I don't think anyone is saying unit tests and you are good to go are they? In any critical system work, there are multiple layers and you can't really skip any

I don't think anyone is saying unit tests and you are good to go are they? In any critical system work, there are multiple layers and you can't really skip any of them. It's also sort of meaningless to talk about such testing without requirements and spec to test against. Traceability is as much a part of it as any of the testing. By the time you get to the "thick book/full run" as you put it, there has typically been a metric crapload of testing done already.