TDD Kata

Acme MultiBuy Checkout Kata

based on Kata @ http://codekata.com/kata/kata09-back-to-the-checkout/

• Think of a self service CHECKOUT that allows a customer to SCAN each ITEM to their BASKET in turn and PRINT a RECEIPT for the items they have purchased.
• The receipt shows each ITEM and it's UNIT PRICE.
• Additionally Acme has a SPECIAL PRICING RULE that allows customers to receive a DISCOUNT when purchasing multiples of the same item (e.g. 3 for 130).
• These MultiBuy Savings are shown in summary at the bottom of the receipt.
• Finally the TOTAL of the BASKET minus multibuy savings is printed at the end of the receipt.

An example stub for the checkout is provided.

public interface Checkout {
  void scan(String item);
  void printReceipt();
}

Required Behaviour

• Implement a simple checkout process that allows items to be scanned (one by one) to a customers checkout basket and a receipt printed as per the below example.

• For the kata the receipt can be printed using print methods of java.io.PrintWriter and passed as a dependency to the receipt printer.

  Item               Price
  ------------------------
    A                   50
    A                   50
    C                   20
    A                   50
    D                   15
    
  MultiBuy Savings
  ------------------------
    A   3-for-130      -20
    
  TOTAL                165
  ------------------------         

• Implement item unit pricing and multi-buy special pricing rules using the pricing table below.

  Item   Unit      Special
         Price     Price
  --------------------------
    A     50       3 for 130
    B     30       2 for 45
    C     20
    D     15

• Assume each item is scanned through the checkout in turn
• Assume the customer payment process is out of scope
• Assume that all items scanned will have a price

Developer rules

• Must use a strict TDD process
• Must not use abbreviations
• Must apply SOLID principles
• Must implement an Event sourcing pattern
• Must use dependency inversion
• Should use lamda programming style where appropriate

Guidence

• Begin with writing
  1. Checkout scan functionality
  2. Then adding basic receipt printing
  3. finally adding the special pricing rules and multibuy receipt printing
• What are the major entities / what design do you have in mind
• In which entity could a simple Event sourcing pattern be implemented ?
• What acceptance tests do you need to write ?
• Which behaviours do you need to test ?
• Do you need to use Mocking ?