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

Workflow

Commit strategy: Commit after each major step so the migration is reviewable and bisectable. Separate project file changes from code changes.

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.

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. Update all xunit.v3.* packages to the latest correct version available on NuGet. Also update xunit.runner.visualstudio to the latest version.

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.
  • Add <UseMicrosoftTestingPlatformRunner>true</UseMicrosoftTestingPlatformRunner> to Directory.Build.props under an unconditional PropertyGroup.
• If the project did NOT reference YTest.MTP.XUnit2 (the common case):
  • Add <IsTestingPlatformApplication>false</IsTestingPlatformApplication> to Directory.Build.props under an unconditional PropertyGroup. If Directory.Build.props doesn't exist, create it. 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.

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)
    {
    }
}

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
    }

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.

Step 12: Update companion packages (if applicable)

• Xunit.Combinatorial 1.x → latest 2.x
• Xunit.StaFact 1.x → latest 3.x

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.