I am reading about Alistair Cockburn's Hexagonal Architecture http://alistair.cockburn.us/Hexagonal+architecture with interest.

One claim he makes is: "Finally, the automated function regression tests detect any violation of the promise to keep business logic out of the presentation layer. The organization can detect, and then correct, the logic leak."

I do not understand this point. Is he saying that because the test is headless, then calls to a ui layer will throw exceptions? That doesn't seem to be a very sound test!