If its anything like a Bandit (E110) AFX system to test it you held down a spring loaded switch while advancing both power levers up to a certain tq setting and then reduced one - it auto feathered - advance that power lever and it un feathered then repeat on the other engine. Armed for takeoff, and with the power levers above whatever the PLA was, if the system sensed a fall in tq/oil press, or however it worked, below a certain level with the thrust lever still fwd it auto feathered the prop on the failing engine.
So merely reducing power on one engine to simulate engine failure would NOT cause autofeather - on training flights it was a manual system - I'd be surprised if the EMB120 works much differently.
I haven't flown a Bandit since 1994 so all this is purely from memory.