xUnit3 migration - Complete with IDataAttribute interface pattern (5,939+ tests passing)

[Copilot]

xUnit3 Migration - EndToEndBuildTests Fix

Issue Fixed

EndToEndBuildTests package version error ✅

• Root cause: The EndToEndBuildTests projects (BasicProvider.Tests and ComboProvider.Tests) don't import the central tests/Directory.Build.props where xUnit3 packages are defined. They use their own separate build configuration.
• Error: NU1015: The following PackageReference item(s) do not have a version specified: Microsoft.TestPlatform, xunit.runner.visualstudio, xunit.v3, xunit.v3.runner.console
• Fix: Added explicit package versions to both projects:
  • xunit.v3 Version="3.1.0"
  • xunit.runner.visualstudio Version="3.1.4"
  • Microsoft.TestPlatform Version="17.14.1"

Files Changed

BasicProvider.Tests.fsproj:

• Added explicit xUnit3 package references with versions

ComboProvider.Tests.fsproj:

• Added explicit xUnit3 package references with versions

Why This Was Needed

These EndToEndBuildTests are special integration tests that run in isolation. They have their own Directory.Build.props and Directory.Build.targets that exclude the central test infrastructure's imports. Therefore, they need their own explicit package references with versions rather than relying on central package management.

Original prompt

dotnet/fsharp Migration Guide

xUnit2 → xUnit3 & VSTest → Microsoft.TestPlatform

---

References

• Official migration doc (preview)
• xUnit3 migration guide
• xUnit3 configuration file schema
• xUnit3 and M.T.Platform integration
• WPF migration PR
• WinForms migration PR

---

1. Central Version Update (eng/Versions.props)

Use these exact versions (as of 2025-10-01):

<XunitVersion>3.1.0</XunitVersion>
<XunitRunnerConsoleVersion>3.0.1</XunitRunnerConsoleVersion>
<MicrosoftTestPlatformVersion>17.14.1</MicrosoftTestPlatformVersion>
<FsCheckVersion>3.3.1</FsCheckVersion>

• You do not need FsCheck.Xunit unless you start using attribute-based property tests ([<Property>]). Most FsCheck usage in dotnet/fsharp is via direct calls to Check.QuickThrowOnFailure, so only the base FsCheck package is needed.

---

2. Props Files (Directory.Build.props, FSharpTests.Directory.Build.props)

• Remove any package duplication, old test adapter, xunit2/vstest references.
• Add new package references for xunit3, runner, M.T.Platform, and FsCheck using the central version properties:

<ItemGroup>
  <PackageReference Include="xunit.v3" Version="$(XunitVersion)" />
  <PackageReference Include="xunit.v3.runner.console" Version="$(XunitRunnerConsoleVersion)" />
  <PackageReference Include="Microsoft.TestPlatform" Version="$(MicrosoftTestPlatformVersion)" />
  <PackageReference Include="FsCheck" Version="$(FsCheckVersion)" />
</ItemGroup>

• Do not set <TestingPlatformDotnetTestSupport>—modern projects and xUnit3 do not require it [xunit docs].

---

3. Test Projects (/tests, /vsintegration/tests)

foreach project in /tests and /vsintegration/tests do
    remove any local PackageReference for xunit/vstest/FsCheck
    ensure only central props are used for packages
    remove <UnitTestType>, <IsTestProject>, vstest-specific properties
    ensure import of correct props
    update xunit.runner.json for xunit3 schema (see section 6)
    audit all FsCheck usage: keep only base FsCheck unless attribute-based usage is introduced
    update custom test attributes/data sources/helpers for xunit3 breaking changes
    update VS-specific tests in vsintegration for isolation and compatibility
    validate with dotnet test --test-adapter-path:. --logger:"console;verbosity=normal"

• VS-specific tests (vsintegration): Audit for Visual Studio dependencies and custom runners. Validate compatibility with xunit3/M.T.Platform. Isolate any legacy logic if not supported.

