Add a unit test for the empty relationship availability.
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
(cherry picked from commit f744dfe60c)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>