Welcome to your fifth and final unit for this course, dedicated to practicing Test-Driven Development (TDD) utilizing Swift and XCTest. We're going to finish building our ShoppingCart system by adding even more features to our class.

In this course, emphasis is placed on hands-on practice, where you'll receive requirements through tests, one at a time. Your task is to write tests AND implement code that makes each test pass, simulating a real-world TDD environment. Previously, I wrote the tests for you; this time, it's all up to you!

Remember to use the core concepts of the Red-Green-Refactor cycle while completing these coding exercises. I'm still here to help! Just ask.

• Description: The cart should enforce a maximum quantity limit of 10 for a single type of product, preventing more than the allowed amount from being added.
• Details
  • Utilize the addItem(item: Product, quantity: Int) method to add products to the cart.
  • Ensure an exception is raised when adding a quantity that exceeds a limit of 10 for a single product.
  • The exception message should clearly state, "Maximum quantity exceeded" when the limit is breached.
• Examples: Attempting to add 11 units of Product(id: "1", name: "Book", price: 10) should raise an exception indicating "Maximum quantity exceeded."

• Description: When a product is added to the cart, it should be possible to retrieve the product details using its ID, which includes the product information and its quantity in the cart.
• Details
  • Enable products to be added using an addItem() method with specific IDs.
  • Ensure getItem(id: String) returns the correct product details, including the quantity after being added to the cart.
• Examples: Adding a product with Product(id: "1", name: "Book", price: 10) and retrieving it by ID "1" should return Product(id: "1", name: "Book", price: 10, quantity: 1).

• Description: Applying a valid discount code should reduce the total price of products in the cart by the specified discount percentage.
• Details
  • Use the applyDiscountCode(code: String) method to apply a discount.
  • Support valid discount codes like "HOLIDAY25" for a 25% discount.
  • Update getTotal() to reflect the discounted price.
• Examples: Applying the discount code "HOLIDAY25" to a product Product(id: "1", name: "Book", price: 100) should reduce the total to 75.

• Description: The system should not accept discount codes that are invalid and should raise an appropriate exception when such a code is applied.
• Details
  • Ensure applyDiscountCode(code: String) checks against a list of valid codes.
  • Raise an exception with the message "Invalid discount code" if the code is not valid.
• Examples: Applying the discount code "INVALID" after adding a product should raise an exception indicating the code is invalid.

• Description: When a product that already exists in the cart is added again, its quantity should increase without duplicates, and the total price should reflect the cumulative price.
• Details
  • Allow products to be added again using the addItem() method without creating duplicates in the cart.
  • Ensure getItem(id: String) returns the updated quantity after adding the same product.
  • Update the total price to reflect the price of the added products' cumulative quantities.
• Examples: Adding Product(id: "1", name: "Book", price: 200) twice should result in a quantity of 2 for that product, with the total updated price reflecting the double addition.

• Description: When an existing product in the cart has more units added to it, the total quantity should not exceed the predefined maximum limit.
• Details
  • Utilize the addItem(item: Product) method to add to an existing product.
  • Ensure that adding a quantity that results in exceeding the maximum allowed quantity raises an exception.
  • The exception message should be "Maximum quantity exceeded" when the quantity limit is breached.
• Example: Adding 3 units of Product(id: "1", name: "Book", price: 200) to an existing 8 units should raise an exception, as it exceeds the limit.

In this unit, you reviewed descriptions for more advanced test cases to expand the functionality of the ShoppingCart class, covering features like handling non-existent products, applying discounts, and updating product quantities. With your solidified TDD skills, let's proceed to writing targeted test cases that capture essential functionality for a robust ShoppingCart class.

As you undertake these exercises, remember to engage in the Red-Green-Refactor cycle. Be sure to practice writing tests first, and do not write implementation code unless the test asks for it.

Red! Green! Refactor!