I would think Testing is pretty much safe, since all the new packages have to live a bit in Sid (10 days by default) before they reach Testing, so they get some

I would think Testing is pretty much safe, since all the new packages have to live a bit in Sid (10 days by default) before they reach Testing, so they get some testing. The only issue I know with Testing is temporary removals of some packages to help with these transitions.