Mocking remote api calls in golang - unit-testing

Question

I'm trying to get better at writing mocked golang tests that call a remote api
I can similate a single call pretty easily with the httptest library but am a
bit stuck handling other functions that call single endpoint calls multiple times.
For example given a simple create function
func createItem(url string, product Product) (int, error) {
// make request
return createdId, nil
}
I can write some tests that look like this
func TestCreateItem(t *testing.T) {
mock_ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
w.Header().Set("Content-Type", "application/json")
w.Write([]byte(`37`))
}))
prod := Product{...}
_, err := createItem(mock_ts.URL, 1, prod)
if err != nil {
t.Errorf("Error saving item: %v", err)
}
}
Now if I have this other wrapper function I won't be able to pass in the
mock test server url.
func someFunctionThatMakesManyItems(...) {
url = "http://www.realapiendpoint.com" // or some func that gets api url
// this function might generate a list of items
for _, item := range items {
createItem(url, item)
}
}
I could need to pass in the url to the someFunctionThatMakesManyItems and any
functions that rely on api functions and that just seems like the wrong approach.
Any advice on how to model this better to help with my tests?

Answer 1

Make the endpoint URL configurable instead of hard-coding it - make it a function parameter, or a field of some configuration struct, or returned from an internal configuration service, something like that. Designing for testability is all about avoiding hard-coded configuration and dependencies: code should receive its configuration values and its dependencies from the caller rather than setting or creating them itself.