A real Pearl is always smooth and there are likely to be no lines on it.
If a real Pearl is held under the Sun and if you try to see through it, the reflection will have a shade and color like that of honey, sandalwood or sugar.
If a Pearl is kept in a fine piece of cloth along with the husk of any kind of food grain and rubbed vigorously then if the Pearl is genuine it will shine brightly. If the Pearl is fake then it will be spoiled or damaged and its shine will disappear.
If a real Pearl is put inside a small quantity of solidified Ghee [Clarified Butter] then the Ghee will start melting.
If a Pearl is mixed with a small quantity of rice grains and rubbed with Clarified Butter then if the Pearl is genuine it will shine brightly. If the Pearl is fake then its artificial shine will disappear and it will get damaged.
A hole made through a real Pearl will have the same overall consistency and size. A hole made through a fake or cultured Pearl will start expanding at the center of the Pearl.
If a Pearl is put in a utensil containing a mixture of warm water, a little bit of cooking oil and salt and kept overnight then if the Pearl is real its color will not undergo a change.
Note: As indicated in the first Paragraph, these methods, which are believed to be proven methods to find out if a Pearl in real or fake are based upon the Ratna Shastra and hence, I am not in position to vouch for the correctness of these methods nor do I take any responsibility if your Pearls are spoilt or damaged while performing these tests.