def test_order(self):
        assert (event.Priority.PRE_CORE
                > event.Priority.CORE
                > event.Priority.POST_CORE
                > event.Priority.PRE_DEFAULT
                > event.Priority.DEFAULT
                > event.Priority.POST_DEFAULT)
def is_overdue(self):
        """
        Returns True when the due date is in the past and the task has not
        yet been completed.
        """
        return not self.is_completed() and self.days_till_due() < 0