I've just scribbled down a rough schematic for what's inside this test box. It follows the vehicle end diagram that's in IEC61851 and J1772, with test buttons to simulate fault conditions and switches to simulate the vehicle being plugged in and requesting a charge. The test equipment connection points aren't needed, I fitted them mainly so that I could hook kit up to the control pilot to see what it was doing. For normal testing they aren't needed.
The charge point should behave like this when plugged into the box:
All switches off, charge point plugged in, no charge power and charge point should sit in the idle state, with the contactor open and no power at the 13 A outlet.
Plugged in switch on, charge request off, charge point should be in the "ready to charge" state, with the CP at 1 kHz, duty cycle indicates available maximum current. Contactor should remain open, with no power at the 13 A outlet.
Plugged in, switch on and charge request switch on, charge point contactor should close, switching power on to the 13 A outlet and illuminating the "charging" panel light.
Pressing either of the fault condition test buttons should cause the charge point to trip out, cutting power.