Mutation Testing

Definitions

1. A technique that evaluates test suite quality by introducing small changes ('mutations') to the source code — flipping operators, changing constants, removing statements — and checking if tests catch them. If a mutation doesn't cause any test to fail, there's a gap in test coverage.

   In plain English: Testing your tests by deliberately breaking your code in small ways and checking if the tests notice.

   Example: "Code coverage says 95%, but mutation testing shows only 60% of mutations are caught — we have a lot of weak assertions."

Related Terms

• Code Coverage
• Test-Driven Development
• Testing
• Unit Testing
• Shift Left
• Property-Based Testing
• Acceptance Testing
• Assertion
• BDD
• End-to-End Test