Hello! I recently got my pocket reform and am loving it so far!
I have been having some issues installing software due to build failures on unstable, and was looking into Debian testing. I have not used Debian before but from my understanding the testing branch should be very similar to the unstable branch, just without failing builds.
Since the system images all use unstable, does anyone know how you might use testing? Is it even supported? Would love to know anyone’s experience here!
Yes, packages only transition from unstable to testing if (amongst other things) they are installable, have been compiled for all release architectures (thus avoiding multi-arch:same version skews) and have no RC-bugs reported against them. Thus, running testing should be a bit safer than running unstable. Since you are regularly upgrading and since RC bugs are of course also reported against packages in testing (which will then be removed from testing if the RC bugs are not fixed) you should still keep using apt-listbugs.
The only practical issue I see these days for running testing with the MNT repos is, that if the kernel in unstable is built against a glibc/libc6-dev version which is not yet in testing, then you will not be able to install that kernel onto your testing machine until the C-library is transitioned to testing as well.
The problems with running testing were bigger in the past when we had much more software to patch like mesa, gtk, blender, ffmpeg, systemd or gstreamer. These days, not much is getting patched anymore (only flash-kernel).
It is not “supported” but I think there should not be much of an issue in trying it out. So maybe just replace “unstable” with “testing” in your /etc/apt/sources.list and report your findings after running it for a while?
If you replace “unstable” with “trixie” you would have another option: you would be testing “testing” today (because the next stable release is called “trixie” and is currently equal to “testing”) but once trixie is released, you could be running Debian stable on your machine.
Thanks for the info! Guess I just got a bit scared off by the Debian docs that said I should reinstall to switch sources. I’m on testing now and will report back if it works fine 
Do you have a link to where it says that?
https://wiki.debian.org/SystemDowngrade
I thought this applied since it mentions moving from unstable to testing but perhaps I misunderstood.
Well, I hope you are not downgrading anything. What you are doing is to switch your apt sources to a distro which has older packages in it than the distro you are coming from. But since packages keep migrating to that, you will likely end up in a state where the packages in “testing” become more recent than what you currently have installed from “unstable”. This is not pretty but it is not downgrading. That you really should indeed not do.