I don't know if mypy allows you to mock the API but at least flow does for javascript. If a library is untyped you get a file with all the exported functions an

I don't know if mypy allows you to mock the API but at least flow does for javascript. If a library is untyped you get a file with all the exported functions and you can quickly set the types for the functions that you interface with. We have been using this for a couple of years and it's a godsend. There's a community project to share these external library definitions https://github.com/flow-typed/flow-typed https://github.com/flow-typed/flow-typed