They are.

Many many companies run tests against the various kernel trees/branches, and will flood you with emails if you break the build.

I can't remember who (I think IBM maybe?), but Greg KH said one company made a fantastic test suite out of nowhere. If you submit six patches, it will try each one, tell you what you broke in patch 3, and recommend a way you can fix it. And this just gets emailed to the person who submitted the patches, and the maintainers if they actually merged it.

He said it was insanely advanced, and was made without the knowledge of the kernel maintainers. A company just made it and started sending emails one day.