You should assume in any crowd, there will be infected people that could infect you. So, self-isolate as much as possible.
There is no cure for Covid-19, so at this point testing is really not important. If your symptoms become severe, you will get directed to a hospital for more medical support, JUST LIKE IT WORKS FOR THE FLU.
The fixation on COVID-19 testing is not productive or rational.
Did testing help South Korea contain this virus or not?