One of the easiest ways to tell if an object is gold or brass is to look at the size. Most large objects are not made of gold.
Another test to use is the magnetic test. Brass is not magnetic. If another test is needed to be completely sure, then acid can be used. Nitric and muriatric acids are two that are popular for this test. Just put a drop or two on the piece. If the spot turns black, then the metal is brass or some other metal treated to resemble gold. If brass has been heavily plated, the acid test does not work.