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CI Integration

GitHub Actions

A minimal workflow that gates on mutation score:

name: Mutation Testing
on:
  push:
    branches: [master]
  pull_request:

jobs:
  mutating:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v6
      - uses: actions/setup-go@v6
        with:
          go-version: stable
      - run: go build -o /tmp/go-mutesting ./cmd/go-mutesting
      - run: |
          /tmp/go-mutesting \
            --coverage \
            --min-msi 70 \
            --min-covered-msi 80 \
            --logger-github \
            ./...

--logger-github emits escaped mutants as ::warning annotations that appear inline on the PR diff.

For high-assurance environments, pin actions to full commit SHAs instead of version tags and enable Dependabot to keep the pins current automatically.

Adopting gates on a legacy codebase

If you have existing surviving mutants, record them first so CI doesn't fail on day one:

# Run once locally to record the current state
go-mutesting --update-baseline ./...
git add go-mutesting-baseline.json
git commit -m "chore: establish mutation baseline"

Then in CI, only fail when something new escapes:

- run: |
    /tmp/go-mutesting \
      --baseline go-mutesting-baseline.json \
      --fail-on-escaped \
      ./...

Once you've written tests to kill the known survivors, remove them from the baseline with --update-baseline and tighten the gate.

PR-only mode (changed lines only)

Limit mutation to lines changed in the PR to keep feedback fast and relevant:

- run: |
    /tmp/go-mutesting \
      --git-diff-lines \
      --git-diff-base origin/master \
      --ignore-msi-with-no-mutations \
      --min-msi 80 \
      --logger-github \
      ./...

--ignore-msi-with-no-mutations exits 0 cleanly when the PR touches no mutable code (docs-only PRs, etc.).

Exit codes

Code Meaning
0 Gates passed (or no mutations generated with --ignore-msi-with-no-mutations)
1 Internal error
4 A quality gate was not met

Use || true only when you want advisory-only output (no gate enforcement).

Maturity --min-msi --min-covered-msi
Legacy/brownfield — (baseline only) —
Active development 60 75
Stable library 75 85
High-assurance 90 95