Bug 22445: Add tests for Koha::Biblio->custom_cover_image_url

Bug 22445: Add tests for Koha::Biblio->custom_cover_image_url

Sponsored-by: Orex Digital
Signed-off-by: Hayley Mapley <hayleymapley@catalyst.net.nz>
Signed-off-by: Hugo Agud <hagud@orex.es>
Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Michal Denar <black23@gmail.com>
Signed-off-by: Kyle Hall <kyle@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>