Mutation Testing in PHP: Beyond Code Coverage with Infection Framework

Your CI pipeline is green. Code coverage sits at 100%. You ship the feature. Three days later, a bug report lands in your inbox, one that your tests should have caught. Sound familiar? This is the dirty secret of code coverage metrics: they measure what lines ran, not whether your tests actually verify anything meaningful. You can hit 100% coverage with tests that assert nothing. Mutation testing fixes this. It doesn't ask "did this code run?" it asks "would your tests notice if this code was