In Paris you notice numerous signs offering tests. They read things like "COVID-19 Dépistage" (screening) or "COVID-19 Test." If you see a sign over a tent that is not in front of a hospital, do not waste your time unless you are a part of the French healthcare system ("Securité Social") as unless you need your account number for billing. Otherwise, go to a pharmacy where they will take cash or your credit card for an amount typically around €25. You will need a smartphone but at the pharmacy where I went, they had spares. The app asked for your phone number. We have French (Orange) accounts so I don't know if they send to American numbers. We got the result by text which required, IIRC, two factor authorization. We saved everything as PDFs and had paper copies printed just in case.

Also, someone up thread provided excellent information about installing the Pass Sanitaire on the Apple Watch. (I thanked him there.) Many establishments are stunned when I show them my watch.