Again, much like with the code, the architecture can benefit from separating pieces into smaller components. The fact that dependencies are now isolated and controlled by separate components leaves us with a cleaner design for the main application, and now it's easier to ignore the boundaries to focus on testing the core of the application.

We could create a patch for the dependencies, and write unit tests that are simpler (they won't need a database), or to launch an entire web service, for instance. Working with pure domain objects means it will be easier to understand the code and the unit tests. Even the adapters will not need that much testing because their logic should be very simple.