I just leave this here.
Debian Testing is currently broken, partially due to GCC 5 transition, partially due to incomplete KDE KF5 stack.
I was using KDE and my test system simply broke, conflict between kwin-x11/-wayland and libkdecorations*.
After installing apt-listbugs I was able to filter even more packages with outstanding bugs and apt managed to partial-upgrade the KDE.
After a week, just a few days back, it still managed to break - now the KDE desktop in unusable in Testing.
On official Debian IRC, Testing is never expected to work and Stable+Backports is suggested for the system which is expected to be reliable.
Here you have it. Obviously, I stick to this opinion.
I used Testing for more than three years, as well as Sidux (Debian Sid) for good a year on my desktop systems.
disclaimer: solydxk user and fan, I am *not* affilated with solydxk project. experienced in - ubuntu, debian, gentoo, calculate, archlinux, linux mint, rhel. my posts are mine. no guarantee for fitness to particular use case.