForField
@@ -1451,6 +1474,7 @@ void test(@SuppressWarnings("unused") @TempDir(factory = Factory.class) Path tem
 			// never called
 		}
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		private static class Factory implements TempDirFactory {
 
 			@Override
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TestInstanceFactoryTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TestInstanceFactoryTests.java
index 8433ad7f5824..ac92484ef037 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TestInstanceFactoryTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TestInstanceFactoryTests.java
@@ -775,6 +775,7 @@ private static class LegacyInstanceFactory extends AbstractTestInstanceFactory {
 	 */
 	private static class NullTestInstanceFactory implements TestInstanceFactory {
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Override
 		public Object createTestInstance(TestInstanceFactoryContext factoryContext, ExtensionContext extensionContext) {
 			return null;
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TestInstancePostProcessorTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TestInstancePostProcessorTests.java
index 698c59068383..2036342affbe 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TestInstancePostProcessorTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TestInstancePostProcessorTests.java
@@ -189,8 +189,8 @@ static abstract class AbstractInstancePostProcessor implements TestInstancePostP
 
 		@Override
 		public void postProcessTestInstance(Object testInstance, ExtensionContext context) {
-			if (testInstance instanceof Named) {
-				((Named) testInstance).setName(name, context.getRequiredTestClass().getSimpleName());
+			if (testInstance instanceof Named named) {
+				named.setName(name, context.getRequiredTestClass().getSimpleName());
 			}
 			String instanceType = testInstance.getClass().getSimpleName();
 			callSequence.add(name + ":" + instanceType);
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TestInstancePreDestroyCallbackTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TestInstancePreDestroyCallbackTests.java
index f2d05a8dc002..bb1c51210ae1 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TestInstancePreDestroyCallbackTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TestInstancePreDestroyCallbackTests.java
@@ -187,8 +187,8 @@ static abstract class AbstractTestInstancePreDestroyCallback implements TestInst
 		public void preDestroyTestInstance(ExtensionContext context) {
 			assertThat(context.getTestInstance()).isPresent();
 			Object testInstance = context.getTestInstance().get();
-			if (testInstance instanceof Destroyable) {
-				((Destroyable) testInstance).setDestroyed();
+			if (testInstance instanceof Destroyable destroyable) {
+				destroyable.setDestroyed();
 			}
 			callSequence.add(name + "PreDestroyCallbackTestInstance:" + testInstance.getClass().getSimpleName());
 		}
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TestReporterParameterResolverTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TestReporterParameterResolverTests.java
index f785fb791744..c6b811a1d684 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TestReporterParameterResolverTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TestReporterParameterResolverTests.java
@@ -31,6 +31,7 @@ class TestReporterParameterResolverTests {
 
 	TestReporterParameterResolver resolver = new TestReporterParameterResolver();
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void supports() {
 		Parameter parameter1 = findParameterOfMethod("methodWithTestReporterParameter", TestReporter.class);
@@ -49,7 +50,7 @@ void resolve() {
 	}
 
 	private Parameter findParameterOfMethod(String methodName, Class<?>... parameterTypes) {
-		Method method = ReflectionSupport.findMethod(Sample.class, methodName, parameterTypes).get();
+		Method method = ReflectionSupport.findMethod(Sample.class, methodName, parameterTypes).orElseThrow();
 		return method.getParameters()[0];
 	}
 
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TestWatcherTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TestWatcherTests.java
index 05d318c12418..8bd2c557e8d6 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TestWatcherTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TestWatcherTests.java
@@ -30,6 +30,8 @@
 import java.util.logging.LogRecord;
 import java.util.stream.Stream;
 
+import org.jspecify.annotations.Nullable;
+import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.DynamicTest;
@@ -304,7 +306,7 @@ Stream<DynamicTest> abortedTest() {
 		@TestFactory
 		@Disabled
 		Stream<DynamicTest> skippedTest() {
-			return Stream.of("A", "B").map(text -> dynamicTest(text, () -> fail()));
+			return Stream.of("A", "B").map(text -> dynamicTest(text, Assertions::fail));
 		}
 
 	}
@@ -385,12 +387,12 @@ public void testSuccessful(ExtensionContext context) {
 		}
 
 		@Override
-		public void testAborted(ExtensionContext context, Throwable cause) {
+		public void testAborted(ExtensionContext context, @Nullable Throwable cause) {
 			trackResult("testAborted", context);
 		}
 
 		@Override
-		public void testFailed(ExtensionContext context, Throwable cause) {
+		public void testFailed(ExtensionContext context, @Nullable Throwable cause) {
 			trackResult("testFailed", context);
 		}
 
@@ -419,12 +421,12 @@ public void testDisabled(ExtensionContext context, Optional<String> reason) {
 		}
 
 		@Override
-		public void testAborted(ExtensionContext context, Throwable cause) {
+		public void testAborted(ExtensionContext context, @Nullable Throwable cause) {
 			throw new JUnitException("Exception in testAborted()");
 		}
 
 		@Override
-		public void testFailed(ExtensionContext context, Throwable cause) {
+		public void testFailed(ExtensionContext context, @Nullable Throwable cause) {
 			throw new JUnitException("Exception in testFailed()");
 		}
 
@@ -432,7 +434,7 @@ public void testFailed(ExtensionContext context, Throwable cause) {
 
 	/**
 	 * {@link TestWatcher} that retrieves data from the {@link ExtensionContext.Store}.
-	 * @see <a href="https://github.com/junit-team/junit5/issues/3944">#3944</a>
+	 * @see <a href="https://github.com/junit-team/junit-framework/issues/3944">#3944</a>
 	 */
 	static class DataRetrievingTestWatcher implements BeforeTestExecutionCallback, TestWatcher {
 
@@ -440,7 +442,7 @@ static class DataRetrievingTestWatcher implements BeforeTestExecutionCallback, T
 
 		private static final String KEY = "key";
 
-		private static final Map<String, String> results = new HashMap<>();
+		private static final Map<String, @Nullable String> results = new HashMap<>();
 
 		@Override
 		public void beforeTestExecution(ExtensionContext context) throws Exception {
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TimeoutExceptionFactoryTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TimeoutExceptionFactoryTests.java
index 3c5c5a29602e..62f5a6f8ceec 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TimeoutExceptionFactoryTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TimeoutExceptionFactoryTests.java
@@ -51,13 +51,14 @@ void createExceptionWithMethodSignatureTimeoutAndThrowable() {
 				.hasSuppressedException(suppressedException);
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway", "ThrowableNotThrown" })
 	@Nested
 	@DisplayName("throws exception when")
 	class ThrowException {
 
 		@Test
 		@DisplayName("method signature is null")
-		void methodSignatureIsnull() {
+		void methodSignatureIsNull() {
 			assertThatThrownBy(() -> create(null, tenMillisDuration, suppressedException)) //
 					.hasMessage("method signature must not be null");
 		}
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TimeoutExtensionTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TimeoutExtensionTests.java
index 8cfd1f1c24d3..b88fcfac4343 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TimeoutExtensionTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TimeoutExtensionTests.java
@@ -37,6 +37,7 @@
 import java.util.concurrent.TimeoutException;
 import java.util.stream.Stream;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.AfterAll;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeAll;
@@ -340,7 +341,8 @@ void reportsIllegalTimeoutDurations() {
 	private static Execution findExecution(Events events, String displayName) {
 		return events.executions()//
 				.filter(execution -> execution.getTestDescriptor().getDisplayName().contains(displayName))//
-				.findFirst().get();
+				.findFirst() //
+				.orElseThrow();
 	}
 
 	@Nested
@@ -618,6 +620,7 @@ void methodThatDoesNotThrowInterruptedException() {
 	@SuppressWarnings("JUnitMalformedDeclaration")
 	static class PlainTestCase {
 
+		@Nullable
 		public static String slowMethod;
 
 		@BeforeAll
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TimeoutInvocationFactoryTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TimeoutInvocationFactoryTests.java
index b630fd112054..a1544c3843dc 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TimeoutInvocationFactoryTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TimeoutInvocationFactoryTests.java
@@ -35,7 +35,9 @@
 // Mockito cannot mock this class: class org.junit.jupiter.engine.execution.NamespaceAwareStore.
 // You are seeing this disclaimer because Mockito is configured to create inlined mocks.
 // Byte Buddy could not instrument all classes within the mock's type hierarchy.
-@DisabledIf(value = "runningInEclipse", disabledReason = "Mockito cannot create a spy for NamespaceAwareStore using the inline MockMaker in Eclipse IDE")
+@DisabledIf(//
+		value = "org.junit.platform.commons.test.IdeUtils#runningInEclipse()", //
+		disabledReason = "Mockito cannot create a spy for NamespaceAwareStore using the inline MockMaker in Eclipse IDE")
 @DisplayName("TimeoutInvocationFactory")
 @ExtendWith(MockitoExtension.class)
 class TimeoutInvocationFactoryTests {
@@ -61,6 +63,7 @@ void setUp() {
 		timeoutInvocationFactory = new TimeoutInvocationFactory(store);
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	@DisplayName("throws exception when null store is provided on create")
 	void shouldThrowExceptionWhenInstantiatingWithNullStore() {
@@ -68,6 +71,7 @@ void shouldThrowExceptionWhenInstantiatingWithNullStore() {
 				.hasMessage("store must not be null");
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	@DisplayName("throws exception when null timeout thread mode is provided on create")
 	void shouldThrowExceptionWhenNullTimeoutThreadModeIsProvidedWhenCreate() {
@@ -75,6 +79,7 @@ void shouldThrowExceptionWhenNullTimeoutThreadModeIsProvidedWhenCreate() {
 				.hasMessage("thread mode must not be null");
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	@DisplayName("throws exception when null timeout invocation parameters is provided on create")
 	void shouldThrowExceptionWhenNullTimeoutInvocationParametersIsProvidedWhenCreate() {
@@ -97,13 +102,4 @@ void shouldCreateTimeoutInvocationForSeparateThreadTimeoutThreadMode() {
 		assertThat(invocation).isInstanceOf(SeparateThreadTimeoutInvocation.class);
 	}
 
-	/**
-	 * Determine if the current code is running in the Eclipse IDE.
-	 * <p>Copied from {@code org.springframework.core.testfixture.ide.IdeUtils}.
-	 */
-	static boolean runningInEclipse() {
-		return StackWalker.getInstance().walk(
-			stream -> stream.anyMatch(stackFrame -> stackFrame.getClassName().startsWith("org.eclipse.jdt")));
-	}
-
 }
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/sub/SystemPropertyCondition.java b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/sub/SystemPropertyCondition.java
index bb50d774a31c..fca7809b51ab 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/sub/SystemPropertyCondition.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/sub/SystemPropertyCondition.java
@@ -56,7 +56,7 @@ public ConditionEvaluationResult evaluateExecutionCondition(ExtensionContext con
 
 			if (!Objects.equals(expected, actual)) {
 				return ConditionEvaluationResult.disabled(
-					String.format("System property [%s] has a value of [%s] instead of [%s]", key, actual, expected));
+					"System property [%s] has a value of [%s] instead of [%s]".formatted(key, actual, expected));
 			}
 		}
 
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/conditions/IgnoreAnnotationIntegrationTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/conditions/IgnoreAnnotationIntegrationTests.java
index 532703006296..20d523c6dc05 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/conditions/IgnoreAnnotationIntegrationTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/conditions/IgnoreAnnotationIntegrationTests.java
@@ -36,6 +36,7 @@
  * @since 5.4
  * @see IgnoreConditionTests
  */
+@SuppressWarnings("removal")
 class IgnoreAnnotationIntegrationTests {
 
 	@Nested
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/conditions/IgnoreConditionTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/conditions/IgnoreConditionTests.java
index d1c3556cec40..620569b75e3e 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/conditions/IgnoreConditionTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/conditions/IgnoreConditionTests.java
@@ -35,6 +35,7 @@
  * @since 5.4
  * @see IgnoreAnnotationIntegrationTests
  */
+@SuppressWarnings("removal")
 class IgnoreConditionTests {
 
 	@Test
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/AbstractTestRuleAdapterTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/AbstractTestRuleAdapterTests.java
index 9890182b4a40..31adeb6039a0 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/AbstractTestRuleAdapterTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/AbstractTestRuleAdapterTests.java
@@ -26,6 +26,7 @@
 /**
  * @since 5.0
  */
+@SuppressWarnings("removal")
 public class AbstractTestRuleAdapterTests {
 
 	@Test
@@ -65,13 +66,7 @@ private static class TestableTestRuleAdapter extends AbstractTestRuleAdapter {
 		}
 	}
 
-	private static class SimpleRuleAnnotatedMember implements TestRuleAnnotatedMember {
-
-		private final TestRule testRule;
-
-		SimpleRuleAnnotatedMember(TestRule testRule) {
-			this.testRule = testRule;
-		}
+	private record SimpleRuleAnnotatedMember(TestRule testRule) implements TestRuleAnnotatedMember {
 
 		@Override
 		public TestRule getTestRule() {
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/EnableRuleMigrationSupportWithBothRuleTypesTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/EnableRuleMigrationSupportWithBothRuleTypesTests.java
index ba149cdf0e1b..e998ddb498f3 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/EnableRuleMigrationSupportWithBothRuleTypesTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/EnableRuleMigrationSupportWithBothRuleTypesTests.java
@@ -16,12 +16,14 @@
 import static org.junit.jupiter.api.Assertions.assertTrue;
 import static org.junit.jupiter.migrationsupport.rules.FailAfterAllHelper.fail;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.Rule;
 import org.junit.jupiter.api.AfterAll;
 import org.junit.jupiter.api.Test;
 import org.junit.rules.ExternalResource;
 import org.junit.rules.Verifier;
 
+@SuppressWarnings("removal")
 @EnableRuleMigrationSupport
 public class EnableRuleMigrationSupportWithBothRuleTypesTests {
 
@@ -52,6 +54,7 @@ public ExternalResource getResource2() {
 				numberOfRule2InstancesCreated++;
 			}
 
+			@Nullable
 			private Object instance;
 
 			@Override
@@ -63,7 +66,7 @@ protected void before() {
 			@Override
 			protected void after() {
 				assertNotNull(instance);
-				assertSame(instance, this);
+				assertSame(this, instance);
 				afterOfRule2WasExecuted = true;
 			}
 		};
@@ -78,10 +81,12 @@ void beforeMethodOfBothRule2WasExecuted() {
 	static void afterMethodsOfBothRulesWereExecuted() {
 		assertEquals(1, numberOfRule1InstancesCreated);
 		assertEquals(1, numberOfRule2InstancesCreated);
-		if (!afterOfRule1WasExecuted)
+		if (!afterOfRule1WasExecuted) {
 			fail();
-		if (!afterOfRule2WasExecuted)
+		}
+		if (!afterOfRule2WasExecuted) {
 			fail();
+		}
 	}
 
 }
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/ExpectedExceptionSupportTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/ExpectedExceptionSupportTests.java
index 2ee4f9155881..9d35bb93ccaa 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/ExpectedExceptionSupportTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/ExpectedExceptionSupportTests.java
@@ -34,6 +34,7 @@
  *
  * @since 5.0
  */
+@SuppressWarnings("removal")
 class ExpectedExceptionSupportTests {
 
 	@Test
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/ExternalResourceSupportForDifferentDeclaredReturnTypesRulesTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/ExternalResourceSupportForDifferentDeclaredReturnTypesRulesTests.java
index c71f63ac9178..c92bcacfff7e 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/ExternalResourceSupportForDifferentDeclaredReturnTypesRulesTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/ExternalResourceSupportForDifferentDeclaredReturnTypesRulesTests.java
@@ -20,6 +20,7 @@
 import org.junit.rules.ExternalResource;
 import org.junit.rules.TestRule;
 
+@SuppressWarnings("removal")
 @ExtendWith(ExternalResourceSupport.class)
 class ExternalResourceSupportForDifferentDeclaredReturnTypesRulesTests {
 
@@ -57,10 +58,12 @@ void beforeMethodsOfBothRulesWereExecuted() {
 
 	@AfterAll
 	static void afterMethodsOfBothRulesWereExecuted() {
-		if (!afterOfRule1WasExecuted)
+		if (!afterOfRule1WasExecuted) {
 			fail();
-		if (!afterOfRule2WasExecuted)
+		}
+		if (!afterOfRule2WasExecuted) {
 			fail();
+		}
 	}
 
 	private static class MyExternalResource1 extends ExternalResource {
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/ExternalResourceSupportForMixedMethodAndFieldRulesTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/ExternalResourceSupportForMixedMethodAndFieldRulesTests.java
index c4fc1b66a0d3..81a66eaea2b6 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/ExternalResourceSupportForMixedMethodAndFieldRulesTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/ExternalResourceSupportForMixedMethodAndFieldRulesTests.java
@@ -25,6 +25,7 @@
 import org.junit.jupiter.api.extension.ExtendWith;
 import org.junit.rules.ExternalResource;
 
+@SuppressWarnings("removal")
 @ExtendWith(ExternalResourceSupport.class)
 public class ExternalResourceSupportForMixedMethodAndFieldRulesTests {
 
@@ -70,8 +71,9 @@ void constructorsAndBeforeEachMethodsOfAllRulesWereExecuted() {
 	@AfterAll
 	static void afterMethodsOfAllRulesWereExecuted() {
 		// beforeEach methods of rules from methods are run before those from fields but in reverse order
-		if (!asList(initEvents.get(2), initEvents.get(3), initEvents.get(0), initEvents.get(1)).equals(afterEvents))
+		if (!asList(initEvents.get(2), initEvents.get(3), initEvents.get(0), initEvents.get(1)).equals(afterEvents)) {
 			fail();
+		}
 	}
 
 	static class MyExternalResource extends ExternalResource {
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/ExternalResourceSupportForMultipleFieldRulesTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/ExternalResourceSupportForMultipleFieldRulesTests.java
index f2ba8354f6cc..4b43744c926b 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/ExternalResourceSupportForMultipleFieldRulesTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/ExternalResourceSupportForMultipleFieldRulesTests.java
@@ -19,6 +19,7 @@
 import org.junit.jupiter.api.extension.ExtendWith;
 import org.junit.rules.ExternalResource;
 
+@SuppressWarnings("removal")
 @ExtendWith(ExternalResourceSupport.class)
 public class ExternalResourceSupportForMultipleFieldRulesTests {
 
@@ -62,10 +63,12 @@ void beforeMethodsOfBothRulesWereExecuted() {
 
 	@AfterAll
 	static void afterMethodsOfBothRulesWereExecuted() {
-		if (!afterOfRule1WasExecuted)
+		if (!afterOfRule1WasExecuted) {
 			fail();
-		if (!afterOfRule2WasExecuted)
+		}
+		if (!afterOfRule2WasExecuted) {
 			fail();
+		}
 	}
 
 }
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/ExternalResourceSupportForMultipleMethodRulesTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/ExternalResourceSupportForMultipleMethodRulesTests.java
index e5ad795f43c0..628fd3abc2e6 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/ExternalResourceSupportForMultipleMethodRulesTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/ExternalResourceSupportForMultipleMethodRulesTests.java
@@ -19,6 +19,7 @@
 import org.junit.jupiter.api.extension.ExtendWith;
 import org.junit.rules.ExternalResource;
 
+@SuppressWarnings("removal")
 @ExtendWith(ExternalResourceSupport.class)
 public class ExternalResourceSupportForMultipleMethodRulesTests {
 
@@ -66,10 +67,12 @@ void beforeMethodsOfBothRulesWereExecuted() {
 
 	@AfterAll
 	static void afterMethodsOfBothRulesWereExecuted() {
-		if (!afterOfRule1WasExecuted)
+		if (!afterOfRule1WasExecuted) {
 			fail();
-		if (!afterOfRule2WasExecuted)
+		}
+		if (!afterOfRule2WasExecuted) {
 			fail();
+		}
 	}
 
 }
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/ExternalResourceSupportForTemporaryFolderFieldTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/ExternalResourceSupportForTemporaryFolderFieldTests.java
index c58690716548..7750eeda31cd 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/ExternalResourceSupportForTemporaryFolderFieldTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/ExternalResourceSupportForTemporaryFolderFieldTests.java
@@ -21,6 +21,7 @@
 import org.junit.jupiter.api.extension.ExtendWith;
 import org.junit.rules.TemporaryFolder;
 
+@SuppressWarnings("removal")
 @ExtendWith(ExternalResourceSupport.class)
 public class ExternalResourceSupportForTemporaryFolderFieldTests {
 
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/LauncherBasedEnableRuleMigrationSupportTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/LauncherBasedEnableRuleMigrationSupportTests.java
index 1a022944706b..116f9d0c5c4d 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/LauncherBasedEnableRuleMigrationSupportTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/LauncherBasedEnableRuleMigrationSupportTests.java
@@ -23,6 +23,7 @@
 import org.junit.rules.ExternalResource;
 import org.junit.rules.Verifier;
 
+@SuppressWarnings("removal")
 class LauncherBasedEnableRuleMigrationSupportTests {
 
 	@Test
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/VerifierSupportForMixedMethodAndFieldRulesTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/VerifierSupportForMixedMethodAndFieldRulesTests.java
index 42a292c7e860..1d533866f38e 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/VerifierSupportForMixedMethodAndFieldRulesTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/VerifierSupportForMixedMethodAndFieldRulesTests.java
@@ -18,6 +18,7 @@
 import org.junit.jupiter.api.extension.ExtendWith;
 import org.junit.rules.Verifier;
 
+@SuppressWarnings("removal")
 @ExtendWith(VerifierSupport.class)
 public class VerifierSupportForMixedMethodAndFieldRulesTests {
 
@@ -53,10 +54,12 @@ void testNothing() {
 
 	@AfterAll
 	static void afterMethodsOfBothRulesWereExecuted() {
-		if (!afterOfRule1WasExecuted)
+		if (!afterOfRule1WasExecuted) {
 			fail();
-		if (!afterOfRule2WasExecuted)
+		}
+		if (!afterOfRule2WasExecuted) {
 			fail();
+		}
 	}
 
 }
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/WrongExtendWithForVerifierFieldTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/WrongExtendWithForVerifierFieldTests.java
index ec4c7871fdb3..e3b2224b11a7 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/WrongExtendWithForVerifierFieldTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/WrongExtendWithForVerifierFieldTests.java
@@ -18,6 +18,7 @@
 import org.junit.jupiter.api.extension.ExtendWith;
 import org.junit.rules.Verifier;
 
+@SuppressWarnings("removal")
 @ExtendWith(ExternalResourceSupport.class)
 public class WrongExtendWithForVerifierFieldTests {
 
@@ -39,8 +40,9 @@ void testNothing() {
 
 	@AfterAll
 	static void afterMethodOfRuleWasNotExecuted() {
-		if (afterOfRule1WasExecuted)
+		if (afterOfRule1WasExecuted) {
 			fail();
+		}
 	}
 
 }
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/WrongExtendWithForVerifierMethodTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/WrongExtendWithForVerifierMethodTests.java
index 77d89f7bddb7..aa67381f3ac2 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/WrongExtendWithForVerifierMethodTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/migrationsupport/rules/WrongExtendWithForVerifierMethodTests.java
@@ -18,6 +18,7 @@
 import org.junit.jupiter.api.extension.ExtendWith;
 import org.junit.rules.Verifier;
 
+@SuppressWarnings("removal")
 @ExtendWith(ExternalResourceSupport.class)
 public class WrongExtendWithForVerifierMethodTests {
 
@@ -43,8 +44,9 @@ void testNothing() {
 
 	@AfterAll
 	static void afterMethodsOfBothRulesWereExecuted() {
-		if (afterOfRule1WasExecuted)
+		if (afterOfRule1WasExecuted) {
 			fail();
+		}
 	}
 
 }
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/params/ParameterizedClassIntegrationTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/params/ParameterizedClassIntegrationTests.java
index 6e678900084e..f8dc13677f1f 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/params/ParameterizedClassIntegrationTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/params/ParameterizedClassIntegrationTests.java
@@ -11,6 +11,7 @@
 package org.junit.jupiter.params;
 
 import static java.util.Comparator.comparing;
+import static java.util.Objects.requireNonNull;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.tuple;
 import static org.junit.jupiter.api.Assertions.assertEquals;
@@ -56,6 +57,7 @@
 import java.util.stream.Stream;
 
 import org.assertj.core.api.Condition;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.AfterAll;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeAll;
@@ -944,11 +946,13 @@ static class FieldInjectionWithRegisteredConversionTestCase {
 
 		@Test
 		void test1() {
+			assertNotNull(value);
 			assertTrue(value.startsWith("minus"), "negative");
 		}
 
 		@Test
 		void test2() {
+			assertNotNull(value);
 			assertTrue(value.startsWith("minus"), "negative");
 		}
 	}
@@ -960,8 +964,8 @@ private static class CustomIntegerToStringConverter extends TypedArgumentConvert
 		}
 
 		@Override
-		protected String convert(Integer source) throws ArgumentConversionException {
-			return switch (source) {
+		protected String convert(@Nullable Integer source) throws ArgumentConversionException {
+			return switch (requireNonNull(source)) {
 				case -1 -> "minus one";
 				case +1 -> "plus one";
 				default -> throw new IllegalArgumentException("Unsupported value: " + source);
@@ -976,12 +980,12 @@ record RecordWithBuiltInAggregatorTestCase(ArgumentsAccessor accessor) {
 
 		@Test
 		void test1() {
-			assertTrue(accessor.getInteger(0) < 0, "negative");
+			assertTrue(requireNonNull(accessor.getInteger(0)) < 0, "negative");
 		}
 
 		@Test
 		void test2() {
-			assertTrue(accessor.getInteger(0) < 0, "negative");
+			assertTrue(requireNonNull(accessor.getInteger(0)) < 0, "negative");
 		}
 
 	}
@@ -996,12 +1000,12 @@ static class FieldInjectionWithBuiltInAggregatorTestCase {
 
 		@Test
 		void test1() {
-			assertTrue(accessor.getInteger(0) < 0, "negative");
+			assertTrue(requireNonNull(accessor.getInteger(0)) < 0, "negative");
 		}
 
 		@Test
 		void test2() {
-			assertTrue(accessor.getInteger(0) < 0, "negative");
+			assertTrue(requireNonNull(accessor.getInteger(0)) < 0, "negative");
 		}
 	}
 
@@ -1055,7 +1059,8 @@ private static class TimesTwoAggregator extends SimpleArgumentsAggregator {
 		protected Object aggregateArguments(ArgumentsAccessor accessor, Class<?> targetType,
 				AnnotatedElementContext context, int parameterIndex) throws ArgumentsAggregationException {
 
-			return accessor.getInteger(0) * 2;
+			assertThat(targetType).isEqualTo(int.class);
+			return requireNonNull(accessor.getInteger(0)) * 2;
 		}
 	}
 
@@ -1712,6 +1717,7 @@ void test(TestReporter reporter) {
 	record ArgumentConversionPerInvocationConstructorInjectionTestCase(
 			@ConvertWith(Wrapper.Converter.class) Wrapper wrapper) {
 
+		@Nullable
 		static Wrapper instance;
 
 		@BeforeAll
@@ -1744,6 +1750,7 @@ private void setOrCheckWrapper() {
 	@ValueSource(ints = 1)
 	static class ArgumentConversionPerInvocationFieldInjectionTestCase {
 
+		@Nullable
 		static Wrapper instance;
 
 		@BeforeAll
@@ -1779,8 +1786,8 @@ private void setOrCheckWrapper() {
 	record Wrapper(int value) {
 		static class Converter extends SimpleArgumentConverter {
 			@Override
-			protected Object convert(Object source, Class<?> targetType) {
-				return new Wrapper((Integer) source);
+			protected Object convert(@Nullable Object source, Class<?> targetType) {
+				return new Wrapper((Integer) requireNonNull(source));
 			}
 		}
 	}
@@ -1971,8 +1978,8 @@ void test2() {
 
 	static class AtomicIntegerConverter extends SimpleArgumentConverter {
 		@Override
-		protected Object convert(Object source, Class<?> targetType) {
-			return new AtomicInteger((Integer) source);
+		protected Object convert(@Nullable Object source, Class<?> targetType) {
+			return new AtomicInteger((Integer) requireNonNull(source));
 		}
 	}
 
@@ -2018,13 +2025,15 @@ void test() {
 
 		class Converter implements ArgumentConverter {
 			@Override
-			public Object convert(Object source, ParameterContext context) throws ArgumentConversionException {
+			public @Nullable Object convert(@Nullable Object source, ParameterContext context)
+					throws ArgumentConversionException {
 				assertNotNull(context.getParameter().getAnnotation(CustomConversion.class));
 				return source;
 			}
 
 			@Override
-			public Object convert(Object source, FieldContext context) throws ArgumentConversionException {
+			public @Nullable Object convert(@Nullable Object source, FieldContext context)
+					throws ArgumentConversionException {
 				assertNotNull(context.getField().getAnnotation(CustomConversion.class));
 				return source;
 			}
@@ -2200,7 +2209,8 @@ void test() {
 
 		static class ToStringConverter extends SimpleArgumentConverter {
 			@Override
-			protected Object convert(Object source, Class<?> targetType) throws ArgumentConversionException {
+			protected @Nullable Object convert(@Nullable Object source, Class<?> targetType)
+					throws ArgumentConversionException {
 				return source == null ? null : String.valueOf(source);
 			}
 		}
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/params/ParameterizedInvocationNameFormatterTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/params/ParameterizedInvocationNameFormatterTests.java
index 7d48e198dfb2..bee72ba81725 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/params/ParameterizedInvocationNameFormatterTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/params/ParameterizedInvocationNameFormatterTests.java
@@ -37,6 +37,8 @@
 import java.util.Arrays;
 import java.util.Locale;
 
+import org.jspecify.annotations.NullUnmarked;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Test;
@@ -154,7 +156,7 @@ void formatsCompleteArgumentsListWithoutNamesForAggregators() {
 	void formatsCompleteArgumentsListWithArrays() {
 		var formatter = formatter(ARGUMENTS_PLACEHOLDER, "enigma");
 
-		// Explicit test for https://github.com/junit-team/junit5/issues/814
+		// Explicit test for https://github.com/junit-team/junit-framework/issues/814
 		assertEquals("[foo, bar]", format(formatter, 1, arguments((Object) new String[] { "foo", "bar" })));
 
 		assertEquals("[foo, bar], 42, true", format(formatter, 1, arguments(new String[] { "foo", "bar" }, 42, true)));
@@ -346,6 +348,7 @@ private static String format(ParameterizedInvocationNameFormatter formatter, int
 		return formatter.format(invocationIndex, EvaluatedArgumentSet.allOf(arguments));
 	}
 
+	@NullUnmarked
 	private static class ToStringReturnsNull {
 
 		@Override
@@ -386,7 +389,7 @@ void processFruits(String fruit1, String fruit2) {
 
 		private static class CustomAggregator extends SimpleArgumentsAggregator {
 			@Override
-			protected Object aggregateArguments(ArgumentsAccessor accessor, Class<?> targetType,
+			protected @Nullable Object aggregateArguments(ArgumentsAccessor accessor, Class<?> targetType,
 					AnnotatedElementContext context, int parameterIndex) {
 				return accessor.get(0);
 			}
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/params/ParameterizedTestExtensionTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/params/ParameterizedTestExtensionTests.java
index 9eb006afbbc9..9f589354ae5c 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/params/ParameterizedTestExtensionTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/params/ParameterizedTestExtensionTests.java
@@ -17,6 +17,7 @@
 import static org.junit.jupiter.api.Assertions.assertTrue;
 import static org.junit.jupiter.params.ParameterizedInvocationContextProvider.arguments;
 import static org.junit.jupiter.params.ParameterizedTestExtension.DECLARATION_CONTEXT_KEY;
+import static org.mockito.Mockito.mock;
 
 import java.io.FileNotFoundException;
 import java.lang.reflect.AnnotatedElement;
@@ -31,6 +32,7 @@
 import java.util.function.Function;
 import java.util.stream.Stream;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.TestInstance.Lifecycle;
 import org.junit.jupiter.api.extension.ExecutableInvoker;
@@ -47,6 +49,7 @@
 import org.junit.jupiter.params.support.ParameterDeclarations;
 import org.junit.platform.commons.JUnitException;
 import org.junit.platform.commons.PreconditionViolationException;
+import org.junit.platform.commons.support.AnnotationSupport;
 import org.junit.platform.commons.util.ReflectionUtils;
 import org.junit.platform.engine.support.store.NamespacedHierarchicalStore;
 
@@ -133,7 +136,7 @@ public Stream<? extends Arguments> provideArguments(ParameterDeclarations parame
 			}
 		};
 
-		var exception = assertThrows(FileNotFoundException.class, () -> arguments(failingProvider, null, null));
+		var exception = assertThrows(FileNotFoundException.class, () -> arguments(failingProvider, mock(), mock()));
 		assertEquals("a message", exception.getMessage());
 	}
 
@@ -182,9 +185,9 @@ void throwsExceptionWhenArgumentsProviderIsNotStatic() {
 		var exception = assertThrows(JUnitException.class, stream::toArray);
 
 		assertThat(exception) //
-				.hasMessage(String.format(
-					"The ArgumentsProvider [%s] must be either a top-level class or a static nested class",
-					NonStaticArgumentsProvider.class.getName()));
+				.hasMessage(
+					"The ArgumentsProvider [%s] must be either a top-level class or a static nested class".formatted(
+						NonStaticArgumentsProvider.class.getName()));
 	}
 
 	@Test
@@ -236,17 +239,17 @@ public ExtensionContext getRoot() {
 
 			@Override
 			public String getUniqueId() {
-				return null;
+				throw new UnsupportedOperationException();
 			}
 
 			@Override
 			public String getDisplayName() {
-				return null;
+				return "display-name";
 			}
 
 			@Override
 			public Set<String> getTags() {
-				return null;
+				throw new UnsupportedOperationException();
 			}
 
 			@Override
@@ -290,7 +293,8 @@ public Optional<String> getConfigurationParameter(String key) {
 			}
 
 			@Override
-			public <T> Optional<T> getConfigurationParameter(String key, Function<String, T> transformer) {
+			public <T> Optional<T> getConfigurationParameter(String key,
+					Function<? super String, ? extends @Nullable T> transformer) {
 				return configurationSupplier.apply(key).map(transformer);
 			}
 
@@ -312,7 +316,7 @@ public Store getStore(Namespace namespace) {
 					org.junit.platform.engine.support.store.Namespace.create(namespace.getParts()));
 				method //
 						.map(it -> new ParameterizedTestContext(testClass, it,
-							it.getAnnotation(ParameterizedTest.class))) //
+							AnnotationSupport.findAnnotation(it, ParameterizedTest.class).orElseThrow())) //
 						.ifPresent(ctx -> store.put(DECLARATION_CONTEXT_KEY, ctx));
 				return store;
 			}
@@ -331,12 +335,12 @@ public ExecutionMode getExecutionMode() {
 			public ExecutableInvoker getExecutableInvoker() {
 				return new ExecutableInvoker() {
 					@Override
-					public Object invoke(Method method, Object target) {
-						return null;
+					public Object invoke(Method method, @Nullable Object target) {
+						throw new UnsupportedOperationException();
 					}
 
 					@Override
-					public <T> T invoke(Constructor<T> constructor, Object outerInstance) {
+					public <T> T invoke(Constructor<T> constructor, @Nullable Object outerInstance) {
 						return ReflectionUtils.newInstance(constructor);
 					}
 				};
@@ -417,7 +421,7 @@ class NonStaticArgumentsProvider implements ArgumentsProvider {
 		@Override
 		public Stream<? extends Arguments> provideArguments(ParameterDeclarations parameters,
 				ExtensionContext context) {
-			return null;
+			throw new UnsupportedOperationException();
 		}
 	}
 
@@ -456,7 +460,7 @@ static class AmbiguousConstructorArgumentsProvider implements ArgumentsProvider
 		@Override
 		public Stream<? extends Arguments> provideArguments(ParameterDeclarations parameters,
 				ExtensionContext context) {
-			return null;
+			throw new UnsupportedOperationException();
 		}
 	}
 
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/params/ParameterizedTestIntegrationTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/params/ParameterizedTestIntegrationTests.java
index be726c17fba1..194be12b1abb 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/params/ParameterizedTestIntegrationTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/params/ParameterizedTestIntegrationTests.java
@@ -63,6 +63,7 @@
 import java.util.function.Supplier;
 import java.util.stream.Stream;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.AfterAll;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.Assumptions;
@@ -224,7 +225,7 @@ void executesLinesFromClasspathResourceUsingTableFormatAndHeadersAndNullValues(S
 		assertFruitTable(fruit, rank, testInfo);
 	}
 
-	private void assertFruitTable(String fruit, double rank, TestInfo testInfo) {
+	private void assertFruitTable(@Nullable String fruit, double rank, TestInfo testInfo) {
 		String displayName = testInfo.getDisplayName();
 
 		if (fruit == null) {
@@ -928,8 +929,7 @@ void streamOfTwoDimensionalObjectArrays() {
 		void reportsContainerWithAssumptionFailureInMethodSourceAsAborted() {
 			execute("assumptionFailureInMethodSourceFactoryMethod", String.class).allEvents().assertThatEvents() //
 					.haveExactly(1, event(container("test-template:assumptionFailureInMethodSourceFactoryMethod"), //
-						abortedWithReason(instanceOf(TestAbortedException.class),
-							message("Assumption failed: nothing to test"))));
+						abortedWithReason(instanceOf(TestAbortedException.class), message("nothing to test"))));
 		}
 
 		@Test
@@ -952,7 +952,7 @@ void nameParametersAlias() {
 
 		/**
 		 * @since 5.9.1
-		 * @see https://github.com/junit-team/junit5/issues/3001
+		 * @see https://github.com/junit-team/junit-framework/issues/3001
 		 */
 		@Test
 		void duplicateMethodNames() {
@@ -1175,8 +1175,8 @@ void failsWithArgumentsSourceProvidingUnusedArguments() {
 			var results = execute(ArgumentCountValidationMode.STRICT, UnusedArgumentsTestCase.class,
 				"testWithTwoUnusedStringArgumentsProvider", String.class);
 			results.allEvents().assertThatEvents() //
-					.haveExactly(1, event(finishedWithFailure(message(String.format(
-						"Configuration error: @ParameterizedTest consumes 1 parameter but there were 2 arguments provided.%nNote: the provided arguments were [foo, unused1]")))));
+					.haveExactly(1, event(finishedWithFailure(message(
+						"Configuration error: @ParameterizedTest consumes 1 parameter but there were 2 arguments provided.%nNote: the provided arguments were [foo, unused1]".formatted()))));
 		}
 
 		@Test
@@ -1184,8 +1184,8 @@ void failsWithMethodSourceProvidingUnusedArguments() {
 			var results = execute(ArgumentCountValidationMode.STRICT, UnusedArgumentsTestCase.class,
 				"testWithMethodSourceProvidingUnusedArguments", String.class);
 			results.allEvents().assertThatEvents() //
-					.haveExactly(1, event(finishedWithFailure(message(String.format(
-						"Configuration error: @ParameterizedTest consumes 1 parameter but there were 2 arguments provided.%nNote: the provided arguments were [foo, unused1]")))));
+					.haveExactly(1, event(finishedWithFailure(message(
+						"Configuration error: @ParameterizedTest consumes 1 parameter but there were 2 arguments provided.%nNote: the provided arguments were [foo, unused1]".formatted()))));
 		}
 
 		@Test
@@ -1193,8 +1193,8 @@ void failsWithCsvSourceUnusedArgumentsAndStrictArgumentCountValidationAnnotation
 			var results = execute(ArgumentCountValidationMode.NONE, UnusedArgumentsTestCase.class,
 				"testWithStrictArgumentCountValidation", String.class);
 			results.allEvents().assertThatEvents() //
-					.haveExactly(1, event(finishedWithFailure(message(String.format(
-						"Configuration error: @ParameterizedTest consumes 1 parameter but there were 2 arguments provided.%nNote: the provided arguments were [foo, unused1]")))));
+					.haveExactly(1, event(finishedWithFailure(message(
+						"Configuration error: @ParameterizedTest consumes 1 parameter but there were 2 arguments provided.%nNote: the provided arguments were [foo, unused1]".formatted()))));
 		}
 
 		@Test
@@ -1202,8 +1202,8 @@ void failsWithCsvSourceUnusedArgumentsButExecutesRemainingArgumentsWhereThereIsN
 			var results = execute(ArgumentCountValidationMode.STRICT, UnusedArgumentsTestCase.class,
 				"testWithCsvSourceContainingDifferentNumbersOfArguments", String.class);
 			results.allEvents().assertThatEvents() //
-					.haveExactly(1, event(finishedWithFailure(message(String.format(
-						"Configuration error: @ParameterizedTest consumes 1 parameter but there were 2 arguments provided.%nNote: the provided arguments were [foo, unused1]"))))) //
+					.haveExactly(1, event(finishedWithFailure(message(
+						"Configuration error: @ParameterizedTest consumes 1 parameter but there were 2 arguments provided.%nNote: the provided arguments were [foo, unused1]".formatted())))) //
 					.haveExactly(1,
 						event(test(), displayName("[2] argument=bar"), finishedWithFailure(message("bar"))));
 		}
@@ -1231,8 +1231,8 @@ void evaluatesArgumentsAtMostOnce() {
 			var results = execute(ArgumentCountValidationMode.STRICT, UnusedArgumentsTestCase.class,
 				"testWithEvaluationReportingArgumentsProvider", String.class);
 			results.allEvents().assertThatEvents() //
-					.haveExactly(1, event(finishedWithFailure(message(String.format(
-						"Configuration error: @ParameterizedTest consumes 1 parameter but there were 2 arguments provided.%nNote: the provided arguments were [foo, unused]")))));
+					.haveExactly(1, event(finishedWithFailure(message(
+						"Configuration error: @ParameterizedTest consumes 1 parameter but there were 2 arguments provided.%nNote: the provided arguments were [foo, unused]".formatted()))));
 			results.allEvents().reportingEntryPublished().assertThatEvents() //
 					.haveExactly(1, event(EventConditions.reportEntry(Map.of("evaluated", "true"))));
 		}
@@ -1928,15 +1928,15 @@ void assumptionFailureInMethodSourceFactoryMethod(String test) {
 		}
 
 		static List<String> assumptionFailureInMethodSourceFactoryMethod() {
-			Assumptions.assumeFalse(true, "nothing to test");
-			return null;
+			Assumptions.abort("nothing to test");
+			return List.of();
 		}
 
 	}
 
 	/**
 	 * @since 5.9.1
-	 * @see https://github.com/junit-team/junit5/issues/3001
+	 * @see https://github.com/junit-team/junit-framework/issues/3001
 	 */
 	static class DuplicateMethodNamesMethodSourceTestCase {
 
@@ -2508,7 +2508,8 @@ public Stream<? extends Arguments> provideArguments(ParameterDeclarations parame
 		record ArgumentConverterWithConstructorParameter(String value) implements ArgumentConverter {
 
 			@Override
-			public Object convert(Object source, ParameterContext context) throws ArgumentConversionException {
+			public Object convert(@Nullable Object source, ParameterContext context)
+					throws ArgumentConversionException {
 				return value;
 			}
 		}
@@ -2593,7 +2594,7 @@ public Stream<? extends Arguments> provideArguments(ParameterDeclarations parame
 	private static class StringLengthConverter implements ArgumentConverter {
 
 		@Override
-		public Object convert(Object source, ParameterContext context) throws ArgumentConversionException {
+		public Object convert(@Nullable Object source, ParameterContext context) throws ArgumentConversionException {
 			return String.valueOf(source).length();
 		}
 	}
@@ -2610,7 +2611,7 @@ protected Object aggregateArguments(ArgumentsAccessor accessor, Class<?> targetT
 	private static class ErroneousConverter implements ArgumentConverter {
 
 		@Override
-		public Object convert(Object source, ParameterContext context) throws ArgumentConversionException {
+		public Object convert(@Nullable Object source, ParameterContext context) throws ArgumentConversionException {
 			throw new ArgumentConversionException("something went horribly wrong");
 		}
 	}
@@ -2666,8 +2667,9 @@ static class ExceptionInStaticInitializerTestCase {
 
 		static {
 			//noinspection ConstantValue
-			if (true)
+			if (true) {
 				throw new RuntimeException("boom");
+			}
 		}
 
 		private static Stream<String> getArguments() {
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/params/aggregator/AggregatorIntegrationTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/params/aggregator/AggregatorIntegrationTests.java
index 999a101abd21..1d57fbf27f51 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/params/aggregator/AggregatorIntegrationTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/params/aggregator/AggregatorIntegrationTests.java
@@ -10,6 +10,7 @@
 
 package org.junit.jupiter.params.aggregator;
 
+import static java.util.Objects.requireNonNull;
 import static java.util.stream.Collectors.toMap;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.entry;
@@ -35,6 +36,8 @@
 import java.util.Map;
 import java.util.stream.IntStream;
 
+import org.jspecify.annotations.NullUnmarked;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.TestInfo;
 import org.junit.jupiter.api.extension.AnnotatedElementContext;
@@ -225,6 +228,7 @@ private EngineExecutionResults execute(DiscoverySelector... selectors) {
 
 	// -------------------------------------------------------------------------
 
+	@NullUnmarked
 	public static class Person {
 
 		final String firstName;
@@ -248,17 +252,8 @@ enum Gender {
 		F, M
 	}
 
-	static class Address {
-
-		final String street;
-		final String city;
-		final int zipCode;
-
-		Address(String street, String city, int zipCode) {
-			this.street = street;
-			this.city = city;
-			this.zipCode = zipCode;
-		}
+	@NullUnmarked
+	record Address(String street, String city, int zipCode) {
 	}
 
 	@Retention(RetentionPolicy.RUNTIME)
@@ -308,7 +303,7 @@ public Address aggregateArguments(ArgumentsAccessor arguments, Class<?> targetTy
 			return new Address(
 				arguments.getString(startIndex + 0),
 				arguments.getString(startIndex + 1),
-				arguments.getInteger(startIndex + 2)
+				requireNonNull(arguments.getInteger(startIndex + 2))
 			);
 			// @formatter:on
 		}
@@ -332,7 +327,7 @@ protected Map<String, Integer> aggregateArguments(ArgumentsAccessor arguments, C
 
 	static class NullAggregator extends SimpleArgumentsAggregator {
 		@Override
-		protected Object aggregateArguments(ArgumentsAccessor accessor, Class<?> targetType,
+		protected @Nullable Object aggregateArguments(ArgumentsAccessor accessor, Class<?> targetType,
 				AnnotatedElementContext context, int parameterIndex) {
 			Preconditions.condition(!targetType.isPrimitive(), () -> "only supports reference types");
 			return null;
@@ -391,7 +386,8 @@ static class InstanceCountingConverter implements ArgumentConverter {
 		}
 
 		@Override
-		public Object convert(Object source, ParameterContext context) throws ArgumentConversionException {
+		public @Nullable Object convert(@Nullable Object source, ParameterContext context)
+				throws ArgumentConversionException {
 			return source;
 		}
 	}
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/params/aggregator/DefaultArgumentsAccessorTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/params/aggregator/DefaultArgumentsAccessorTests.java
index b5f6e941bc6e..8bad1f29d436 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/params/aggregator/DefaultArgumentsAccessorTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/params/aggregator/DefaultArgumentsAccessorTests.java
@@ -20,6 +20,7 @@
 
 import java.util.Arrays;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExtensionContext;
 import org.junit.platform.commons.PreconditionViolationException;
@@ -31,6 +32,7 @@
  */
 class DefaultArgumentsAccessorTests {
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void argumentsMustNotBeNull() {
 		assertThrows(PreconditionViolationException.class, () -> defaultArgumentsAccessor(1, (Object[]) null));
@@ -52,12 +54,12 @@ void indexMustBeSmallerThanLength() {
 
 	@Test
 	void getNull() {
-		assertNull(defaultArgumentsAccessor(1, new Object[] { null }).get(0));
+		assertNull(defaultArgumentsAccessor(1, new @Nullable Object[] { null }).get(0));
 	}
 
 	@Test
 	void getWithNullCastToWrapperType() {
-		assertNull(defaultArgumentsAccessor(1, (Object[]) new Integer[] { null }).get(0, Integer.class));
+		assertNull(defaultArgumentsAccessor(1, (Object[]) new @Nullable Integer[] { null }).get(0, Integer.class));
 	}
 
 	@Test
@@ -79,7 +81,7 @@ void getWithCastToPrimitiveType() {
 			"Argument at index [0] with value [1] and type [java.lang.Integer] could not be converted or cast to type [int].");
 
 		exception = assertThrows(ArgumentAccessException.class,
-			() -> defaultArgumentsAccessor(1, new Object[] { null }).get(0, int.class));
+			() -> defaultArgumentsAccessor(1, new @Nullable Object[] { null }).get(0, int.class));
 		assertThat(exception.getMessage()).isEqualTo(
 			"Argument at index [0] with value [null] and type [null] could not be converted or cast to type [int].");
 	}
@@ -165,7 +167,8 @@ void size() {
 		assertEquals(5, defaultArgumentsAccessor(1, 'a', 'b', 'c', 'd', 'e').size());
 	}
 
-	private static DefaultArgumentsAccessor defaultArgumentsAccessor(int invocationIndex, Object... arguments) {
+	private static DefaultArgumentsAccessor defaultArgumentsAccessor(int invocationIndex,
+			@Nullable Object... arguments) {
 		var context = mock(ExtensionContext.class);
 		var classLoader = DefaultArgumentsAccessorTests.class.getClassLoader();
 		return DefaultArgumentsAccessor.create(context, invocationIndex, classLoader, arguments);
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/params/converter/DefaultArgumentConverterTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/params/converter/DefaultArgumentConverterTests.java
index 501f4c09a40c..405828e97fbb 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/params/converter/DefaultArgumentConverterTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/params/converter/DefaultArgumentConverterTests.java
@@ -29,6 +29,7 @@
 import java.util.Locale;
 import java.util.Optional;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExtensionContext;
 import org.junit.jupiter.params.ParameterizedTest;
@@ -168,7 +169,7 @@ void delegatesStringToClassWithCustomTypeFromDifferentClassLoaderConversion() th
 
 			var clazz = (Class<?>) convert(customTypeName, Class.class, testClassLoader);
 			assertThat(clazz).isNotEqualTo(Enigma.class);
-			assertThat(clazz).isEqualTo(customType);
+			assertThat(clazz).isNotNull().isEqualTo(customType);
 			assertThat(clazz.getClassLoader()).isSameAs(testClassLoader);
 
 			verify(underTest).convert(customTypeName, Class.class, testClassLoader);
@@ -177,7 +178,7 @@ void delegatesStringToClassWithCustomTypeFromDifferentClassLoaderConversion() th
 
 	// -------------------------------------------------------------------------
 
-	private void assertConverts(Object input, Class<?> targetClass, Object expectedOutput) {
+	private void assertConverts(@Nullable Object input, Class<?> targetClass, @Nullable Object expectedOutput) {
 		var result = convert(input, targetClass);
 
 		assertThat(result) //
@@ -187,11 +188,11 @@ private void assertConverts(Object input, Class<?> targetClass, Object expectedO
 		verify(underTest, never()).convert(any(), any(), any(ClassLoader.class));
 	}
 
-	private Object convert(Object input, Class<?> targetClass) {
+	private @Nullable Object convert(@Nullable Object input, Class<?> targetClass) {
 		return convert(input, targetClass, ClassLoaderUtils.getClassLoader(getClass()));
 	}
 
-	private Object convert(Object input, Class<?> targetClass, ClassLoader classLoader) {
+	private @Nullable Object convert(@Nullable Object input, Class<?> targetClass, ClassLoader classLoader) {
 		return underTest.convert(input, targetClass, classLoader);
 	}
 
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/params/converter/JavaTimeArgumentConverterTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/params/converter/JavaTimeArgumentConverterTests.java
index 2cee9d79f7c9..f2bb6db3f720 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/params/converter/JavaTimeArgumentConverterTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/params/converter/JavaTimeArgumentConverterTests.java
@@ -30,6 +30,7 @@
 import java.time.chrono.ChronoLocalDateTime;
 import java.time.chrono.ChronoZonedDateTime;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 
 /**
@@ -37,66 +38,77 @@
  */
 class JavaTimeArgumentConverterTests {
 
+	@SuppressWarnings("DataFlowIssue")
 	@Test
 	void convertsStringToChronoLocalDate() {
 		assertThat(convert("01.02.2017", "dd.MM.yyyy", ChronoLocalDate.class)) //
 				.isEqualTo(LocalDate.of(2017, 2, 1));
 	}
 
+	@SuppressWarnings("DataFlowIssue")
 	@Test
 	void convertsStringToChronoLocalDateTime() {
 		assertThat(convert("01.02.2017 12:34:56.789", "dd.MM.yyyy HH:mm:ss.SSS", ChronoLocalDateTime.class)) //
 				.isEqualTo(LocalDateTime.of(2017, 2, 1, 12, 34, 56, 789_000_000));
 	}
 
+	@SuppressWarnings("DataFlowIssue")
 	@Test
 	void convertsStringToChronoZonedDateTime() {
 		assertThat(convert("01.02.2017 12:34:56.789 Z", "dd.MM.yyyy HH:mm:ss.SSS X", ChronoZonedDateTime.class)) //
 				.isEqualTo(ZonedDateTime.of(2017, 2, 1, 12, 34, 56, 789_000_000, UTC));
 	}
 
+	@SuppressWarnings("DataFlowIssue")
 	@Test
 	void convertsStringToLocalDate() {
 		assertThat(convert("01.02.2017", "dd.MM.yyyy", LocalDate.class)) //
 				.isEqualTo(LocalDate.of(2017, 2, 1));
 	}
 
+	@SuppressWarnings("DataFlowIssue")
 	@Test
 	void convertsStringToLocalDateTime() {
 		assertThat(convert("01.02.2017 12:34:56.789", "dd.MM.yyyy HH:mm:ss.SSS", LocalDateTime.class)) //
 				.isEqualTo(LocalDateTime.of(2017, 2, 1, 12, 34, 56, 789_000_000));
 	}
 
+	@SuppressWarnings("DataFlowIssue")
 	@Test
 	void convertsStringToLocalTime() {
 		assertThat(convert("12:34:56.789", "HH:mm:ss.SSS", LocalTime.class)) //
 				.isEqualTo(LocalTime.of(12, 34, 56, 789_000_000));
 	}
 
+	@SuppressWarnings("DataFlowIssue")
 	@Test
 	void convertsStringToOffsetDateTime() {
 		assertThat(convert("01.02.2017 12:34:56.789 +02", "dd.MM.yyyy HH:mm:ss.SSS X", OffsetDateTime.class)) //
 				.isEqualTo(OffsetDateTime.of(2017, 2, 1, 12, 34, 56, 789_000_000, ZoneOffset.ofHours(2)));
 	}
 
+	@SuppressWarnings("DataFlowIssue")
 	@Test
 	void convertsStringToOffsetTime() {
 		assertThat(convert("12:34:56.789 -02", "HH:mm:ss.SSS X", OffsetTime.class)) //
 				.isEqualTo(OffsetTime.of(12, 34, 56, 789_000_000, ZoneOffset.ofHours(-2)));
 	}
 
+	@SuppressWarnings("DataFlowIssue")
 	@Test
 	void convertsStringToYear() {
 		assertThat(convert("2017", "yyyy", Year.class)) //
 				.isEqualTo(Year.of(2017));
 	}
 
+	@SuppressWarnings("DataFlowIssue")
 	@Test
 	void convertsStringToYearMonth() {
 		assertThat(convert("03/2017", "MM/yyyy", YearMonth.class)) //
 				.isEqualTo(YearMonth.of(2017, 3));
 	}
 
+	@SuppressWarnings("DataFlowIssue")
 	@Test
 	void convertsStringToZonedDateTime() {
 		assertThat(convert("01.02.2017 12:34:56.789 Europe/Berlin", "dd.MM.yyyy HH:mm:ss.SSS VV", ZonedDateTime.class)) //
@@ -125,16 +137,17 @@ void throwsExceptionOnNullParameterWithoutNullable() {
 	/**
 	 * @since 5.12
 	 */
+	@SuppressWarnings("DataFlowIssue")
 	@Test
 	void convertsNullableParameter() {
 		assertThat(convert(null, "dd.MM.yyyy", true, LocalDate.class)).isNull();
 	}
 
-	private Object convert(Object input, String pattern, Class<?> targetClass) {
+	private @Nullable Object convert(@Nullable Object input, String pattern, Class<?> targetClass) {
 		return convert(input, pattern, false, targetClass);
 	}
 
-	private Object convert(Object input, String pattern, boolean nullable, Class<?> targetClass) {
+	private @Nullable Object convert(@Nullable Object input, String pattern, boolean nullable, Class<?> targetClass) {
 		var converter = new JavaTimeArgumentConverter();
 		var annotation = mock(JavaTimeConversionPattern.class);
 		when(annotation.value()).thenReturn(pattern);
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/params/converter/TypedArgumentConverterTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/params/converter/TypedArgumentConverterTests.java
index 599f3d2e9163..dc93874d7d32 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/params/converter/TypedArgumentConverterTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/params/converter/TypedArgumentConverterTests.java
@@ -23,6 +23,7 @@
 import java.lang.reflect.Method;
 import java.lang.reflect.Parameter;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ParameterContext;
@@ -47,6 +48,7 @@ class UnitTests {
 		/**
 		 * @since 5.8
 		 */
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void preconditions() {
 			assertThatExceptionOfType(PreconditionViolationException.class)//
@@ -67,7 +69,7 @@ void convertsSourceToTarget() {
 			);
 		}
 
-		private void assertConverts(String input, int expected) {
+		private void assertConverts(@Nullable String input, int expected) {
 			assertThat(this.converter.convert(input)).isEqualTo(expected);
 		}
 
@@ -168,7 +170,7 @@ private static class StringLengthArgumentConverter extends TypedArgumentConverte
 		}
 
 		@Override
-		protected Integer convert(String source) throws ArgumentConversionException {
+		protected Integer convert(@Nullable String source) throws ArgumentConversionException {
 			return (source != null ? source.length() : 0);
 		}
 	}
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/params/provider/AnnotationBasedArgumentsProviderTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/params/provider/AnnotationBasedArgumentsProviderTests.java
index 885ba7a77591..4e75630c5d39 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/params/provider/AnnotationBasedArgumentsProviderTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/params/provider/AnnotationBasedArgumentsProviderTests.java
@@ -38,6 +38,7 @@ protected Stream<? extends Arguments> provideArguments(
 		}
 	};
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	@DisplayName("should throw exception when null annotation is provided to accept method")
 	void shouldThrowExceptionWhenNullAnnotationIsProvidedToAccept() {
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/params/provider/CsvArgumentsProviderTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/params/provider/CsvArgumentsProviderTests.java
index 9beac70e9616..4e6eab77eec9 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/params/provider/CsvArgumentsProviderTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/params/provider/CsvArgumentsProviderTests.java
@@ -17,6 +17,8 @@
 
 import java.util.stream.Stream;
 
+import org.assertj.core.api.ThrowingConsumer;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExtensionContext;
 import org.junit.jupiter.params.ParameterizedTest;
@@ -29,12 +31,12 @@
 class CsvArgumentsProviderTests {
 
 	@Test
-	void throwsExceptionForInvalidCsv() {
-		var annotation = csvSource("foo", "bar", "");
+	void throwsExceptionForBlankLines() {
+		var annotation = csvSource("foo", "bar", " ");
 
 		assertThatExceptionOfType(JUnitException.class)//
 				.isThrownBy(() -> provideArguments(annotation).toArray())//
-				.withMessage("Record at index 3 contains invalid CSV: \"\"");
+				.withMessage("CSV record at index 3 must not be blank");
 	}
 
 	@Test
@@ -185,7 +187,7 @@ void understandsEscapeCharacters() {
 	}
 
 	@Test
-	void understandsEscapeCharactersWithCutomQuoteCharacter() {
+	void understandsEscapeCharactersWithCustomQuoteCharacter() {
 		var annotation = csvSource().quoteCharacter('~').lines("~foo or ~~bar~~~, baz").build();
 
 		var arguments = provideArguments(annotation);
@@ -232,20 +234,20 @@ void throwsExceptionIfBothDelimitersAreSimultaneouslySet() {
 
