'Test that retrieve_client_credentials will return the credentials.
We must assert that when set, this function will return them.'

def test_retrieve_client_credentials_when_set(self):

    s = self.build_session()
    s.params = {'client_id': 'id', 'client_secret': 'secret'}
    assert (s.retrieve_client_credentials() == ('id', 'secret'))
