def test_receipt_add_product(self): toothbrush = Product("toothbrush", ProductUnit.EACH) apples = Product("apples", ProductUnit.KILO) receipt_toothbrush = ReceiptItem(toothbrush, 2, 1.5, 3) receipt = Receipt() receipt.discount = [] receipt._items = [receipt_toothbrush] self.assertEqual(1, len(receipt._items)) receipt.add_product(apples, 2, 1, 2) self.assertEqual(2, len(receipt._items))