The modified armhair test, as Dylandog put it, is far more reliable. In fact, if you wave your razor a centimeter away from your arm over your armhair and you hear a quiet raspy sound and the razor effortlessly pops (catches and cuts) all the hair in its path, it is almost certain to be shaving sharp. It may not be smooth enough, but is usually within 2-3 more strokes to being properly honed.

You have to pay attention to the quality of the cut though - a lot of razors will catch the hair - including grossly overhoned ones, and even ones honed on a 2K stone. It is the quality of how they cut the hair after the catch that is an indication of shaving sharpness. A properly honed razor will cut the hair effortlessly, without bending the hair, without splitting it lengthwise, without pulling the follicle and without much noise, just a quiet pop.