Bug 33161: Unit tests

Bug 33161: Unit tests

To test:
1. Apply this patch
2. Run:
   $ ktd --shell
  k$ prove t/db_dependent/Koha/Item.t
=> SUCCESS: Tests pass!
3. Sign off :-D

Edit: added missing test for unmapped attribute

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
(cherry picked from commit 35dd17735f4e5b39b0a56a3d72d010fd7d176a32)
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>