[stickfigure]

This is true at a blackbox level but you can pretty effectively create automated tests of finer grained software components. The idea is presumably that if you have a bunch of components that work well, the overall system will tend to work better.

I think this is generally true although it has limits; the higher up you go in the stack, the more value the test has. Still, if it's prohibitively difficult to test higher up the stack, might as well test what you can, no?

I found from my years in at EA in the early 2000s that no matter what the technical issues, the absence of automated testing was at the very least a significant cultural issue. Engineers just didn't think about unit tests. Sounds like that hasn't changed.