title: TypeError: argument of type 'Mock' is not iterable
body: <p>How could I mock an iterable item?</p>
  
  <p>In trying to test this method:</p>
  
  <pre><code>    def convert_time_field(klass, field, default=None):
          time = GrapheneHelper.get_json_field(klass, field, default)
  
          if time is None:
              return None
          else:
              return iso8601.parse_date(time)
  </code></pre>
  
  <p>My first test returns this error: <code>TypeError: argument of type 'Mock' is not iterable</code></p>
  
  <pre><code>    def test_convert_time_field(self):
          """ Return YYYY-MM-DDTHH:MM:FF in iso8601 format """
          time = '2017-09-18T23:09:57Z'
          expected_time = '2017-09-18 23:09:57+00:00'
          mock_klass = Mock()
          self.assertEqual(GrapheneHelper.convert_time_field(mock_klass, time, default=None), expected_time)
  </code></pre>
  
  <p>What am I misunderstanding about mocks in this case?</p>