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

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:

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);
        // Possibly some custom logic here
    }

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

it must be changed to this:

    public override void Before(MethodInfo methodUnderTest, IXunitTest test)
    {
        // Possibly some custom logic here
        base.Before(methodUnderTest, test);
        // Possibly some custom logic here
    }

    public override void After(MethodInfo methodUnderTest, IXunitTest test)
    {
        // Possibly some custom logic here
        base.After(methodUnderTest, test);
        // Possibly some custom logic here
    }

Keep the BeforeAfterTestAttribute base class, retain the override modifiers, and preserve the existing base calls and their ordering relative to custom logic. Implementing IBeforeAfterTestAttribute directly may compile, but it is not the mechanical v2-to-v3 migration and can discard base-class behavior.

Before reporting completion, read the resulting attribute file and quote the actual Before(MethodInfo, IXunitTest) and After(MethodInfo, IXunitTest) signatures. Explicitly confirm that both base.Before and base.After receive the same IXunitTest argument; a generic claim that the overrides were updated is insufficient evidence.

Step 10: Address new xUnit analyzer warnings (if applicable)

xunit.v3 introduced new analyzer warnings. The most notable is xUnit1051 (use TestContext.Current.CancellationToken for methods accepting CancellationToken). Address these if present.

Step 11: Migrate Xunit.SkippableFact (if applicable)

If there are any package references to Xunit.SkippableFact, remove all these package references entirely.

Then, follow these steps to eliminate usages of APIs coming from the removed package reference:

• Update any SkippableFact attribute to the regular Fact attribute.
• Update any SkippableTheory attribute to the regular Theory attribute.
• Change Skip.If method calls to Assert.SkipWhen.
• Change Skip.IfNot method calls to Assert.SkipUnless.

Verify both branches when the fixture makes that practical: the default condition should report the intended skip reason, and the enabled condition should execute and pass. A grep plus a generic passing run does not prove the runtime skip semantics were preserved.

Limit this conversion to the existing project/central-package file and the source files containing these APIs. Do not create a new Directory.Build.props merely to perform this companion-package migration; any required runner property belongs in the existing test project when no shared props file already exists.

Step 12: Update companion packages (if applicable)

• Query the configured feeds for a mutually compatible set instead of resolving each package independently. Xunit.Combinatorial 1.x moves to 2.x or later, and Xunit.StaFact 1.x moves to a line compatible with the selected xunit.v3 major.
• Do not infer companion compatibility from the product name or matching major numbers. Use package dependency constraints and the versions available on the configured feeds, then prove the selected set through test discovery.
• On net*-windows projects built from Linux/macOS after switching to executable output, set EnableWindowsTargeting=true if cross-targeting is intended.
• Run tests and confirm expected platform skips (such as STA tests on Linux) separately from failures.

Step 13: Build and verify

Build the solution and fix any remaining compilation errors. Run dotnet test to verify all tests pass with the same results as before migration.