Fix Call.Unset() panic (issue #1236)

[lisitsky]

Summary

Unset() doesn't work as expected in documentation. Instead of unsetting call specification it causes panic.

Reason: During call specification filtering Unset() changes len of a ExpectedCalls slice while using index from original slice. Under some circumstances it tries to reslice elements beyond of the slice boundaries. That causes panic.

Changes

The proposed solution uses independent write index to count elements kept in result slice.
Tests (the simplest and a more complicated cases) and comments are included.

Motivation

Because core functionality required by users to write tests doesn't work as expected.

// Unset removes a mock handler from being called.
test.On("func", mock.Anything).Return(nil)  // OK
test.On("func", mock.Anything).Unset()      // panic

Related issues

Closes #1236

[lisitsky]

Hello, @glesica , @boyan-soubachov , @mvdkleijn !
Could you please check this MR - it closes panic and makes tests behavior as it is documented.
Thank you very much!

[mweibel]

ping - that'd be great to have fixed 👍

[felixliou]

modify looks good to me

[lisitsky]

thank you

[lisitsky]

Hello, @felixliou!
Perhaps I misunderstood you.
Do you mean "looks ok now, and ready for merge" or you ask me modify the code?
If so, could you pls clarify which modifications are required? Thank you.

[felixliou]

looks ok now, and ready for merge，but I have not authorized to merge this PR.

[lisitsky]

Thank you for your feedback. Do you know anybody (possibly maintainers?) who can do it? Could you ping they please?

[felixliou]

Hi，
@ernesto-jimenez
@matryer
@boyan-soubachov

Please check this pull request.

Thank you very much

[lisitsky]

ping - that'd be great to have fixed 👍

@mweibel, yes, but how to promote it to accept? )

[boyan-soubachov]

Thank you for this contribution, approved and merging :)

[lefinal]

When can we expect this to be released?