Mutation
Modifies your source code to verify your tests actually catch bugs. Runs via the GitHub Action because it executes your test suite; the website-only Forensic scan does not include it.
One of 122 modules in the GateTest scan suite. Catches the issue before it reaches code review, and on paid tiers opens a pull request with the fix already written.
Mutated return true → return false, 11/11 tests still pass
Why we catch it
Where deterministic scanning stops and reasoning starts. Used sparingly, not by default.
The Mutation module sits in this category alongside 6 related modules. Together they form one of the layers of a GateTest scan — checks fire in parallel, findings cluster by root cause, and on paid tiers the AI auto-fix loop reads each finding, writes the fix, validates against the scanner, and opens a PR.
How GateTest covers mutation
- Runs where your CI runs. The CLI and the GitHub Action. It executes your project (tests, a linter toolchain or a headless browser), so the hosted website scan never runs it on our servers — no website tier includes it. On the Action it belongs to the Forensic (nuclear) suite. No additional configuration.
- Free CLI.
npm i -g @gatetest/cli && gatetest --module mutationagainst any local repo. No paywall on the scanning itself. - AI auto-fix PR. On the GitHub Action, with your own ANTHROPIC_API_KEY, --auto-pr opens the fix PR from the same fix engine that powers Scan + Fix and Forensic.
- Honest confidence rating. Findings come with high / medium / low confidence so noisy patterns don't block the gate. The confidence-calibrator trainer reads customer suppressions and tightens rules over time.
Scan your repo for mutation
Free preview of the headline findings. Pay per scan, not per seat — one-time scans never auto-renew.
Frequently asked questions
What does the Mutation module catch?
Modifies your source code to verify your tests actually catch bugs. Runs via the GitHub Action because it executes your test suite; the website-only Forensic scan does not include it. Example finding: Mutated return true → return false, 11/11 tests still pass
Does GateTest fix Mutation issues automatically?
On the GitHub Action, with your own ANTHROPIC_API_KEY, `--auto-pr` opens the fix PR from the same fix engine. The hosted Scan + Fix ($199) and Forensic ($399) tiers auto-fix the repository findings they run.
Which tiers include the Mutation module?
The CLI and the GitHub Action. It executes your project (tests, a linter toolchain or a headless browser), so the hosted website scan never runs it on our servers — no website tier includes it. On the Action it belongs to the Forensic (nuclear) suite.
Can I run the Mutation module from the CLI for free?
Yes — install with `npm i -g @gatetest/cli` and run `gatetest --module mutation`. The local CLI is free; paid tiers add AI auto-fix and the cross-finding correlation work.