These test cases need the Linux::Clone module, which is not yet in Debian.
See http://michael.stapelberg.de/cpan/#Linux::Clone on how to install it.
Note that you need to run the test cases as root because they use Linux mount
namespaces and bind mounts (requires Linux ≥ 2.4.19).
Note that you should mark / as a private subtree before running these tests, or
they will fail. Use mount --make-rprivate /. Unfortunately, the version of
util-linux in Debian at the time of writing (2.20.1) is broken and its
--make-rprivate does not actually work. See #731574.
The intention is that the testcases are _not_ run automatically during package
building because they might be too fragile and additional dependencies make it
harder to port this package to Ubuntu or Debian backports. It is enough if the
test cases are run on every code change.