Bug 19278: Unit tests

Bug 19278: Unit tests

This patch introduces tests for a behaviour change in
Koha::REST::Plugin::Pagination.

To test:
- Run:
  $ sudo koha-shell kohadev
 k$ cd kohaclone
 k$ prove t/Koha/REST/Plugin/Pagination.t
=> FAIL: Tests should fail without the followup patch applied

Sponsored-by: Camden County
Sponsored-by: Bywater Solutions
Signed-off-by: Lari Taskula <lari.taskula@jns.fi>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>