[throw_m239339]

> Why do fakes need tests, but mocks don't?

because no new class or method is created with mocks, it's merely declarative, no new logic is created than needs to be tested. Fakes very much have logic since they are implementations of classes.

> Or do you have a rule in your company that every class needs a test? Maybe this rule is the problem.

No Fakes are, not the fact that every unit should be tested. Fakes are very much a unit, the fact that they are classes is irrelevant.

furthermore:

https://news.ycombinator.com/item?id=24774752

which demonstrates my point. I don't want to have to write tests for tests.

[srtjstjsj]

To put it differently, mocks aren't tested because they can't be wrong, be at they are "not even wrong". You have to have faith that mock behavior is actually a reasonable emulation of the real system, without ever checking. The weakness is that your tests of the system under test don't help you find flaws in how the system under test uses the lower level dependency, because you are simply forcing the lower level dependency to behave the way you wish it would.