Without getting into the pros and cons of python (which will likely get me downvoted to oblivion), 'get' is an example of what I would call a coordination metho

Without getting into the pros and cons of python (which will likely get me downvoted to oblivion), 'get' is an example of what I would call a coordination method. I coach my teams to think of two kinds of methods: methods that do data processing, and methods that coordinate. To test a coordination method, you don't need to care about the value of the things it has to deal with. Maybe you care the they are not null, if your language has nulls. But other than that, what you are testing is that if your method A is supposed to pass arguments 1 thru 5 to method B, and 4 thru 10 to method C, then that's what you test. You don't need to test that argument 1 is a positive integer. The test for method B will do that, if it needs to. And finally you might test that if we expect the result of method B to be passed to method C, the test for our method A would do that using a mock B. Again, what mock B returned could be any object: we only care that it got passed to C. So it looks like its 1,125, but its actually three. If we have classes that are SOLID, then we tend to see the processing methods and the coordination methods end up in different classes. sessions.py isn't a great example of SOLID, and I would have a hard time writing tests for it. It is certainly not the kind of code you get if it was written with TDD.