A common method to test for COVID-19 is to use a long swab to collect a specimen from the nasopharyngeal region, which is located at the back of the inside of the nose.
Please note: this article discusses viral testing used to diagnose if an individual currently has COVID-19. This article does not discuss antibody testing used to determine if an individual was exposed to COVID-19 previously and developed some level of immunity to COVID-19.
Source: Advocate Medical Group Adult Down Syndrome Center