You'd use a bore gauge on the bearing itself and a mic on the journal. For the most part, if this is a new build, then your primary consideration is does the cam turn freely with no drag or binding anywhere in the rotation? If the cam turns freely, then you've done about as much as you can do. If the cam binds, then you see if you have a cocked bearing or if the bearing needs a shave. Giving the cam a wiggle tells you nothing even if you highly instrument it.
The reason cam bearings don't get the same fastidious attention as main and rod bearings is that there's not much you can do if the bearing isn't right other than replace it and see if the replacement works better.
If this is an older build, then the primary indicator of worn cam bearings is low idle oil pressure and a little less at higher rpm. It's not really the end of the world as long as your mains and rods look okay. Most of the time, low oil pressure is oil going past the cam bearings.