I agree with your point. OP wrote: > Many (sometimes even all) of these interfaces have just one implementation. They are missing that mocks are the seco

I agree with your point. OP wrote: > Many (sometimes even all) of these interfaces have just one implementation. They are missing that mocks are the second implementation. (It took me years to see this point.) I would say that in most of my code at work, 95+% of my interfaces only have a single implementation for the production code, but any/all of them can have a second implementation when mocking for unit tests.