Apparently there are 3 types of Covid 19 tests.
1. Nucleic acid amplification tests (molecular tests)
– also known as genetic, RNA or PCR tests.
2. Antibody tests – also known as serology tests.
3. Antigen test
Diagnostic or PCR test. This is the one with the long stick getting mucus from your nose. Even though it takes a few days for the virus to replicate in the nose, this method is so far the most reliable one.
Antibody test. This is a blood test to look for antibodies to the virus. Since it takes time (at least 4 days) for your body to generate antibodies, and without FDA authorization, the result may not mean much.
Antigen test. This method tries to detect proteins from the virus in nose. It is a quick screening test for just a few minutes, but accuracy is still to be determined.
ref:
https://asm.org/Articles/2020/April/COVID-19-Testing-FAQs
https://www.npr.org/sections/health-shots/2020/05/01/847368012/how-reliable-are-covid-19-tests-depends-which-one-you-mean
BrianChan.us 
PCR tests in the US are typically performed by a human (skilled technician) and accuracy varies wildly. They amplify even very small amounts of viral DNA and do not distinguish between an active infection and, aside from quantitative PCR, do not determine viral load. There is no “FDA certification” as this is a standard research lab procedure. At least one company offers an Ab (antibody) test that is FDA certified. A positive result reveals whether a patient has EVER encountered COVID-19 and has possible immunity. They are generally simpler to perform and should, in theory, be more reliable than PCR. An Ag (antigen) test actually determines that viral replication is occurring (i.e. patient is in the midst of an infection). In a perfect world, every test would either be an Ab or Ag test, but PCR is more flexible (which is why it was the first method introduced).
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