mstest

MSTest.Sdk 4.5 and Microsoft.Testing.Platform 2.5 make the UWP or WinUI 3 app the test host itself. [UITestMethod] runs each test on the real dispatcher, packaged and AppContainer apps are activated by AUMID through a sidecar controller, and unpackaged WinUI finally works.

MSTest 4.4.0 added Span<T> and ReadOnlySpan<T> overloads to Assert.Contains and Assert.DoesNotContain, which made ordinary array and string assertions fail with CS0121 on net8.0, net9.0, or any project below C# 14. MSTest 4.4.1, published on 2026-09-16, adds exact array overloads and constrained forwarders. Two explicit-generic call shapes still fail.

MSTest 4.4 moves MSTest.SourceGeneration out of experimental and aligns it with the MSTest version. Native AOT test projects pick it up with no opt-in, ReflectionFree mode can now skip runtime discovery for plain [TestMethod] and [DataRow], and five AOTSG diagnostics tell you which test shapes will not survive.

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.