| name | mutation-testing |
| description | Use PIT (Pitest) mutation testing to identify weak tests and improve test quality in Java projects. Finds tests that pass but don't actually verify behavior correctly. Use when improving test suite quality beyond line coverage metrics.
|
| compatibility | Java projects using Gradle 8.x+ with JUnit 5 or Spock |
| metadata | {"version":"2.0.0","technology":"java","category":"testing","tags":["java","gradle","testing","mutation-testing","pitest","quality"]} |
Mutation Testing
Use PIT mutation testing to identify tests that pass but don't verify behavior correctly.
When to use this skill
- Improving test quality beyond line coverage metrics
- Finding weak test assertions that don't catch bugs
- Validating critical business logic has strong tests
- Setting up mutation testing in CI pipelines
- Analyzing which tests need strengthening
- When asked to "improve test quality with mutation testing"
Skill Contents
Sections
Available Resources
📚 references/ - Detailed documentation
Quick Start
1. Check readiness
bash java/scripts/check-pitest-readiness.sh
2. Apply PIT configuration
Copy java/templates/pitest.gradle to gradle/pitest.gradle and apply in build.gradle.
3. Run mutation testing
./gradlew pitest -Ppitest.mutators=DEFAULTS
./gradlew pitest -Ppitest.mutators=STRONGER
./gradlew pitest -Ppitest.mutators=ALL
4. Analyze results
open build/reports/pitest/index.html
Focus on SURVIVED mutants - these indicate weak tests.
5. Improve tests
Add specific assertions that kill the surviving mutants.
Key Concepts
Mutation Score vs Line Coverage
- Line coverage: Does your test execute the code?
- Mutation score: Does your test actually verify the code works correctly?
High line coverage with low mutation score = tests run code but don't verify results.
Intensity Levels
| Level | Mutators | Use Case | Time |
|---|
| QUICK | DEFAULTS (~11) | Initial analysis, CI | 1x |
| STANDARD | STRONGER (~14) | Regular improvement | 1.5x |
| COMPREHENSIVE | ALL (~30+) | Critical logic | 3-5x |
Mutation Statuses
| Status | Meaning | Action |
|---|
| Killed | Test detected mutation | Good |
| Survived | Test missed mutation | Improve test |
| No Coverage | No test covers code | Write test |
| Timed Out | Infinite loop | Usually OK |
References
Related Rules
Related Skills
