Testing provides at best a snapshot. Someone who doesn’t have the bug at the time of the test could get it literally minutes later, and that wouldn’t be captured in the test. That’s why it makes sense mainly for people who are symptomatic to get tested, and then for all the people they’ve been in contact with to be tested as well.
Mostly agreed, but,
A) If other diseases that might prompt someone to desire testing are way down (flu, and [normally big numbers] colds*) then testing might level off or decrease while spread of COVID-19 continues. This is in one sense just a data oddity, as positive symptomatic COVID-19 cases are still detected, but it might explain lack of further increases in testing.
*I don’t know about anyone else, but several years ago I went through a few years of occasional colds that would knock me on my behind for a day or so. Definitely they were bad enough that in today’s environment, I’d have attempted to get tested. Thankfully I’ve not had more of those recently. I doubt I’m “healthier” otherwise, now, so I attribute them to some specific cold virus I was particularly prone to getting whacked hard by.
B) “A” leaves us with still a poor idea of the number of asymptotic cases. There are the antibody tests*, I suppose, but those are a rather lagging indicator. This virus can move so fast that I’m not exactly thrilled by lagging indicators when it comes to tamping down hotspots. We don’t even really have more than guesses on how many people in varying groups (racial, disease history, obesity, etc.) may be asymptomatic.
*Are positive antibody tests included in reported “positives”? “Recovered” cases? I do not know.