 	@Test
 	void defaultEmptyValueAndDefaultNullValue() {
-		var annotation = csvSource("'', null, , apple");
+		var annotation = csvSource("'', null, ,, apple");
 
 		var arguments = provideArguments(annotation);
 
-		assertThat(arguments).containsExactly(array("", "null", null, "apple"));
+		assertThat(arguments).containsExactly(array("", "null", null, null, "apple"));
 	}
 
 	@Test
 	void customEmptyValueAndDefaultNullValue() {
-		var annotation = csvSource().emptyValue("EMPTY").lines("'', null, , apple").build();
+		var annotation = csvSource().emptyValue("EMPTY").lines("'', null, ,, apple").build();
 
 		var arguments = provideArguments(annotation);
 
-		assertThat(arguments).containsExactly(array("EMPTY", "null", null, "apple"));
+		assertThat(arguments).containsExactly(array("EMPTY", "null", null, null, "apple"));
 	}
 
 	@Test
@@ -258,6 +260,18 @@ void customNullValues() {
 		assertThat(arguments).containsExactly(array("apple", null, null, "", null, "banana", null));
 	}
 
+	@Test
+	void customNullValueInHeader() {
+		var annotation = csvSource().useHeadersInDisplayName(true).nullValues("NIL").textBlock("""
+				FRUIT, NIL
+				apple, 1
+				""").build();
+
+		assertThat(headersToValues(annotation)).containsExactly(//
+			array("FRUIT = apple", "null = 1")//
+		);
+	}
+
 	@Test
 	void convertsEmptyValuesToNullInLinesAfterFirstLine() {
 		var annotation = csvSource("'', ''", " , ");
@@ -274,7 +288,7 @@ void throwsExceptionIfSourceExceedsMaxCharsPerColumnConfig() {
 		assertThatExceptionOfType(CsvParsingException.class)//
 				.isThrownBy(() -> provideArguments(annotation).findAny())//
 				.withMessageStartingWith("Failed to parse CSV input configured via Mock for CsvSource")//
-				.withRootCauseInstanceOf(ArrayIndexOutOfBoundsException.class);
+				.havingRootCause().satisfies(isCsvParseException());
 	}
 
 	@Test
@@ -293,7 +307,7 @@ void throwsExceptionWhenSourceExceedsDefaultMaxCharsPerColumnConfig() {
 		assertThatExceptionOfType(CsvParsingException.class)//
 				.isThrownBy(() -> provideArguments(annotation).findAny())//
 				.withMessageStartingWith("Failed to parse CSV input configured via Mock for CsvSource")//
-				.withRootCauseInstanceOf(ArrayIndexOutOfBoundsException.class);
+				.havingRootCause().satisfies(isCsvParseException());
 	}
 
 	@Test
@@ -339,31 +353,38 @@ void honorsCommentCharacterWhenUsingTextBlockAttribute() {
 
 	@Test
 	void supportsCsvHeadersWhenUsingTextBlockAttribute() {
-		supportsCsvHeaders(csvSource().useHeadersInDisplayName(true).textBlock("""
+		var annotation = csvSource().useHeadersInDisplayName(true).textBlock("""
 				FRUIT, RANK
 				apple, 1
 				banana, 2
-				""").build());
+				""").build();
+
+		assertThat(headersToValues(annotation)).containsExactly(//
+			array("FRUIT = apple", "RANK = 1"), //
+			array("FRUIT = banana", "RANK = 2")//
+		);
 	}
 
 	@Test
 	void supportsCsvHeadersWhenUsingValueAttribute() {
-		supportsCsvHeaders(csvSource().useHeadersInDisplayName(true)//
-				.lines("FRUIT, RANK", "apple, 1", "banana, 2").build());
+		var annotation = csvSource().useHeadersInDisplayName(true)//
+				.lines("FRUIT, RANK", "apple, 1", "banana, 2").build();
+
+		assertThat(headersToValues(annotation)).containsExactly(//
+			array("FRUIT = apple", "RANK = 1"), //
+			array("FRUIT = banana", "RANK = 2")//
+		);
 	}
 
-	private void supportsCsvHeaders(CsvSource csvSource) {
+	private Stream<String[]> headersToValues(CsvSource csvSource) {
 		var arguments = provideArguments(csvSource);
-		Stream<String[]> argumentsAsStrings = arguments.map(array -> {
+		return arguments.map(array -> {
 			String[] strings = new String[array.length];
 			for (int i = 0; i < array.length; i++) {
 				strings[i] = String.valueOf(array[i]);
 			}
 			return strings;
 		});
-
-		assertThat(argumentsAsStrings).containsExactly(array("FRUIT = apple", "RANK = 1"),
-			array("FRUIT = banana", "RANK = 2"));
 	}
 
 	@Test
@@ -387,8 +408,12 @@ private Stream<Object[]> provideArguments(CsvSource annotation) {
 	}
 
 	@SuppressWarnings("unchecked")
-	private static <T> T[] array(T... elements) {
+	private static <T> @Nullable T[] array(@Nullable T... elements) {
 		return elements;
 	}
 
+	static ThrowingConsumer<Throwable> isCsvParseException() {
+		return ex -> ex.getClass().getName().contains("de.siegmar.fastcsv.reader.CsvParseException");
+	}
+
 }
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/params/provider/CsvFileArgumentsProviderTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/params/provider/CsvFileArgumentsProviderTests.java
index 3a7269f4ee0f..ef7c13f4c330 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/params/provider/CsvFileArgumentsProviderTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/params/provider/CsvFileArgumentsProviderTests.java
@@ -13,6 +13,7 @@
 import static java.nio.charset.StandardCharsets.UTF_8;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.params.provider.CsvArgumentsProviderTests.isCsvParseException;
 import static org.junit.jupiter.params.provider.MockCsvAnnotationBuilder.csvFileSource;
 import static org.mockito.Mockito.doCallRealMethod;
 import static org.mockito.Mockito.mock;
@@ -26,6 +27,7 @@
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.stream.Stream;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExtensionContext;
 import org.junit.jupiter.api.io.TempDir;
@@ -39,11 +41,26 @@
  */
 class CsvFileArgumentsProviderTests {
 
+	@Test
+	void providesArgumentsForEachSupportedLineSeparator() {
+		var annotation = csvFileSource()//
+				.resources("test.csv")//
+				.build();
+
+		var arguments = provideArguments(annotation, "foo, bar \n baz, qux \r quux, corge \r\n grault, garply");
+
+		assertThat(arguments).containsExactly(//
+			array("foo", "bar"), //
+			array("baz", "qux"), //
+			array("quux", "corge"), //
+			array("grault", "garply")//
+		);
+	}
+
 	@Test
 	void providesArgumentsForNewlineAndComma() {
 		var annotation = csvFileSource()//
 				.resources("test.csv")//
-				.lineSeparator("\n")//
 				.delimiter(',')//
 				.build();
 
@@ -56,7 +73,6 @@ void providesArgumentsForNewlineAndComma() {
 	void providesArgumentsForCarriageReturnAndSemicolon() {
 		var annotation = csvFileSource()//
 				.resources("test.csv")//
-				.lineSeparator("\r")//
 				.delimiter(';')//
 				.build();
 
@@ -378,14 +394,13 @@ void throwsExceptionForInvalidCsvFormat() {
 
 		assertThat(exception)//
 				.hasMessageStartingWith("Failed to parse CSV input configured via Mock for CsvFileSource")//
-				.hasRootCauseInstanceOf(ArrayIndexOutOfBoundsException.class);
+				.rootCause().satisfies(isCsvParseException());
 	}
 
 	@Test
 	void emptyValueIsAnEmptyWithCustomNullValueString() {
 		var annotation = csvFileSource()//
 				.resources("test.csv")//
-				.lineSeparator("\n")//
 				.delimiter(',')//
 				.nullValues("NIL")//
 				.build();
@@ -482,7 +497,7 @@ void throwsExceptionForExceedsMaxCharsFileWithDefaultConfig(@TempDir Path tempDi
 
 		assertThat(exception)//
 				.hasMessageStartingWith("Failed to parse CSV input configured via Mock for CsvFileSource")//
-				.hasRootCauseInstanceOf(ArrayIndexOutOfBoundsException.class);
+				.rootCause().satisfies(isCsvParseException());
 	}
 
 	@Test
@@ -548,7 +563,7 @@ private Stream<Object[]> provideArguments(CsvFileArgumentsProvider provider, Csv
 	}
 
 	@SuppressWarnings("unchecked")
-	private static <T> T[] array(T... elements) {
+	private static <T> @Nullable T[] array(@Nullable T... elements) {
 		return elements;
 	}
 
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/params/provider/EnumArgumentsProviderTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/params/provider/EnumArgumentsProviderTests.java
index e15bc98e7308..02ba3d442a7b 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/params/provider/EnumArgumentsProviderTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/params/provider/EnumArgumentsProviderTests.java
@@ -212,8 +212,8 @@ private <E extends Enum<E>> Stream<Object[]> provideArguments(Class<E> enumClass
 		when(annotation.mode()).thenReturn(mode);
 		when(annotation.names()).thenReturn(names);
 		when(annotation.toString()).thenReturn(
-			String.format("@EnumSource(value=%s.class, from=%s, to=%s, mode=%s, names=%s)", enumClass.getSimpleName(),
-				from, to, mode, Arrays.toString(names)));
+			"@EnumSource(value=%s.class, from=%s, to=%s, mode=%s, names=%s)".formatted(enumClass.getSimpleName(), from,
+				to, mode, Arrays.toString(names)));
 
 		var provider = new EnumArgumentsProvider();
 		provider.accept(annotation);
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/params/provider/FieldArgumentsProviderTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/params/provider/FieldArgumentsProviderTests.java
index f8a9a9c6c299..9271b3a97141 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/params/provider/FieldArgumentsProviderTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/params/provider/FieldArgumentsProviderTests.java
@@ -28,6 +28,7 @@
 import java.util.stream.LongStream;
 import java.util.stream.Stream;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.TestInstance.Lifecycle;
@@ -519,6 +520,7 @@ void test() {
 
 		// --- Invalid ---------------------------------------------------------
 
+		@Nullable
 		static List<String> nullList = null;
 
 		static Object object = -1;
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/params/provider/MethodArgumentsProviderTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/params/provider/MethodArgumentsProviderTests.java
index da3a2994bb8e..1f64d9dbc047 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/params/provider/MethodArgumentsProviderTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/params/provider/MethodArgumentsProviderTests.java
@@ -29,6 +29,8 @@
 import java.util.stream.LongStream;
 import java.util.stream.Stream;
 
+import org.jspecify.annotations.NullUnmarked;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Test;
@@ -49,7 +51,7 @@
  */
 class MethodArgumentsProviderTests {
 
-	private MutableExtensionRegistry extensionRegistry;
+	private @Nullable MutableExtensionRegistry extensionRegistry;
 
 	@Test
 	void providesArgumentsUsingStream() {
@@ -729,15 +731,15 @@ private static Object[] array(Object... objects) {
 		return objects;
 	}
 
-	private Stream<Object[]> provideArguments(String... factoryMethodNames) {
+	private Stream<@Nullable Object[]> provideArguments(String... factoryMethodNames) {
 		return provideArguments(TestCase.class, false, factoryMethodNames);
 	}
 
-	private Stream<Object[]> provideArguments(Method testMethod, String factoryMethodName) {
+	private Stream<@Nullable Object[]> provideArguments(Method testMethod, String factoryMethodName) {
 		return provideArguments(TestCase.class, testMethod, false, factoryMethodName);
 	}
 
-	private Stream<Object[]> provideArguments(Class<?> testClass, boolean allowNonStaticMethod,
+	private Stream<@Nullable Object[]> provideArguments(Class<?> testClass, boolean allowNonStaticMethod,
 			String... factoryMethodNames) {
 
 		// Ensure we have a non-null test method, even if it's not a real test method.
@@ -746,8 +748,8 @@ private Stream<Object[]> provideArguments(Class<?> testClass, boolean allowNonSt
 		return provideArguments(testClass, testMethod, allowNonStaticMethod, factoryMethodNames);
 	}
 
-	private Stream<Object[]> provideArguments(Class<?> testClass, Method testMethod, boolean allowNonStaticMethod,
-			String... factoryMethodNames) {
+	private Stream<@Nullable Object[]> provideArguments(Class<?> testClass, Method testMethod,
+			boolean allowNonStaticMethod, String... factoryMethodNames) {
 
 		var methodSource = mock(MethodSource.class);
 
@@ -756,8 +758,7 @@ private Stream<Object[]> provideArguments(Class<?> testClass, Method testMethod,
 		var extensionContext = mock(ExtensionContext.class);
 		when(extensionContext.getTestClass()).thenReturn(Optional.of(testClass));
 		when(extensionContext.getTestMethod()).thenReturn(Optional.of(testMethod));
-		when(extensionContext.getExecutableInvoker()).thenReturn(
-			new DefaultExecutableInvoker(extensionContext, extensionRegistry));
+		when(extensionContext.getExecutableInvoker()).thenReturn(getExecutableInvoker(extensionContext));
 
 		doCallRealMethod().when(extensionContext).getRequiredTestClass();
 
@@ -772,6 +773,11 @@ private Stream<Object[]> provideArguments(Class<?> testClass, Method testMethod,
 		return provider.provideArguments(mock(), extensionContext).map(Arguments::get);
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
+	private DefaultExecutableInvoker getExecutableInvoker(ExtensionContext extensionContext) {
+		return new DefaultExecutableInvoker(extensionContext, extensionRegistry);
+	}
+
 	// -------------------------------------------------------------------------
 
 	static class DefaultFactoryMethodNameTestCase {
@@ -803,6 +809,7 @@ static Stream<Integer> test(int num) {
 		}
 	}
 
+	@NullUnmarked
 	static class MultipleInvalidDefaultFactoriesTestCase {
 
 		// Test
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/params/provider/MockCsvAnnotationBuilder.java b/jupiter-tests/src/test/java/org/junit/jupiter/params/provider/MockCsvAnnotationBuilder.java
index 22434b0f243f..7386fed94278 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/params/provider/MockCsvAnnotationBuilder.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/params/provider/MockCsvAnnotationBuilder.java
@@ -144,7 +144,6 @@ static class MockCsvFileSourceBuilder extends MockCsvAnnotationBuilder<CsvFileSo
 		private String[] resources = {};
 		private String[] files = {};
 		private String encoding = "UTF-8";
-		private String lineSeparator = "\n";
 		private int numLinesToSkip = 0;
 
 		private MockCsvFileSourceBuilder() {
@@ -171,11 +170,6 @@ MockCsvFileSourceBuilder encoding(String encoding) {
 			return this;
 		}
 
-		MockCsvFileSourceBuilder lineSeparator(String lineSeparator) {
-			this.lineSeparator = lineSeparator;
-			return this;
-		}
-
 		MockCsvFileSourceBuilder numLinesToSkip(int numLinesToSkip) {
 			this.numLinesToSkip = numLinesToSkip;
 			return this;
@@ -199,7 +193,6 @@ CsvFileSource build() {
 			when(annotation.resources()).thenReturn(this.resources);
 			when(annotation.files()).thenReturn(this.files);
 			when(annotation.encoding()).thenReturn(this.encoding);
-			when(annotation.lineSeparator()).thenReturn(this.lineSeparator);
 			when(annotation.numLinesToSkip()).thenReturn(this.numLinesToSkip);
 
 			return annotation;
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/params/support/AnnotationConsumerInitializerTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/params/support/AnnotationConsumerInitializerTests.java
index 16306451bca4..0cbcceb950b5 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/params/support/AnnotationConsumerInitializerTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/params/support/AnnotationConsumerInitializerTests.java
@@ -23,17 +23,22 @@
 import java.time.LocalDate;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.function.Supplier;
 import java.util.stream.Stream;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Named;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExtensionContext;
 import org.junit.jupiter.api.extension.ParameterContext;
+import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.converter.AnnotationBasedArgumentConverter;
 import org.junit.jupiter.params.converter.JavaTimeConversionPattern;
 import org.junit.jupiter.params.provider.AnnotationBasedArgumentsProvider;
 import org.junit.jupiter.params.provider.Arguments;
 import org.junit.jupiter.params.provider.CsvSource;
+import org.junit.jupiter.params.provider.FieldSource;
 import org.junit.platform.commons.JUnitException;
 
 @DisplayName("AnnotationConsumerInitializer")
@@ -51,10 +56,11 @@ void shouldInitializeAnnotationConsumer() throws NoSuchMethodException {
 					source -> assertThat(source.value()).containsExactly("a", "b"));
 	}
 
-	@Test
+	@ParameterizedTest
+	@FieldSource("argumentsProviders")
 	@DisplayName("should initialize annotation-based ArgumentsProvider")
-	void shouldInitializeAnnotationBasedArgumentsProvider() throws NoSuchMethodException {
-		var instance = new SomeAnnotationBasedArgumentsProvider();
+	void shouldInitializeAnnotationBasedArgumentsProvider(AbstractAnnotationBasedArgumentsProvider instance)
+			throws NoSuchMethodException {
 		var method = SubjectClass.class.getDeclaredMethod("foo");
 		var initialisedAnnotationConsumer = initialize(method, instance);
 
@@ -101,9 +107,11 @@ void shouldThrowExceptionWhenParameterIsNotAnnotated() throws NoSuchMethodExcept
 		assertThatThrownBy(() -> initialize(parameter, instance)).isInstanceOf(JUnitException.class);
 	}
 
-	@Test
-	void shouldInitializeForEachAnnotations() throws NoSuchMethodException {
-		var instance = spy(new SomeAnnotationBasedArgumentsProvider());
+	@ParameterizedTest
+	@FieldSource("argumentsProviders")
+	void shouldInitializeForEachAnnotations(AbstractAnnotationBasedArgumentsProvider provider)
+			throws NoSuchMethodException {
+		var instance = spy(provider);
 		var method = SubjectClass.class.getDeclaredMethod("repeatableAnnotation", String.class);
 
 		initialize(method, instance);
@@ -111,10 +119,20 @@ void shouldInitializeForEachAnnotations() throws NoSuchMethodException {
 		verify(instance, times(2)).accept(any(CsvSource.class));
 	}
 
-	private static class SomeAnnotationBasedArgumentsProvider extends AnnotationBasedArgumentsProvider<CsvSource> {
+	static Supplier<List<Named<? extends AbstractAnnotationBasedArgumentsProvider>>> argumentsProviders = () -> List.of( //
+		Named.of("current", new SomeAnnotationBasedArgumentsProvider()), //
+		Named.of("deprecated", new DeprecatedAnnotationBasedArgumentsProvider()) //
+	);
+
+	private static abstract class AbstractAnnotationBasedArgumentsProvider
+			extends AnnotationBasedArgumentsProvider<CsvSource> {
 
 		List<CsvSource> annotations = new ArrayList<>();
 
+	}
+
+	private static class SomeAnnotationBasedArgumentsProvider extends AbstractAnnotationBasedArgumentsProvider {
+
 		@Override
 		protected Stream<? extends Arguments> provideArguments(ParameterDeclarations parameters,
 				ExtensionContext context, CsvSource annotation) {
@@ -123,13 +141,25 @@ protected Stream<? extends Arguments> provideArguments(ParameterDeclarations par
 		}
 	}
 
+	private static class DeprecatedAnnotationBasedArgumentsProvider extends AbstractAnnotationBasedArgumentsProvider {
+
+		@Override
+		@SuppressWarnings("deprecation")
+		protected Stream<? extends Arguments> provideArguments(ExtensionContext context, CsvSource annotation) {
+			annotations.add(annotation);
+			return Stream.empty();
+		}
+	}
+
 	private static class SomeAnnotationBasedArgumentConverter
 			extends AnnotationBasedArgumentConverter<JavaTimeConversionPattern> {
 
+		@Nullable
 		JavaTimeConversionPattern annotation;
 
 		@Override
-		protected Object convert(Object source, Class<?> targetType, JavaTimeConversionPattern annotation) {
+		protected @Nullable Object convert(@Nullable Object source, Class<?> targetType,
+				JavaTimeConversionPattern annotation) {
 			this.annotation = annotation;
 			return null;
 		}
@@ -137,6 +167,7 @@ protected Object convert(Object source, Class<?> targetType, JavaTimeConversionP
 
 	private static class SomeAnnotationConsumer implements AnnotationConsumer<CsvSource> {
 
+		@Nullable
 		CsvSource annotation;
 
 		@Override
diff --git a/jupiter-tests/src/test/java/org/junit/jupiter/params/support/ParameterInfoIntegrationTests.java b/jupiter-tests/src/test/java/org/junit/jupiter/params/support/ParameterInfoIntegrationTests.java
index 2b62f8d691e3..c1990a02aa4e 100644
--- a/jupiter-tests/src/test/java/org/junit/jupiter/params/support/ParameterInfoIntegrationTests.java
+++ b/jupiter-tests/src/test/java/org/junit/jupiter/params/support/ParameterInfoIntegrationTests.java
@@ -11,6 +11,7 @@
 package org.junit.jupiter.params.support;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertNull;
 
 import org.junit.jupiter.api.Nested;
@@ -34,7 +35,7 @@ class ParameterInfoIntegrationTests extends AbstractJupiterTestEngineTests {
 	void storesParameterInfoInExtensionContextStoreOnDifferentLevels() {
 		var results = executeTestsForClass(TestCase.class);
 
-		results.allEvents().assertStatistics(stats -> stats.started(7).succeeded(7));
+		results.allEvents().debug().assertStatistics(stats -> stats.started(7).succeeded(7));
 	}
 
 	@ParameterizedClass
@@ -102,6 +103,7 @@ public void beforeEach(ExtensionContext parameterizedTestInvocationContext) {
 
 		private static void assertParameterInfo(ExtensionContext context, String parameterName, int argumentValue) {
 			var parameterInfo = ParameterInfo.get(context);
+			assertNotNull(parameterInfo);
 			var declaration = parameterInfo.getDeclarations().get(0).orElseThrow();
 			assertEquals(parameterName, declaration.getParameterName().orElseThrow());
 			assertEquals(int.class, declaration.getParameterType());
diff --git a/jupiter-tests/src/test/kotlin/org/junit/jupiter/api/KotlinAssertTimeoutAssertionsTests.kt b/jupiter-tests/src/test/kotlin/org/junit/jupiter/api/KotlinAssertTimeoutAssertionsTests.kt
index a10d58420c8d..54b01a0ec3a4 100644
--- a/jupiter-tests/src/test/kotlin/org/junit/jupiter/api/KotlinAssertTimeoutAssertionsTests.kt
+++ b/jupiter-tests/src/test/kotlin/org/junit/jupiter/api/KotlinAssertTimeoutAssertionsTests.kt
@@ -156,17 +156,18 @@ internal class KotlinAssertTimeoutAssertionsTests {
     }
 
     @Test
-    fun `assertTimeout with value initialization in lambda`() {
+    fun `assertTimeout with value assignment in lambda`() {
         val value: Int
 
-        assertTimeout(ofMillis(500)) { value = 10 }
-
-        assertEquals(10, value)
+        assertTimeout(ofMillis(500)) {
+            value = 10 // Val can be assigned in the message supplier lambda.
+            assertEquals(10, value)
+        }
     }
 
     @Test
-    fun `assertTimeout with message and value initialization in lambda`() {
-        val value: Int
+    fun `assertTimeout with message and value assignment in lambda`() {
+        var value = 0
 
         assertTimeout(ofMillis(500), "message") { value = 10 }
 
@@ -174,8 +175,8 @@ internal class KotlinAssertTimeoutAssertionsTests {
     }
 
     @Test
-    fun `assertTimeout with message supplier and value initialization in lambda`() {
-        val value: Int
+    fun `assertTimeout with message supplier and value assignment in lambda`() {
+        var value = 0
 
         @Suppress("ASSIGNED_BUT_NEVER_ACCESSED_VARIABLE")
         val valueInMessageSupplier: Int
diff --git a/jupiter-tests/src/test/kotlin/org/junit/jupiter/api/KotlinFailAssertionsTests.kt b/jupiter-tests/src/test/kotlin/org/junit/jupiter/api/KotlinFailAssertionsTests.kt
index d0e026669a22..c5da45e59173 100644
--- a/jupiter-tests/src/test/kotlin/org/junit/jupiter/api/KotlinFailAssertionsTests.kt
+++ b/jupiter-tests/src/test/kotlin/org/junit/jupiter/api/KotlinFailAssertionsTests.kt
@@ -65,7 +65,7 @@ class KotlinFailAssertionsTests {
             }
         assertMessageEquals(ex, message)
         val cause = ex.cause
-        assertMessageContains(cause, throwableCause)
+        assertMessageContains(cause!!, throwableCause)
     }
 
     @Test
@@ -77,7 +77,7 @@ class KotlinFailAssertionsTests {
             }
         assertEmptyMessage(ex)
         val cause = ex.cause
-        assertMessageContains(cause, throwableCause)
+        assertMessageContains(cause!!, throwableCause)
     }
 
     @Test
@@ -102,7 +102,7 @@ class KotlinFailAssertionsTests {
             }
         assertEmptyMessage(ex)
         val cause = ex.cause
-        assertMessageContains(cause, throwableCause)
+        assertMessageContains(cause!!, throwableCause)
     }
 
     @Test
diff --git a/jupiter-tests/src/test/kotlin/org/junit/jupiter/api/KotlinSuspendFunctionsTests.kt b/jupiter-tests/src/test/kotlin/org/junit/jupiter/api/KotlinSuspendFunctionsTests.kt
new file mode 100644
index 000000000000..c5b0c742c186
--- /dev/null
+++ b/jupiter-tests/src/test/kotlin/org/junit/jupiter/api/KotlinSuspendFunctionsTests.kt
@@ -0,0 +1,190 @@
+/*
+ * Copyright 2015-2025 the original author or authors.
+ *
+ * All rights reserved. This program and the accompanying materials are
+ * made available under the terms of the Eclipse Public License v2.0 which
+ * accompanies this distribution and is available at
+ *
+ * https://www.eclipse.org/legal/epl-v20.html
+ */
+package org.junit.jupiter.api
+
+import kotlinx.coroutines.runBlocking
+import org.assertj.core.api.Assertions.assertThat
+import org.junit.jupiter.api.DynamicTest.dynamicTest
+import org.junit.jupiter.api.TestInstance.Lifecycle.PER_CLASS
+import org.junit.jupiter.engine.AbstractJupiterTestEngineTests
+import org.junit.jupiter.params.AfterParameterizedClassInvocation
+import org.junit.jupiter.params.BeforeParameterizedClassInvocation
+import org.junit.jupiter.params.Parameter
+import org.junit.jupiter.params.ParameterizedClass
+import org.junit.jupiter.params.ParameterizedTest
+import org.junit.jupiter.params.provider.ValueSource
+import org.junit.platform.engine.reporting.ReportEntry
+import org.junit.platform.testkit.engine.EngineExecutionResults
+import java.util.stream.Stream
+
+class KotlinSuspendFunctionsTests : AbstractJupiterTestEngineTests() {
+    @Test
+    fun suspendingTestMethodsAreSupported() {
+        val results = executeTestsForClass(TestMethodTestCase::class)
+        assertAllTestsPassed(results, 1)
+        assertThat(getPublishedEvents(results)).containsExactly("test")
+    }
+
+    @Test
+    fun suspendingTestTemplateMethodsAreSupported() {
+        val results = executeTestsForClass(TestTemplateTestCase::class)
+        assertAllTestsPassed(results, 2)
+        assertThat(getPublishedEvents(results)).containsExactly("foo", "bar")
+    }
+
+    @Test
+    fun suspendingTestFactoryMethodsAreSupported() {
+        val results = executeTestsForClass(TestFactoryTestCase::class)
+        assertAllTestsPassed(results, 2)
+        assertThat(getPublishedEvents(results)).containsExactly("test", "foo", "bar")
+    }
+
+    @Test
+    fun suspendingLifecycleMethodsAreSupported() {
+        val results = executeTestsForClass(LifecycleMethodsTestCase::class)
+        assertAllTestsPassed(results, 1)
+        assertThat(getPublishedEvents(results)).containsExactly("beforeAll", "beforeEach", "test", "afterEach", "afterAll")
+    }
+
+    @Test
+    fun suspendingParameterizedLifecycleMethodsAreSupported() {
+        val results = executeTestsForClass(ParameterizedLifecycleMethodsTestCase::class)
+        assertAllTestsPassed(results, 2)
+        assertThat(
+            getPublishedEvents(results)
+        ).containsExactly("beforeInvocation[1]", "test[1]", "afterInvocation[1]", "beforeInvocation[2]", "test[2]", "afterInvocation[2]")
+    }
+
+    private fun assertAllTestsPassed(
+        results: EngineExecutionResults,
+        numTests: Long
+    ) {
+        results.testEvents().assertStatistics {
+            it.started(numTests).succeeded(numTests)
+        }
+    }
+
+    private fun getPublishedEvents(results: EngineExecutionResults) =
+        results
+            .allEvents()
+            .reportingEntryPublished() //
+            .map { it.getRequiredPayload(ReportEntry::class.java) } //
+            .map(ReportEntry::getKeyValuePairs)
+            .map { it["value"] }
+
+    @Suppress("JUnitMalformedDeclaration")
+    class TestMethodTestCase {
+        @Test
+        suspend fun test(reporter: TestReporter) {
+            suspendingPublish(reporter, "test")
+        }
+    }
+
+    @Suppress("JUnitMalformedDeclaration")
+    class TestTemplateTestCase {
+        @ParameterizedTest
+        @ValueSource(strings = ["foo", "bar"])
+        suspend fun test(
+            message: String,
+            reporter: TestReporter
+        ) {
+            suspendingPublish(reporter, message)
+        }
+    }
+
+    class TestFactoryTestCase {
+        @TestFactory
+        suspend fun test(reporter: TestReporter): Stream<DynamicTest> {
+            suspendingPublish(reporter, "test")
+            return Stream.of("foo", "bar").map {
+                dynamicTest(it) {
+                    runBlocking {
+                        suspendingPublish(reporter, it)
+                    }
+                }
+            }
+        }
+    }
+
+    @Suppress("JUnitMalformedDeclaration")
+    @TestInstance(PER_CLASS)
+    class LifecycleMethodsTestCase {
+        @BeforeAll
+        suspend fun beforeAll(reporter: TestReporter) {
+            suspendingPublish(reporter, "beforeAll")
+        }
+
+        @BeforeEach
+        suspend fun beforeEach(reporter: TestReporter) {
+            suspendingPublish(reporter, "beforeEach")
+        }
+
+        @Test
+        suspend fun test(reporter: TestReporter) {
+            suspendingPublish(reporter, "test")
+        }
+
+        @AfterEach
+        suspend fun afterEach(reporter: TestReporter) {
+            suspendingPublish(reporter, "afterEach")
+        }
+
+        @AfterAll
+        suspend fun afterAll(reporter: TestReporter) {
+            suspendingPublish(reporter, "afterAll")
+        }
+    }
+
+    @Suppress("JUnitMalformedDeclaration", "RedundantSuspendModifier")
+    @ParameterizedClass
+    @ValueSource(ints = [1, 2])
+    @TestInstance(PER_CLASS)
+    class ParameterizedLifecycleMethodsTestCase {
+        @BeforeParameterizedClassInvocation
+        suspend fun beforeInvocation() {}
+
+        @BeforeParameterizedClassInvocation
+        suspend fun beforeInvocation(
+            parameter: Int,
+            reporter: TestReporter
+        ) {
+            suspendingPublish(reporter, "beforeInvocation[$parameter]")
+        }
+
+        @AfterParameterizedClassInvocation
+        suspend fun afterInvocation() {}
+
+        @AfterParameterizedClassInvocation
+        suspend fun afterInvocation(
+            parameter: Int,
+            reporter: TestReporter
+        ) {
+            suspendingPublish(reporter, "afterInvocation[$parameter]")
+        }
+
+        @Parameter
+        var parameter: Int = 0
+
+        @Test
+        suspend fun test(reporter: TestReporter) {
+            suspendingPublish(reporter, "test[$parameter]")
+        }
+    }
+
+    @Suppress("RedundantSuspendModifier")
+    companion object {
+        suspend fun suspendingPublish(
+            reporter: TestReporter,
+            message: String
+        ) {
+            reporter.publishEntry(message)
+        }
+    }
+}
diff --git a/jupiter-tests/src/test/kotlin/org/junit/jupiter/params/aggregator/DisplayNameTests.kt b/jupiter-tests/src/test/kotlin/org/junit/jupiter/params/aggregator/DisplayNameTests.kt
index 6a1f91cbb19f..c43a26d46a8d 100644
--- a/jupiter-tests/src/test/kotlin/org/junit/jupiter/params/aggregator/DisplayNameTests.kt
+++ b/jupiter-tests/src/test/kotlin/org/junit/jupiter/params/aggregator/DisplayNameTests.kt
@@ -16,16 +16,16 @@ import org.junit.jupiter.api.TestInfo
 import org.junit.jupiter.params.ParameterizedTest
 import org.junit.jupiter.params.provider.MethodSource
 
-// https://github.com/junit-team/junit5/issues/1836
+// https://github.com/junit-team/junit-framework/issues/1836
 object DisplayNameTests {
     @JvmStatic
     fun data() =
         arrayOf(
-            arrayOf("A", 1),
-            arrayOf("B", 2),
-            arrayOf("C", 3),
-            arrayOf("", 4), // empty is okay
-            arrayOf(null, 5) // null was the problem
+            arrayOf<Any>("A", 1),
+            arrayOf<Any>("B", 2),
+            arrayOf<Any>("C", 3),
+            arrayOf<Any>("", 4), // empty is okay
+            arrayOf<Any?>(null, 5) // null was the problem
         )
 
     @ParameterizedTest
diff --git a/platform-tests/platform-tests.gradle.kts b/platform-tests/platform-tests.gradle.kts
index 38e1b9ed1e4e..604850053ece 100644
--- a/platform-tests/platform-tests.gradle.kts
+++ b/platform-tests/platform-tests.gradle.kts
@@ -2,9 +2,12 @@ import junitbuild.extensions.capitalized
 import junitbuild.extensions.dependencyProject
 import org.gradle.api.tasks.PathSensitivity.RELATIVE
 import org.gradle.internal.os.OperatingSystem
+import org.gradle.plugins.ide.eclipse.model.Classpath
+import org.gradle.plugins.ide.eclipse.model.SourceFolder
 
 plugins {
 	id("junitbuild.java-library-conventions")
+	id("junitbuild.java-nullability-conventions")
 	id("junitbuild.junit4-compatibility")
 	id("junitbuild.testing-conventions")
 	id("junitbuild.jmh-conventions")
@@ -33,13 +36,11 @@ dependencies {
 	testImplementation(projects.junitPlatformCommons)
 	testImplementation(projects.junitPlatformConsole)
 	testImplementation(projects.junitPlatformEngine)
-	testImplementation(projects.junitPlatformJfr)
 	testImplementation(projects.junitPlatformLauncher)
 	testImplementation(projects.junitPlatformSuiteCommons)
 	testImplementation(projects.junitPlatformSuiteEngine)
 
 	// --- Things we are testing with ---------------------------------------------
-	testImplementation(projects.junitPlatformRunner)
 	testImplementation(projects.junitPlatformTestkit)
 	testImplementation(testFixtures(projects.junitPlatformCommons))
 	testImplementation(testFixtures(projects.junitPlatformEngine))
@@ -132,7 +133,7 @@ tasks {
 		dependsOn(testWoodstox)
 	}
 	named<JavaCompile>(processStarter.compileJavaTaskName).configure {
-		options.release = javaLibrary.testJavaVersion.majorVersion.toInt()
+		options.release = javaLibrary.testJavaVersion.map { it.majorVersion.toInt() }
 	}
 	named<Checkstyle>("checkstyle${processStarter.name.capitalized()}").configure {
 		config = resources.text.fromFile(checkstyle.configDirectory.file("checkstyleMain.xml"))
@@ -143,6 +144,15 @@ eclipse {
 	classpath {
 		plusConfigurations.add(dependencyProject(projects.junitPlatformConsole).configurations["shadowedClasspath"])
 	}
+	classpath.file.whenMerged {
+		this as Classpath
+		entries.filterIsInstance<SourceFolder>().forEach {
+			if (it.path == "src/test/resources") {
+				// Exclude Foo.java and FooBar.java in the modules-2500 folder.
+				it.excludes.add("**/Foo*.java")
+			}
+		}
+	}
 }
 
 idea {
diff --git a/platform-tests/src/test/java/org/junit/platform/StackTracePruningTests.java b/platform-tests/src/test/java/org/junit/platform/StackTracePruningTests.java
index d5dbca29324e..5f7b97f88728 100644
--- a/platform-tests/src/test/java/org/junit/platform/StackTracePruningTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/StackTracePruningTests.java
@@ -182,7 +182,7 @@ private static Throwable getThrowable(EngineExecutionResults results) {
 	private static void assertStackTraceMatch(List<StackTraceElement> stackTrace, String expectedLines) {
 		List<String> stackStraceAsLines = stackTrace.stream() //
 				.map(StackTraceElement::toString) //
-				.collect(Collectors.toList());
+				.toList();
 		assertLinesMatch(expectedLines.lines().toList(), stackStraceAsLines);
 	}
 
diff --git a/platform-tests/src/test/java/org/junit/platform/commons/function/TryTests.java b/platform-tests/src/test/java/org/junit/platform/commons/function/TryTests.java
index 4ad2dce22055..d7901d7aac7d 100644
--- a/platform-tests/src/test/java/org/junit/platform/commons/function/TryTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/commons/function/TryTests.java
@@ -27,7 +27,9 @@ void successfulTriesCanBeTransformed() throws Exception {
 		var success = Try.success("foo");
 
 		assertThat(success.get()).isEqualTo("foo");
+		assertThat(success.getNonNull()).isEqualTo("foo");
 		assertThat(success.getOrThrow(RuntimeException::new)).isEqualTo("foo");
+		assertThat(success.getNonNullOrThrow(RuntimeException::new)).isEqualTo("foo");
 		assertThat(success.toOptional()).contains("foo");
 
 		assertThat(success.andThen(v -> {
@@ -70,11 +72,14 @@ void failedTriesCanBeTransformed() throws Exception {
 		assertThat(exception.get()).isSameAs(cause);
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void successfulTriesCanStoreNull() throws Exception {
 		var success = Try.success(null);
 		assertThat(success.get()).isNull();
+		assertThrows(JUnitException.class, success::getNonNull);
 		assertThat(success.getOrThrow(RuntimeException::new)).isNull();
+		assertThrows(RuntimeException.class, () -> success.getNonNullOrThrow(RuntimeException::new));
 		assertThat(success.toOptional()).isEmpty();
 	}
 
@@ -96,6 +101,7 @@ void triesWithSameContentAreEqual() {
 		assertThat(failure).isEqualTo(Try.failure(cause));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void methodPreconditionsAreChecked() {
 		assertThrows(JUnitException.class, () -> Try.call(null));
diff --git a/platform-tests/src/test/java/org/junit/platform/commons/support/AnnotationSupportTests.java b/platform-tests/src/test/java/org/junit/platform/commons/support/AnnotationSupportTests.java
index b882977606a1..67c36c8a7c12 100644
--- a/platform-tests/src/test/java/org/junit/platform/commons/support/AnnotationSupportTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/commons/support/AnnotationSupportTests.java
@@ -23,6 +23,7 @@
 import java.util.List;
 import java.util.Optional;
 
+import org.jspecify.annotations.NullUnmarked;
 import org.junit.jupiter.api.Tag;
 import org.junit.jupiter.api.Test;
 import org.junit.platform.commons.PreconditionViolationException;
@@ -34,6 +35,7 @@
  */
 class AnnotationSupportTests {
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void isAnnotatedPreconditions() {
 		var optional = Optional.of(Probe.class);
@@ -57,6 +59,7 @@ void isAnnotatedDelegates() {
 			AnnotationSupport.isAnnotated(element, Override.class));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void findAnnotationOnElementPreconditions() {
 		var optional = Optional.of(Probe.class);
@@ -81,7 +84,7 @@ void findAnnotationOnElementDelegates() {
 			AnnotationSupport.findAnnotation(element, Override.class));
 	}
 
-	@SuppressWarnings("deprecation")
+	@SuppressWarnings({ "deprecation", "DataFlowIssue", "NullAway" })
 	@Test
 	void findAnnotationOnClassWithSearchModePreconditions() {
 		assertPreconditionViolationException("annotationType",
@@ -90,6 +93,7 @@ void findAnnotationOnClassWithSearchModePreconditions() {
 			() -> AnnotationSupport.findAnnotation(Probe.class, Override.class, (SearchOption) null));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void findAnnotationOnClassWithEnclosingInstanceTypesPreconditions() {
 		assertPreconditionViolationException("enclosingInstanceTypes",
@@ -120,6 +124,7 @@ void findAnnotationOnClassWithSearchModeDelegates() {
 			AnnotationSupport.findAnnotation(clazz, Override.class, SearchOption.INCLUDE_ENCLOSING_CLASSES));
 	}
 
+	@NullUnmarked
 	@Test
 	void findAnnotationOnClassWithEnclosingInstanceTypes() {
 		assertThat(AnnotationSupport.findAnnotation(Probe.class, Tag.class, List.of())) //
@@ -130,6 +135,7 @@ void findAnnotationOnClassWithEnclosingInstanceTypes() {
 				.contains(Probe.class.getDeclaredAnnotation(Tag.class));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void findPublicAnnotatedFieldsPreconditions() {
 		assertPreconditionViolationException("Class",
@@ -148,6 +154,7 @@ void findPublicAnnotatedFieldsDelegates() {
 			AnnotationSupport.findPublicAnnotatedFields(Probe.class, Throwable.class, Override.class));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void findAnnotatedMethodsPreconditions() {
 		assertPreconditionViolationException("Class",
@@ -192,6 +199,7 @@ void findRepeatableAnnotationsDelegates() throws Throwable {
 		assertEquals(expected.toString(), actual.toString(), "expected equal exception toString representation");
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void findRepeatableAnnotationsPreconditions() {
 		assertPreconditionViolationException("annotationType",
@@ -217,6 +225,7 @@ void findAnnotatedFieldsDelegates() {
 				HierarchyTraversalMode.TOP_DOWN));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void findAnnotatedFieldsPreconditions() {
 		assertPreconditionViolationException("Class",
@@ -268,6 +277,7 @@ void findAnnotatedFieldValuesForStaticFieldsByType() {
 				.containsExactlyInAnyOrder("s1", "s2");
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void findAnnotatedFieldValuesPreconditions() {
 		assertPreconditionViolationException("instance",
diff --git a/platform-tests/src/test/java/org/junit/platform/commons/support/ClassSupportTests.java b/platform-tests/src/test/java/org/junit/platform/commons/support/ClassSupportTests.java
index e2b972348253..98e90a516900 100644
--- a/platform-tests/src/test/java/org/junit/platform/commons/support/ClassSupportTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/commons/support/ClassSupportTests.java
@@ -24,6 +24,7 @@
  */
 class ClassSupportTests {
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void nullSafeToStringPreconditions() {
 		Function<? super Class<?>, ? extends String> mapper = null;
diff --git a/platform-tests/src/test/java/org/junit/platform/commons/support/ModifierSupportTests.java b/platform-tests/src/test/java/org/junit/platform/commons/support/ModifierSupportTests.java
index 18332317aa51..bf9957b9a2d6 100644
--- a/platform-tests/src/test/java/org/junit/platform/commons/support/ModifierSupportTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/commons/support/ModifierSupportTests.java
@@ -34,6 +34,7 @@
  */
 class ModifierSupportTests {
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void isPublicPreconditions() {
 		assertPreconditionViolationException("Class", () -> ModifierSupport.isPublic((Class<?>) null));
@@ -51,6 +52,7 @@ void isPublicDelegates(Method method) {
 		assertEquals(ReflectionUtils.isPublic(method), ModifierSupport.isPublic(method));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void isPrivatePreconditions() {
 		assertPreconditionViolationException("Class", () -> ModifierSupport.isPrivate((Class<?>) null));
@@ -68,6 +70,7 @@ void isPrivateDelegates(Method method) {
 		assertEquals(ReflectionUtils.isPrivate(method), ModifierSupport.isPrivate(method));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void isNotPrivatePreconditions() {
 		assertPreconditionViolationException("Class", () -> ModifierSupport.isNotPrivate((Class<?>) null));
@@ -85,6 +88,7 @@ void isNotPrivateDelegates(Method method) {
 		assertEquals(ReflectionUtils.isNotPrivate(method), ModifierSupport.isNotPrivate(method));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void isAbstractPreconditions() {
 		assertPreconditionViolationException("Class", () -> ModifierSupport.isAbstract((Class<?>) null));
@@ -102,6 +106,7 @@ void isAbstractDelegates(Method method) {
 		assertEquals(ReflectionUtils.isAbstract(method), ModifierSupport.isAbstract(method));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void isNotAbstractPreconditions() {
 		assertPreconditionViolationException("Class", () -> ModifierSupport.isNotAbstract((Class<?>) null));
@@ -119,6 +124,7 @@ void isNotAbstractDelegates(Method method) {
 		assertEquals(ReflectionUtils.isNotAbstract(method), ModifierSupport.isNotAbstract(method));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void isStaticPreconditions() {
 		assertPreconditionViolationException("Class", () -> ModifierSupport.isStatic((Class<?>) null));
@@ -136,6 +142,7 @@ void isStaticDelegates(Method method) {
 		assertEquals(ReflectionUtils.isStatic(method), ModifierSupport.isStatic(method));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void isNotStaticPreconditions() {
 		assertPreconditionViolationException("Class", () -> ModifierSupport.isNotStatic((Class<?>) null));
@@ -153,6 +160,7 @@ void isNotStaticDelegates(Method method) {
 		assertEquals(ReflectionUtils.isNotStatic(method), ModifierSupport.isNotStatic(method));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void isFinalPreconditions() {
 		assertPreconditionViolationException("Class", () -> ModifierSupport.isFinal((Class<?>) null));
@@ -170,6 +178,7 @@ void isFinalDelegates(Method method) {
 		assertEquals(ReflectionUtils.isFinal(method), ModifierSupport.isFinal(method));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void isNotFinalPreconditions() {
 		assertPreconditionViolationException("Class", () -> ModifierSupport.isNotFinal((Class<?>) null));
diff --git a/platform-tests/src/test/java/org/junit/platform/commons/support/ReflectionSupportTests.java b/platform-tests/src/test/java/org/junit/platform/commons/support/ReflectionSupportTests.java
index 0d1d9fc05454..4aea6556942f 100644
--- a/platform-tests/src/test/java/org/junit/platform/commons/support/ReflectionSupportTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/commons/support/ReflectionSupportTests.java
@@ -46,21 +46,6 @@ class ReflectionSupportTests {
 	static final String staticField = "static";
 	final String instanceField = "instance";
 
-	@Test
-	@SuppressWarnings("deprecation")
-	void loadClassDelegates() {
-		assertEquals(ReflectionUtils.loadClass("-"), ReflectionSupport.loadClass("-"));
-		assertEquals(ReflectionUtils.loadClass("A"), ReflectionSupport.loadClass("A"));
-		assertEquals(ReflectionUtils.loadClass("java.nio.Bits"), ReflectionSupport.loadClass("java.nio.Bits"));
-	}
-
-	@Test
-	@SuppressWarnings("deprecation")
-	void loadClassPreconditions() {
-		assertPreconditionViolationExceptionForString("Class name", () -> ReflectionSupport.loadClass(null));
-		assertPreconditionViolationExceptionForString("Class name", () -> ReflectionSupport.loadClass(""));
-	}
-
 	@Test
 	void tryToLoadClassDelegates() {
 		assertEquals(ReflectionUtils.tryToLoadClass("-").toOptional(),
@@ -71,6 +56,7 @@ void tryToLoadClassDelegates() {
 			ReflectionSupport.tryToLoadClass("java.nio.Bits"));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void tryToLoadClassPreconditions() {
 		assertPreconditionViolationExceptionForString("Class name", () -> ReflectionSupport.tryToLoadClass(null));
@@ -95,6 +81,7 @@ void tryToLoadClassWithExplicitClassLoaderDelegates() {
 	/**
 	 * @since 1.10
 	 */
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void tryToLoadClassWithExplicitClassLoaderPreconditions() {
 		var cl = getClass().getClassLoader();
@@ -123,6 +110,7 @@ List<DynamicTest> findAllClassesInClasspathRootDelegates() throws Throwable {
 	/**
 	 * @since 1.12
 	 */
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void tryToGetResourcesPreconditions() {
 		assertPreconditionViolationExceptionForString("Resource name", () -> ReflectionSupport.tryToGetResources(null));
@@ -145,6 +133,7 @@ void tryToGetResources() {
 			ReflectionSupport.tryToGetResources("default-package.resource", getDefaultClassLoader()).toOptional());
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void findAllClassesInClasspathRootPreconditions() {
 		var path = Path.of(".").toUri();
@@ -178,6 +167,7 @@ List<DynamicTest> findAllResourcesInClasspathRootDelegates() throws Throwable {
 	/**
 	 * @since 1.11
 	 */
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void findAllResourcesInClasspathRootPreconditions() {
 		var path = Path.of(".").toUri();
@@ -209,6 +199,7 @@ List<DynamicTest> streamAllResourcesInClasspathRootDelegates() throws Throwable
 	/**
 	 * @since 1.11
 	 */
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void streamAllResourcesInClasspathRootPreconditions() {
 		var path = Path.of(".").toUri();
@@ -225,6 +216,7 @@ void findAllClassesInPackageDelegates() {
 			ReflectionSupport.findAllClassesInPackage("org.junit", allTypes, allNames));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void findAllClassesInPackagePreconditions() {
 		assertPreconditionViolationExceptionForString("basePackageName",
@@ -249,6 +241,7 @@ void findAllResourcesInPackageDelegates() {
 	/**
 	 * @since 1.11
 	 */
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void findAllResourcesInPackagePreconditions() {
 		assertPreconditionViolationExceptionForString("basePackageName",
@@ -271,6 +264,7 @@ void streamAllResourcesInPackageDelegates() {
 	/**
 	 * @since 1.11
 	 */
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void streamAllResourcesInPackagePreconditions() {
 		assertPreconditionViolationExceptionForString("basePackageName",
@@ -285,6 +279,7 @@ void findAllClassesInModuleDelegates() {
 			ReflectionSupport.findAllClassesInModule("org.junit.platform.commons", allTypes, allNames));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void findAllClassesInModulePreconditions() {
 		var exception = assertThrows(PreconditionViolationException.class,
@@ -308,6 +303,7 @@ void findAllResourcesInModuleDelegates() {
 	/**
 	 * @since 1.11
 	 */
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void findAllResourcesInModulePreconditions() {
 		var exception = assertThrows(PreconditionViolationException.class,
@@ -329,6 +325,7 @@ void streamAllResourcesInModuleDelegates() {
 	/**
 	 * @since 1.11
 	 */
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void streamAllResourcesInModulePreconditions() {
 		var exception = assertThrows(PreconditionViolationException.class,
@@ -344,6 +341,7 @@ void newInstanceDelegates() {
 			ReflectionSupport.newInstance(String.class, "foo"));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void newInstancePreconditions() {
 		assertPreconditionViolationException("Class", () -> ReflectionSupport.newInstance(null));
@@ -360,6 +358,7 @@ void invokeMethodDelegates() throws Exception {
 			ReflectionSupport.invokeMethod(method, null, "true"));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void invokeMethodPreconditions() throws Exception {
 		assertPreconditionViolationException("Method", () -> ReflectionSupport.invokeMethod(null, null, "true"));
@@ -383,6 +382,7 @@ void findFieldsDelegates() {
 			ReflectionSupport.findFields(ReflectionSupportTests.class, allFields, HierarchyTraversalMode.TOP_DOWN));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void findFieldsPreconditions() {
 		assertPreconditionViolationException("Class",
@@ -408,6 +408,7 @@ void tryToReadFieldValueDelegates() throws Exception {
 			ReflectionSupport.tryToReadFieldValue(instanceField, this));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void tryToReadFieldValuePreconditions() throws Exception {
 		assertPreconditionViolationException("Field", () -> ReflectionSupport.tryToReadFieldValue(null, this));
@@ -429,6 +430,7 @@ void findMethodDelegates() {
 			ReflectionSupport.findMethod(Boolean.class, "valueOf", String.class));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void findMethodPreconditions() {
 		assertPreconditionViolationException("Class",
@@ -462,6 +464,7 @@ void findMethodsDelegates() {
 			ReflectionSupport.findMethods(ReflectionSupportTests.class, allMethods, HierarchyTraversalMode.TOP_DOWN));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void findMethodsPreconditions() {
 		assertPreconditionViolationException("Class",
@@ -482,6 +485,7 @@ void findNestedClassesDelegates() {
 			ReflectionSupport.findNestedClasses(ClassWithNestedClasses.class, ReflectionUtils::isStatic));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void findNestedClassesPreconditions() {
 		assertPreconditionViolationException("Class",
diff --git a/platform-tests/src/test/java/org/junit/platform/commons/support/conversion/ConversionSupportTests.java b/platform-tests/src/test/java/org/junit/platform/commons/support/conversion/ConversionSupportTests.java
index 3a57fbe3b5a3..4b9cfaf1b4dd 100644
--- a/platform-tests/src/test/java/org/junit/platform/commons/support/conversion/ConversionSupportTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/commons/support/conversion/ConversionSupportTests.java
@@ -22,7 +22,6 @@
 import java.nio.charset.Charset;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.Path;
-import java.nio.file.Paths;
 import java.time.Duration;
 import java.time.Instant;
 import java.time.LocalDate;
@@ -42,6 +41,7 @@
 import java.util.UUID;
 import java.util.concurrent.TimeUnit;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.ValueSource;
@@ -202,9 +202,9 @@ void convertsStringToFile() {
 
 	@Test
 	void convertsStringToPath() {
-		assertConverts("path", Path.class, Paths.get("path"));
-		assertConverts("/path", Path.class, Paths.get("/path"));
-		assertConverts("/some/path", Path.class, Paths.get("/some/path"));
+		assertConverts("path", Path.class, Path.of("path"));
+		assertConverts("/path", Path.class, Path.of("/path"));
+		assertConverts("/some/path", Path.class, Path.of("/some/path"));
 	}
 
 	// --- java.lang -----------------------------------------------------------
@@ -229,12 +229,11 @@ void convertsStringToClassWithCustomTypeFromDifferentClassLoader() throws Except
 			var customType = testClassLoader.loadClass(customTypeName);
 			assertThat(customType.getClassLoader()).isSameAs(testClassLoader);
 
-			var declaringExecutable = ReflectionSupport.findMethod(customType, "foo").get();
+			var declaringExecutable = ReflectionSupport.findMethod(customType, "foo").orElseThrow();
 			assertThat(declaringExecutable.getDeclaringClass().getClassLoader()).isSameAs(testClassLoader);
 
 			var clazz = (Class<?>) convert(customTypeName, Class.class, classLoader(declaringExecutable));
-			assertThat(clazz).isNotEqualTo(Enigma.class);
-			assertThat(clazz).isEqualTo(customType);
+			assertThat(clazz).isNotNull().isNotEqualTo(Enigma.class).isEqualTo(customType);
 			assertThat(clazz.getClassLoader()).isSameAs(testClassLoader);
 		}
 	}
@@ -261,7 +260,7 @@ void convertsStringToURI() {
 
 	@Test
 	void convertsStringToURL() throws Exception {
-		assertConverts("https://junit.org/junit5", URL.class, URI.create("https://junit.org/junit5").toURL());
+		assertConverts("https://junit.org", URL.class, URI.create("https://junit.org").toURL());
 	}
 
 	// --- java.time -----------------------------------------------------------
@@ -309,7 +308,7 @@ void convertsStringToUUID() {
 
 	// -------------------------------------------------------------------------
 
-	private void assertConverts(String input, Class<?> targetClass, Object expectedOutput) {
+	private void assertConverts(@Nullable String input, Class<?> targetClass, @Nullable Object expectedOutput) {
 		var result = convert(input, targetClass);
 
 		assertThat(result) //
@@ -317,16 +316,16 @@ private void assertConverts(String input, Class<?> targetClass, Object expectedO
 				.isEqualTo(expectedOutput);
 	}
 
-	private Object convert(String input, Class<?> targetClass) {
+	private @Nullable Object convert(@Nullable String input, Class<?> targetClass) {
 		return convert(input, targetClass, classLoader());
 	}
 
-	private Object convert(String input, Class<?> targetClass, ClassLoader classLoader) {
+	private @Nullable Object convert(@Nullable String input, Class<?> targetClass, ClassLoader classLoader) {
 		return ConversionSupport.convert(input, targetClass, classLoader);
 	}
 
 	private static ClassLoader classLoader() {
-		Method declaringExecutable = ReflectionSupport.findMethod(ConversionSupportTests.class, "foo").get();
+		Method declaringExecutable = ReflectionSupport.findMethod(ConversionSupportTests.class, "foo").orElseThrow();
 		return classLoader(declaringExecutable);
 	}
 
diff --git a/platform-tests/src/test/java/org/junit/platform/commons/support/conversion/FallbackStringToObjectConverterTests.java b/platform-tests/src/test/java/org/junit/platform/commons/support/conversion/FallbackStringToObjectConverterTests.java
index cc2e8b38469d..5bfc428ec8d7 100644
--- a/platform-tests/src/test/java/org/junit/platform/commons/support/conversion/FallbackStringToObjectConverterTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/commons/support/conversion/FallbackStringToObjectConverterTests.java
@@ -158,13 +158,7 @@ Book nonStaticFactory(String title) {
 
 		@Override
 		public boolean equals(Object obj) {
-			if (this == obj) {
-				return true;
-			}
-			if (!(obj instanceof Book that)) {
-				return false;
-			}
-			return Objects.equals(this.title, that.title);
+			return (this == obj) || (obj instanceof Book that && Objects.equals(this.title, that.title));
 		}
 
 		@Override
@@ -184,13 +178,7 @@ static class Journal {
 
 		@Override
 		public boolean equals(Object obj) {
-			if (this == obj) {
-				return true;
-			}
-			if (!(obj instanceof Journal that)) {
-				return false;
-			}
-			return Objects.equals(this.title, that.title);
+			return (this == obj) || (obj instanceof Journal that && Objects.equals(this.title, that.title));
 		}
 
 		@Override
@@ -218,13 +206,7 @@ static Newspaper of(String title) {
 
 		@Override
 		public boolean equals(Object obj) {
-			if (this == obj) {
-				return true;
-			}
-			if (!(obj instanceof Newspaper that)) {
-				return false;
-			}
-			return Objects.equals(this.title, that.title);
+			return (this == obj) || (obj instanceof Newspaper that && Objects.equals(this.title, that.title));
 		}
 
 		@Override
diff --git a/platform-tests/src/test/java/org/junit/platform/commons/support/scanning/DefaultClasspathScannerTests.java b/platform-tests/src/test/java/org/junit/platform/commons/support/scanning/DefaultClasspathScannerTests.java
index 26349cb7ce6f..c2515661ffe0 100644
--- a/platform-tests/src/test/java/org/junit/platform/commons/support/scanning/DefaultClasspathScannerTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/commons/support/scanning/DefaultClasspathScannerTests.java
@@ -31,7 +31,6 @@
 import java.nio.file.FileSystems;
 import java.nio.file.Files;
 import java.nio.file.Path;
-import java.nio.file.Paths;
 import java.util.ArrayList;
 import java.util.Enumeration;
 import java.util.List;
@@ -41,9 +40,9 @@
 import java.util.logging.Level;
 import java.util.logging.LogRecord;
 import java.util.spi.ToolProvider;
-import java.util.stream.Collectors;
 
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.condition.DisabledIf;
 import org.junit.jupiter.api.fixtures.TrackLogRecords;
 import org.junit.jupiter.api.io.TempDir;
 import org.junit.platform.commons.PreconditionViolationException;
@@ -301,8 +300,8 @@ void scanForResourcesInPackage() {
 			uriOf("/org/junit/platform/commons/other-example.resource"));
 	}
 
