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