I just built a test track for my hobby work shop, and I'd like to pass on a suggestion. Include a turnout with your test track. That way, if one of your cars is hanging up at the turnouts on the layout, it should do the same on the test track.
I put a couple cars on the RIP track and didn't get back to them before I forgot why I did. When they started hanging up on the turnout on the test track, I knew why.
Puckdropper