the rules may be different for Travis county, but for the Harris county area on 1996 & newer, Texas doesn't use the "sniffer" any more.
it used to be if the inspection machine wouldn't communicate with the vehicle, then you would run it on the dyno. now if it doesn't communicate the inspection & test end and you have to repair the vehicle, or if its the fault of the inspection machine, go to another inspection station.
for the emissions part of the test they will do a visual check for emissions components & check the CEL light being on. they also check for codes and a maximum of 2 readiness monitors not complete.
if its a 2001 or newer, you can only have 1 readiness monitor not complete.