I see far too many young developers neglect unit testing citing reasons as "they take too much time" or "they're unnecessary, my app works". Experienced developers understand the importance of writing thorough tests and how much time they save in the long run.
Younger developer should be aware of the tools that exist to expedite the process, such as test coverage reporting and framework extensions. Check out the following video tutorial for properly unit testing a flask web application. I introduce invaluable python tools such as unittest, flask-testing and nose2. Would love to hear about your favorite workflow tools for writing unit tests!