Testing
Teams routinely hit 90% code coverage targets while shipping code with significant test gaps. The coverage metric is satisfied. The tests are weak. Mutation score reveals what coverage hides — but it comes with its own blind spots. This post is a direct comparison: what each metric measures, what each misses,
Testing
You've hit 100% code coverage. Every line, every branch, every condition — green. Time to ship with confidence, right? Not quite. Code coverage tells you which lines were executed during tests. It says nothing about whether your tests would catch a bug if one appeared. Mutation testing does. The
Testing
You've run your first mutation testing report. Mutation score: 58%. Now what? Improving mutation score isn't about writing more tests — it's about writing better assertions. Here's a systematic approach to turning surviving mutants into killed ones, starting with the changes that matter