Unit tests test the parts of the library that are in use implicitly.
As does integration testing, user acceptance testing and whole system testing (QA engineers, frontend testing, etc.)
Nothing has been forgotten. Python isn't Java, nor should you develop your Python code as if it were Java. Python has it's own software development practices that take advantage of the language's strengths including dynamic typing.
It you don't know how to work with a dynamically typed language properly, that's on you. And I guarantee you will get poor results pretending it's a statically typed language.
