# User 2 should be able to add item to their cart once the

        # reservation duration is elapsed

        self.add_timedelta(self.RESERVATION + datetime.timedelta(seconds=1))

        second_cart.add_to_cart(self.PROD_1, 1)

        # User 2 pays for their cart

        # User 1 should not be able to add item to their cart

        # because user 2 has paid for their reserved item, exhausting

        # the ceiling, regardless of the reservation time.

        self.add_timedelta(self.RESERVATION * 20)

        with self.assertRaises(ValidationError):

        # Unpaid cart within reservation window

        second_cart.add_to_cart(self.PROD_1, 1)

        with self.assertRaises(ValidationError):

            first_cart.validate_cart()

        # Paid cart outside the reservation window

        self.add_timedelta(self.RESERVATION + datetime.timedelta(seconds=1))

        with self.assertRaises(ValidationError):

            first_cart.validate_cart()

    def test_items_released_from_ceiling_by_refund(self):

        self.make_ceiling("Limit ceiling", limit=1)

        first_cart = TestingCartController.for_user(self.USER_1)

        first_cart.add_to_cart(self.PROD_1, 1)

        second_cart = TestingCartController.for_user(self.USER_2)

        with self.assertRaises(ValidationError):

            second_cart.add_to_cart(self.PROD_1, 1)

        first_cart.cart.released = True

        second_cart.add_to_cart(self.PROD_1, 1)

    def test_discount_ceiling_only_counts_items_covered_by_ceiling(self):

        self.make_discount_ceiling("Limit ceiling", limit=1, percentage=50)

        voucher = self.new_voucher(code="VOUCHER")

        # the 100% discount from the voucher should apply to the first item

        # and not the ceiling discount.

        cart.apply_voucher("VOUCHER")

        cart.add_to_cart(self.PROD_1, 1)

        self.assertEqual(1, len(cart.cart.discountitem_set.all()))

        # The second cart has no voucher attached, so should apply the

        # ceiling discount

        cart = TestingCartController.for_user(self.USER_1)

        cart.add_to_cart(self.PROD_1, 1)

        self.assertEqual(1, len(cart.cart.discountitem_set.all()))