Three stage process in my case. One professional interviews with my future manager, one short interview with higher manager, and IQ test. In the professional interview Iwas asked questions like what is WRED, leaky bucket scheduler (position is IP router related), write simple class controlling IO line and write down a state machine allowing to toggle the line, or keep the line up/down depending on what application required. Specify API for connecting hardware driver (can be a class too) which actually writes to the hardware. All writing was done on paper.