We will be flying back to the US early on a Monday from Lyon. Covid tests are available at many locations in the city on Mondays through Saturdays but we can't find any location except the airport on Sunday. Since our flight is early and the airport test center opens at 8:00am, it appears our only option is going to the airport a day before our flight to get tested. Do we have other test options in Lyon on a Sunday? Feel free to response to this enquiry generically since this must be a typical problem in France and other countries where test centers are typically closed on Sundays. Thank you.
Ask the staff at the hotel where you are staying that last night. They will know what your options are - you will not be the first to ask them (everybody is figuring out this stuff now).
Personally, I'd be testing the day-before (I'd also be self-testing every day in the days leading up to the test that counts). Less stress on travel day is always better. Good luck.
Are you there now? If not you could buy one those online proctored tests before you leave and do it from the comfort of your hotel room the day before: https://www.emed.com/airline-travel.
Most airlines when you buy a ticket for international flight offer this also.
Take a proctored test kit with you then you don't have to waste time going to the airport for a test.
https://www.emed.com/products/covid-at-home-testkit-six-pack
https://www.azova.com/testing/flowflex/
https://www.cityhealth.com/rapidreturn/ (personally this is my favorite of the three. The test kit is the size of a glasses case. )