How does it handle tests that don't have a business scenario?

The skill enforces a 'no test without scenario' rule. If a surviving mutant isn't covered by a domain scenario, it suggests either deleting the unnecessary code or updating the specification.

Which languages and tools does this skill support?

It currently supports Rust (cargo-mutants), JavaScript/TypeScript (Stryker), Python (mutmut), and Elixir (Muzak).

Can I use this skill if my project doesn't have a mutation tool installed?

Yes, the skill will detect if the tool is missing and provide specific installation instructions tailored to your project's ecosystem.

What is mutation testing?

Mutation testing involves making small, intentional changes to your source code (mutants) to see if your existing tests fail. If the tests pass despite the change, the mutant 'survives,' indicating a gap in your testing.

Why does this skill require a 100% kill rate?

A 100% kill rate ensures that every piece of logic in your changed code is strictly verified by your test suite, leaving no room for undetected bugs in production.

Mutation Testing Quality Gate

Name: Mutation Testing Quality Gate
Author: jwilger

byjwilger

•

Security & Testing

Validates test effectiveness by injecting code mutations and enforcing a 100% kill rate before code deployment.

This skill automates mutation testing to verify that your test suite actually catches potential bugs, moving beyond simple code coverage. It automatically detects your project type across Rust, JavaScript, TypeScript, Python, or Elixir, runs the appropriate mutation tool, and analyzes surviving mutants to identify logic gaps. By enforcing a 100% kill rate quality gate and requiring that every new test aligns with a specific domain scenario, it ensures your code is robust and your tests provide genuine confidence rather than just fulfilling arbitrary coverage metrics.

Key Features

01Scenario coverage verification to ensure tests map to real business requirements

02Automatic detection of mutation tools like cargo-mutants, Stryker, mutmut, and Muzak

03Enforcement of a 100% kill rate quality gate for Pull Request readiness

042 GitHub stars

05Detailed analysis of surviving mutants by type including arithmetic, logic, and return values

06Structured MUTATION_RESULT JSON output for automated audit trails and CI/CD

Use Cases

01Validating test suite quality before opening a Pull Request

02Closing the verification loop in TDD workflows to ensure tests detect failures

03Identifying untested boundary conditions and logic branches in existing code

What are Skills?·How to Install

Install with 🐟 Skill.Fish

npx skillfish add jwilger/agent-skills mutation-testing

For use in Claude.ai and ChatGPT

Download Skill