The Supermarket Receipt Refactoring Kata
This is a variation of a popular kata described in http://codekata.com/kata/kata01-supermarket-pricing/. The aim of the exercise is to build automated tests for this code, refactor it, and add a new feature.
The supermarket has a catalog with different types of products (rice, apples, milk, toothbrushes,...). Each product has a price, and the total price of the shopping cart is the total of all the prices of the items. You get a receipt that details the items you've bought, the total price and any discounts that were applied.
The supermarket runs special deals, e.g.
- Buy two toothbrushes, get one free. Normal toothbrush price is €0.99
- 20% discount on apples, normal price €1.99 per kilo.
- 10% discount on rice, normal price €2.49 per bag
- Five tubes of toothpaste for €7.49, normal price €1.79
- Two boxes of cherry tomatoes for €0.99, normal price €0.69 per box.
These are just examples: the actual special deals change each week.
Create some test cases and aim to get good enough code coverage that you feel confident to do some refactoring.
When you have good test cases, identify code smells such as Long Method, Feature Envy. Apply relevant refactorings.
When you're confident you can handle this code, implement the new feature described below
New feature: discounted bundles
The owner of the system has a new feature request. They want to introduce a new kind of special offer - bundles. When you buy all the items in a product bundle you get 10% off the total for those items. For example you could make a bundle offer of one toothbrush and one toothpaste. If you then you buy one toothbrush and one toothpaste, the discount will be 10% of €0.99 + €1.79. If you instead buy two toothbrushes and one toothpaste, you get the same discount as if you'd bought only one of each - ie only complete bundles are discounted.
New feature: HTML receipt
Currently we print a traditional ticket receipt. Now beeing a modern business we'd like to be able to print or send a HTML version of the same receipt. All the data and number formatting should be the same. However the layout should be html. You don't have to worry about the HTML template - a designer will care of that - but we do need someone to keep duplication between the reports to a bare minimum.
Start with the refactoring
If you would like to just do the refactoring part of this exercise, you can instead check out the 'with_tests' branch. Those tests have reasonably good coverage and should support most kinds of refactorings you'd like to do.
Use this exercise in a Learning Hour
You can use the Supermarket Receipt Kata in learning hours if you are using the Samman coaching method.