mutation-testing

Mutation testing measures test effectiveness by injecting small mutations into production code and verifying if the existing test suite catches the injected bugs. It generates mutants, runs tests against each, and reports killed, survived, or no-coverage outcomes.

To assess test strength after TDD, run a mutation testing workflow on your codebase. This process injects controlled mutations into production code and evaluates whether your test suite detects the changes, reporting survived mutants to identify weak tests.

Yes, mutation testing identifies missing edge cases during branch code reviews by injecting mutations into production code and evaluating mutant outcomes. It highlights scenarios where tests fail to kill mutants, guiding you to strengthen test coverage for specific branches.

To start validating your test suite with a tool like Stryker, install the mutation testing tool in your JavaScript or TypeScript project. Run the mutation testing workflow to generate mutants, execute the test suite against them, and review the killed or survived metrics.

High test coverage misses bugs during refactoring because coverage only measures code execution, not test assertions. Mutation testing solves this by injecting bugs into production code to verify if tests actually detect them, exposing weak tests that pass despite flawed logic.

Standard test coverage measures which lines of code execute during tests, while mutation testing evaluates if tests actually detect bugs by injecting mutations into production code. Mutation testing provides killed, survived, and no-coverage metrics to reveal weak test assertions.