Yeah its been pretty much explained, when rocking the wheel hold it with a hand on the top and a hand on the bottom, you should feel a slight knocking through your hands if the bearing is loose, whilst its on the stands put your ear close to the hub and spin the wheel, if its gone you'll hear it whir.
Bearings are cheap to buy but make sure you don't knacker them putting them in the discs. I always use an old outer race to drive the new ones in.