I don't know how many LOC you could trigger with a write. Including all drivers, filesystems , ..., perhaps millions. Hardly a unit test. And then, a driver is

I don't know how many LOC you could trigger with a write. Including all drivers, filesystems , ..., perhaps millions. Hardly a unit test. And then, a driver is difficult to unit test. BUT some parts of the kernel could use unit tests. The thing is, they don't and the usage of the kernel shows that they would be triggered by usage, but it wouldn't harm.