You can't reasonably use functors of all your code dependencies (function arguments mostly). I am amazed to see how the MirageOS team used this, but this metho

You can't reasonably use functors of all your code dependencies (function arguments mostly). I am amazed to see how the MirageOS team used this, but this method cannot be used for all the code. > As a side note, I usually see mocking being used to test badly structured code. You could want to mock just because you are inspecting particular stack frames in a specific call stack, trying to reproduce a bug. It happens.