-	@Test
-	// #2500
+	@Test // #2500
+	@DisabledIf("runningInEclipse")
 	void scanForClassesInPackageWithinModulesSharingNamePrefix(@TempDir Path temp) throws Exception {
 		var moduleSourcePath = Path.of(getClass().getResource("/modules-2500/").toURI()).toString();
 		run("javac", "--module", "foo,foo.bar", "--module-source-path", moduleSourcePath, "-d", temp.toString());
@@ -335,12 +334,12 @@ private void checkModules2500(ModuleFinder finder) {
 			ReflectionUtils::tryToLoadClass);
 		{
 			var classes = classpathScanner.scanForClassesInPackage("foo", allClasses);
-			var classNames = classes.stream().map(Class::getName).collect(Collectors.toList());
+			var classNames = classes.stream().map(Class::getName).toList();
 			assertThat(classNames).hasSize(2).contains("foo.Foo", "foo.bar.FooBar");
 		}
 		{
 			var classes = classpathScanner.scanForClassesInPackage("foo.bar", allClasses);
-			var classNames = classes.stream().map(Class::getName).collect(Collectors.toList());
+			var classNames = classes.stream().map(Class::getName).toList();
 			assertThat(classNames).hasSize(1).contains("foo.bar.FooBar");
 		}
 	}
@@ -442,12 +441,14 @@ void resourcesCanBeRead() throws IOException {
 		}
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void scanForClassesInPackageForNullBasePackage() {
 		assertThrows(PreconditionViolationException.class,
 			() -> classpathScanner.scanForClassesInPackage(null, allClasses));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void scanForResourcesInPackageForNullBasePackage() {
 		assertThrows(PreconditionViolationException.class,
@@ -466,6 +467,7 @@ void scanForResourcesInPackageForWhitespaceBasePackage() {
 			() -> classpathScanner.scanForResourcesInPackage("    ", allResources));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void scanForClassesInPackageForNullClassFilter() {
 		assertThrows(PreconditionViolationException.class,
@@ -549,6 +551,7 @@ void findAllClassesInClasspathRootWithFilter() throws Exception {
 		assertTrue(classes.contains(DefaultClasspathScannerTests.class));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void findAllClassesInClasspathRootForNullRoot() {
 		assertThrows(PreconditionViolationException.class,
@@ -558,9 +561,10 @@ void findAllClassesInClasspathRootForNullRoot() {
 	@Test
 	void findAllClassesInClasspathRootForNonExistingRoot() {
 		assertThrows(PreconditionViolationException.class,
-			() -> classpathScanner.scanForClassesInClasspathRoot(Paths.get("does_not_exist").toUri(), allClasses));
+			() -> classpathScanner.scanForClassesInClasspathRoot(Path.of("does_not_exist").toUri(), allClasses));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void findAllClassesInClasspathRootForNullClassFilter() {
 		assertThrows(PreconditionViolationException.class,
@@ -626,4 +630,12 @@ public Enumeration<URL> getResources(String name) throws IOException {
 		}
 	}
 
+	/**
+	 * Determine if the current code is running in the Eclipse IDE.
+	 */
+	static boolean runningInEclipse() {
+		return StackWalker.getInstance().walk(
+			stream -> stream.anyMatch(stackFrame -> stackFrame.getClassName().startsWith("org.eclipse.jdt")));
+	}
+
 }
diff --git a/platform-tests/src/test/java/org/junit/platform/commons/util/AnnotationUtilsTests.java b/platform-tests/src/test/java/org/junit/platform/commons/util/AnnotationUtilsTests.java
index 20a282e723bf..03bd7938e141 100644
--- a/platform-tests/src/test/java/org/junit/platform/commons/util/AnnotationUtilsTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/commons/util/AnnotationUtilsTests.java
@@ -41,6 +41,7 @@
 import java.util.Optional;
 import java.util.function.Predicate;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.BeforeAll;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
@@ -93,7 +94,7 @@ void findAnnotationIndirectlyPresentOnClass() {
 	}
 
 	/**
-	 * Test for https://github.com/junit-team/junit5/issues/1133
+	 * Test for https://github.com/junit-team/junit-framework/issues/1133
 	 */
 	@Test
 	void findInheritedAnnotationMetaPresentOnNonInheritedComposedAnnotationPresentOnSuperclass() {
@@ -334,12 +335,14 @@ private void assertExtensionsFound(Class<?> clazz, String... tags) {
 			() -> "Extensions found for class " + clazz.getName());
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void findAnnotatedMethodsForNullClass() {
 		assertThrows(PreconditionViolationException.class,
 			() -> findAnnotatedMethods(null, Annotation1.class, TOP_DOWN));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void findAnnotatedMethodsForNullAnnotationType() {
 		assertThrows(PreconditionViolationException.class,
@@ -388,7 +391,7 @@ void findAnnotatedMethodsForAnnotationUsedInClassAndSuperclassHierarchyDown() th
 	}
 
 	/*
-	 * see https://github.com/junit-team/junit5/issues/3553
+	 * see https://github.com/junit-team/junit-framework/issues/3553
 	 */
 	@Test
 	void findAnnotatedMethodsDoesNotAllowInstanceMethodToHideStaticMethod() throws Exception {
@@ -420,18 +423,21 @@ void findAnnotatedMethodsForAnnotationUsedInInterface() throws Exception {
 
 	// === findAnnotatedFields() ===============================================
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void findAnnotatedFieldsForNullClass() {
 		assertThrows(PreconditionViolationException.class,
 			() -> findAnnotatedFields(null, Annotation1.class, isStringField, TOP_DOWN));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void findAnnotatedFieldsForNullAnnotationType() {
 		assertThrows(PreconditionViolationException.class,
 			() -> findAnnotatedFields(ClassWithAnnotatedFields.class, null, isStringField, TOP_DOWN));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void findAnnotatedFieldsForNullPredicate() {
 		assertThrows(PreconditionViolationException.class,
@@ -498,23 +504,6 @@ void findAnnotatedFieldsFindsAllFieldsInTypeHierarchy() {
 				.containsExactly("interface", "interface-shadow");
 	}
 
-	@Test
-	void findAnnotatedFieldsForShadowedFieldsInLegacyMode() {
-		try {
-			ReflectionUtils.useLegacySearchSemantics = true;
-
-			assertThat(findShadowingAnnotatedFields(Annotation1.class))//
-					.containsExactly("super-shadow", "foo-shadow", "baz-shadow");
-			assertThat(findShadowingAnnotatedFields(Annotation2.class))//
-					.containsExactly("bar-shadow", "baz-shadow");
-			assertThat(findShadowingAnnotatedFields(Annotation3.class))//
-					.containsExactly("interface-shadow");
-		}
-		finally {
-			ReflectionUtils.useLegacySearchSemantics = false;
-		}
-	}
-
 	private List<String> findShadowingAnnotatedFields(Class<? extends Annotation> annotationType) {
 		var fields = findAnnotatedFields(ClassWithShadowedAnnotatedFields.class, annotationType, isStringField);
 		var values = ReflectionUtils.readFieldValues(fields, new ClassWithShadowedAnnotatedFields());
@@ -522,7 +511,7 @@ private List<String> findShadowingAnnotatedFields(Class<? extends Annotation> an
 	}
 
 	/*
-	 * see https://github.com/junit-team/junit5/issues/3553
+	 * see https://github.com/junit-team/junit-framework/issues/3553
 	 */
 	@Test
 	void findAnnotatedFieldsDoesNotAllowInstanceFieldToHideStaticField() throws Exception {
@@ -545,18 +534,21 @@ void findAnnotatedFieldsDoesNotAllowInstanceFieldToHideStaticField() throws Exce
 
 	// === findPublicAnnotatedFields() =========================================
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void findPublicAnnotatedFieldsForNullClass() {
 		assertThrows(PreconditionViolationException.class,
 			() -> findPublicAnnotatedFields(null, String.class, Annotation1.class));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void findPublicAnnotatedFieldsForNullFieldType() {
 		assertThrows(PreconditionViolationException.class,
 			() -> findPublicAnnotatedFields(getClass(), null, Annotation1.class));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void findPublicAnnotatedFieldsForNullAnnotationType() {
 		assertThrows(PreconditionViolationException.class,
@@ -1004,13 +996,13 @@ static class ClassWithShadowedAnnotatedFields extends ClassWithAnnotatedFields {
 	// -------------------------------------------------------------------------
 
 	@Annotation1
-	private Boolean privateDirectlyAnnotatedField;
+	private @Nullable Boolean privateDirectlyAnnotatedField;
 
 	@Annotation1
-	public String directlyAnnotatedField;
+	public @Nullable String directlyAnnotatedField;
 
 	@ComposedAnnotation
-	public Integer metaAnnotatedField;
+	public @Nullable Integer metaAnnotatedField;
 
 	interface InterfaceWithAnnotatedFields {
 
diff --git a/platform-tests/src/test/java/org/junit/platform/commons/util/ClassLoaderUtilsTests.java b/platform-tests/src/test/java/org/junit/platform/commons/util/ClassLoaderUtilsTests.java
index 3d8a72df921a..562a0fea2499 100644
--- a/platform-tests/src/test/java/org/junit/platform/commons/util/ClassLoaderUtilsTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/commons/util/ClassLoaderUtilsTests.java
@@ -29,6 +29,7 @@
  */
 class ClassLoaderUtilsTests {
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void getClassLoaderPreconditions() {
 		assertThatExceptionOfType(PreconditionViolationException.class)//
@@ -100,6 +101,7 @@ void getDefaultClassLoaderWithNullContextClassLoader() {
 		}
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void getLocationFromNullFails() {
 		var exception = assertThrows(PreconditionViolationException.class, () -> ClassLoaderUtils.getLocation(null));
diff --git a/platform-tests/src/test/java/org/junit/platform/commons/util/CollectionUtilsTests.java b/platform-tests/src/test/java/org/junit/platform/commons/util/CollectionUtilsTests.java
index 749f62161073..b6b5780c1e41 100644
--- a/platform-tests/src/test/java/org/junit/platform/commons/util/CollectionUtilsTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/commons/util/CollectionUtilsTests.java
@@ -16,7 +16,6 @@
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 import static org.junit.jupiter.api.DynamicTest.dynamicTest;
-import static org.junit.platform.commons.util.CollectionUtils.toUnmodifiableList;
 
 import java.lang.reflect.Array;
 import java.util.ArrayList;
@@ -32,6 +31,7 @@
 import java.util.stream.LongStream;
 import java.util.stream.Stream;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.DynamicTest;
 import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Test;
@@ -57,6 +57,7 @@ class CollectionUtilsTests {
 	@Nested
 	class OnlyElement {
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void nullCollection() {
 			var exception = assertThrows(PreconditionViolationException.class,
@@ -89,6 +90,7 @@ void multiElementCollection() {
 	@Nested
 	class FirstElement {
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void nullCollection() {
 			var exception = assertThrows(PreconditionViolationException.class,
@@ -118,16 +120,6 @@ void collectionWithNullValues() {
 		}
 	}
 
-	@Nested
-	class UnmodifiableList {
-
-		@Test
-		void throwsOnMutation() {
-			var numbers = Stream.of(1).collect(toUnmodifiableList());
-			assertThrows(UnsupportedOperationException.class, numbers::clear);
-		}
-	}
-
 	@Nested
 	class StreamConversion {
 
@@ -191,6 +183,7 @@ void isConvertibleToStreamForNull() {
 			assertThat(CollectionUtils.isConvertibleToStream(null)).isFalse();
 		}
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void toStreamWithNull() {
 			Exception exception = assertThrows(PreconditionViolationException.class,
@@ -247,7 +240,7 @@ void toStreamWithLongStream() {
 		}
 
 		@Test
-		@SuppressWarnings({ "unchecked" })
+		@SuppressWarnings({ "unchecked", "serial" })
 		void toStreamWithCollection() {
 			var collectionStreamClosed = new AtomicBoolean(false);
 			var input = new ArrayList<>(List.of("foo", "bar")) {
@@ -368,7 +361,8 @@ void iteratesListElementsInReverseOrder(@ConvertWith(CommaSeparator.class) List<
 
 		private static class CommaSeparator implements ArgumentConverter {
 			@Override
-			public Object convert(Object source, ParameterContext context) throws ArgumentConversionException {
+			public Object convert(@Nullable Object source, ParameterContext context)
+					throws ArgumentConversionException {
 				return source == null ? List.of() : List.of(((String) source).split(","));
 			}
 		}
diff --git a/platform-tests/src/test/java/org/junit/platform/commons/util/ExceptionUtilsTests.java b/platform-tests/src/test/java/org/junit/platform/commons/util/ExceptionUtilsTests.java
index 798185711c3c..cc30b382ceac 100644
--- a/platform-tests/src/test/java/org/junit/platform/commons/util/ExceptionUtilsTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/commons/util/ExceptionUtilsTests.java
@@ -31,8 +31,10 @@
  *
  * @since 1.0
  */
+@SuppressWarnings("ThrowableNotThrown")
 class ExceptionUtilsTests {
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void throwAsUncheckedExceptionWithNullException() {
 		assertThrows(PreconditionViolationException.class, () -> throwAsUncheckedException(null));
@@ -48,6 +50,7 @@ void throwAsUncheckedExceptionWithUncheckedException() {
 		assertThrows(RuntimeException.class, () -> throwAsUncheckedException(new NumberFormatException()));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void readStackTraceForNullThrowable() {
 		assertThrows(PreconditionViolationException.class, () -> readStackTrace(null));
diff --git a/platform-tests/src/test/java/org/junit/platform/commons/util/FunctionUtilsTests.java b/platform-tests/src/test/java/org/junit/platform/commons/util/FunctionUtilsTests.java
index ee74043ceb39..42d9938ff5af 100644
--- a/platform-tests/src/test/java/org/junit/platform/commons/util/FunctionUtilsTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/commons/util/FunctionUtilsTests.java
@@ -26,12 +26,14 @@
  */
 class FunctionUtilsTests {
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void whereWithNullFunction() {
 		var exception = assertThrows(PreconditionViolationException.class, () -> FunctionUtils.where(null, o -> true));
 		assertEquals("function must not be null", exception.getMessage());
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void whereWithNullPredicate() {
 		var exception = assertThrows(PreconditionViolationException.class, () -> FunctionUtils.where(o -> o, null));
diff --git a/platform-tests/src/test/java/org/junit/platform/commons/util/PackageUtilsTests.java b/platform-tests/src/test/java/org/junit/platform/commons/util/PackageUtilsTests.java
index 801500ccede9..de415b7c4467 100644
--- a/platform-tests/src/test/java/org/junit/platform/commons/util/PackageUtilsTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/commons/util/PackageUtilsTests.java
@@ -33,6 +33,7 @@
  */
 class PackageUtilsTests {
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void getAttributeWithNullType() {
 		var exception = assertThrows(PreconditionViolationException.class,
@@ -40,6 +41,7 @@ void getAttributeWithNullType() {
 		assertEquals("type must not be null", exception.getMessage());
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void getAttributeWithNullFunction() {
 		var exception = assertThrows(PreconditionViolationException.class,
@@ -47,6 +49,7 @@ void getAttributeWithNullFunction() {
 		assertEquals("function must not be null", exception.getMessage());
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void getAttributeWithFunctionReturningNullIsEmpty() {
 		assertFalse(PackageUtils.getAttribute(ValueWrapper.class, p -> null).isPresent());
@@ -54,7 +57,7 @@ void getAttributeWithFunctionReturningNullIsEmpty() {
 
 	@Test
 	void getAttributeFromDefaultPackageMemberIsEmpty() throws Exception {
-		var classInDefaultPackage = ReflectionUtils.tryToLoadClass("DefaultPackageTestCase").get();
+		var classInDefaultPackage = ReflectionUtils.tryToLoadClass("DefaultPackageTestCase").getNonNull();
 		assertFalse(PackageUtils.getAttribute(classInDefaultPackage, Package::getSpecificationTitle).isPresent());
 	}
 
@@ -75,6 +78,7 @@ private Executable isPresent(Function<Package, String> function) {
 		return () -> assertTrue(PackageUtils.getAttribute(ValueWrapper.class, function).isPresent());
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void getAttributeWithNullTypeAndName() {
 		var exception = assertThrows(PreconditionViolationException.class,
@@ -82,6 +86,7 @@ void getAttributeWithNullTypeAndName() {
 		assertEquals("type must not be null", exception.getMessage());
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void getAttributeWithNullName() {
 		var exception = assertThrows(PreconditionViolationException.class,
diff --git a/platform-tests/src/test/java/org/junit/platform/commons/util/ReflectionUtilsTests.java b/platform-tests/src/test/java/org/junit/platform/commons/util/ReflectionUtilsTests.java
index 11c2259b28a1..22022c758fcc 100644
--- a/platform-tests/src/test/java/org/junit/platform/commons/util/ReflectionUtilsTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/commons/util/ReflectionUtilsTests.java
@@ -20,6 +20,7 @@
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTimeoutPreemptively;
 import static org.junit.jupiter.api.Assertions.assertTrue;
@@ -30,7 +31,6 @@
 import static org.junit.platform.commons.util.ReflectionUtils.findMethods;
 import static org.junit.platform.commons.util.ReflectionUtils.invokeMethod;
 import static org.junit.platform.commons.util.ReflectionUtils.isWideningConversion;
-import static org.junit.platform.commons.util.ReflectionUtils.readFieldValue;
 import static org.junit.platform.commons.util.ReflectionUtils.readFieldValues;
 import static org.junit.platform.commons.util.ReflectionUtils.tryToReadFieldValue;
 
@@ -60,6 +60,8 @@
 import java.util.stream.IntStream;
 import java.util.stream.Stream;
 
+import org.assertj.core.api.Assertions;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.fixtures.TrackLogRecords;
@@ -69,6 +71,7 @@
 import org.junit.platform.commons.logging.LogRecordListener;
 import org.junit.platform.commons.support.Resource;
 import org.junit.platform.commons.test.TestClassLoader;
+import org.junit.platform.commons.util.ReflectionUtils.CycleErrorHandling;
 import org.junit.platform.commons.util.ReflectionUtilsTests.NestedClassTests.ClassWithNestedClasses.Nested1;
 import org.junit.platform.commons.util.ReflectionUtilsTests.NestedClassTests.ClassWithNestedClasses.Nested2;
 import org.junit.platform.commons.util.ReflectionUtilsTests.NestedClassTests.ClassWithNestedClasses.Nested3;
@@ -114,6 +117,7 @@ void returnsPrimitiveVoid() throws Exception {
 			assertFalse(ReflectionUtils.returnsPrimitiveVoid(clazz.getDeclaredMethod("methodReturningPrimitive")));
 		}
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void getAllAssignmentCompatibleClassesWithNullClass() {
 			assertThrows(PreconditionViolationException.class,
@@ -128,6 +132,7 @@ void getAllAssignmentCompatibleClasses() {
 			assertTrue(superclasses.stream().allMatch(clazz -> clazz.isAssignableFrom(B.class)));
 		}
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void newInstance() {
 			// @formatter:off
@@ -211,6 +216,19 @@ void wideningConversion() {
 			assertFalse(isWideningConversion(String.class, int.class)); // neither a primitive nor a wrapper
 		}
 
+		@Test
+		void getWrapperType() {
+			assertEquals(Boolean.class, ReflectionUtils.getWrapperType(boolean.class));
+			assertEquals(Byte.class, ReflectionUtils.getWrapperType(byte.class));
+			assertEquals(Character.class, ReflectionUtils.getWrapperType(char.class));
+			assertEquals(Short.class, ReflectionUtils.getWrapperType(short.class));
+			assertEquals(Integer.class, ReflectionUtils.getWrapperType(int.class));
+			assertEquals(Long.class, ReflectionUtils.getWrapperType(long.class));
+			assertEquals(Float.class, ReflectionUtils.getWrapperType(float.class));
+			assertEquals(Double.class, ReflectionUtils.getWrapperType(double.class));
+			assertNull(ReflectionUtils.getWrapperType(Object.class));
+		}
+
 		@Test
 		void getAllClasspathRootDirectories(@TempDir Path tempDirectory) throws Exception {
 			var root1 = tempDirectory.resolve("root1").toAbsolutePath();
@@ -234,6 +252,7 @@ private static void createDirectories(Path... paths) throws IOException {
 			}
 		}
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void getDeclaredConstructorPreconditions() {
 			// @formatter:off
@@ -265,7 +284,7 @@ void isGeneric() {
 		}
 
 		/**
-		 * @see <a href="https://github.com/junit-team/junit5/issues/3684">#3684</a>
+		 * @see <a href="https://github.com/junit-team/junit-framework/issues/3684">#3684</a>
 		 */
 		@Test
 		void getInterfaceMethodIfPossible() throws Exception {
@@ -532,6 +551,7 @@ static void staticMethod() {
 	@Nested
 	class IsClassAssignableToClassTests {
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void isAssignableToForNullSourceType() {
 			assertThatExceptionOfType(PreconditionViolationException.class)//
@@ -546,6 +566,7 @@ void isAssignableToForPrimitiveSourceType() {
 					.withMessage("source type must not be a primitive type");
 		}
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void isAssignableToForNullTargetType() {
 			assertThatExceptionOfType(PreconditionViolationException.class)//
@@ -602,6 +623,7 @@ void isAssignableTo() {
 	@Nested
 	class IsObjectAssignableToClassTests {
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void isAssignableToForNullClass() {
 			assertThrows(PreconditionViolationException.class,
@@ -667,6 +689,7 @@ void isAssignableToForNullObjectAndPrimitive() {
 	@Nested
 	class MethodInvocationTests {
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void invokeMethodPreconditions() {
 			// @formatter:off
@@ -733,6 +756,7 @@ private void privateMethod() {
 	@Nested
 	class ResourceLoadingTests {
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void tryToGetResourcePreconditions() {
 			assertThrows(PreconditionViolationException.class, () -> ReflectionUtils.tryToGetResources(""));
@@ -774,6 +798,7 @@ void tryToGetResourceWhenResourceNotFound() {
 	@Nested
 	class ClassLoadingTests {
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void tryToLoadClassPreconditions() {
 			assertThrows(PreconditionViolationException.class, () -> ReflectionUtils.tryToLoadClass(null));
@@ -785,12 +810,6 @@ void tryToLoadClassPreconditions() {
 				() -> ReflectionUtils.tryToLoadClass(getClass().getName(), null));
 		}
 
-		@Test
-		@SuppressWarnings("deprecation")
-		void loadClassWhenClassNotFoundException() {
-			assertThat(ReflectionUtils.loadClass("foo.bar.EnigmaClassThatDoesNotExist")).isEmpty();
-		}
-
 		@Test
 		void tryToLoadClassWhenClassNotFoundException() {
 			assertThrows(ClassNotFoundException.class,
@@ -811,13 +830,6 @@ void tryToLoadClassFailsWithinReasonableTimeForInsanelyLargeAndInvalidMultidimen
 				() -> ReflectionUtils.tryToLoadClass(className).get()));
 		}
 
-		@Test
-		@SuppressWarnings("deprecation")
-		void loadClass() {
-			var optional = ReflectionUtils.loadClass(Integer.class.getName());
-			assertThat(optional).contains(Integer.class);
-		}
-
 		@Test
 		void tryToLoadClass() {
 			assertTryToLoadClass(getClass().getName(), getClass());
@@ -953,6 +965,7 @@ private static void assertTryToLoadClass(String name, Class<?> type) {
 	@Nested
 	class FullyQualifiedMethodNameTests {
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void getFullyQualifiedMethodNamePreconditions() {
 			// @formatter:off
@@ -988,6 +1001,7 @@ void getFullyQualifiedMethodNameForMethodWithMultipleParameters() {
 			// @formatter:on
 		}
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void parseFullyQualifiedMethodNamePreconditions() {
 			// @formatter:off
@@ -1027,6 +1041,7 @@ void parseFullyQualifiedMethodNameForMethodWithMultipleParameters() {
 	@Nested
 	class NestedClassTests {
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void findNestedClassesPreconditions() {
 			// @formatter:off
@@ -1036,12 +1051,14 @@ void findNestedClassesPreconditions() {
 			// @formatter:on
 		}
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void isNestedClassPresentPreconditions() {
 			// @formatter:off
-			assertThrows(PreconditionViolationException.class, () -> ReflectionUtils.isNestedClassPresent(null, null));
-			assertThrows(PreconditionViolationException.class, () -> ReflectionUtils.isNestedClassPresent(null, clazz -> true));
-			assertThrows(PreconditionViolationException.class, () -> ReflectionUtils.isNestedClassPresent(getClass(), null));
+			assertThrows(PreconditionViolationException.class, () -> ReflectionUtils.isNestedClassPresent(null, null, null));
+			assertThrows(PreconditionViolationException.class, () -> ReflectionUtils.isNestedClassPresent(null, clazz -> true, CycleErrorHandling.THROW_EXCEPTION));
+			assertThrows(PreconditionViolationException.class, () -> ReflectionUtils.isNestedClassPresent(getClass(), null, CycleErrorHandling.ABORT_VISIT));
+			assertThrows(PreconditionViolationException.class, () -> ReflectionUtils.isNestedClassPresent(getClass(), clazz -> true, null));
 			// @formatter:on
 		}
 
@@ -1058,12 +1075,12 @@ void findNestedClasses() {
 
 			assertThat(ReflectionUtils.findNestedClasses(ClassWithNestedClasses.class, clazz -> clazz.getName().contains("1")))
 					.containsExactly(Nested1.class);
-			assertThat(ReflectionUtils.isNestedClassPresent(ClassWithNestedClasses.class, clazz -> clazz.getName().contains("1")))
+			assertThat(ReflectionUtils.isNestedClassPresent(ClassWithNestedClasses.class, clazz -> clazz.getName().contains("1"), CycleErrorHandling.THROW_EXCEPTION))
 					.isTrue();
 
 			assertThat(ReflectionUtils.findNestedClasses(ClassWithNestedClasses.class, ReflectionUtils::isStatic))
 					.containsExactly(Nested3.class);
-			assertThat(ReflectionUtils.isNestedClassPresent(ClassWithNestedClasses.class, ReflectionUtils::isStatic))
+			assertThat(ReflectionUtils.isNestedClassPresent(ClassWithNestedClasses.class, ReflectionUtils::isStatic, CycleErrorHandling.THROW_EXCEPTION))
 					.isTrue();
 
 			assertThat(findNestedClasses(ClassExtendingClassWithNestedClasses.class))
@@ -1088,14 +1105,16 @@ void findNestedClassesWithSeeminglyRecursiveHierarchies() {
 
 			// OuterClass contains recursive hierarchies, but the non-matching
 			// predicate should prevent cycle detection.
-			// See https://github.com/junit-team/junit5/issues/2249
+			// See https://github.com/junit-team/junit-framework/issues/2249
 			assertThat(ReflectionUtils.findNestedClasses(OuterClass.class, clazz -> false)).isEmpty();
-			assertThat(ReflectionUtils.isNestedClassPresent(OuterClass.class, clazz -> false)).isFalse();
+			assertThat(ReflectionUtils.isNestedClassPresent(OuterClass.class, clazz -> false,
+				CycleErrorHandling.THROW_EXCEPTION)).isFalse();
 
 			// RecursiveInnerInnerClass is part of a recursive hierarchy, but the non-matching
 			// predicate should prevent cycle detection.
 			assertThat(ReflectionUtils.findNestedClasses(RecursiveInnerInnerClass.class, clazz -> false)).isEmpty();
-			assertThat(ReflectionUtils.isNestedClassPresent(RecursiveInnerInnerClass.class, clazz -> false)).isFalse();
+			assertThat(ReflectionUtils.isNestedClassPresent(RecursiveInnerInnerClass.class, clazz -> false,
+				CycleErrorHandling.THROW_EXCEPTION)).isFalse();
 
 			// Sibling types don't actually result in cycles.
 			assertThat(findNestedClasses(StaticNestedSiblingClass.class))//
@@ -1138,7 +1157,7 @@ private static List<Class<?>> findNestedClasses(Class<?> clazz) {
 		}
 
 		private static boolean isNestedClassPresent(Class<?> clazz) {
-			return ReflectionUtils.isNestedClassPresent(clazz, c -> true);
+			return ReflectionUtils.isNestedClassPresent(clazz, c -> true, CycleErrorHandling.THROW_EXCEPTION);
 		}
 
 		private void assertNestedCycle(Class<?> from, Class<?> to) {
@@ -1149,7 +1168,7 @@ private void assertNestedCycle(Class<?> start, Class<?> from, Class<?> to) {
 			assertThatExceptionOfType(JUnitException.class)//
 					.as("expected cycle from %s to %s", from.getSimpleName(), to.getSimpleName())//
 					.isThrownBy(() -> findNestedClasses(start))//
-					.withMessageMatching(String.format("Detected cycle in inner class hierarchy between .+%s and .+%s",
+					.withMessageMatching("Detected cycle in inner class hierarchy between .+%s and .+%s".formatted(
 						from.getSimpleName(), to.getSimpleName()));
 		}
 
@@ -1213,6 +1232,7 @@ static class ClassExtendingClassWithNestedClasses extends ClassWithNestedClasses
 	@Nested
 	class MethodUtilitiesTests {
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void tryToGetMethodPreconditions() {
 			assertThrows(PreconditionViolationException.class, () -> ReflectionUtils.tryToGetMethod(null, null));
@@ -1237,6 +1257,7 @@ void tryToGetMethod() throws Exception {
 			assertThat(ReflectionUtils.tryToGetMethod(Object.class, "clone", int.class).toOptional()).isEmpty();
 		}
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void isMethodPresentPreconditions() {
 			assertThrows(PreconditionViolationException.class, () -> ReflectionUtils.isMethodPresent(null, m -> true));
@@ -1258,6 +1279,7 @@ void isMethodPresent() {
 	@Nested
 	class FindMethodTests {
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void findMethodByParameterTypesPreconditions() {
 			// @formatter:off
@@ -1446,6 +1468,7 @@ void methodWithParameterizedMap(Map<String, String> map) {
 	@Nested
 	class FindMethodsTests {
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void findMethodsPreconditions() {
 			// @formatter:off
@@ -1475,7 +1498,7 @@ private static void assertOneFooMethodIn(Class<?> clazz) {
 
 		/**
 		 * @since 1.9.1
-		 * @see https://github.com/junit-team/junit5/issues/2993
+		 * @see https://github.com/junit-team/junit-framework/issues/2993
 		 */
 		@Test
 		void findMethodsFindsDistinctMethodsDeclaredInMultipleInterfaces() {
@@ -1647,41 +1670,6 @@ void findMethodsWithoutStaticHidingUsingHierarchyUpMode() throws Exception {
 			assertThat(methods.subList(7, 9)).containsOnly(ifcMethod1, ifcMethod2);
 		}
 
-		/**
-		 * In legacy mode, "static hiding" occurs.
-		 */
-		@Test
-		void findMethodsWithStaticHidingUsingHierarchyUpModeInLegacyMode() throws Exception {
-			try {
-				ReflectionUtils.useLegacySearchSemantics = true;
-
-				Class<?> ifc = StaticMethodHidingInterface.class;
-				Class<?> parent = StaticMethodHidingParent.class;
-				Class<?> child = StaticMethodHidingChild.class;
-
-				var ifcMethod2 = ifc.getDeclaredMethod("method2", int.class, int.class);
-				var childMethod1 = child.getDeclaredMethod("method1", String.class);
-				var childMethod4 = child.getDeclaredMethod("method4", boolean.class);
-				var childMethod5 = child.getDeclaredMethod("method5", Long.class);
-				var parentMethod2 = parent.getDeclaredMethod("method2", int.class, int.class, int.class);
-				var parentMethod5 = parent.getDeclaredMethod("method5", String.class);
-
-				assertThat(findMethods(child, methodContains1, BOTTOM_UP)).containsExactly(childMethod1);
-				assertThat(findMethods(child, methodContains2, BOTTOM_UP)).containsExactly(parentMethod2, ifcMethod2);
-				assertThat(findMethods(child, methodContains4, BOTTOM_UP)).containsExactly(childMethod4);
-				assertThat(findMethods(child, methodContains5, BOTTOM_UP)).containsExactly(childMethod5, parentMethod5);
-
-				var methods = findMethods(child, method -> true, BOTTOM_UP);
-				assertEquals(6, methods.size());
-				assertThat(methods.subList(0, 3)).containsOnly(childMethod1, childMethod4, childMethod5);
-				assertThat(methods.subList(3, 5)).containsOnly(parentMethod2, parentMethod5);
-				assertEquals(ifcMethod2, methods.get(5));
-			}
-			finally {
-				ReflectionUtils.useLegacySearchSemantics = false;
-			}
-		}
-
 		/**
 		 * In non-legacy mode, "static hiding" does not occur.
 		 */
@@ -1714,41 +1702,6 @@ void findMethodsWithoutStaticHidingUsingHierarchyDownMode() throws Exception {
 			assertThat(methods.subList(6, 9)).containsOnly(childMethod1, childMethod4, childMethod5);
 		}
 
-		/**
-		 * In legacy mode, "static hiding" occurs.
-		 */
-		@Test
-		void findMethodsWithStaticHidingUsingHierarchyDownModeInLegacyMode() throws Exception {
-			try {
-				ReflectionUtils.useLegacySearchSemantics = true;
-
-				Class<?> ifc = StaticMethodHidingInterface.class;
-				Class<?> parent = StaticMethodHidingParent.class;
-				Class<?> child = StaticMethodHidingChild.class;
-
-				var ifcMethod2 = ifc.getDeclaredMethod("method2", int.class, int.class);
-				var childMethod1 = child.getDeclaredMethod("method1", String.class);
-				var childMethod4 = child.getDeclaredMethod("method4", boolean.class);
-				var childMethod5 = child.getDeclaredMethod("method5", Long.class);
-				var parentMethod2 = parent.getDeclaredMethod("method2", int.class, int.class, int.class);
-				var parentMethod5 = parent.getDeclaredMethod("method5", String.class);
-
-				assertThat(findMethods(child, methodContains1, TOP_DOWN)).containsExactly(childMethod1);
-				assertThat(findMethods(child, methodContains2, TOP_DOWN)).containsExactly(ifcMethod2, parentMethod2);
-				assertThat(findMethods(child, methodContains4, TOP_DOWN)).containsExactly(childMethod4);
-				assertThat(findMethods(child, methodContains5, TOP_DOWN)).containsExactly(parentMethod5, childMethod5);
-
-				var methods = findMethods(child, method -> true, TOP_DOWN);
-				assertEquals(6, methods.size());
-				assertEquals(ifcMethod2, methods.getFirst());
-				assertThat(methods.subList(1, 3)).containsOnly(parentMethod2, parentMethod5);
-				assertThat(methods.subList(3, 6)).containsOnly(childMethod1, childMethod4, childMethod5);
-			}
-			finally {
-				ReflectionUtils.useLegacySearchSemantics = false;
-			}
-		}
-
 		@Test
 		void findMethodsDoesNotReturnOverriddenMethods() {
 			Predicate<Method> isSpecial = method -> method.isAnnotationPresent(Special.class);
@@ -1768,7 +1721,7 @@ void findMethodsDoesNotReturnOverriddenMethods() {
 		}
 
 		@Test
-		void findMethodsReturnsAllOverloadedMethodsInGenericTypeHieararchy() {
+		void findMethodsReturnsAllOverloadedMethodsInGenericTypeHierarchy() {
 			Class<?> clazz = InterfaceWithGenericDefaultMethodImpl.class;
 
 			// Search for all foo(*) methods.
@@ -1799,7 +1752,7 @@ void findMethodsDoesNotReturnOverriddenDefaultMethods() {
 		private static List<String> signaturesOf(List<Method> methods) {
 			// @formatter:off
 			return methods.stream()
-					.map(m -> String.format("%s(%s)", m.getName(), ClassUtils.nullSafeToString(m.getParameterTypes())))
+					.map(m -> "%s(%s)".formatted(m.getName(), ClassUtils.nullSafeToString(m.getParameterTypes())))
 					.toList();
 			// @formatter:on
 		}
@@ -1819,7 +1772,7 @@ void findMethodsIgnoresBridgeMethods() throws Exception {
 		}
 
 		/**
-		 * @see https://github.com/junit-team/junit5/issues/3553
+		 * @see https://github.com/junit-team/junit-framework/issues/3553
 		 */
 		@Test
 		void findMethodsDoesNotAllowInstanceMethodToHideStaticMethod() throws Exception {
@@ -1921,13 +1874,6 @@ String specialBaz() {
 	@Nested
 	class ReadFieldTests {
 
-		@Test
-		@SuppressWarnings("deprecation")
-		void readFieldValueOfNonexistentStaticField() {
-			assertThat(readFieldValue(MyClass.class, "doesNotExist", null)).isNotPresent();
-			assertThat(readFieldValue(MySubClass.class, "staticField", null)).isNotPresent();
-		}
-
 		@Test
 		void tryToReadFieldValueOfNonexistentStaticField() {
 			assertThrows(NoSuchFieldException.class,
@@ -1936,13 +1882,6 @@ void tryToReadFieldValueOfNonexistentStaticField() {
 				() -> tryToReadFieldValue(MySubClass.class, "staticField", null).get());
 		}
 
-		@Test
-		@SuppressWarnings("deprecation")
-		void readFieldValueOfNonexistentInstanceField() {
-			assertThat(readFieldValue(MyClass.class, "doesNotExist", new MyClass(42))).isNotPresent();
-			assertThat(readFieldValue(MyClass.class, "doesNotExist", new MySubClass(42))).isNotPresent();
-		}
-
 		@Test
 		void tryToReadFieldValueOfNonexistentInstanceField() {
 			assertThrows(NoSuchFieldException.class,
@@ -1951,16 +1890,7 @@ void tryToReadFieldValueOfNonexistentInstanceField() {
 				() -> tryToReadFieldValue(MyClass.class, "doesNotExist", new MySubClass(42)).get());
 		}
 
-		@Test
-		@SuppressWarnings("deprecation")
-		void readFieldValueOfExistingStaticField() throws Exception {
-			assertThat(readFieldValue(MyClass.class, "staticField", null)).contains(42);
-
-			var field = MyClass.class.getDeclaredField("staticField");
-			assertThat(readFieldValue(field)).contains(42);
-			assertThat(readFieldValue(field, null)).contains(42);
-		}
-
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void tryToReadFieldValueOfExistingStaticField() throws Exception {
 			assertThat(tryToReadFieldValue(MyClass.class, "staticField", null).get()).isEqualTo(42);
@@ -1971,42 +1901,27 @@ void tryToReadFieldValueOfExistingStaticField() throws Exception {
 		}
 
 		@Test
-		@SuppressWarnings("deprecation")
-		void readFieldValueOfExistingInstanceField() throws Exception {
+		void tryToReadFieldValueOfExistingInstanceField() throws Exception {
 			var instance = new MyClass(42);
-			assertThat(readFieldValue(MyClass.class, "instanceField", instance)).contains(42);
+			assertThat(tryToReadFieldValue(MyClass.class, "instanceField", instance).get()).isEqualTo(42);
 
 			var field = MyClass.class.getDeclaredField("instanceField");
-			assertThat(readFieldValue(field, instance)).contains(42);
-		}
+			assertThat(tryToReadFieldValue(field, instance).getNonNull()).isEqualTo(42);
 
-		@Test
-		@SuppressWarnings("deprecation")
-		void attemptToReadFieldValueOfExistingInstanceFieldAsStaticField() throws Exception {
-			var field = MyClass.class.getDeclaredField("instanceField");
-			Exception exception = assertThrows(PreconditionViolationException.class, () -> readFieldValue(field, null));
+			var exception = assertThrows(PreconditionViolationException.class,
+				() -> tryToReadFieldValue(field, null).get());
 			assertThat(exception)//
 					.hasMessageStartingWith("Cannot read non-static field")//
 					.hasMessageEndingWith("on a null instance.");
 		}
 
-		@Test
-		void tryToReadFieldValueOfExistingInstanceField() throws Exception {
-			var instance = new MyClass(42);
-			assertThat(tryToReadFieldValue(MyClass.class, "instanceField", instance).get()).isEqualTo(42);
-
-			var field = MyClass.class.getDeclaredField("instanceField");
-			assertThat(tryToReadFieldValue(field, instance).get()).isEqualTo(42);
-			assertThrows(PreconditionViolationException.class, () -> tryToReadFieldValue(field, null).get());
-		}
-
 	}
 
 	@Nested
 	class FindAndReadFieldsTests {
 
 		/**
-		 * @see https://github.com/junit-team/junit5/issues/3553
+		 * @see https://github.com/junit-team/junit-framework/issues/3553
 		 */
 		@Test
 		void findFieldsDoesNotAllowInstanceFieldToHideStaticField() throws Exception {
@@ -2027,6 +1942,7 @@ void findFieldsDoesNotAllowInstanceFieldToHideStaticField() throws Exception {
 			assertThat(fields).containsExactly(nonStaticField);
 		}
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void readFieldValuesPreconditions() {
 			List<Field> fields = new ArrayList<>();
@@ -2041,7 +1957,8 @@ void readFieldValuesFromInstance() {
 
 			var values = readFieldValues(fields, new ClassWithFields());
 
-			assertThat(values).containsExactly("enigma", 3.14, "text", 2.5, null, 42, "constant", 99);
+			Assertions.<Object> assertThat(values).containsExactly("enigma", 3.14, "text", 2.5, null, 42, "constant",
+				99);
 		}
 
 		@Test
@@ -2050,26 +1967,26 @@ void readFieldValuesFromClass() {
 
 			var values = readFieldValues(fields, null);
 
-			assertThat(values).containsExactly(2.5, "constant", 99);
+			Assertions.<Object> assertThat(values).containsExactly(2.5, "constant", 99);
 		}
 
 		/**
-		 * @see https://github.com/junit-team/junit5/issues/3646
+		 * @see https://github.com/junit-team/junit-framework/issues/3646
 		 * @since 1.11
 		 */
 		@Test
-		void readFieldValuesFromInteracesAndClassesInTypeHierarchy() {
+		void readFieldValuesFromInterfacesAndClassesInTypeHierarchy() {
 			var fields = findFields(InterfaceWithField.class, ReflectionUtils::isStatic, TOP_DOWN);
 			var values = readFieldValues(fields, null);
-			assertThat(values).containsOnly("ifc");
+			Assertions.<Object> assertThat(values).containsOnly("ifc");
 
 			fields = findFields(SuperclassWithFieldAndFieldFromInterface.class, ReflectionUtils::isStatic, TOP_DOWN);
 			values = readFieldValues(fields, null);
-			assertThat(values).containsExactly("ifc", "super");
+			Assertions.<Object> assertThat(values).containsExactly("ifc", "super");
 
 			fields = findFields(SubclassWithFieldAndFieldFromInterface.class, ReflectionUtils::isStatic, TOP_DOWN);
 			values = readFieldValues(fields, null);
-			assertThat(values).containsExactly("ifc", "super", "sub");
+			Assertions.<Object> assertThat(values).containsExactly("ifc", "super", "sub");
 		}
 
 		@Test
@@ -2078,7 +1995,7 @@ void readFieldValuesFromInstanceWithTypeFilterForString() {
 
 			var values = readFieldValues(fields, new ClassWithFields(), isA(String.class));
 
-			assertThat(values).containsExactly("enigma", "text", null, "constant");
+			Assertions.<Object> assertThat(values).containsExactly("enigma", "text", null, "constant");
 		}
 
 		@Test
@@ -2087,7 +2004,7 @@ void readFieldValuesFromClassWithTypeFilterForString() {
 
 			var values = readFieldValues(fields, null, isA(String.class));
 
-			assertThat(values).containsExactly("constant");
+			Assertions.<Object> assertThat(values).containsExactly("constant");
 		}
 
 		@Test
@@ -2096,7 +2013,7 @@ void readFieldValuesFromInstanceWithTypeFilterForInteger() {
 
 			var values = readFieldValues(fields, new ClassWithFields(), isA(int.class));
 
-			assertThat(values).containsExactly(42);
+			Assertions.<Object> assertThat(values).containsExactly(42);
 		}
 
 		@Test
@@ -2105,7 +2022,7 @@ void readFieldValuesFromClassWithTypeFilterForInteger() {
 
 			var values = readFieldValues(fields, null, isA(Integer.class));
 
-			assertThat(values).containsExactly(99);
+			Assertions.<Object> assertThat(values).containsExactly(99);
 		}
 
 		@Test
@@ -2114,7 +2031,7 @@ void readFieldValuesFromInstanceWithTypeFilterForDouble() {
 
 			var values = readFieldValues(fields, new ClassWithFields(), isA(double.class));
 
-			assertThat(values).containsExactly(3.14);
+			Assertions.<Object> assertThat(values).containsExactly(3.14);
 		}
 
 		@Test
@@ -2123,7 +2040,7 @@ void readFieldValuesFromClassWithTypeFilterForDouble() {
 
 			var values = readFieldValues(fields, null, isA(Double.class));
 
-			assertThat(values).containsExactly(2.5);
+			Assertions.<Object> assertThat(values).containsExactly(2.5);
 		}
 
 		private static Predicate<Field> isA(Class<?> type) {
@@ -2143,6 +2060,7 @@ public static class ClassWithFields {
 			@SuppressWarnings("unused")
 			private final String privateStringField = "enigma";
 
+			@Nullable
 			final String nullStringField = null;
 
 			public final int integerField = 42;
diff --git a/platform-tests/src/test/java/org/junit/platform/commons/util/StringUtilsTests.java b/platform-tests/src/test/java/org/junit/platform/commons/util/StringUtilsTests.java
index ca66fe79c766..315fdb472500 100644
--- a/platform-tests/src/test/java/org/junit/platform/commons/util/StringUtilsTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/commons/util/StringUtilsTests.java
@@ -27,6 +27,7 @@
 import static org.junit.platform.commons.util.StringUtils.replaceIsoControlCharacters;
 import static org.junit.platform.commons.util.StringUtils.replaceWhitespaceCharacters;
 
+import org.jspecify.annotations.NullUnmarked;
 import org.junit.jupiter.api.Test;
 import org.junit.platform.commons.PreconditionViolationException;
 
@@ -49,6 +50,7 @@ void blankness() {
 		// @formatter:on
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void whitespace() {
 		// @formatter:off
@@ -72,6 +74,7 @@ void whitespace() {
 		// @formatter:on
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void controlCharacters() {
 		// @formatter:off
@@ -95,6 +98,7 @@ void controlCharacters() {
 		// @formatter:on
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void replaceControlCharacters() {
 		assertNull(replaceIsoControlCharacters(null, ""));
@@ -108,6 +112,7 @@ void replaceControlCharacters() {
 		assertThrows(PreconditionViolationException.class, () -> replaceIsoControlCharacters("", null));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void replaceWhitespaces() {
 		assertNull(replaceWhitespaceCharacters(null, ""));
@@ -150,29 +155,29 @@ void nullSafeToStringForObjectWhoseToStringImplementationThrowsAnException() {
 	}
 
 	private void shouldContainWhitespace(String str) {
-		assertTrue(containsWhitespace(str), () -> String.format("'%s' should contain whitespace", str));
-		assertFalse(doesNotContainWhitespace(str), () -> String.format("'%s' should contain whitespace", str));
+		assertTrue(containsWhitespace(str), () -> "'%s' should contain whitespace".formatted(str));
+		assertFalse(doesNotContainWhitespace(str), () -> "'%s' should contain whitespace".formatted(str));
 	}
 
 	private void shouldNotContainWhitespace(String str) {
-		assertTrue(doesNotContainWhitespace(str), () -> String.format("'%s' should not contain whitespace", str));
-		assertFalse(containsWhitespace(str), () -> String.format("'%s' should not contain whitespace", str));
+		assertTrue(doesNotContainWhitespace(str), () -> "'%s' should not contain whitespace".formatted(str));
+		assertFalse(containsWhitespace(str), () -> "'%s' should not contain whitespace".formatted(str));
 	}
 
 	private void shouldContainIsoControlCharacter(String str) {
-		assertTrue(containsIsoControlCharacter(str),
-			() -> String.format("'%s' should contain ISO control character", str));
+		assertTrue(containsIsoControlCharacter(str), () -> "'%s' should contain ISO control character".formatted(str));
 		assertFalse(doesNotContainIsoControlCharacter(str),
-			() -> String.format("'%s' should contain ISO control character", str));
+			() -> "'%s' should contain ISO control character".formatted(str));
 	}
 
 	private void shouldNotContainIsoControlCharacter(String str) {
 		assertTrue(doesNotContainIsoControlCharacter(str),
-			() -> String.format("'%s' should not contain ISO control character", str));
+			() -> "'%s' should not contain ISO control character".formatted(str));
 		assertFalse(containsIsoControlCharacter(str),
-			() -> String.format("'%s' should not contain ISO control character", str));
+			() -> "'%s' should not contain ISO control character".formatted(str));
 	}
 
+	@NullUnmarked
 	private static class ToStringReturnsNull {
 
 		@Override
diff --git a/platform-tests/src/test/java/org/junit/platform/commons/util/ToStringBuilderTests.java b/platform-tests/src/test/java/org/junit/platform/commons/util/ToStringBuilderTests.java
index c030ba8673de..10d268699f55 100644
--- a/platform-tests/src/test/java/org/junit/platform/commons/util/ToStringBuilderTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/commons/util/ToStringBuilderTests.java
@@ -16,6 +16,7 @@
 import java.util.LinkedHashMap;
 import java.util.Map;
 
+import org.jspecify.annotations.NullUnmarked;
 import org.junit.jupiter.api.Test;
 import org.junit.platform.commons.PreconditionViolationException;
 
@@ -26,16 +27,19 @@
  */
 class ToStringBuilderTests {
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void withNullObject() {
 		assertThrows(PreconditionViolationException.class, () -> new ToStringBuilder((Object) null));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void withNullClass() {
 		assertThrows(PreconditionViolationException.class, () -> new ToStringBuilder((Class<?>) null));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void appendWithIllegalName() {
 		var builder = new ToStringBuilder("");
@@ -141,6 +145,7 @@ void withDemoImplementation() {
 		assertEquals("RoleModel [name = 'Dilbert', age = 42]", roleModel.toString());
 	}
 
+	@NullUnmarked
 	static class RoleModel {
 
 		String name;
diff --git a/platform-tests/src/test/java/org/junit/platform/commons/util/pkg1/SuperclassWithStaticPackagePrivateBeforeMethod.java b/platform-tests/src/test/java/org/junit/platform/commons/util/pkg1/SuperclassWithStaticPackagePrivateBeforeMethod.java
index f5d579ac3f39..e6346ac7d1b5 100644
--- a/platform-tests/src/test/java/org/junit/platform/commons/util/pkg1/SuperclassWithStaticPackagePrivateBeforeMethod.java
+++ b/platform-tests/src/test/java/org/junit/platform/commons/util/pkg1/SuperclassWithStaticPackagePrivateBeforeMethod.java
@@ -13,7 +13,7 @@
 import org.junit.jupiter.api.BeforeAll;
 
 /**
- * @see https://github.com/junit-team/junit5/issues/3553
+ * @see https://github.com/junit-team/junit-framework/issues/3553
  */
 public class SuperclassWithStaticPackagePrivateBeforeMethod {
 
diff --git a/platform-tests/src/test/java/org/junit/platform/commons/util/pkg1/SuperclassWithStaticPackagePrivateTempDirField.java b/platform-tests/src/test/java/org/junit/platform/commons/util/pkg1/SuperclassWithStaticPackagePrivateTempDirField.java
index eccfc241a6f8..37fd4d702ab2 100644
--- a/platform-tests/src/test/java/org/junit/platform/commons/util/pkg1/SuperclassWithStaticPackagePrivateTempDirField.java
+++ b/platform-tests/src/test/java/org/junit/platform/commons/util/pkg1/SuperclassWithStaticPackagePrivateTempDirField.java
@@ -13,7 +13,7 @@
 import java.nio.file.Path;
 
 /**
- * @see https://github.com/junit-team/junit5/issues/3553
+ * @see https://github.com/junit-team/junit-framework/issues/3553
  */
 public class SuperclassWithStaticPackagePrivateTempDirField {
 
diff --git a/platform-tests/src/test/java/org/junit/platform/commons/util/pkg1/subpkg/SubclassWithNonStaticPackagePrivateBeforeMethod.java b/platform-tests/src/test/java/org/junit/platform/commons/util/pkg1/subpkg/SubclassWithNonStaticPackagePrivateBeforeMethod.java
index 0ed8b8ad1212..c9e1b46eb5c0 100644
--- a/platform-tests/src/test/java/org/junit/platform/commons/util/pkg1/subpkg/SubclassWithNonStaticPackagePrivateBeforeMethod.java
+++ b/platform-tests/src/test/java/org/junit/platform/commons/util/pkg1/subpkg/SubclassWithNonStaticPackagePrivateBeforeMethod.java
@@ -14,7 +14,7 @@
 import org.junit.platform.commons.util.pkg1.SuperclassWithStaticPackagePrivateBeforeMethod;
 
 /**
- * @see https://github.com/junit-team/junit5/issues/3553
+ * @see https://github.com/junit-team/junit-framework/issues/3553
  */
 public class SubclassWithNonStaticPackagePrivateBeforeMethod extends SuperclassWithStaticPackagePrivateBeforeMethod {
 
diff --git a/platform-tests/src/test/java/org/junit/platform/commons/util/pkg1/subpkg/SubclassWithNonStaticPackagePrivateTempDirField.java b/platform-tests/src/test/java/org/junit/platform/commons/util/pkg1/subpkg/SubclassWithNonStaticPackagePrivateTempDirField.java
index 1c6efa40cdfb..49ec56b1b15a 100644
--- a/platform-tests/src/test/java/org/junit/platform/commons/util/pkg1/subpkg/SubclassWithNonStaticPackagePrivateTempDirField.java
+++ b/platform-tests/src/test/java/org/junit/platform/commons/util/pkg1/subpkg/SubclassWithNonStaticPackagePrivateTempDirField.java
@@ -16,7 +16,7 @@
 import org.junit.platform.commons.util.pkg1.SuperclassWithStaticPackagePrivateTempDirField;
 
 /**
- * @see https://github.com/junit-team/junit5/issues/3553
+ * @see https://github.com/junit-team/junit-framework/issues/3553
  */
 public class SubclassWithNonStaticPackagePrivateTempDirField extends SuperclassWithStaticPackagePrivateTempDirField {
 
diff --git a/platform-tests/src/test/java/org/junit/platform/console/ConsoleDetailsTests.java b/platform-tests/src/test/java/org/junit/platform/console/ConsoleDetailsTests.java
index b908ab457893..3c69d48b2dbf 100644
--- a/platform-tests/src/test/java/org/junit/platform/console/ConsoleDetailsTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/console/ConsoleDetailsTests.java
@@ -10,7 +10,6 @@
 
 package org.junit.platform.console;
 
-import static java.lang.String.format;
 import static java.nio.charset.StandardCharsets.UTF_8;
 import static org.junit.jupiter.api.Assertions.assertLinesMatch;
 import static org.junit.jupiter.api.Assertions.fail;
@@ -25,7 +24,7 @@
 import java.net.URI;
 import java.net.URISyntaxException;
 import java.nio.file.Files;
-import java.nio.file.Paths;
+import java.nio.file.Path;
 import java.util.ArrayList;
 import java.util.EnumMap;
 import java.util.LinkedHashMap;
@@ -87,6 +86,7 @@ private List<DynamicNode> scanContainerClassAndCreateDynamicTests(Class<?> conta
 				for (var theme : Theme.values()) {
 					var caption = containerName + "-" + methodName + "-" + details + "-" + theme;
 					String[] args = { //
+							"execute", //
 							"--include-engine", "junit-jupiter", //
 							"--details", details.name(), //
 							"--details-theme", theme.name(), //
@@ -198,17 +198,7 @@ void reportMultiEntriesWithMultiMappings(TestReporter reporter) {
 
 	}
 
-	private static class Runner implements Executable {
-
-		private final String dirName;
-		private final String outName;
-		private final String[] args;
-
-		private Runner(String dirName, String outName, String... args) {
-			this.dirName = dirName;
-			this.outName = outName;
-			this.args = args;
-		}
+	private record Runner(String dirName, String outName, String... args) implements Executable {
 
 		@Override
 		public void execute() throws Throwable {
@@ -219,16 +209,16 @@ public void execute() throws Throwable {
 			if (optionalUri.isEmpty()) {
 				if (Boolean.getBoolean("org.junit.platform.console.ConsoleDetailsTests.writeResultOut")) {
 					// do not use Files.createTempDirectory(prefix) as we want one folder for one container
-					var temp = Paths.get(System.getProperty("java.io.tmpdir"), dirName.replace('/', '-'));
+					var temp = Path.of(System.getProperty("java.io.tmpdir"), dirName.replace('/', '-'));
 					Files.createDirectories(temp);
 					var path = Files.writeString(temp.resolve(outName), result.out);
 					throw new TestAbortedException(
-						format("resource `%s` not found\nwrote console stdout to: %s/%s", dirName, outName, path));
+						"resource `%s` not found\nwrote console stdout to: %s/%s".formatted(dirName, outName, path));
 				}
 				fail("could not load resource named `" + dirName + "/" + outName + "`");
 			}
 
-			var path = Paths.get(optionalUri.get());
+			var path = Path.of(optionalUri.get());
 			assumeTrue(Files.exists(path), "path does not exist: " + path);
 			assumeTrue(Files.isReadable(path), "can not read: " + path);
 
diff --git a/platform-tests/src/test/java/org/junit/platform/console/ConsoleLauncherIntegrationTests.java b/platform-tests/src/test/java/org/junit/platform/console/ConsoleLauncherIntegrationTests.java
index 49b4a159e118..6fe058ff2493 100644
--- a/platform-tests/src/test/java/org/junit/platform/console/ConsoleLauncherIntegrationTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/console/ConsoleLauncherIntegrationTests.java
@@ -36,35 +36,24 @@
 class ConsoleLauncherIntegrationTests {
 
 	@Test
-	void executeWithoutArgumentsFailsAndPrintsHelpInformation() {
+	void executeWithoutSubcommandFailsAndPrintsHelpInformation() {
 		var result = new ConsoleLauncherWrapper().execute(-1);
 		assertAll("empty args array results in display of help information and an exception stacktrace", //
 			() -> assertThat(result.err).contains("help information"), //
-			() -> assertThat(result.err).contains(
-				"Please specify an explicit selector option or use --scan-class-path or --scan-modules") //
+			() -> assertThat(result.err).contains("Missing required subcommand") //
 		);
 	}
 
-	@ParameterizedTest
-	@ValueSource(strings = { //
-			"-e junit-jupiter -p org.junit.platform.console.subpackage", //
-			"execute -e junit-jupiter -p org.junit.platform.console.subpackage" //
-	})
-	void executeWithoutExcludeClassnameOptionDoesNotExcludeClassesAndMustIncludeAllClassesMatchingTheStandardClassnamePattern(
-			String line) {
-		var args = line.split(" ");
+	@Test
+	void executeWithoutExcludeClassnameOptionDoesNotExcludeClassesAndMustIncludeAllClassesMatchingTheStandardClassnamePattern() {
+		String[] args = { "execute", "-e", "junit-jupiter", "-p", "org.junit.platform.console.subpackage" };
 		assertEquals(9, new ConsoleLauncherWrapper().execute(args).getTestsFoundCount());
 	}
 
-	@ParameterizedTest
-	@ValueSource(strings = {
-			"-e junit-jupiter -p org.junit.platform.console.subpackage --exclude-classname"
-					+ " ^org\\.junit\\.platform\\.console\\.subpackage\\..*",
-			"execute -e junit-jupiter -p org.junit.platform.console.subpackage --exclude-classname"
-					+ " ^org\\.junit\\.platform\\.console\\.subpackage\\..*" //
-	})
-	void executeWithExcludeClassnameOptionExcludesClasses(String line) {
-		var args = line.split(" ");
+	@Test
+	void executeWithExcludeClassnameOptionExcludesClasses() {
+		String[] args = { "execute", "-e", "junit-jupiter", "-p", "org.junit.platform.console.subpackage",
+				"--exclude-classname", "^org\\.junit\\.platform\\.console\\.subpackage\\..*" };
 		var result = new ConsoleLauncherWrapper().execute(args);
 		assertAll("all subpackage test classes are excluded by the class name filter", //
 			() -> assertArrayEquals(args, result.args), //
@@ -88,18 +77,17 @@ void executeWithExcludeMethodNameOptionExcludesMethods() {
 
