Mutation testing: Who tests the testers?

Mutation testing is an advanced software testing technique. Imagine altering a '<' to '>' in your code; ideally, your unit tests should catch this. But do they? This walkthrough will explore the principles of mutation testing, demonstrating how it can uncover hidden weaknesses within supposedly robust test suites. Using the third-party Python package Mutmut, I will illustrate common pitfalls in unit testing and show how mutation testing can expose these effectively. These examples will cover some simple examples and then go on some examples found in code bases. I will also show how mutation testing can be used as a teaching tool for better testing, including how it can highlight edge cases in unit tests. A recording of this session is available on YouTube: https://youtu.be/uoxT2pRenQs