Quick Start

1. Install

go install github.com/jonbaldie/go-mutesting/v2/cmd/go-mutesting@latest

2. Run against your package

go-mutesting ./...

Each mutation prints PASS (killed — tests detected it) or FAIL (escaped — tests missed it). Escaped mutants print a diff showing exactly what changed.

3. Add coverage-awareness

Without --coverage, uncovered code inflates the "not covered" bucket and can produce a misleadingly low MSI. With it, mutants on untested lines are separated out and excluded from the covered-MSI denominator.

go-mutesting --coverage ./...

4. Set quality gates

go-mutesting --coverage --min-msi 70 --min-covered-msi 80 ./...

Exit code 4 means a gate wasn't met. Exit code 0 means all gates passed.

5. Reduce noise

Use --quiet to suppress killed/skipped output and only show escaped mutants and the summary.

go-mutesting --quiet --coverage ./...

6. Limit to changed lines (PR mode)

go-mutesting \
  --git-diff-lines \
  --git-diff-base main \
  --ignore-msi-with-no-mutations \
  --min-msi 80 \
  ./...

7. Get LLM-ready suggestions

go-mutesting --logger-agentic-json --quiet ./...
# Feed go-mutesting-agentic.json to an LLM for targeted test suggestions.