> If the first person writes elaborate mocks instead of simplifying the design to not need them, they've locked in the implementation in a way that unit tests

> If the first person writes elaborate mocks instead of simplifying the design to not need them, they've locked in the implementation in a way that unit tests don't (Sunk Cost). This can turn a masochistic programmer into a sadist. You mostly use elaborate mocks for unit tests. There is much less need for mocking in integration tests.