The talk is about why, what and how to test. It is brief overview of the testing concepts and techniques. I'd like to talk about the goals of testing (some of them are obvious and others are not) to show what exactly tests suppose to do. On other hand I would show some examples of how to do testing and where potential bottlenecks are. The talk is oriented on beginners and middle-skilled python programmers who already tried to write tests but I hope the programmers of any level will find something interesting in this talk.