A kernel unit-testing framework

"All models are wrong. Some are useful."

But the "useful" threshold varies widely depending on what you're trying to accomplish.

The majority of my headaches with respect to device drivers was due to the hardware not working the way it was documented. Spurious interrupts, clock phasing, interactions/collisions with shared resources, subtle sleep/wake sequencing issues, sensitivity to environmental conditions (eg clocks drifting between -40C -> 85C), dma peripheral quirks, workarounds for things fixed in later revisions.. and so forth.

Granted, I also had plenty of headaches due to the upper stacks not behaving as specified either. Or perhaps I should say significantly underspecified -- While it was actually well-tested (unit and system-level) the tests were written from the same incorrect/incomplete set of spherical-cow specifications/assumptions.