" if you have kept your frameworks at arm’s length, then you should be able to unit-test all those use cases without any of the frameworks in place. You shouldn’t need the web server running to run your tests. You shouldn’t need the database connected to run your tests. Your Entity objects should be plain old objects that have no dependencies on frameworks or databases or other complications. Your use case objects should coordinate your Entity objects. Finally, all of them together should be testable in situ, without any of the complications of frameworks. "

― Robert C. Martin , Clean Architecture