If the walls are covered with wallpaper, eventually to be removed, can one test for lead in the paint under it without stripping the wallpaper? Or does one first have to strip everything, and then test?
You don't need to remove all of the wallpaper, but you will need to expose the paint so it can be swabbed / tested. Looking online, you can just make a small slice through the wallpaper / paint and swab your test kit that way. Other test kits may need more paint exposed, in which case you'd just remove a small section of the wallpaper.