'With showanswer="past_due" should only show answer after the problem is closed
for everyone--e.g. after due date + grace period.'

def test_showanswer_past_due(self):

    used_all_attempts = CapaFactory.create(showanswer='past_due', max_attempts='1', attempts='1', due=self.tomorrow_str)
    self.assertFalse(used_all_attempts.answer_available())
    past_due_date = CapaFactory.create(showanswer='past_due', max_attempts='1', attempts='0', due=self.yesterday_str)
    self.assertTrue(past_due_date.answer_available())
    attempts_left_open = CapaFactory.create(showanswer='past_due', max_attempts='1', attempts='0', due=self.tomorrow_str)
    self.assertFalse(attempts_left_open.answer_available())
    still_in_grace = CapaFactory.create(showanswer='past_due', max_attempts='1', attempts='1', due=self.yesterday_str, graceperiod=self.two_day_delta_str)
    self.assertFalse(still_in_grace.answer_available())
