The tests I use, roughly in order of how much they predict real kitchen behaviour. Slicing a ripe tomato with no downward pressure, using only the weight of the knife, is the best cheap test I know because tomato skin is unforgiving and it tests the edge along its whole length rather than at one spot. Cutting a sheet of paper held vertically tells you the apex is clean but only at the point you cut. Shaving tells you almost nothing useful because a burr shaves.
The one that changed how I sharpen was the onion. If the first cut into an onion skin skates instead of biting, the edge is not there regardless of what the paper said.