Apple Maps in iOS and iPadOS can now show you locations in the United States (including Puerto Rico) where you can be tested for COVID-19. To see those testing sites, tap the search field to bring up Recent Searches and Search Nearby. The first item under Search Nearby is COVID-19 Testing, which you can tap to see testing sites on the map.
Unfortunately, where I am in Tennessee, none of the state’s free testing sites show on the map. Instead, it shows only various hospitals and doctors’ offices. Let us know in the comments what sort of results it shows you and whether or not they’re helpful.