xUnit v3 vs NUnit vs MSTest in 2026: which should you pick?

Pick xUnit v3 for greenfield .NET projects, NUnit 4.6 if you live in its constraint model, MSTest 4 if you already ship it. A measured comparison on .NET SDK 10.0.201 covering parallelism defaults, test class lifecycle, assertion failure output, and the Microsoft.Testing.Platform version conflict that breaks the NUnit runner.