Yes EXDAC, I have been testing a not unrelated failure mode. The airplane I "found" to have the ESP system also has an MT electric reversing propeller. That propeller has an airspeed pilot line diaphragm switch to disable the reverse system at flight speeds. That same switch on my airplane ('same reversing prop) had a hole form in the diaphragm, which caused about a 40 MPH too low airspeed indication. ('took me a bit to trouble shoot that!). So I had a valve put in the pitot line of the airplane I have been testing, which I can open in flight to bleed down pitot pressure, simulating the same failure, and resulting IAS error. Sure enough, open the valve as though I've have a pitot leak and the airplane pitches down considerably. Garmin told me it wouldn't, but it does.
So I have some issues to resolve before I'll issue an STC for this combination of mods to the airplane - and those were not what I was sent to flight test for, I found this by happenstance. The point is to know what you're flying, and what systems are installed. I have also recommended that airplanes equipped with background autoflight systems be placarded as such. Ultimately, an instructor could be asked to do an insurance check flight for a new owner of such an [equipped] airplane - best that instructor be on the top of their game, to prevent a check ride surprise, and to assure that the new pilot gets the whole training for the systems on that plane! This system was not installed in the original 1977 version of this airplane, so I was not expecting it to be there - my bad, lesson learned!