Mock can be deadlocked by a panic

[brackendawson]

Summary

If an argumentMatcher function panics and AssertExpectations is deferred then the test would deadlock.

Changes

• Capture panics from argumentMatcher functions and show them to the user as a difference

Motivation

It was reported that when AssertExpectations() is deferred and an argumentMatcher function panics, that the test will deadlock.

Example from linked issue:

import (
	"testing"

	"github.com/stretchr/testify/mock"
)

type Mock struct {
	mock.Mock
}

func (_m *Mock) F() {
	_m.Called()
}

func TestMatcherPanic(t *testing.T) {
  m := &Mock{}
  defer m.AssertExpectations(t)

  matcher := mock.MatchedBy(func(_ interface{}) bool {
    panic("my hovercraft is full of eels")
  })
  m.On("F", matcher)

  m.F()
}

After this change the output will now look like:

--- FAIL: TestMatcherPanic (0.00s)
    /Users/alandaws/src/github.com/brackendawson/kata/mock.go:264: 
        
        mock: Unexpected Method Call
        -----------------------------
        
        F()
        		
        
        The closest call I have is: 
        
        F(mock.argumentMatcher)
        		0: mock.argumentMatcher{fn:reflect.Value{typ:(*reflect.rtype)(0x126a520), ptr:(unsafe.Pointer)(0x12b5f88), flag:0x13}}
        
        Provided 1 arguments, mocked for 0 arguments
        Diff: 0: FAIL:  panic in argument matcher: my hovercraft is full of eels not matched by func(interface {}) bool
    /Users/alandaws/src/github.com/brackendawson/kata/panic.go:661: FAIL:	F(mock.argumentMatcher)
        		at: [kata_test.go:25]
    /Users/alandaws/src/github.com/brackendawson/kata/panic.go:661: FAIL: 0 out of 1 expectation(s) were met.
        	The code you are testing needs to make 1 more call(s).
        	at: [panic.go:661 testing.go:756 kata_test.go:14 kata_test.go:27]

I wonder if that is obvious enough?

Related issues

fixes #1155

[lzambarda]

It would be really good to have this merged as it's really hard to write tests when you need to guess why it is hanging!

[boyan-soubachov]

Thank you for your contribution!