feat(api): add onBrowserInit event

docs/advanced/api/reporters.md

@@ -81,6 +81,14 @@ export default new MyReporter()
 ```
 :::
 
+## onBrowserInit <Badge type="warning">experimental</Badge> {#onbrowserinit}
+
+```ts
+function onBrowserInit(project: TestProject): Awaitable<void>
+```
+
+This method is called when the browser instance is initiated. It receives an instance of the project for which the browser is initiated. `project.browser` will always be defined when this method is called.
+
 ## onTestRunStart
 
 ```ts

packages/vitest/src/node/project.ts

@@ -531,6 +531,7 @@ export class TestProject {
 
     if (!this.browser && this._parent?._parentBrowser) {
       this.browser = this._parent._parentBrowser.spawn(this)
+      await this.vitest.report('onBrowserInit', this)
     }
   })
 

packages/vitest/src/node/types/reporter.ts

@@ -3,13 +3,20 @@ import type { SerializedError } from '@vitest/utils'
 import type { SerializedTestSpecification } from '../../runtime/types/utils'
 import type { Awaitable, UserConsoleLog } from '../../types/general'
 import type { Vitest } from '../core'
+import type { TestProject } from '../project'
 import type { ReportedHookContext, TestCase, TestModule, TestSuite } from '../reporters/reported-tasks'
 import type { TestSpecification } from '../spec'
 
 export type TestRunEndReason = 'passed' | 'interrupted' | 'failed'
 
 export interface Reporter {
   onInit?: (vitest: Vitest) => void
+  /**
+   * Called when the project initiated the browser instance.
+   * project.browser will always be defined.
+   * @experimental
+   */
+  onBrowserInit?: (project: TestProject) => Awaitable<void>
   /**
    * @deprecated use `onTestRunStart` instead
    */

test/browser/specs/runner.test.ts

@@ -4,20 +4,45 @@ import { readFile } from 'node:fs/promises'
 import { beforeAll, describe, expect, onTestFailed, test } from 'vitest'
 import { instances, provider, runBrowserTests } from './utils'
 
+function noop() {}
+
 describe('running browser tests', async () => {
   let stderr: string
   let stdout: string
   let browserResultJson: JsonTestResults
   let passedTests: any[]
   let failedTests: any[]
   let vitest: Vitest
+  const events: string[] = []
 
   beforeAll(async () => {
     ({
       stderr,
       stdout,
       ctx: vitest,
-    } = await runBrowserTests())
+    } = await runBrowserTests({
+      reporters: [
+        {
+          onBrowserInit(project) {
+            events.push(`onBrowserInit ${project.name}`)
+          },
+        },
+        'json',
+        {
+          onInit: noop,
+          onPathsCollected: noop,
+          onCollected: noop,
+          onFinished: noop,
+          onTaskUpdate: noop,
+          onTestRemoved: noop,
+          onWatcherStart: noop,
+          onWatcherRerun: noop,
+          onServerRestart: noop,
+          onUserConsoleLog: noop,
+        },
+        'default',
+      ],
+    }))
 
     const browserResult = await readFile('./browser.json', 'utf-8')
     browserResultJson = JSON.parse(browserResult)
@@ -34,6 +59,11 @@ describe('running browser tests', async () => {
 
     const testFiles = browserResultJson.testResults.map(t => t.name)
 
+    vitest.projects.forEach((project) => {
+      // the order is non-deterministic
+      expect(events).toContain(`onBrowserInit ${project.name}`)
+    })
+
     // test files are optimized automatically
     expect(vitest.projects.map(p => p.browser?.vite.config.optimizeDeps.entries))
       .toEqual(vitest.projects.map(() => expect.arrayContaining(testFiles)))

test/browser/vitest.config.mts

@@ -6,8 +6,6 @@ import { defineConfig } from 'vitest/config'
 
 const dir = dirname(fileURLToPath(import.meta.url))
 
-function noop() {}
-
 const provider = process.env.PROVIDER || 'playwright'
 const browser = process.env.BROWSER || (provider === 'playwright' ? 'chromium' : 'chrome')
 
@@ -106,18 +104,6 @@ export default defineConfig({
       html: './html/index.html',
       json: './browser.json',
     },
-    reporters: ['json', {
-      onInit: noop,
-      onPathsCollected: noop,
-      onCollected: noop,
-      onFinished: noop,
-      onTaskUpdate: noop,
-      onTestRemoved: noop,
-      onWatcherStart: noop,
-      onWatcherRerun: noop,
-      onServerRestart: noop,
-      onUserConsoleLog: noop,
-    }, 'default'],
     env: {
       BROWSER: browser,
     },