The one for speed should have a small wheel on it. The speed the wheel turns tells the instrument how fast you're moving. Turn the instrument on and give the wheel a spin. Does it give you a speed reading? If so, you're in luck. When I tested mine, I got to 10.5 knots. Think you can beat that?
I know there is a way to test the depth sounder, but I haven't done that and I'll let someone else chime in on that.