 	@ParameterizedTest
 	@ValueSource(strings = { //
-			"-e junit-jupiter -o java.base", "-e junit-jupiter --select-module java.base", //
-			"execute -e junit-jupiter -o java.base", "execute -e junit-jupiter --select-module java.base" //
+			"execute -e junit-jupiter -o java.base", //
+			"execute -e junit-jupiter --select-module java.base" //
 	})
 	void executeSelectingModuleNames(String line) {
 		var args = line.split(" ");
 		assertEquals(0, new ConsoleLauncherWrapper().execute(args).getTestsFoundCount());
 	}
 
-	@ParameterizedTest
-	@ValueSource(strings = { "-e junit-jupiter --scan-modules", "execute -e junit-jupiter --scan-modules" })
-	void executeScanModules(String line) {
-		var args = line.split(" ");
+	@Test
+	void executeScanModules() {
+		String[] args = { "execute", "-e", "junit-jupiter", "--scan-modules" };
 		assertEquals(0, new ConsoleLauncherWrapper().execute(args).getTestsFoundCount());
 	}
 
@@ -109,7 +97,7 @@ void executeWithRedirectedStdStream(String redirectedStream, int outputFileSize,
 			throws IOException {
 
 		var outputFile = tempDir.resolve("output.txt");
-		var line = String.format("execute -e junit-jupiter --select-class %s %s %s", StdStreamTestCase.class.getName(),
+		var line = "execute -e junit-jupiter --select-class %s %s %s".formatted(StdStreamTestCase.class.getName(),
 			redirectedStream, outputFile);
 		var args = line.split(" ");
 		new ConsoleLauncherWrapper().execute(args);
@@ -125,7 +113,7 @@ void executeWithRedirectedStdStream(String redirectedStream, int outputFileSize,
 	@Test
 	void executeWithRedirectedStdStreamsToSameFile(@TempDir Path tempDir) throws IOException {
 		var outputFile = tempDir.resolve("output.txt");
-		var line = String.format("execute -e junit-jupiter --select-class %s --redirect-stdout %s --redirect-stderr %s",
+		var line = "execute -e junit-jupiter --select-class %s --redirect-stdout %s --redirect-stderr %s".formatted(
 			StdStreamTestCase.class.getName(), outputFile, outputFile);
 		var args = line.split(" ");
 		new ConsoleLauncherWrapper().execute(args);
diff --git a/platform-tests/src/test/java/org/junit/platform/console/ConsoleLauncherWrapperResult.java b/platform-tests/src/test/java/org/junit/platform/console/ConsoleLauncherWrapperResult.java
index f7fd34632fe5..4f2c6f6a1eff 100644
--- a/platform-tests/src/test/java/org/junit/platform/console/ConsoleLauncherWrapperResult.java
+++ b/platform-tests/src/test/java/org/junit/platform/console/ConsoleLauncherWrapperResult.java
@@ -10,9 +10,12 @@
 
 package org.junit.platform.console;
 
+import static java.util.Objects.requireNonNull;
+
 import java.io.PrintWriter;
 import java.util.List;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.console.options.CommandResult;
 import org.junit.platform.launcher.listeners.TestExecutionSummary;
 
@@ -25,7 +28,8 @@ class ConsoleLauncherWrapperResult implements TestExecutionSummary {
 	final String out;
 	final String err;
 	final int code;
-	private final TestExecutionSummary summary;
+
+	private final @Nullable TestExecutionSummary summary;
 
 	ConsoleLauncherWrapperResult(String[] args, String out, String err, CommandResult<?> result) {
 		this.args = args;
@@ -33,7 +37,7 @@ class ConsoleLauncherWrapperResult implements TestExecutionSummary {
 		this.err = err;
 		this.code = result.getExitCode();
 		this.summary = (TestExecutionSummary) result.getValue() //
-				.filter(it -> it instanceof TestExecutionSummary) //
+				.filter(TestExecutionSummary.class::isInstance) //
 				.orElse(null);
 	}
 
@@ -46,114 +50,118 @@ private void checkTestExecutionSummaryState() {
 	@Override
 	public long getTimeStarted() {
 		checkTestExecutionSummaryState();
-		return summary.getTimeStarted();
+		return requiredSummary().getTimeStarted();
 	}
 
 	@Override
 	public long getTimeFinished() {
 		checkTestExecutionSummaryState();
-		return summary.getTimeFinished();
+		return requiredSummary().getTimeFinished();
 	}
 
 	@Override
 	public long getTotalFailureCount() {
 		checkTestExecutionSummaryState();
-		return summary.getTotalFailureCount();
+		return requiredSummary().getTotalFailureCount();
 	}
 
 	@Override
 	public long getContainersFoundCount() {
 		checkTestExecutionSummaryState();
-		return summary.getContainersFoundCount();
+		return requiredSummary().getContainersFoundCount();
 	}
 
 	@Override
 	public long getContainersStartedCount() {
 		checkTestExecutionSummaryState();
-		return summary.getContainersStartedCount();
+		return requiredSummary().getContainersStartedCount();
 	}
 
 	@Override
 	public long getContainersSkippedCount() {
 		checkTestExecutionSummaryState();
-		return summary.getContainersSkippedCount();
+		return requiredSummary().getContainersSkippedCount();
 	}
 
 	@Override
 	public long getContainersAbortedCount() {
 		checkTestExecutionSummaryState();
-		return summary.getContainersAbortedCount();
+		return requiredSummary().getContainersAbortedCount();
 	}
 
 	@Override
 	public long getContainersSucceededCount() {
 		checkTestExecutionSummaryState();
-		return summary.getContainersSucceededCount();
+		return requiredSummary().getContainersSucceededCount();
 	}
 
 	@Override
 	public long getContainersFailedCount() {
 		checkTestExecutionSummaryState();
-		return summary.getContainersFailedCount();
+		return requiredSummary().getContainersFailedCount();
 	}
 
 	@Override
 	public long getTestsFoundCount() {
 		checkTestExecutionSummaryState();
-		return summary.getTestsFoundCount();
+		return requiredSummary().getTestsFoundCount();
 	}
 
 	@Override
 	public long getTestsStartedCount() {
 		checkTestExecutionSummaryState();
-		return summary.getTestsStartedCount();
+		return requiredSummary().getTestsStartedCount();
 	}
 
 	@Override
 	public long getTestsSkippedCount() {
 		checkTestExecutionSummaryState();
-		return summary.getTestsSkippedCount();
+		return requiredSummary().getTestsSkippedCount();
 	}
 
 	@Override
 	public long getTestsAbortedCount() {
 		checkTestExecutionSummaryState();
-		return summary.getTestsAbortedCount();
+		return requiredSummary().getTestsAbortedCount();
 	}
 
 	@Override
 	public long getTestsSucceededCount() {
 		checkTestExecutionSummaryState();
-		return summary.getTestsSucceededCount();
+		return requiredSummary().getTestsSucceededCount();
 	}
 
 	@Override
 	public long getTestsFailedCount() {
 		checkTestExecutionSummaryState();
-		return summary.getTestsFailedCount();
+		return requiredSummary().getTestsFailedCount();
 	}
 
 	@Override
 	public void printTo(PrintWriter writer) {
 		checkTestExecutionSummaryState();
-		summary.printTo(writer);
+		requiredSummary().printTo(writer);
 	}
 
 	@Override
 	public void printFailuresTo(PrintWriter writer) {
 		checkTestExecutionSummaryState();
-		summary.printFailuresTo(writer);
+		requiredSummary().printFailuresTo(writer);
 	}
 
 	@Override
 	public void printFailuresTo(PrintWriter writer, int maxStackTraceLines) {
 		checkTestExecutionSummaryState();
-		summary.printFailuresTo(writer, maxStackTraceLines);
+		requiredSummary().printFailuresTo(writer, maxStackTraceLines);
 	}
 
 	@Override
 	public List<Failure> getFailures() {
 		checkTestExecutionSummaryState();
-		return summary.getFailures();
+		return requiredSummary().getFailures();
+	}
+
+	private TestExecutionSummary requiredSummary() {
+		return requireNonNull(summary);
 	}
 }
diff --git a/platform-tests/src/test/java/org/junit/platform/console/options/CommandLineOptionsParsingTests.java b/platform-tests/src/test/java/org/junit/platform/console/options/CommandLineOptionsParsingTests.java
index a10094a023da..0bb925ef8bb1 100644
--- a/platform-tests/src/test/java/org/junit/platform/console/options/CommandLineOptionsParsingTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/console/options/CommandLineOptionsParsingTests.java
@@ -29,12 +29,12 @@
 import static org.junit.platform.engine.discovery.DiscoverySelectors.selectPackage;
 import static org.junit.platform.engine.discovery.DiscoverySelectors.selectUniqueId;
 import static org.junit.platform.engine.discovery.DiscoverySelectors.selectUri;
+import static org.mockito.Mockito.mock;
 
 import java.io.File;
 import java.io.IOException;
 import java.nio.file.Files;
 import java.nio.file.Path;
-import java.nio.file.Paths;
 import java.util.List;
 import java.util.Map;
 import java.util.stream.Stream;
@@ -318,13 +318,10 @@ void parseInvalidExcludedEngines() {
 	@ParameterizedTest
 	@EnumSource
 	void parseValidAdditionalClasspathEntries(ArgsType type) {
-		var dir = Paths.get(".");
+		var dir = Path.of(".");
 		// @formatter:off
 		assertAll(
 			() -> assertEquals(List.of(dir), type.parseArgLine("-cp .").discovery.getAdditionalClasspathEntries()),
-			() -> assertEquals(List.of(dir), type.parseArgLine("--cp .").discovery.getAdditionalClasspathEntries()),
-			() -> assertEquals(List.of(dir), type.parseArgLine("-classpath .").discovery.getAdditionalClasspathEntries()),
-			() -> assertEquals(List.of(dir), type.parseArgLine("-classpath=.").discovery.getAdditionalClasspathEntries()),
 			() -> assertEquals(List.of(dir), type.parseArgLine("--classpath .").discovery.getAdditionalClasspathEntries()),
 			() -> assertEquals(List.of(dir), type.parseArgLine("--classpath=.").discovery.getAdditionalClasspathEntries()),
 			() -> assertEquals(List.of(dir), type.parseArgLine("--class-path .").discovery.getAdditionalClasspathEntries()),
@@ -361,9 +358,6 @@ void parseValidUriSelectors(ArgsType type) {
 		// @formatter:off
 		assertAll(
 			() -> assertEquals(List.of(selectUri("file:///foo.txt")), type.parseArgLine("-u file:///foo.txt").discovery.getSelectedUris()),
-			() -> assertEquals(List.of(selectUri("file:///foo.txt")), type.parseArgLine("--u file:///foo.txt").discovery.getSelectedUris()),
-			() -> assertEquals(List.of(selectUri("file:///foo.txt")), type.parseArgLine("-select-uri file:///foo.txt").discovery.getSelectedUris()),
-			() -> assertEquals(List.of(selectUri("file:///foo.txt")), type.parseArgLine("-select-uri=file:///foo.txt").discovery.getSelectedUris()),
 			() -> assertEquals(List.of(selectUri("file:///foo.txt")), type.parseArgLine("--select-uri file:///foo.txt").discovery.getSelectedUris()),
 			() -> assertEquals(List.of(selectUri("file:///foo.txt")), type.parseArgLine("--select-uri=file:///foo.txt").discovery.getSelectedUris()),
 			() -> assertEquals(List.of(selectUri("file:///foo.txt"), selectUri("https://example")), type.parseArgLine("-u file:///foo.txt -u https://example").discovery.getSelectedUris()),
@@ -383,9 +377,6 @@ void parseValidFileSelectors(ArgsType type) {
 		// @formatter:off
 		assertAll(
 			() -> assertEquals(List.of(selectFile("foo.txt")), type.parseArgLine("-f foo.txt").discovery.getSelectedFiles()),
-			() -> assertEquals(List.of(selectFile("foo.txt")), type.parseArgLine("--f foo.txt").discovery.getSelectedFiles()),
-			() -> assertEquals(List.of(selectFile("foo.txt")), type.parseArgLine("-select-file foo.txt").discovery.getSelectedFiles()),
-			() -> assertEquals(List.of(selectFile("foo.txt")), type.parseArgLine("-select-file=foo.txt").discovery.getSelectedFiles()),
 			() -> assertEquals(List.of(selectFile("foo.txt")), type.parseArgLine("--select-file foo.txt").discovery.getSelectedFiles()),
 			() -> assertEquals(List.of(selectFile("foo.txt")), type.parseArgLine("--select-file=foo.txt").discovery.getSelectedFiles()),
 			() -> assertEquals(List.of(selectFile("foo.txt"), selectFile("bar.csv")), type.parseArgLine("-f foo.txt -f bar.csv").discovery.getSelectedFiles()),
@@ -407,9 +398,6 @@ void parseValidDirectorySelectors(ArgsType type) {
 		// @formatter:off
 		assertAll(
 			() -> assertEquals(List.of(selectDirectory("foo/bar")), type.parseArgLine("-d foo/bar").discovery.getSelectedDirectories()),
-			() -> assertEquals(List.of(selectDirectory("foo/bar")), type.parseArgLine("--d foo/bar").discovery.getSelectedDirectories()),
-			() -> assertEquals(List.of(selectDirectory("foo/bar")), type.parseArgLine("-select-directory foo/bar").discovery.getSelectedDirectories()),
-			() -> assertEquals(List.of(selectDirectory("foo/bar")), type.parseArgLine("-select-directory=foo/bar").discovery.getSelectedDirectories()),
 			() -> assertEquals(List.of(selectDirectory("foo/bar")), type.parseArgLine("--select-directory foo/bar").discovery.getSelectedDirectories()),
 			() -> assertEquals(List.of(selectDirectory("foo/bar")), type.parseArgLine("--select-directory=foo/bar").discovery.getSelectedDirectories()),
 			() -> assertEquals(List.of(selectDirectory("foo/bar"), selectDirectory("bar/qux")), type.parseArgLine("-d foo/bar -d bar/qux").discovery.getSelectedDirectories()),
@@ -429,9 +417,6 @@ void parseValidModuleSelectors(ArgsType type) {
 		// @formatter:off
 		assertAll(
 			() -> assertEquals(List.of(selectModule("com.acme.foo")), type.parseArgLine("-o com.acme.foo").discovery.getSelectedModules()),
-			() -> assertEquals(List.of(selectModule("com.acme.foo")), type.parseArgLine("--o com.acme.foo").discovery.getSelectedModules()),
-			() -> assertEquals(List.of(selectModule("com.acme.foo")), type.parseArgLine("-select-module com.acme.foo").discovery.getSelectedModules()),
-			() -> assertEquals(List.of(selectModule("com.acme.foo")), type.parseArgLine("-select-module=com.acme.foo").discovery.getSelectedModules()),
 			() -> assertEquals(List.of(selectModule("com.acme.foo")), type.parseArgLine("--select-module com.acme.foo").discovery.getSelectedModules()),
 			() -> assertEquals(List.of(selectModule("com.acme.foo")), type.parseArgLine("--select-module=com.acme.foo").discovery.getSelectedModules()),
 			() -> assertEquals(List.of(selectModule("com.acme.foo"), selectModule("com.example.bar")), type.parseArgLine("-o com.acme.foo -o com.example.bar").discovery.getSelectedModules()),
@@ -451,9 +436,6 @@ void parseValidPackageSelectors(ArgsType type) {
 		// @formatter:off
 		assertAll(
 			() -> assertEquals(List.of(selectPackage("com.acme.foo")), type.parseArgLine("-p com.acme.foo").discovery.getSelectedPackages()),
-			() -> assertEquals(List.of(selectPackage("com.acme.foo")), type.parseArgLine("--p com.acme.foo").discovery.getSelectedPackages()),
-			() -> assertEquals(List.of(selectPackage("com.acme.foo")), type.parseArgLine("-select-package com.acme.foo").discovery.getSelectedPackages()),
-			() -> assertEquals(List.of(selectPackage("com.acme.foo")), type.parseArgLine("-select-package=com.acme.foo").discovery.getSelectedPackages()),
 			() -> assertEquals(List.of(selectPackage("com.acme.foo")), type.parseArgLine("--select-package com.acme.foo").discovery.getSelectedPackages()),
 			() -> assertEquals(List.of(selectPackage("com.acme.foo")), type.parseArgLine("--select-package=com.acme.foo").discovery.getSelectedPackages()),
 			() -> assertEquals(List.of(selectPackage("com.acme.foo"), selectPackage("com.example.bar")), type.parseArgLine("-p com.acme.foo -p com.example.bar").discovery.getSelectedPackages()),
@@ -473,9 +455,6 @@ void parseValidClassSelectors(ArgsType type) {
 		// @formatter:off
 		assertAll(
 			() -> assertEquals(List.of(selectClass("com.acme.Foo")), type.parseArgLine("-c com.acme.Foo").discovery.getSelectedClasses()),
-			() -> assertEquals(List.of(selectClass("com.acme.Foo")), type.parseArgLine("--c com.acme.Foo").discovery.getSelectedClasses()),
-			() -> assertEquals(List.of(selectClass("com.acme.Foo")), type.parseArgLine("-select-class com.acme.Foo").discovery.getSelectedClasses()),
-			() -> assertEquals(List.of(selectClass("com.acme.Foo")), type.parseArgLine("-select-class=com.acme.Foo").discovery.getSelectedClasses()),
 			() -> assertEquals(List.of(selectClass("com.acme.Foo")), type.parseArgLine("--select-class com.acme.Foo").discovery.getSelectedClasses()),
 			() -> assertEquals(List.of(selectClass("com.acme.Foo")), type.parseArgLine("--select-class=com.acme.Foo").discovery.getSelectedClasses()),
 			() -> assertEquals(List.of(selectClass("com.acme.Foo"), selectClass("com.example.Bar")), type.parseArgLine("-c com.acme.Foo -c com.example.Bar").discovery.getSelectedClasses()),
@@ -495,9 +474,6 @@ void parseValidMethodSelectors(ArgsType type) {
 		// @formatter:off
 		assertAll(
 			() -> assertEquals(List.of(selectMethod("com.acme.Foo#m()")), type.parseArgLine("-m com.acme.Foo#m()").discovery.getSelectedMethods()),
-			() -> assertEquals(List.of(selectMethod("com.acme.Foo#m()")), type.parseArgLine("--m com.acme.Foo#m()").discovery.getSelectedMethods()),
-			() -> assertEquals(List.of(selectMethod("com.acme.Foo#m()")), type.parseArgLine("-select-method com.acme.Foo#m()").discovery.getSelectedMethods()),
-			() -> assertEquals(List.of(selectMethod("com.acme.Foo#m()")), type.parseArgLine("-select-method=com.acme.Foo#m()").discovery.getSelectedMethods()),
 			() -> assertEquals(List.of(selectMethod("com.acme.Foo#m()")), type.parseArgLine("--select-method com.acme.Foo#m()").discovery.getSelectedMethods()),
 			() -> assertEquals(List.of(selectMethod("com.acme.Foo#m()")), type.parseArgLine("--select-method=com.acme.Foo#m()").discovery.getSelectedMethods()),
 			() -> assertEquals(List.of(selectMethod("com.acme.Foo#m()"), selectMethod("com.example.Bar#method(java.lang.Object)")),
@@ -519,9 +495,6 @@ void parseValidClasspathResourceSelectors(ArgsType type) {
 		// @formatter:off
 		assertAll(
 			() -> assertEquals(List.of(selectClasspathResource("/foo.csv")), type.parseArgLine("-r /foo.csv").discovery.getSelectedClasspathResources()),
-			() -> assertEquals(List.of(selectClasspathResource("/foo.csv")), type.parseArgLine("--r /foo.csv").discovery.getSelectedClasspathResources()),
-			() -> assertEquals(List.of(selectClasspathResource("/foo.csv")), type.parseArgLine("-select-resource /foo.csv").discovery.getSelectedClasspathResources()),
-			() -> assertEquals(List.of(selectClasspathResource("/foo.csv")), type.parseArgLine("-select-resource=/foo.csv").discovery.getSelectedClasspathResources()),
 			() -> assertEquals(List.of(selectClasspathResource("/foo.csv")), type.parseArgLine("--select-resource /foo.csv").discovery.getSelectedClasspathResources()),
 			() -> assertEquals(List.of(selectClasspathResource("/foo.csv")), type.parseArgLine("--select-resource=/foo.csv").discovery.getSelectedClasspathResources()),
 			() -> assertEquals(List.of(selectClasspathResource("/foo.csv"), selectClasspathResource("bar.json")), type.parseArgLine("-r /foo.csv -r bar.json").discovery.getSelectedClasspathResources()),
@@ -543,9 +516,9 @@ void parseValidIterationSelectors(ArgsType type) {
 		// @formatter:off
 		assertAll(
 			() -> assertEquals(List.of(selectIteration(selectClasspathResource("/foo.csv"), 0)), type.parseArgLine("-i resource:/foo.csv[0]").discovery.getSelectedIterations()),
-			() -> assertEquals(List.of(selectIteration(selectMethod("com.acme.Foo#m()"), 1, 2)), type.parseArgLine("--i method:com.acme.Foo#m()[1..2]").discovery.getSelectedIterations()),
-			() -> assertEquals(List.of(selectIteration(selectClass("com.acme.Foo"), 0, 2)), type.parseArgLine("-select-iteration class:com.acme.Foo[0,2]").discovery.getSelectedIterations()),
-			() -> assertEquals(List.of(selectIteration(selectPackage("com.acme.foo"), 3)), type.parseArgLine("-select-iteration=package:com.acme.foo[3]").discovery.getSelectedIterations()),
+			() -> assertEquals(List.of(selectIteration(selectMethod("com.acme.Foo#m()"), 1, 2)), type.parseArgLine("-i method:com.acme.Foo#m()[1..2]").discovery.getSelectedIterations()),
+			() -> assertEquals(List.of(selectIteration(selectClass("com.acme.Foo"), 0, 2)), type.parseArgLine("--select-iteration class:com.acme.Foo[0,2]").discovery.getSelectedIterations()),
+			() -> assertEquals(List.of(selectIteration(selectPackage("com.acme.foo"), 3)), type.parseArgLine("--select-iteration=package:com.acme.foo[3]").discovery.getSelectedIterations()),
 			() -> assertEquals(List.of(selectIteration(selectModule("com.acme.foo"), 0, 1, 2, 4, 5, 6)), type.parseArgLine("--select-iteration module:com.acme.foo[0..2,4..6]").discovery.getSelectedIterations()),
 			() -> assertEquals(List.of(selectIteration(selectDirectory("foo/bar"), 1, 5)), type.parseArgLine("--select-iteration=directory:foo/bar[1,5]").discovery.getSelectedIterations()),
 			() -> assertEquals(List.of(selectIteration(selectFile("foo.txt"), 6), selectIteration(selectUri("file:///foo.txt"), 7)), type.parseArgLine("-i file:foo.txt[6] -i uri:file:///foo.txt[7]").discovery.getSelectedIterations()),
@@ -580,7 +553,7 @@ void parseInvalidUniqueIdSelectors() {
 	@ParameterizedTest
 	@EnumSource
 	void parseClasspathScanningEntries(ArgsType type) {
-		var dir = Paths.get(".");
+		var dir = Path.of(".");
 		// @formatter:off
 		assertAll(
 			() -> assertTrue(type.parseArgLine("--scan-class-path").discovery.isScanClasspath()),
@@ -590,10 +563,8 @@ void parseClasspathScanningEntries(ArgsType type) {
 			() -> assertTrue(type.parseArgLine("--scan-class-path .").discovery.isScanClasspath()),
 			() -> assertEquals(List.of(dir), type.parseArgLine("--scan-class-path .").discovery.getSelectedClasspathEntries()),
 			() -> assertEquals(List.of(dir), type.parseArgLine("--scan-class-path=.").discovery.getSelectedClasspathEntries()),
-			() -> assertEquals(List.of(dir), type.parseArgLine("-scan-class-path .").discovery.getSelectedClasspathEntries()),
-			() -> assertEquals(List.of(dir), type.parseArgLine("-scan-class-path=.").discovery.getSelectedClasspathEntries()),
-			() -> assertEquals(List.of(dir, Paths.get("src/test/java")), type.parseArgLine("--scan-class-path . --scan-class-path src/test/java").discovery.getSelectedClasspathEntries()),
-			() -> assertEquals(List.of(dir, Paths.get("src/test/java")), type.parseArgLine("--scan-class-path ." + File.pathSeparator + "src/test/java").discovery.getSelectedClasspathEntries())
+			() -> assertEquals(List.of(dir, Path.of("src/test/java")), type.parseArgLine("--scan-class-path . --scan-class-path src/test/java").discovery.getSelectedClasspathEntries()),
+			() -> assertEquals(List.of(dir, Path.of("src/test/java")), type.parseArgLine("--scan-class-path ." + File.pathSeparator + "src/test/java").discovery.getSelectedClasspathEntries())
 		);
 		// @formatter:on
 	}
@@ -603,10 +574,6 @@ void parseClasspathScanningEntries(ArgsType type) {
 	void parseValidConfigurationParameters(ArgsType type) {
 		// @formatter:off
 		assertAll(
-			() -> assertThat(type.parseArgLine("-config foo=bar").discovery.getConfigurationParameters())
-					.containsOnly(entry("foo", "bar")),
-			() -> assertThat(type.parseArgLine("-config=foo=bar").discovery.getConfigurationParameters())
-					.containsOnly(entry("foo", "bar")),
 			() -> assertThat(type.parseArgLine("--config foo=bar").discovery.getConfigurationParameters())
 					.containsOnly(entry("foo", "bar")),
 			() -> assertThat(type.parseArgLine("--config=foo=bar").discovery.getConfigurationParameters())
@@ -632,13 +599,13 @@ void parseValidConfigurationParametersResource(ArgsType type) {
 
 	@Test
 	void parseInvalidConfigurationParameters() {
-		assertOptionWithMissingRequiredArgumentThrowsException("-config", "--config");
+		assertOptionWithMissingRequiredArgumentThrowsException("--config");
 	}
 
 	@ParameterizedTest
 	@EnumSource
 	void parseValidStdoutRedirectionFile(ArgsType type) {
-		var file = Paths.get("foo.txt");
+		var file = Path.of("foo.txt");
 		// @formatter:off
 		assertAll(
 			() -> assertNull(type.parseArgLine("").output.getStdoutPath()),
@@ -652,7 +619,7 @@ void parseValidStdoutRedirectionFile(ArgsType type) {
 	@ParameterizedTest
 	@EnumSource
 	void parseValidStderrRedirectionFile(ArgsType type) {
-		var file = Paths.get("foo.txt");
+		var file = Path.of("foo.txt");
 		// @formatter:off
 		assertAll(
 			() -> assertNull(type.parseArgLine("").output.getStderrPath()),
@@ -742,12 +709,12 @@ Result parseArgLine(String argLine) throws IOException {
 		abstract Result parseArgLine(String argLine) throws IOException;
 
 		private static String[] split(String argLine) {
-			return "".equals(argLine) ? new String[0] : argLine.split("\\s+");
+			return argLine.isEmpty() ? new String[0] : argLine.split("\\s+");
 		}
 	}
 
 	private static Result parse(String... args) {
-		ExecuteTestsCommand command = new ExecuteTestsCommand((__, ___) -> null);
+		ExecuteTestsCommand command = new ExecuteTestsCommand((__, ___) -> mock());
 		command.parseArgs(args);
 		return new Result(command.toTestDiscoveryOptions(), command.toTestConsoleOutputOptions());
 	}
diff --git a/platform-tests/src/test/java/org/junit/platform/console/options/ExecuteTestsCommandTests.java b/platform-tests/src/test/java/org/junit/platform/console/options/ExecuteTestsCommandTests.java
index d7186357b51c..f259409c39a6 100644
--- a/platform-tests/src/test/java/org/junit/platform/console/options/ExecuteTestsCommandTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/console/options/ExecuteTestsCommandTests.java
@@ -17,7 +17,7 @@
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.when;
 
-import java.nio.file.Paths;
+import java.nio.file.Path;
 import java.util.Optional;
 
 import org.junit.jupiter.api.BeforeEach;
@@ -96,7 +96,7 @@ void hasStatusCode0ForNoTestsAndNotFailIfNoTestsFound() {
 
 	@Test
 	void parseValidXmlReportsDirs() {
-		var dir = Paths.get("build", "test-results");
+		var dir = Path.of("build", "test-results");
 		// @formatter:off
 		assertAll(
 				() -> assertEquals(Optional.empty(), parseArgs().getReportsDir()),
diff --git a/platform-tests/src/test/java/org/junit/platform/console/tasks/ConsoleTestExecutorTests.java b/platform-tests/src/test/java/org/junit/platform/console/tasks/ConsoleTestExecutorTests.java
index f3c99037a180..76da53bcc218 100644
--- a/platform-tests/src/test/java/org/junit/platform/console/tasks/ConsoleTestExecutorTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/console/tasks/ConsoleTestExecutorTests.java
@@ -19,7 +19,7 @@
 
 import java.io.PrintWriter;
 import java.io.StringWriter;
-import java.nio.file.Paths;
+import java.nio.file.Path;
 import java.util.List;
 import java.util.Optional;
 
@@ -98,7 +98,7 @@ void printsFailuresEvenIfDetailsAreHidden() {
 
 	@Test
 	void usesCustomClassLoaderIfAdditionalClassPathEntriesArePresent() {
-		discoveryOptions.setAdditionalClasspathEntries(List.of(Paths.get(".")));
+		discoveryOptions.setAdditionalClasspathEntries(List.of(Path.of(".")));
 
 		var oldClassLoader = getDefaultClassLoader();
 		dummyTestEngine.addTest("failingTest",
diff --git a/platform-tests/src/test/java/org/junit/platform/console/tasks/DiscoveryRequestCreatorTests.java b/platform-tests/src/test/java/org/junit/platform/console/tasks/DiscoveryRequestCreatorTests.java
index e1ec970f3ecd..fdef039fe467 100644
--- a/platform-tests/src/test/java/org/junit/platform/console/tasks/DiscoveryRequestCreatorTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/console/tasks/DiscoveryRequestCreatorTests.java
@@ -22,11 +22,12 @@
 import static org.junit.platform.engine.discovery.DiscoverySelectors.selectIteration;
 import static org.junit.platform.engine.discovery.DiscoverySelectors.selectMethod;
 import static org.junit.platform.engine.discovery.DiscoverySelectors.selectPackage;
+import static org.junit.platform.engine.discovery.DiscoverySelectors.selectUniqueId;
 import static org.junit.platform.engine.discovery.DiscoverySelectors.selectUri;
 
 import java.io.File;
 import java.net.URI;
-import java.nio.file.Paths;
+import java.nio.file.Path;
 import java.util.List;
 import java.util.Map;
 import java.util.Map.Entry;
@@ -36,6 +37,7 @@
 import org.junit.platform.commons.PreconditionViolationException;
 import org.junit.platform.console.options.TestDiscoveryOptions;
 import org.junit.platform.engine.Filter;
+import org.junit.platform.engine.UniqueId;
 import org.junit.platform.engine.discovery.ClassNameFilter;
 import org.junit.platform.engine.discovery.ClassSelector;
 import org.junit.platform.engine.discovery.ClasspathResourceSelector;
@@ -46,6 +48,7 @@
 import org.junit.platform.engine.discovery.MethodSelector;
 import org.junit.platform.engine.discovery.PackageNameFilter;
 import org.junit.platform.engine.discovery.PackageSelector;
+import org.junit.platform.engine.discovery.UniqueIdSelector;
 import org.junit.platform.engine.discovery.UriSelector;
 import org.junit.platform.launcher.LauncherDiscoveryRequest;
 
@@ -73,7 +76,7 @@ void convertsScanClasspathOptionWithoutExplicitRootDirectories() {
 	@Test
 	void convertsScanClasspathOptionWithExplicitRootDirectories() {
 		options.setScanClasspath(true);
-		options.setSelectedClasspathEntries(List.of(Paths.get("."), Paths.get("..")));
+		options.setSelectedClasspathEntries(List.of(Path.of("."), Path.of("..")));
 
 		var request = convert();
 
@@ -87,7 +90,7 @@ void convertsScanClasspathOptionWithExplicitRootDirectories() {
 	@Test
 	void convertsScanClasspathOptionWithAdditionalClasspathEntries() {
 		options.setScanClasspath(true);
-		options.setAdditionalClasspathEntries(List.of(Paths.get("."), Paths.get("..")));
+		options.setAdditionalClasspathEntries(List.of(Path.of("."), Path.of("..")));
 
 		var request = convert();
 
@@ -218,6 +221,21 @@ void convertsEngineOptions() {
 		assertThat(engineFilters.get(1).toString()).contains("excludes", "[engine2]");
 	}
 
+	@Test
+	void propagatesUniqueIdSelectors() {
+		options.setSelectedUniqueId(List.of(selectUniqueId("[engine:a]/[1:1]"), selectUniqueId("[engine:b]/[2:2]")));
+
+		var request = convert();
+		var uriSelectors = request.getSelectorsByType(UniqueIdSelector.class);
+
+		assertThat(uriSelectors) //
+				.extracting(UniqueIdSelector::getUniqueId) //
+				.containsExactly( //
+					UniqueId.parse("[engine:a]/[1:1]"), //, //
+					UniqueId.parse("[engine:b]/[2:2]") //
+				);
+	}
+
 	@Test
 	void propagatesUriSelectors() {
 		options.setSelectedUris(List.of(selectUri("a"), selectUri("b")));
@@ -329,7 +347,6 @@ void propagatesSelectorIdentifiers() {
 	}
 
 	@Test
-	@SuppressWarnings("deprecation")
 	void convertsConfigurationParameters() {
 		options.setScanClasspath(true);
 		options.setConfigurationParameters(mapOf(entry("foo", "bar"), entry("baz", "true")));
@@ -337,13 +354,11 @@ void convertsConfigurationParameters() {
 		var request = convert();
 		var configurationParameters = request.getConfigurationParameters();
 
-		assertThat(configurationParameters.size()).isEqualTo(2);
 		assertThat(configurationParameters.get("foo")).contains("bar");
 		assertThat(configurationParameters.getBoolean("baz")).contains(true);
 	}
 
 	@Test
-	@SuppressWarnings("deprecation")
 	void convertsConfigurationParametersResources() {
 		options.setScanClasspath(true);
 		options.setConfigurationParameters(mapOf(entry("foo", "bar"), entry("com.example.prop.first", "baz")));
@@ -352,7 +367,6 @@ void convertsConfigurationParametersResources() {
 		var request = convert();
 		var configurationParameters = request.getConfigurationParameters();
 
-		assertThat(configurationParameters.size()).isEqualTo(2);
 		assertThat(configurationParameters.get("foo")).contains("bar");
 		assertThat(configurationParameters.get("com.example.prop.first")).contains("baz");
 		assertThat(configurationParameters.get("com.example.prop.second")).contains("second value");
diff --git a/platform-tests/src/test/java/org/junit/platform/console/tasks/TreePrinterTests.java b/platform-tests/src/test/java/org/junit/platform/console/tasks/TreePrinterTests.java
index b4f712a639f4..da51d1b3c959 100644
--- a/platform-tests/src/test/java/org/junit/platform/console/tasks/TreePrinterTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/console/tasks/TreePrinterTests.java
@@ -69,7 +69,7 @@ void emptyEngines() {
 	}
 
 	@Test
-	// https://github.com/junit-team/junit5/issues/786
+	// https://github.com/junit-team/junit-framework/issues/786
 	void printNodeHandlesNullMessageThrowableGracefully() {
 		var result = TestExecutionResult.failed(new NullPointerException());
 		var node = new TreeNode(identifier("NPE", "test()")).setResult(result);
@@ -78,7 +78,7 @@ void printNodeHandlesNullMessageThrowableGracefully() {
 	}
 
 	@Test
-	// https://github.com/junit-team/junit5/issues/1531
+	// https://github.com/junit-team/junit-framework/issues/1531
 	void reportsAreTabbedCorrectly() {
 		var root = new TreeNode("<root>");
 		var e1 = new TreeNode(identifier("e-1", "engine one")).setResult(successful());
diff --git a/platform-tests/src/test/java/org/junit/platform/engine/CompositeTestDescriptorVisitorTests.java b/platform-tests/src/test/java/org/junit/platform/engine/CompositeTestDescriptorVisitorTests.java
index 88ee3f0ed7aa..675de2bd7002 100644
--- a/platform-tests/src/test/java/org/junit/platform/engine/CompositeTestDescriptorVisitorTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/engine/CompositeTestDescriptorVisitorTests.java
@@ -22,6 +22,7 @@
 
 class CompositeTestDescriptorVisitorTests {
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void checksPreconditions() {
 		assertThrows(PreconditionViolationException.class, Visitor::composite);
diff --git a/platform-tests/src/test/java/org/junit/platform/engine/TestTagTests.java b/platform-tests/src/test/java/org/junit/platform/engine/TestTagTests.java
index 63adfe5e51a5..0a8bf6fae4cf 100644
--- a/platform-tests/src/test/java/org/junit/platform/engine/TestTagTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/engine/TestTagTests.java
@@ -28,6 +28,7 @@
  */
 class TestTagTests {
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void validSyntax() {
 		// @formatter:off
@@ -65,6 +66,7 @@ void factory() {
 		assertEquals("foo-tag", TestTag.create("\t  foo-tag  \n").getName());
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void factoryPreconditions() {
 		assertSyntaxViolation(null);
@@ -89,11 +91,11 @@ void toStringPrintsName() {
 	}
 
 	private static void yep(String tag) {
-		assertTrue(TestTag.isValid(tag), () -> String.format("'%s' should be a valid tag", tag));
+		assertTrue(TestTag.isValid(tag), () -> "'%s' should be a valid tag".formatted(tag));
 	}
 
 	private static void nope(String tag) {
-		assertFalse(TestTag.isValid(tag), () -> String.format("'%s' should not be a valid tag", tag));
+		assertFalse(TestTag.isValid(tag), () -> "'%s' should not be a valid tag".formatted(tag));
 	}
 
 	private void assertSyntaxViolation(String tag) {
diff --git a/platform-tests/src/test/java/org/junit/platform/engine/UniqueIdFormatTests.java b/platform-tests/src/test/java/org/junit/platform/engine/UniqueIdFormatTests.java
index 47d1913f19e2..bedc9014524f 100644
--- a/platform-tests/src/test/java/org/junit/platform/engine/UniqueIdFormatTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/engine/UniqueIdFormatTests.java
@@ -10,9 +10,9 @@
 
 package org.junit.platform.engine;
 
+import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertThrows;
-import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Test;
@@ -115,7 +115,7 @@ interface ParsingTestTrait {
 		@Test
 		default void parseMalformedUid() {
 			Throwable throwable = assertThrows(JUnitException.class, () -> getFormat().parse("malformed UID"));
-			assertTrue(throwable.getMessage().contains("malformed UID"));
+			assertThat(throwable).hasMessageContaining("malformed UID");
 		}
 
 		@Test
diff --git a/platform-tests/src/test/java/org/junit/platform/engine/UniqueIdTests.java b/platform-tests/src/test/java/org/junit/platform/engine/UniqueIdTests.java
index 9001186fa9f3..4a18ec05cf05 100644
--- a/platform-tests/src/test/java/org/junit/platform/engine/UniqueIdTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/engine/UniqueIdTests.java
@@ -61,7 +61,7 @@ void retrievingOptionalEngineId() {
 			var uniqueIdWithEngine = UniqueId.forEngine(ENGINE_ID);
 			assertThat(uniqueIdWithEngine.getEngineId()).contains("junit-jupiter");
 
-			var uniqueIdWithoutEngine = UniqueId.root("root", "avalue");
+			var uniqueIdWithoutEngine = UniqueId.root("root", "aValue");
 			assertEquals(Optional.empty(), uniqueIdWithoutEngine.getEngineId());
 		}
 
@@ -123,6 +123,7 @@ void appendingSegmentInstance() {
 			assertSegment(uniqueId.getSegments().get(2), "t2", "v2");
 		}
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void appendingNullIsNotAllowed() {
 			var uniqueId = UniqueId.forEngine(ENGINE_ID);
@@ -229,6 +230,7 @@ void additionalSegmentMakesItNotEqual() {
 	@Nested
 	class Prefixing {
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void nullIsNotAPrefix() {
 			var id = UniqueId.forEngine(ENGINE_ID);
diff --git a/platform-tests/src/test/java/org/junit/platform/engine/discovery/ClassNameFilterTests.java b/platform-tests/src/test/java/org/junit/platform/engine/discovery/ClassNameFilterTests.java
index fd14be421e26..158f086fae47 100644
--- a/platform-tests/src/test/java/org/junit/platform/engine/discovery/ClassNameFilterTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/engine/discovery/ClassNameFilterTests.java
@@ -23,6 +23,7 @@
  */
 class ClassNameFilterTests {
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void includeClassNamePatternsChecksPreconditions() {
 		assertThatThrownBy(() -> ClassNameFilter.includeClassNamePatterns((String[]) null)) //
@@ -85,6 +86,7 @@ void includeClassNamePatternsWithMultiplePatterns() {
 					+ secondRegex + "'");
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void excludeClassNamePatternsChecksPreconditions() {
 		assertThatThrownBy(() -> ClassNameFilter.excludeClassNamePatterns((String[]) null)) //
diff --git a/platform-tests/src/test/java/org/junit/platform/engine/discovery/DiscoverySelectorsTests.java b/platform-tests/src/test/java/org/junit/platform/engine/discovery/DiscoverySelectorsTests.java
index c384a90434d2..85ca8917a208 100644
--- a/platform-tests/src/test/java/org/junit/platform/engine/discovery/DiscoverySelectorsTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/engine/discovery/DiscoverySelectorsTests.java
@@ -37,13 +37,11 @@
 import java.lang.reflect.Method;
 import java.net.URI;
 import java.nio.file.Path;
-import java.nio.file.Paths;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
 import java.util.Optional;
 import java.util.Set;
-import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
 import org.junit.jupiter.api.DisplayName;
@@ -71,6 +69,7 @@ class DiscoverySelectorsTests {
 	@Nested
 	class SelectUriTests {
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void selectUriByName() {
 			assertViolatesPrecondition(() -> selectUri((String) null));
@@ -83,6 +82,7 @@ void selectUriByName() {
 			assertEquals(uri, selector.getUri().toString());
 		}
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void selectUriByURI() {
 			assertViolatesPrecondition(() -> selectUri((URI) null));
@@ -108,6 +108,7 @@ void parseUriSelector() {
 					.isEqualTo(URI.create("https://junit.org"));
 		}
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void selectFileByName() {
 			assertViolatesPrecondition(() -> selectFile((String) null));
@@ -118,9 +119,10 @@ void selectFileByName() {
 			var selector = selectFile(path);
 			assertEquals(path, selector.getRawPath());
 			assertEquals(new File(path), selector.getFile());
-			assertEquals(Paths.get(path), selector.getPath());
+			assertEquals(Path.of(path), selector.getPath());
 		}
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void selectFileByNameAndPosition() {
 			var filePosition = FilePosition.from(12, 34);
@@ -132,10 +134,11 @@ void selectFileByNameAndPosition() {
 			var selector = selectFile(path, filePosition);
 			assertEquals(path, selector.getRawPath());
 			assertEquals(new File(path), selector.getFile());
-			assertEquals(Paths.get(path), selector.getPath());
+			assertEquals(Path.of(path), selector.getPath());
 			assertEquals(filePosition, selector.getPosition().orElseThrow());
 		}
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void selectFileByFileReference() throws Exception {
 			assertViolatesPrecondition(() -> selectFile((File) null));
@@ -149,9 +152,10 @@ void selectFileByFileReference() throws Exception {
 			var selector = selectFile(file);
 			assertEquals(path, selector.getRawPath());
 			assertEquals(file.getCanonicalFile(), selector.getFile());
-			assertEquals(Paths.get(path), selector.getPath());
+			assertEquals(Path.of(path), selector.getPath());
 		}
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void selectFileByFileReferenceAndPosition() throws Exception {
 			var filePosition = FilePosition.from(12, 34);
@@ -166,7 +170,7 @@ void selectFileByFileReferenceAndPosition() throws Exception {
 			var selector = selectFile(file, filePosition);
 			assertEquals(path, selector.getRawPath());
 			assertEquals(file.getCanonicalFile(), selector.getFile());
-			assertEquals(Paths.get(path), selector.getPath());
+			assertEquals(Path.of(path), selector.getPath());
 			assertEquals(FilePosition.from(12, 34), selector.getPosition().orElseThrow());
 		}
 
@@ -184,7 +188,7 @@ void parseFileSelectorWithRelativePath() {
 					.asInstanceOf(type(FileSelector.class)) //
 					.extracting(FileSelector::getRawPath, FileSelector::getFile, FileSelector::getPath,
 						FileSelector::getPosition) //
-					.containsExactly(path, new File(path), Paths.get(path), Optional.empty());
+					.containsExactly(path, new File(path), Path.of(path), Optional.empty());
 		}
 
 		@Test
@@ -197,7 +201,7 @@ void parseFileSelectorWithAbsolutePath() {
 					.asInstanceOf(type(FileSelector.class)) //
 					.extracting(FileSelector::getRawPath, FileSelector::getFile, FileSelector::getPath,
 						FileSelector::getPosition) //
-					.containsExactly(absolutePath, new File(absolutePath), Paths.get(absolutePath), Optional.empty());
+					.containsExactly(absolutePath, new File(absolutePath), Path.of(absolutePath), Optional.empty());
 		}
 
 		@Test
@@ -210,7 +214,7 @@ void parseFileSelectorWithRelativePathAndFilePosition() {
 					.asInstanceOf(type(FileSelector.class)) //
 					.extracting(FileSelector::getRawPath, FileSelector::getFile, FileSelector::getPath,
 						FileSelector::getPosition) //
-					.containsExactly(path, new File(path), Paths.get(path), Optional.of(filePosition));
+					.containsExactly(path, new File(path), Path.of(path), Optional.of(filePosition));
 		}
 
 		@Test
@@ -224,10 +228,11 @@ void parseFileSelectorWithAbsolutePathAndFilePosition() {
 					.asInstanceOf(type(FileSelector.class)) //
 					.extracting(FileSelector::getRawPath, FileSelector::getFile, FileSelector::getPath,
 						FileSelector::getPosition) //
-					.containsExactly(absolutePath, new File(absolutePath), Paths.get(absolutePath),
+					.containsExactly(absolutePath, new File(absolutePath), Path.of(absolutePath),
 						Optional.of(filePosition));
 		}
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void selectDirectoryByName() {
 			assertViolatesPrecondition(() -> selectDirectory((String) null));
@@ -238,9 +243,10 @@ void selectDirectoryByName() {
 			var selector = selectDirectory(path);
 			assertEquals(path, selector.getRawPath());
 			assertEquals(new File(path), selector.getDirectory());
-			assertEquals(Paths.get(path), selector.getPath());
+			assertEquals(Path.of(path), selector.getPath());
 		}
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void selectDirectoryByFileReference() throws Exception {
 			assertViolatesPrecondition(() -> selectDirectory((File) null));
@@ -254,7 +260,7 @@ void selectDirectoryByFileReference() throws Exception {
 			var selector = selectDirectory(directory);
 			assertEquals(path, selector.getRawPath());
 			assertEquals(directory.getCanonicalFile(), selector.getDirectory());
-			assertEquals(Paths.get(path), selector.getPath());
+			assertEquals(Path.of(path), selector.getPath());
 		}
 
 	}
@@ -272,7 +278,7 @@ void parseDirectorySelectorWithRelativePath() {
 					.asInstanceOf(type(DirectorySelector.class)) //
 					.extracting(DirectorySelector::getRawPath, DirectorySelector::getDirectory,
 						DirectorySelector::getPath) //
-					.containsExactly(path, new File(path), Paths.get(path));
+					.containsExactly(path, new File(path), Path.of(path));
 		}
 
 		@Test
@@ -285,9 +291,10 @@ void parseDirectorySelectorWithAbsolutePath() {
 					.asInstanceOf(type(DirectorySelector.class)) //
 					.extracting(DirectorySelector::getRawPath, DirectorySelector::getDirectory,
 						DirectorySelector::getPath) //
-					.containsExactly(path, new File(path), Paths.get(path));
+					.containsExactly(path, new File(path), Path.of(path));
 		}
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void selectClasspathResourcesPreconditions() {
 			assertViolatesPrecondition(() -> selectClasspathResource((String) null));
@@ -331,6 +338,7 @@ void getMissingClasspathResources() {
 			assertViolatesPrecondition(selector::getClasspathResources);
 		}
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void selectClasspathResourcesWithFilePosition() {
 			var filePosition = FilePosition.from(12, 34);
@@ -398,7 +406,7 @@ public String getName() {
 
 			@Override
 			public URI getUri() {
-				return null;
+				throw new UnsupportedOperationException();
 			}
 		}
 	}
@@ -421,6 +429,7 @@ void parseModuleByName() {
 					.isEqualTo("java.base");
 		}
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void selectModuleByNamePreconditions() {
 			assertViolatesPrecondition(() -> selectModule(null));
@@ -431,10 +440,11 @@ void selectModuleByNamePreconditions() {
 		@Test
 		void selectModulesByNames() {
 			var selectors = selectModules(Set.of("a", "b"));
-			var names = selectors.stream().map(ModuleSelector::getModuleName).collect(Collectors.toList());
+			var names = selectors.stream().map(ModuleSelector::getModuleName).toList();
 			assertThat(names).containsExactlyInAnyOrder("b", "a");
 		}
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void selectModulesByNamesPreconditions() {
 			assertViolatesPrecondition(() -> selectModules(null));
@@ -468,14 +478,14 @@ class SelectClasspathRootsTests {
 
 		@Test
 		void selectClasspathRootsWithNonExistingDirectory() {
-			var selectors = selectClasspathRoots(Set.of(Paths.get("some", "local", "path")));
+			var selectors = selectClasspathRoots(Set.of(Path.of("some", "local", "path")));
 
 			assertThat(selectors).isEmpty();
 		}
 
 		@Test
 		void selectClasspathRootsWithNonExistingJarFile() {
-			var selectors = selectClasspathRoots(Set.of(Paths.get("some.jar")));
+			var selectors = selectClasspathRoots(Set.of(Path.of("some.jar")));
 
 			assertThat(selectors).isEmpty();
 		}
@@ -490,7 +500,7 @@ void selectClasspathRootsWithExistingDirectory(@TempDir Path tempDir) {
 		@Test
 		void selectClasspathRootsWithExistingJarFile() throws Exception {
 			var jarUri = requireNonNull(getClass().getResource("/jartest.jar")).toURI();
-			var jarFile = Paths.get(jarUri);
+			var jarFile = Path.of(jarUri);
 
 			var selectors = selectClasspathRoots(Set.of(jarFile));
 
@@ -534,6 +544,7 @@ void selectClassByNameWithExplicitClassLoader() throws Exception {
 	@Nested
 	class SelectMethodTests {
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		@DisplayName("Preconditions: selectMethod(className, methodName)")
 		void selectMethodByClassNameAndMethodNamePreconditions() {
@@ -545,6 +556,7 @@ void selectMethodByClassNameAndMethodNamePreconditions() {
 			assertViolatesPrecondition(() -> selectMethod("   ", "method"));
 		}
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		@DisplayName("Preconditions: selectMethod(className, methodName, parameterTypeNames)")
 		void selectMethodByClassNameMethodNameAndParameterTypeNamesPreconditions() {
@@ -557,6 +569,7 @@ void selectMethodByClassNameMethodNameAndParameterTypeNamesPreconditions() {
 			assertViolatesPrecondition(() -> selectMethod("TestClass", "method", (String) null));
 		}
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		@DisplayName("Preconditions: selectMethod(className, methodName, parameterTypes)")
 		void selectMethodByClassNameMethodNameAndParameterTypesPreconditions() {
@@ -570,6 +583,7 @@ void selectMethodByClassNameMethodNameAndParameterTypesPreconditions() {
 			assertViolatesPrecondition(() -> selectMethod("TestClass", "method", new Class<?>[] { int.class, null }));
 		}
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		@DisplayName("Preconditions: selectMethod(class, methodName)")
 		void selectMethodByClassAndMethodNamePreconditions() {
@@ -579,6 +593,7 @@ void selectMethodByClassAndMethodNamePreconditions() {
 			assertViolatesPrecondition(() -> selectMethod((Class<?>) null, "method"));
 		}
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		@DisplayName("Preconditions: selectMethod(class, methodName, parameterTypeNames)")
 		void selectMethodByClassMethodNameAndParameterTypeNamesPreconditions() {
@@ -589,6 +604,7 @@ void selectMethodByClassMethodNameAndParameterTypeNamesPreconditions() {
 			assertViolatesPrecondition(() -> selectMethod(testClass(), "method", (String) null));
 		}
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		@DisplayName("Preconditions: selectMethod(class, method)")
 		void selectMethodByClassAndMethodPreconditions() {
@@ -824,7 +840,7 @@ void selectMethodByFullyQualifiedNameContainingHashtagsAndWithParameterList() {
 			var className = "org.example.CalculatorSpec";
 			var methodName = "#a plus #b equals #c";
 			var methodParameters = "int, int, int";
-			var fqmn = String.format("%s#%s(%s)", className, methodName, methodParameters);
+			var fqmn = "%s#%s(%s)".formatted(className, methodName, methodParameters);
 
 			var selector = selectMethod(fqmn);
 			assertEquals(className, selector.getClassName());
@@ -875,7 +891,7 @@ void selectMethodByFullyQualifiedNameEndingWithParenthesesAndWithParameterList()
 			var className = "org.example.KotlinTestCase";
 			var methodName = "test name ends with parentheses()";
 			var methodParameters = "int, int, int";
-			var fqmn = String.format("%s#%s(%s)", className, methodName, methodParameters);
+			var fqmn = "%s#%s(%s)".formatted(className, methodName, methodParameters);
 
 			var selector = selectMethod(fqmn);
 
@@ -1132,6 +1148,7 @@ void selectDoubleNestedClassByClassNames() {
 			assertThat(parseIdentifier(selector)).isEqualTo(selector);
 		}
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void selectNestedClassPreconditions() {
 			assertViolatesPrecondition(() -> selectNestedClass(null, "ClassName"));
@@ -1299,6 +1316,7 @@ void selectDoubleNestedMethodByEnclosingClassNamesAndMethodName() throws Excepti
 			assertThat(parseIdentifier(selector)).isEqualTo(selector);
 		}
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		@DisplayName("Preconditions: selectNestedMethod(enclosingClassNames, nestedClassName, methodName)")
 		void selectNestedMethodByEnclosingClassNamesAndMethodNamePreconditions() {
@@ -1310,6 +1328,7 @@ void selectNestedMethodByEnclosingClassNamesAndMethodNamePreconditions() {
 			assertViolatesPrecondition(() -> selectNestedMethod(List.of("ClassName"), "ClassName", " "));
 		}
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		@DisplayName("Preconditions: selectNestedMethod(enclosingClassNames, nestedClassName, methodName, parameterTypeNames)")
 		void selectNestedMethodByEnclosingClassNamesMethodNameAndParameterTypeNamesPreconditions() {
@@ -1326,6 +1345,7 @@ void selectNestedMethodByEnclosingClassNamesMethodNameAndParameterTypeNamesPreco
 		/**
 		 * @since 1.10
 		 */
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		@DisplayName("Preconditions: selectNestedMethod(enclosingClassNames, nestedClassName, methodName, parameterTypes)")
 		void selectNestedMethodByEnclosingClassNamesMethodNameAndParameterTypesPreconditions() {
@@ -1344,6 +1364,7 @@ void selectNestedMethodByEnclosingClassNamesMethodNameAndParameterTypesPrecondit
 		/**
 		 * @since 1.10
 		 */
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		@DisplayName("Preconditions: selectNestedMethod(enclosingClasses, nestedClass, methodName, parameterTypes)")
 		void selectNestedMethodByEnclosingClassesClassMethodNameAndParameterTypesPreconditions() {
@@ -1440,7 +1461,7 @@ private static String fqmn(Class<?> clazz, String methodName, Class<?>... params
 	}
 
 	private static String fqmnWithParamNames(String... params) {
-		return String.format("%s#%s(%s)", DiscoverySelectorsTests.class.getName(), "myTest", join(", ", params));
+		return "%s#%s(%s)".formatted(DiscoverySelectorsTests.class.getName(), "myTest", join(", ", params));
 	}
 
 	interface TestInterface {
diff --git a/platform-tests/src/test/java/org/junit/platform/engine/discovery/PackageNameFilterTests.java b/platform-tests/src/test/java/org/junit/platform/engine/discovery/PackageNameFilterTests.java
index b93ba77a34c9..fb52e9c9858b 100644
--- a/platform-tests/src/test/java/org/junit/platform/engine/discovery/PackageNameFilterTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/engine/discovery/PackageNameFilterTests.java
@@ -23,6 +23,7 @@
  */
 class PackageNameFilterTests {
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void includePackageChecksPreconditions() {
 		assertThatThrownBy(() -> PackageNameFilter.includePackageNames((String[]) null)) //
@@ -74,6 +75,7 @@ void includePackageWithMultiplePackages() {
 					+ includedPackage2 + "'");
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void excludePackageChecksPreconditions() {
 		assertThatThrownBy(() -> PackageNameFilter.excludePackageNames((String[]) null)) //
diff --git a/platform-tests/src/test/java/org/junit/platform/engine/support/config/PrefixedConfigurationParametersTests.java b/platform-tests/src/test/java/org/junit/platform/engine/support/config/PrefixedConfigurationParametersTests.java
index ae64f77463d3..c2f4fa7f0fb2 100644
--- a/platform-tests/src/test/java/org/junit/platform/engine/support/config/PrefixedConfigurationParametersTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/engine/support/config/PrefixedConfigurationParametersTests.java
@@ -37,6 +37,7 @@ class PrefixedConfigurationParametersTests {
 	@Mock
 	private ConfigurationParameters delegate;
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void preconditions() {
 		assertThrows(PreconditionViolationException.class, () -> new PrefixedConfigurationParameters(null, "example."));
@@ -76,15 +77,4 @@ void delegatesGetWithTransformerCalls() {
 		verify(delegate).get("foo.bar.qux", transformer);
 	}
 
-	@Test
-	@SuppressWarnings("deprecation")
-	void delegatesSizeCalls() {
-		when(delegate.size()).thenReturn(42);
-		var parameters = new PrefixedConfigurationParameters(delegate, "foo.bar.");
-
-		assertThat(parameters.size()).isEqualTo(42);
-
-		verify(delegate).size();
-	}
-
 }
diff --git a/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/AbstractTestDescriptorTests.java b/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/AbstractTestDescriptorTests.java
index bfa105bf1168..9f2954636e74 100644
--- a/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/AbstractTestDescriptorTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/AbstractTestDescriptorTests.java
@@ -111,8 +111,9 @@ void visitAllNodes() {
 	@Test
 	void pruneLeaf() {
 		TestDescriptor.Visitor visitor = descriptor -> {
-			if (descriptor.getUniqueId().equals(UniqueId.root("leaf", "leaf1-1")))
+			if (descriptor.getUniqueId().equals(UniqueId.root("leaf", "leaf1-1"))) {
 				descriptor.removeFromHierarchy();
+			}
 		};
 		engineDescriptor.accept(visitor);
 
