Omitting to_return_value changes expectation checks about testslide

[fornellas]

The error message is indeed misleading, but it is doing the right thing. Looking at

self.mock_callable(
    mock_service, "func"
).for_call(expected_request).and_assert_called_once()

you are telling the mock to accept a specific call, but not telling it what to do when this call is made. In this case, using and_assert_called_once() makes little sense, as the test would never pass, as the call can never succeed.

I just put #85 that makes this case a ValueError:

    1) ValueError: You must first define a behavior. Eg: self.mock_callable(target, 'func').to_return_value(value).and_assert_called_exactly(times)