Validate test effectiveness with mutation testing using Stryker (TypeScript/JavaScript) and mutmut (Python). Find weak tests that pass despite code mutations. Use to improve test quality.
Install
npx skills add secondsky/claude-skills --skill mutation-testingnpx skills add secondsky/claude-skills --skill mutation-testing -a claude-code -gnpx skills add secondsky/claude-skills --skill mutation-testing -a codex -ggemini skills install https://github.com/secondsky/claude-skills.git --path plugins/mutation-testing/skills/mutation-testinggh skill install secondsky/claude-skills mutation-testinggit clone --depth 1 https://github.com/secondsky/claude-skills /tmp/secondsky__claude-skills
mkdir -p ~/.claude/skills ~/.agents/skills
cp -R /tmp/secondsky__claude-skills/plugins/mutation-testing/skills/mutation-testing ~/.claude/skills/mutation-testing # Claude Code
cp -R /tmp/secondsky__claude-skills/plugins/mutation-testing/skills/mutation-testing ~/.agents/skills/mutation-testing # Codex, Cursor, Gemini CLI, Copilot, OpenCode