Nice work!

Testing it electrically, or for clearances?

For the former, If it was me, I'd go for a small board, and some high-tack double-sided tape. Maybe some copperclad for a temporary tiebar. and some exit road extensions. Then connect your controller and a known good loco and have a play

If you want to check it for gaps being where they should be (i.e.crossing nose/blades), I guess the good old meter is the best way. Or a buzzer...

If you want to check it for clearances, a suitable wagon (perhaps a fully fitted cattle wagon... ) and derfingerpokking with a single digit is a good method; you'll be amazed how sensitive your finger is at discerning fouling rails etc.. if it feels good, it probably is...

If you are interested in the clearances, then get a "mint gauge" from the stores.

These are very effective at finding even the tiniest of tight spots.