Presently in unstable - Sid there is a transition to prepare for upgrades in C++ in the future.
https://lists.debian.org/debian-devel-announce/2015/07/msg00000.html
For those in Sid presently who blindly say yes to all dist-upgrades (or the small numbers who use synaptic gui in sid) the result is removal of programs like libre-office, and others.
It is possible that some of these difficulties will occur in Testing in 5 days (Happy Hiroshima Day - bad joke). Ways to avoid - don't dist-upgrade. You can just hold off on dist-upgrading and watch #debian-next.
"apt-get -s upgrade" will be perfectly safe with the -s(imulate) option and then apt-get upgrade to lower the numbers of programs to upgrade in your que.
"apt-get dist-upgrade -d" - the -d means just download. That way you can see what programs will be deleted if you continue.
To sum up, in a few days, nothing of interest might occur in testing - or there might be some breakage and if you rush you will lose programs you might need. There is a thread on the Siduction forum tracking this in Sid,
Peace out.