@@ -128,8 +129,9 @@ void pruneLeaf() {
 	void pruneGroup() {
 		final var countVisited = new AtomicInteger();
 		TestDescriptor.Visitor visitor = descriptor -> {
-			if (descriptor.getUniqueId().equals(UniqueId.root("group", "group1")))
+			if (descriptor.getUniqueId().equals(UniqueId.root("group", "group1"))) {
 				descriptor.removeFromHierarchy();
+			}
 			countVisited.incrementAndGet();
 		};
 		engineDescriptor.accept(visitor);
diff --git a/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/ClassSourceTests.java b/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/ClassSourceTests.java
index 078c9f629c76..e1ee9cd4e0e3 100644
--- a/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/ClassSourceTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/ClassSourceTests.java
@@ -39,6 +39,7 @@ Stream<Serializable> createSerializableInstances() {
 		);
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void preconditions() {
 		assertThrows(PreconditionViolationException.class, () -> ClassSource.from((String) null));
diff --git a/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/ClasspathResourceSourceTests.java b/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/ClasspathResourceSourceTests.java
index 9141a47fd5bb..a84a471d9b92 100644
--- a/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/ClasspathResourceSourceTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/ClasspathResourceSourceTests.java
@@ -38,6 +38,7 @@ Stream<ClasspathResourceSource> createSerializableInstances() {
 		return Stream.of(ClasspathResourceSource.from(FOO_RESOURCE));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void preconditions() {
 		assertThrows(PreconditionViolationException.class, () -> ClasspathResourceSource.from((String) null));
diff --git a/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/CompositeTestSourceTests.java b/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/CompositeTestSourceTests.java
index 2702e480ae33..f09f0efbcaa3 100644
--- a/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/CompositeTestSourceTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/CompositeTestSourceTests.java
@@ -37,6 +37,7 @@ Stream<CompositeTestSource> createSerializableInstances() {
 		return Stream.of(CompositeTestSource.from(sources));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void createCompositeTestSourceFromNullList() {
 		assertThrows(PreconditionViolationException.class, () -> CompositeTestSource.from(null));
diff --git a/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/DefaultUriSourceTests.java b/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/DefaultUriSourceTests.java
index 03f5edd70f6b..f68fc5e6d8c3 100644
--- a/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/DefaultUriSourceTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/DefaultUriSourceTests.java
@@ -33,6 +33,7 @@ Stream<UriSource> createSerializableInstances() {
 		return Stream.of(new DefaultUriSource(URI.create("sample://instance")));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void nullSourceUriYieldsException() {
 		assertThrows(PreconditionViolationException.class, () -> new DefaultUriSource(null));
diff --git a/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/DemoMethodTestDescriptor.java b/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/DemoMethodTestDescriptor.java
index 2c4dcb8b7402..9b90b9f63ca7 100644
--- a/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/DemoMethodTestDescriptor.java
+++ b/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/DemoMethodTestDescriptor.java
@@ -32,7 +32,7 @@ public class DemoMethodTestDescriptor extends AbstractTestDescriptor {
 
 	public DemoMethodTestDescriptor(UniqueId uniqueId, Method testMethod) {
 		super(uniqueId,
-			String.format("%s(%s)", Preconditions.notNull(testMethod, "Method must not be null").getName(),
+			"%s(%s)".formatted(Preconditions.notNull(testMethod, "Method must not be null").getName(),
 				ClassUtils.nullSafeToString(Class::getSimpleName, testMethod.getParameterTypes())),
 			MethodSource.from(testMethod));
 
diff --git a/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/FileSystemSourceTests.java b/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/FileSystemSourceTests.java
index 307193a02774..9f6723b85e31 100644
--- a/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/FileSystemSourceTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/FileSystemSourceTests.java
@@ -34,6 +34,7 @@ Stream<FileSource> createSerializableInstances() {
 			FileSource.from(new File("file.and.position"), FilePosition.from(42, 23)));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void nullSourceFileOrDirectoryYieldsException() {
 		assertThrows(PreconditionViolationException.class, () -> FileSource.from(null));
diff --git a/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/MethodSourceTests.java b/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/MethodSourceTests.java
index 4f97624c7ce6..df9106349d16 100644
--- a/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/MethodSourceTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/MethodSourceTests.java
@@ -57,6 +57,7 @@ void equalsAndHashCodeForMethodSource() throws Exception {
 		assertEqualsAndHashCode(MethodSource.from(method1), MethodSource.from(method1), MethodSource.from(method2));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void instantiatingWithNullNamesShouldThrowPreconditionViolationException() {
 		assertThrows(PreconditionViolationException.class, () -> MethodSource.from("foo", null));
@@ -75,11 +76,13 @@ void instantiatingWithBlankNamesShouldThrowPreconditionViolationException() {
 		assertThrows(PreconditionViolationException.class, () -> MethodSource.from("  ", "foo"));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void instantiationWithNullMethodShouldThrowPreconditionViolationException() {
 		assertThrows(PreconditionViolationException.class, () -> MethodSource.from(null));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void instantiationWithNullClassOrMethodShouldThrowPreconditionViolationException() {
 		assertThrows(PreconditionViolationException.class,
diff --git a/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/PackageSourceTests.java b/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/PackageSourceTests.java
index 8da7f16a8545..f964343c4c2d 100644
--- a/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/PackageSourceTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/PackageSourceTests.java
@@ -32,6 +32,7 @@ Stream<Serializable> createSerializableInstances() {
 		return Stream.of(PackageSource.from("package.source"));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void packageSourceFromNullPackageName() {
 		assertThrows(PreconditionViolationException.class, () -> PackageSource.from((String) null));
@@ -42,6 +43,7 @@ void packageSourceFromEmptyPackageName() {
 		assertThrows(PreconditionViolationException.class, () -> PackageSource.from("  "));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void packageSourceFromNullPackageReference() {
 		assertThrows(PreconditionViolationException.class, () -> PackageSource.from((Package) null));
diff --git a/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/TestDescriptorOrderChildrenTests.java b/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/TestDescriptorOrderChildrenTests.java
index 55e0d80a20b9..8d0e8e239dc1 100644
--- a/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/TestDescriptorOrderChildrenTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/TestDescriptorOrderChildrenTests.java
@@ -116,6 +116,7 @@ default void orderChildrenDuplicatesDescriptor() {
 		assertThat(exception).hasMessage("orderer may not add or remove test descriptors");
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	default void orderChildrenOrdererReturnsNull() {
 		var testDescriptor = createTestDescriptorWithChildren();
diff --git a/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/TestDescriptorTests.java b/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/TestDescriptorTests.java
index 2d7d96308ecd..b1b0591d5b3a 100644
--- a/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/TestDescriptorTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/engine/support/descriptor/TestDescriptorTests.java
@@ -15,6 +15,7 @@
 import java.util.Optional;
 import java.util.Set;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.platform.engine.TestDescriptor;
 import org.junit.platform.engine.TestSource;
 import org.junit.platform.engine.TestTag;
@@ -57,7 +58,7 @@ public Optional<TestDescriptor> getParent() {
 		}
 
 		@Override
-		public void setParent(TestDescriptor parent) {
+		public void setParent(@Nullable TestDescriptor parent) {
 			throw new UnsupportedOperationException("Not implemented");
 		}
 
diff --git a/platform-tests/src/test/java/org/junit/platform/engine/support/hierarchical/DefaultParallelExecutionConfigurationStrategyTests.java b/platform-tests/src/test/java/org/junit/platform/engine/support/hierarchical/DefaultParallelExecutionConfigurationStrategyTests.java
index 9a55301ab6af..d4683aad6d7b 100644
--- a/platform-tests/src/test/java/org/junit/platform/engine/support/hierarchical/DefaultParallelExecutionConfigurationStrategyTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/engine/support/hierarchical/DefaultParallelExecutionConfigurationStrategyTests.java
@@ -49,6 +49,7 @@ void fixedStrategyCreatesValidConfiguration() {
 		assertThat(configuration.getMinimumRunnable()).isEqualTo(42);
 		assertThat(configuration.getMaxPoolSize()).isEqualTo(256 + 42);
 		assertThat(configuration.getKeepAliveSeconds()).isEqualTo(30);
+		assertThat(configuration.getSaturatePredicate()).isNotNull();
 		assertThat(configuration.getSaturatePredicate().test(null)).isTrue();
 	}
 
@@ -62,6 +63,7 @@ void fixedSaturateStrategyCreatesValidConfiguration() {
 		var configuration = strategy.createConfiguration(configParams);
 		assertThat(configuration.getParallelism()).isEqualTo(42);
 		assertThat(configuration.getMaxPoolSize()).isEqualTo(42);
+		assertThat(configuration.getSaturatePredicate()).isNotNull();
 		assertThat(configuration.getSaturatePredicate().test(null)).isFalse();
 	}
 
@@ -78,6 +80,7 @@ void dynamicStrategyCreatesValidConfiguration() {
 		assertThat(configuration.getMinimumRunnable()).isEqualTo(availableProcessors * 2);
 		assertThat(configuration.getMaxPoolSize()).isEqualTo(256 + (availableProcessors * 2));
 		assertThat(configuration.getKeepAliveSeconds()).isEqualTo(30);
+		assertThat(configuration.getSaturatePredicate()).isNotNull();
 		assertThat(configuration.getSaturatePredicate().test(null)).isTrue();
 	}
 
@@ -96,6 +99,7 @@ void dynamicSaturateStrategyCreatesValidConfiguration() {
 		assertThat(configuration.getMinimumRunnable()).isEqualTo(availableProcessors * 2);
 		assertThat(configuration.getMaxPoolSize()).isEqualTo(availableProcessors * 6);
 		assertThat(configuration.getKeepAliveSeconds()).isEqualTo(30);
+		assertThat(configuration.getSaturatePredicate()).isNotNull();
 		assertThat(configuration.getSaturatePredicate().test(null)).isFalse();
 	}
 
diff --git a/platform-tests/src/test/java/org/junit/platform/engine/support/hierarchical/ForkJoinDeadLockTests.java b/platform-tests/src/test/java/org/junit/platform/engine/support/hierarchical/ForkJoinDeadLockTests.java
index 5663e4e0be8c..81afa0225570 100644
--- a/platform-tests/src/test/java/org/junit/platform/engine/support/hierarchical/ForkJoinDeadLockTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/engine/support/hierarchical/ForkJoinDeadLockTests.java
@@ -36,7 +36,7 @@
 import org.junit.platform.engine.discovery.DiscoverySelectors;
 import org.junit.platform.testkit.engine.EngineTestKit;
 
-// https://github.com/junit-team/junit5/issues/3945
+// https://github.com/junit-team/junit-framework/issues/3945
 @Timeout(10)
 public class ForkJoinDeadLockTests {
 
diff --git a/platform-tests/src/test/java/org/junit/platform/engine/support/hierarchical/ForkJoinPoolHierarchicalTestExecutorServiceTests.java b/platform-tests/src/test/java/org/junit/platform/engine/support/hierarchical/ForkJoinPoolHierarchicalTestExecutorServiceTests.java
index 59dfbba0f789..a31f31598a4a 100644
--- a/platform-tests/src/test/java/org/junit/platform/engine/support/hierarchical/ForkJoinPoolHierarchicalTestExecutorServiceTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/engine/support/hierarchical/ForkJoinPoolHierarchicalTestExecutorServiceTests.java
@@ -33,6 +33,7 @@
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.atomic.AtomicReference;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.Timeout;
 import org.junit.jupiter.api.function.Executable;
@@ -105,6 +106,7 @@ static List<Arguments> incompatibleLockCombinations() {
 		);
 	}
 
+	@SuppressWarnings("NullAway")
 	@ParameterizedTest
 	@MethodSource("incompatibleLockCombinations")
 	void defersTasksWithIncompatibleLocks(Set<ExclusiveResource> initialResources,
@@ -166,6 +168,7 @@ static List<Arguments> compatibleLockCombinations() {
 		);
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@ParameterizedTest
 	@MethodSource("compatibleLockCombinations")
 	void canWorkStealTaskWithCompatibleLocks(Set<ExclusiveResource> initialResources,
@@ -198,6 +201,8 @@ void defersTasksWithIncompatibleLocksOnMultipleLevels() throws Throwable {
 
 		var deferred = new ConcurrentHashMap<TestTask, CountDownLatch>();
 		var deferredTasks = new CopyOnWriteArrayList<TestTask>();
+
+		@SuppressWarnings("NullAway")
 		TaskEventListener taskEventListener = testTask -> {
 			deferredTasks.add(testTask);
 			deferred.get(testTask).countDown();
@@ -305,9 +310,11 @@ static final class DummyTestTask implements TestTask {
 		private final ResourceLock resourceLock;
 		private final Executable action;
 
+		@Nullable
 		private volatile String threadName;
+
 		private final CountDownLatch started = new CountDownLatch(1);
-		private final CompletableFuture<Void> completion = new CompletableFuture<>();
+		private final CompletableFuture<@Nullable Void> completion = new CompletableFuture<>();
 
 		DummyTestTask(String identifier, ResourceLock resourceLock, Executable action) {
 			this.identifier = identifier;
diff --git a/platform-tests/src/test/java/org/junit/platform/engine/support/hierarchical/MemoryLeakTests.java b/platform-tests/src/test/java/org/junit/platform/engine/support/hierarchical/MemoryLeakTests.java
index e8daa4b230a5..a0292fc2aca1 100644
--- a/platform-tests/src/test/java/org/junit/platform/engine/support/hierarchical/MemoryLeakTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/engine/support/hierarchical/MemoryLeakTests.java
@@ -19,7 +19,7 @@
  * exist with regard to the "context" held by {@link NodeTestTask}.
  *
  * @since 5.3.1
- * @see <a href="https://github.com/junit-team/junit5/issues/1578">GitHub issue #1578</a>
+ * @see <a href="https://github.com/junit-team/junit-framework/issues/1578">GitHub issue #1578</a>
  */
 // Explicitly specifying Lifecycle.PER_METHOD to be certain that the
 // test instance state is recreated for every test method executed.
@@ -29,7 +29,7 @@ class MemoryLeakTests {
 	// Allocate 500 MB of memory per test method.
 	//
 	// If the test instance is garbage collected, this should not cause any
-	// problems for the JUnit 5 build; however, if the instances of this test
+	// problems for the JUnit build; however, if the instances of this test
 	// class are NOT garbage collected, we should run out of memory pretty
 	// quickly since the instances of this test class would consume 5GB of
 	// heap space.
diff --git a/platform-tests/src/test/java/org/junit/platform/engine/support/hierarchical/ParallelExecutionIntegrationTests.java b/platform-tests/src/test/java/org/junit/platform/engine/support/hierarchical/ParallelExecutionIntegrationTests.java
index 2775585bb9da..a311559c9cea 100644
--- a/platform-tests/src/test/java/org/junit/platform/engine/support/hierarchical/ParallelExecutionIntegrationTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/engine/support/hierarchical/ParallelExecutionIntegrationTests.java
@@ -176,7 +176,7 @@ void afterHooksAreCalledAfterConcurrentDynamicTestsAreFinished() {
 
 	/**
 	 * @since 1.4
-	 * @see <a href="https://github.com/junit-team/junit5/issues/1688">gh-1688</a>
+	 * @see <a href="https://github.com/junit-team/junit-framework/issues/1688">gh-1688</a>
 	 */
 	@Test
 	void threadInterruptedByUserCode() {
@@ -265,8 +265,8 @@ void runsIsolatedTestsLastToMaximizeParallelism() {
 		List<Event> parallelTestMethodEvents = events.reportingEntryPublished() //
 				.filter(e -> e.getTestDescriptor().getSource() //
 						.filter(it -> //
-						it instanceof MethodSource
-								&& SuccessfulParallelTestCase.class.equals(((MethodSource) it).getJavaClass()) //
+						it instanceof MethodSource methodSource
+								&& SuccessfulParallelTestCase.class.equals(methodSource.getJavaClass()) //
 						).isPresent() //
 				) //
 				.toList();
diff --git a/platform-tests/src/test/java/org/junit/platform/engine/support/hierarchical/ResourceLockSupport.java b/platform-tests/src/test/java/org/junit/platform/engine/support/hierarchical/ResourceLockSupport.java
index 8325fb7b30a9..6760d4726e8e 100644
--- a/platform-tests/src/test/java/org/junit/platform/engine/support/hierarchical/ResourceLockSupport.java
+++ b/platform-tests/src/test/java/org/junit/platform/engine/support/hierarchical/ResourceLockSupport.java
@@ -19,8 +19,8 @@ static List<Lock> getLocks(ResourceLock resourceLock) {
 		if (resourceLock instanceof NopLock) {
 			return List.of();
 		}
-		if (resourceLock instanceof SingleLock) {
-			return List.of(((SingleLock) resourceLock).getLock());
+		if (resourceLock instanceof SingleLock lock) {
+			return List.of(lock.getLock());
 		}
 		return ((CompositeLock) resourceLock).getLocks();
 	}
diff --git a/platform-tests/src/test/java/org/junit/platform/engine/support/hierarchical/SameThreadExecutionIntegrationTests.java b/platform-tests/src/test/java/org/junit/platform/engine/support/hierarchical/SameThreadExecutionIntegrationTests.java
index c6e82bb1ae37..85bbea069341 100644
--- a/platform-tests/src/test/java/org/junit/platform/engine/support/hierarchical/SameThreadExecutionIntegrationTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/engine/support/hierarchical/SameThreadExecutionIntegrationTests.java
@@ -29,7 +29,7 @@
 class SameThreadExecutionIntegrationTests {
 
 	/**
-	 * @see <a href="https://github.com/junit-team/junit5/issues/1688">gh-1688</a>
+	 * @see <a href="https://github.com/junit-team/junit-framework/issues/1688">gh-1688</a>
 	 */
 	@Test
 	void threadInterruptedByUserCode(@TrackLogRecords LogRecordListener listener) {
diff --git a/platform-tests/src/test/java/org/junit/platform/engine/support/hierarchical/SingleTestExecutorTests.java b/platform-tests/src/test/java/org/junit/platform/engine/support/hierarchical/SingleTestExecutorTests.java
deleted file mode 100644
index 35b139b12243..000000000000
--- a/platform-tests/src/test/java/org/junit/platform/engine/support/hierarchical/SingleTestExecutorTests.java
+++ /dev/null
@@ -1,62 +0,0 @@
-/*
- * Copyright 2015-2025 the original author or authors.
- *
- * All rights reserved. This program and the accompanying materials are
- * made available under the terms of the Eclipse Public License v2.0 which
- * accompanies this distribution and is available at
- *
- * https://www.eclipse.org/legal/epl-v20.html
- */
-
-package org.junit.platform.engine.support.hierarchical;
-
-import static org.junit.jupiter.api.Assertions.assertEquals;
-import static org.junit.jupiter.api.Assertions.assertSame;
-import static org.junit.platform.engine.TestExecutionResult.Status.ABORTED;
-import static org.junit.platform.engine.TestExecutionResult.Status.FAILED;
-import static org.junit.platform.engine.TestExecutionResult.Status.SUCCESSFUL;
-
-import java.util.Optional;
-
-import org.junit.jupiter.api.Test;
-import org.opentest4j.TestAbortedException;
-
-/**
- * @since 1.0
- */
-@SuppressWarnings("deprecation")
-class SingleTestExecutorTests {
-
-	@Test
-	void executeSafelySuccessful() {
-		var result = new SingleTestExecutor().executeSafely(() -> {
-		});
-
-		assertEquals(SUCCESSFUL, result.getStatus());
-		assertEquals(Optional.empty(), result.getThrowable());
-	}
-
-	@Test
-	void executeSafelyAborted() {
-		var testAbortedException = new TestAbortedException("assumption violated");
-
-		var result = new SingleTestExecutor().executeSafely(() -> {
-			throw testAbortedException;
-		});
-
-		assertEquals(ABORTED, result.getStatus());
-		assertSame(testAbortedException, result.getThrowable().get());
-	}
-
-	@Test
-	void executeSafelyFailed() {
-		var assertionError = new AssertionError("assumption violated");
-
-		var result = new SingleTestExecutor().executeSafely(() -> {
-			throw assertionError;
-		});
-
-		assertEquals(FAILED, result.getStatus());
-		assertSame(assertionError, result.getThrowable().get());
-	}
-}
diff --git a/platform-tests/src/test/java/org/junit/platform/engine/support/store/NamespacedHierarchicalStoreTests.java b/platform-tests/src/test/java/org/junit/platform/engine/support/store/NamespacedHierarchicalStoreTests.java
index 81b1797c8b2b..0cc43881b122 100644
--- a/platform-tests/src/test/java/org/junit/platform/engine/support/store/NamespacedHierarchicalStoreTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/engine/support/store/NamespacedHierarchicalStoreTests.java
@@ -10,6 +10,7 @@
 
 package org.junit.platform.engine.support.store;
 
+import static java.util.Objects.requireNonNull;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNull;
@@ -189,6 +190,7 @@ void getWithTypeSafety() {
 			assertEquals(value, requiredTypeValue);
 		}
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void getWithTypeSafetyAndPrimitiveValueType() {
 			String key = "enigma";
@@ -239,6 +241,7 @@ void getOrComputeIfAbsentWithTypeSafety() {
 			assertEquals(value, computedValue);
 		}
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void getOrComputeIfAbsentWithTypeSafetyAndPrimitiveValueType() {
 			String key = "enigma";
@@ -285,6 +288,7 @@ void removeWithTypeSafety() {
 			assertNull(store.get(namespace, key));
 		}
 
+		@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 		@Test
 		void removeWithTypeSafetyAndPrimitiveValueType() {
 			String key = "enigma";
@@ -320,7 +324,8 @@ void simulateRaceConditionInGetOrComputeIfAbsent() throws Exception {
 
 			try (var localStore = new NamespacedHierarchicalStore<>(null)) {
 				values = executeConcurrently(threads, //
-					() -> localStore.getOrComputeIfAbsent(namespace, key, it -> counter.incrementAndGet()));
+					() -> requireNonNull(
+						localStore.getOrComputeIfAbsent(namespace, key, it -> counter.incrementAndGet())));
 			}
 
 			assertEquals(1, counter.get());
@@ -520,7 +525,7 @@ void closeIsIdempotent() throws Throwable {
 		}
 
 		/**
-		 * @see <a href="https://github.com/junit-team/junit5/issues/3944">#3944</a>
+		 * @see <a href="https://github.com/junit-team/junit-framework/issues/3944">#3944</a>
 		 */
 		@Test
 		void acceptsQueryAfterClose() {
diff --git a/platform-tests/src/test/java/org/junit/platform/launcher/MethodFilterTests.java b/platform-tests/src/test/java/org/junit/platform/launcher/MethodFilterTests.java
index b868986c1d31..af47b9fabd3d 100644
--- a/platform-tests/src/test/java/org/junit/platform/launcher/MethodFilterTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/launcher/MethodFilterTests.java
@@ -39,6 +39,7 @@ class MethodFilterTests {
 	private static final TestDescriptor CLASS2_TEST1 = methodTestDescriptor("class2", Class2.class, "test1");
 	private static final TestDescriptor CLASS2_TEST2 = methodTestDescriptor("class2", Class2.class, "test2");
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void includeMethodNamePatternsChecksPreconditions() {
 		assertThatThrownBy(() -> includeMethodNamePatterns((String[]) null)) //
@@ -58,14 +59,14 @@ void includeSingleMethodNamePattern() {
 		var filter = includeMethodNamePatterns(regex);
 
 		assertIncluded(filter.apply(CLASS1_TEST1),
-			String.format("Method name [%s] matches included pattern: '%s'", CLASS1_TEST1_NAME, regex));
+			"Method name [%s] matches included pattern: '%s'".formatted(CLASS1_TEST1_NAME, regex));
 		assertIncluded(filter.apply(CLASS1_TEST2),
-			String.format("Method name [%s] matches included pattern: '%s'", CLASS1_TEST2_NAME, regex));
+			"Method name [%s] matches included pattern: '%s'".formatted(CLASS1_TEST2_NAME, regex));
 
 		assertExcluded(filter.apply(CLASS2_TEST1),
-			String.format("Method name [%s] does not match any included pattern: '%s'", CLASS2_TEST1_NAME, regex));
+			"Method name [%s] does not match any included pattern: '%s'".formatted(CLASS2_TEST1_NAME, regex));
 		assertExcluded(filter.apply(CLASS2_TEST2),
-			String.format("Method name [%s] does not match any included pattern: '%s'", CLASS2_TEST2_NAME, regex));
+			"Method name [%s] does not match any included pattern: '%s'".formatted(CLASS2_TEST2_NAME, regex));
 	}
 
 	@Test
@@ -75,17 +76,18 @@ void includeMultipleMethodNamePatterns() {
 		var filter = includeMethodNamePatterns(firstRegex, secondRegex);
 
 		assertIncluded(filter.apply(CLASS1_TEST1),
-			String.format("Method name [%s] matches included pattern: '%s'", CLASS1_TEST1_NAME, firstRegex));
+			"Method name [%s] matches included pattern: '%s'".formatted(CLASS1_TEST1_NAME, firstRegex));
 		assertIncluded(filter.apply(CLASS1_TEST2),
-			String.format("Method name [%s] matches included pattern: '%s'", CLASS1_TEST2_NAME, firstRegex));
+			"Method name [%s] matches included pattern: '%s'".formatted(CLASS1_TEST2_NAME, firstRegex));
 		assertIncluded(filter.apply(CLASS2_TEST1),
-			String.format("Method name [%s] matches included pattern: '%s'", CLASS2_TEST1_NAME, secondRegex));
+			"Method name [%s] matches included pattern: '%s'".formatted(CLASS2_TEST1_NAME, secondRegex));
 
 		assertExcluded(filter.apply(CLASS2_TEST2),
-			String.format("Method name [%s] does not match any included pattern: '%s' OR '%s'", CLASS2_TEST2_NAME,
+			"Method name [%s] does not match any included pattern: '%s' OR '%s'".formatted(CLASS2_TEST2_NAME,
 				firstRegex, secondRegex));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void excludeMethodNamePatternsChecksPreconditions() {
 		assertThatThrownBy(() -> excludeMethodNamePatterns((String[]) null)) //
@@ -105,14 +107,14 @@ void excludeSingleMethodNamePattern() {
 		var filter = excludeMethodNamePatterns(regex);
 
 		assertExcluded(filter.apply(CLASS1_TEST1),
-			String.format("Method name [%s] matches excluded pattern: '%s'", CLASS1_TEST1_NAME, regex));
+			"Method name [%s] matches excluded pattern: '%s'".formatted(CLASS1_TEST1_NAME, regex));
 		assertExcluded(filter.apply(CLASS1_TEST2),
-			String.format("Method name [%s] matches excluded pattern: '%s'", CLASS1_TEST2_NAME, regex));
+			"Method name [%s] matches excluded pattern: '%s'".formatted(CLASS1_TEST2_NAME, regex));
 
 		assertIncluded(filter.apply(CLASS2_TEST1),
-			String.format("Method name [%s] does not match any excluded pattern: '%s'", CLASS2_TEST1_NAME, regex));
+			"Method name [%s] does not match any excluded pattern: '%s'".formatted(CLASS2_TEST1_NAME, regex));
 		assertIncluded(filter.apply(CLASS2_TEST2),
-			String.format("Method name [%s] does not match any excluded pattern: '%s'", CLASS2_TEST2_NAME, regex));
+			"Method name [%s] does not match any excluded pattern: '%s'".formatted(CLASS2_TEST2_NAME, regex));
 	}
 
 	@Test
@@ -122,14 +124,14 @@ void excludeMultipleMethodNamePatterns() {
 		var filter = excludeMethodNamePatterns(firstRegex, secondRegex);
 
 		assertExcluded(filter.apply(CLASS1_TEST1),
-			String.format("Method name [%s] matches excluded pattern: '%s'", CLASS1_TEST1_NAME, firstRegex));
+			"Method name [%s] matches excluded pattern: '%s'".formatted(CLASS1_TEST1_NAME, firstRegex));
 		assertExcluded(filter.apply(CLASS1_TEST2),
-			String.format("Method name [%s] matches excluded pattern: '%s'", CLASS1_TEST2_NAME, firstRegex));
+			"Method name [%s] matches excluded pattern: '%s'".formatted(CLASS1_TEST2_NAME, firstRegex));
 		assertExcluded(filter.apply(CLASS2_TEST1),
-			String.format("Method name [%s] matches excluded pattern: '%s'", CLASS2_TEST1_NAME, secondRegex));
+			"Method name [%s] matches excluded pattern: '%s'".formatted(CLASS2_TEST1_NAME, secondRegex));
 
 		assertIncluded(filter.apply(CLASS2_TEST2),
-			String.format("Method name [%s] does not match any excluded pattern: '%s' OR '%s'", CLASS2_TEST2_NAME,
+			"Method name [%s] does not match any excluded pattern: '%s' OR '%s'".formatted(CLASS2_TEST2_NAME,
 				firstRegex, secondRegex));
 	}
 
diff --git a/platform-tests/src/test/java/org/junit/platform/launcher/TagFilterTests.java b/platform-tests/src/test/java/org/junit/platform/launcher/TagFilterTests.java
index d81e7879ef0b..734bbcdb0a34 100644
--- a/platform-tests/src/test/java/org/junit/platform/launcher/TagFilterTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/launcher/TagFilterTests.java
@@ -20,6 +20,7 @@
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Tag;
 import org.junit.jupiter.api.Test;
 import org.junit.platform.commons.PreconditionViolationException;
@@ -60,7 +61,8 @@ void includeTagsWithInvalidSyntax() {
 		// @formatter:on
 	}
 
-	private void assertSyntaxViolationForIncludes(String tag) {
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
+	private void assertSyntaxViolationForIncludes(@Nullable String tag) {
 		var exception = assertThrows(PreconditionViolationException.class, () -> includeTags(tag));
 		assertThat(exception).hasMessageStartingWith("Unable to parse tag expression");
 	}
@@ -77,7 +79,8 @@ void excludeTagsWithInvalidSyntax() {
 		// @formatter:on
 	}
 
-	private void assertSyntaxViolationForExcludes(String tag) {
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
+	private void assertSyntaxViolationForExcludes(@Nullable String tag) {
 		var exception = assertThrows(PreconditionViolationException.class, () -> excludeTags(tag));
 		assertThat(exception).hasMessageStartingWith("Unable to parse tag expression");
 	}
diff --git a/platform-tests/src/test/java/org/junit/platform/launcher/core/ClasspathAlignmentCheckerTests.java b/platform-tests/src/test/java/org/junit/platform/launcher/core/ClasspathAlignmentCheckerTests.java
index c15ad7aa543f..bc2497202056 100644
--- a/platform-tests/src/test/java/org/junit/platform/launcher/core/ClasspathAlignmentCheckerTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/launcher/core/ClasspathAlignmentCheckerTests.java
@@ -23,7 +23,9 @@
 import io.github.classgraph.ClassGraph;
 import io.github.classgraph.PackageInfo;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.condition.DisabledIf;
 
 class ClasspathAlignmentCheckerTests {
 
@@ -36,7 +38,7 @@ void classpathIsAligned() {
 	void wrapsLinkageErrorForUnalignedClasspath() {
 		var cause = new LinkageError();
 		AtomicInteger counter = new AtomicInteger();
-		Function<String, Package> packageLookup = name -> {
+		Function<String, @Nullable Package> packageLookup = name -> {
 			var pkg = mock(Package.class);
 			when(pkg.getName()).thenReturn(name);
 			when(pkg.getImplementationVersion()).thenReturn(counter.incrementAndGet() + ".0.0");
@@ -50,7 +52,7 @@ void wrapsLinkageErrorForUnalignedClasspath() {
 				.hasMessageStartingWith("The wrapped LinkageError is likely caused by the versions of "
 						+ "JUnit jars on the classpath/module path not being properly aligned.") //
 				.hasMessageContaining("Please ensure consistent versions are used") //
-				.hasMessageFindingMatch("https://junit\\.org/junit5/docs/.*/user-guide/#dependency-metadata") //
+				.hasMessageFindingMatch("https://docs\\.junit\\.org/.*/user-guide/#dependency-metadata") //
 				.hasMessageContaining("The following conflicting versions were detected:") //
 				.hasMessageContaining("- org.junit.jupiter.api: 1.0.0") //
 				.hasMessageContaining("- org.junit.jupiter.engine: 2.0.0") //
@@ -58,6 +60,7 @@ void wrapsLinkageErrorForUnalignedClasspath() {
 	}
 
 	@Test
+	@DisabledIf("org.junit.platform.commons.test.IdeUtils#runningInEclipse()")
 	void allRootPackagesAreChecked() {
 		var allowedFileNames = Pattern.compile("junit-(?:platform|jupiter|vintage)-.+[\\d.]+(?:-SNAPSHOT)?\\.jar");
 		var classGraph = new ClassGraph() //
@@ -82,4 +85,5 @@ void allRootPackagesAreChecked() {
 					.allMatch(name -> foundPackages.stream().anyMatch(it -> it.startsWith(name)));
 		}
 	}
+
 }
diff --git a/platform-tests/src/test/java/org/junit/platform/launcher/core/DefaultLauncherTests.java b/platform-tests/src/test/java/org/junit/platform/launcher/core/DefaultLauncherTests.java
index d03bc43c3a0d..adf70020ca02 100644
--- a/platform-tests/src/test/java/org/junit/platform/launcher/core/DefaultLauncherTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/launcher/core/DefaultLauncherTests.java
@@ -129,6 +129,7 @@ void discoverEmptyTestPlanWithEngineWithoutAnyTests() {
 	void discoverTestPlanForEngineThatReturnsNullForItsRootDescriptor() {
 		TestEngine engine = new TestEngineStub("some-engine-id") {
 
+			@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 			@Override
 			public TestDescriptor discover(EngineDiscoveryRequest discoveryRequest, UniqueId uniqueId) {
 				return null;
@@ -149,6 +150,7 @@ public TestDescriptor discover(EngineDiscoveryRequest discoveryRequest, UniqueId
 	void discoverErrorTestDescriptorForEngineThatThrowsInDiscoveryPhase(Class<? extends Throwable> throwableClass) {
 		TestEngine engine = new TestEngineStub("my-engine-id") {
 
+			@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 			@Override
 			public TestDescriptor discover(EngineDiscoveryRequest discoveryRequest, UniqueId uniqueId) {
 				try {
@@ -421,34 +423,29 @@ void launcherAppliesPostDiscoveryFilters() {
 	}
 
 	@Test
-	@SuppressWarnings("deprecation")
 	void withoutConfigurationParameters_LauncherPassesEmptyConfigurationParametersIntoTheExecutionRequest() {
 		var engine = new TestEngineSpy();
 
 		var launcher = createLauncher(engine);
 		launcher.execute(request().build());
 
-		var configurationParameters = engine.requestForExecution.getConfigurationParameters();
+		var configurationParameters = requireNonNull(engine.requestForExecution).getConfigurationParameters();
 		assertThat(configurationParameters.get("key")).isNotPresent();
-		assertThat(configurationParameters.size()).isEqualTo(0);
 	}
 
 	@Test
-	@SuppressWarnings("deprecation")
 	void withConfigurationParameters_LauncherPassesPopulatedConfigurationParametersIntoTheExecutionRequest() {
 		var engine = new TestEngineSpy();
 
 		var launcher = createLauncher(engine);
 		launcher.execute(request().configurationParameter("key", "value").build());
 
-		var configurationParameters = engine.requestForExecution.getConfigurationParameters();
-		assertThat(configurationParameters.size()).isEqualTo(1);
+		var configurationParameters = requireNonNull(engine.requestForExecution).getConfigurationParameters();
 		assertThat(configurationParameters.get("key")).isPresent();
 		assertThat(configurationParameters.get("key")).contains("value");
 	}
 
 	@Test
-	@SuppressWarnings("deprecation")
 	void withoutConfigurationParameters_LookupFallsBackToSystemProperty() {
 		System.setProperty(FOO, BAR);
 
@@ -458,8 +455,7 @@ void withoutConfigurationParameters_LookupFallsBackToSystemProperty() {
 			var launcher = createLauncher(engine);
 			launcher.execute(request().build());
 
-			var configurationParameters = engine.requestForExecution.getConfigurationParameters();
-			assertThat(configurationParameters.size()).isEqualTo(0);
+			var configurationParameters = requireNonNull(engine.requestForExecution).getConfigurationParameters();
 			var optionalFoo = configurationParameters.get(FOO);
 			assertTrue(optionalFoo.isPresent(), "foo should have been picked up via system property");
 			assertEquals(BAR, optionalFoo.get(), "foo property");
@@ -601,25 +597,6 @@ void launcherCanExecuteTestPlanExactlyOnce() {
 		assertEquals("TestPlan must only be executed once", e.getMessage());
 	}
 
-	@Test
-	@SuppressWarnings("deprecation")
-	void testPlanThrowsExceptionWhenModified() {
-		TestEngine engine = new TestEngineSpy();
-		var launcher = createLauncher(engine);
-		var testPlan = launcher.discover(request().build());
-		var engineIdentifier = getOnlyElement(testPlan.getRoots());
-		var engineUniqueId = engineIdentifier.getUniqueIdObject();
-		assertThat(testPlan.getChildren(engineIdentifier)).hasSize(1);
-
-		var addedIdentifier = TestIdentifier.from(
-			new TestDescriptorStub(engineUniqueId.append("test", "test2"), "test2"));
-
-		var exception = assertThrows(JUnitException.class, () -> testPlan.add(addedIdentifier));
-		assertThat(exception).hasMessage("Unsupported attempt to modify the TestPlan was detected. "
-				+ "Please contact your IDE/tool vendor and request a fix or downgrade to JUnit 5.7.x (see https://github.com/junit-team/junit5/issues/1732 for details).");
-		assertThat(testPlan.getChildren(engineIdentifier)).hasSize(1).doesNotContain(addedIdentifier);
-	}
-
 	@Test
 	void thirdPartyEngineUsingReservedEngineIdPrefixEmitsWarning(@TrackLogRecords LogRecordListener listener) {
 		var id = "junit-using-reserved-prefix";
diff --git a/platform-tests/src/test/java/org/junit/platform/launcher/core/ExecutionListenerAdapterTests.java b/platform-tests/src/test/java/org/junit/platform/launcher/core/ExecutionListenerAdapterTests.java
index d8a29dc6e105..f1c05f80fc37 100644
--- a/platform-tests/src/test/java/org/junit/platform/launcher/core/ExecutionListenerAdapterTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/launcher/core/ExecutionListenerAdapterTests.java
@@ -16,6 +16,7 @@
 
 import java.util.Map;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 import org.junit.platform.commons.util.ReflectionUtils;
 import org.junit.platform.engine.TestDescriptor;
@@ -65,7 +66,10 @@ void nothing() {
 
 	static class MockTestExecutionListener implements TestExecutionListener {
 
+		@Nullable
 		public TestIdentifier testIdentifier;
+
+		@Nullable
 		public ReportEntry entry;
 
 		@Override
diff --git a/platform-tests/src/test/java/org/junit/platform/launcher/core/LauncherConfigTests.java b/platform-tests/src/test/java/org/junit/platform/launcher/core/LauncherConfigTests.java
index c3b518dcd3b2..7b3a92d90e5b 100644
--- a/platform-tests/src/test/java/org/junit/platform/launcher/core/LauncherConfigTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/launcher/core/LauncherConfigTests.java
@@ -30,6 +30,7 @@
  */
 class LauncherConfigTests {
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void preconditions() {
 		assertThrows(PreconditionViolationException.class,
diff --git a/platform-tests/src/test/java/org/junit/platform/launcher/core/LauncherConfigurationParametersTests.java b/platform-tests/src/test/java/org/junit/platform/launcher/core/LauncherConfigurationParametersTests.java
index 2bd8b5aea1da..9d8899b9402a 100644
--- a/platform-tests/src/test/java/org/junit/platform/launcher/core/LauncherConfigurationParametersTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/launcher/core/LauncherConfigurationParametersTests.java
@@ -10,6 +10,7 @@
 
 package org.junit.platform.launcher.core;
 
+import static org.assertj.core.api.Assertions.as;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertThrows;
@@ -18,12 +19,12 @@
 import java.net.URLClassLoader;
 import java.nio.file.Files;
 import java.nio.file.Path;
-import java.util.List;
 import java.util.Map;
 import java.util.Properties;
 import java.util.logging.Level;
 import java.util.logging.LogRecord;
 
+import org.assertj.core.api.InstanceOfAssertFactories;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
@@ -44,7 +45,6 @@
  *
  * @since 1.0
  */
-@SuppressWarnings("deprecation")
 class LauncherConfigurationParametersTests {
 
 	private static final String CONFIG_FILE_NAME = "test-junit-platform.properties";
@@ -60,6 +60,7 @@ void reset() {
 		System.clearProperty(KEY);
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void constructorPreconditions() {
 		assertThrows(PreconditionViolationException.class, () -> fromMap(null));
@@ -68,6 +69,7 @@ void constructorPreconditions() {
 		assertThrows(PreconditionViolationException.class, () -> fromMapAndFile(Map.of(), "  "));
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void getPreconditions() {
 		ConfigurationParameters configParams = fromMap(Map.of());
@@ -79,7 +81,6 @@ void getPreconditions() {
 	@Test
 	void noConfigParams() {
 		ConfigurationParameters configParams = fromMap(Map.of());
-		assertThat(configParams.size()).isEqualTo(0);
 		assertThat(configParams.get(KEY)).isEmpty();
 		assertThat(configParams.keySet()).doesNotContain(KEY);
 		assertThat(configParams.toString()).doesNotContain(KEY);
@@ -204,31 +205,32 @@ void ignoresSystemPropertyAndConfigFileWhenImplicitLookupsAreDisabled() {
 	@Test
 	void warnsOnMultiplePropertyResources(@TempDir Path tempDir, @TrackLogRecords LogRecordListener logRecordListener)
 			throws Exception {
+
 		Properties properties = new Properties();
 		properties.setProperty(KEY, "from second config file");
 		try (var out = Files.newOutputStream(tempDir.resolve(CONFIG_FILE_NAME))) {
 			properties.store(out, "");
 		}
+
 		ClassLoader originalClassLoader = Thread.currentThread().getContextClassLoader();
+		URL originalResource = originalClassLoader.getResource(CONFIG_FILE_NAME);
+
 		try (var customClassLoader = new URLClassLoader(new URL[] { tempDir.toUri().toURL() }, originalClassLoader)) {
 			Thread.currentThread().setContextClassLoader(customClassLoader);
 			ConfigurationParameters configParams = fromMapAndFile(Map.of(), CONFIG_FILE_NAME);
 
 			assertThat(configParams.get(KEY)).contains(CONFIG_FILE);
 
-			List<String> loggedWarnings = logRecordListener.stream(Level.WARNING) //
-					.map(LogRecord::getMessage) //
-					.toList();
-			assertThat(loggedWarnings) //
-					.hasSize(1);
-			assertThat(loggedWarnings.getFirst()) //
-					.contains("Discovered 2 '" + CONFIG_FILE_NAME
-							+ "' configuration files on the classpath (see below); only the first (*) will be used.") //
-					.contains("- "
-							+ Path.of(
-								"build/resources/test/test-junit-platform.properties").toAbsolutePath().toUri().toURL()
-							+ " (*)") //
-					.contains("- " + tempDir.resolve(CONFIG_FILE_NAME).toUri().toURL());
+			assertThat(logRecordListener.stream(Level.WARNING).map(LogRecord::getMessage)) //
+					.hasSize(1) //
+					.first(as(InstanceOfAssertFactories.STRING)) //
+					.contains("""
+							Discovered 2 '%s' configuration files on the classpath (see below); \
+							only the first (*) will be used.
+							- %s (*)
+							- %s"""//
+							.formatted(CONFIG_FILE_NAME, originalResource,
+								tempDir.resolve(CONFIG_FILE_NAME).toUri().toURL()));
 		}
 		finally {
 			Thread.currentThread().setContextClassLoader(originalClassLoader);
diff --git a/platform-tests/src/test/java/org/junit/platform/launcher/core/LauncherFactoryTests.java b/platform-tests/src/test/java/org/junit/platform/launcher/core/LauncherFactoryTests.java
index f1687ea26d97..9ce3bb561f58 100644
--- a/platform-tests/src/test/java/org/junit/platform/launcher/core/LauncherFactoryTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/launcher/core/LauncherFactoryTests.java
@@ -10,19 +10,17 @@
 
 package org.junit.platform.launcher.core;
 
+import static java.util.Objects.requireNonNull;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.TemporaryClasspathExecutor.withAdditionalClasspathRoot;
 import static org.junit.platform.engine.discovery.DiscoverySelectors.selectClass;
 import static org.junit.platform.launcher.LauncherConstants.DEACTIVATE_LISTENERS_PATTERN_PROPERTY_NAME;
 import static org.junit.platform.launcher.LauncherConstants.ENABLE_LAUNCHER_INTERCEPTORS;
 import static org.junit.platform.launcher.core.LauncherDiscoveryRequestBuilder.request;
 
-import java.io.IOException;
-import java.io.UncheckedIOException;
-import java.net.URL;
-import java.net.URLClassLoader;
 import java.util.concurrent.atomic.AtomicReference;
 import java.util.logging.LogRecord;
 
@@ -65,6 +63,7 @@
  */
 class LauncherFactoryTests {
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void preconditions() {
 		assertThrows(PreconditionViolationException.class, () -> LauncherFactory.create(null));
@@ -331,7 +330,7 @@ public void executionFinished(TestIdentifier testIdentifier, TestExecutionResult
 				}
 			});
 
-			assertThat(result.get().getThrowable().orElseThrow()) //
+			assertThat(requireNonNull(result.get()).getThrowable().orElseThrow()) //
 					.hasRootCauseMessage("from execution") //
 					.hasStackTraceContaining(TestLauncherInterceptor1.class.getName() + ".intercept(") //
 					.hasStackTraceContaining(TestLauncherInterceptor2.class.getName() + ".intercept(");
@@ -434,18 +433,7 @@ private static void withSystemProperty(String key, String value, Runnable runnab
 	}
 
 	private static void withTestServices(Runnable runnable) {
-		var current = Thread.currentThread().getContextClassLoader();
-		var url = LauncherFactoryTests.class.getClassLoader().getResource("testservices/");
-		try (var classLoader = new URLClassLoader(new URL[] { url }, current)) {
-			Thread.currentThread().setContextClassLoader(classLoader);
-			runnable.run();
-		}
-		catch (IOException e) {
-			throw new UncheckedIOException(e);
-		}
-		finally {
-			Thread.currentThread().setContextClassLoader(current);
-		}
+		withAdditionalClasspathRoot("testservices/", runnable);
 	}
 
 	private LauncherDiscoveryRequest createLauncherDiscoveryRequestForBothStandardEngineExampleClasses() {
@@ -453,6 +441,7 @@ private LauncherDiscoveryRequest createLauncherDiscoveryRequestForBothStandardEn
 		return request()
 				.selectors(selectClass(JUnit4Example.class))
 				.selectors(selectClass(JUnit5Example.class))
+				.enableImplicitConfigurationParameters(false)
 				.build();
 		// @formatter:on
 	}
@@ -591,6 +580,7 @@ public void launcherSessionClosed(LauncherSession session) {
 					.getStore() //
 					.get(Namespace.GLOBAL, "sessionResource", CloseTrackingResource.class);
 
+			assertThat(sessionResource).isNotNull();
 			assertThat(sessionResource.isClosed()).isFalse();
 		}
 	}
diff --git a/platform-tests/src/test/java/org/junit/platform/launcher/core/ListenerRegistryTests.java b/platform-tests/src/test/java/org/junit/platform/launcher/core/ListenerRegistryTests.java
index 1c3a08783764..9f7052c2fd06 100644
--- a/platform-tests/src/test/java/org/junit/platform/launcher/core/ListenerRegistryTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/launcher/core/ListenerRegistryTests.java
@@ -13,14 +13,17 @@
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 
+import java.util.List;
+
 import org.junit.jupiter.api.Test;
 import org.junit.platform.commons.PreconditionViolationException;
 
 public class ListenerRegistryTests {
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void registerWithNullArray() {
-		var registry = ListenerRegistry.create(l -> l.getFirst());
+		var registry = ListenerRegistry.create(List::getFirst);
 
 		var exception = assertThrows(PreconditionViolationException.class, () -> registry.addAll((Object[]) null));
 
@@ -29,16 +32,17 @@ void registerWithNullArray() {
 
 	@Test
 	void registerWithEmptyArray() {
-		var registry = ListenerRegistry.create(l -> l.getFirst());
+		var registry = ListenerRegistry.create(List::getFirst);
 
 		var exception = assertThrows(PreconditionViolationException.class, registry::addAll);
 
 		assertThat(exception).hasMessageContaining("listeners array must not be null or empty");
 	}
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void registerWithArrayContainingNullElements() {
-		var registry = ListenerRegistry.create(l -> l.getFirst());
+		var registry = ListenerRegistry.create(List::getFirst);
 
 		var exception = assertThrows(PreconditionViolationException.class,
 			() -> registry.addAll(new Object[] { null }));
diff --git a/platform-tests/src/test/java/org/junit/platform/launcher/core/StreamInterceptorTests.java b/platform-tests/src/test/java/org/junit/platform/launcher/core/StreamInterceptorTests.java
index 2b5f35ca86bb..cb8aa8856663 100644
--- a/platform-tests/src/test/java/org/junit/platform/launcher/core/StreamInterceptorTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/launcher/core/StreamInterceptorTests.java
@@ -20,6 +20,7 @@
 import java.io.PrintStream;
 import java.util.stream.IntStream;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.AutoClose;
 import org.junit.jupiter.api.Test;
 
@@ -32,6 +33,7 @@ class StreamInterceptorTests {
 	PrintStream targetStream = new PrintStream(originalOut);
 
 	@AutoClose
+	@Nullable
 	StreamInterceptor streamInterceptor;
 
 	@Test
diff --git a/platform-tests/src/test/java/org/junit/platform/jfr/FlightRecordingDiscoveryListenerIntegrationTests.java b/platform-tests/src/test/java/org/junit/platform/launcher/jfr/FlightRecordingDiscoveryListenerIntegrationTests.java
similarity index 98%
rename from platform-tests/src/test/java/org/junit/platform/jfr/FlightRecordingDiscoveryListenerIntegrationTests.java
rename to platform-tests/src/test/java/org/junit/platform/launcher/jfr/FlightRecordingDiscoveryListenerIntegrationTests.java
index c734d70e06f4..a595137f6210 100644
--- a/platform-tests/src/test/java/org/junit/platform/jfr/FlightRecordingDiscoveryListenerIntegrationTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/launcher/jfr/FlightRecordingDiscoveryListenerIntegrationTests.java
@@ -8,7 +8,7 @@
  * https://www.eclipse.org/legal/epl-v20.html
  */
 
-package org.junit.platform.jfr;
+package org.junit.platform.launcher.jfr;
 
 import static org.junit.platform.commons.util.ExceptionUtils.readStackTrace;
 import static org.junit.platform.engine.discovery.DiscoverySelectors.selectClass;
diff --git a/platform-tests/src/test/java/org/junit/platform/jfr/FlightRecordingExecutionListenerIntegrationTests.java b/platform-tests/src/test/java/org/junit/platform/launcher/jfr/FlightRecordingExecutionListenerIntegrationTests.java
similarity index 97%
rename from platform-tests/src/test/java/org/junit/platform/jfr/FlightRecordingExecutionListenerIntegrationTests.java
rename to platform-tests/src/test/java/org/junit/platform/launcher/jfr/FlightRecordingExecutionListenerIntegrationTests.java
index afda445bc142..82483f0492af 100644
--- a/platform-tests/src/test/java/org/junit/platform/jfr/FlightRecordingExecutionListenerIntegrationTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/launcher/jfr/FlightRecordingExecutionListenerIntegrationTests.java
@@ -8,7 +8,7 @@
  * https://www.eclipse.org/legal/epl-v20.html
  */
 
-package org.junit.platform.jfr;
+package org.junit.platform.launcher.jfr;
 
 import static org.junit.platform.engine.discovery.DiscoverySelectors.selectClass;
 import static org.junit.platform.launcher.core.LauncherDiscoveryRequestBuilder.request;
@@ -47,7 +47,7 @@ void reportsEvents(@TempDir Path tempDir) {
 				.outputDirectoryProvider(hierarchicalOutputDirectoryProvider(tempDir)) //
 				.build();
 
-		launcher.execute(request, new FlightRecordingExecutionListener());
+		launcher.execute(request);
 		jfrEvents.awaitEvents();
 
 		var testFile = findPath(tempDir, "glob:**/test.txt");
diff --git a/platform-tests/src/test/java/org/junit/platform/launcher/listeners/UniqueIdTrackingListenerIntegrationTests.java b/platform-tests/src/test/java/org/junit/platform/launcher/listeners/UniqueIdTrackingListenerIntegrationTests.java
index dd916c324636..35fd8cc2692d 100644
--- a/platform-tests/src/test/java/org/junit/platform/launcher/listeners/UniqueIdTrackingListenerIntegrationTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/launcher/listeners/UniqueIdTrackingListenerIntegrationTests.java
@@ -10,6 +10,7 @@
 
 package org.junit.platform.launcher.listeners;
 
+import static java.util.Objects.requireNonNull;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.fail;
@@ -44,6 +45,7 @@
 import java.util.stream.Stream;
 
 import org.assertj.core.api.Condition;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.DynamicTest;
@@ -214,6 +216,7 @@ private List<String> executeTests(Map<String, String> configurationParameters, C
 				.build();
 		LauncherFactory.create().execute(request, new TestExecutionListener() {
 
+			@Nullable
 			private TestPlan testPlan;
 
 			@Override
@@ -227,7 +230,8 @@ public void executionSkipped(TestIdentifier testIdentifier, String reason) {
 					uniqueIds.add(testIdentifier.getUniqueId());
 				}
 				else {
-					this.testPlan.getChildren(testIdentifier).forEach(child -> executionSkipped(child, reason));
+					requireNonNull(this.testPlan).getChildren(testIdentifier).forEach(
+						child -> executionSkipped(child, reason));
 				}
 			}
 
diff --git a/platform-tests/src/test/java/org/junit/platform/launcher/tagexpression/ParserErrorTests.java b/platform-tests/src/test/java/org/junit/platform/launcher/tagexpression/ParserErrorTests.java
index 648d624cac3c..1d5bcd3cb0dc 100644
--- a/platform-tests/src/test/java/org/junit/platform/launcher/tagexpression/ParserErrorTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/launcher/tagexpression/ParserErrorTests.java
@@ -15,6 +15,7 @@
 
 import java.util.stream.Stream;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.Arguments;
@@ -24,11 +25,6 @@ class ParserErrorTests {
 
 	private final Parser parser = new Parser();
 
-	@Test
-	void cantParseExpressionFromNull() {
-		assertThat(parseErrorFromParsing(null)).contains("empty tag expression");
-	}
-
 	@Test
 	void emptyExpression() {
 		assertThat(parseErrorFromParsing("")).contains("empty tag expression");
@@ -94,7 +90,7 @@ private static Stream<Arguments> data() {
 		// @formatter:on
 	}
 
-	private String parseErrorFromParsing(String tagExpression) {
+	private @Nullable String parseErrorFromParsing(String tagExpression) {
 		try {
 			var parseResult = parser.parse(tagExpression);
 			parseResult.tagExpressionOrThrow(RuntimeException::new);
diff --git a/platform-tests/src/test/java/org/junit/platform/launcher/tagexpression/ParserTests.java b/platform-tests/src/test/java/org/junit/platform/launcher/tagexpression/ParserTests.java
index 4d3133f66f27..dd036b1ffb70 100644
--- a/platform-tests/src/test/java/org/junit/platform/launcher/tagexpression/ParserTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/launcher/tagexpression/ParserTests.java
@@ -76,7 +76,7 @@ private static Stream<Arguments> data() {
 
 	private TagExpression tagExpressionParsedFrom(String tagExpression) {
 		return parser.parse(tagExpression).tagExpressionOrThrow(
-			(error) -> new RuntimeException("[" + tagExpression + "] should be parsable"));
+			error -> new RuntimeException("[" + tagExpression + "] should be parsable"));
 	}
 
 }
diff --git a/platform-tests/src/test/java/org/junit/platform/launcher/tagexpression/TokenTests.java b/platform-tests/src/test/java/org/junit/platform/launcher/tagexpression/TokenTests.java
index edee8f37edaf..46d8fd92b86e 100644
--- a/platform-tests/src/test/java/org/junit/platform/launcher/tagexpression/TokenTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/launcher/tagexpression/TokenTests.java
@@ -43,8 +43,8 @@ void concatenateTwoTokens() {
 		var one = tokens.get(0);
 		var two = tokens.get(1);
 		var joined = one.concatenate(two);
-		assertThat(joined.rawString).isEqualTo(" ! foo");
-		assertThat(joined.startIndex).isEqualTo(0);
+		assertThat(joined.rawString()).isEqualTo(" ! foo");
+		assertThat(joined.startIndex()).isEqualTo(0);
 	}
 
 }
diff --git a/platform-tests/src/test/java/org/junit/platform/launcher/tagexpression/TokenizerTests.java b/platform-tests/src/test/java/org/junit/platform/launcher/tagexpression/TokenizerTests.java
index 37cfb09786e6..9682e8ee6f21 100644
--- a/platform-tests/src/test/java/org/junit/platform/launcher/tagexpression/TokenizerTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/launcher/tagexpression/TokenizerTests.java
@@ -15,6 +15,7 @@
 import java.util.List;
 import java.util.stream.Stream;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 
 class TokenizerTests {
@@ -78,18 +79,18 @@ void extractStartPositionOfRawString() {
 	}
 
 	private Stream<Integer> startIndicesExtractedFrom(String expression) {
-		return tokensExtractedFrom(expression).map(token -> token.startIndex);
+		return tokensExtractedFrom(expression).map(Token::startIndex);
 	}
 
 	private Stream<String> rawStringsExtractedFrom(String expression) {
-		return tokensExtractedFrom(expression).map(token -> token.rawString);
+		return tokensExtractedFrom(expression).map(Token::rawString);
 	}
 
-	private List<String> tokenStringsExtractedFrom(String expression) {
+	private List<String> tokenStringsExtractedFrom(@Nullable String expression) {
 		return tokensExtractedFrom(expression).map(Token::string).toList();
 	}
 
