Mock Google Directory Admin API

I have a code snipped that retrieves lists of users from google domain. I'm trying to write a unittest to return the list of users. But I do not want to query googleapi server to return the users list for the unittest. How do I mock http? Kindly keep in mind that google apiclient wraps the api post request.

An answer that also gives insight into mocking the build service object would be helpful as well.