Calling create_client_mock() repeatedly takes about a second each time it's called. This is because calling APIClient(local_api_spec=...) creates new resource classes from the endpoints JSON every time, instead of using the normal resource cache like it does when calling APIClient() without a local_api_spec.
Total test time on Travis (this PR is on top, previous build is bottom):
Total test time on Travis (this PR is on top, previous build is bottom):
Not sure if this deserves a changelog entry?