After the aircraft is in cruise and properly leaned (5 to 15d LOP is
  fine at 12,000 feet)   the point is to do whatever you want with the
  prop and throttle lever to descend as fast as you care to do so.
  
Feel free to play fooseball with the prop and throttle - - - !!!
  
  The issue is to do this without touching the mixture control - - - and
  then to see what happens when you apply power at lower altitude, such as
  might be the case upon entering the traffic pattern.
 
   Does the engine quit?
 
   Does it continue to run - - at high power - - although lean of peak or
  around peak EGT ?