mutation-testing

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

Skill Contents

Sections

• When to use this skill (L25-L32)
• Quick Start (L54-L90)
• Key Concepts (L91-L116)
• References (L117-L125)
• Related Rules (L126-L130)
• Related Skills (L131-L136)

Available Resources

📚 references/ - Detailed documentation

• configuration
• improving tests
• intensity levels
• troubleshooting

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

# QUICK level - fast feedback
./gradlew pitest -Ppitest.mutators=DEFAULTS

# STANDARD level - recommended
./gradlew pitest -Ppitest.mutators=STRONGER

# COMPREHENSIVE level - thorough
./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

Mutation Statuses

References

Related Rules

• .cursor/rules/java-testing-guidelines.mdc - Spock/JUnit patterns
• .cursor/rules/java-jacoco-coverage.mdc - Line coverage configuration

Related Skills