Comment by ahartmetz
9 hours ago
This is from like 20 years ago, but I remember Debian Testing as the one where updates broke the system most frequently, or maybe the longest without fixes: Stable was stable, Sid / unstable was what most Debian developers were using... and Testing was the weird thing that was neither a release nor tested and fixed "live" by developers.
What changed?
Most of the problems that break a system are being resolved in unstable rather than testing.
I've ran testing on my home server, though since it's a bit old now I've switched it over to stable when testing switched to stable.
This is how the flow happens: [upstream] -> [Debian Sid] -> [Debian Testing] -> [Debian stable]
The testing happens in Debian Sid.
But who actually tests Testing? If it's not the Debian developers themselves, fixes could take a while. I seem to recall Testing breaking because of package version combinations that never existed, so were never tested, in Sid.