False sense of security: Why 90% code coverage does not save you from bugs

▤ Summary

This article explains why high line coverage can still miss bugs and why branch and mutation coverage provide stronger testing signals. It uses payment-processing code examples to show how different tests can look complete while leaving logic flaws uncovered. It also introduces tools such as JaCoCo, coverage.py, PITest, mutmut, Cosmic Ray, and Stryker. The piece closes by framing mutation testing as a practical CI safeguard for teams that want better release confidence.

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