How to mock for same input and different return values in a for loop in golang

Question

I'm running a test with multiple parameters in a for loop using go lang testing.

I ran into a situation where same return value (and first set) is returned every time the mock is called. What I want to be able to do is change the return value for each test when the input is same i.e., same On but different Return in a loop.

I am using stretchr/testify for mocks. It looks like it will not overwrite already created mock when On is same.

func TestUpdateContactWithNewActions(t *testing.T) {
    tests := []struct {
        testName  string
        getParams func() *activities.UpdateContactWithNewActionsActivity
        mockError error
    }{

        {"UpdateContactWithNewActions with error from contact service",
            func() *activities.UpdateContactWithNewActionsActivity {
                return fixtures.GetUpdateContactWithNewActionsActivity()
            }, fixtures.Err},
        {"UpdateContactWithNewActions valid",
            func() *activities.UpdateContactWithNewActionsActivity {
                return fixtures.GetUpdateContactWithNewActionsActivity()
            }, nil},
    }

    lib.LoadWithMockClients()

    for _, test := range tests {
        test := test
        t.Run(test.testName, func(t *testing.T) {
            lib.MockCSClient.On(
                "UpdateContactWithNewActions",
                mock.AnythingOfType("tchannel.headerCtx"),
                fixtures.UpdateContactWithNewActions).Return(test.mockError)

            returnedResult, err := test.getParams().Execute(fixtures.Ctx)
            if test.mockError == nil {
                // some assertion
            }
            assert.Error(t, err)
        })
    }
}

Answer 1

I had a similar problem.

The solution was the method Once()

In your mock add an .Once() and repeat the mock with each result you need.

Something like this:

lib.Mock.On("method", arg).Return(test.mockError).Once()
lib.Mock.On("method", arg).Return(nil).Once()

Each mock result will be returned only once.

https://godoc.org/github.com/stretchr/testify/mock#Call.Once

Answer 2

The answer @Marcos provided works well when the result needs to be returned exactly once.
But in the scenario where each return value needs to be returned multiple (unknown) times, it won't work.

The way I solved it is by manipulating the mock.ExpectedCalls directly. In my case the mock was holding only a single method, so it was simple to just cleanup the whole ExpectedCalls slice, but in case there are multiple methods, the ExpectedCalls slice can be iterated, and update only the required call.

here is a working example for the simple case:

lib.Mock.On("method", arg).Return("1")

assert.Equal(t, lib.Mock.method(arg), "1")
assert.Equal(t, lib.Mock.method(arg), "1")
....
assert.Equal(t, lib.Mock.method(arg), "1")

lib.Mock.ExpectedCalls = nil // cleanup the previous return value
lib.Mock.On("method", arg).Return("2")
assert.Equal(t, lib.Mock.method(arg), "2")
assert.Equal(t, lib.Mock.method(arg), "2")
....
assert.Equal(t, lib.Mock.method(arg), "2")