nw-mutation-test

Feature-scoped mutation testing validates test-suite effectiveness by injecting faults into implementation files. You invoke it by specifying a feature-id and target scope, requiring an execution-log.json and a prepared mutation workflow to generate a dedicated mutation report.

Mutation testing tools vary by language: cosmic-ray for Python, PIT for Java, and Stryker for JavaScript and TypeScript. The appropriate tool is selected automatically by detecting the language from your project configuration.

Mutation testing matters for feature delivery because it validates that test coverage is meaningful, ensuring bugs are actually caught. It assesses test-suite effectiveness after implementation rather than just measuring line coverage.

Yes, you need an execution-log.json containing implementation file lists and a prepared mutation workflow before running. These prerequisites define the feature scope and ensure the mutation tool targets the correct files.

The mutation testing report is saved as a markdown file at docs/feature/{feature-id}/deliver/mutation/mutation-report.md. This dedicated location organizes results per feature for quality assurance tracking.

Yes, mutation testing detects real bugs by applying small changes to your code and checking if your tests catch them. If tests pass despite mutations, it indicates gaps in test-suite effectiveness that need attention.