I'm not sure I really understand what you're saying, but in any case, this is a problem with any dynamically typed language, and isn't in any way specific to Fl

I'm not sure I really understand what you're saying, but in any case, this is a problem with any dynamically typed language, and isn't in any way specific to Flask or even Python. If writing applications without the guarantees of a "proper type system" is painful for you, then Python is probably the wrong language. That said, you shouldn't have to manually test anything—that's what automated tests are for. With regard to testing Flask applications specifically, there is a guide[0] in the docs that covers everything you need to get started. [0]: http://flask.pocoo.org/docs/0.11/testing/ http://flask.pocoo.org/docs/0.11/testing/