I agree that the confusion was probably due to assumptions rather than a misreading of the doc, and I would not object to closing this issue.

However, Robert did object so I would like to suggest an adjustment that may help:

Currently the documentation of assert_not_called is just after that of assert_has_calls.   If we reverse their order, then there can be less room for confusion about how to check that nothing was called - you would read that first. 

https://docs.python.org/3/library/unittest.mock.html#unittest.mock.Mock.assert_has_calls