The Beverages Prices Refactoring kata: a kata to practice refactoring away from an awful application of inheritance.

I created the Beverages Prices Refactoring kata for the Deliberate Practice Program I’m running at Lifull Connect offices in Barcelona (previously Trovit). Its goal is to practice refactoring away from a bad usage of inheritance.

The code computes the price of the different beverages that are sold in a coffee house. There are some supplements that can be added to those beverages. Each supplement increases the price a bit. Not all combinations of drinks and supplements are possible.

Just having a quick look at the tests of the initial code would give you an idea of the kind of problems it might have:

If that’s not enough have a look at its inheritance hierarchy:

To make things worse, we are asked to add an optional cinnamon supplement that costs 0.05€ to all our existing catalog of beverages. We think we should refactor this code a bit before introducing the new feature.

We hope you have fun practicing refactoring with this kata.

Originally published in Manuel Rivero's blog.