Yes. This. What then happens is that the mocked out functions change what they return, or the order of what they do inside (e.g so that for a given set of inp

Yes. This. What then happens is that the mocked out functions change what they return, or the order of what they do inside (e.g so that for a given set of inputs now throws a different exception). Someone forgets to update the mocks. All the tests continue to pass, even though none of the conditions are actually possible in the program.