the way to test 4wd operation is to put the truck up on 4 jack stands.
(or at least put the front up if you don't have 4)
normal operation is as follows.

transmission in park, crank the truck, t-case in 2wd, leave it running.
turn the passenger side front tire.
when the CAD is disengaged properly for 2wd, the right front tire will spin independently.

shift tcase to 4wd. leave it running. repeat the turn of the passenger side front. CAD should engage the two axle halves and drivers side front tire should spin backwards.

shift tcase back to 2wd, leave it running, repeat tire turn. CAD should disengage and passenger side should freewheel.