Mutation testing is a technique that measures the quality of a test suite and helps you write more robust code. This is done by making small changes (mutations) to code under the assumption that each mutation introduces a bug. By automating this process we can find bugs in our code that can't be detected by traditional code coverage tools.

This talk introduces the concept of mutation testing. First we show that using code coverage as a metric of quality of a test suite is flawed. Next we show that by using mutation testing we can find bugs in code which has 100% code coverage. An overview is given on how a mutation testing tool works and some of its disadvantages are discussed. Most of these disadvantages however, can be solved by writing well designed software. Lastly we will take a look at Humbug, a mutation testing tool for PHP and we conclude with a few examples of how a mutation testing tool can help you improve your software and how it can fit in your current workflow.