add-mutation-testing

Mutation testing is added by configuring the PIT Gradle plugin with pinned versions and a targetClasses pattern in build.gradle.kts, then running the on-demand pitest task to validate unit tests against injected code changes.

Surviving mutants indicate gaps in unit test assertions where injected code changes go undetected. You fix them by adding stronger assertions to kill mutants or documenting true equivalence if the mutation does not alter behavior.

PIT mutation testing is fully compatible with Gradle Kotlin DSL, requiring a pinned PIT plugin configuration in build.gradle.kts along with a targetClasses pattern for your project package.

Generated OpenAPI code is excluded from PIT mutation testing by adding explicit excludedClasses for the api.* and dto.* packages, keeping the mutation report focused on meaningful business logic.

PIT mutation testing will not slow down your CI pipeline because the pitest task is configured as an on-demand workflow that is explicitly excluded from the standard tasks.check execution.

Mutation testing measures unit test quality by injecting code changes to verify tests detect behavioral bugs, whereas line coverage only confirms code paths are executed without validating assertions.