Coolbits OC setting 'test' vs RivaTuner OC setting 'test'?

Curious as to what the difference is between the Coolbits 'test' button and the RivaTuner 'test' button when one is changing speeds?

I notice that the Riva Tuner takes about a second and the Coolbits takes about 15 seconds to test the new settings. What are they doing during this time?

somegeek