Does Linux have a comprehensive test suite (comparable eg. to SQLite)? I'm wondering because it seems to be quite bug free, and is a large project, and a kernel seems to be quite suitable for unit testing (compared to your typical CRUD app for example).

I suspect there's not much formal testing (at least done or required by Linus, some external projects may be available). So it seems that testing isn't that necessary for a quality project? On the other hand Linux has a large community so maybe that substitutes for a comprehensive test suite?