[SOLVED] "Problem" With Update Result

A few months ago, I went back to the Testing branch, I had used "testing" rather than "Stretch" due to the fact that a few years ago I missed the general upgrade for MONTHS, and I felt kind of "stoopid".

Also, I use the command line (because I am an "old fart") and I ALWAYS use aptitude rather than apt-get (because I like aptitude)

Then a general update happened, which I hadn't noticed, but my output threw some problems.

//begin ===========================================

E: Repository 'http://deb.debian.org/debian testing InRelease' changed its 'Codename' value from 'buster' to 'bullseye'
E: Failed to download some files
W: Failed to fetch http://deb.debian.org/debian/dists/testing/InRelease:
E: Some index files failed to download. They have been ignored, or old ones used instead.

//end =============================================

This has never produced before, and I cannot figure out how to "fix" it.

My /etc/apt/sources.list is

//begin ===========================================

deb http://deb.debian.org/debian/ testing non-free contrib main

deb http://deb.opera.com/opera/ stable non-free
deb http://deb.opera.com/opera-beta/ stable non-free
deb http://deb.opera.com/opera-developer/ stable non-free

//end ==========================================

Can someone help me fix my problem/concern/whatever?

A few month ago testing was buster, now it is changed, testing is bullseye.
You ought to change testing to buster in your config.

Yeah, I still want Testing, and that is why I specified Testing rather than Bullseye.
But how that address the notice when I do my updates.
It is, for me, to specify the category testing rather than referring to it by its name (Bullseye, Buster, or whatever the Testing name is)

And is this message on my updates a warning, an indication of a problem, a notice, or what?

testing changed (from buster to bullseye). That means a distro upgrade. If you want to "stay" on testing you need to dist-upgrade. But I think it is documented somewhere.

OK, I did an experiment: Replaced "Testing" to "Bullseye".

Massive upgrading begun.

Did a "Poweroff" and a reboot, just in case

OK.... it seems to be working fine, thus I will do a backup (hey! I backup EVERYTHING.... just in case)

I will call this SOLVED, and then I will look up documentation for "dist-upgrade"