They used to test you when you donated blood but I think they stopped telling you. They don’t want a cure or treatment. They want you to OBEY
I may be wrong but simply having Covid anti-bodies does not constitute immunity. My local blood donor folks told me that the 'blood donor' test simply shows whether anti-bodies were or were not detected in your blood; that it doesn't tell the person if they have a level of anti-bodies that offers protection.