Do you get tested for endometriosis at the hospital or gynecologist office?

Hospital. Surgery is the only way to diagnose endometriosis, period. Surgery is usually outpatient. Ultrasound, blood tests, imaging studies, may be helpful but they do not make a diagnosis.
You need surgery,but. Our research that will be published soon shows two very accurate predictions of endometriosis. First, if you had bad periods (worse than peers or missed school )as a teenager, you have nearly 100% chance of endo at surgery. Second, testing for ovarian reserve with Clomid (clomiphene) challenge test: if abnormal 90% chance of endometriosis at surgery. Need good excisional surgery not band aid.
Ultimately at hospit. Endometriosis can be definitively diagnosed at the time of surgery. There are certain symptoms or diagnostic tests that are suggestive for endometriosis, but are not definitive. Therefore the answer is at the hospital.