How old? I would want prelims on hips and elbows at the minimum and then test the dog's drive level for food and/or toys, how it reacts to changes in environment and obstacles. No fun doing agility with a dog that you have to baby through everything because they can't deal with the obstacles or the stress of the environment during trials. I would also look at structure. Balance works best and the dog will stay sounder over the long haul. No extremes (too angulated or too straight).