A Rather Embarrassing Reason for the "Expression references a method that does not belong to the mocked object" Exception When Using Moq

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I've been using Moq for ages, but today while writing a unit test ran into a runtime exception I'd never had before:

Expression references a method that does not belong to the mocked object: mock => mock.GetExpiredCredentials(It.IsAny<DateTime>(), It.IsAny<DateTime>(), It.IsAny<Boolean>()).Returns<IEnumerable`1>(.fakeResults, new[] {  })

I couldn't understand why. The method in question was on the interface, and if it wasn't, the code shouldn't have even compiled, yet it did. Even more confusing was that, when I Googled the error message, all the results seemed to point toward extension methods, and this method was not an extension method.

It turns out, what I had done was to misplace my parentheses (facepalm)! Here's what my original take looked like:

_credentialServiceMock
    .Setup(mock => 
        mock.GetExpiredCredentials(
            It.IsAny<DateTime>(), 
            It.IsAny<DateTime>(), 
            It.IsAny<bool>())
    .Returns(fakeResults));

And here was the corrected version (notice there's an additional parenthesis at the end of the Setup() call, and one less at the end of the Returns() call...(sigh)...):

_credentialServiceMock
    .Setup(mock => 
        mock.GetExpiredCredentials(
            It.IsAny<DateTime>(), 
            It.IsAny<DateTime>(), 
            It.IsAny<bool>()))
    .Returns(fakeResults);

I've been using Moq for many years, and I can't believe I made this mistake, but hopefully this post will help someone else who's made the same one.

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