Configures and runs xUnit.net (xUnit v2 + v3) - current de facto .NET test framework with `[Fact]` for single tests + `[Theory]` + `[InlineData]`/`[ClassData]`/`[MemberData]` for parametrized; collection fixtures (`[Collection]`) + class fixtures (`IClassFixture`) for shared setup; output via `ITestOutputHelper`; parallel test config via assembly attribute. Use when working with .NET (C# / F# / VB.NET) on the modern test stack.