The Gilded Rose Refactoring Kata in Go
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Gilded Rose Refactoring Kata

After watching Sandi Metz's talk I thought I'd try this in Go. This is a fork of Emily Bache's repo. The master branch is the original code. I am using the refactor branch to refactor the code.


go test -v -cover

To include the example tests:

go test -tags example

From original repo

This Kata was originally created by Terry Hughes (!/TerryHughes). It is already on GitHub here. See also Bobby Johnson's description of the kata.

I translated the original C# into a few other languages, (with a little help from my friends!), and slightly changed the starting position. This means I've actually done a small amount of refactoring already compared with the original form of the kata, and made it easier to get going with writing tests by giving you one failing unit test to start with. I also added test fixtures for Text-Based approval testing with TextTest (see the TextTests)

As Bobby Johnson points out in his article "Why Most Solutions to Gilded Rose Miss The Bigger Picture", it'll actually give you better practice at handling a legacy code situation if you do this Kata in the original C#. However, I think this kata is also really useful for practicing writing good tests using different frameworks and approaches, and the small changes I've made help with that. I think it's also interesting to compare what the refactored code and tests look like in different programming languages.

I wrote this article "Writing Good Tests for the Gilded Rose Kata" about how you could use this kata in a coding dojo.

How to use this Kata

The simplest way is to just clone the code and start hacking away improving the design. You'll want to look at the "Gilded Rose Requirements" which explains what the code is for. I strongly advise you that you'll also need some tests if you want to make sure you don't break the code while you refactor.

You could write some unit tests yourself, using the requirements to identify suitable test cases. I've provided a failing unit test in a popular test framework as a starting point for most languages.

Alternatively, use the "Text-Based" tests provided in this repository. (Read more about that in the next section)

Whichever testing approach you choose, the idea of the exercise is to do some deliberate practice, and improve your skills at designing test cases and refactoring. The idea is not to re-write the code from scratch, but rather to practice designing tests, taking small steps, running the tests often, and incrementally improving the design.

Gilded Rose Requirements Specification

Hi and welcome to team Gilded Rose. As you know, we are a small inn with a prime location in a prominent city ran by a friendly innkeeper named Allison. We also buy and sell only the finest goods. Unfortunately, our goods are constantly degrading in quality as they approach their sell by date. We have a system in place that updates our inventory for us. It was developed by a no-nonsense type named Leeroy, who has moved on to new adventures. Your task is to add the new feature to our system so that we can begin selling a new category of items. First an introduction to our system:

  • All items have a SellIn value which denotes the number of days we have to sell the item
  • All items have a Quality value which denotes how valuable the item is
  • At the end of each day our system lowers both values for every item

Pretty simple, right? Well this is where it gets interesting:

  • Once the sell by date has passed, Quality degrades twice as fast
  • The Quality of an item is never negative
  • "Aged Brie" actually increases in Quality the older it gets
  • The Quality of an item is never more than 50
  • "Sulfuras", being a legendary item, never has to be sold or decreases in Quality
  • "Backstage passes", like aged brie, increases in Quality as its SellIn value approaches;
    • Quality increases by 2 when there are 10 days or less and by 3 when there are 5 days or less but
    • Quality drops to 0 after the concert

We have recently signed a supplier of conjured items. This requires an update to our system:

  • "Conjured" items degrade in Quality twice as fast as normal items

Feel free to make any changes to the UpdateQuality method and add any new code as long as everything still works correctly. However, do not alter the Item class or Items property as those belong to the goblin in the corner who will insta-rage and one-shot you as he doesn't believe in shared code ownership (you can make the UpdateQuality method and Items property static if you like, we'll cover for you).

Just for clarification, an item can never have its Quality increase above 50, however "Sulfuras" is a legendary item and as such its Quality is 80 and it never alters.