Fix panic in AssertExpectations for mocks without expectations

[tabboud]

Summary

Regression was introduced in #1182 (released in v1.7.3) which updated the mock mutex to be a pointer and updated most call sites that check this mutex to initialize if it's not yet, however the mock.AssertExpectationsForObjects and thus the mockObject.AssertExpectations did not take this into account which results in a panic. It's common to initialize mocks at the start of a test and then defer asserting expectations for the end of the test regardless of if a mock had expectations set on it or not. This happens in cases where the test mock does not set any On() methods or does not call mockedObject.Test(t) which would initialize the mutex if it's not set. Calling mockedObject.Test(t) is a fine workaround, but regardless this is a regression.

I added a test case that repro's the issue without the change. I'm happy to update this to be it's own test, but for now, I just left a comment about why it's there.

Changes

Updates the mock.AssertExpectationsForObjects to initialize the mutex if it's not created yet.

Motivation

Regression introduced in #1182 which causes a panic for previously working test code

Related issues

Closes #1206

[boyan-soubachov]

Thank you! I must've missed that one.