I built another test jig, this one to exercise the business end of the Watt-A-Live. It has a barrel connector to adapt to an external power supply and a selection of 5 load resistors for different current settings.

The resistor values are 0.5 Ohm, 2 Ohm, 110 Ohm, 12 kOhm and 10 MOhm (still missing :( ) for a full range of current settings. They can all be selected by jumpers.
This is how it looks, when plugged into the shield/wing.