The testing and unstable repositories of Debian provide with a higher version of software applications than what is present in the stable repository. Note that these names are actually aliases such that the stable repository points to the current Debian stable release and the Testing repository is what is going to be part of the next Debian stable release. So at the time of this post, Wheezy 7.x is the Stable release and Jessie is the Testing source which is going to be the next stable release.
At times, when you need to get a more recent version of a particular application, then the testing/unstable repository is a good option. I had the task of installing Apache 2.4.x onto a Debian wheezy system. But the repo had only 2.2.x and the testing repo had the required 2.4.x version. So the solution is to grab it from the testing repo.
Most of the time, when looking for newer versions of software applications, we would fiddle with the "Testing" repository only.
This post is going to show you how to setup the Testing and Unstable sources on a Debian system and how to install software from them, without breaking your existing system.
Read full post here
How to enable testing and unstable repository on Debian