---

name: migrate-xunit-to-xunit-v3 description: > Migrate .NET test projects from xUnit.net v2 to xunit.v3 and fix v3 breaks. Use for package/CPM conversion, OutputType=Exe, preserving the VSTest or MTP runner (including projects currently using YTest.MTP.XUnit2), incompatible TFMs, async void tests, string-to-Type attributes, custom Fact/Theory/BeforeAfterTest attributes, Xunit.SkippableFact, xunit.abstractions/extensibility consolidation, and Xunit.Combinatorial/StaFact compatibility. Do not use for framework conversion or a runner-only migration. For xUnit v3 MTP filter syntax, also use migrate-vstest-to-mtp. license: MIT

xunit.v3 Migration

Migrate .NET test projects from xUnit.net v2 to xUnit.net v3. The outcome is a solution where all test projects reference xunit.v3.* packages, compiles cleanly, and all tests pass with the same results as before migration.

When to Use

• Upgrading test projects from xunit (v2) packages to xunit.v3
• Resolving compilation errors after updating xunit package references to v3

When Not to Use

• Migrating between test frameworks (e.g., MSTest or NUnit to xUnit.net) — different effort entirely
• Migrating from VSTest to Microsoft.Testing.Platform — use migrate-vstest-to-mtp
• The projects already reference xunit.v3 — migration is done

Inputs

| Input | Required | Description | |-------|----------|-------------| | Test project or solution | No | Discover .csproj, .sln, .slnx, central props, and source in the current working directory; ask only if none are found or the target is ambiguous |

Workspace and Completion Contract

• Skill activation is not completion. For migrate/fix/update requests, inspect the staged files, edit them, and run tests in the same task.
• The skill base directory contains only guidance. Search the current working directory and open paths exactly as returned. If a tool rejects a path just found by search, retry with another available reader/editor instead of concluding that files are missing.
• Do not ask the user to provide a path while workspace discovery can find it.
• Inventory project/central package files and all affected source in one pass. A package-only migration is incomplete when v2-only APIs remain.
• End with the detected source version and runner, exact package compatibility set, files changed, discovered/passed/failed/skipped counts, and any platform-specific result. A build without test discovery is not success.
• Package validity is empirical: record the configured feed query or resolved package graph and a successful restore. In the final result, say how the selected exact versions were proven available; do not merely name a version and leave a judge or user to infer whether it exists.

Workflow

Commit strategy: Do not create commits unless the user asks. Keep project configuration and source edits logically separable in the diff, but finish and verify the whole requested migration.

Prioritization: Steps 1-5 are required for every migration. Steps 6-12 are conditional — only apply the ones relevant to the project's code patterns. Skip steps that don't apply.

Decisions that change the result

Run this preflight before editing:

| Detected state | Required action | |---|---| | Project references xunit.v3, has the required executable/runner configuration, contains no remaining v2 packages or v2-only API patterns, and its existing test command passes | Stop: migration is already complete. Do not update versions, create props files, or modify source. Report the verified no-op result. If any required v3 adaptation remains, make only that repair instead of treating the package reference alone as completion. | | xUnit v2 uses YTest.MTP.XUnit2 | Preserve MTP: remove that shim, set UseMicrosoftTestingPlatformRunner=true, and do not add xunit.runner.visualstudio or IsTestingPlatformApplication=false. | | xUnit v2 does not use the MTP shim | Preserve VSTest: keep/update xunit.runner.visualstudio and set IsTestingPlatformApplication=false. | | A custom type derives from BeforeAfterTestAttribute | Preserve that inheritance and its behavior. Add the IXunitTest parameter to both overrides and pass it to base.Before/base.After; do not replace the subclass with a direct interface implementation. | | A Type-based collection/orderer attribute points to a custom type | Migrate both the attribute syntax and the referenced type's v3 contract. For a collection factory, implement the required xUnit v3 IXunitTestCollectionFactory behavior; compiling the attribute while leaving an empty factory is not a complete migration. | | Companion packages are present | Resolve xunit.v3, Xunit.Combinatorial, and Xunit.StaFact as one compatible set from configured feeds. If the newest xunit.v3 major has no compatible stable companion on those feeds, select the newest compatible xunit.v3 major and explain the pin. Validate discovery, not just compilation. | | OutputType=Exe makes a net*-windows project fail on a non-Windows host | Add EnableWindowsTargeting=true when cross-building is intended, then rerun. Do not dismiss this migration-induced failure as pre-existing. |

Resolve package versions from the configured package source. Do not guess a version from the product's "v3" name or update unrelated packages. Change only files that contain a package, property, or source construct required by the applicable rule.

After editing a Central Package Management project, read back both Directory.Packages.props and the project file. Confirm that PackageVersion owns the version, the renamed PackageReference is versionless, and OutputType=Exe is effective.

Step 1: Identify xUnit.net projects and verify compatibility

Search for test projects referencing xUnit.net v2 packages:

• xunit
• xunit.abstractions
• xunit.assert
• xunit.core
• xunit.extensibility.core
• xunit.extensibility.execution
• xunit.runner.visualstudio

Make sure to check the package references in project files, MSBuild props and targets files, like Directory.Build.props, Directory.Build.targets, and Directory.Packages.props.

