Sorry, I might not be understanding where you're going with this. I initially thought you meant "you can know you're at risk of spreading COVID, because everyone is at risk of spreading COVID."
Certainly, anyone who receives a positive PCR test for COVID should quarantine ASAP. But if you're incubating COVID, but not infectious yet, the tests will return negative. A test only tells you whether you were infectious at the time of the test, so by the time you've seen the results, the information is already outdated.
Certainly, anyone who receives a positive PCR test for COVID should quarantine ASAP. But if you're incubating COVID, but not infectious yet, the tests will return negative. A test only tells you whether you were infectious at the time of the test, so by the time you've seen the results, the information is already outdated.