While tracking testing as described in the above example you can
manage the system by using the following commands:
aptitude upgrade (or apt-get upgrade or
aptitude dist-upgrade or apt-get dist-upgrade)
These track the testing distribution — they upgrade each
package on the system, after installing versions of packages upon which it
Depends, from the testing distribution. 
aptitude install -t unstable package
This installs package from the unstable distribution
while installing its dependencies also from the unstable
distribution by setting the Pin-Priority of unstable to 990.
In the above examples, giving
apt-get the -u option
causes it to print a list of all packages that are to be upgraded and to prompt
the user before taking action. The following makes
$ cat >> /etc/apt/apt.conf << .
// Always show packages to be upgraded (-u)
Use the --no-act option to simulate actions without actually
installing, removing, etc., any packages.