xUnit.net v3 is a mature, open-source unit testing framework for .NET (C#, F#, VB). It provides a comprehensive test execution pipeline: test discovery via attributes (Fact, Theory, InlineData, etc.), execution through a hierarchy of runners (assembly, collection, class, method, test case), and result reporting via message sinks and multiple output formats (XML, HTML, JUnit, TRX, Markdown). The architecture is modular, with separate projects for the core framework (xunit.v3.core), runner infrastructure (xunit.v3.runner.common), console runner (xunit.v3.runner.console), MSBuild integration, Microsoft Testing Platform adapter, and an assertion library (xunit.v3.assert). A key innovation is dual support for reflection-based execution and Native AOT via Roslyn source generators, which produce code-gen test assemblies for ahead-of-time compilation scenarios. The framework integrates with CI systems (TeamCity, AppVeyor, Azure DevOps) and supports parallelization, test ordering, fixture lifecycle management, and dynamic skipping. External dependencies include the .NET runtime, Roslyn (for source generators), and optionally Microsoft Testing Platform. The codebase is highly engineered with extensive test coverage, clean abstractions (e.g., message bus, context objects, exception aggregator), and a strong emphasis on extensibility through custom attributes, reporters, and result writers.

This repository contains Roslyn diagnostic analyzers and code fix providers for the xUnit.net test framework (v2 and v3, including Native AOT). It enforces best practices, detects common anti-patterns (e.g., misuse of Assert methods, serialization issues with theory data, incorrect async handling, and structural problems in test classes), and provides automated code fixes. The codebase is organized around version-aware context classes (XunitContext) that resolve xUnit types and version-specific behavior, allowing a single analyzer to target multiple xUnit versions. It includes a rich test suite using a custom CSharpVerifier base class, building on Microsoft.CodeAnalysis.Testing. The infrastructure is well-abstracted with reusable base classes for analyzers, suppressors, and fix providers, and the project is packaged as a NuGet package automatically referenced by xUnit projects.