If a person is infected, there are several days when a person is infectious before they get any symptoms. However, a test will let an asymptomatic person know if they are infectious, so they can try to prevent infecting others.

@snytiger6 Since infection can occur at any time we should each be conducting affairs as if we're contagious. Look away from people so we're not breathing at them and be mindful of our distances. Even for those who oppose masks this should be done but we are not civilized enough for that. Testing won't help incivility.