jit-regression-test

name	jit-regression-test
description	Extract a standalone JIT regression test case from a given GitHub issue and save it under the JitBlue folder. Use this when asked to create or extract a JIT regression test from an issue.

JIT Regression Test Extraction

When you need to extract a JIT regression test case from a GitHub issue, follow this process to create a properly structured test under src/tests/JIT/Regression/JitBlue/.

Step 1: Gather Information from the GitHub Issue

From the GitHub issue, extract:

1. Issue number - Used to name the test folder and files (e.g., issue #99391 → Runtime_99391)
2. Reproduction code - The C# code that demonstrates the bug. If no code provided, try to compose it yourself.
3. Environment variables - Any DOTNET_* environment variables required to reproduce the bug
4. Expected behavior - What the correct output/behavior should be

Step 2: Create the Test Directory

Create a new folder under src/tests/JIT/Regression/JitBlue/:

src/tests/JIT/Regression/JitBlue/Runtime_<issue_number>/

Step 3: Create the Test File

Create a Runtime_<issue_number>.cs file following these conventions:

Example:

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System;
using System.Runtime.CompilerServices;
using Xunit;

public class Runtime_<issue_number>
{
    [Fact]
    public static void TestEntryPoint()
    {
        // Test code that exercises the bug
        // Use Assert.Equal, Assert.True, etc. for validation
    }
}

Key Conventions

• License header: Always include the standard .NET Foundation license header
• Class name: Match the file name exactly (Runtime_<issue_number>)
• Test method: Use [Fact] attribute and name the method TestEntryPoint() or Test()
• Assertions: Use Xunit's helpers or just throw plain exceptions.

Example: Simple Test (from Runtime_99391)

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.


namespace Runtime_99391;

using System;
using System.Runtime.CompilerServices;
using System.Numerics;
using Xunit;

public class Runtime_99391
{
    [Fact]
    public static void TestEntryPoint()
    {
        Vector2 result2a = Vector2.Normalize(Value2);
        Assert.Equal(new Vector2(0, 1), result2a);
    }

    private static Vector2 Value2
    {
        [MethodImpl(MethodImplOptions.NoInlining)]
        get => new Vector2(0, 2);
    }
}

[Optional] Step 4: Create a .csproj File (Only When Needed)

A custom .csproj file is only required when:

• Environment variables are needed to reproduce the bug (such as DOTNET_JitStressModeNames)
• Special compilation settings are required

It should be located next to the test source file with the following name: Runtime_<issue_number>.csproj. Example:

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <Optimize>True</Optimize>
    <DebugType>None</DebugType>
    <!-- Needed for CLRTestEnvironmentVariable -->
    <RequiresProcessIsolation>true</RequiresProcessIsolation>
  </PropertyGroup>
  <ItemGroup>
    <Compile Include="$(MSBuildProjectName).cs" />

    <CLRTestEnvironmentVariable Include="DOTNET_TieredCompilation" Value="0" />
  </ItemGroup>
</Project>

Important Notes

• No .csproj needed for simple tests: Most tests only need the .cs file. The test infrastructure uses default settings that work for most cases.
• Look at recent tests: When in doubt, examine recent tests under src/tests/JIT/Regression/JitBlue/Runtime_* for the latest conventions.
• Use [MethodImpl(MethodImplOptions.NoInlining)]: When you need to prevent inlining to reproduce a JIT bug.
• Minimize the reproduction: Strip down the test code to the minimal case that reproduces the issue.