Bug 26470: Regression tests

Bug 26470: Regression tests

This patch tweaks the test plugin so it composes an exception based on
the fact that the hook was called with the item and item_id parameters
defined.

It then makes the tests expect a specific exception message with
information about this.

To test:
1. Apply this patch
2. Run:
   $ kshell
  k$ prove t/db_dependent/Koha/Plugins/Biblio_and_Items_plugin_hooks.t
=> FAIL: Tests fail!

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>