You say "that room". Circuits are not nearly always designated to one room or area. Many, many times a room will have some devices on one circuit while others on another circuit. It is pretty rare that rooms are strictly wired so that one circuit distinctly feeds one room.
Also, panel directories are not always extremely accurate. So something that says the breaker is for one room might also have other things one it.
Again, a tester is the ONLY way to be sure what you are working on is dead. IMO you should not even pick up a tool or open a box until you are in possession of a decent tester.