Automated tests are an essential part of any long-term project. However, the purpose of tests is also often misunderstood (spoiler: it’s not just for catching bugs). In this presentation, I’ll discuss the surprisingly nuanced relationship between unit, kernel and functional tests, the role of dependencies and why dependency injection is so important, how to identify code that is worthy of tests, and finally, how tests go hand-in-hand with great software design. By the end of this presentation you’ll have a better understanding of the true purpose of tests, how to write tests that are sustainable, and offer value for the entire life of the project.