Endometriosis question


So I thought I was having an implantation bleed but this has become more of a full period. I started bleeding (spotting) on the 19 th off and on. brown pink a little red then it stop throughout the day never reaching my pad. It’s worrisome but it bothers me because my period never came so early. Is this a normal occurrence. My doc told me it cold be endometriosis and I should go in for test. What test do that perform