Stickybottle is simply pointing out Fruitsalad's incorrect use of English. (She should have typed 'have', not 'of'). However SB's failure to include the quotation marks renders his sentence meaningless.
With regard to the original post, unless a person is displaying relevant symptoms, Covid tests are useless unless they're repeated frequently. So a one-off snaphot on census day wouldn't be of much value. It would also be totally impractical, as there's nowhere near sufficient laboratory capacity available to process the tests.