Design an application that manages your shopping lists.
The application should let you make shopping lists that have multiple items to buy. (There can be a limit of 100 items per list.) It should allow the user to keep multiple lists, such as a separate list per store.
Shopping items should specify the product to buy and the quantity of the product. They should also allow the user to get the total cost for that quantity of the product.
Users should be able to add items to the list by selecting from a set of predefined products that are available for them to choose from.
Users should also be able to get the total cost for a list, which is the total cost of buying all items on that list.