This post makes the mistake of thinking that writing a bunch of tests will make everything better. In my experience, the only thing that will help you when it comes to expanding/fixing an existing codebase is knowin what the code is doing. When the app crashes and you look at the traceback, you need your brain to be able to understand why the program crashed. No matter how many tests fail or how many email alerts you get from travis-ci, your primary task is to understand what the code is doing.