[$] A kernel unit-testing framework

For much of its history, the kernel has had little in the way of formal
testing infrastructure. It is not entirely an exaggeration to say that
testing is what the kernel community kept users around for. Over the
years, though, that situation has improved; internal features like
kselftest and services like the 0day testing system have increased our test
coverage considerably. The story is unlikely to end there, though; the
next addition to the kernel's testing arsenal may be a unit-testing framework
called KUnit.