We do this everyday and still get fooled. You have to plan on the worst, because the test is only a small fraction of the wall surface. You can't assume that every area of the room will strip exactly like the test area. By putting a spongeful of water on a paper you can quickly determine if it's porous or not. If porous, the paper will darken and will swell and blister as the moisture sinks in.
Porous papers are good candidates for wet removal.
If non-porous, the water simply beads up on the surface with no color change. The strippable category of vinyls will dry-strip cleanly from the wall, while the peelable types leave a layer of paper. This paper laminate layer is easily moistened and removed, though it may be left on the wall if stable and if compatible with the new wallcovering. The type of wall is just as important as the type of wallcovering. Stripping from plaster is a lot easier than stripping from drywall because the hardness of the plaster provides resistance for scraping.