What is an extinction test?
It's a behavioral thing. 
The abstract of the paper says: "...mixtures of two drugs from vehicle in two-lever procedures with food reinforcers..."

In operant behavior, rats (in this case) are trained to associate a stimulus (a tone, an odor, a light, etc.) with an action that leads to a reward, the association is trained by delivering a reward only when the 'correct' action is performed, e.g.:

stim A -> press left lever -> get a reward

stim A -> press right lever -> get nothing (or a punishment, but that is a whole different question)

One can quantify the performance of the animal by looking at the probability of responding left (in this case) when stim A is presented.

Now, we think of the association between stim A and left pressing as being reinforced whenever a reward is present, we call it extinction whenever the reward is not present, basically because the reinforced behavior will eventually extinguish, and we say its extinguished when the probability of response to the left and right is 50%.

"...generali[z]ation to ethanol was examined in extinction tests..." 
basically means that they substituted stim A for ethanol (I imagine its all olfactory, just read the abstract sorry) and characterize the response to ethanol without ever reinforcing it, hence the extinction.