def test_type(self):
        rset = event.ResultSet()
        with pytest.raises(NotImplementedError):
            rset.extend([])
        with pytest.raises(NotImplementedError):
            rset.extend(False)
def _update_height(self, height_diff):
    if self._items_total_height is None:
      self._items_total_height = self.get_allocation().height