The cylinders will have the latest test date stamped near the valve. That must be within the range required by the place you are in. In addition, no dents, deep scratches, or deep rust pits.

With everything assembled and the adjustment screws backed out. Turn on the oxygen. The high side gauge should read the cylinder pressure the low side should read zero. Turn in the adjustment screw until the low side gauge shows some low pressure say 5 psi (I'm not sure what that is in metric units). Turn the cylinder valve back off. The high side gauge should retain its reading for at least several minutes (some will say forever) otherwise something is leaking. Turn the cylinder valve back on. The low side gauge should not increase its reading over time. Do the same for the fuel side.

Light the torch. Nothing should leak. The valve stems, and the connections between the parts of the torch are likely spots. Soapy water is a good way to test. The flame should be symetrical. If it is a cutting torch activating the cutting valve should not cause a dramatic change in the flame.

That's all I've got.
Bill