Is it recommended to have an ADS-B transponder in ALT mode on the ground? Early on in training I was told that unless the airport specifically noted it on the chart, that the transponder was turned to ALT (altitude) mode just prior to taking the runway for take-off (lights, camera, action), and was changed back to SBY (standby) immediately after exiting the runway.

Recently we had a Garmin GTX-345 ADS-B transponder installed in our aircraft and as part of the ADS-B rebate program you need to do a check-out in "rule airspace". When I got the test report from the FAA I noticed that I passed the air portion but failed the ground portion due to an insufficient number of reports (messages) while on the ground. I retook the test making sure to put the transponder in ALT mode at the hangar and subsequently passed.

This leads me to believe that the transponder should be in ALT mode pretty much all the time. Is there any recommendations from the FAA that say that ADS-B transponders should be active while on the ground?

The GTX-345 Manual (2-1) has this to say:


  The transponder system no longer supports a pilot selectable GND mode. The
  transponder should always be in ALT mode prior to moving on the airport surface.
  It must be in ALT mode when operating in certain controlled airspace, in
  accordance with 14 CFR 91.215. For guidance on transponder operation, refer to
  the FAA Aeronautical Information Manual (AIM), 4-1-20(a)(3)


(Emphasis mine)
Is this backed up by the FAA?
Yes, it's in the the AIM 4-1-20:


  3. Transponder and ADS-B operations on the
  ground. Civil and military aircraft should operate with the transponder in
  the altitude reporting mode (consult the aircraft’s flight manual to
  determine the specific transponder position to enable altitude
  reporting) and ADS-B Out transmissions enabled (if equipped) at all
  airports, any time the aircraft is positioned on any portion of an
  airport movement area. This includes all defined taxiways and runways.