The metal bar that was placed behind the thrust levers was known as the 'Bodie Bar'. From memory there was a USAF pilot who used to do slam accelerations, and decelerations of engines. That is how it got its name...
One fairly standard engineering test is called the "Bodie burst"; starting from a high thrust setting, chop to idle, then as the rotor is spooling down, "burst" or slam back to high power. This is a pretty severe test, because any slop (hysteresis) or wear in the control system will take the compressor closer to the stall/surge boundary.
There is also a "reverse Bodie"; starting at idle, begin an acceleration, then chop back to idle. It is a good test of combustor stability.
These tests are part of the engine development routine, and may also be applied as required to field engines.