To be clear, the power feed that can be switched between the grid and the PV system is the power that will charge the EV when the relay closes. The separate mains power feed that will power the electronics and control circuitry inside the openEVSE itself will always be fed from the grid.
I do not believe it has ever been tried. The AC_Test should work okay if everything has a common ground. The test is just power through an LED and detector.