We often design our code so that one procedure comprises many classes, often grouped by layers. For example, in web dev, that could be controllers, models, repositories, etc:
Layers are good. Often at least two layers are desirable for maintainability: domain and low-level. If you’re like me, you like 2-5 layers but not too many.
Now how do you test such code? It comes naturally to want to test each component separately and mock out the collaborators from other layers. I believe it’s because unit tests are said to be run “in isolation”:
My advice – don’t automatically do this. Aim for this instead:
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