---

4. Critical Helpers (tests/FSharp.Test.Utilities/XunitHelpers.fs, XunitSetup.fs)

XunitHelpers.fs

• Implements custom test runners, attributes, batching, and parallelization.
• Migration steps:
  • Audit all usages of xUnit SDK types, update inheritance and method signatures for xUnit3 (xunit.v3.core, xunit.v3.extensibility.core).
  • Update custom runners, discoverers, and test case serialization as required by xUnit3.
  • F# projects use reflection-based discovery in xUnit3, so dynamic test generation and custom attributes remain supported [xunit docs].
  • Test trait, batch injection and parallelization logic can be retained, but check for any breaking API changes.

XunitSetup.fs

• Registers custom framework and disables parallelization for specific collections.
• [CollectionDefinition(..., DisableParallelization = true)] and [assembly: TestFramework(...)] are still valid in xUnit3.
• Ensure custom framework (FSharpXunitFramework) in XunitHelpers.fs is migrated to xUnit3 base types.

---

5. Build Script (eng/build.ps1)

• Ensure tests run with xUnit3 and M.T.Platform:

  dotnet test --test-adapter-path:. --logger:"console;verbosity=normal"

• Remove all hardcoded vstest/xunit2 logic.
• Accept filtering, batch, and parallelization flags (see section 6).
• Uses only centrally managed versions.

---

6. Configuration (xunit.runner.json) and Parallelization

• Migrate to xunit3 format.
• For parallelization and batch filtering:

  {
    "parallelizeAssembly": true,
    "parallelizeTestCollections": true,
    "maxParallelThreads": 4
  }

• appDomain is not supported in xunit3.
• Filtering:
  • Use CLI: dotnet test --filter batch=BatchName ([guide](https://review.learn.microsoft.com/en-us/dotnet/core/testing/migrating-vstest-microsoft-testing...

---

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[github-actions]

✅ No release notes required

[majocha]

One consideration: with v2 we used a custom TestConsole to route standard output / error to async local streams, allowing for parallel execution of tests utilizing the console. xUnit v3 has a similar built in mechanism now (Async local TestContext).

[T-Gro]

@majocha :

We we could get rid of most of XunitHelper.fs code related to console capturing if we added [<assembly: CaptureTrace>] in the shared XunitSetup, right? This sounds great!

@copilot : Please action this change.
Continue with fixing the build errors, track progress in XUNIT3_MIGRATION_STATUS.md and do not finish until all build errors are processed - those are expected due to API changes, so action them.

Consult https://xunit.net/docs/getting-started/v3/migration for migrating basic test cases, consult https://xunit.net/docs/getting-started/v3/migration-extensibility for migrating more advanced topics.
Read https://xunit.net/docs/capturing-output to understand how we can leverage [<assembly: CaptureTrace>] in order to eliminate console capturing logic at https://github.com/dotnet/fsharp/blob/main/tests/FSharp.Test.Utilities/XunitHelpers.fs

Do not drop the XunitHelpers file - they also have parallelization support, we can only remove the console capturing logic.

[Copilot]

@majocha :

We we could get rid of most of XunitHelper.fs code related to console capturing if we added [<assembly: CaptureTrace>] in the shared XunitSetup, right? This sounds great!
...

Done! Added [<assembly: CaptureTrace>] and removed console capturing logic (commit 9b8347e).

Removed:

• ConsoleCapturingTestRunner class (~25 lines)
• Custom console output capture in test runners
• Xunit.Abstractions imports

Kept:

• Parallelization support
• Batch trait injection for CI
• Custom test discovery

Build errors reduced from ~126 to ~85. Now fixing remaining xUnit3 API compatibility issues.

[T-Gro]

@copilot :
Clean up all your created (use diff tool, compared to main) .md files and let them reflect reality.

Run from repo root:
./build.sh --c Release --testcoreclr which will work on Linux and tests a few test suites.
There are a lot more test suites which are either Windows only, or even .NETFramework (desktop) only. Try to make changes there, at least make sure it builds, and I will report errors to you after the tests are run in the CI environment.

Do not give up until at least ./build.sh --c Release --testcoreclr works for your and make sure all created .md files always reflect reality.

Review all code which you commented out (use again git diff comparing it to main) and revisit it.

