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Mutation Testing

Checked
aj-geddes·vlatest·testing·MIT

Automatically generates code mutations to identify gaps in test suite coverage and improve software reliability.

Repository

Install on your platform

Showing Claude Code. One command installs this skill into any of the agents below.

  1. 1

    Run this in your project

    terminal
    $ npx skills add aj-geddes/useful-ai-prompts --skill mutation-testing -a claude-code

  2. Uses the open-source skills CLI and needs Node.js. Add -g to install it for your user instead of this project.

What we know about this skill

Publisher

aj-geddes

Taken from the source listing. We haven't verified who controls this account.

Install target

Live repository

Not pinned. Installing fetches whatever the repository holds at the time you run the command.

No human has reviewed this code. The checks below are a static scan of the files at one commit — nobody has run this skill or judged whether it works. A skill runs with whatever access you give your agent, so read the source before you install it.

Automated safety checks

scanned

This skill passed all 6 checks. We read its files at one commit and looked for the things that make a skill dangerous to run — not for whether it works.

  • Declares what it does: passed

    SKILL.md parses and declares a name and a description.

    SKILL.md exists, its frontmatter parses, and it declares a name and a description.

  • No undeclared network calls: passed

    Makes no network calls.

    Every host the skill dials — from its scripts, its config endpoints or the commands it tells the agent to run — is either well-known package and API infrastructure or declared in its own frontmatter. Links in documentation are not counted.

  • No obfuscated payloads: passed

    No encoded or obfuscated payloads.

    No base64, hex or compressed blob is decoded and then executed, and no encoded shell commands.

  • No credential access: passed

    Reads no keys, tokens, keychains or credential files.

    Neither the code nor the SKILL.md instructions read SSH keys, cloud credentials, keychains, token stores, browser cookie databases or dotfiles that hold secrets.

  • No pipe-to-shell installers: passed

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    No `curl … | sh` pattern, in the code or in the instructions, that runs code fetched at run time.

  • Pinned to a commit: passed

    Scanned aj-geddes/useful-ai-prompts at 3f5182cfd7.

    The exact upstream commit SHA that was scanned is recorded, so the result refers to specific bytes.

Commit
3f5182cfd7
Manifest
skills/mutation-testing/SKILL.md
Scanned
7 files, 550 lines
This is a static scan, not a review. It reads the skill's files; it does not run them, and it cannot tell you whether the skill is any good or whether the code does what its description says. A skill runs with whatever access you give your agent.
What each check looks for →

About this skill

What it does

This skill enables AI agents to perform mutation testing, a technique for evaluating test suite quality. It works by introducing small changes ("mutations") into source code and verifying that existing tests fail when these mutations are present. If a mutation survives (tests don't catch it), this indicates gaps in test coverage or weaknesses in the tests themselves, helping to improve software reliability. The skill supports implementations for JavaScript/TypeScript, Java, and Python.

When to use it

  • Evaluating the effectiveness of your existing test suite.
  • Identifying code paths that are not adequately tested.
  • Improving test quality metrics and ensuring tests actually verify behavior.
  • Validating critical business logic is well-tested.
  • Measuring real test coverage beyond simple line coverage.

Key capabilities

  • Generates mutations (small changes) in source code.
  • Verifies that existing tests fail when mutations are introduced.
  • Identifies "survived mutants" indicating gaps in test coverage or ineffective tests.
  • Supports Stryker for JavaScript/TypeScript, PITest for Java, and mutmut for Python implementations.
  • Allows marking equivalent mutants to exclude them from analysis.

Example prompts

  • "Run mutation testing on the payment_processing module."
  • "Analyze test coverage using mutation testing and report any survived mutants."
  • "Evaluate the quality of our unit tests with a mutation testing run, focusing on critical business logic."

Tips & gotchas

  • Mutation testing can be slow, so focus on critical modules rather than running it against all code.
  • Aim for an 80%+ mutation score on important code but don't expect or strive for 100% everywhere.
  • Review and address any survived mutants to improve test quality.