Jon-- I wouldn't worry about sparks or short circuits or anything bad, merely, either the horn will make no sound or it will make a shit bucket of sound. When I said jumpers, I actually meant scrap wire pieces that will functionally jump between the terminals and / or mount lug on the horn and the battery poles. And, implied the horn would be in your hands at the time of the test. Thus you likely will be holding onto a horn in the process of doing what it is designed to do. Horns are very simple noise makers, don't sweat the small stuff.