A 'bump' test is what I usually use when fiddling with triggers. With the gun unloaded (very important) and the action cocked and the gun held vertically, rap the butt sharply on a lightly padded floor (don't break anything, just a bit harder than any normal handling could get you). Do this several times until you're satisfied that the action will not accidently go off. Also a few good raps by hand on either side of the stock.
If the action cannot be made to go off in this manner, it is judged fairly safe for use.