Thorsten first provides a high-level overview of unit testing in general, and classifies it in terms of test level, and testing methods and techniques. He then explores and explains different possible units. The second part of the talk is dominated by one of the key principles of unit testing: testing in isolation. What is it? How can it be done? What is this mocking that pops up here and there? Next, Thorsten shows different unit test examples, involving both PHP and JavaScript, and highlighting different (yet simplified) aspects of real-life code. Thorsten concludes with a few tips for writing good unit tests.