cat /etc/apt/preferences
Package: *
Pin: release a=testing
Pin-Priority: 900

Package: *
Pin: release o=Debian
Pin-Priority: -10

apt-cache policy vim
vim:
  Installed: 1:7.0-035+1
  Candidate: 1:7.0-035+1
  Version table:
 *** 1:7.0-035+1 0
        900 http://cudlug.cudenver.edu testing/main Packages
        -10 http://cudlug.cudenver.edu unstable/main Packages
        100 /var/lib/dpkg/status