Yeah, don’t do that.

You may have been lucky, but the testing repository is really not meant for daily use.

Noone cares about packages there, so depending on what you have installed and when you update, you might have critical security vulnerabilities that have been patched for weeks on Stable or other incompatibilities/broken dependencies.

Unstable is not meant for daily use either, but at least you brainlessly get pushed the latest updates at all times. I have used it for a while, but it broke on me, too.

If you need newer software, just use Stable with backports or Flatpaks.