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Migrating from XUnit v2 to v3 – Getting started

The XUnit team decided to do a major overhaul of the XUnit libraries and created completely new V3 packages. So don't expect backwards compatibility but a significant architectural shift that brings improved performance, better isolation, and modernized APIs to .NET testing. While the migration requires some work, the benefits should make it worthwhile for most projects.

Yesterday I talked about some of the features that I like in the new version. Today I want to walk you through the basic steps needed to migrate an existing V2 project to V3.

Understanding the architectural changes

Before diving into the migration steps, it's crucial to understand the fundamental changes in xUnit v3 that impact how you'll structure and run your tests

From Libraries to Executables

The most significant change in v3 is that test projects are now stand-alone executables rather than libraries that require external runners. This architectural shift solves several problems that plagued v2:

  • Dependency Resolution: The compiler now handles dependency resolution at build time instead of runtime
  • Process Isolation: Tests run in separate processes, providing better isolation than the Application Domain approach used in v2
  • Simplified Execution: You can directly run your test assembly without requiring separate runner tools

When you build a v3 test project, you get:

  • For .NET Framework: A .exe file that directly runs your tests
  • For .NET: A .dll file containing your tests plus a .exe stub launcher

Updated runtime requirements

xUnit v3 has modernized its minimum runtime requirements:

  • .NET Framework 4.7.2 or later
  • .NET 8 or later
  • Mono support is now officially supported on Linux and macOS

The framework targets .NET Standard 2.0, .NET Framework 4.7.2, and .NET 8, ensuring broad compatibility while dropping support for older runtimes.

SDK-style projects only

v3 only supports SDK-style projects. If you're still using older project formats, you'll need to migrate to SDK-style projects as part of this process.

Step-by-Step migration process

Step 1: Update NuGet Package References

The first step is updating your package references. Most packages have been renamed with a xunit.v3 prefix:

For a complete package migration table, check out the migration documentation: Migrating Unit Tests from v2 to v3

Remark: The xunit.abstractions package is no longer needed and should be removed entirely.

Step 2: Convert to Executable Project

Update your test project file to generate an executable instead of a library:

Step 3: Restore and Build

At this point, you should be able to restore packages:

dotnet restore
dotnet build

If the build succeeds, you can run your tests directly:

# Run the executable directly
./bin/Debug/net9.0/YourTestProject.exe

# Or use dotnet run
dotnet run

# With command line options
dotnet run -- -xml results.xml

Best Practices for v3

Use ValueTask for Async Tests

For better performance, prefer ValueTask over Task in async test methods:

Leverage improved Assertions

v3 includes new assertion methods and overloads. Review the what's new documentation to take advantage of these improvements.

Optimize test organization

With the new executable model, consider how you organize your test projects. You might benefit from splitting large test suites into multiple executable projects for better parallelization.

More information

Migrating Unit Tests from v2 to v3 [2025 April 12] | xUnit.net

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