The way I check wheel bearings is to first be sure they are very clean, and look for any pitting or obvious discoloration on the rollers and look at the outer race (which will be in the drum or rotor)for any markings that look suspiciously like wear. Then the bearing inside the outer race, hold pressure on the inner race and rotate it back and forth. If the bearing is OK it will feel very smooth as you turn it. If it is not smooth-replace it.