That's why everyone needs to stay home until we have enough testing to accurately determine who can safely go out.
Having the ability to test quickly means you can save hospital isolation wards from unnecessary overcrowding, because you can now know whether a person who comes in with respiratory symptoms actually has Covid-19 rather than having to treat everyone as though they might. "It means you can move from a presumptive stance to a more informed stance"[1]
If doctors know you're sick with COVID-19 and your disease is severe enough, they might offer you one of the experimental treatments for it, or you might be offered to participate in one of the hundreds of ongoing research studies.
Testing will also help determine where scarce medical resources need to be allocated, which people need to be isolated, and around which people medical personnel need to wear protective equipment.
Finally, testing will let epidemiologists track the progress of the disease and have better estimates about how severe it's going to be, and possibly predict in which communities it'll get better or worse. This will help public health officials decide where and when to declare or end quarantines/lockdowns.
[1] - https://www.wired.com/story/fda-approves-the-first-commercia...
Evidence is developing that as much as 75% of transmission events is from non-symptomatic individuals.
A good intro: https://www.youtube.com/watch?v=vE4_LsftNKM
I mean, if I'm feeling sick wouldn't I just proceed as if I had it? How doesn't actually knowing change anything? My course of action should be identical.