I was looking at this yesterday too. Using USPS as the back end for COVIDtests.gov was particularly apt because (a) USPS is typically the US government website

I was looking at this yesterday too. Using USPS as the back end for COVIDtests.gov was particularly apt because (a) USPS is typically the US government website with the highest traffic and (b) verifying and storing addresses is their bread and butter.