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mutation-testing

Guide developers through mutation testing to assess and improve test suite quality

Packaged view

This page reorganizes the original catalog entry around fit, installability, and workflow context first. The original raw source lives below.

Stars

Hot score

Updated

March 20, 2026

Overall rating

C2.2

Composite score

2.2

Best-practice grade

B80.4

Install command

npx @skill-hub/cli install rubrical-studios-idpf-praxis-dist-mutation-testing

Repository

rubrical-studios/idpf-praxis-dist

Skill path: Skills/mutation-testing

Guide developers through mutation testing to assess and improve test suite quality

Open repository

Best for

Primary workflow: Ship Full Stack.

Technical facets: Full Stack, Testing.

Target audience: everyone.

License: Complete terms in LICENSE.txt.

Original source

Catalog source: SkillHub Club.

Repository owner: rubrical-studios.

This is still a mirrored public skill entry. Review the repository before installing into production workflows.

What it helps with

Install mutation-testing into Claude Code, Codex CLI, Gemini CLI, or OpenCode workflows
Review https://github.com/rubrical-studios/idpf-praxis-dist before adding mutation-testing to shared team environments
Use mutation-testing for development workflows

Works across

Claude CodeCodex CLIGemini CLIOpenCode

Favorites: 0.

Sub-skills: 0.

Aggregator: No.

Original source / Raw SKILL.md

---
name: mutation-testing
description: Guide developers through mutation testing to assess and improve test suite quality
license: Complete terms in LICENSE.txt
---

# Mutation Testing
**Version:** 0.17.0

## When to Use
- Assessing test suite quality beyond coverage
- Identifying weak test coverage
- Evaluating test meaningfulness
- Improving test effectiveness

## Core Concept
1. **Mutate:** Make small code changes
2. **Test:** Run test suite against mutated code
3. **Evaluate:** Check if tests detect (kill) mutations

## Key Terms
- **Mutant:** Modified code with one change
- **Killed:** Test detected mutation (good)
- **Survived:** Test missed mutation (bad)
- **Equivalent:** Mutation behaves identically (can't kill)
- **Mutation Score:** killed / (total - equivalent)

## Mutation Operators

### Arithmetic
| Original | Mutated |
|----------|---------|
| `+` | `-` |
| `*` | `/` |

### Relational
| Original | Mutated |
|----------|---------|
| `<` | `<=` |
| `==` | `!=` |
| `>` | `>=` |

### Logical
| Original | Mutated |
|----------|---------|
| `and` | `or` |
| `not` | (removed) |

### Constants
| Original | Mutated |
|----------|---------|
| `0` | `1` |
| `true` | `false` |

## Score Interpretation
| Score | Quality |
|-------|---------|
| 90-100% | Excellent |
| 75-89% | Good |
| 60-74% | Acceptable |
| <60% | Weak |

**Context matters:** High-risk code (payment, auth) should target 90%+

## Analyzing Survivors
1. Review the mutant code change
2. Understand what behavior changed
3. Decide: Add test, mark equivalent, or accept risk

**Common survival patterns:**
- Missing boundary tests
- Missing error case tests
- Missing assertions on return values

## Framework Examples

**Python (mutmut):**
```bash
pip install mutmut
mutmut run
mutmut results
```

**JavaScript (Stryker):**
```bash
npm install @stryker-mutator/core
npx stryker init
npx stryker run
```

**Java (PIT):**
```bash
mvn org.pitest:pitest-maven:mutationCoverage
```

## Best Practices
1. Start small (critical modules first)
2. Set realistic goals (not 100%)
3. Address survivors systematically
4. Integrate with CI (limited scope on PRs)
5. Balance cost vs value

## Common Pitfalls
- Running on everything (too slow)
- Ignoring equivalent mutants
- Adding tests without understanding
- Over-testing to kill mutants

---

**End of Mutation Testing Skill**