So what's the whole point of testing?
The point of testing to find out who is infected so that you can quarantine them to stop the infection spreading further.
You also need to trace all of their contacts, test them, and quarantine the positives.
This is basic pandemic control, as recommended by the WHO.
The US attempted to do this at the beginning of the outbreak, but failed. That is why there is a lockdown. Now you get to try again. But to do this successfully you need many more tests, and a whole army of contact-tracers.
(Most other countries are in the same position.)