Correctly mocking external entities in your unit tests is a bit tricky syntactically, and I have to look up the exact incantations to type every single time they're needed. Thus, I'll make a quick sales pitch about mocking, quickly explain it to the best of my current understanding, and end with a sequence of tricks to be updated as I learn more. In essence, it's my own personal cheat sheet, stored in an accessible location I'm unlikely to misplace.