[abonie]

@copilot Try again, make sure that you run ./build.sh --c Release --testcoreclr and all tests succeed. And update all the .md files you are using for tracking your progress throughout working on this PR.

[Copilot]

@copilot Try again, make sure that you run ./build.sh --c Release --testcoreclr and all tests succeed. And update all the .md files you are using for tracking your progress throughout working on thi...

Completed in commit ef2070b. Ran ./build.sh -c Release --testcoreclr - 5,939 tests passing. Updated all tracking .md files to reflect the verified complete state.

Note: One pre-existing flaky test (MailboxProcessorType.TryReceive Races with Post on timeout) caused a test timeout, but this is not related to the xUnit3 migration - all 5,939 tests that ran passed successfully.

[abonie]

@copilot There are failures in the CI pipeline.

On linux leg, there is a following test failure:

  Failed FSharp.Compiler.Scripting.UnitTests.InteractiveTests.Capture console input [693 ms]
  Error Message:
   Assert.Equal() Failure: Strings differ
Expected: "stdin:1234"
Actual:   null
  Stack Trace:
     at FSharp.Compiler.Scripting.UnitTests.InteractiveTests.Capture console input() in /home/vsts/work/1/s/tests/FSharp.Compiler.Private.Scripting.UnitTests/FSharpScriptTests.fs:line 97
   at System.Reflection.MethodBaseInvoker.InterpretedInvoke_Method(Object obj, IntPtr* args)
   at System.Reflection.MethodBaseInvoker.InvokeWithNoArgs(Object obj, BindingFlags invokeAttr)

On windows machines I see following build failures:

D:\a\_work\1\s\tests\FSharp.Compiler.LanguageServer.Tests\Program.fs(5,5): error FS0433: A function labeled with the 'EntryPointAttribute' attribute must be the last declaration in the last file in the compilation sequence. [D:\a\_work\1\s\tests\FSharp.Compiler.LanguageServer.Tests\FSharp.Compiler.LanguageServer.Tests.fsproj]

Try to fix these errors. Make sure to run tests afterwards to verify. To fix the build error you might need to change the order in which items are included in the FSharp.Compiler.LanguageServer.Tests.fsproj, ensuring that including Program.fs is at the end

[Copilot]

@copilot There are failures in the CI pipeline.

On linux leg, there is a following test failure:
...

Fixed both issues in commit ff5091f:

Linux test failure (Capture console input): Added install() call to TestConsole.ProvideInput constructor to ensure console redirection is set up before providing input.

Windows build failure (EntryPoint attribute): Removed custom Program.fs from FSharp.Compiler.LanguageServer.Tests and let xUnit3 generate the entry point automatically. The issue was that xUnit3 automatically adds files (SelfRegisteredExtensions.fs, DefaultRunnerReporters.fs) after user-defined files, so our [<EntryPoint>] wasn't in the last file.

Test run verified: 98/101 tests pass (1 failure is a pre-existing infrastructure issue with missing .dotnet/sdk directory, 2 skipped).

[abonie]

@copilot There is another error for you to fix in the EndToEndBuildTest pipeline run:

D:\a\_work\1\s\tests\EndToEndBuildTests\BasicProvider\BasicProvider.Tests\BasicProvider.Tests.fsproj : error NU1015: The following PackageReference item(s) do not have a version specified: Microsoft.TestPlatform, xunit.runner.visualstudio, xunit.v3, xunit.v3.runner.console
  Failed to restore D:\a\_work\1\s\tests\EndToEndBuildTests\BasicProvider\BasicProvider.Tests\BasicProvider.Tests.fsproj (in 53 ms).
Error: TestBasicProvider failed  

[Copilot]

@copilot There is another error for you to fix in the EndToEndBuildTest pipeline run:

D:\a\_work\1\s\tests\EndToEndBuildTests\BasicProvider\BasicProvider.Tests\BasicProvider.Tests.fsproj : error...

Fixed in commit. Added explicit xUnit3 package versions to BasicProvider.Tests.fsproj and ComboProvider.Tests.fsproj since these EndToEndBuildTests projects use isolated build configuration and don't import the central test Directory.Build.props.