21 November 2019

Promotion Service Kata

In September I attended a small, club-like unconference. The umbrella topic of the event was katas and their use in teaching and technical coaching. A kata, or code kata, is defined as an exercise in programming which helps hone your skills through practice and repetition. We spent two days creating, practising and reviewing different exercises. I came home with a load of new challenges for my clients.

Kata Factory
One session, run by Bastien David, a software crafter from Grenoble, was named Kata Factory. Bastien guided us to create a short exercise with a very small code base, focused on a single topic. In the first part of the session we created small tasks working in pairs. Then we solved a task from another pair in the second part. A total of four new coding exercises was created, tried and refined. It was awesome.

Promotion Service Kata
I worked with Dmitry Kandalov and we created the Promotion Service Kata. It is a small refactoring exercise, based on Feature Envy, a code smell listed in Martin Fowler's book. (Did you know that there is a second edition of this great book? No, so get it quickly.) The code base contains a single service, the promotion service, which calculates discounts for promoted items. It is a bit crazy because it also reduces the tax. The data is stored in a classic DTO and its fields are not encapsulated. The task is to make it a rich object and encapsulate its fields. There are existing unit tests to make sure things are still working.

After the Kata Factory, I spent some time on porting the kata to different languages. Currently the code is available in C#, Java, Kotlin, PHP and Python. Pull requests porting the code to other languages are very welcome. Check out the code here.

Promotion Service RetrospectiveNotes from first run
I already facilitated the exercise with a small team of C# developers. Here is what they said about the kata:
  • It is a good exercise.
  • It is a short exercise. It is small, so there is no need for context.
  • Encapsulate all the things!
  • I learned to separate concerns.
  • I learned about string.Format (a C# specific function).
  • I did not know the goal of the exercise.
  • Maybe rename the Persist() method to Save().
  • The Item class should be in its own file.
Bastien's approach shows that it is possible to create a brand new and highly focused coding exercise in a short time. As with most development related things, pair work is superior and it is easy to come up with new code katas when working in pairs. Small exercises - I call them micro exercises - are easy to get started because there is little context to know. Context is part of what makes coding assignments difficult. I am very happy with this new exercise.

Give it a try!

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