GD
https://www.germany.info/us-en/coronavirus/2317268
Air travel
From 30 March 2021, all persons travelling to Germany by air must present a negative COVID‑19 test result before embarking on their journey. This applies regardless of the country from where the individual has travelled and also to passengers only traversing Germany (i.e. for international transit). Persons under six years of age and aircraft crews are exempt. The negative test result must be presented to the airline before departure.
https://www.bundesgesundheitsministerium.de/en/coronavirus-infos-reisende/faq-testpflicht-einreisevo/testing-obligation.html