My test dummy is an unfinished 1:48 Scale B-17G. I use it to test my painting abilities. Currently the port wing is in German Splinter camo, the starboard wing is a test of gloss black. The port fuselage is two tone blue and white like the US Navy colors and the starboard fuselage is mostly a test of different primers and pressures. About to coat the whole thing in a single primer color and start over!
But I find having a test dummy is a great way to experiment on an actual model without risking botching my actual work in progress. I don't tend to cry as much if I fudge it up.