mutation-test

Run mutation testing across JavaScript, Python, Java projects and report scores and weak tests.

175|26|Updated Aug 14, 2025

Search Tags:#mutation-testing #test-quality #stryker #mutmut #pitest

Ready to run

npx skills add https://github.com/jmagly/ai-writing-guide --skill mutation-test

💬 Prompt for ChatGPT / Claude Chat▼

Please help me install this Agent Skill.
Skill: mutation-test
Source: https://github.com/jmagly/ai-writing-guide/tree/main/.factory/skills/mutation-test
Command: npx skills add https://github.com/jmagly/ai-writing-guide --skill mutation-test

SYSTEM DOCUMENTATION & REQUIREMENTS

What problem does it solve?

Uses mutation testing to reveal weak tests and verify test effectiveness beyond coverage.

Core Features & Use Cases

Mutant generation: Create and evaluate small code mutations.
Score interpretation: Mutation score and survivor analysis.
Reporting: Actionable remediation for weak tests.

Quick Start

Run mutation analysis for a JavaScript module and review the mutation report.

Frequently Asked Questions about mutation-test

High-intent search queries and answers about installing and using this skill.

FAQPage Schema

How do I measure test quality beyond code coverage?▼

Mutation testing measures test effectiveness by introducing small code changes (mutants) and checking if your tests catch them. A higher mutation score indicates stronger tests that detect actual bugs, not just line execution.

Can I run mutation testing on JavaScript, Python, and Java projects?▼

Yes. Mutation testing supports multi-language projects using language-specific tools: Stryker for JavaScript, mutmut for Python, and PITest for Java. Each generates a mutation report with scores and survivor analysis.

What does a mutation score tell me about my test suite?▼

Mutation score is the percentage of introduced code mutations your tests detected and killed. Survivors are mutants your tests missed, revealing gaps in coverage and guiding which tests need improvement before release.

How do I set up mutation testing for my codebase?▼

Configure the appropriate tool for your language (Stryker, mutmut, or PITest), run the mutation analysis on your test suite, then review the generated report for killed mutants, survivors, timeouts, and recommended test improvements.

Why do some mutants timeout during mutation testing?▼

Timeouts occur when introduced mutations cause infinite loops or extremely slow execution. The mutation report flags these alongside killed and survived mutants to give you a complete picture of test effectiveness and code behavior under mutation.