You've got 85% code coverage. Your CI pipeline is green. You ship to production — and things break in ways your tests never caught. Sound familiar?

I've been there. And for a long time, I thought the answer was more tests. What I actually needed was better tests. That's exactly what mutation testing taught me, and after using Infection PHP in production projects through 2025 and into 2026, I can confidently say it changed how I think about test quality entirely.

Previous article in this category: https://codecraftdiary.com/2026/04/18/laravel-testing-mistakes/

The Dirty Secret of Code Coverage

Code coverage tells you which lines were executed during your test run.…