nw-mutation-test

Feature-scoped mutation testing verifies your test suite's strength by injecting intentional faults into a feature's implementation files and measuring the kill rate of those mutations to see if your tests detect real bugs.

To run mutation testing for a feature, invoke the workflow with a feature-id. It supports Python via cosmic-ray, Java via PIT, and JavaScript, TypeScript, or C# via Stryker to generate per-feature mutation reports.

Yes, mutation testing supports Java codebases using PIT and JavaScript, TypeScript, or C# codebases using Stryker, applying language-appropriate tools to generate mutation reports for feature-based implementations.

Before running feature mutation testing, you need extracted implementation files, on-disk verification, language detection, and passing tests to satisfy pre-invocation checks for the selected feature.

The mutation testing report is saved as a markdown file at docs/feature/{feature-id}/deliver/mutation/mutation-report.md, providing analysis and traceability for the evaluated feature's test suite.

The best way to validate that your Python tests detect real bugs is through mutation testing, which uses cosmic-ray to inject faults into your implementation files and measures whether your test suite catches them.