Your comment was clear about mocks, but not why mocks are relevant to the topic at hand. The original comment was equally clear that it was in reference to where there is only one implementation. In fact, just to make sure you didn't overlook that bit amid the other words, the author extracted that segment out into a secondary comment about that and that alone.
Mocks, by definition, are always a supplemental implementation – in other words, where there is two or more implementations. What you failed to make clear is why you would bring up mocks at all. Where is the relevance in a discussion about single implementations the other commenter has observed? I wondered if you had missed (twice!) the "one implementation" part, but it seems you deny that, making this ordeal even stranger.
It is easy to generate mock implementation code (GoMock has mockgen, testify has mockery, etc.) The lack of a hand-rolled mock implementation doesn't mean that much. For example, many people do not like to put generated code under source control. So, just because you don't see a mock implementation right away doesn't mean one isn't meant to be there. Also, the original author of the function that consumed the apparently unnecessary interface type may have intended to test it, but not had the time to write the tests or generate the mocks. If we are going to be this pedantic, I did say "mockable" interface, implying the usefulness and possibility, but not necessarily existence, of a mock implementation.
Since we are examining code we can't see, we can only speak about it in the abstract. That means the discussion may be broader than just what one person contributes to it. If this offends you or the OP, that was not the intent, but in the spirit of constructive discussion, if you find my response so unhelpful, it is better to disregard it and move along than to repeat the same point over and over again.
Not in any reusable way. Take a look at mockgen and testify: All they do is provide a mechanism to push implementation into being defined at runtime by user code. So, if they, or something like it, is in use the implementation is still necessarily there for all to see.
> Also, the original author of the function that consumed the apparently unnecessary interface type may have intended to test it
Okay, sure, but this is exactly what the commenter replied to was talking about initially. What is a repetition of what he said meant to convey?
> That means the discussion may be broader than just what one person contributes to it.
Hence why we're asking where the relevance is. There very well may be something broader to consider here, but what that is remains unclear. Mocking in and of itself is not in any way interesting. Especially when you could say all the very same things about stubs, spies, fakes, etc. yet nobody is talking about those, and for good reason.
> If this offends you
For what logical reason would an internet comment offend?
Mocks, by definition, are always a supplemental implementation – in other words, where there is two or more implementations. What you failed to make clear is why you would bring up mocks at all. Where is the relevance in a discussion about single implementations the other commenter has observed? I wondered if you had missed (twice!) the "one implementation" part, but it seems you deny that, making this ordeal even stranger.