As serious as Luxembourg is about masks, it is also incredibly proactive about testing for COVID-19. On an everage weekday, about 1.5% of the entire population is tested. The equivalent in the US would be about 5.5 million people tested each day.
For travelers returning to Luxembourg, it could not be easier. A voucher is handed out to each passenger at baggage claim, good for 1 free COVID test over the next 10 days. Sounds easy enough, but it gets "better". When leaving baggage claim, there is a testing station on the right hand side, allowing anyone who wants to use their voucher to get tested on the spot. Impressive, most impressive.