I was working through Bowling Game Kata  trying to learn more about Test Driven Development. When I took a rabbit trail, and I found this little nugget: Uncle Bob’s Transformation Priority Premise.

As the tests get more specific, the code gets more generic.

At the heart of this article is that production code goes through a sequence of transformations. The thought being that it goes from specific to generic. This understanding that refactoring simply changed the structure of code without changing it’s behavior as the transformations used to go from Red to Green had a type of pattern.

And by going in a specific order, or has the writer says Priority Premise, these transformations would make writing tests easier.

…the idea that transformations on the top of the list should be preferred to those that are lower. It is better (or simpler) to change a constant into a variable than it is to add an if statement. So when making a test pass, you try to do so with transformations that are simpler (higher on the list) than those that are more complex.

What’s more, when you pose a test, you try to pose one that allows simpler transformations rather than complex transformations; since the more complexity required by the test the larger the risk you take to get that test to pass.

Overall, this is an interesting concept that quickly gives me a checklist of steps to take when starting out. Even if it is a reminder that all tests should start by failing due to an empty/null return.