-	private Stream<Token> tokensExtractedFrom(String expression) {
+	private Stream<Token> tokensExtractedFrom(@Nullable String expression) {
 		return new Tokenizer().tokenize(expression).stream();
 	}
 }
diff --git a/platform-tests/src/test/java/org/junit/platform/reporting/legacy/LegacyReportingUtilsTests.java b/platform-tests/src/test/java/org/junit/platform/reporting/legacy/LegacyReportingUtilsTests.java
deleted file mode 100644
index 6f5e67291f2f..000000000000
--- a/platform-tests/src/test/java/org/junit/platform/reporting/legacy/LegacyReportingUtilsTests.java
+++ /dev/null
@@ -1,94 +0,0 @@
-/*
- * Copyright 2015-2025 the original author or authors.
- *
- * All rights reserved. This program and the accompanying materials are
- * made available under the terms of the Eclipse Public License v2.0 which
- * accompanies this distribution and is available at
- *
- * https://www.eclipse.org/legal/epl-v20.html
- */
-
-package org.junit.platform.reporting.legacy;
-
-import static org.assertj.core.api.Assertions.assertThat;
-import static org.junit.platform.launcher.core.OutputDirectoryProviders.dummyOutputDirectoryProvider;
-import static org.mockito.Mockito.mock;
-
-import java.util.Set;
-
-import org.junit.jupiter.api.Test;
-import org.junit.platform.engine.TestDescriptor;
-import org.junit.platform.engine.TestSource;
-import org.junit.platform.engine.UniqueId;
-import org.junit.platform.engine.support.descriptor.AbstractTestDescriptor;
-import org.junit.platform.engine.support.descriptor.ClassSource;
-import org.junit.platform.engine.support.descriptor.EngineDescriptor;
-import org.junit.platform.launcher.TestPlan;
-
-/**
- * @since 1.0.3
- */
-class LegacyReportingUtilsTests {
-
-	private TestDescriptor engineDescriptor = new EngineDescriptor(UniqueId.forEngine("foo"), "Foo");
-
-	@Test
-	void legacyReportingClassNameForTestIdentifierWithoutClassSourceIsParentLegacyReportingName() {
-		var uniqueId = engineDescriptor.getUniqueId().append("child", "bar");
-		var testDescriptor = createTestDescriptor(uniqueId, "Bar", null);
-		engineDescriptor.addChild(testDescriptor);
-
-		assertThat(getClassName(engineDescriptor.getUniqueId())).isEqualTo("<unrooted>");
-		assertThat(getClassName(uniqueId)).isEqualTo("Foo");
-
-		assertThat(getClassNameFromOldLocation(engineDescriptor.getUniqueId())).isEqualTo("<unrooted>");
-		assertThat(getClassNameFromOldLocation(uniqueId)).isEqualTo("Foo");
-	}
-
-	@Test
-	void legacyReportingClassNameForDescendantOfTestIdentifierWithClassSourceIsClassName() {
-		var classUniqueId = engineDescriptor.getUniqueId().append("class", "class");
-		var classDescriptor = createTestDescriptor(classUniqueId, "Class",
-			ClassSource.from(LegacyReportingUtilsTests.class));
-		engineDescriptor.addChild(classDescriptor);
-
-		var subUniqueId = classUniqueId.append("sub", "baz");
-		var subDescriptor = createTestDescriptor(subUniqueId, "Baz", null);
-		classDescriptor.addChild(subDescriptor);
-
-		var subSubUniqueId = subUniqueId.append("subsub", "qux");
-		var subSubDescriptor = createTestDescriptor(subSubUniqueId, "Qux", null);
-		subDescriptor.addChild(subSubDescriptor);
-
-		assertThat(getClassName(engineDescriptor.getUniqueId())).isEqualTo("<unrooted>");
-		assertThat(getClassName(classUniqueId)).isEqualTo(LegacyReportingUtilsTests.class.getName());
-		assertThat(getClassName(subUniqueId)).isEqualTo(LegacyReportingUtilsTests.class.getName());
-		assertThat(getClassName(subSubUniqueId)).isEqualTo(LegacyReportingUtilsTests.class.getName());
-
-		assertThat(getClassNameFromOldLocation(engineDescriptor.getUniqueId())).isEqualTo("<unrooted>");
-		assertThat(getClassNameFromOldLocation(classUniqueId)).isEqualTo(LegacyReportingUtilsTests.class.getName());
-		assertThat(getClassNameFromOldLocation(subUniqueId)).isEqualTo(LegacyReportingUtilsTests.class.getName());
-		assertThat(getClassNameFromOldLocation(subSubUniqueId)).isEqualTo(LegacyReportingUtilsTests.class.getName());
-	}
-
-	private String getClassName(UniqueId uniqueId) {
-		var testPlan = TestPlan.from(true, Set.of(engineDescriptor), mock(), dummyOutputDirectoryProvider());
-		return LegacyReportingUtils.getClassName(testPlan, testPlan.getTestIdentifier(uniqueId));
-	}
-
-	@SuppressWarnings("deprecation")
-	private String getClassNameFromOldLocation(UniqueId uniqueId) {
-		var testPlan = TestPlan.from(true, Set.of(engineDescriptor), mock(), dummyOutputDirectoryProvider());
-		return org.junit.platform.launcher.listeners.LegacyReportingUtils.getClassName(testPlan,
-			testPlan.getTestIdentifier(uniqueId));
-	}
-
-	private TestDescriptor createTestDescriptor(UniqueId uniqueId, String displayName, TestSource source) {
-		return new AbstractTestDescriptor(uniqueId, displayName, source) {
-			@Override
-			public Type getType() {
-				return Type.CONTAINER_AND_TEST;
-			}
-		};
-	}
-}
diff --git a/platform-tests/src/test/java/org/junit/platform/reporting/open/xml/JUnitContributorTests.java b/platform-tests/src/test/java/org/junit/platform/reporting/open/xml/JUnitContributorTests.java
index e13f7b44fce4..294431df165a 100644
--- a/platform-tests/src/test/java/org/junit/platform/reporting/open/xml/JUnitContributorTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/reporting/open/xml/JUnitContributorTests.java
@@ -28,7 +28,7 @@ void contributesJUnitSpecificMetadata(@TempDir Path tempDir) throws Exception {
 			"""
 					<e:events xmlns="https://schemas.opentest4j.org/reporting/core/0.2.0" xmlns:e="https://schemas.opentest4j.org/reporting/events/0.2.0" xmlns:java="https://schemas.opentest4j.org/reporting/java/0.2.0"
 					          xmlns:junit="https://schemas.junit.org/open-test-reporting" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-					          xsi:schemaLocation="https://schemas.junit.org/open-test-reporting https://junit.org/junit5/schemas/open-test-reporting/junit-1.9.xsd">
+					          xsi:schemaLocation="https://schemas.junit.org/open-test-reporting https://schemas.junit.org/open-test-reporting/junit-1.9.xsd">
 					    <e:started id="1" name="dummy" time="2024-11-10T16:31:35.000Z">
 					        <metadata>
 					            <junit:uniqueId>[engine:dummy]</junit:uniqueId>
diff --git a/platform-tests/src/test/java/org/junit/platform/reporting/open/xml/OpenTestReportGeneratingListenerTests.java b/platform-tests/src/test/java/org/junit/platform/reporting/open/xml/OpenTestReportGeneratingListenerTests.java
index 80a076abaa59..e1bd359935ee 100644
--- a/platform-tests/src/test/java/org/junit/platform/reporting/open/xml/OpenTestReportGeneratingListenerTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/reporting/open/xml/OpenTestReportGeneratingListenerTests.java
@@ -23,6 +23,7 @@
 import static org.junit.platform.launcher.core.LauncherDiscoveryRequestBuilder.request;
 import static org.junit.platform.launcher.core.LauncherFactoryForTestingPurposesOnly.createLauncher;
 import static org.junit.platform.reporting.open.xml.OpenTestReportGeneratingListener.ENABLED_PROPERTY_NAME;
+import static org.junit.platform.reporting.open.xml.OpenTestReportGeneratingListener.GIT_ENABLED_PROPERTY_NAME;
 import static org.junit.platform.reporting.testutil.FileUtils.findPath;
 
 import java.io.PrintStream;
@@ -36,6 +37,7 @@
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.io.TempDir;
 import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.CsvSource;
 import org.junit.jupiter.params.provider.ValueSource;
 import org.junit.platform.commons.util.ExceptionUtils;
 import org.junit.platform.engine.TestEngine;
@@ -58,6 +60,12 @@
  */
 public class OpenTestReportGeneratingListenerTests {
 
+	private static final Map<String, String> NAMESPACE_CONTEXT = Map.of( //
+		"core", Namespace.REPORTING_CORE.getUri(), //
+		"e", Namespace.REPORTING_EVENTS.getUri(), //
+		"git", Namespace.REPORTING_GIT.getUri() //
+	);
+
 	private PrintStream originalOut;
 	private PrintStream originalErr;
 
@@ -81,7 +89,7 @@ void writesValidXmlReport(@TempDir Path tempDirectory) throws Exception {
 		var engine = new DemoHierarchicalTestEngine("dummy");
 		engine.addTest("failingTest", "display<-->Name 😎", (context, descriptor) -> {
 			try {
-				var listener = context.request.getEngineExecutionListener();
+				var listener = context.request().getEngineExecutionListener();
 				listener.reportingEntryPublished(descriptor, ReportEntry.from("key", "value"));
 				listener.fileEntryPublished(descriptor, FileEntry.from(
 					Files.writeString(tempDirectory.resolve("test.txt"), "Hello, world!"), "text/plain"));
@@ -108,7 +116,7 @@ void writesValidXmlReport(@TempDir Path tempDirectory) throws Exception {
 				          xmlns:java="https://schemas.opentest4j.org/reporting/java/0.2.0"
 				          xmlns:junit="https://schemas.junit.org/open-test-reporting"
 				          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-				          xsi:schemaLocation="https://schemas.junit.org/open-test-reporting https://junit.org/junit5/schemas/open-test-reporting/junit-1.9.xsd">
+				          xsi:schemaLocation="https://schemas.junit.org/open-test-reporting https://schemas.junit.org/open-test-reporting/junit-1.9.xsd">
 				    <infrastructure>
 				        <hostName>${xmlunit.ignore}</hostName>
 				        <userName>${xmlunit.ignore}</userName>
@@ -170,8 +178,9 @@ void writesValidXmlReport(@TempDir Path tempDirectory) throws Exception {
 	}
 
 	@ParameterizedTest
-	@ValueSource(strings = { "https://github.com/junit-team/junit5.git", "git@github.com:junit-team/junit5.git" })
-	void includesGitInfo(String originUrl, @TempDir Path tempDirectory) throws Exception {
+	@ValueSource(strings = { "https://github.com/junit-team/junit-framework.git",
+			"git@github.com:junit-team/junit-framework.git" })
+	void includesGitInfoWhenEnabled(String originUrl, @TempDir Path tempDirectory) throws Exception {
 
 		assumeTrue(tryExecGit(tempDirectory, "--version").exitCode() == 0, "git not installed");
 		execGit(tempDirectory, "init", "--initial-branch=my_branch");
@@ -191,36 +200,76 @@ void includesGitInfo(String originUrl, @TempDir Path tempDirectory) throws Excep
 		var xmlFile = findPath(tempDirectory, "glob:**/open-test-report.xml");
 		assertThat(validate(xmlFile)).isEmpty();
 
-		var namespaceContext = Map.of("core", Namespace.REPORTING_CORE.getUri(), "e",
-			Namespace.REPORTING_EVENTS.getUri(), "git", Namespace.REPORTING_GIT.getUri());
+		assertThatXml(xmlFile) //
+				.doesNotHaveXPath("/e:events/core:infrastructure/git:repository");
+		assertThatXml(xmlFile) //
+				.doesNotHaveXPath("/e:events/core:infrastructure/git:branch");
+		assertThatXml(xmlFile) //
+				.doesNotHaveXPath("/e:events/core:infrastructure/git:commit");
+		assertThatXml(xmlFile) //
+				.doesNotHaveXPath("/e:events/core:infrastructure/git:status");
+
+		executeTests(tempDirectory, engine, tempDirectory.resolve("junit-reports"),
+			Map.of(GIT_ENABLED_PROPERTY_NAME, "true"));
+
+		assertThat(validate(xmlFile)).isEmpty();
 
-		XmlAssert.assertThat(xmlFile) //
-				.withNamespaceContext(namespaceContext) //
+		assertThatXml(xmlFile) //
 				.valueByXPath("/e:events/core:infrastructure/git:repository/@originUrl") //
 				.isEqualTo(originUrl);
 
-		XmlAssert.assertThat(xmlFile) //
-				.withNamespaceContext(namespaceContext) //
+		assertThatXml(xmlFile) //
 				.valueByXPath("/e:events/core:infrastructure/git:branch") //
 				.isEqualTo("my_branch");
 
 		var commitHash = execGit(tempDirectory, "rev-parse", "--verify", "HEAD").stdOut().trim();
-		XmlAssert.assertThat(xmlFile) //
-				.withNamespaceContext(namespaceContext) //
+		assertThatXml(xmlFile) //
 				.valueByXPath("/e:events/core:infrastructure/git:commit") //
 				.isEqualTo(commitHash);
 
-		XmlAssert.assertThat(xmlFile) //
-				.withNamespaceContext(namespaceContext) //
+		assertThatXml(xmlFile) //
 				.valueByXPath("/e:events/core:infrastructure/git:status/@clean") //
 				.isEqualTo(false);
 
-		XmlAssert.assertThat(xmlFile) //
-				.withNamespaceContext(namespaceContext) //
+		assertThatXml(xmlFile) //
 				.valueByXPath("/e:events/core:infrastructure/git:status") //
 				.startsWith("?? junit-reports");
 	}
 
+	@ParameterizedTest
+	@CsvSource(textBlock = """
+				https://foo:bar@github.com/junit-team/junit5.git, https://***@github.com/junit-team/junit5.git
+				https://token@github.com/junit-team/junit5.git,   https://***@github.com/junit-team/junit5.git
+				foo@github.com:junit-team/junit5.git,             ***@github.com:junit-team/junit5.git
+				ssh://foo@github.com:junit-team/junit5.git,       ssh://***@github.com:junit-team/junit5.git
+				git@github.com:junit-team/junit5.git,             git@github.com:junit-team/junit5.git
+				ssh://git@github.com:junit-team/junit5.git,       ssh://git@github.com:junit-team/junit5.git
+			""")
+	void stripsCredentialsFromOriginUrl(String configuredUrl, String reportedUrl, @TempDir Path tempDirectory)
+			throws Exception {
+
+		assumeTrue(tryExecGit(tempDirectory, "--version").exitCode() == 0, "git not installed");
+		execGit(tempDirectory, "init", "--initial-branch=my_branch");
+		execGit(tempDirectory, "remote", "add", "origin", configuredUrl);
+
+		var engine = new DemoHierarchicalTestEngine("dummy");
+
+		executeTests(tempDirectory, engine, tempDirectory.resolve("junit-reports"),
+			Map.of(GIT_ENABLED_PROPERTY_NAME, "true"));
+
+		var xmlFile = findPath(tempDirectory, "glob:**/open-test-report.xml");
+		assertThat(validate(xmlFile)).isEmpty();
+
+		assertThatXml(xmlFile) //
+				.valueByXPath("/e:events/core:infrastructure/git:repository/@originUrl") //
+				.isEqualTo(reportedUrl);
+	}
+
+	private static XmlAssert assertThatXml(Path xmlFile) {
+		return XmlAssert.assertThat(xmlFile) //
+				.withNamespaceContext(NAMESPACE_CONTEXT);
+	}
+
 	private static ProcessResult execGit(Path workingDir, String... arguments) throws InterruptedException {
 		var result = tryExecGit(workingDir, arguments);
 		assertEquals(0, result.exitCode(), "git " + String.join(" ", arguments) + " failed");
@@ -241,15 +290,22 @@ private ValidationResult validate(Path xmlFile) throws URISyntaxException {
 		return new DefaultValidator(catalogUri).validate(xmlFile);
 	}
 
-	private void executeTests(Path tempDirectory, TestEngine engine, Path outputDir) {
-		var build = request() //
+	private static void executeTests(Path tempDirectory, TestEngine engine, Path outputDir) {
+		executeTests(tempDirectory, engine, outputDir, Map.of());
+	}
+
+	private static void executeTests(Path tempDirectory, TestEngine engine, Path outputDir,
+			Map<String, String> extraConfigurationParameters) {
+		var request = request() //
 				.selectors(selectUniqueId(UniqueId.forEngine(engine.getId()))) //
+				.enableImplicitConfigurationParameters(false) //
 				.configurationParameter(ENABLED_PROPERTY_NAME, String.valueOf(true)) //
 				.configurationParameter(CAPTURE_STDOUT_PROPERTY_NAME, String.valueOf(true)) //
 				.configurationParameter(CAPTURE_STDERR_PROPERTY_NAME, String.valueOf(true)) //
 				.configurationParameter(OUTPUT_DIR_PROPERTY_NAME, outputDir.toString()) //
+				.configurationParameters(extraConfigurationParameters) //
 				.build();
-		createLauncher(engine).execute(build, new OpenTestReportGeneratingListener(tempDirectory));
+		createLauncher(engine).execute(request, new OpenTestReportGeneratingListener(tempDirectory));
 	}
 
 }
diff --git a/platform-tests/src/test/java/org/junit/platform/runner/JUnitPlatformRunnerTests.java b/platform-tests/src/test/java/org/junit/platform/runner/JUnitPlatformRunnerTests.java
deleted file mode 100644
index 5dc8bb014f62..000000000000
--- a/platform-tests/src/test/java/org/junit/platform/runner/JUnitPlatformRunnerTests.java
+++ /dev/null
@@ -1,905 +0,0 @@
-/*
- * Copyright 2015-2025 the original author or authors.
- *
- * All rights reserved. This program and the accompanying materials are
- * made available under the terms of the Eclipse Public License v2.0 which
- * accompanies this distribution and is available at
- *
- * https://www.eclipse.org/legal/epl-v20.html
- */
-
-package org.junit.platform.runner;
-
-import static java.util.stream.Collectors.toSet;
-import static org.assertj.core.api.Assertions.assertThat;
-import static org.assertj.core.api.Assertions.fail;
-import static org.junit.jupiter.api.Assertions.assertAll;
-import static org.junit.jupiter.api.Assertions.assertEquals;
-import static org.junit.jupiter.api.Assertions.assertNull;
-import static org.junit.jupiter.api.Assertions.assertThrows;
-import static org.junit.jupiter.api.Assumptions.assumeFalse;
-import static org.junit.platform.commons.util.CollectionUtils.getOnlyElement;
-import static org.junit.platform.engine.TestExecutionResult.successful;
-import static org.junit.platform.engine.discovery.ClassNameFilter.STANDARD_INCLUDE_PATTERN;
-import static org.junit.platform.launcher.core.LauncherFactoryForTestingPurposesOnly.createLauncher;
-import static org.junit.platform.launcher.core.OutputDirectoryProviders.dummyOutputDirectoryProvider;
-import static org.junit.runner.Description.createSuiteDescription;
-import static org.junit.runner.Description.createTestDescription;
-import static org.junit.runner.manipulation.Filter.matchMethodDescription;
-import static org.mockito.ArgumentMatchers.any;
-import static org.mockito.ArgumentMatchers.eq;
-import static org.mockito.Mockito.doAnswer;
-import static org.mockito.Mockito.inOrder;
-import static org.mockito.Mockito.mock;
-import static org.mockito.Mockito.verify;
-import static org.mockito.Mockito.verifyNoMoreInteractions;
-import static org.mockito.Mockito.when;
-
-import java.util.Arrays;
-import java.util.List;
-import java.util.Set;
-
-import org.junit.jupiter.api.DisplayName;
-import org.junit.jupiter.api.Nested;
-import org.junit.jupiter.api.Tag;
-import org.junit.jupiter.api.Test;
-import org.junit.platform.engine.ConfigurationParameters;
-import org.junit.platform.engine.EngineDiscoveryRequest;
-import org.junit.platform.engine.ExecutionRequest;
-import org.junit.platform.engine.Filter;
-import org.junit.platform.engine.TestDescriptor;
-import org.junit.platform.engine.TestEngine;
-import org.junit.platform.engine.TestExecutionResult;
-import org.junit.platform.engine.TestTag;
-import org.junit.platform.engine.UniqueId;
-import org.junit.platform.engine.discovery.ClassNameFilter;
-import org.junit.platform.engine.discovery.ClassSelector;
-import org.junit.platform.engine.discovery.PackageNameFilter;
-import org.junit.platform.engine.discovery.PackageSelector;
-import org.junit.platform.engine.discovery.UniqueIdSelector;
-import org.junit.platform.engine.support.descriptor.AbstractTestDescriptor;
-import org.junit.platform.engine.support.descriptor.ClassSource;
-import org.junit.platform.engine.support.descriptor.EngineDescriptor;
-import org.junit.platform.engine.support.descriptor.MethodSource;
-import org.junit.platform.engine.support.hierarchical.DemoHierarchicalTestDescriptor;
-import org.junit.platform.engine.support.hierarchical.DemoHierarchicalTestEngine;
-import org.junit.platform.fakes.TestDescriptorStub;
-import org.junit.platform.fakes.TestEngineStub;
-import org.junit.platform.launcher.Launcher;
-import org.junit.platform.launcher.LauncherDiscoveryRequest;
-import org.junit.platform.launcher.TestPlan;
-import org.junit.platform.suite.api.ExcludeClassNamePatterns;
-import org.junit.platform.suite.api.ExcludeEngines;
-import org.junit.platform.suite.api.ExcludePackages;
-import org.junit.platform.suite.api.ExcludeTags;
-import org.junit.platform.suite.api.IncludeClassNamePatterns;
-import org.junit.platform.suite.api.IncludeEngines;
-import org.junit.platform.suite.api.IncludePackages;
-import org.junit.platform.suite.api.IncludeTags;
-import org.junit.platform.suite.api.SelectClasses;
-import org.junit.platform.suite.api.SelectPackages;
-import org.junit.platform.suite.api.SuiteDisplayName;
-import org.junit.platform.suite.api.UseTechnicalNames;
-import org.junit.runner.Description;
-import org.junit.runner.manipulation.NoTestsRemainException;
-import org.junit.runner.notification.RunListener;
-import org.junit.runner.notification.RunNotifier;
-import org.mockito.ArgumentCaptor;
-
-/**
- * Tests for the {@link JUnitPlatform} runner.
- *
- * @since 1.0
- */
-@Tag("junit4")
-@SuppressWarnings("deprecation")
-class JUnitPlatformRunnerTests {
-
-	@Nested
-	class Discovery {
-
-		@Test
-		void requestsClassSelectorForAnnotatedClassWhenNoAdditionalAnnotationsArePresent() {
-
-			class TestCase {
-			}
-
-			var request = instantiateRunnerAndCaptureGeneratedRequest(TestCase.class);
-
-			var selectors = request.getSelectorsByType(ClassSelector.class);
-			assertThat(selectors).hasSize(1);
-			var classSelector = getOnlyElement(selectors);
-			assertEquals(TestCase.class, classSelector.getJavaClass());
-		}
-
-		@Test
-		void requestsClassSelectorsWhenSelectClassesAnnotationIsPresent() {
-
-			@SelectClasses({ Short.class, Byte.class })
-			class TestCase {
-			}
-
-			var request = instantiateRunnerAndCaptureGeneratedRequest(TestCase.class);
-
-			var selectors = request.getSelectorsByType(ClassSelector.class);
-			assertThat(selectors).hasSize(2);
-			assertEquals(Short.class, selectors.get(0).getJavaClass());
-			assertEquals(Byte.class, selectors.get(1).getJavaClass());
-		}
-
-		@Test
-		void updatesIncludeClassNameFilterWhenSelectClassesAnnotationIsPresent() {
-
-			@SelectClasses({ Short.class, Byte.class })
-			class TestCase {
-			}
-
-			var request = instantiateRunnerAndCaptureGeneratedRequest(TestCase.class);
-
-			var filters = request.getFiltersByType(ClassNameFilter.class);
-			assertThat(filters).hasSize(1);
-
-			var filter = filters.getFirst();
-
-			// Excluded by default
-			assertExcludes(filter, "example.MyClass");
-			assertExcludes(filter, "example.MyTestClass");
-			assertExcludes(filter, "example.Short");
-			assertExcludes(filter, "example.Byte");
-
-			// Included due to ClassNameFilter.STANDARD_INCLUDE_PATTERN
-			assertIncludes(filter, "TestClass");
-			assertIncludes(filter, "example.TestClass");
-			assertIncludes(filter, "example.MyTests");
-			assertIncludes(filter, "example.MyTest");
-
-			// Included due to @SelectClasses({ Short.class, Byte.class })
-			assertIncludes(filter, Short.class.getName());
-			assertIncludes(filter, Byte.class.getName());
-		}
-
-		@Test
-		void requestsPackageSelectorsWhenPackagesAnnotationIsPresent() {
-
-			@SelectPackages({ "foo", "bar" })
-			class TestCase {
-			}
-
-			var request = instantiateRunnerAndCaptureGeneratedRequest(TestCase.class);
-
-			var selectors = request.getSelectorsByType(PackageSelector.class);
-			assertThat(selectors).hasSize(2);
-			assertEquals("foo", selectors.get(0).getPackageName());
-			assertEquals("bar", selectors.get(1).getPackageName());
-		}
-
-		@Test
-		void addsPackageFiltersToRequestWhenIncludePackageAnnotationIsPresent() {
-
-			@IncludePackages({ "includedpackage1", "includedpackage2" })
-			class TestCase {
-			}
-
-			var request = instantiateRunnerAndCaptureGeneratedRequest(TestCase.class);
-
-			var filters = request.getFiltersByType(PackageNameFilter.class);
-			assertThat(filters).hasSize(1);
-
-			var filter = filters.getFirst();
-			assertIncludes(filter, "includedpackage1.TestClass");
-			assertIncludes(filter, "includedpackage2.TestClass");
-			assertExcludes(filter, "excludedpackage1.TestClass");
-		}
-
-		@Test
-		void addsPackageFiltersToRequestWhenExcludePackageAnnotationIsPresent() {
-
-			@ExcludePackages({ "excludedpackage1", "excludedpackage2" })
-			class TestCase {
-			}
-
-			var request = instantiateRunnerAndCaptureGeneratedRequest(TestCase.class);
-
-			var filters = request.getFiltersByType(PackageNameFilter.class);
-			assertThat(filters).hasSize(1);
-
-			var filter = filters.getFirst();
-			assertIncludes(filter, "includedpackage1.TestClass");
-			assertExcludes(filter, "excludedpackage1.TestClass");
-			assertExcludes(filter, "excludedpackage2.TestClass");
-		}
-
-		@Test
-		void addsTagFilterToRequestWhenIncludeTagsAnnotationIsPresent() {
-
-			@IncludeTags({ "foo", "bar" })
-			class TestCase {
-			}
-
-			var request = instantiateRunnerAndCaptureGeneratedRequest(TestCase.class);
-
-			var filters = request.getPostDiscoveryFilters();
-			assertThat(filters).hasSize(1);
-
-			var filter = filters.getFirst();
-			assertIncludes(filter, testDescriptorWithTags("foo"));
-			assertIncludes(filter, testDescriptorWithTags("bar"));
-			assertExcludes(filter, testDescriptorWithTags("baz"));
-		}
-
-		@Test
-		void addsTagFilterToRequestWhenExcludeTagsAnnotationIsPresent() {
-
-			@ExcludeTags({ "foo", "bar" })
-			class TestCase {
-			}
-
-			var request = instantiateRunnerAndCaptureGeneratedRequest(TestCase.class);
-
-			var filters = request.getPostDiscoveryFilters();
-			assertThat(filters).hasSize(1);
-
-			var filter = filters.getFirst();
-			assertExcludes(filter, testDescriptorWithTags("foo"));
-			assertExcludes(filter, testDescriptorWithTags("bar"));
-			assertIncludes(filter, testDescriptorWithTags("baz"));
-		}
-
-		@Test
-		void includeTagsAcceptsTagExpressions() {
-
-			@IncludeTags("foo & !bar")
-			class TestCase {
-			}
-
-			var request = instantiateRunnerAndCaptureGeneratedRequest(TestCase.class);
-
-			var filters = request.getPostDiscoveryFilters();
-			assertThat(filters).hasSize(1);
-
-			var filter = filters.getFirst();
-			assertIncludes(filter, testDescriptorWithTags("foo"));
-			assertIncludes(filter, testDescriptorWithTags("foo", "any_other_tag"));
-			assertExcludes(filter, testDescriptorWithTags("foo", "bar"));
-			assertExcludes(filter, testDescriptorWithTags("bar"));
-			assertExcludes(filter, testDescriptorWithTags("bar", "any_other_tag"));
-		}
-
-		@Test
-		void excludeTagsAcceptsTagExpressions() {
-
-			@ExcludeTags("foo & !bar")
-			class TestCase {
-			}
-
-			var request = instantiateRunnerAndCaptureGeneratedRequest(TestCase.class);
-
-			var filters = request.getPostDiscoveryFilters();
-			assertThat(filters).hasSize(1);
-
-			var filter = filters.getFirst();
-			assertExcludes(filter, testDescriptorWithTags("foo"));
-			assertExcludes(filter, testDescriptorWithTags("foo", "any_other_tag"));
-			assertIncludes(filter, testDescriptorWithTags("foo", "bar"));
-			assertIncludes(filter, testDescriptorWithTags("bar"));
-			assertIncludes(filter, testDescriptorWithTags("bar", "any_other_tag"));
-		}
-
-		@Test
-		void addsEngineFiltersToRequestWhenIncludeEnginesOrExcludeEnginesAnnotationsArePresent() {
-
-			@IncludeEngines({ "foo", "bar", "baz" })
-			@ExcludeEngines({ "bar", "quux" })
-			class TestCase {
-			}
-
-			TestEngine fooEngine = new TestEngineStub("foo");
-			TestEngine barEngine = new TestEngineStub("bar");
-			TestEngine bazEngine = new TestEngineStub("baz");
-			TestEngine quuxEngine = new TestEngineStub("quux");
-
-			var request = instantiateRunnerAndCaptureGeneratedRequest(TestCase.class);
-
-			var filters = request.getEngineFilters();
-			assertThat(filters).hasSize(2);
-
-			var includeFilter = filters.get(1);
-			assertIncludes(includeFilter, fooEngine);
-			assertIncludes(includeFilter, barEngine);
-			assertIncludes(includeFilter, bazEngine);
-			assertExcludes(includeFilter, quuxEngine);
-
-			var excludeFilter = filters.getFirst();
-			assertIncludes(excludeFilter, fooEngine);
-			assertExcludes(excludeFilter, barEngine);
-			assertIncludes(excludeFilter, bazEngine);
-			assertExcludes(excludeFilter, quuxEngine);
-		}
-
-		@Test
-		void addsDefaultClassNameFilterToRequestWhenFilterClassNameAnnotationIsNotPresentOnTestSuite() {
-
-			@SelectPackages("foo")
-			class TestCase {
-			}
-
-			var request = instantiateRunnerAndCaptureGeneratedRequest(TestCase.class);
-
-			var filters = request.getFiltersByType(ClassNameFilter.class);
-			assertThat(getOnlyElement(filters).toString()).contains(STANDARD_INCLUDE_PATTERN);
-		}
-
-		@Test
-		void addsDefaultClassNameFilterToRequestWhenFilterClassNameAnnotationIsNotPresentOnTestClass() {
-
-			class TestCase {
-			}
-
-			var request = instantiateRunnerAndCaptureGeneratedRequest(TestCase.class);
-
-			var filters = request.getFiltersByType(ClassNameFilter.class);
-			assertThat(filters).isEmpty();
-		}
-
-		@Test
-		void addsSingleExplicitClassNameFilterToRequestWhenIncludeClassNamePatternsAnnotationIsPresent() {
-
-			@IncludeClassNamePatterns(".*Foo")
-			class TestCase {
-			}
-
-			var request = instantiateRunnerAndCaptureGeneratedRequest(TestCase.class);
-
-			var filters = request.getFiltersByType(ClassNameFilter.class);
-			assertThat(getOnlyElement(filters).toString()).contains(".*Foo");
-		}
-
-		@Test
-		void addsSingleClassNameFilterToRequestWhenExcludeClassNamePatternsAnnotationIsPresent() {
-
-			@ExcludeClassNamePatterns(".*Foo")
-			class TestCase {
-			}
-
-			var request = instantiateRunnerAndCaptureGeneratedRequest(TestCase.class);
-
-			var filters = request.getFiltersByType(ClassNameFilter.class);
-			assertThat(getOnlyElement(filters).toString()).contains(".*Foo");
-		}
-
-		@Test
-		void addsMultipleExplicitClassNameFilterToRequestWhenIncludeClassNamePatternsAnnotationIsPresent() {
-
-			@IncludeClassNamePatterns({ ".*Foo", "Bar.*" })
-			class TestCase {
-			}
-
-			var request = instantiateRunnerAndCaptureGeneratedRequest(TestCase.class);
-
-			var filters = request.getFiltersByType(ClassNameFilter.class);
-			assertThat(getOnlyElement(filters).toString()).contains(".*Foo", "Bar.*");
-		}
-
-		@Test
-		void addsMultipleClassNameFilterToRequestWhenExcludeClassNamePatternsAnnotationIsPresent() {
-
-			@ExcludeClassNamePatterns({ ".*Foo", "Bar.*" })
-			class TestCase {
-			}
-
-			var request = instantiateRunnerAndCaptureGeneratedRequest(TestCase.class);
-
-			var filters = request.getFiltersByType(ClassNameFilter.class);
-			assertThat(getOnlyElement(filters).toString()).contains(".*Foo", "Bar.*");
-		}
-
-		@Test
-		void usesStandardIncludePatternWhenIncludeClassNamePatternsAnnotationIsPresentWithoutArguments() {
-
-			@IncludeClassNamePatterns
-			class TestCase {
-			}
-
-			var request = instantiateRunnerAndCaptureGeneratedRequest(TestCase.class);
-
-			var filters = request.getFiltersByType(ClassNameFilter.class);
-			assertThat(getOnlyElement(filters).toString()).contains(STANDARD_INCLUDE_PATTERN);
-		}
-
-		@Test
-		void doesNotAddClassNameFilterWhenIncludeClassNamePatternsAnnotationIsPresentWithEmptyArguments() {
-
-			@IncludeClassNamePatterns({})
-			class TestCase {
-			}
-
-			var request = instantiateRunnerAndCaptureGeneratedRequest(TestCase.class);
-
-			var filters = request.getFiltersByType(ClassNameFilter.class);
-			assertThat(filters).isEmpty();
-		}
-
-		@Test
-		void doesNotAddClassNameFilterWhenExcludeClassNamePatternsAnnotationIsPresentWithEmptyArguments() {
-
-			@ExcludeClassNamePatterns({})
-			class TestCase {
-			}
-
-			var request = instantiateRunnerAndCaptureGeneratedRequest(TestCase.class);
-
-			var filters = request.getFiltersByType(ClassNameFilter.class);
-			assertThat(filters).isEmpty();
-		}
-
-		@Test
-		void trimsArgumentsOfIncludeClassNamePatternsAnnotation() {
-
-			@IncludeClassNamePatterns({ " foo", "bar " })
-			class TestCase {
-			}
-
-			var request = instantiateRunnerAndCaptureGeneratedRequest(TestCase.class);
-
-			var filters = request.getFiltersByType(ClassNameFilter.class);
-			assertThat(getOnlyElement(filters).toString()).contains("'foo'", "'bar'");
-		}
-
-		@Test
-		void trimsArgumentsOfExcludeClassNamePatternsAnnotation() {
-
-			@ExcludeClassNamePatterns({ " foo", "bar " })
-			class TestCase {
-			}
-
-			var request = instantiateRunnerAndCaptureGeneratedRequest(TestCase.class);
-
-			var filters = request.getFiltersByType(ClassNameFilter.class);
-			assertThat(getOnlyElement(filters).toString()).contains("'foo'", "'bar'");
-		}
-
-		@Test
-		void convertsTestIdentifiersIntoDescriptions() {
-
-			TestDescriptor container1 = new TestDescriptorStub(UniqueId.root("root", "container1"), "container1");
-			container1.addChild(new TestDescriptorStub(UniqueId.root("root", "test1"), "test1"));
-			TestDescriptor container2 = new TestDescriptorStub(UniqueId.root("root", "container2"), "container2");
-			container2.addChild(new TestDescriptorStub(UniqueId.root("root", "test2a"), "test2a"));
-			container2.addChild(new TestDescriptorStub(UniqueId.root("root", "test2b"), "test2b"));
-			var testPlan = TestPlan.from(true, List.of(container1, container2), mock(), dummyOutputDirectoryProvider());
-
-			var launcher = mock(Launcher.class);
-			when(launcher.discover(any())).thenReturn(testPlan);
-
-			var runner = new JUnitPlatform(TestClass.class, launcher);
-
-			var runnerDescription = runner.getDescription();
-			assertEquals(createSuiteDescription(TestClass.class), runnerDescription);
-
-			List<Description> containerDescriptions = runnerDescription.getChildren();
-			assertThat(containerDescriptions).hasSize(2);
-			assertEquals(suiteDescription("[root:container1]"), containerDescriptions.get(0));
-			assertEquals(suiteDescription("[root:container2]"), containerDescriptions.get(1));
-
-			List<Description> testDescriptions = containerDescriptions.get(0).getChildren();
-			assertEquals(testDescription("[root:test1]"), getOnlyElement(testDescriptions));
-
-			testDescriptions = containerDescriptions.get(1).getChildren();
-			assertThat(testDescriptions).hasSize(2);
-			assertEquals(testDescription("[root:test2a]"), testDescriptions.get(0));
-			assertEquals(testDescription("[root:test2b]"), testDescriptions.get(1));
-		}
-
-		private static <T> void assertIncludes(Filter<T> filter, T included) {
-			assertThat(filter.apply(included).included()).isTrue();
-		}
-
-		private static <T> void assertExcludes(Filter<T> filter, T excluded) {
-			assertThat(filter.apply(excluded).excluded()).isTrue();
-		}
-
-	}
-
-	@Nested
-	class Filtering {
-
-		private final ConfigurationParameters configParams = mock();
-
-		@Test
-		void appliesFilter() throws Exception {
-
-			TestDescriptor originalParent1 = new TestDescriptorStub(UniqueId.root("root", "parent1"), "parent1");
-			originalParent1.addChild(new TestDescriptorStub(UniqueId.root("root", "leaf1"), "leaf1"));
-			TestDescriptor originalParent2 = new TestDescriptorStub(UniqueId.root("root", "parent2"), "parent2");
-			originalParent2.addChild(new TestDescriptorStub(UniqueId.root("root", "leaf2a"), "leaf2a"));
-			originalParent2.addChild(new TestDescriptorStub(UniqueId.root("root", "leaf2b"), "leaf2b"));
-			var fullTestPlan = TestPlan.from(true, List.of(originalParent1, originalParent2), configParams,
-				dummyOutputDirectoryProvider());
-
-			TestDescriptor filteredParent = new TestDescriptorStub(UniqueId.root("root", "parent2"), "parent2");
-			filteredParent.addChild(new TestDescriptorStub(UniqueId.root("root", "leaf2b"), "leaf2b"));
-			var filteredTestPlan = TestPlan.from(true, Set.of(filteredParent), configParams,
-				dummyOutputDirectoryProvider());
-
-			var launcher = mock(Launcher.class);
-			var captor = ArgumentCaptor.forClass(LauncherDiscoveryRequest.class);
-			when(launcher.discover(captor.capture())).thenReturn(fullTestPlan).thenReturn(filteredTestPlan);
-
-			var runner = new JUnitPlatform(TestClass.class, launcher);
-			runner.filter(matchMethodDescription(testDescription("[root:leaf2b]")));
-
-			var lastDiscoveryRequest = captor.getValue();
-			var uniqueIdSelectors = lastDiscoveryRequest.getSelectorsByType(UniqueIdSelector.class);
-			assertEquals("[root:leaf2b]", getOnlyElement(uniqueIdSelectors).getUniqueId().toString());
-
-			var parentDescription = getOnlyElement(runner.getDescription().getChildren());
-			assertEquals(suiteDescription("[root:parent2]"), parentDescription);
-
-			var testDescription = getOnlyElement(parentDescription.getChildren());
-			assertEquals(testDescription("[root:leaf2b]"), testDescription);
-		}
-
-		@Test
-		void throwsNoTestsRemainExceptionWhenNoTestIdentifierMatchesFilter() {
-			var testPlan = TestPlan.from(true, Set.of(new TestDescriptorStub(UniqueId.root("root", "test"), "test")),
-				configParams, dummyOutputDirectoryProvider());
-
-			var launcher = mock(Launcher.class);
-			when(launcher.discover(any())).thenReturn(testPlan);
-
-			var runner = new JUnitPlatform(TestClass.class, launcher);
-
-			assertThrows(NoTestsRemainException.class,
-				() -> runner.filter(matchMethodDescription(suiteDescription("[root:doesNotExist]"))));
-		}
-
-	}
-
-	@Nested
-	class Execution {
-
-		@Test
-		void notifiesRunListenerOfTestExecution() throws Exception {
-			var engine = new DemoHierarchicalTestEngine("dummy");
-			engine.addTest("failingTest", () -> fail("expected to fail"));
-			engine.addTest("succeedingTest", () -> {
-			});
-			engine.addTest("abortedTest", () -> assumeFalse(true));
-			engine.addTest("skippedTest", () -> fail("never called")).markSkipped("should be skipped");
-
-			var runListener = mock(RunListener.class);
-
-			var notifier = new RunNotifier();
-			notifier.addListener(runListener);
-			new JUnitPlatform(TestClass.class, createLauncher(engine)).run(notifier);
-
-			var inOrder = inOrder(runListener);
-
-			inOrder.verify(runListener).testStarted(testDescription("[engine:dummy]/[test:failingTest]"));
-			inOrder.verify(runListener).testFailure(any());
-			inOrder.verify(runListener).testFinished(testDescription("[engine:dummy]/[test:failingTest]"));
-
-			inOrder.verify(runListener).testStarted(testDescription("[engine:dummy]/[test:succeedingTest]"));
-			inOrder.verify(runListener).testFinished(testDescription("[engine:dummy]/[test:succeedingTest]"));
-
-			inOrder.verify(runListener).testStarted(testDescription("[engine:dummy]/[test:abortedTest]"));
-			inOrder.verify(runListener).testAssumptionFailure(any());
-			inOrder.verify(runListener).testFinished(testDescription("[engine:dummy]/[test:abortedTest]"));
-
-			inOrder.verify(runListener).testIgnored(testDescription("[engine:dummy]/[test:skippedTest]"));
-
-			inOrder.verifyNoMoreInteractions();
-		}
-
-		@Test
-		void supportsDynamicTestRegistration() throws Exception {
-			var runListener = mock(RunListener.class);
-			var notifier = new RunNotifier();
-			// notifier.addListener(new LoggingRunListener());
-			notifier.addListener(runListener);
-			new JUnitPlatform(TestClass.class, createLauncher(new DynamicTestEngine())).run(notifier);
-
-			var inOrder = inOrder(runListener);
-
-			inOrder.verify(runListener).testStarted(testDescription("[engine:dynamic]/[container:1]/[test:1]"));
-			inOrder.verify(runListener).testFinished(testDescription("[engine:dynamic]/[container:1]/[test:1]"));
-
-			inOrder.verify(runListener).testStarted(testDescription("[engine:dynamic]/[container:1]/[test:2]"));
-			inOrder.verify(runListener).testFinished(testDescription("[engine:dynamic]/[container:1]/[test:2]"));
-
-			inOrder.verify(runListener).testStarted(testDescription("[engine:dynamic]/[container:1]/[test:3]"));
-			inOrder.verify(runListener).testFinished(testDescription("[engine:dynamic]/[container:1]/[test:3]"));
-
-			inOrder.verify(runListener).testStarted(
-				testDescription("[engine:dynamic]/[container:1]/[test:3]/[test:3a]"));
-			inOrder.verify(runListener).testFinished(
-				testDescription("[engine:dynamic]/[container:1]/[test:3]/[test:3a]"));
-
-			inOrder.verifyNoMoreInteractions();
-		}
-
-		@Test
-		void reportsIgnoredEventsForLeavesWhenContainerIsSkipped() throws Exception {
-			var uniqueEngineId = UniqueId.forEngine("engine");
-			TestDescriptor engineDescriptor = new EngineDescriptor(uniqueEngineId, "engine");
-			TestDescriptor container = new TestDescriptorStub(UniqueId.root("root", "container"), "container");
-			container.addChild(new TestDescriptorStub(UniqueId.root("root", "leaf"), "leaf"));
-			engineDescriptor.addChild(container);
-
-			var engine = mock(TestEngine.class);
-			when(engine.getId()).thenReturn("engine");
-			when(engine.discover(any(), eq(uniqueEngineId))).thenReturn(engineDescriptor);
-			doAnswer(invocation -> {
-				ExecutionRequest request = invocation.getArgument(0);
-				var listener = request.getEngineExecutionListener();
-				listener.executionStarted(engineDescriptor);
-				listener.executionSkipped(container, "deliberately skipped container");
-				listener.executionFinished(engineDescriptor, successful());
-				return null;
-			}).when(engine).execute(any());
-
-			var runListener = mock(RunListener.class);
-
-			var notifier = new RunNotifier();
-			notifier.addListener(runListener);
-			new JUnitPlatform(TestClass.class, createLauncher(engine)).run(notifier);
-
-			verify(runListener).testIgnored(testDescription("[root:leaf]"));
-			verifyNoMoreInteractions(runListener);
-		}
-
-	}
-
-	@Nested
-	class Descriptions {
-
-		@Test
-		@DisplayName("Suite with default display name")
-		void descriptionForTestSuiteWithDefaultDisplayName() {
-			Class<?> testClass = TestSuiteWithDefaultDisplayName.class;
-			var platformRunner = new JUnitPlatform(testClass,
-				createLauncher(new DemoHierarchicalTestEngine("suite names")));
-
-			assertEquals(testClass.getName(), platformRunner.getDescription().getDisplayName());
-		}
-
-		@Test
-		@DisplayName("Suite with @SuiteDisplayName")
-		void descriptionForTestSuiteWithCustomDisplayName() {
-			var platformRunner = new JUnitPlatform(TestSuiteWithCustomDisplayName.class,
-				createLauncher(new DemoHierarchicalTestEngine("suite names")));
-
-			assertEquals("Sweeeeeeet Name!", platformRunner.getDescription().getDisplayName());
-		}
-
-		@Test
-		@DisplayName("Suite with @SuiteDisplayName and @UseTechnicalNames")
-		void descriptionForTestSuiteWithCustomDisplayNameAndTechnicalNames() {
-			Class<?> testClass = TestSuiteWithCustomDisplayNameAndTechnicalNames.class;
-			var platformRunner = new JUnitPlatform(testClass,
-				createLauncher(new DemoHierarchicalTestEngine("suite names")));
-
-			assertEquals(testClass.getName(), platformRunner.getDescription().getDisplayName());
-		}
-
-		@Test
-		void descriptionForJavaMethodAndClassSources() throws Exception {
-			var engine = new DemoHierarchicalTestEngine("dummy");
-			var failingTest = getClass().getDeclaredMethod("failingTest");
-			var containerDescriptor = engine.addContainer("uniqueContainerName", "containerDisplayName",
-				ClassSource.from(getClass()));
-			containerDescriptor.addChild(
-				new DemoHierarchicalTestDescriptor(containerDescriptor.getUniqueId().append("test", "failingTest"),
-					"testDisplayName", MethodSource.from(failingTest), (c, t) -> {
-					}));
-
-			var platformRunner = new JUnitPlatform(TestClass.class, createLauncher(engine));
-
-			List<Description> children = platformRunner.getDescription().getChildren();
-			assertEquals(1, children.size());
-			var engineDescription = children.getFirst();
-			assertEquals("dummy", engineDescription.getDisplayName());
-
-			var containerDescription = getOnlyElement(engineDescription.getChildren());
-			var testDescription = getOnlyElement(containerDescription.getChildren());
-
-			// @formatter:off
-			assertAll(
-					() -> assertEquals("dummy", engineDescription.getDisplayName(), "engine display name"),
-					() -> assertEquals("dummy", engineDescription.getClassName(), "engine class name"),
-					() -> assertNull(engineDescription.getMethodName(), "engine method name"),
-					() -> assertEquals("containerDisplayName", containerDescription.getDisplayName(), "container display name"),
-					() -> assertEquals("containerDisplayName", containerDescription.getClassName(), "container class name"),
-					() -> assertNull(containerDescription.getMethodName(), "container method name"),
-					() -> assertEquals("testDisplayName(containerDisplayName)", testDescription.getDisplayName(), "test display name"),
-					() -> assertEquals("containerDisplayName", testDescription.getClassName(), "test class name"),
-					() -> assertEquals("testDisplayName", testDescription.getMethodName(), "test method name")
-			);
-			// @formatter:on
-		}
-
-		@Test
-		void descriptionForJavaMethodAndClassSourcesUsingTechnicalNames() throws Exception {
-			var engine = new DemoHierarchicalTestEngine("dummy");
-			var failingTest = getClass().getDeclaredMethod("failingTest");
-			var containerDescriptor = engine.addContainer("uniqueContainerName", "containerDisplayName",
-				ClassSource.from(getClass()));
-			containerDescriptor.addChild(
-				new DemoHierarchicalTestDescriptor(containerDescriptor.getUniqueId().append("test", "failingTest"),
-					"testDisplayName", MethodSource.from(failingTest), (c, t) -> {
-					}));
-
-			var platformRunner = new JUnitPlatform(TestClassWithTechnicalNames.class, createLauncher(engine));
-
-			List<Description> children = platformRunner.getDescription().getChildren();
-			assertEquals(1, children.size());
-			var engineDescription = children.getFirst();
-			assertEquals("dummy", engineDescription.getDisplayName());
-
-			var containerDescription = getOnlyElement(engineDescription.getChildren());
-			var testDescription = getOnlyElement(containerDescription.getChildren());
-
-			// @formatter:off
-			assertAll(
-					() -> assertEquals("dummy", engineDescription.getDisplayName(), "engine display name"),
-					() -> assertEquals("dummy", engineDescription.getClassName(), "engine class name"),
-					() -> assertNull(engineDescription.getMethodName(), "engine method name"),
-					() -> assertEquals(getClass().getName(), containerDescription.getDisplayName(), "container display name"),
-					() -> assertEquals(getClass().getName(), containerDescription.getClassName(), "container class name"),
-					() -> assertNull(containerDescription.getMethodName(), "container method name"),
-					() -> assertEquals("failingTest(" + getClass().getName() + ")", testDescription.getDisplayName(), "test display name"),
-					() -> assertEquals(getClass().getName(), testDescription.getClassName(), "test class name"),
-					() -> assertEquals("failingTest", testDescription.getMethodName(), "test method name")
-			);
-			// @formatter:on
-		}
-
-		void failingTest() {
-			// not actually invoked
-		}
-
-	}
-
-	// -------------------------------------------------------------------------
-
-	private static Description suiteDescription(String uniqueId) {
-		return createSuiteDescription(uniqueId, UniqueId.parse(uniqueId));
-	}
-
-	private static Description testDescription(String uniqueId) {
-		return createTestDescription(uniqueId, uniqueId, UniqueId.parse(uniqueId));
-	}
-
-	private TestDescriptor testDescriptorWithTags(String... tag) {
-		var testDescriptor = mock(TestDescriptor.class);
-		var tags = Arrays.stream(tag).map(TestTag::create).collect(toSet());
-		when(testDescriptor.getTags()).thenReturn(tags);
-		return testDescriptor;
-	}
-
-	private LauncherDiscoveryRequest instantiateRunnerAndCaptureGeneratedRequest(Class<?> testClass) {
-		var launcher = mock(Launcher.class);
-		var captor = ArgumentCaptor.forClass(LauncherDiscoveryRequest.class);
-		when(launcher.discover(captor.capture())).thenReturn(
-			TestPlan.from(true, Set.of(), mock(), dummyOutputDirectoryProvider()));
-
-		new JUnitPlatform(testClass, launcher);
-
-		return captor.getValue();
-	}
-
-	private static class TestClass {
-	}
-
-	@UseTechnicalNames
-	private static class TestClassWithTechnicalNames {
-	}
-
-	private static class TestSuiteWithDefaultDisplayName {
-	}
-
-	@SuiteDisplayName("Sweeeeeeet Name!")
-	private static class TestSuiteWithCustomDisplayName {
-	}
-
-	@SuiteDisplayName("Sweeeeeeet Name!")
-	@UseTechnicalNames
-	private static class TestSuiteWithCustomDisplayNameAndTechnicalNames {
-	}
-
-	private static class DynamicTestEngine implements TestEngine {
-
-		@Override
-		public String getId() {
-			return "dynamic";
-		}
-
-		@Override
-		public TestDescriptor discover(EngineDiscoveryRequest discoveryRequest, UniqueId uniqueId) {
-			return new EngineDescriptor(uniqueId, "Dynamic Engine");
-		}
-
-		@Override
-		public void execute(ExecutionRequest request) {
-			var engineExecutionListener = request.getEngineExecutionListener();
-			var root = request.getRootTestDescriptor();
-
-			TestDescriptor container = new DemoContainerTestDescriptor(root.getUniqueId().append("container", "1"),
-				"container #1");
-			root.addChild(container);
-
-			engineExecutionListener.dynamicTestRegistered(container);
-			engineExecutionListener.executionStarted(container);
-
-			var containerUid = container.getUniqueId();
-
-			TestDescriptor dynamicTest1 = new DemoTestTestDescriptor(containerUid.append("test", "1"),
-				"dynamic test #1");
-			container.addChild(dynamicTest1);
-			engineExecutionListener.dynamicTestRegistered(dynamicTest1);
-			engineExecutionListener.executionStarted(dynamicTest1);
-			engineExecutionListener.executionFinished(dynamicTest1, TestExecutionResult.successful());
-
-			TestDescriptor dynamicTest2 = new DemoTestTestDescriptor(containerUid.append("test", "2"),
-				"dynamic test #2");
-			container.addChild(dynamicTest2);
-			engineExecutionListener.dynamicTestRegistered(dynamicTest2);
-			engineExecutionListener.executionStarted(dynamicTest2);
-			engineExecutionListener.executionFinished(dynamicTest2, TestExecutionResult.successful());
-
-			TestDescriptor dynamicTest3 = new DemoContainerAndTestTestDescriptor(containerUid.append("test", "3"),
-				"dynamic test #3");
-			container.addChild(dynamicTest3);
-			engineExecutionListener.dynamicTestRegistered(dynamicTest3);
-			engineExecutionListener.executionStarted(dynamicTest3);
-			engineExecutionListener.executionFinished(dynamicTest3, TestExecutionResult.successful());
-
-			TestDescriptor dynamicTest3a = new DemoTestTestDescriptor(dynamicTest3.getUniqueId().append("test", "3a"),
-				"dynamic test #3a");
-			dynamicTest3.addChild(dynamicTest3a);
-			engineExecutionListener.dynamicTestRegistered(dynamicTest3a);
-			engineExecutionListener.executionStarted(dynamicTest3a);
-			engineExecutionListener.executionFinished(dynamicTest3a, TestExecutionResult.successful());
-
-			engineExecutionListener.executionFinished(container, TestExecutionResult.successful());
-		}
-
-	}
-
-	private static class DemoContainerTestDescriptor extends AbstractTestDescriptor {
-
-		DemoContainerTestDescriptor(UniqueId uniqueId, String displayName) {
-			super(uniqueId, displayName);
-		}
-
-		@Override
-		public Type getType() {
-			return Type.CONTAINER;
-		}
-	}
-
-	private static class DemoTestTestDescriptor extends AbstractTestDescriptor {
-
-		DemoTestTestDescriptor(UniqueId uniqueId, String displayName) {
-			super(uniqueId, displayName);
-		}
-
-		@Override
-		public Type getType() {
-			return Type.TEST;
-		}
-	}
-
-	private static class DemoContainerAndTestTestDescriptor extends AbstractTestDescriptor {
-
-		DemoContainerAndTestTestDescriptor(UniqueId uniqueId, String displayName) {
-			super(uniqueId, displayName);
-		}
-
-		@Override
-		public Type getType() {
-			return Type.CONTAINER_AND_TEST;
-		}
-	}
-
-}
diff --git a/platform-tests/src/test/java/org/junit/platform/suite/commons/SuiteLauncherDiscoveryRequestBuilderTests.java b/platform-tests/src/test/java/org/junit/platform/suite/commons/SuiteLauncherDiscoveryRequestBuilderTests.java
index b2239ca97817..efa86382c9bc 100644
--- a/platform-tests/src/test/java/org/junit/platform/suite/commons/SuiteLauncherDiscoveryRequestBuilderTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/suite/commons/SuiteLauncherDiscoveryRequestBuilderTests.java
@@ -22,7 +22,7 @@
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
 import java.net.URI;
-import java.nio.file.Paths;
+import java.nio.file.Path;
 import java.util.Collections;
 import java.util.List;
 import java.util.Map;
@@ -487,7 +487,7 @@ class Suite {
 
 		LauncherDiscoveryRequest request = builder.applySelectorsAndFiltersFromSuite(Suite.class).build();
 		List<DirectorySelector> selectors = request.getSelectorsByType(DirectorySelector.class);
-		assertEquals(Paths.get("path/to/root"), exactlyOne(selectors).getPath());
+		assertEquals(Path.of("path/to/root"), exactlyOne(selectors).getPath());
 	}
 
 	@Test
@@ -508,7 +508,7 @@ class Suite {
 
 		LauncherDiscoveryRequest request = builder.applySelectorsAndFiltersFromSuite(Suite.class).build();
 		List<FileSelector> selectors = request.getSelectorsByType(FileSelector.class);
-		assertEquals(Paths.get("path/to/root"), exactlyOne(selectors).getPath());
+		assertEquals(Path.of("path/to/root"), exactlyOne(selectors).getPath());
 	}
 
 	@Test
@@ -689,15 +689,9 @@ public Optional<Boolean> getBoolean(String key) {
 			return Optional.empty();
 		}
 
-		@Override
-		@SuppressWarnings("deprecation")
-		public int size() {
-			return map.size();
-		}
-
 		@Override
 		public Set<String> keySet() {
-			return null;
+			return Set.of();
 		}
 
 	}
diff --git a/platform-tests/src/test/java/org/junit/platform/suite/engine/BeforeAndAfterSuiteTests.java b/platform-tests/src/test/java/org/junit/platform/suite/engine/BeforeAndAfterSuiteTests.java
index 186cd71304f3..bcfb56f8ecc0 100644
--- a/platform-tests/src/test/java/org/junit/platform/suite/engine/BeforeAndAfterSuiteTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/suite/engine/BeforeAndAfterSuiteTests.java
@@ -16,20 +16,6 @@
 import static org.junit.platform.commons.util.CollectionUtils.getOnlyElement;
 import static org.junit.platform.engine.discovery.DiscoverySelectors.selectClass;
 import static org.junit.platform.suite.engine.SuiteEngineDescriptor.ENGINE_ID;
-import static org.junit.platform.suite.engine.testsuites.LifecycleMethodsSuites.FailingAfterSuite;
-import static org.junit.platform.suite.engine.testsuites.LifecycleMethodsSuites.FailingBeforeAndAfterSuite;
-import static org.junit.platform.suite.engine.testsuites.LifecycleMethodsSuites.FailingBeforeSuite;
-import static org.junit.platform.suite.engine.testsuites.LifecycleMethodsSuites.NonStaticAfterSuite;
-import static org.junit.platform.suite.engine.testsuites.LifecycleMethodsSuites.NonStaticBeforeSuite;
-import static org.junit.platform.suite.engine.testsuites.LifecycleMethodsSuites.NonVoidAfterSuite;
-import static org.junit.platform.suite.engine.testsuites.LifecycleMethodsSuites.NonVoidBeforeSuite;
-import static org.junit.platform.suite.engine.testsuites.LifecycleMethodsSuites.ParameterAcceptingAfterSuite;
-import static org.junit.platform.suite.engine.testsuites.LifecycleMethodsSuites.ParameterAcceptingBeforeSuite;
-import static org.junit.platform.suite.engine.testsuites.LifecycleMethodsSuites.PrivateAfterSuite;
-import static org.junit.platform.suite.engine.testsuites.LifecycleMethodsSuites.PrivateBeforeSuite;
-import static org.junit.platform.suite.engine.testsuites.LifecycleMethodsSuites.SeveralFailingBeforeAndAfterSuite;
-import static org.junit.platform.suite.engine.testsuites.LifecycleMethodsSuites.SubclassWithBeforeAndAfterSuite;
-import static org.junit.platform.suite.engine.testsuites.LifecycleMethodsSuites.SuccessfulBeforeAndAfterSuite;
 import static org.junit.platform.testkit.engine.EventConditions.container;
 import static org.junit.platform.testkit.engine.EventConditions.event;
 import static org.junit.platform.testkit.engine.EventConditions.finishedSuccessfully;
@@ -52,6 +38,20 @@
 import org.junit.platform.suite.api.AfterSuite;
 import org.junit.platform.suite.api.BeforeSuite;
 import org.junit.platform.suite.engine.testcases.StatefulTestCase;
+import org.junit.platform.suite.engine.testsuites.LifecycleMethodsSuites.FailingAfterSuite;
+import org.junit.platform.suite.engine.testsuites.LifecycleMethodsSuites.FailingBeforeAndAfterSuite;
+import org.junit.platform.suite.engine.testsuites.LifecycleMethodsSuites.FailingBeforeSuite;
+import org.junit.platform.suite.engine.testsuites.LifecycleMethodsSuites.NonStaticAfterSuite;
+import org.junit.platform.suite.engine.testsuites.LifecycleMethodsSuites.NonStaticBeforeSuite;
+import org.junit.platform.suite.engine.testsuites.LifecycleMethodsSuites.NonVoidAfterSuite;
+import org.junit.platform.suite.engine.testsuites.LifecycleMethodsSuites.NonVoidBeforeSuite;
+import org.junit.platform.suite.engine.testsuites.LifecycleMethodsSuites.ParameterAcceptingAfterSuite;
+import org.junit.platform.suite.engine.testsuites.LifecycleMethodsSuites.ParameterAcceptingBeforeSuite;
+import org.junit.platform.suite.engine.testsuites.LifecycleMethodsSuites.PrivateAfterSuite;
+import org.junit.platform.suite.engine.testsuites.LifecycleMethodsSuites.PrivateBeforeSuite;
+import org.junit.platform.suite.engine.testsuites.LifecycleMethodsSuites.SeveralFailingBeforeAndAfterSuite;
+import org.junit.platform.suite.engine.testsuites.LifecycleMethodsSuites.SubclassWithBeforeAndAfterSuite;
+import org.junit.platform.suite.engine.testsuites.LifecycleMethodsSuites.SuccessfulBeforeAndAfterSuite;
 import org.junit.platform.testkit.engine.EngineExecutionResults;
 import org.junit.platform.testkit.engine.EngineTestKit;
 
diff --git a/platform-tests/src/test/java/org/junit/platform/suite/engine/SuiteTestDescriptorTests.java b/platform-tests/src/test/java/org/junit/platform/suite/engine/SuiteTestDescriptorTests.java
index d9b2be9a741e..1d75e9555ae7 100644
--- a/platform-tests/src/test/java/org/junit/platform/suite/engine/SuiteTestDescriptorTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/suite/engine/SuiteTestDescriptorTests.java
@@ -113,12 +113,6 @@ public Optional<Boolean> getBoolean(String key) {
 			return Optional.empty();
 		}
 
