Bug 28421: Unit Tests

Bug 28421: Unit Tests

This patch adds test test cases for both a Voided Payment and Voided
Writeoff. These cases need special handling in the refund process.

Test plan
0/ Don't apply
1/ Run t/db_dependent/Koha/Items.t
2/ Prior to this commit the test should pass
3/ Apply this commit but not the dependency(bug 22435)
3/ The test should fail
4/ Bug 22435 should make the test pass again.

Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>