Bug 25663: Add unit tests

Bug 25663: Add unit tests

This patch adds unit tests for a new get_lostretun_policy method which
is getting added to Koha::CirculationRules.

Test plan:
1/ Read the additions to t/db_dependent/CirculationRules.t code
   and compare to the t/db_dependent/RefundLostItemFeeRule.t.
2/ Run the test after applying the patch that adds the new method
3/ If the tests all pass, signoff

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>