COVID-19 Testing Shortages

Because the image lack a graph of the number of test ? Because tests were scarse at first and only done only to people coming to hospitals and relatives and now anyone can pass one ?

No. It's early testing and quarantine at scale

All three are barely testing.https://en.wikipedia.org/wiki/COVID-19_testingThere's your explanation right there.

My guess is that we're still short on tests, so only people who most likely have the virus are getting tested.

Yes.There's between 50k and 500k people in the US with covid19. At this stage it's fairly immaterial to give people tests that take 2 days to run.If you have a temperature or a new cough, just assume you have it, and self isolate, ideally asking people to report they are self isolating too.They should be doing mass temperature scans to find people with high temperatures at large events, subway stations, shopping malls, etc. Far easier to test en-mass, and gives an indication.

In absence of large scale testing, how do you know that?

Multiple countries have sustained mass testing of at least certain groups of population. The argument about undetected asymptomatic cases would be valid in early 2020 when tests were scarce, but now there are good continuous metrics from people who get tested even if asymptomatic.

Bit like testing for COVID-19, if you don't test for it how can you have it?

It's hard to test positive given the extremely limited supply of tests and all the effort you'd have to go through to get tested. I really can't imagine anybody willingly testing -more so with new invasive tracking- unless they are really ill and in need of medical attention.

Are they doing population-level randomly sampled testing?