How about inform everyone without being tested?
Unless s/o is diagnosed positive, his contacts are highly unlikely to quarantine as it's a big disruption to life and work. And "close contact" is typically with ppl in the general public, who he'll have no way to contact.
Nor do i think that most ppl who refuse to test despite having symptoms are actually self-quarantining in order to keep those around them safe.
Hopefully, they'll be able to crack down and punish ppl who purposely put others in danger.