Bug 26963: (QA follow-up) Migrate unit tests into pickup_location

Bug 26963: (QA follow-up) Migrate unit tests into pickup_location

We wrote unit tests for _can_pickup_locations as part of this patchset,
but then I inlined the method whilst golfing. This patch moves those
tests into the existing pickup_locations test so we more thoroughly
cover the case where branch transfer limits are in play.

NOTE: The tests all assume that all items have an effective_itemtype and
ccode. I'm pretty sure items all have a type at this point, but I'm less
sure we enforce collection codes?

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>