apt-cache policy shorewall
------------------------------

shorewall:
  Installed: (none)
  Candidate: (none)
  Package Pin: (not found)
  Version Table:
     2.2.3-2 700
        500 http://security.debian.org stable/updates/main Packages
        500 ftp://ftp.us.debian.org stable/main Packages

/etc/apt/preferences
------------------------------
Package: shorewall
Pin: release o=Debian,a=testing
Pin-Priority: 700