Mutation testing is one of the most underused techniques in software quality, and it directly answers the question: 'If my code has a bug, will my tests catch it?' In this episode, Lucas and Luna explore how mutation testing works by deliberately introducing small faults—mutations—into your code and checking whether your test suite detects them. They walk through a concrete example with a simple function and show how a 100% line-coverage test suite can still miss critical edge cases. Lucas shares data from a 2025 study at a major fintech firm that found mutation testing revealed 42% of their 'covered' code had undetected bugs. They discuss practical tooling (PIT for Java, mutmut for Python), how to integrate mutation testing into CI without breaking your build, and why aiming for 100% mutation coverage is a trap. The episode closes with a quick reflection on the trade-off between test quality and speed, and a light donation moment tied to the value of a single actionable insight.

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