[ExtraToast]

A reusable workflow that shows, on a pull request, which mutants survive on the lines it changes. A surviving mutant is a line a test runs but never checks: the code changed, and no test failed. This is the diff-scoped mutation report from the estate testing standard (ADR-0022).

• mutation-report.yml. The caller passes go-directory, web-directory, or both.
  • Go runs gremlins unleash --diff origin/<base> (gremlins v0.6.0 by default).
  • TypeScript and Vue run Stryker with --mutate set to the changed source files under src. Specs, generated clients and *.gen.ts are left out.
  • The toolchain comes from the caller's mise.toml. Stryker runs through the caller's own devDependencies, so it uses the project's vitest.
• One comment per pull request. It is found again by a marker line and edited on the next run, and the same text goes to the job summary. Both tools' steps are continue-on-error, so the report never fails the build. Whether it becomes a gate, and at which threshold, is decided later.
• scripts/mutation_report.py turns gremlins' JSON (LIVED, NOT COVERED) and Stryker's mutation-testing-report JSON (Survived, NoCoverage) into that comment. Survivors are sorted by file and line, and mutants no test reaches get their own section. A missing report counts as no mutants, and an unreadable one is named in the comment. Its tests follow the testing standard: one behaviour per test, named as a sentence. CI holds the script to 100% line and branch coverage, like path_buckets.py.
• Release. release-please keeps the self-checkout ref in step with the tag, as for the other reusable workflows.
• Billing. One job with steps, so a pull request pays for one runner-minute block, not one per tool.

Part of JorisJonkers-dev/workspace#128. #155 closes once identity calls a released version and a deliberately weak test shows up as a survivor.

Checks

• tests/test_mutation_report.py: 14 tests, 100% line and branch coverage.
• All 190 tests in tests/ pass.
• actionlint passes on both changed workflows.