[Proposal] Performance/usability improvements for analyzer tests

src/Microsoft.CodeAnalysis.Testing/Directory.Build.props

@@ -16,7 +16,7 @@
       netstandard1.6/net46: Roslyn 2.x
       netstandard2.0/net472: Roslyn 3.x
     -->
-    <TestingLibraryTargetFrameworks>netcoreapp3.1;netstandard1.6;netstandard2.0;net452;net46;net472</TestingLibraryTargetFrameworks>
+    <TestingLibraryTargetFrameworks>net7.0;netcoreapp3.1;netstandard1.6;netstandard2.0;net452;net46;net472</TestingLibraryTargetFrameworks>
 
     <!--
       netcoreapp3.1: Ensures full support for nullable reference types

src/Microsoft.CodeAnalysis.Testing/Microsoft.CodeAnalysis.Analyzer.Testing/ReferenceAssemblies.cs

@@ -103,6 +103,8 @@ public static ReferenceAssemblies Default
                 return NetFramework.Net472.Default;
 #elif NETCOREAPP3_1
                 return NetCore.NetCoreApp31;
+#elif NET7_0
+                return Net.Net70;
 #endif
             }
         }

src/Microsoft.CodeAnalysis.Testing/Microsoft.CodeAnalysis.CSharp.Analyzer.Testing/CSharpAnalyzerTest`2.cs

@@ -9,7 +9,7 @@
 
 namespace Microsoft.CodeAnalysis.CSharp.Testing
 {
-    public class CSharpAnalyzerTest<TAnalyzer, TVerifier> : AnalyzerTest<TVerifier>
+    public partial class CSharpAnalyzerTest<TAnalyzer, TVerifier> : AnalyzerTest<TVerifier>
         where TAnalyzer : DiagnosticAnalyzer, new()
         where TVerifier : IVerifier, new()
     {

src/Microsoft.CodeAnalysis.Testing/Microsoft.CodeAnalysis.CSharp.Analyzer.Testing/CSharpAnalyzerTest`2.net7.cs

@@ -0,0 +1,21 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Diagnostics.CodeAnalysis;
+using Microsoft.CodeAnalysis.Testing;
+
+namespace Microsoft.CodeAnalysis.CSharp.Testing;
+
+public partial class CSharpAnalyzerTest<TAnalyzer, TVerifier>
+{
+    // For net9.0 the second parameter could be 'params ReadOnlySpan<DiagnosticResult> expectedDiagnostics'
+    public static CSharpAnalyzerTest<TAnalyzer, TVerifier> Create([StringSyntax("C#-test")] string source, params DiagnosticResult[] expectedDiagnostics)
+    {
+        var test = new CSharpAnalyzerTest<TAnalyzer, TVerifier> { TestCode = source };
+        test.ExpectedDiagnostics.AddRange(expectedDiagnostics);
+
+        return test;
+    }
+}

src/Microsoft.CodeAnalysis.Testing/Microsoft.CodeAnalysis.CSharp.Analyzer.Testing/Extensions/CSharpAnalyzerTestExtensions.net7.cs

@@ -0,0 +1,20 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Diagnostics.CodeAnalysis;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Microsoft.CodeAnalysis.Testing;
+
+namespace Microsoft.CodeAnalysis.CSharp.Testing;
+
+public static class CSharpAnalyzerTestExtensions
+{
+    public static CSharpAnalyzerTest<TAnalyzer, TVerifier> WithSource<TAnalyzer, TVerifier>(this CSharpAnalyzerTest<TAnalyzer, TVerifier> test, [StringSyntax("C#-test")] string source)
+        where TAnalyzer : DiagnosticAnalyzer, new()
+        where TVerifier : IVerifier, new()
+    {
+        test.TestState.Sources.Add(source);
+        return test;
+    }
+}

src/Microsoft.CodeAnalysis.Testing/Microsoft.CodeAnalysis.CSharp.Analyzer.Testing/Microsoft.CodeAnalysis.CSharp.Analyzer.Testing.csproj

@@ -13,6 +13,16 @@
     <PackageTags>Roslyn Analyzer Test Framework C# Types</PackageTags>
   </PropertyGroup>
 
+  <ItemGroup>
+    <Compile Remove="CSharpAnalyzerTest`2.net7.cs" />
+    <Compile Remove="Extensions/CSharpAnalyzerTestExtensions.net7.cs" />
+  </ItemGroup>
+
+  <ItemGroup Condition="$([MSBuild]::IsTargetFrameworkCompatible('$(TargetFramework)', 'net7.0'))">
+    <Compile Include="CSharpAnalyzerTest`2.net7.cs" />
+    <Compile Include="Extensions/CSharpAnalyzerTestExtensions.net7.cs" />
+  </ItemGroup>
+
   <ItemGroup>
     <PackageReference Include="Microsoft.CodeAnalysis.CSharp.Workspaces" Version="1.0.1" />
   </ItemGroup>