作证在函数内部模拟函数返回

Question

I would like to Mock the response of a function. But this function is located or called inside another function. Let say I have this function

// main.go
func TheFunction() int {
   // Some code
   val := ToMockResponse()
   return val
}

func ToMockResponse() int {
    return 123
}

Now on my test file

// main_test.go
func TestTheFunction(t *testing.T) {
    mockInstance = new(randomMock)
    mockInstance.On("ToMockResponse").Return(456)

    returned := TheFunction()
    assert.Equal(t, 456, returned)
}

As you can see within function TheFunction() a call to function ToMockResponse is made. Now I would like to test TheFunction but I would like to Mock the response of ToMockResponse how can I achieve this?

Answer 1

You should consider passing in the second function is as an parameter to the first.

You have a few options for doing that. You could simply pass it as a parameter.

func DoX(doY func()) {
   doY()
}

That’s simple but doesn’t work well as the core get more complex. The better alternative is often to make the functions methods on a struct.

type X struct {
   Y Y
}

type Y interface {
   Do()
}

func (x *X) Do() {
   x.Y.Do()
}

Then Y can be replaced with a mock.