A good bearing on a pulley will NOT freewheel. It should feel smooth and "creamy" and make no noise, but if spun, should stop pretty well immediately. If it keeps on coasting, the bearing is toast. Something like an alternator that has some mass to it is another story, but a tensioner pulley should NOT freewheel.

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]