Tests are watching our code, helping it to not regress. But who’s watching the watchmen? Code coverage is often used to determine the quality of automated tests, trying to “test the tests”. Unfortunately all it does is ensure which lines of code have been executed by the tests, not if they are actually checking anything! Mutation testing is a way to really watch the watchmen. Matthew will give an introduction to mutation testing, why it’s better than traditional code coverage for measuring test quality, and demo examples using Java code and PiTest (Java mutation testing framework).