mutation-testing

High code coverage often hides weak assertions or accidental correctness, meaning tests pass even when logic is broken. Mutation testing solves this by injecting faults into your code and checking if your tests actually fail, identifying gaps in test quality.

You can check assertion strength by running mutation testing, which injects small faults into your codebase. If a mutant survives because your tests did not fail, it pinpoints areas where your assertions are too weak and generates recommendations for new test cases.

Mutation testing supports various languages through tools like PIT, Stryker, and mutmut. You can inject faults into your codebase regardless of your stack to verify test robustness and identify surviving mutants.

To verify test suite quality, run mutation testing to inject faults into your new feature's logic. This verifies that your existing tests will indeed fail if critical parts like conditional statements or return values are accidentally changed.

The best way to improve test robustness is to run mutation testing to identify surviving mutants. The process guides the creation of new test cases specifically designed to kill these mutants, leading to a more reliable test suite.