mutation.yml

name: Mutation

# NIGHTLY AND NON-GATING, deliberately. It re-runs the whole suite once per
# mutant, which is minutes rather than the seconds a commit gate can spend, and a
# survivor is information rather than a reason to block a merge.
#
# The mutants are committed (test/mutation/mutants.json) rather than generated. A
# list written by the author of the tests contains the mutations those tests
# already catch: an author-written set scored 18/18 on this package while an
# independent sweep found ten survivors. A list a reviewer can read is the part
# that makes the score mean anything.
#
# The Python SDK carries the same job and the same file shape. This is one
# command with two implementations, and the two should stay comparable.
on:
  schedule:
    - cron: '51 4 * * *'
  workflow_dispatch:
  # On demand from a PR too, because the moment a mutant is worth adding is the
  # moment a defect is being fixed.
  pull_request:
    paths:
      - 'test/mutation/**'

jobs:
  mutate:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v7
      - uses: actions/setup-node@v7
        with:
          node-version: 22
          cache: npm
      - run: npm ci
      # The suite must be green BEFORE anything is mutated, or every mutant
      # "survives" against an already-red suite and the run means nothing.
      - name: Baseline
        run: npx vitest run test/unit
      - name: Mutate
        id: mutate
        continue-on-error: true
        run: node test/mutation/run.mjs | tee "$GITHUB_STEP_SUMMARY"
      - name: Say so in the log when something survived
        if: steps.mutate.outcome == 'failure'
        run: |
          echo "::warning::A mutant survived or went stale — see the job summary."
          echo "Not a failure: a survivor is a gap to close, not a merge to block."