This is a lightning talk I delivered (shouted?) during PyCon 2013 at the infamous TIP-BOF open space. It covers potential ways your unit tests may be yielding false positives when they should indeed be failing when using the Mock library.
I include some example code to demonstrate how not using autospec is bad and present an example of how to extend the basic Mock and MagicMock classes to add new test assertions to further prevent common testing mistakes.
Code and slides can be found here: Your Tests Are Lying To You