Bug 25755: Add Unit tests for update to get_transfer

Bug 25755: Add Unit tests for update to get_transfer

We updated Koha::Item->get_transfer here to account for the new
daterequested field availability. It is now possible to set requested
without setting datesent simultaneiously.. as such we need to update
get_transfer to ensure we always return the right transfer (either the
one 'in transit' or the oldest request first.

This patch update the unit tests to test for this.

Signed-off-by: Kathleen Milne <kathleen.milne@cne-siar.gov.uk>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Joonas Kylmälä <joonas.kylmala@helsinki.fi>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>