PCR tests are indeed a waste of time for Viral detection. One does not use a manufacturing technique which is unsuitable to duplicating simple RNA fragments like Viruses to test. When an RNA fragment denatures there is 0 guarantee it will be remotely in the sort of state de-natured DNA is expected to be in the annealing step. You could produce practically any outcome, or even all of them at once. And guess what, all coronaviruses are RNA viruses.