There are three primary types of tests being deployed during this pandemic: RT-PCR, rapid antibody, and rapid antigen.
PCR is a molecular or nucleic acid test, which determines if SARS-CoV-2, the coronavirus that causes COVID-19, is present in the sample. The sample is typically obtained via deep nasopharyngeal swab. However, doing less invasive sampling -- anterior nasal swab or saliva -- is gaining traction. PCR testing is the gold standard. It takes at least a day to get the results, and it can sometimes take a week or more. Note that these PCR tests, which require assay in a lab, are quite expensive -- typically costing over $100.
The rapid antibody test looks for antibodies to the coronavirus in a fingerstick of blood. Since these antibodies (IgM and IgG) do not appear in the blood until perhaps 1-2 weeks following the onset of symptoms, this test is only useful to know if some has had the disease and might now have some immunity. It is of virtually no use for diagnosing current illness.
The rapid antigen test will diagnose the disease as with PCR, and they provide results very quickly like antibody testing, but these antigen tests are typically not as sensitive as PCR since they do not amplify the viral DNA. Thus, there can be false negatives. However, they do have very high specificity. If you test positive, you are virtually certain to have COVID-19. Therefore, they are often used for screening applications. The Siemens Rapid Antigen Test, marketed by Narratek, has uniquely high sensitivity, at 96.72%, which means that there are very few false negatives. It is almost as accurate as the PCR tests; results are available within 15 minutes, and the price is a fraction of the cost of PCR testing. The delivered price is $13 per test for the minimum order quantity of 400 tests. There are discounts for larger orders.