def test_bool(self):
        prio_set_list = event._PrioritizedSetList()

        assert bool(prio_set_list) is False

        prio_set_list.add(0, None)
        assert bool(prio_set_list) is True
def _update_height(self, height_diff):
    if self._items_total_height is None:
      self._items_total_height = self.get_allocation().height