def test_should_return_number_of_items_on_a_delivery(self): po = PurchaseOrderFactory(order_number=123456) po_item_one = PurchaseOrderItemFactory(purchase_order=po) po_item_two = PurchaseOrderItemFactory(purchase_order=po) delivery = DeliveryFactory() DeliveryNodeFactory(distribution_plan=delivery, item=po_item_one) self.assertEqual(delivery.number_of_items(), 1) DeliveryNodeFactory(distribution_plan=delivery, item=po_item_two) self.assertEqual(delivery.number_of_items(), 2)