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testland/pitest-mutation

Configures PIT (PITest) for mutation testing of JVM projects (Java, Kotlin via the Kotlin plugin) - wires the `pitest-maven` or `pitest-gradle-plugin` with `mutationThreshold`, `coverageThreshold`, target classes/tests filtering, runs `mvn pitest:mutationCoverage`, parses the HTML + XML reports. Use when the JVM suite needs mutation-quality verification - the canonical Java mutation testing tool, fast (PIT analyzes "in minutes rather than days").

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Overview
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Files

pitest-pitfalls.mdreferences/

PIT - anti-patterns and limitations

Detailed pitfalls and constraints for pitest-mutation. Linked inline from that skill's SKILL.md.

Anti-patterns

Anti-patternWhy it failsFix
Mutating the entire codebase every PRSlow; team disables.withHistory + per-changed-file scope.
mutationThreshold: 100Unreachable; first failed run blocks all PRs.Start at the current baseline; ratchet up.
Mixed Maven/Gradle config (both plugins active)Conflicting configurations; cryptic errors.Pick one build tool.
Missing JUnit 5 plugin dependencyTests don't run; mutation coverage 0.Add pitest-junit5-plugin for JUnit 5.
Targeting test classes in targetClassesMutates test code; meaningless.targetClasses = production package; targetTests = test package.
All mutators (ALL mutator set)Many irrelevant mutants; long runtime.DEFAULTS (default) or STRONGER.

Limitations

  • Bytecode-level. PIT mutates compiled .class files; some language-level constructs (Kotlin sealed classes, certain generics) produce equivalent mutants.
  • Build-time integration. Requires Maven / Gradle; standalone PIT is awkward for Bazel / Pants.
  • Commercial Kotlin / Spring features. ArcMutate is paid; open-source PIT covers the basics.
  • Per-class scope only. No file-level or method-level scoping out of the box; use targetClasses patterns.

references

pitest-pitfalls.md

SKILL.md

tile.json