Good point, Joe. The thumbnail test isn't anything I would recommend for a razor that is ready for stropping. The fine fin of a properly honed razor is easily damaged.

A few other tests that work for me are to gently try to push cut the very surface of the "fingerprint" along the side of the ball of my thumb. If it will effortlessly shave a micro-fine sliver with the lightest pus, it will also shave.

Or run the blade parallel to my arm just enough to catch the very tips of some arm hair. If it cuts the tips with no pulling or "popping", it'll shave. A well-honed and stropped razor will cut hair neatly and easily without pulling and that goes for whether it's against the skin or whether the hair is free-standing. I don't have bare patches on my arms, but the hair is always a bit shorter than it used to be.