Debian Testing broke my install just now (already fixed)
Standard apt-get update and apt-get upgrade broke just now and it was typically easy to fix. dhclient didn't bring up my wifi card so I plugged it in to bring up the network card, quick dpkg --configure -a didn't return anything so I just did apt full-upgrade at the recovery console and that fixed it.
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.