Right now, we’re talking about swab testing the back of the nose to find virus particles that are being shed by someone with an active infection.
Blood testing for antibodies -- which provides evidence of a prior infection -- isn’t ready for widespread use, but swab testing also has challenges.
The first thing you need is a swab, but for the test to work, the swabs have to be specially made.
An issue many people have identified is that the swab tests can only tell if a person is shedding virus at the time it’s done.
It is only sampling a single point in time, which is also why -- even with widespread testing -- the use of masks, hand washing, and social distancing will not go away.