no check engine light or nothing. will the car pass smog or does smog determine other things?

 

SMOG tests the way your engine runs. How well it combusts and burns in a given situation.
It tests the amount of fuel used, and compared to burns (through the spark process)
It checks the viability of the ignition system to burn said fuel mix.
It checks the operation of the exhaust system in its operation of the Cat converter.

The visual check to is make sure everything is there that is supposed to be there.
If you get a good guy that knows alot, they can give tips on what to do to gain things here and there and get away with by the read out of the test.