Experimental: Add mocking integration

[jackkleeman]

See mocking example in examples/ticketreservation/main_test.go

[github-actions]

Test Results

  7 files  ±0    7 suites  ±0   3m 4s ⏱️ +5s
 45 tests ±0   44 ✅ ±0  1 💤 ±0  0 ❌ ±0 
172 runs  ±0  169 ✅ ±0  3 💤 ±0  0 ❌ ±0 

Results for commit 8025b4e. ± Comparison against base commit 1df62ed.

[co-go]

Can we add another helper to reduce this boilerplate a little? I found myself duplicating this a decent bit!

Proposed API:

mockCtx.EXPECT().RandUUID().Return(uuid.Max)

Implementation:

func (_e *MockContext_Expecter) RandUUID() *MockRand_UUID_Call {
	mockRand := &MockRand{}
	_e.Rand().Return(mockRand)
	return mockRand.EXPECT().UUID()
}

[co-go]

Tweak to use t in the initialization:

func (_e *MockContext_Expecter) RandUUID(t *testing.T) *MockRand_UUID_Call {
	mockRand := NewMockRand(t)
	_e.Rand().Return(mockRand)
	return mockRand.EXPECT().UUID()
}

[co-go]

This is a nice addition as well, makes writing tests for promises much easier! One suggestion specifically for these promises is another helper with initializing them:

func (_e *MockContext_Expecter) PromiseByName(t *testing.T, promiseName string) *MockDurablePromise_Expecter {
	mockPromise := NewMockDurablePromise(t)
	_e.Promise(promiseName, mock.Anything).Return(mockPromise)
	return mockPromise.EXPECT()
}

Usage might look like:

	mockCtx.EXPECT().
		PromiseByName(t, "some_cool_promise").
		ResultAndReturn(neat.Data{Wow: "Amazing"}, nil)

[co-go]

For the helpers I suggested, they don't need the t param passed into them, but it would be nice. Having the user pass these through params is also not ideal, especially because the mock has already been initialized with t.

I did some digging to see if we could pull that from the mock context itself, but testify/mock keeps it private. So the next best thing might be to alter the generated template from mockery to persist the passed in t into the Mock struct, which currently is hardcoded, but I'd imagine another config var to allow tweaking these templates might be received better in mockery than tweaking a core struct in testify.