-		@Override
-		@SuppressWarnings("deprecation")
-		public int size() {
-			return 0;
-		}
-
 		@Override
 		public Set<String> keySet() {
 			return Collections.emptySet();
diff --git a/platform-tests/src/test/java/org/junit/platform/testkit/engine/EventsTests.java b/platform-tests/src/test/java/org/junit/platform/testkit/engine/EventsTests.java
index 2d519bede3b6..bd8009c8f4ff 100644
--- a/platform-tests/src/test/java/org/junit/platform/testkit/engine/EventsTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/testkit/engine/EventsTests.java
@@ -10,9 +10,9 @@
 
 package org.junit.platform.testkit.engine;
 
+import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertThrows;
-import static org.junit.jupiter.api.Assertions.assertTrue;
 import static org.junit.platform.testkit.engine.EventConditions.engine;
 import static org.junit.platform.testkit.engine.EventConditions.event;
 import static org.junit.platform.testkit.engine.EventConditions.finishedSuccessfully;
@@ -171,7 +171,7 @@ void assertEventsMatchLooselyInOrderWithAllEventsInWrongOrderFails() {
 		);
 
 		var error = assertThrows(AssertionFailedError.class, willFail);
-		assertTrue(error.getMessage().contains("Conditions are not in the correct order."));
+		assertThat(error).hasMessageContaining("Conditions are not in the correct order.");
 	}
 
 	@Test
@@ -201,7 +201,7 @@ void assertEventsMatchLooselyInOrderWithASubsetInWrongOrderFails() {
 		);
 
 		var error = assertThrows(AssertionFailedError.class, willFail);
-		assertTrue(error.getMessage().contains("Conditions are not in the correct order."));
+		assertThat(error).hasMessageContaining("Conditions are not in the correct order.");
 	}
 
 	@Test
@@ -266,7 +266,7 @@ void assertEventsMatchLooselyInOrderWithSecondAndLastEventInBadOrderFails() {
 		);
 
 		var error = assertThrows(AssertionFailedError.class, willFail);
-		assertTrue(error.getMessage().contains("Conditions are not in the correct order."));
+		assertThat(error).hasMessageContaining("Conditions are not in the correct order.");
 	}
 
 	@Test
@@ -281,7 +281,7 @@ void assertEventsMatchLooselyInOrderWithTooManyEventsFails() {
 			event(engine(), finishedSuccessfully()));
 
 		var error = assertThrows(AssertionError.class, willFail);
-		assertTrue(error.getMessage().endsWith("to be less than or equal to 4 but was 6"));
+		assertThat(error).hasMessageEndingWith("to be less than or equal to 4 but was 6");
 	}
 
 }
diff --git a/platform-tests/src/test/java/org/junit/platform/testkit/engine/NestedContainerEventConditionTests.java b/platform-tests/src/test/java/org/junit/platform/testkit/engine/NestedContainerEventConditionTests.java
index d109969008b1..dcece1a3a020 100644
--- a/platform-tests/src/test/java/org/junit/platform/testkit/engine/NestedContainerEventConditionTests.java
+++ b/platform-tests/src/test/java/org/junit/platform/testkit/engine/NestedContainerEventConditionTests.java
@@ -41,6 +41,7 @@
  */
 class NestedContainerEventConditionTests {
 
+	@SuppressWarnings({ "DataFlowIssue", "NullAway" })
 	@Test
 	void preconditions() {
 		assertThatExceptionOfType(PreconditionViolationException.class)//
diff --git a/platform-tooling-support-tests/platform-tooling-support-tests.gradle.kts b/platform-tooling-support-tests/platform-tooling-support-tests.gradle.kts
index 2f2d9cd00a68..d2a769977d0c 100644
--- a/platform-tooling-support-tests/platform-tooling-support-tests.gradle.kts
+++ b/platform-tooling-support-tests/platform-tooling-support-tests.gradle.kts
@@ -7,6 +7,7 @@ import java.time.Duration
 
 plugins {
 	id("junitbuild.build-parameters")
+	id("junitbuild.java-nullability-conventions")
 	id("junitbuild.kotlin-library-conventions")
 	id("junitbuild.testing-conventions")
 }
@@ -59,6 +60,7 @@ dependencies {
 	thirdPartyJars(libs.assertj)
 	thirdPartyJars(libs.apiguardian)
 	thirdPartyJars(libs.hamcrest)
+	thirdPartyJars(libs.jspecify)
 	thirdPartyJars(libs.opentest4j)
 	thirdPartyJars(libs.openTestReporting.tooling.spi)
 	thirdPartyJars(libs.jimfs)
@@ -114,11 +116,15 @@ val normalizeMavenRepo by tasks.registering(Sync::class) {
 val archUnit by testing.suites.registering(JvmTestSuite::class) {
 	dependencies {
 		implementation(libs.archunit) {
-			because("checking the architecture of JUnit 5")
+			because("checking the architecture")
 		}
 		implementation(libs.apiguardian) {
 			because("we validate that public classes are annotated")
 		}
+		implementation(libs.jspecify) {
+			because("we validate that packages are annotated")
+		}
+		implementation(libs.assertj)
 		runtimeOnly.bundle(libs.bundles.log4j)
 		val modularProjects: List<Project> by rootProject
 		modularProjects.forEach {
@@ -211,15 +217,15 @@ val test by testing.suites.getting(JvmTestSuite::class) {
 
 				develocity {
 					testDistribution {
-						requirements.add("jdk=8")
+						requirements.add("jdk=17")
 						this as TestDistributionConfigurationInternal
 						preferredMaxDuration = Duration.ofMillis(500)
 					}
 				}
-				jvmArgumentProviders += JavaHomeDir(project, 8, develocity.testDistribution.enabled)
+				jvmArgumentProviders += JavaHomeDir(project, 17, develocity.testDistribution.enabled)
 				jvmArgumentProviders += JavaHomeDir(project, 17, develocity.testDistribution.enabled)
 
-				val gradleJavaVersion = JavaVersion.current().majorVersion.toInt()
+				val gradleJavaVersion = 21
 				jvmArgumentProviders += JavaHomeDir(project, gradleJavaVersion, develocity.testDistribution.enabled)
 				jvmArgumentProviders += JavaHomeDir(project, gradleJavaVersion, develocity.testDistribution.enabled, nativeImage = true)
 				systemProperty("gradle.java.version", gradleJavaVersion)
diff --git a/platform-tooling-support-tests/projects/graalvm-starter/build.gradle.kts b/platform-tooling-support-tests/projects/graalvm-starter/build.gradle.kts
index 7bdc3af69a56..da1548337dea 100644
--- a/platform-tooling-support-tests/projects/graalvm-starter/build.gradle.kts
+++ b/platform-tooling-support-tests/projects/graalvm-starter/build.gradle.kts
@@ -3,21 +3,14 @@ plugins {
 	id("org.graalvm.buildtools.native")
 }
 
-val jupiterVersion: String by project
-val platformVersion: String by project
-val vintageVersion: String by project
-
-repositories {
-	maven { url = uri(file(System.getProperty("maven.repo"))) }
-	mavenCentral()
-}
+val junitVersion: String by project
 
 dependencies {
-	testImplementation("org.junit.jupiter:junit-jupiter:$jupiterVersion")
+	testImplementation("org.junit.jupiter:junit-jupiter:$junitVersion")
 	testImplementation("junit:junit:4.13.2")
-	testImplementation("org.junit.platform:junit-platform-suite:$platformVersion")
-	testRuntimeOnly("org.junit.vintage:junit-vintage-engine:$vintageVersion")
-	testRuntimeOnly("org.junit.platform:junit-platform-reporting:$platformVersion")
+	testImplementation("org.junit.platform:junit-platform-suite:$junitVersion")
+	testRuntimeOnly("org.junit.vintage:junit-vintage-engine:$junitVersion")
+	testRuntimeOnly("org.junit.platform:junit-platform-reporting:$junitVersion")
 }
 
 tasks.test {
@@ -34,29 +27,40 @@ tasks.test {
 	}
 }
 
-// These will be part of the next version of native-build-tools
-// see https://github.com/graalvm/native-build-tools/pull/693
-val initializeAtBuildTime = listOf(
-	"org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor\$ClassInfo",
-	"org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor\$LifecycleMethods",
-	"org.junit.jupiter.engine.descriptor.ClassTemplateInvocationTestDescriptor",
-	"org.junit.jupiter.engine.descriptor.ClassTemplateTestDescriptor",
-	"org.junit.jupiter.engine.descriptor.DynamicDescendantFilter\$Mode",
-	"org.junit.jupiter.engine.descriptor.ExclusiveResourceCollector\$1",
-	"org.junit.jupiter.engine.descriptor.MethodBasedTestDescriptor\$MethodInfo",
-	"org.junit.jupiter.engine.discovery.ClassSelectorResolver\$DummyClassTemplateInvocationContext",
-	"org.junit.platform.launcher.core.DiscoveryIssueNotifier",
-	"org.junit.platform.launcher.core.HierarchicalOutputDirectoryProvider",
-	"org.junit.platform.launcher.core.LauncherDiscoveryResult\$EngineResultInfo",
-	"org.junit.platform.suite.engine.SuiteTestDescriptor\$LifecycleMethods",
+val initializeAtBuildTime = mapOf(
+	// These will be part of the next version of native-build-tools
+	// see https://github.com/graalvm/native-build-tools/pull/693
+	"5.13" to listOf(
+		"org.junit.jupiter.api.DisplayNameGenerator\$IndicativeSentences",
+		"org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor\$ClassInfo",
+		"org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor\$LifecycleMethods",
+		"org.junit.jupiter.engine.descriptor.ClassTemplateInvocationTestDescriptor",
+		"org.junit.jupiter.engine.descriptor.ClassTemplateTestDescriptor",
+		"org.junit.jupiter.engine.descriptor.DynamicDescendantFilter\$Mode",
+		"org.junit.jupiter.engine.descriptor.ExclusiveResourceCollector\$1",
+		"org.junit.jupiter.engine.descriptor.MethodBasedTestDescriptor\$MethodInfo",
+		"org.junit.jupiter.engine.discovery.ClassSelectorResolver\$DummyClassTemplateInvocationContext",
+		"org.junit.platform.engine.support.store.NamespacedHierarchicalStore\$EvaluatedValue",
+		"org.junit.platform.launcher.core.DiscoveryIssueNotifier",
+		"org.junit.platform.launcher.core.HierarchicalOutputDirectoryProvider",
+		"org.junit.platform.launcher.core.LauncherDiscoveryResult\$EngineResultInfo",
+		"org.junit.platform.launcher.core.LauncherPhase",
+		"org.junit.platform.suite.engine.DiscoverySelectorResolver",
+		"org.junit.platform.suite.engine.SuiteTestDescriptor\$DiscoveryIssueForwardingListener",
+		"org.junit.platform.suite.engine.SuiteTestDescriptor\$LifecycleMethods",
+	),
+	// These need to be added to native-build-tools
+	"6.0" to listOf(
+		"org.junit.platform.commons.util.KotlinReflectionUtils",
+		"org.junit.platform.launcher.core.DiscoveryIssueNotifier\$1",
+	)
 )
 
 graalvmNative {
 	binaries {
 		named("test") {
-			buildArgs.add("--strict-image-heap")
 			buildArgs.add("-H:+ReportExceptionStackTraces")
-			buildArgs.add("--initialize-at-build-time=${initializeAtBuildTime.joinToString(",")}")
+			buildArgs.add("--initialize-at-build-time=${initializeAtBuildTime.values.flatten().joinToString(",")}")
 		}
 	}
 }
diff --git a/platform-tooling-support-tests/projects/graalvm-starter/settings.gradle.kts b/platform-tooling-support-tests/projects/graalvm-starter/settings.gradle.kts
index a53a82439ab6..6a59f78e05fd 100644
--- a/platform-tooling-support-tests/projects/graalvm-starter/settings.gradle.kts
+++ b/platform-tooling-support-tests/projects/graalvm-starter/settings.gradle.kts
@@ -1,16 +1,35 @@
 pluginManagement {
 	plugins {
 		// TODO Remove custom config in build.gradle.kts when upgrading
-		id("org.graalvm.buildtools.native") version "0.10.6"
+		id("org.graalvm.buildtools.native") version "0.11.0-SNAPSHOT"
 	}
 	repositories {
 		mavenCentral()
 		gradlePluginPortal()
+		maven(url = "https://raw.githubusercontent.com/graalvm/native-build-tools/snapshots") {
+			mavenContent {
+				snapshotsOnly()
+			}
+		}
 	}
 }
 
 plugins {
-	id("org.gradle.toolchains.foojay-resolver-convention") version "0.10.0"
+	id("org.gradle.toolchains.foojay-resolver-convention") version "1.0.0"
+}
+
+dependencyResolutionManagement {
+	repositories {
+		repositories {
+			maven { url = uri(file(System.getProperty("maven.repo"))) }
+			mavenCentral()
+			maven(url = "https://raw.githubusercontent.com/graalvm/native-build-tools/snapshots") {
+				mavenContent {
+					snapshotsOnly()
+				}
+			}
+		}
+	}
 }
 
 rootProject.name = "graalvm-starter"
diff --git a/platform-tooling-support-tests/projects/graalvm-starter/src/test/java/com/example/project/CalculatorParameterizedClassTests.java b/platform-tooling-support-tests/projects/graalvm-starter/src/test/java/com/example/project/CalculatorParameterizedClassTests.java
index b26b3795d62e..4dfa9ce8352f 100644
--- a/platform-tooling-support-tests/projects/graalvm-starter/src/test/java/com/example/project/CalculatorParameterizedClassTests.java
+++ b/platform-tooling-support-tests/projects/graalvm-starter/src/test/java/com/example/project/CalculatorParameterizedClassTests.java
@@ -37,7 +37,7 @@ void parameterizedTest(int j) {
 	@Nested
 	@ParameterizedClass
 	@ValueSource(ints = { 1, 2 })
-	@Disabled("https://github.com/junit-team/junit5/issues/4440")
+	@Disabled("https://github.com/junit-team/junit-framework/issues/4440")
 	class Inner {
 
 		final int j;
diff --git a/platform-tooling-support-tests/projects/gradle-kotlin-extensions/build.gradle.kts b/platform-tooling-support-tests/projects/gradle-kotlin-extensions/build.gradle.kts
index b8a6f83ed106..16fb43ea32d5 100644
--- a/platform-tooling-support-tests/projects/gradle-kotlin-extensions/build.gradle.kts
+++ b/platform-tooling-support-tests/projects/gradle-kotlin-extensions/build.gradle.kts
@@ -1,7 +1,9 @@
 import org.jetbrains.kotlin.gradle.tasks.KotlinCompile
+import org.jetbrains.kotlin.gradle.dsl.JvmTarget.JVM_17
+import org.jetbrains.kotlin.gradle.dsl.KotlinVersion.KOTLIN_2_1
 
 plugins {
-	kotlin("jvm") version "2.1.21"
+	kotlin("jvm") version "2.2.0"
 }
 
 repositories {
@@ -9,26 +11,26 @@ repositories {
 	mavenCentral()
 }
 
-val jupiterVersion: String by project
-val platformVersion: String by project
+val junitVersion: String by project
 
 dependencies {
-	testImplementation(kotlin("stdlib-jdk8"))
-	testImplementation("org.junit.jupiter:junit-jupiter:$jupiterVersion")
-	testRuntimeOnly("org.junit.platform:junit-platform-launcher:$platformVersion")
+	testImplementation(kotlin("stdlib"))
+	testImplementation("org.junit.jupiter:junit-jupiter:$junitVersion")
+	testRuntimeOnly("org.junit.platform:junit-platform-launcher:$junitVersion")
 }
 
 java {
 	toolchain {
-		languageVersion = JavaLanguageVersion.of(8)
+		languageVersion = JavaLanguageVersion.of(17)
 	}
 }
 
 tasks.withType<KotlinCompile>().configureEach {
-	kotlinOptions {
-		jvmTarget = "1.8"
-		apiVersion = "1.6"
-		languageVersion = "1.6"
+	compilerOptions {
+		jvmTarget = JVM_17
+		apiVersion = KOTLIN_2_1
+		languageVersion = KOTLIN_2_1
+		freeCompilerArgs.addAll("-Xskip-prerelease-check")
 	}
 }
 
diff --git a/platform-tooling-support-tests/projects/gradle-kotlin-extensions/gradle.properties b/platform-tooling-support-tests/projects/gradle-kotlin-extensions/gradle.properties
index 79b428ebc70c..bed2250e4577 100644
--- a/platform-tooling-support-tests/projects/gradle-kotlin-extensions/gradle.properties
+++ b/platform-tooling-support-tests/projects/gradle-kotlin-extensions/gradle.properties
@@ -1 +1 @@
-org.gradle.java.installations.fromEnv=JDK8
+org.gradle.java.installations.fromEnv=JDK17
diff --git a/platform-tooling-support-tests/projects/gradle-kotlin-extensions/settings.gradle.kts b/platform-tooling-support-tests/projects/gradle-kotlin-extensions/settings.gradle.kts
index 963ac745898a..f8ef92d0510a 100644
--- a/platform-tooling-support-tests/projects/gradle-kotlin-extensions/settings.gradle.kts
+++ b/platform-tooling-support-tests/projects/gradle-kotlin-extensions/settings.gradle.kts
@@ -1,5 +1,5 @@
 plugins {
-    id("org.gradle.toolchains.foojay-resolver-convention") version "0.10.0"
+    id("org.gradle.toolchains.foojay-resolver-convention") version "1.0.0"
 }
 
 rootProject.name = "gradle-kotlin-extensions"
diff --git a/platform-tooling-support-tests/projects/gradle-missing-engine/build.gradle.kts b/platform-tooling-support-tests/projects/gradle-missing-engine/build.gradle.kts
index 50b4e7b2924b..0e7612cf3be1 100644
--- a/platform-tooling-support-tests/projects/gradle-missing-engine/build.gradle.kts
+++ b/platform-tooling-support-tests/projects/gradle-missing-engine/build.gradle.kts
@@ -2,8 +2,7 @@ plugins {
 	java
 }
 
-val jupiterVersion: String by project
-val platformVersion: String by project
+val junitVersion: String by project
 
 repositories {
 	maven { url = uri(file(System.getProperty("maven.repo"))) }
@@ -11,14 +10,14 @@ repositories {
 }
 
 dependencies {
-	testImplementation("org.junit.jupiter:junit-jupiter-api:$jupiterVersion") {
+	testImplementation("org.junit.jupiter:junit-jupiter-api:$junitVersion") {
 		exclude(group = "org.junit.jupiter", module = "junit-jupiter-engine")
 	}
-	testRuntimeOnly("org.junit.platform:junit-platform-launcher:$platformVersion")}
+	testRuntimeOnly("org.junit.platform:junit-platform-launcher:$junitVersion")}
 
 java {
 	toolchain {
-		languageVersion = JavaLanguageVersion.of(8)
+		languageVersion = JavaLanguageVersion.of(17)
 	}
 }
 
diff --git a/platform-tooling-support-tests/projects/gradle-missing-engine/gradle.properties b/platform-tooling-support-tests/projects/gradle-missing-engine/gradle.properties
index 79b428ebc70c..bed2250e4577 100644
--- a/platform-tooling-support-tests/projects/gradle-missing-engine/gradle.properties
+++ b/platform-tooling-support-tests/projects/gradle-missing-engine/gradle.properties
@@ -1 +1 @@
-org.gradle.java.installations.fromEnv=JDK8
+org.gradle.java.installations.fromEnv=JDK17
diff --git a/platform-tooling-support-tests/projects/gradle-missing-engine/settings.gradle.kts b/platform-tooling-support-tests/projects/gradle-missing-engine/settings.gradle.kts
index 4e05cf034d46..27afc44c06b2 100644
--- a/platform-tooling-support-tests/projects/gradle-missing-engine/settings.gradle.kts
+++ b/platform-tooling-support-tests/projects/gradle-missing-engine/settings.gradle.kts
@@ -1,5 +1,5 @@
 plugins {
-    id("org.gradle.toolchains.foojay-resolver-convention") version "0.10.0"
+    id("org.gradle.toolchains.foojay-resolver-convention") version "1.0.0"
 }
 
 rootProject.name = "gradle-missing-engine"
diff --git a/platform-tooling-support-tests/projects/jar-describe-module/junit-jupiter-api.expected.txt b/platform-tooling-support-tests/projects/jar-describe-module/junit-jupiter-api.expected.txt
index 26719afdbe79..7fa1fa9cf145 100644
--- a/platform-tooling-support-tests/projects/jar-describe-module/junit-jupiter-api.expected.txt
+++ b/platform-tooling-support-tests/projects/jar-describe-module/junit-jupiter-api.expected.txt
@@ -1,4 +1,4 @@
-org.junit.jupiter.api@${jupiterVersion} jar:file:.+/junit-jupiter-api-\d.+\.jar..module-info\.class
+org.junit.jupiter.api@${version} jar:file:.+/junit-jupiter-api-\d.+\.jar..module-info\.class
 exports org.junit.jupiter.api
 exports org.junit.jupiter.api.condition
 exports org.junit.jupiter.api.extension
@@ -7,7 +7,9 @@ exports org.junit.jupiter.api.function
 exports org.junit.jupiter.api.io
 exports org.junit.jupiter.api.parallel
 requires java.base mandated
+requires kotlin.stdlib static
 requires org.apiguardian.api static transitive
+requires org.jspecify static
 requires org.junit.platform.commons transitive
 requires org.opentest4j transitive
 qualified opens org.junit.jupiter.api.condition to org.junit.platform.commons
diff --git a/platform-tooling-support-tests/projects/jar-describe-module/junit-jupiter-engine.expected.txt b/platform-tooling-support-tests/projects/jar-describe-module/junit-jupiter-engine.expected.txt
index 5c637457863f..65a155299cf8 100644
--- a/platform-tooling-support-tests/projects/jar-describe-module/junit-jupiter-engine.expected.txt
+++ b/platform-tooling-support-tests/projects/jar-describe-module/junit-jupiter-engine.expected.txt
@@ -1,6 +1,7 @@
-org.junit.jupiter.engine@${jupiterVersion} jar:file:.+/junit-jupiter-engine-\d.+\.jar..module-info\.class
+org.junit.jupiter.engine@${version} jar:file:.+/junit-jupiter-engine-\d.+\.jar..module-info\.class
 requires java.base mandated
 requires org.apiguardian.api static
+requires org.jspecify static
 requires org.junit.jupiter.api
 requires org.junit.platform.commons
 requires org.junit.platform.engine
diff --git a/platform-tooling-support-tests/projects/jar-describe-module/junit-jupiter-migrationsupport.expected.txt b/platform-tooling-support-tests/projects/jar-describe-module/junit-jupiter-migrationsupport.expected.txt
index 747125710426..933d05fecf74 100644
--- a/platform-tooling-support-tests/projects/jar-describe-module/junit-jupiter-migrationsupport.expected.txt
+++ b/platform-tooling-support-tests/projects/jar-describe-module/junit-jupiter-migrationsupport.expected.txt
@@ -1,4 +1,4 @@
-org.junit.jupiter.migrationsupport@${jupiterVersion} jar:file:.+/junit-jupiter-migrationsupport-\d.+\.jar..module-info\.class
+org.junit.jupiter.migrationsupport@${version} jar:file:.+/junit-jupiter-migrationsupport-\d.+\.jar..module-info\.class
 exports org.junit.jupiter.migrationsupport
 exports org.junit.jupiter.migrationsupport.conditions
 exports org.junit.jupiter.migrationsupport.rules
@@ -7,5 +7,6 @@ exports org.junit.jupiter.migrationsupport.rules.member
 requires java.base mandated
 requires junit transitive
 requires org.apiguardian.api static transitive
+requires org.jspecify static
 requires org.junit.jupiter.api transitive
 requires org.junit.platform.commons
diff --git a/platform-tooling-support-tests/projects/jar-describe-module/junit-jupiter-params.expected.txt b/platform-tooling-support-tests/projects/jar-describe-module/junit-jupiter-params.expected.txt
index 05e8b8ac4675..95e8e08ab7f7 100644
--- a/platform-tooling-support-tests/projects/jar-describe-module/junit-jupiter-params.expected.txt
+++ b/platform-tooling-support-tests/projects/jar-describe-module/junit-jupiter-params.expected.txt
@@ -1,4 +1,4 @@
-org.junit.jupiter.params@${jupiterVersion} jar:file:.+/junit-jupiter-params-\d.+\.jar..module-info\.class
+org.junit.jupiter.params@${version} jar:file:.+/junit-jupiter-params-\d.+\.jar..module-info\.class
 exports org.junit.jupiter.params
 exports org.junit.jupiter.params.aggregator
 exports org.junit.jupiter.params.converter
@@ -6,6 +6,7 @@ exports org.junit.jupiter.params.provider
 exports org.junit.jupiter.params.support
 requires java.base mandated
 requires org.apiguardian.api static transitive
+requires org.jspecify static
 requires org.junit.jupiter.api transitive
 requires org.junit.platform.commons transitive
 qualified opens org.junit.jupiter.params to org.junit.platform.commons
diff --git a/platform-tooling-support-tests/projects/jar-describe-module/junit-jupiter.expected.txt b/platform-tooling-support-tests/projects/jar-describe-module/junit-jupiter.expected.txt
index 768342398c7e..11da5f5567bf 100644
--- a/platform-tooling-support-tests/projects/jar-describe-module/junit-jupiter.expected.txt
+++ b/platform-tooling-support-tests/projects/jar-describe-module/junit-jupiter.expected.txt
@@ -1,4 +1,4 @@
-org.junit.jupiter@${jupiterVersion} jar:file:.+/junit-jupiter-\d.+\.jar..module-info\.class
+org.junit.jupiter@${version} jar:file:.+/junit-jupiter-\d.+\.jar..module-info\.class
 requires java.base mandated
 requires org.junit.jupiter.api transitive
 requires org.junit.jupiter.engine transitive
diff --git a/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-commons.expected.txt b/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-commons.expected.txt
index e8104a7e3dd8..4a2879865c72 100644
--- a/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-commons.expected.txt
+++ b/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-commons.expected.txt
@@ -1,4 +1,4 @@
-org.junit.platform.commons@${platformVersion} jar:file:.+/junit-platform-commons-\d.+\.jar..module-info\.class
+org.junit.platform.commons@${version} jar:file:.+/junit-platform-commons-\d.+\.jar..module-info\.class
 exports org.junit.platform.commons
 exports org.junit.platform.commons.annotation
 exports org.junit.platform.commons.function
@@ -8,7 +8,11 @@ exports org.junit.platform.commons.support.scanning
 requires java.base mandated
 requires java.logging
 requires java.management
+requires kotlin.reflect static
+requires kotlin.stdlib static
+requires kotlinx.coroutines.core static
 requires org.apiguardian.api static transitive
+requires org.jspecify static transitive
 uses org.junit.platform.commons.support.scanning.ClasspathScanner
-qualified exports org.junit.platform.commons.logging to org.junit.jupiter.api org.junit.jupiter.engine org.junit.jupiter.migrationsupport org.junit.jupiter.params org.junit.platform.console org.junit.platform.engine org.junit.platform.launcher org.junit.platform.reporting org.junit.platform.runner org.junit.platform.suite.api org.junit.platform.suite.engine org.junit.platform.testkit org.junit.vintage.engine
-qualified exports org.junit.platform.commons.util to org.junit.jupiter.api org.junit.jupiter.engine org.junit.jupiter.migrationsupport org.junit.jupiter.params org.junit.platform.console org.junit.platform.engine org.junit.platform.jfr org.junit.platform.launcher org.junit.platform.reporting org.junit.platform.runner org.junit.platform.suite.api org.junit.platform.suite.commons org.junit.platform.suite.engine org.junit.platform.testkit org.junit.vintage.engine
+qualified exports org.junit.platform.commons.logging to org.junit.jupiter.api org.junit.jupiter.engine org.junit.jupiter.migrationsupport org.junit.jupiter.params org.junit.platform.console org.junit.platform.engine org.junit.platform.launcher org.junit.platform.reporting org.junit.platform.suite.api org.junit.platform.suite.engine org.junit.platform.testkit org.junit.vintage.engine
+qualified exports org.junit.platform.commons.util to org.junit.jupiter.api org.junit.jupiter.engine org.junit.jupiter.migrationsupport org.junit.jupiter.params org.junit.platform.console org.junit.platform.engine org.junit.platform.launcher org.junit.platform.reporting org.junit.platform.suite.api org.junit.platform.suite.commons org.junit.platform.suite.engine org.junit.platform.testkit org.junit.vintage.engine
diff --git a/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-console.expected.txt b/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-console.expected.txt
index 4324e45eccfe..01086247b6b6 100644
--- a/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-console.expected.txt
+++ b/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-console.expected.txt
@@ -1,6 +1,7 @@
-org.junit.platform.console@${platformVersion} jar:file:.+/junit-platform-console-\d.+\.jar..module-info\.class
+org.junit.platform.console@${version} jar:file:.+/junit-platform-console-\d.+\.jar..module-info\.class
 requires java.base mandated
 requires org.apiguardian.api static
+requires org.jspecify static
 requires org.junit.platform.commons
 requires org.junit.platform.engine
 requires org.junit.platform.launcher
diff --git a/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-engine.expected.txt b/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-engine.expected.txt
index 04812758a63f..cc88b0d84c7e 100644
--- a/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-engine.expected.txt
+++ b/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-engine.expected.txt
@@ -1,15 +1,15 @@
-org.junit.platform.engine@${platformVersion} jar:file:.+/junit-platform-engine-\d.+\.jar..module-info\.class
+org.junit.platform.engine@${version} jar:file:.+/junit-platform-engine-\d.+\.jar..module-info\.class
 exports org.junit.platform.engine
 exports org.junit.platform.engine.discovery
 exports org.junit.platform.engine.reporting
 exports org.junit.platform.engine.support.config
 exports org.junit.platform.engine.support.descriptor
 exports org.junit.platform.engine.support.discovery
-exports org.junit.platform.engine.support.filter
 exports org.junit.platform.engine.support.hierarchical
 exports org.junit.platform.engine.support.store
 requires java.base mandated
 requires org.apiguardian.api static transitive
+requires org.jspecify static
 requires org.junit.platform.commons transitive
 requires org.opentest4j transitive
 uses org.junit.platform.engine.discovery.DiscoverySelectorIdentifierParser
diff --git a/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-jfr.expected.txt b/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-jfr.expected.txt
deleted file mode 100644
index 10bec3decdaf..000000000000
--- a/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-jfr.expected.txt
+++ /dev/null
@@ -1,9 +0,0 @@
-org.junit.platform.jfr@${platformVersion} jar:file:.+/junit-platform-jfr-\d.+\.jar..module-info\.class
-requires java.base mandated
-requires jdk.jfr
-requires org.apiguardian.api static
-requires org.junit.platform.engine
-requires org.junit.platform.launcher
-provides org.junit.platform.launcher.LauncherDiscoveryListener with org.junit.platform.jfr.FlightRecordingDiscoveryListener
-provides org.junit.platform.launcher.TestExecutionListener with org.junit.platform.jfr.FlightRecordingExecutionListener
-contains org.junit.platform.jfr
diff --git a/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-launcher.expected.txt b/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-launcher.expected.txt
index 41bb2afac024..7c7beb927250 100644
--- a/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-launcher.expected.txt
+++ b/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-launcher.expected.txt
@@ -1,11 +1,13 @@
-org.junit.platform.launcher@${platformVersion} jar:file:.+/junit-platform-launcher-\d.+\.jar..module-info\.class
+org.junit.platform.launcher@${version} jar:file:.+/junit-platform-launcher-\d.+\.jar..module-info\.class
 exports org.junit.platform.launcher
 exports org.junit.platform.launcher.core
 exports org.junit.platform.launcher.listeners
 exports org.junit.platform.launcher.listeners.discovery
 requires java.base mandated
 requires java.logging transitive
+requires jdk.jfr static
 requires org.apiguardian.api static transitive
+requires org.jspecify static
 requires org.junit.platform.commons transitive
 requires org.junit.platform.engine transitive
 uses org.junit.platform.engine.TestEngine
diff --git a/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-reporting.expected.txt b/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-reporting.expected.txt
index 2362fbb8152f..c9f06e55f62b 100644
--- a/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-reporting.expected.txt
+++ b/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-reporting.expected.txt
@@ -1,10 +1,11 @@
-org.junit.platform.reporting@${platformVersion} jar:file:.+/junit-platform-reporting-\d.+\.jar..module-info\.class
+org.junit.platform.reporting@${version} jar:file:.+/junit-platform-reporting-\d.+\.jar..module-info\.class
 exports org.junit.platform.reporting.legacy
 exports org.junit.platform.reporting.legacy.xml
 exports org.junit.platform.reporting.open.xml
 requires java.base mandated
 requires java.xml
 requires org.apiguardian.api static transitive
+requires org.jspecify static
 requires org.junit.platform.commons
 requires org.junit.platform.engine transitive
 requires org.junit.platform.launcher transitive
diff --git a/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-runner.expected.txt b/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-runner.expected.txt
deleted file mode 100644
index ee4ae1791204..000000000000
--- a/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-runner.expected.txt
+++ /dev/null
@@ -1,8 +0,0 @@
-org.junit.platform.runner@${platformVersion} jar:file:.+/junit-platform-runner-\d.+\.jar..module-info\.class
-exports org.junit.platform.runner
-requires java.base mandated
-requires junit transitive
-requires org.apiguardian.api static transitive
-requires org.junit.platform.launcher transitive
-requires org.junit.platform.suite.api transitive
-requires org.junit.platform.suite.commons
diff --git a/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-suite-api.expected.txt b/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-suite-api.expected.txt
index 5e3da71afa28..5b5b0b36a9b3 100644
--- a/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-suite-api.expected.txt
+++ b/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-suite-api.expected.txt
@@ -1,5 +1,6 @@
-org.junit.platform.suite.api@${platformVersion} jar:file:.+/junit-platform-suite-api-\d.+\.jar..module-info\.class
+org.junit.platform.suite.api@${version} jar:file:.+/junit-platform-suite-api-\d.+\.jar..module-info\.class
 exports org.junit.platform.suite.api
 requires java.base mandated
 requires org.apiguardian.api static transitive
+requires org.jspecify static
 requires org.junit.platform.commons transitive
diff --git a/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-suite-commons.expected.txt b/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-suite-commons.expected.txt
index 493962b6b97d..1d5c6b9f584c 100644
--- a/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-suite-commons.expected.txt
+++ b/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-suite-commons.expected.txt
@@ -1,8 +1,9 @@
-org.junit.platform.suite.commons@${platformVersion} jar:file:.+/junit-platform-suite-commons-\d.+\.jar..module-info\.class
+org.junit.platform.suite.commons@${version} jar:file:.+/junit-platform-suite-commons-\d.+\.jar..module-info\.class
 requires java.base mandated
 requires org.apiguardian.api static transitive
+requires org.jspecify static
 requires org.junit.platform.commons
 requires org.junit.platform.engine
 requires org.junit.platform.launcher transitive
 requires org.junit.platform.suite.api
-qualified exports org.junit.platform.suite.commons to org.junit.platform.runner org.junit.platform.suite.engine
+qualified exports org.junit.platform.suite.commons to org.junit.platform.suite.engine
diff --git a/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-suite-engine.expected.txt b/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-suite-engine.expected.txt
index 4a5694586dd4..d655ec351ed3 100644
--- a/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-suite-engine.expected.txt
+++ b/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-suite-engine.expected.txt
@@ -1,6 +1,7 @@
-org.junit.platform.suite.engine@${platformVersion} jar:file:.+/junit-platform-suite-engine-\d.+\.jar..module-info\.class
+org.junit.platform.suite.engine@${version} jar:file:.+/junit-platform-suite-engine-\d.+\.jar..module-info\.class
 requires java.base mandated
 requires org.apiguardian.api static
+requires org.jspecify static
 requires org.junit.platform.commons
 requires org.junit.platform.engine
 requires org.junit.platform.launcher
diff --git a/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-suite.expected.txt b/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-suite.expected.txt
index d6114f727332..83276251b80b 100644
--- a/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-suite.expected.txt
+++ b/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-suite.expected.txt
@@ -1,4 +1,4 @@
-org.junit.platform.suite@${platformVersion} jar:file:.+/junit-platform-suite-\d.+\.jar..module-info\.class
+org.junit.platform.suite@${version} jar:file:.+/junit-platform-suite-\d.+\.jar..module-info\.class
 requires java.base mandated
 requires org.junit.platform.suite.api transitive
 requires org.junit.platform.suite.engine transitive
diff --git a/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-testkit.expected.txt b/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-testkit.expected.txt
index c530e1bf68f8..008e2f1caf0a 100644
--- a/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-testkit.expected.txt
+++ b/platform-tooling-support-tests/projects/jar-describe-module/junit-platform-testkit.expected.txt
@@ -1,8 +1,9 @@
-org.junit.platform.testkit@${platformVersion} jar:file:.+/junit-platform-testkit-\d.+\.jar..module-info\.class
+org.junit.platform.testkit@${version} jar:file:.+/junit-platform-testkit-\d.+\.jar..module-info\.class
 exports org.junit.platform.testkit.engine
 requires java.base mandated
 requires org.apiguardian.api static transitive
 requires org.assertj.core transitive
+requires org.jspecify static
 requires org.junit.platform.commons
 requires org.junit.platform.engine transitive
 requires org.junit.platform.launcher transitive
diff --git a/platform-tooling-support-tests/projects/jar-describe-module/junit-vintage-engine.expected.txt b/platform-tooling-support-tests/projects/jar-describe-module/junit-vintage-engine.expected.txt
index 854b4981242a..79a358e40a59 100644
--- a/platform-tooling-support-tests/projects/jar-describe-module/junit-vintage-engine.expected.txt
+++ b/platform-tooling-support-tests/projects/jar-describe-module/junit-vintage-engine.expected.txt
@@ -1,7 +1,8 @@
-org.junit.vintage.engine@${vintageVersion} jar:file:.+/junit-vintage-engine-\d.+\.jar..module-info\.class
+org.junit.vintage.engine@${version} jar:file:.+/junit-vintage-engine-\d.+\.jar..module-info\.class
 requires java.base mandated
 requires junit
 requires org.apiguardian.api static
+requires org.jspecify static
 requires org.junit.platform.engine
 provides org.junit.platform.engine.TestEngine with org.junit.vintage.engine.VintageTestEngine
 contains org.junit.vintage.engine
diff --git a/platform-tooling-support-tests/projects/java-versions/pom.xml b/platform-tooling-support-tests/projects/java-versions/pom.xml
deleted file mode 100644
index 664c9092e437..000000000000
--- a/platform-tooling-support-tests/projects/java-versions/pom.xml
+++ /dev/null
@@ -1,63 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
-    <modelVersion>4.0.0</modelVersion>
-
-    <groupId>platform.tooling.support.tests</groupId>
-    <artifactId>java-versions</artifactId>
-    <version>1.0-SNAPSHOT</version>
-
-    <properties>
-        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
-    </properties>
-
-    <dependencies>
-        <dependency>
-            <groupId>org.junit.jupiter</groupId>
-            <artifactId>junit-jupiter-engine</artifactId>
-            <version>${junit.jupiter.version}</version>
-            <scope>test</scope>
-        </dependency>
-        <dependency>
-            <groupId>org.junit.platform</groupId>
-            <artifactId>junit-platform-commons</artifactId>
-            <version>${junit.platform.version}</version>
-            <scope>test</scope>
-        </dependency>
-    </dependencies>
-
-    <build>
-        <pluginManagement>
-            <plugins>
-                <plugin>
-                    <artifactId>maven-compiler-plugin</artifactId>
-                    <version>3.14.0</version>
-                    <configuration>
-                        <source>1.8</source>
-                        <target>1.8</target>
-                    </configuration>
-                </plugin>
-                <plugin>
-                    <artifactId>maven-surefire-plugin</artifactId>
-                    <version>3.5.3</version>
-                </plugin>
-            </plugins>
-        </pluginManagement>
-    </build>
-
-    <repositories>
-        <repository>
-            <id>local-temp</id>
-            <url>file://${maven.repo}</url>
-            <snapshots>
-                <enabled>true</enabled>
-                <checksumPolicy>ignore</checksumPolicy>
-            </snapshots>
-            <releases>
-                <enabled>true</enabled>
-                <checksumPolicy>ignore</checksumPolicy>
-            </releases>
-        </repository>
-    </repositories>
-
-</project>
diff --git a/platform-tooling-support-tests/projects/java-versions/src/test/java/JUnitPlatformCommonsTests.java b/platform-tooling-support-tests/projects/java-versions/src/test/java/JUnitPlatformCommonsTests.java
deleted file mode 100644
index 7e7a888bdd6b..000000000000
--- a/platform-tooling-support-tests/projects/java-versions/src/test/java/JUnitPlatformCommonsTests.java
+++ /dev/null
@@ -1,37 +0,0 @@
-
-/*
- * Copyright 2015-2025 the original author or authors.
- *
- * All rights reserved. This program and the accompanying materials are
- * made available under the terms of the Eclipse Public License v2.0 which
- * accompanies this distribution and is available at
- *
- * https://www.eclipse.org/legal/epl-v20.html
- */
-import static org.junit.jupiter.api.Assertions.assertEquals;
-import static org.junit.jupiter.api.Assertions.assertFalse;
-import static org.junit.jupiter.api.Assertions.assertTrue;
-
-import org.junit.jupiter.api.Test;
-import org.junit.jupiter.api.condition.DisabledOnJre;
-import org.junit.jupiter.api.condition.EnabledOnJre;
-import org.junit.jupiter.api.condition.JRE;
-import org.junit.platform.commons.util.ModuleUtils;
-
-class JUnitPlatformCommonsTests {
-
-	@Test
-	@EnabledOnJre(JRE.JAVA_8)
-	void onJava8() {
-		assertFalse(ModuleUtils.isJavaPlatformModuleSystemAvailable());
-		assertFalse(ModuleUtils.getModuleName(Object.class).isPresent());
-	}
-
-	@Test
-	@DisabledOnJre(JRE.JAVA_8)
-	void onJava9OrHigher() {
-		assertTrue(ModuleUtils.isJavaPlatformModuleSystemAvailable());
-		assertEquals("java.base", ModuleUtils.getModuleName(Object.class).orElseThrow(Error::new));
-	}
-
-}
diff --git a/platform-tooling-support-tests/projects/jupiter-starter/build.gradle.kts b/platform-tooling-support-tests/projects/jupiter-starter/build.gradle.kts
index 74e76f07d3c1..2714c5c41b51 100644
--- a/platform-tooling-support-tests/projects/jupiter-starter/build.gradle.kts
+++ b/platform-tooling-support-tests/projects/jupiter-starter/build.gradle.kts
@@ -2,8 +2,7 @@ plugins {
 	java
 }
 
-val jupiterVersion: String by project
-val platformVersion: String by project
+val junitVersion: String by project
 
 repositories {
 	maven { url = uri(file(System.getProperty("maven.repo"))) }
@@ -11,8 +10,8 @@ repositories {
 }
 
 dependencies {
-	testImplementation("org.junit.jupiter:junit-jupiter:$jupiterVersion")
-	testRuntimeOnly("org.junit.platform:junit-platform-reporting:$platformVersion")
+	testImplementation("org.junit.jupiter:junit-jupiter:$junitVersion")
+	testRuntimeOnly("org.junit.platform:junit-platform-reporting:$junitVersion")
 }
 
 java {
diff --git a/platform-tooling-support-tests/projects/jupiter-starter/build.xml b/platform-tooling-support-tests/projects/jupiter-starter/build.xml
index 79d22fcebc4a..b2c2a3bf08e1 100644
--- a/platform-tooling-support-tests/projects/jupiter-starter/build.xml
+++ b/platform-tooling-support-tests/projects/jupiter-starter/build.xml
@@ -34,7 +34,7 @@
         <javac destdir="build/test" classpathref="test.classpath" srcdir="src/test/java" includeantruntime="true"/>
     </target>
 
-    <!-- https://junit.org/junit5/docs/snapshot/user-guide/#running-tests-build-ant -->
+    <!-- https://docs.junit.org/snapshot/user-guide/#running-tests-build-ant -->
     <target name="test.junit.launcher" depends="compile">
         <junitlauncher haltOnFailure="true" printSummary="true">
             <classpath refid="test.classpath"/>
@@ -48,7 +48,7 @@
         </junitlauncher>
     </target>
 
-    <!-- https://junit.org/junit5/docs/current/user-guide/#running-tests-console-launcher -->
+    <!-- https://docs.junit.org/current/user-guide/#running-tests-console-launcher -->
     <target name="test.console.launcher" depends="compile">
         <java classpathref="test.classpath" classname="org.junit.platform.console.ConsoleLauncher" fork="true">
             <arg value="execute"/>
diff --git a/platform-tooling-support-tests/projects/jupiter-starter/gradle.properties b/platform-tooling-support-tests/projects/jupiter-starter/gradle.properties
index 35b90dc7fdf0..bed2250e4577 100644
--- a/platform-tooling-support-tests/projects/jupiter-starter/gradle.properties
+++ b/platform-tooling-support-tests/projects/jupiter-starter/gradle.properties
@@ -1 +1 @@
-org.gradle.java.installations.fromEnv=JDK8,JDK17
+org.gradle.java.installations.fromEnv=JDK17
diff --git a/platform-tooling-support-tests/projects/jupiter-starter/pom.xml b/platform-tooling-support-tests/projects/jupiter-starter/pom.xml
index 5fa4fdabaebb..823e264d76f8 100644
--- a/platform-tooling-support-tests/projects/jupiter-starter/pom.xml
+++ b/platform-tooling-support-tests/projects/jupiter-starter/pom.xml
@@ -9,9 +9,8 @@
 
     <properties>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
-        <maven.compiler.source>1.8</maven.compiler.source>
-        <maven.compiler.target>${maven.compiler.source}</maven.compiler.target>
-        <junit.platform.commons.version>${junit.platform.version}</junit.platform.commons.version>
+        <maven.compiler.release>17</maven.compiler.release>
+        <junit.platform.commons.version>${junit.version}</junit.platform.commons.version>
     </properties>
 
     <dependencies>
@@ -38,7 +37,7 @@
             <dependency>
                 <groupId>org.junit</groupId>
                 <artifactId>junit-bom</artifactId>
-                <version>${junit.bom.version}</version>
+                <version>${junit.version}</version>
                 <type>pom</type>
                 <scope>import</scope>
             </dependency>
diff --git a/platform-tooling-support-tests/projects/jupiter-starter/settings.gradle.kts b/platform-tooling-support-tests/projects/jupiter-starter/settings.gradle.kts
index 2301fb77b192..f6b40adf9c41 100644
--- a/platform-tooling-support-tests/projects/jupiter-starter/settings.gradle.kts
+++ b/platform-tooling-support-tests/projects/jupiter-starter/settings.gradle.kts
@@ -1,5 +1,5 @@
 plugins {
-    id("org.gradle.toolchains.foojay-resolver-convention") version "0.10.0"
+    id("org.gradle.toolchains.foojay-resolver-convention") version "1.0.0"
 }
 
 rootProject.name = "gradle-starter"
diff --git a/platform-tooling-support-tests/projects/kotlin-coroutines/build.gradle.kts b/platform-tooling-support-tests/projects/kotlin-coroutines/build.gradle.kts
new file mode 100644
index 000000000000..19078dc7da57
--- /dev/null
+++ b/platform-tooling-support-tests/projects/kotlin-coroutines/build.gradle.kts
@@ -0,0 +1,37 @@
+plugins {
+	kotlin("jvm") version "2.2.0"
+}
+
+val junitVersion: String by project
+
+repositories {
+	maven { url = uri(file(System.getProperty("maven.repo"))) }
+	mavenCentral()
+}
+
+dependencies {
+	testImplementation("org.junit.jupiter:junit-jupiter:$junitVersion")
+	testRuntimeOnly("org.junit.platform:junit-platform-launcher")
+
+	if (!project.hasProperty("withoutKotlinReflect")) {
+		testImplementation(kotlin("reflect"))
+	}
+
+	if (!project.hasProperty("withoutKotlinxCoroutines")) {
+		testImplementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.10.2")
+	}
+}
+
+java {
+	toolchain {
+		languageVersion = JavaLanguageVersion.of(17)
+	}
+}
+
+tasks.test {
+	useJUnitPlatform()
+	testLogging {
+		exceptionFormat = org.gradle.api.tasks.testing.logging.TestExceptionFormat.FULL
+	}
+	systemProperty("junit.platform.stacktrace.pruning.enabled", "false")
+}
diff --git a/platform-tooling-support-tests/projects/kotlin-coroutines/settings.gradle.kts b/platform-tooling-support-tests/projects/kotlin-coroutines/settings.gradle.kts
new file mode 100644
index 000000000000..1d23e10e72b6
--- /dev/null
+++ b/platform-tooling-support-tests/projects/kotlin-coroutines/settings.gradle.kts
@@ -0,0 +1,5 @@
+plugins {
+    id("org.gradle.toolchains.foojay-resolver-convention") version "1.0.0"
+}
+
+rootProject.name = "kotlin-coroutines"
diff --git a/platform-tooling-support-tests/projects/kotlin-coroutines/src/test/kotlin/com/example/project/SuspendFunctionTests.kt b/platform-tooling-support-tests/projects/kotlin-coroutines/src/test/kotlin/com/example/project/SuspendFunctionTests.kt
new file mode 100644
index 000000000000..6c0e8a9b9149
--- /dev/null
+++ b/platform-tooling-support-tests/projects/kotlin-coroutines/src/test/kotlin/com/example/project/SuspendFunctionTests.kt
@@ -0,0 +1,20 @@
+/*
+ * Copyright 2015-2025 the original author or authors.
+ *
+ * All rights reserved. This program and the accompanying materials are
+ * made available under the terms of the Eclipse Public License v2.0 which
+ * accompanies this distribution and is available at
+ *
+ * https://www.eclipse.org/legal/epl-v20.html
+ */
+package com.example.project
+
+import org.junit.jupiter.api.Test
+import org.junit.jupiter.api.fail
+
+class SuspendFunctionTests {
+    @Test
+    suspend fun test() {
+        fail("expected")
+    }
+}
diff --git a/platform-tooling-support-tests/projects/maven-surefire-compatibility/pom.xml b/platform-tooling-support-tests/projects/maven-surefire-compatibility/pom.xml
index 47aba716ed6a..175fbbd18363 100644
--- a/platform-tooling-support-tests/projects/maven-surefire-compatibility/pom.xml
+++ b/platform-tooling-support-tests/projects/maven-surefire-compatibility/pom.xml
@@ -9,8 +9,7 @@
 
     <properties>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
-        <maven.compiler.source>1.8</maven.compiler.source>
-        <maven.compiler.target>${maven.compiler.source}</maven.compiler.target>
+        <maven.compiler.release>17</maven.compiler.release>
     </properties>
 
     <dependencies>
@@ -26,7 +25,7 @@
             <dependency>
                 <groupId>org.junit</groupId>
                 <artifactId>junit-bom</artifactId>
-                <version>${junit.bom.version}</version>
+                <version>${junit.version}</version>
                 <type>pom</type>
                 <scope>import</scope>
             </dependency>
@@ -68,17 +67,4 @@
         </repository>
     </repositories>
 
-    <profiles>
-        <profile>
-            <id>manual-platform-dependency</id>
-            <dependencies>
-                <dependency>
-                    <groupId>org.junit.platform</groupId>
-                    <artifactId>junit-platform-launcher</artifactId>
-                    <scope>test</scope>
-                </dependency>
-            </dependencies>
-        </profile>
-    </profiles>
-
 </project>
diff --git a/platform-tooling-support-tests/projects/multi-release-jar/pom.xml b/platform-tooling-support-tests/projects/multi-release-jar/pom.xml
index b9e4b86ed82f..4794ece6f303 100644
--- a/platform-tooling-support-tests/projects/multi-release-jar/pom.xml
+++ b/platform-tooling-support-tests/projects/multi-release-jar/pom.xml
@@ -15,13 +15,13 @@
         <dependency>
             <groupId>org.junit.jupiter</groupId>
             <artifactId>junit-jupiter-engine</artifactId>
-            <version>${junit.jupiter.version}</version>
+            <version>${junit.version}</version>
             <scope>test</scope>
         </dependency>
         <dependency>
             <groupId>org.junit.platform</groupId>
             <artifactId>junit-platform-reporting</artifactId>
-            <version>${junit.platform.version}</version>
+            <version>${junit.version}</version>
             <scope>test</scope>
         </dependency>
     </dependencies>
diff --git a/platform-tooling-support-tests/projects/multi-release-jar/src/test/java/integration/integration/JupiterIntegrationTests.java b/platform-tooling-support-tests/projects/multi-release-jar/src/test/java/integration/integration/JupiterIntegrationTests.java
index 1ec807b3a8dc..f80fde9fd7db 100644
--- a/platform-tooling-support-tests/projects/multi-release-jar/src/test/java/integration/integration/JupiterIntegrationTests.java
+++ b/platform-tooling-support-tests/projects/multi-release-jar/src/test/java/integration/integration/JupiterIntegrationTests.java
@@ -15,13 +15,13 @@
 import static org.junit.platform.launcher.EngineFilter.includeEngines;
 import static org.junit.platform.launcher.core.LauncherDiscoveryRequestBuilder.request;
 
-import org.junit.jupiter.api.MethodOrderer.Alphanumeric;
+import org.junit.jupiter.api.MethodOrderer.MethodName;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.TestMethodOrder;
 import org.junit.platform.engine.discovery.DiscoverySelectors;
 import org.junit.platform.launcher.core.LauncherFactory;
 
-@TestMethodOrder(Alphanumeric.class)
+@TestMethodOrder(MethodName.class)
 class JupiterIntegrationTests {
 
 	@Test
diff --git a/platform-tooling-support-tests/projects/reflection-tests/build.gradle.kts b/platform-tooling-support-tests/projects/reflection-tests/build.gradle.kts
index 0dea5aab80a1..c1eff1a2aa88 100644
--- a/platform-tooling-support-tests/projects/reflection-tests/build.gradle.kts
+++ b/platform-tooling-support-tests/projects/reflection-tests/build.gradle.kts
@@ -2,8 +2,7 @@ plugins {
 	java
 }
 
-val jupiterVersion: String by project
-val platformVersion: String by project
+val junitVersion: String by project
 
 repositories {
 	maven { url = uri(file(System.getProperty("maven.repo"))) }
@@ -11,14 +10,14 @@ repositories {
 }
 
 dependencies {
-	testImplementation("org.junit.jupiter:junit-jupiter:$jupiterVersion")
-	testImplementation("org.junit.jupiter:junit-jupiter-engine:$jupiterVersion")
-	testRuntimeOnly("org.junit.platform:junit-platform-reporting:$platformVersion")
+	testImplementation("org.junit.jupiter:junit-jupiter:$junitVersion")
+	testImplementation("org.junit.jupiter:junit-jupiter-engine:$junitVersion")
+	testRuntimeOnly("org.junit.platform:junit-platform-launcher:$junitVersion")
 }
 
 java {
 	toolchain {
-		languageVersion = JavaLanguageVersion.of(8)
+		languageVersion = JavaLanguageVersion.of(17)
 	}
 }
 
@@ -32,12 +31,4 @@ tasks.test {
 	reports {
 		html.required = true
 	}
-
-	val outputDir = reports.junitXml.outputLocation
-	jvmArgumentProviders += CommandLineArgumentProvider {
-		listOf(
-			"-Djunit.platform.reporting.open.xml.enabled=true",
-			"-Djunit.platform.reporting.output.dir=${outputDir.get().asFile.absolutePath}"
-		)
-	}
 }
diff --git a/platform-tooling-support-tests/projects/reflection-tests/gradle.properties b/platform-tooling-support-tests/projects/reflection-tests/gradle.properties
index 79b428ebc70c..bed2250e4577 100644
--- a/platform-tooling-support-tests/projects/reflection-tests/gradle.properties
+++ b/platform-tooling-support-tests/projects/reflection-tests/gradle.properties
@@ -1 +1 @@
-org.gradle.java.installations.fromEnv=JDK8
+org.gradle.java.installations.fromEnv=JDK17
diff --git a/platform-tooling-support-tests/projects/reflection-tests/settings.gradle.kts b/platform-tooling-support-tests/projects/reflection-tests/settings.gradle.kts
index dc695374e2d9..222e53054a3d 100644
--- a/platform-tooling-support-tests/projects/reflection-tests/settings.gradle.kts
+++ b/platform-tooling-support-tests/projects/reflection-tests/settings.gradle.kts
@@ -1,5 +1,5 @@
 plugins {
-    id("org.gradle.toolchains.foojay-resolver-convention") version "0.10.0"
+    id("org.gradle.toolchains.foojay-resolver-convention") version "1.0.0"
 }
 
 rootProject.name = "reflection-tests"
diff --git a/platform-tooling-support-tests/projects/standalone/expected-err.txt b/platform-tooling-support-tests/projects/standalone/expected-err.txt
index 53ca33b7f6f0..23779eeaa528 100644
--- a/platform-tooling-support-tests/projects/standalone/expected-err.txt
+++ b/platform-tooling-support-tests/projects/standalone/expected-err.txt
@@ -18,3 +18,7 @@
 - junit-platform-suite .+
 - junit-jupiter .+
 - junit-vintage .+
+>> LOGGER >>
+INFO: TestEngine with ID 'junit-vintage' encountered a non-critical issue during test discovery:
+
+(1) [INFO] The JUnit Vintage engine is deprecated and should only be used temporarily while migrating tests to JUnit Jupiter or another testing framework with native JUnit Platform support.
diff --git a/platform-tooling-support-tests/projects/vintage/build.gradle.kts b/platform-tooling-support-tests/projects/vintage/build.gradle.kts
index 37bab7448d5b..4e959fcb8d7c 100644
--- a/platform-tooling-support-tests/projects/vintage/build.gradle.kts
+++ b/platform-tooling-support-tests/projects/vintage/build.gradle.kts
@@ -9,24 +9,23 @@ repositories {
 	mavenCentral()
 }
 
-val platformVersion: String by project
-val vintageVersion: String by project
+val junitVersion: String by project
 
 dependencies {
 	val junit4Version = System.getProperty("junit4Version", "4.12")
 	testImplementation("junit:junit:$junit4Version")
 
-	testImplementation("org.junit.vintage:junit-vintage-engine:$vintageVersion") {
+	testImplementation("org.junit.vintage:junit-vintage-engine:$junitVersion") {
 		exclude(group = "junit")
 		because("we want to override it to test against different versions")
 	}
 
-	testRuntimeOnly("org.junit.platform:junit-platform-launcher:$platformVersion")
+	testRuntimeOnly("org.junit.platform:junit-platform-launcher:$junitVersion")
 }
 
 java {
 	toolchain {
-		languageVersion = JavaLanguageVersion.of(8)
+		languageVersion = JavaLanguageVersion.of(17)
 	}
 }
 
diff --git a/platform-tooling-support-tests/projects/vintage/gradle.properties b/platform-tooling-support-tests/projects/vintage/gradle.properties
index 79b428ebc70c..bed2250e4577 100644
--- a/platform-tooling-support-tests/projects/vintage/gradle.properties
+++ b/platform-tooling-support-tests/projects/vintage/gradle.properties
@@ -1 +1 @@
-org.gradle.java.installations.fromEnv=JDK8
+org.gradle.java.installations.fromEnv=JDK17
diff --git a/platform-tooling-support-tests/projects/vintage/pom.xml b/platform-tooling-support-tests/projects/vintage/pom.xml
index 74d0ef2dc367..e4219de31c9b 100644
--- a/platform-tooling-support-tests/projects/vintage/pom.xml
+++ b/platform-tooling-support-tests/projects/vintage/pom.xml
@@ -9,15 +9,14 @@
 
     <properties>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
-        <maven.compiler.source>1.8</maven.compiler.source>
-        <maven.compiler.target>${maven.compiler.source}</maven.compiler.target>
+        <maven.compiler.release>17</maven.compiler.release>
     </properties>
 
