A lot of the ultra-isolated test advocates seem to come from the kind of development world where you can exercise most of the value without needing to interact

A lot of the ultra-isolated test advocates seem to come from the kind of development world where you can exercise most of the value without needing to interact with external dependencies. With aggressive enough mocking, you can deceive yourself into thinking that any application is in that domain. I know I have done it, and the application worked PERFECTLY until I hooked it up to a real database.