Shopping Cart (Outside-In TDD)

Scenario 1 - Add items to shopping basket

Given I add 2 units of "The Hobbit" to my shopping basket And I add 5 units of "Breaking Bad" When I check the content of my shopping basket Then it should contain the following information:

• Creation date (of the shopping basket)
• 2 x The Hobbit // 2 x 5.00 = £10.00
• 5 x Breaking Bad // 5 x 7.00 = £35.00
• Total: £45.00

Acceptance criteria:

• Shopping basket should be created when the first product is added.
• Shopping basket should be persisted (In-memory, DB later)
• Each user should have her own shopping basket.

Products available (in-memory repository):

• Books
  • 10001: Lord of the Rings - £10.00
  • 10002: The Hobbit - £5.00
• Videos
  • 20001: Game of Thrones - £9.00
  • 20110: Breaking Bad - £7.00

    public class ShoppingBasketService {
    
        public void addItem(UserID userId, ProductID productId, int quantity) { }

        public <?> basketFor(UserID userId) { }
    
    }    

Scenario 2 - Stock restriction

• If there are not enough items available in stock for purchase, throw exception

Scenario 3 - Multi-buy discount

• Shopping cart should contain multi-buy discount:
  • 10% discount if 3 or more books are in the cart
  • 20% discount if at least one book and one video are in the cart
• In case both discounts on shopping basket apply, the biggest discount is selected.

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Scenario 4 - Payment

• Order should be created, with an OrderId.
• User submits payment, providing user and payment details
• Payment should be sent to payment gateway (external component)
• If payment is rejected, exception is thrown

    public class ShoppingBasketService {
   
        public void makePayment(UserId userId, PaymentDetails paymentDetails) { }        
   
    }
    
    public class PaymentGateway {
    
        public PaymentReference pay(Order order, UserId userId, PaymentDetails paymentDetails) 
    
    }

Scenario 5 - Notify purchase system

• Once items are sold (payment is made) if items in stock is below threshold, notify purchase component.

    public class PurchaseSystem {
    
        public void orderMore(ProductId productId, int actualQuantity)
     
    }

Scenario 6 - Send purchase confirmation email to user

• User should receive an email confirmation containing the order id, items bought, and price. (external)

    public class OrderConfirmation {
    
        public void send(UserId userId, OrderId orderId, PaymentReference paymentReference) { } 
    
    }

Scenarion 7 - Item reservation

• When items are added to shopping basket, items should be reserved, that means, if there were 10 items in stock, and one user adds 8 to her shopping cart, we should have only 2 available for being purchase by another user.

For these exercise, stock should be controlled with in-memory data (as long as it can be replaced with a DB in the future without breaking anything)