TDD as if you Meant It: Refactor Primitives to Concepts (Episode 3)
Each primitive is always hiding a business concept (or call them Domain Entities if you wish). During this episode these primitives will get better names (“Maximize Clarity” from the Four Elements of Simple Design) and when I see duplication between them, it will be removed (“Minimize Duplication” from the Four Elements of Simple Design).
Whenever these concepts remain hidden, the cost of change is big. The more hidden design concepts we have, the bigger the cost of change. I optimize my code for fast and cheap changeability. Because this example is written using Object Oriented Programming concepts, each of these concepts needs at the end to become a class.
Classical Evolutionary Design Layers
The business concepts grow in layers from: primitives, to variables, methods and then classes. With TDD as if you Meant It we always use the rule of three when evolving from one layer to another. I always use refactorings to make duplication explicit and then minimize it. I never skip a layer, because that would be a much too bigger step. We could call this approach Evolutionary Design in Baby Steps.
This approach is useful when starting bottom-up, when there are no, or not may classes and methods, but tests. This approach would not be suitable usually when having a top-down approach.
Check the video below with the codecast:
Check the next episode on TDD as if you Meant it here: http://blog.adrianbolboaca.ro/evolutionary-design
On the same page you can find more ideas on Evolutionary Design.
Many thanks to Keith Braithwaite for creating the concept of TDD as if you Meant It
Teddy bear thanks to Erik Talboom for all the pairing, discussions that lead to so many twists we discovered together with TDD as if you Meant It.
Special regards to JB Rainsberger for the fun pairing we did using TDD as if you Meant It