How Mutation Testing Exposes the Truth (PHP 2026 Edition)

Short summary

Mutation testing automatically injects intentional bugs into code to verify your test suite actually catches them—revealing gaps where 100% coverage masks real failures. Using Infection PHP, the author demonstrates how a pricing engine test achieved perfect coverage but failed to catch critical boundary conditions. Integrating mutation testing into CI/CD catches regression holes that traditional code coverage metrics cannot detect.

• •Mutation testing injects bugs to verify test effectiveness beyond code coverage percentage
• •Infection PHP integrates with PHPUnit and CI/CD with configurable mutation score thresholds
• •Real example: 100% coverage test missed boundary conditions until mutations exposed the gap

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