ahhh just put it in gear and push it forward a few feet and let the clutch out.... the bike should abruptly stop !
do that for each gear.... that should indicate a intact transmission,.....though it's not as good as a motor running step through the gears
its better than nothing you'll learn that it can go into each gear and that the resistance from the cylinders gets a little less and less the higher in the gears you get....
Or..... get the rear wheel off the ground and put it in 1st and kick it through ( take the plugs out) and see if the rear wheel turns
do that for each gear ... then you can be fairly certain the trans is in good shape...
Bob........