For anyone reading this who is unfamiliar with Debian's release process, the Testing distribution is not a release. Rather, it is a holding area for packages that may eventually become part of a release.
Some people choose to run it instead of Debian Stable in order to get more recent non-security updates to packages, with the understanding that occasional breakage is normal for Testing.
https://wiki.debian.org/DebianUnstable#What_are_some_best_practices_for_testing.2Fsid_users.3F