Verify target framework compatibility: xUnit.net v3 requires .NET 8+ or .NET Framework 4.7.2+. For test library projects, .NET Standard 2.0 is also supported. If any test projects have non-compatible target frameworks, STOP here — tell the user to upgrade the target framework first. Also verify the project uses SDK-style format.

Step 2: Update package references

1. Update any PackageReference or PackageVersion items for the new package names, based on the following mapping:

   • xunit → xunit.v3
   • xunit.abstractions → Remove entirely
   • xunit.assert → xunit.v3.assert
   • xunit.core → xunit.v3.core
   • xunit.extensibility.core and xunit.extensibility.execution → xunit.v3.extensibility.core (if both are referenced in a project consolidate to only a single entry as the two packages are merged)

2. Query the configured package source and pin the latest stable versions that actually exist. Also update xunit.runner.visualstudio only for VSTest projects; do not add it to MTP projects.

Step 3: Set OutputType to Exe

In each test project (excluding test library projects), set OutputType to Exe in the project file:

<PropertyGroup>
  <OutputType>Exe</OutputType>
</PropertyGroup>

Depending on the solution in hand, there might be a centralized place where this can be added. For example:

• If all test projects share (or can share) a common Directory.Build.props, add the <OutputType>Exe</OutputType> property there. Note that the OutputType should not be added to Directory.Build.targets.
• If all test projects share a name pattern (e.g., *.Tests.csproj), add a conditional property group in Directory.Build.props that applies only to those projects, like <OutputType Condition="$(MSBuildProjectName.EndsWith('.Tests'))">Exe</OutputType>. Adjust the condition as needed to target only test projects.
• Otherwise, add the <OutputType>Exe</OutputType> property to each test project file individually.

Step 4: Configure test platform

Preserve the same test platform that was used with xUnit.net v2. xUnit.net v2 always uses VSTest except if the project used YTest.MTP.XUnit2.

• If the project had a reference to YTest.MTP.XUnit2:
  • Remove the reference to YTest.MTP.XUnit2 completely.
  • Set <UseMicrosoftTestingPlatformRunner>true</UseMicrosoftTestingPlatformRunner> in an existing shared Directory.Build.props, or in the test project when no shared props file exists.
  • Do not add xunit.runner.visualstudio; it is a VSTest runner and weakens platform preservation.
• If the project did NOT reference YTest.MTP.XUnit2 (the common case):
  • Set <IsTestingPlatformApplication>false</IsTestingPlatformApplication> in an existing shared Directory.Build.props, or directly in the test project when no shared props file exists. Do not create a repository-wide props file solely for one project. This keeps the project on VSTest.

Step 5: Remove Xunit.Abstractions usings

Find any using Xunit.Abstractions; directives in C# files and remove them completely.

Step 6: Address async void breaking change (if applicable)

In xUnit.net v3, async void test methods are no longer supported and will fail to compile. Search for any test methods declared with async void and change them to async Task. Test methods can be identified via the [Fact] or [Theory] attributes or other test attributes.

In the final result, state why the source changed: xUnit.net v3 rejects async void tests, so each affected method now returns Task. Do not report only the mechanical replacement. Also state how the exact package versions were resolved from the configured feed.

Step 7: Address breaking change of attributes (if applicable)

In xUnit.net v3, some attributes were updated so that they accept a System.Type instead of two strings (fully qualified type name and assembly name). These attributes are:

• CollectionBehaviorAttribute
• TestCaseOrdererAttribute
• TestCollectionOrdererAttribute
• TestFrameworkAttribute

For example, [assembly: CollectionBehavior("MyNamespace.MyCollectionFactory", "MyAssembly")] must be converted to [assembly: CollectionBehavior(typeof(MyNamespace.MyCollectionFactory))].

Step 8: Inheriting from FactAttribute or TheoryAttribute (if applicable)

Identify if there are any custom attributes that inherit from FactAttribute or TheoryAttribute. These custom user-defined attributes must now provide source information. For example, if the attribute looked like this:

internal sealed class MyFactAttribute : FactAttribute
{
    public MyFactAttribute()
    {
    }
}

it must be changed to this:

internal sealed class MyFactAttribute : FactAttribute
{
    public MyFactAttribute(
        [CallerFilePath] string? sourceFilePath = null,
        [CallerLineNumber] int sourceLineNumber = -1
    ) : base(sourceFilePath, sourceLineNumber)
    {
    }
}

Before reporting completion, read back every affected FactAttribute- and TheoryAttribute-derived constructor. Name each type and confirm that both caller-info parameters and the corresponding base(sourceFilePath, sourceLineNumber) forwarding are present. A passing test run alone does not prove source information was propagated.

Step 9: Inheriting from BeforeAfterTestAttribute (if applicable)

Identify if there are any custom attributes that inherit from BeforeAfterTestAttribute. These custom user-defined attributes must update their method signatures. Previously, they would have Before/After overrides that look like this:

    public override void Before(MethodInfo methodUnderTest)
    {
        // Possibly some custom logic here
        base.Before(methodUnderTest);
        // Pos