Test Behaviour not Implementation

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• A unit isn't a fixed size

  Indeed, Test from the outside-in produces this kind of effect, whereas focusing too much on testing everything in too small a unit of isolation can lead to overspecification and complexity, either through having too many mocks (Overmocking creates alternative facts) or focusing on the implementation (Test behaviour not implementation)

• Indirection without Abstraction is Waste

  Fix by Test behaviour not implementation

• Overmocking Creates Alternative Facts

  Fixed by Test behaviour not implementation

• Test-Driven Development

  Test behaviour not implementation, so that tests do not become tightly-coupled or overspecified