Fill in the blank below.

Let's say you're working on an e$-$commerce website, and you have an element called ShoppingCart that handles adding items to the shopping cart, calculating the total price, and applying discounts. The ShoppingCart element interacts with other elements such as ProductCatalog to fetch product information and DiscountEngine to apply discounts.

You complete the following steps:

Create an instance of the ShoppingCart component.

Call the addItem$($productId$,$ quantity$)$ method with a valid product ID and quantity, such as "ABC$123"$ and $2.$

Use assertions to verify that the item is added to the cart successfully and the cart contains the correct number of items.

This scenario is an example of $\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_$ testing.

$*$Please write your answer in lowercase and ensure spelling is correct.