One of the easiest ways to test for sterling silver is to look for the authentication stamp. The stamp is likely STER, STERLING, 92.5, STERLING 925, S/S or 925/1000.
There are instances where the stamp is fraudulent. This method can be used if buying from a trusted store. Another way to test the metal is to rub a soft cloth over the surface. The genuine alloy leaves black marks from the tarnishing. New sterling jewelry has a coat to protect against this. This method is best for older jewelry. The next way to test sterling silver jewelry is to use a magnet. Authentic sterling silver jewelry is not magnetic.