Remove mandatory SetupAdd & SetupRemove for eventhandler subscription verification.

[80O]

What is the reason that having to add this setup:
_mock.SetupRemove(d => d.Event -= It.IsAny<EventHandler>());

To verify this...
_mock.VerifyRemove(d => d.Event -= It.IsAny<EventHandler>(), Times.Once);

... is mandatory?

Normal function calls do not require to be 'registered' beforehand either. I think it will help if these setups are not required and act more like any other Verify() call.

[stakx]

IIRC (from #825 and #857), the reason was backward compatibility. Verify{Add,Remove} was added only recently (unlike Setup{Add,Remove} which has been around much longer). Those methods can only work iff event += and -= are recorded in mock.Invocations, but previously this didn't happen, and that's why those verification methods weren't introduced for so long.

If we had simply started unconditionally recording += and -=, that would have been a breaking change with respect to e.g. VerifyNoOtherCalls: existing code might have assumed that this call would succeed but now there might suddenly be additional invocations that weren't there before.

That's why we figured, if your test is already aware of event (un-) subscriptions, it should be safe in that case to record them as invocations. And we chose the presence of the setup methods as the criterion whether your test is "aware of" event (un-) subscriptions.

Does this explanation make sense?

I agree that ideally, those Verify{Add,Remove} methods should work without their Setup... counterparts (as is otherwise the case), but it was simply the safest thing to do at the time. It enabled additional verification with only a small risk of breaking existing code.