Hidden Concepts 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<\/a>) and when I see duplication between them, it will be removed (“Minimize Duplication” from the Four Elements of Simple Design<\/a>).<\/p>\n 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.<\/p>\n 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<\/em>.<\/p>\n 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.<\/p>\n <\/p>\n Check the video below with the codecast:<\/p>\n
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