Definitely 2G+ Test from a Test Center at the same day as described above.I surely hope it's not the case...but a lot of German people I spoke to in Köln last saturday thought the same.
One thing's for sure, if clubbing is still on, count on 2G+ in all clubs. So that's vaccinated or recovered AND a test on the same day.
As a tourist you'll pay 25 Euros per test.
From Thursday in in Frankfurt Area. Thats what I definitely know. Self Tests are Not enough .
Bavaria + Saxony maybe Clubs closed.
Berlin ? Dont know , the Situation in Germany is a desaster