we are only interested in the return value from the final call to
`start_call` so we don't have much configuration to do. Let's assume the
object it returns is 'file-like', so we'll ensure that our response object
-uses the builtin `file` as its `spec`.
+uses the builtin `open` as its `spec`.
To do this we create a mock instance as our mock backend and create a mock
response object for it. To set the response as the return value for that final
method to directly set the return value for us:
>>> something = Something()
- >>> mock_response = Mock(spec=file)
+ >>> mock_response = Mock(spec=open)
>>> mock_backend = Mock()
>>> config = {'get_endpoint.return_value.create_call.return_value.start_call.return_value': mock_response}
>>> mock_backend.configure_mock(**config)