     <dependencies>
         <dependency>
             <groupId>org.junit.vintage</groupId>
             <artifactId>junit-vintage-engine</artifactId>
-            <version>${junit.vintage.version}</version>
+            <version>${junit.version}</version>
             <scope>test</scope>
             <exclusions>
                 <exclusion>
diff --git a/platform-tooling-support-tests/projects/vintage/settings.gradle.kts b/platform-tooling-support-tests/projects/vintage/settings.gradle.kts
index 00a3ba7dcdba..871f35f417a1 100644
--- a/platform-tooling-support-tests/projects/vintage/settings.gradle.kts
+++ b/platform-tooling-support-tests/projects/vintage/settings.gradle.kts
@@ -1,5 +1,5 @@
 plugins {
-    id("org.gradle.toolchains.foojay-resolver-convention") version "0.10.0"
+    id("org.gradle.toolchains.foojay-resolver-convention") version "1.0.0"
 }
 
 rootProject.name = "vintage"
diff --git a/platform-tooling-support-tests/projects/vintage/src/test/java/DefaultPackageTest.java b/platform-tooling-support-tests/projects/vintage/src/test/java/DefaultPackageTest.java
index 8d73c776b02b..ee59cbdc36a4 100644
--- a/platform-tooling-support-tests/projects/vintage/src/test/java/DefaultPackageTest.java
+++ b/platform-tooling-support-tests/projects/vintage/src/test/java/DefaultPackageTest.java
@@ -13,7 +13,7 @@
 import org.junit.Ignore;
 
 /**
- * Reproducer for https://github.com/junit-team/junit5/issues/4076
+ * Reproducer for https://github.com/junit-team/junit-framework/issues/4076
  */
 @Ignore
 public class DefaultPackageTest extends VintageTest {
diff --git a/platform-tooling-support-tests/src/archUnit/java/platform/tooling/support/tests/ArchUnitTests.java b/platform-tooling-support-tests/src/archUnit/java/platform/tooling/support/tests/ArchUnitTests.java
index 71f04fba2256..bfb4882b58d6 100644
--- a/platform-tooling-support-tests/src/archUnit/java/platform/tooling/support/tests/ArchUnitTests.java
+++ b/platform-tooling-support-tests/src/archUnit/java/platform/tooling/support/tests/ArchUnitTests.java
@@ -15,8 +15,8 @@
 import static com.tngtech.archunit.core.domain.JavaClass.Predicates.ANONYMOUS_CLASSES;
 import static com.tngtech.archunit.core.domain.JavaClass.Predicates.TOP_LEVEL_CLASSES;
 import static com.tngtech.archunit.core.domain.JavaClass.Predicates.resideInAPackage;
-import static com.tngtech.archunit.core.domain.JavaClass.Predicates.resideInAnyPackage;
 import static com.tngtech.archunit.core.domain.JavaClass.Predicates.simpleName;
+import static com.tngtech.archunit.core.domain.JavaClass.Predicates.simpleNameEndingWith;
 import static com.tngtech.archunit.core.domain.JavaModifier.PUBLIC;
 import static com.tngtech.archunit.core.domain.properties.HasModifiers.Predicates.modifier;
 import static com.tngtech.archunit.core.domain.properties.HasName.Predicates.name;
@@ -26,6 +26,7 @@
 import static com.tngtech.archunit.lang.conditions.ArchPredicates.have;
 import static com.tngtech.archunit.lang.syntax.ArchRuleDefinition.classes;
 import static com.tngtech.archunit.library.dependencies.SlicesRuleDefinition.slices;
+import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import java.lang.annotation.Annotation;
@@ -34,10 +35,13 @@
 import java.lang.annotation.Target;
 import java.util.Arrays;
 import java.util.function.BiPredicate;
+import java.util.stream.Stream;
 
 import com.tngtech.archunit.base.DescribedPredicate;
 import com.tngtech.archunit.core.domain.JavaClass;
 import com.tngtech.archunit.core.domain.JavaClasses;
+import com.tngtech.archunit.core.domain.JavaPackage;
+import com.tngtech.archunit.core.domain.PackageMatcher;
 import com.tngtech.archunit.junit.AnalyzeClasses;
 import com.tngtech.archunit.junit.ArchTest;
 import com.tngtech.archunit.lang.ArchCondition;
@@ -45,6 +49,7 @@
 import com.tngtech.archunit.library.GeneralCodingRules;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.NullMarked;
 
 @AnalyzeClasses(packages = { "org.junit.platform", "org.junit.jupiter", "org.junit.vintage" })
 class ArchUnitTests {
@@ -61,7 +66,9 @@ class ArchUnitTests {
 			.and(TOP_LEVEL_CLASSES) //
 			.and(not(ANONYMOUS_CLASSES)) //
 			.and(not(describe("are Kotlin SAM type implementations", simpleName("")))) //
-			.and(not(describe("are shadowed", resideInAnyPackage("..shadow..")))) //
+			.and(not(describe("are Kotlin-generated classes that contain only top-level functions",
+				simpleNameEndingWith("Kt")))) //
+			.and(not(describe("are shadowed", resideInAPackage("..shadow..")))) //
 			.should().beAnnotatedWith(API.class);
 
 	@SuppressWarnings("unused")
@@ -73,6 +80,27 @@ class ArchUnitTests {
 			.should(haveContainerAnnotationWithSameRetentionPolicy()) //
 			.andShould(haveContainerAnnotationWithSameTargetTypes());
 
+	@ArchTest
+	void packagesShouldBeNullMarked(JavaClasses classes) {
+		var exclusions = Stream.of( //
+			"..shadow.." //
+		).map(PackageMatcher::of).toList();
+
+		var subpackages = Stream.of("org.junit.platform", "org.junit.jupiter", "org.junit.vintage") //
+				.map(classes::getPackage) //
+				.flatMap(rootPackage -> rootPackage.getSubpackagesInTree().stream()) //
+				.filter(pkg -> exclusions.stream().noneMatch(it -> it.matches(pkg.getName()))) //
+				.filter(pkg -> !pkg.getClasses().isEmpty()) //
+				.toList();
+		assertThat(subpackages).isNotEmpty();
+
+		var violations = subpackages.stream() //
+				.filter(pkg -> !pkg.isAnnotatedWith(NullMarked.class)) //
+				.map(JavaPackage::getName) //
+				.sorted();
+		assertThat(violations).describedAs("The following packages are missing the @NullMarked annotation").isEmpty();
+	}
+
 	@ArchTest
 	void allAreIn(JavaClasses classes) {
 		// about 928 classes found in all jars
@@ -106,12 +134,11 @@ void avoidAccessingStandardStreams(JavaClasses classes) {
 				.that(are(not(name("org.junit.platform.console.ConsoleLauncher")))) //
 				.that(are(not(name("org.junit.platform.console.tasks.ConsoleTestExecutor")))) //
 				.that(are(not(name("org.junit.platform.launcher.core.StreamInterceptor")))) //
-				.that(are(not(name("org.junit.platform.runner.JUnitPlatformRunnerListener")))) //
 				.that(are(not(name("org.junit.platform.testkit.engine.Events")))) //
 				.that(are(not(name("org.junit.platform.testkit.engine.Executions")))) //
 				//The PreInterruptThreadDumpPrinter writes to StdOut by contract to dump threads
 				.that(are(not(name("org.junit.jupiter.engine.extension.PreInterruptThreadDumpPrinter")))) //
-				.that(are(not(resideInAPackage("org.junit.platform.console.shadow.picocli"))));
+				.that(are(not(nameContaining(".shadow."))));
 		GeneralCodingRules.NO_CLASSES_SHOULD_ACCESS_STANDARD_STREAMS.check(subset);
 	}
 
diff --git a/platform-tooling-support-tests/src/main/java/platform/tooling/support/Helper.java b/platform-tooling-support-tests/src/main/java/platform/tooling/support/Helper.java
index 0841181a1903..0df95dd15ca8 100644
--- a/platform-tooling-support-tests/src/main/java/platform/tooling/support/Helper.java
+++ b/platform-tooling-support-tests/src/main/java/platform/tooling/support/Helper.java
@@ -12,7 +12,6 @@
 
 import java.nio.file.Files;
 import java.nio.file.Path;
-import java.nio.file.Paths;
 import java.util.List;
 import java.util.Objects;
 import java.util.Optional;
@@ -26,7 +25,7 @@
  */
 public class Helper {
 
-	private static final Path ROOT = Paths.get("..");
+	private static final Path ROOT = Path.of("..");
 	private static final Path GRADLE_PROPERTIES = ROOT.resolve("gradle.properties");
 	private static final Path SETTINGS_GRADLE = ROOT.resolve("settings.gradle.kts");
 
@@ -41,17 +40,8 @@ public class Helper {
 		}
 	}
 
-	public static String version(String module) {
-		if (module.startsWith("junit-jupiter")) {
-			return gradleProperties.getProperty("version");
-		}
-		if (module.startsWith("junit-platform")) {
-			return gradleProperties.getProperty("platformVersion");
-		}
-		if (module.startsWith("junit-vintage")) {
-			return gradleProperties.getProperty("vintageVersion");
-		}
-		throw new AssertionError("Unknown module: " + module);
+	public static String version() {
+		return gradleProperties.getProperty("version");
 	}
 
 	public static List<String> loadModuleDirectoryNames() {
diff --git a/platform-tooling-support-tests/src/main/java/platform/tooling/support/MavenRepo.java b/platform-tooling-support-tests/src/main/java/platform/tooling/support/MavenRepo.java
index d5ebac39bc92..d7b3ea0cfaf4 100644
--- a/platform-tooling-support-tests/src/main/java/platform/tooling/support/MavenRepo.java
+++ b/platform-tooling-support-tests/src/main/java/platform/tooling/support/MavenRepo.java
@@ -47,7 +47,7 @@ private static Path artifact(String artifactId, Predicate<String> fileNamePredic
 		var parentDir = dir() //
 				.resolve(groupId(artifactId).replace('.', File.separatorChar)) //
 				.resolve(artifactId) //
-				.resolve(Helper.version(artifactId));
+				.resolve(Helper.version());
 		try (var files = Files.list(parentDir)) {
 			return files.filter(
 				file -> fileNamePredicate.test(file.getFileName().toString())).findFirst().orElseThrow();
diff --git a/platform-tooling-support-tests/src/main/java/platform/tooling/support/ProcessStarters.java b/platform-tooling-support-tests/src/main/java/platform/tooling/support/ProcessStarters.java
index e2519e89f958..94df6091b784 100644
--- a/platform-tooling-support-tests/src/main/java/platform/tooling/support/ProcessStarters.java
+++ b/platform-tooling-support-tests/src/main/java/platform/tooling/support/ProcessStarters.java
@@ -47,9 +47,7 @@ public static ProcessStarter gradlew() {
 		return new ProcessStarter() //
 				.executable(Path.of("..").resolve(windowsOrOtherExecutable("gradlew.bat", "gradlew")).toAbsolutePath()) //
 				.putEnvironment("JAVA_HOME", getGradleJavaHome().orElseThrow(TestAbortedException::new)) //
-				.addArguments("-PjupiterVersion=" + Helper.version("junit-jupiter")) //
-				.addArguments("-PvintageVersion=" + Helper.version("junit-vintage")) //
-				.addArguments("-PplatformVersion=" + Helper.version("junit-platform"));
+				.addArguments("-PjunitVersion=" + Helper.version());
 	}
 
 	public static ProcessStarter maven() {
@@ -61,10 +59,7 @@ public static ProcessStarter maven(Path javaHome) {
 				.executable(Path.of(System.getProperty("mavenDistribution")).resolve("bin").resolve(
 					windowsOrOtherExecutable("mvn.cmd", "mvn")).toAbsolutePath()) //
 				.putEnvironment("JAVA_HOME", javaHome) //
-				.addArguments("-Djunit.jupiter.version=" + Helper.version("junit-jupiter")) //
-				.addArguments("-Djunit.bom.version=" + Helper.version("junit-jupiter")) //
-				.addArguments("-Djunit.vintage.version=" + Helper.version("junit-vintage")) //
-				.addArguments("-Djunit.platform.version=" + Helper.version("junit-platform"));
+				.addArguments("-Djunit.version=" + Helper.version());
 	}
 
 	private static String windowsOrOtherExecutable(String cmdOrExe, String other) {
diff --git a/platform-tooling-support-tests/src/test/java/platform/tooling/support/HelperTests.java b/platform-tooling-support-tests/src/test/java/platform/tooling/support/HelperTests.java
index 001e02c5bddc..156d19e0bbb7 100644
--- a/platform-tooling-support-tests/src/test/java/platform/tooling/support/HelperTests.java
+++ b/platform-tooling-support-tests/src/test/java/platform/tooling/support/HelperTests.java
@@ -39,10 +39,8 @@ void loadModuleDirectoryNames() {
 			"junit-platform-commons", //
 			"junit-platform-console", //
 			"junit-platform-engine", //
-			"junit-platform-jfr", //
 			"junit-platform-launcher", //
 			"junit-platform-reporting", //
-			"junit-platform-runner", //
 			"junit-platform-suite", //
 			"junit-platform-suite-api", //
 			"junit-platform-suite-commons", //
@@ -54,9 +52,7 @@ void loadModuleDirectoryNames() {
 
 	@Test
 	void version() {
-		assertNotNull(Helper.version("junit-jupiter"));
-		assertNotNull(Helper.version("junit-vintage"));
-		assertNotNull(Helper.version("junit-platform"));
+		assertNotNull(Helper.version());
 	}
 
 	@Test
@@ -65,7 +61,7 @@ void nonExistingJdkVersionYieldsAnEmptyOptional() {
 	}
 
 	@ParameterizedTest
-	@ValueSource(ints = 8)
+	@ValueSource(ints = 17)
 	void checkJavaHome(int version) {
 		var home = Helper.getJavaHome(version);
 		assumeTrue(home.isPresent(), "No 'jdk' element found in Maven toolchain for: " + version);
diff --git a/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/GraalVmStarterTests.java b/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/GraalVmStarterTests.java
index e74c1400bd9c..35cd950de960 100644
--- a/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/GraalVmStarterTests.java
+++ b/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/GraalVmStarterTests.java
@@ -46,11 +46,10 @@ void runsTestsInNativeImage(@TempDir Path workspace, @FilePrefix("gradle") Outpu
 
 		var result = ProcessStarters.gradlew() //
 				.workingDir(copyToWorkspace(Projects.GRAALVM_STARTER, workspace)) //
-				.putEnvironment("GRAALVM_HOME",
-					graalVmHome.orElseThrow(TestAbortedException::new).toString()).addArguments(
-						"-Dmaven.repo=" + MavenRepo.dir()) //
+				.putEnvironment("GRAALVM_HOME", graalVmHome.orElseThrow(TestAbortedException::new).toString()) //
+				.addArguments("-Dmaven.repo=" + MavenRepo.dir()) //
 				.addArguments("javaToolchains", "nativeTest", "--no-daemon", "--stacktrace", "--no-build-cache",
-					"--warning-mode=fail") //
+					"--warning-mode=fail", "--refresh-dependencies") //
 				.redirectOutput(outputFiles) //
 				.startAndWait();
 
diff --git a/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/GradleKotlinExtensionsTests.java b/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/GradleKotlinExtensionsTests.java
index 750f628ceeb2..1891b8225213 100644
--- a/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/GradleKotlinExtensionsTests.java
+++ b/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/GradleKotlinExtensionsTests.java
@@ -36,7 +36,7 @@ void gradle_wrapper(@TempDir Path workspace, @FilePrefix("gradle") OutputFiles o
 				.workingDir(copyToWorkspace(Projects.GRADLE_KOTLIN_EXTENSIONS, workspace)) //
 				.addArguments("-Dmaven.repo=" + MavenRepo.dir()) //
 				.addArguments("build", "--no-daemon", "--stacktrace", "--no-build-cache", "--warning-mode=fail") //
-				.putEnvironment("JDK8", Helper.getJavaHome(8).orElseThrow(TestAbortedException::new).toString()) //
+				.putEnvironment("JDK17", Helper.getJavaHome(17).orElseThrow(TestAbortedException::new).toString()) //
 				.redirectOutput(outputFiles) //
 				.startAndWait();
 
diff --git a/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/GradleMissingEngineTests.java b/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/GradleMissingEngineTests.java
index e70d548761c6..846a41c6adf9 100644
--- a/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/GradleMissingEngineTests.java
+++ b/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/GradleMissingEngineTests.java
@@ -37,7 +37,7 @@ void gradle_wrapper(@TempDir Path workspace, @FilePrefix("gradle") OutputFiles o
 				.workingDir(copyToWorkspace(Projects.GRADLE_MISSING_ENGINE, workspace)) //
 				.addArguments("-Dmaven.repo=" + MavenRepo.dir()) //
 				.addArguments("build", "--no-daemon", "--stacktrace", "--no-build-cache", "--warning-mode=fail") //
-				.putEnvironment("JDK8", Helper.getJavaHome(8).orElseThrow(TestAbortedException::new).toString()) //
+				.putEnvironment("JDK17", Helper.getJavaHome(17).orElseThrow(TestAbortedException::new).toString()) //
 				.redirectOutput(outputFiles).startAndWait();
 
 		assertEquals(1, result.exitCode());
diff --git a/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/GradleModuleFileTests.java b/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/GradleModuleFileTests.java
index c79c2b4e54f4..f86fdef3acde 100644
--- a/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/GradleModuleFileTests.java
+++ b/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/GradleModuleFileTests.java
@@ -46,7 +46,7 @@ void jupiterAggregatorGradleModuleMetadataVariants() throws Exception {
 			"      \"attributes\": {", //
 			"        \"org.gradle.category\": \"library\",", //
 			"        \"org.gradle.dependency.bundling\": \"external\",", //
-			"        \"org.gradle.jvm.version\": 8,", //
+			"        \"org.gradle.jvm.version\": 17,", //
 			"        \"org.gradle.libraryelements\": \"jar\",", //
 			"        \"org.gradle.usage\": \"java-api\"", //
 			"      },", //
@@ -88,12 +88,19 @@ void jupiterAggregatorGradleModuleMetadataVariants() throws Exception {
 			"      \"attributes\": {", //
 			"        \"org.gradle.category\": \"library\",", //
 			"        \"org.gradle.dependency.bundling\": \"external\",", //
-			"        \"org.gradle.jvm.version\": 8,", //
+			"        \"org.gradle.jvm.version\": 17,", //
 			"        \"org.gradle.libraryelements\": \"jar\",", //
 			"        \"org.gradle.usage\": \"java-runtime\"", //
 			"      },", //
 			"      \"dependencies\": [", //
 			"        {", //
+			"          \"group\": \"org.junit.jupiter\",", //
+			"          \"module\": \"junit-jupiter-engine\",", //
+			"          \"version\": {", //
+			">> VERSION >>", //
+			"          }", //
+			"        },", //
+			"        {", //
 			"          \"group\": \"org.junit\",", //
 			"          \"module\": \"junit-bom\",", //
 			"          \"version\": {", //
@@ -117,13 +124,6 @@ void jupiterAggregatorGradleModuleMetadataVariants() throws Exception {
 			"          \"version\": {", //
 			">> VERSION >>", //
 			"          }", //
-			"        },", //
-			"        {", //
-			"          \"group\": \"org.junit.jupiter\",", //
-			"          \"module\": \"junit-jupiter-engine\",", //
-			"          \"version\": {", //
-			">> VERSION >>", //
-			"          }", //
 			"        }", //
 			"      ],", //
 			"      \"files\": [", //
diff --git a/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/GradleStarterTests.java b/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/GradleStarterTests.java
index 02b7a6c26861..62ad2b94cd6d 100644
--- a/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/GradleStarterTests.java
+++ b/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/GradleStarterTests.java
@@ -24,8 +24,6 @@
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.io.TempDir;
-import org.junit.jupiter.params.ParameterizedTest;
-import org.junit.jupiter.params.provider.ValueSource;
 import org.junit.platform.tests.process.OutputFiles;
 import org.junit.platform.tests.process.ProcessResult;
 import org.opentest4j.TestAbortedException;
@@ -49,12 +47,10 @@ void prepareWorkspace() throws Exception {
 		copyToWorkspace(Projects.JUPITER_STARTER, workspace);
 	}
 
-	@ParameterizedTest(name = "Java {0}")
-	@ValueSource(ints = { 8, 17 })
-	void buildJupiterStarterProject(int javaVersion, @FilePrefix("gradle") OutputFiles outputFiles, Snapshot snapshot)
-			throws Exception {
+	@Test
+	void buildJupiterStarterProject(@FilePrefix("gradle") OutputFiles outputFiles, Snapshot snapshot) throws Exception {
 
-		var result = runGradle(outputFiles, javaVersion, "build");
+		var result = runGradle(outputFiles, "build");
 
 		assertThat(result.stdOut()) //
 				.contains( //
@@ -64,7 +60,7 @@ void buildJupiterStarterProject(int javaVersion, @FilePrefix("gradle") OutputFil
 					"CalculatorParameterizedClassTests > [2] i=2 > parameterizedTest(int)", //
 					"CalculatorParameterizedClassTests > [2] i=2 > Inner > [1] 1 > regularTest() PASSED", //
 					"CalculatorParameterizedClassTests > [2] i=2 > Inner > [2] 2 > regularTest() PASSED", //
-					"Using Java version: " + (javaVersion == 8 ? "1.8" : javaVersion), //
+					"Using Java version: 17", //
 					"CalculatorTests > 1 + 1 = 2 PASSED", //
 					"CalculatorTests > add(int, int, int) > 0 + 1 = 1 PASSED", //
 					"CalculatorTests > add(int, int, int) > 1 + 2 = 3 PASSED", //
@@ -79,7 +75,7 @@ void buildJupiterStarterProject(int javaVersion, @FilePrefix("gradle") OutputFil
 	@Test
 	void runOnlyOneMethodInClassTemplate(@FilePrefix("gradle") OutputFiles outputFiles) throws Exception {
 
-		var result = runGradle(outputFiles, 8, "test", "--tests", "CalculatorParameterized*.regular*");
+		var result = runGradle(outputFiles, "test", "--tests", "CalculatorParameterized*.regular*");
 
 		assertThat(result.stdOut()) //
 				.contains( //
@@ -90,7 +86,7 @@ void runOnlyOneMethodInClassTemplate(@FilePrefix("gradle") OutputFiles outputFil
 				) //
 				.doesNotContain("parameterizedTest(int)", "CalculatorTests");
 
-		result = runGradle(outputFiles, 8, "test", "--tests", "*ParameterizedClassTests.parameterized*");
+		result = runGradle(outputFiles, "test", "--tests", "*ParameterizedClassTests.parameterized*");
 
 		assertThat(result.stdOut()) //
 				.contains( //
@@ -100,16 +96,14 @@ void runOnlyOneMethodInClassTemplate(@FilePrefix("gradle") OutputFiles outputFil
 				.doesNotContain("regularTest()", "CalculatorTests");
 	}
 
-	private ProcessResult runGradle(OutputFiles outputFiles, int javaVersion, String... extraArgs)
-			throws InterruptedException {
+	private ProcessResult runGradle(OutputFiles outputFiles, String... extraArgs) throws InterruptedException {
 		var result = ProcessStarters.gradlew() //
 				.workingDir(workspace) //
 				.addArguments("-Dmaven.repo=" + MavenRepo.dir()) //
-				.addArguments("-Djava.toolchain.version=" + javaVersion) //
+				.addArguments("-Djava.toolchain.version=17") //
 				.addArguments("--stacktrace", "--no-build-cache", "--warning-mode=fail") //
-				.addArguments(extraArgs) //
-				.putEnvironment("JDK8", Helper.getJavaHome(8).orElseThrow(TestAbortedException::new).toString()) //
-				.putEnvironment("JDK17", Helper.getJavaHome(17).orElseThrow(TestAbortedException::new).toString()) //
+				.addArguments(extraArgs).putEnvironment("JDK17",
+					Helper.getJavaHome(17).orElseThrow(TestAbortedException::new).toString()) //
 				.redirectOutput(outputFiles) //
 				.startAndWait();
 
diff --git a/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/JarDescribeModuleTests.java b/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/JarDescribeModuleTests.java
index 4a03dcd5270f..94de63eef317 100644
--- a/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/JarDescribeModuleTests.java
+++ b/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/JarDescribeModuleTests.java
@@ -65,9 +65,7 @@ void packageNamesStartWithNameOfTheModule(String module) {
 	}
 
 	private static String replaceVersionPlaceholders(String line) {
-		line = line.replace("${jupiterVersion}", Helper.version("junit-jupiter"));
-		line = line.replace("${vintageVersion}", Helper.version("junit-vintage"));
-		line = line.replace("${platformVersion}", Helper.version("junit-platform"));
+		line = line.replace("${version}", Helper.version());
 		return line;
 	}
 
diff --git a/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/JavaVersionsTests.java b/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/JavaVersionsTests.java
deleted file mode 100644
index e2316b2520d6..000000000000
--- a/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/JavaVersionsTests.java
+++ /dev/null
@@ -1,72 +0,0 @@
-/*
- * Copyright 2015-2025 the original author or authors.
- *
- * All rights reserved. This program and the accompanying materials are
- * made available under the terms of the Eclipse Public License v2.0 which
- * accompanies this distribution and is available at
- *
- * https://www.eclipse.org/legal/epl-v20.html
- */
-
-package platform.tooling.support.tests;
-
-import static org.junit.jupiter.api.Assertions.assertEquals;
-import static org.junit.jupiter.api.Assertions.assertTrue;
-import static org.junit.jupiter.api.Assumptions.assumeTrue;
-import static platform.tooling.support.ProcessStarters.currentJdkHome;
-import static platform.tooling.support.tests.Projects.copyToWorkspace;
-
-import java.nio.file.Path;
-import java.util.List;
-import java.util.Map;
-
-import org.junit.jupiter.api.Test;
-import org.junit.jupiter.api.condition.JRE;
-import org.junit.jupiter.api.io.TempDir;
-import org.junit.platform.tests.process.OutputFiles;
-
-import platform.tooling.support.Helper;
-import platform.tooling.support.MavenRepo;
-import platform.tooling.support.ProcessStarters;
-
-/**
- * @since 1.4
- */
-class JavaVersionsTests {
-
-	@ManagedResource
-	LocalMavenRepo localMavenRepo;
-
-	@TempDir
-	Path workspace;
-
-	@Test
-	void java_8(@FilePrefix("maven") OutputFiles outputFiles) throws Exception {
-		var java8Home = Helper.getJavaHome(8);
-		assumeTrue(java8Home.isPresent(), "Java 8 installation directory not found!");
-		var actualLines = execute(java8Home.get(), outputFiles, Map.of());
-
-		assertTrue(actualLines.contains("[WARNING] Tests run: 2, Failures: 0, Errors: 0, Skipped: 1"));
-	}
-
-	@Test
-	void java_default(@FilePrefix("maven") OutputFiles outputFiles) throws Exception {
-		var actualLines = execute(currentJdkHome(), outputFiles, MavenEnvVars.forJre(JRE.currentJre()));
-
-		assertTrue(actualLines.contains("[WARNING] Tests run: 2, Failures: 0, Errors: 0, Skipped: 1"));
-	}
-
-	List<String> execute(Path javaHome, OutputFiles outputFiles, Map<String, String> environmentVars) throws Exception {
-		var result = ProcessStarters.maven(javaHome) //
-				.workingDir(copyToWorkspace(Projects.JAVA_VERSIONS, workspace)) //
-				.putEnvironment(environmentVars) //
-				.addArguments(localMavenRepo.toCliArgument(), "-Dmaven.repo=" + MavenRepo.dir()) //
-				.addArguments("--update-snapshots", "--batch-mode", "verify") //
-				.startAndWait();
-
-		assertEquals(0, result.exitCode());
-		assertEquals("", result.stdErr());
-		return result.stdOutLines();
-	}
-
-}
diff --git a/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/KotlinCoroutinesTests.java b/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/KotlinCoroutinesTests.java
new file mode 100644
index 000000000000..94f95d669a3e
--- /dev/null
+++ b/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/KotlinCoroutinesTests.java
@@ -0,0 +1,83 @@
+/*
+ * Copyright 2015-2025 the original author or authors.
+ *
+ * All rights reserved. This program and the accompanying materials are
+ * made available under the terms of the Eclipse Public License v2.0 which
+ * accompanies this distribution and is available at
+ *
+ * https://www.eclipse.org/legal/epl-v20.html
+ */
+
+package platform.tooling.support.tests;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static platform.tooling.support.tests.Projects.copyToWorkspace;
+
+import java.io.IOException;
+import java.nio.file.Path;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+import org.junit.platform.tests.process.OutputFiles;
+import org.junit.platform.tests.process.ProcessResult;
+import org.opentest4j.TestAbortedException;
+
+import platform.tooling.support.Helper;
+import platform.tooling.support.MavenRepo;
+import platform.tooling.support.ProcessStarters;
+
+/**
+ * @since 6.0
+ */
+class KotlinCoroutinesTests {
+
+	@Test
+	void failsExpectedlyWhenAllOptionalDependenciesArePresent(@TempDir Path workspace,
+			@FilePrefix("gradle") OutputFiles outputFiles) throws Exception {
+		var result = runBuild(workspace, outputFiles);
+
+		assertEquals(1, result.exitCode(), "result=" + result);
+		assertThat(result.stdOut()).contains("AssertionFailedError: expected");
+		assertThat(result.stdErr()).contains("BUILD FAILED");
+	}
+
+	@Test
+	void failsWithHelpfulErrorMessageWhenKotlinxCoroutinesIsMissing(@TempDir Path workspace,
+			@FilePrefix("gradle") OutputFiles outputFiles) throws Exception {
+		var result = runBuild(workspace, outputFiles, "-PwithoutKotlinxCoroutines");
+
+		assertEquals(1, result.exitCode(), "result=" + result);
+		assertThat(result.stdOut()).contains("PreconditionViolationException: Kotlin suspending function "
+				+ "[public final java.lang.Object com.example.project.SuspendFunctionTests.test(kotlin.coroutines.Continuation<? super kotlin.Unit>)] "
+				+ "requires org.jetbrains.kotlinx:kotlinx-coroutines-core to be on the classpath or module path. "
+				+ "Please add a corresponding dependency.");
+		assertThat(result.stdErr()).contains("BUILD FAILED");
+	}
+
+	@Test
+	void failsWithHelpfulErrorMessageWhenKotlinReflectIsMissing(@TempDir Path workspace,
+			@FilePrefix("gradle") OutputFiles outputFiles) throws Exception {
+		var result = runBuild(workspace, outputFiles, "-PwithoutKotlinReflect");
+
+		assertEquals(1, result.exitCode(), "result=" + result);
+		assertThat(result.stdOut()).contains("PreconditionViolationException: Kotlin suspending function "
+				+ "[public final java.lang.Object com.example.project.SuspendFunctionTests.test(kotlin.coroutines.Continuation<? super kotlin.Unit>)] "
+				+ "requires org.jetbrains.kotlin:kotlin-reflect to be on the classpath or module path. "
+				+ "Please add a corresponding dependency.");
+		assertThat(result.stdErr()).contains("BUILD FAILED");
+	}
+
+	private static ProcessResult runBuild(Path workspace, OutputFiles outputFiles, String... extraArgs)
+			throws InterruptedException, IOException {
+
+		return ProcessStarters.gradlew() //
+				.workingDir(copyToWorkspace(Projects.KOTLIN_COROUTINES, workspace)) //
+				.addArguments("-Dmaven.repo=" + MavenRepo.dir()) //
+				.addArguments("build", "--no-daemon", "--stacktrace", "--no-build-cache", "--warning-mode=fail") //
+				.addArguments(extraArgs).putEnvironment("JDK17",
+					Helper.getJavaHome(17).orElseThrow(TestAbortedException::new).toString()) //
+				.redirectOutput(outputFiles) //
+				.startAndWait();
+	}
+}
diff --git a/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/ManifestTests.java b/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/ManifestTests.java
index d215ca8e99c0..f71b3f14eb12 100644
--- a/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/ManifestTests.java
+++ b/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/ManifestTests.java
@@ -39,7 +39,7 @@ class ManifestTests {
 	@ParameterizedTest
 	@MethodSource("platform.tooling.support.Helper#loadModuleDirectoryNames")
 	void manifestEntriesAdhereToConventions(String module) throws Exception {
-		var version = Helper.version(module);
+		var version = Helper.version();
 		var jarFile = MavenRepo.jar(module).toFile();
 		try (var jar = new Jar(jarFile)) {
 			var manifest = jar.getManifest();
@@ -56,10 +56,8 @@ void manifestEntriesAdhereToConventions(String module) throws Exception {
 			assertValue(attributes, "Bundle-SymbolicName", module);
 			assertValue(attributes, "Bundle-Version",
 				MavenVersion.parseMavenString(version).getOSGiVersion().toString());
-			switch (module) {
-				case "junit-platform-commons" -> assertValue(attributes, "Multi-Release", "true");
-				case "junit-platform-console" -> assertValue(attributes, "Main-Class",
-					"org.junit.platform.console.ConsoleLauncher");
+			if (module.equals("junit-platform-console")) {
+				assertValue(attributes, "Main-Class", "org.junit.platform.console.ConsoleLauncher");
 			}
 			var domain = Domain.domain(manifest);
 			domain.getExportPackage().forEach((pkg, attrs) -> {
@@ -88,6 +86,6 @@ private static String specificationVersion(String version) {
 	private static void assertValue(Attributes attributes, String name, String expected) {
 		var actual = attributes.getValue(name);
 		assertEquals(expected, actual,
-			String.format("Manifest attribute %s expected to be %s, but is: %s", name, expected, actual));
+			"Manifest attribute %s expected to be %s, but is: %s".formatted(name, expected, actual));
 	}
 }
diff --git a/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/MavenRepoProxy.java b/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/MavenRepoProxy.java
index 2525a5c8c588..b9c85d6ddaed 100644
--- a/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/MavenRepoProxy.java
+++ b/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/MavenRepoProxy.java
@@ -40,19 +40,16 @@ private MavenRepoProxy(String proxiedUrl, int port) throws IOException {
 		httpServer.createContext("/", exchange -> {
 			try (exchange) {
 				switch (exchange.getRequestMethod()) {
-					case "HEAD":
-					case "GET":
-						if (FORBIDDEN_PATHS.stream().anyMatch(
-							it -> exchange.getRequestURI().getPath().startsWith(it))) {
+					case "HEAD", "GET" -> {
+						if (FORBIDDEN_PATHS.stream().anyMatch(exchange.getRequestURI().getPath()::startsWith)) {
 							exchange.sendResponseHeaders(404, -1);
 							break;
 						}
 						var redirectUrl = proxiedUrl + exchange.getRequestURI().getPath();
 						exchange.getResponseHeaders().add("Location", redirectUrl);
 						exchange.sendResponseHeaders(302, -1);
-						break;
-					default:
-						exchange.sendResponseHeaders(405, -1);
+					}
+					default -> exchange.sendResponseHeaders(405, -1);
 				}
 			}
 			catch (Exception e) {
diff --git a/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/MavenStarterTests.java b/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/MavenStarterTests.java
index 03eb57945fa2..1a998b2c96a2 100644
--- a/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/MavenStarterTests.java
+++ b/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/MavenStarterTests.java
@@ -58,7 +58,7 @@ void verifyJupiterStarterProject(@FilePrefix("maven") OutputFiles outputFiles, S
 		var result = runMaven(outputFiles, "verify");
 
 		assertThat(result.stdOutLines()).contains("[INFO] Tests run: 13, Failures: 0, Errors: 0, Skipped: 0");
-		assertThat(result.stdOut()).contains("Using Java version: 1.8");
+		assertThat(result.stdOut()).contains("Using Java version: 17");
 
 		var testResultsDir = workspace.resolve("target/surefire-reports");
 		verifyContainsExpectedStartedOpenTestReport(testResultsDir, snapshot);
@@ -81,7 +81,7 @@ void runOnlyOneMethodInClassTemplate(@FilePrefix("maven") OutputFiles outputFile
 	}
 
 	private ProcessResult runMaven(OutputFiles outputFiles, String... extraArgs) throws InterruptedException {
-		var result = ProcessStarters.maven(Helper.getJavaHome(8).orElseThrow(TestAbortedException::new)) //
+		var result = ProcessStarters.maven(Helper.getJavaHome(17).orElseThrow(TestAbortedException::new)) //
 				.workingDir(workspace) //
 				.addArguments(localMavenRepo.toCliArgument(), "-Dmaven.repo=" + MavenRepo.dir()) //
 				.addArguments("-Dsnapshot.repo.url=" + mavenRepoProxy.getBaseUri()) //
diff --git a/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/MavenSurefireCompatibilityTests.java b/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/MavenSurefireCompatibilityTests.java
index 5228ed35b8e7..e5aa1542614a 100644
--- a/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/MavenSurefireCompatibilityTests.java
+++ b/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/MavenSurefireCompatibilityTests.java
@@ -18,9 +18,8 @@
 import java.nio.file.Files;
 import java.nio.file.Path;
 
+import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.io.TempDir;
-import org.junit.jupiter.params.ParameterizedTest;
-import org.junit.jupiter.params.provider.CsvSource;
 import org.junit.platform.tests.process.OutputFiles;
 import org.opentest4j.TestAbortedException;
 
@@ -33,23 +32,19 @@
  */
 class MavenSurefireCompatibilityTests {
 
+	static final String MINIMUM_SUPPORTED_SUREFIRE_VERSION = "3.0.0";
+
 	@ManagedResource
 	LocalMavenRepo localMavenRepo;
 
-	@ParameterizedTest
-	@CsvSource(delimiter = '|', nullValues = "<none>", textBlock = """
-			2.22.2   | --activate-profiles=manual-platform-dependency
-			3.0.0-M4 | <none>
-			""")
-	void testMavenSurefireCompatibilityProject(String surefireVersion, String extraArg, @TempDir Path workspace,
-			@FilePrefix("maven") OutputFiles outputFiles) throws Exception {
-		var extraArgs = extraArg == null ? new String[0] : new String[] { extraArg };
-		var result = ProcessStarters.maven(Helper.getJavaHome(8).orElseThrow(TestAbortedException::new)) //
+	@Test
+	void testMavenSurefireCompatibilityProject(@TempDir Path workspace, @FilePrefix("maven") OutputFiles outputFiles)
+			throws Exception {
+		var result = ProcessStarters.maven(Helper.getJavaHome(17).orElseThrow(TestAbortedException::new)) //
 				.workingDir(copyToWorkspace(Projects.MAVEN_SUREFIRE_COMPATIBILITY, workspace)) //
 				.addArguments(localMavenRepo.toCliArgument(), "-Dmaven.repo=" + MavenRepo.dir()) //
-				.addArguments("-Dsurefire.version=" + surefireVersion) //
+				.addArguments("-Dsurefire.version=" + MINIMUM_SUPPORTED_SUREFIRE_VERSION) //
 				.addArguments("--update-snapshots", "--batch-mode", "test") //
-				.addArguments(extraArgs) //
 				.redirectOutput(outputFiles) //
 				.startAndWait();
 
diff --git a/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/ModularUserGuideTests.java b/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/ModularUserGuideTests.java
index e7987317cdd2..7882fc19847b 100644
--- a/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/ModularUserGuideTests.java
+++ b/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/ModularUserGuideTests.java
@@ -53,7 +53,7 @@ class ModularUserGuideTests {
 
 			  requires org.junit.platform.engine;
 			  requires org.junit.platform.reporting;
-			  requires org.junit.platform.runner;
+			  requires org.junit.platform.suite;
 			  requires org.junit.platform.testkit;
 
 			  // Byte Buddy is used by AssertJ's soft assertions which are used by the Engine Test Kit
@@ -89,6 +89,7 @@ private static List<String> compile(Path temp, Writer out, Writer err) throws Ex
 		ThirdPartyJars.copy(lib, "net.bytebuddy", "byte-buddy");
 		ThirdPartyJars.copy(lib, "org.apiguardian", "apiguardian-api");
 		ThirdPartyJars.copy(lib, "org.hamcrest", "hamcrest");
+		ThirdPartyJars.copy(lib, "org.jspecify", "jspecify");
 		ThirdPartyJars.copy(lib, "org.opentest4j", "opentest4j");
 		ThirdPartyJars.copy(lib, "org.opentest4j.reporting", "open-test-reporting-tooling-spi");
 		ThirdPartyJars.copy(lib, "com.google.jimfs", "jimfs");
@@ -172,6 +173,7 @@ void runTestsFromUserGuideWithinModularBoundaries(@TempDir Path temp,
 			"lib/guava-.+\\.jar", //
 			"lib/hamcrest-.+\\.jar", //
 			"lib/jimfs-.+\\.jar", //
+			"lib/jspecify-.+\\.jar", //
 			"lib/junit-.+\\.jar", //
 			">> ALL JUNIT 5 JARS >>", //
 			"lib/opentest4j-.+\\.jar", //
diff --git a/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/Projects.java b/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/Projects.java
index 8d806b6b67e4..63b4588d2650 100644
--- a/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/Projects.java
+++ b/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/Projects.java
@@ -21,8 +21,8 @@ public class Projects {
 	public static final String GRADLE_KOTLIN_EXTENSIONS = "gradle-kotlin-extensions";
 	public static final String GRADLE_MISSING_ENGINE = "gradle-missing-engine";
 	public static final String JAR_DESCRIBE_MODULE = "jar-describe-module";
-	public static final String JAVA_VERSIONS = "java-versions";
 	public static final String JUPITER_STARTER = "jupiter-starter";
+	public static final String KOTLIN_COROUTINES = "kotlin-coroutines";
 	public static final String MAVEN_SUREFIRE_COMPATIBILITY = "maven-surefire-compatibility";
 	public static final String MULTI_RELEASE_JAR = "multi-release-jar";
 	public static final String REFLECTION_TESTS = "reflection-tests";
diff --git a/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/ReflectionCompatibilityTests.java b/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/ReflectionCompatibilityTests.java
index 1eb8272082bb..86e2b2d96390 100644
--- a/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/ReflectionCompatibilityTests.java
+++ b/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/ReflectionCompatibilityTests.java
@@ -37,12 +37,12 @@ void gradle_wrapper(@TempDir Path workspace, @FilePrefix("gradle") OutputFiles o
 				.workingDir(copyToWorkspace(Projects.REFLECTION_TESTS, workspace)) //
 				.addArguments("-Dmaven.repo=" + MavenRepo.dir()) //
 				.addArguments("build", "--no-daemon", "--stacktrace", "--no-build-cache", "--warning-mode=fail") //
-				.putEnvironment("JDK8", Helper.getJavaHome(8).orElseThrow(TestAbortedException::new).toString()) //
+				.putEnvironment("JDK17", Helper.getJavaHome(17).orElseThrow(TestAbortedException::new).toString()) //
 				.redirectOutput(outputFiles) //
 				.startAndWait();
 
 		assertEquals(0, result.exitCode());
 		assertTrue(result.stdOut().lines().anyMatch(line -> line.contains("BUILD SUCCESSFUL")));
-		assertThat(result.stdOut()).contains("Using Java version: 1.8");
+		assertThat(result.stdOut()).contains("Using Java version: 17");
 	}
 }
diff --git a/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/StandaloneTests.java b/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/StandaloneTests.java
index a86b65a8aa51..9c63c991b8b7 100644
--- a/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/StandaloneTests.java
+++ b/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/StandaloneTests.java
@@ -87,14 +87,11 @@ void listAllObservableEngines(@FilePrefix("java") OutputFiles outputFiles) throw
 
 		assertEquals(0, result.exitCode());
 
-		var jupiterVersion = Helper.version("junit-jupiter-engine");
-		var suiteVersion = Helper.version("junit-platform-suite-engine");
-		var vintageVersion = Helper.version("junit-vintage-engine");
 		assertLinesMatch("""
-				junit-jupiter (org.junit.jupiter:junit-jupiter-engine:%s)
-				junit-platform-suite (org.junit.platform:junit-platform-suite-engine:%s)
-				junit-vintage (org.junit.vintage:junit-vintage-engine:%s)
-				""".formatted(jupiterVersion, suiteVersion, vintageVersion).lines(), //
+				junit-jupiter (org.junit.jupiter:junit-jupiter-engine:%1$s)
+				junit-platform-suite (org.junit.platform:junit-platform-suite-engine:%1$s)
+				junit-vintage (org.junit.vintage:junit-vintage-engine:%1$s)
+				""".formatted(Helper.version()).lines(), //
 			result.stdOut().lines());
 	}
 
@@ -110,7 +107,7 @@ void printVersionViaJar(@FilePrefix("java") OutputFiles outputFiles) throws Exce
 
 		assertEquals(0, result.exitCode());
 
-		var version = Helper.version("junit-platform-console");
+		var version = Helper.version();
 		assertLinesMatch("""
 				JUnit Platform Console Launcher %s
 				JVM: .*
@@ -142,7 +139,7 @@ void printVersionViaModule(@FilePrefix("java") OutputFiles outputFiles) throws E
 
 		assertEquals(0, result.exitCode());
 
-		var version = Helper.version("junit-platform-console");
+		var version = Helper.version();
 		assertLinesMatch("""
 				JUnit Platform Console Launcher %s
 				JVM: .*
@@ -158,7 +155,7 @@ void compile(@FilePrefix("javac") OutputFiles javacOutputFiles) throws Exception
 		var result = ProcessStarters.javaCommand("javac") //
 				.workingDir(workspace) //
 				.addArguments("-Xlint:-options") //
-				.addArguments("--release", "8") //
+				.addArguments("--release", "17") //
 				.addArguments("-proc:none") //
 				.addArguments("-d", workspace.resolve("bin").toString()) //
 				.addArguments("--class-path", MavenRepo.jar("junit-platform-console-standalone").toString()) //
@@ -425,9 +422,9 @@ void execute(@FilePrefix("console-launcher") OutputFiles outputFiles) throws Exc
 	@Test
 	@Order(4)
 	@Execution(SAME_THREAD)
-	void executeOnJava8(@FilePrefix("console-launcher") OutputFiles outputFiles) throws Exception {
-		var java8Home = Helper.getJavaHome(8).orElseThrow(TestAbortedException::new);
-		var result = ProcessStarters.java(java8Home) //
+	void executeOnJava17(@FilePrefix("console-launcher") OutputFiles outputFiles) throws Exception {
+		var javaHome = Helper.getJavaHome(17).orElseThrow(TestAbortedException::new);
+		var result = ProcessStarters.java(javaHome) //
 				.workingDir(workspace) //
 				.addArguments("-showversion") //
 				.addArguments("-enableassertions") //
@@ -445,25 +442,23 @@ void executeOnJava8(@FilePrefix("console-launcher") OutputFiles outputFiles) thr
 		assertEquals(1, result.exitCode());
 
 		var expectedOutLines = Files.readAllLines(workspace.resolve("expected-out.txt"));
-		var expectedErrLines = getExpectedErrLinesOnJava8(workspace);
+		var expectedErrLines = getExpectedErrLinesOnJava17(workspace);
 		assertLinesMatch(expectedOutLines, result.stdOutLines());
 		assertLinesMatch(expectedErrLines, result.stdErrLines());
 
-		var jupiterVersion = Helper.version("junit-jupiter-engine");
-		var vintageVersion = Helper.version("junit-vintage-engine");
 		assertTrue(result.stdErr().contains("junit-jupiter"
-				+ " (group ID: org.junit.jupiter, artifact ID: junit-jupiter-engine, version: " + jupiterVersion));
+				+ " (group ID: org.junit.jupiter, artifact ID: junit-jupiter-engine, version: " + Helper.version()));
 		assertTrue(result.stdErr().contains("junit-vintage"
-				+ " (group ID: org.junit.vintage, artifact ID: junit-vintage-engine, version: " + vintageVersion));
+				+ " (group ID: org.junit.vintage, artifact ID: junit-vintage-engine, version: " + Helper.version()));
 	}
 
 	@Test
 	@Order(5)
 	@Execution(SAME_THREAD)
-	// https://github.com/junit-team/junit5/issues/2600
-	void executeOnJava8SelectPackage(@FilePrefix("console-launcher") OutputFiles outputFiles) throws Exception {
-		var java8Home = Helper.getJavaHome(8).orElseThrow(TestAbortedException::new);
-		var result = ProcessStarters.java(java8Home) //
+	// https://github.com/junit-team/junit-framework/issues/2600
+	void executeOnJava17SelectPackage(@FilePrefix("console-launcher") OutputFiles outputFiles) throws Exception {
+		var javaHome = Helper.getJavaHome(17).orElseThrow(TestAbortedException::new);
+		var result = ProcessStarters.java(javaHome) //
 				.workingDir(workspace).addArguments("-showversion") //
 				.addArguments("-enableassertions") //
 				.addArguments("-Djava.util.logging.config.file=logging.properties") //
@@ -480,19 +475,17 @@ void executeOnJava8SelectPackage(@FilePrefix("console-launcher") OutputFiles out
 		assertEquals(1, result.exitCode());
 
 		var expectedOutLines = Files.readAllLines(workspace.resolve("expected-out.txt"));
-		var expectedErrLines = getExpectedErrLinesOnJava8(workspace);
+		var expectedErrLines = getExpectedErrLinesOnJava17(workspace);
 		assertLinesMatch(expectedOutLines, result.stdOutLines());
 		assertLinesMatch(expectedErrLines, result.stdErrLines());
 
-		var jupiterVersion = Helper.version("junit-jupiter-engine");
-		var vintageVersion = Helper.version("junit-vintage-engine");
 		assertTrue(result.stdErr().contains("junit-jupiter"
-				+ " (group ID: org.junit.jupiter, artifact ID: junit-jupiter-engine, version: " + jupiterVersion));
+				+ " (group ID: org.junit.jupiter, artifact ID: junit-jupiter-engine, version: " + Helper.version()));
 		assertTrue(result.stdErr().contains("junit-vintage"
-				+ " (group ID: org.junit.vintage, artifact ID: junit-vintage-engine, version: " + vintageVersion));
+				+ " (group ID: org.junit.vintage, artifact ID: junit-vintage-engine, version: " + Helper.version()));
 	}
 
-	private static List<String> getExpectedErrLinesOnJava8(Path workspace) throws IOException {
+	private static List<String> getExpectedErrLinesOnJava17(Path workspace) throws IOException {
 		var expectedErrLines = new ArrayList<String>();
 		expectedErrLines.add(">> JAVA VERSION >>");
 		expectedErrLines.addAll(Files.readAllLines(workspace.resolve("expected-err.txt")));
@@ -548,11 +541,9 @@ private static void assertOutputOnCurrentJvm(ProcessResult result) throws IOExce
 		}
 		assertLinesMatch(expectedErrLines, actualErrLines);
 
-		var jupiterVersion = Helper.version("junit-jupiter-engine");
-		var vintageVersion = Helper.version("junit-vintage-engine");
 		assertTrue(result.stdErr().contains("junit-jupiter"
-				+ " (group ID: org.junit.jupiter, artifact ID: junit-jupiter-engine, version: " + jupiterVersion));
+				+ " (group ID: org.junit.jupiter, artifact ID: junit-jupiter-engine, version: " + Helper.version()));
 		assertTrue(result.stdErr().contains("junit-vintage"
-				+ " (group ID: org.junit.vintage, artifact ID: junit-vintage-engine, version: " + vintageVersion));
+				+ " (group ID: org.junit.vintage, artifact ID: junit-vintage-engine, version: " + Helper.version()));
 	}
 }
diff --git a/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/UnalignedClasspathTests.java b/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/UnalignedClasspathTests.java
index ab84f6f83392..372f1d2f5fee 100644
--- a/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/UnalignedClasspathTests.java
+++ b/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/UnalignedClasspathTests.java
@@ -67,7 +67,7 @@ void verifyErrorMessageForUnalignedClasspath(JRE jre, Path javaHome, @TempDir Pa
 
 	static Stream<Arguments> javaVersions() {
 		return Stream.concat( //
-			Helper.getJavaHome(8).map(path -> Arguments.of(JRE.JAVA_8, path)).stream(), //
+			Helper.getJavaHome(17).map(path -> Arguments.of(JRE.JAVA_17, path)).stream(), //
 			Stream.of(Arguments.of(JRE.currentJre(), currentJdkHome())) //
 		);
 	}
diff --git a/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/VintageGradleIntegrationTests.java b/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/VintageGradleIntegrationTests.java
index 92d88ef4ab91..35c64f2b2be5 100644
--- a/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/VintageGradleIntegrationTests.java
+++ b/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/VintageGradleIntegrationTests.java
@@ -59,7 +59,7 @@ void supportedVersions(String version, @FilePrefix("gradle") OutputFiles outputF
 	private ProcessResult run(OutputFiles outputFiles, String version) throws Exception {
 		return ProcessStarters.gradlew() //
 				.workingDir(copyToWorkspace(Projects.VINTAGE, workspace)) //
-				.putEnvironment("JDK8", Helper.getJavaHome(8).orElseThrow(TestAbortedException::new).toString()) //
+				.putEnvironment("JDK17", Helper.getJavaHome(17).orElseThrow(TestAbortedException::new).toString()) //
 				.addArguments("build", "--no-daemon", "--stacktrace", "--no-build-cache", "--warning-mode=fail") //
 				.addArguments("-Dmaven.repo=" + MavenRepo.dir()) //
 				.addArguments("-Djunit4Version=" + version) //
diff --git a/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/VintageMavenIntegrationTests.java b/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/VintageMavenIntegrationTests.java
index 4b2d909f28c6..ca5d9bc800a4 100644
--- a/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/VintageMavenIntegrationTests.java
+++ b/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/VintageMavenIntegrationTests.java
@@ -62,7 +62,7 @@ void supportedVersions(String version, @FilePrefix("maven") OutputFiles outputFi
 	}
 
 	private ProcessResult run(OutputFiles outputFiles, String version) throws Exception {
-		return ProcessStarters.maven(Helper.getJavaHome(8).orElseThrow(TestAbortedException::new)) //
+		return ProcessStarters.maven(Helper.getJavaHome(17).orElseThrow(TestAbortedException::new)) //
 				.workingDir(copyToWorkspace(Projects.VINTAGE, workspace)) //
 				.addArguments("clean", "test", "--update-snapshots", "--batch-mode") //
 				.addArguments(localMavenRepo.toCliArgument(), "-Dmaven.repo=" + MavenRepo.dir()) //
diff --git a/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/XmlAssertions.java b/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/XmlAssertions.java
index f55c60c4d821..7aa7052999ce 100644
--- a/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/XmlAssertions.java
+++ b/platform-tooling-support-tests/src/test/java/platform/tooling/support/tests/XmlAssertions.java
@@ -73,8 +73,8 @@ private static SnapshotSerializer obfuscatingSnapshotSerializer(SnapshotSerializ
 			UnaryOperator<String> obfuscator) {
 		return testResult -> {
 			Object obfuscatedTestResult = testResult;
-			if (testResult instanceof String) {
-				obfuscatedTestResult = obfuscator.apply((String) testResult);
+			if (testResult instanceof String string) {
+				obfuscatedTestResult = obfuscator.apply(string);
 			}
 			return delegate.serialize(obfuscatedTestResult);
 		};
diff --git a/platform-tooling-support-tests/src/test/resources/platform/tooling/support/tests/AntStarterTests_snapshots/open-test-report.xml.snapshot b/platform-tooling-support-tests/src/test/resources/platform/tooling/support/tests/AntStarterTests_snapshots/open-test-report.xml.snapshot
index 240a71ef3fd3..b6193859beec 100644
--- a/platform-tooling-support-tests/src/test/resources/platform/tooling/support/tests/AntStarterTests_snapshots/open-test-report.xml.snapshot
+++ b/platform-tooling-support-tests/src/test/resources/platform/tooling/support/tests/AntStarterTests_snapshots/open-test-report.xml.snapshot
@@ -9,7 +9,7 @@ test-method: ant_starter
 			xmlns:git="https://schemas.opentest4j.org/reporting/git/0.2.0"
 			xmlns:java="https://schemas.opentest4j.org/reporting/java/0.2.0"
 			xmlns:junit="https://schemas.junit.org/open-test-reporting"
-			xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="https://schemas.junit.org/open-test-reporting https://junit.org/junit5/schemas/open-test-reporting/junit-1.9.xsd">
+			xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="https://schemas.junit.org/open-test-reporting https://schemas.junit.org/open-test-reporting/junit-1.9.xsd">
   
   <infrastructure>
     <hostName>obfuscated</hostName>
diff --git a/platform-tooling-support-tests/src/test/resources/platform/tooling/support/tests/GradleStarterTests_snapshots/open-test-report.xml.snapshot b/platform-tooling-support-tests/src/test/resources/platform/tooling/support/tests/GradleStarterTests_snapshots/open-test-report.xml.snapshot
index ce4ce4f15535..09377aa77dd2 100644
--- a/platform-tooling-support-tests/src/test/resources/platform/tooling/support/tests/GradleStarterTests_snapshots/open-test-report.xml.snapshot
+++ b/platform-tooling-support-tests/src/test/resources/platform/tooling/support/tests/GradleStarterTests_snapshots/open-test-report.xml.snapshot
@@ -9,7 +9,7 @@ test-method: buildJupiterStarterProject
 			xmlns:git="https://schemas.opentest4j.org/reporting/git/0.2.0"
 			xmlns:java="https://schemas.opentest4j.org/reporting/java/0.2.0"
 			xmlns:junit="https://schemas.junit.org/open-test-reporting"
-			xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="https://schemas.junit.org/open-test-reporting https://junit.org/junit5/schemas/open-test-reporting/junit-1.9.xsd">
+			xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="https://schemas.junit.org/open-test-reporting https://schemas.junit.org/open-test-reporting/junit-1.9.xsd">
   
   <infrastructure>
     <hostName>obfuscated</hostName>
diff --git a/platform-tooling-support-tests/src/test/resources/platform/tooling/support/tests/MavenStarterTests_snapshots/open-test-report.xml.snapshot b/platform-tooling-support-tests/src/test/resources/platform/tooling/support/tests/MavenStarterTests_snapshots/open-test-report.xml.snapshot
index 52ad3af973c1..ee2d20a63f1c 100644
--- a/platform-tooling-support-tests/src/test/resources/platform/tooling/support/tests/MavenStarterTests_snapshots/open-test-report.xml.snapshot
+++ b/platform-tooling-support-tests/src/test/resources/platform/tooling/support/tests/MavenStarterTests_snapshots/open-test-report.xml.snapshot
@@ -9,7 +9,7 @@ test-method: verifyJupiterStarterProject
 			xmlns:git="https://schemas.opentest4j.org/reporting/git/0.2.0"
 			xmlns:java="https://schemas.opentest4j.org/reporting/java/0.2.0"
 			xmlns:junit="https://schemas.junit.org/open-test-reporting"
-			xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="https://schemas.junit.org/open-test-reporting https://junit.org/junit5/schemas/open-test-reporting/junit-1.9.xsd">
+			xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="https://schemas.junit.org/open-test-reporting https://schemas.junit.org/open-test-reporting/junit-1.9.xsd">
   
   <infrastructure>
     <hostName>obfuscated</hostName>
diff --git a/settings.gradle.kts b/settings.gradle.kts
index ba5ae9fd677f..9c65c66f87c3 100644
--- a/settings.gradle.kts
+++ b/settings.gradle.kts
@@ -57,7 +57,7 @@ buildCache {
 	if (useDevelocityInstance) {
 		remote(develocity.buildCache) {
 			server = buildCacheServer.orNull
-			val authenticated = System.getenv("DEVELOCITY_ACCESS_KEY") != null
+			val authenticated = !System.getenv("DEVELOCITY_ACCESS_KEY").isNullOrEmpty()
 			isPush = buildParameters.ci && authenticated
 		}
 	} else {
@@ -69,7 +69,7 @@ buildCache {
 
 includeBuild("gradle/base")
 
-rootProject.name = "junit5"
+rootProject.name = "junit-framework"
 
 include("documentation")
 include("junit-jupiter")
@@ -81,10 +81,8 @@ include("junit-platform-commons")
 include("junit-platform-console")
 include("junit-platform-console-standalone")
 include("junit-platform-engine")
-include("junit-platform-jfr")
 include("junit-platform-launcher")
 include("junit-platform-reporting")
-include("junit-platform-runner")
 include("junit-platform-suite")
 include("junit-platform-suite-api")
 include("junit-platform-suite-commons")