i just changed "buster" to "testing" everywhere in /etc/apt/sources.list, even though it says to remove the security lines at this
I'm not sure if you just misspoke but I'll add this for clarity:
Changing the sources.list from "buster" to "testing" has no effect this moment. Currently Debian testing is called "buster" and there is absolutely no difference between them. That will of course change when "buster" gets released as Debian "stable". From that moment on, "testing" will be pointing to Debian version 11 "bullseye" and so on.
What does this really mean?
Leave "buster" in your sources.list and you will be using "testing" for now. After its release, you will still be using "buster" - but then it is Debian "stable".
Put "testing" in your sources.list and you will be using "testing" for now. After "buster" is released as "stable" you will still be using "testing" but then it's the upcoming version 11 "bullsye"
And so it goes on...
A word to the "rolling release" nature of Debian testing. It is more or less that as long as the Development has not been frozen. Quite a few months before a Debian release, "testing" gets frozen. That means that (almost) no new software will be included and only bugs will be hunted instead. In that case, it is no longer rolling and some packages might get a bit stale. That might or might not be a problem for you if you want to be on a rolling Linux Distro. I use Debian for almost everything and don't care too much about it. But for bleeding edge "rolling" there are other Linux Distributions like Arch that I would also recommend.
That information is of course not specific to the Pyra but for Debian generally. Maybe you knew that anyway and actually meant "stretch" instead of "buster". But anyway - I thought to include this explanation because not everyone here is a Linux crack - yet ;-)