How do you test gold yourself to find out if it's real?

Use a magnet to see if it responds. If it is attracted to the magnet solidly, it is NOT gold, if it has a light magnetic attraction, it may be plated or impure. Pure gold does not respond to a magnet.

If the item passes the magnet test, you will need to buy a nitric acid test kit on eBay. Acid testing kits run about $20 - $30 and are very simple to use. Rub your item firmly on the testing stone that comes with the kit, drip a single drop of acid onto the area you have just polished. If the area stays the same color, your item is gold. If it turns a yellow-orange color it may be gold but a lower quality karat. If the area changes any other color - it is not gold.

Check for any mark in the jewelry, usually gold jewelry has standard hallmarks like 916, 750, 18kt, 14kt, 10kt, etc. (Costume jewelry might not contain such symbols.)

If the object is (apparently) solid gold, with no stones or other materials attached, one can weigh it suspended by a thin thread in air and then weigh it again submersed in water, using a sensitive laboratory scale. From the difference in weights one can calculate its density. Since pure gold has a known density, if the number one gets is different, it's likely an alloy or may be a base metal with a gold plating. A method similar to this was employed by the Greek polymath and inventor Archimedes (c. 287 BC - c. 212 BC), when he was asked to prove whether the king's crown was of pure gold without damaging or destroying the crown.