Bug 22321: Add unit tests

Bug 22321: Add unit tests

To test:
1. prove t/db_dependent/Illrequests.t
2. Observe test failure

    1..3
    ok 1 - before change, original borrowernumber found
    not ok 2 - after change, changed borrowernumber found in holds
    #   Failed test 'after change, changed borrowernumber found in holds'
    #   at t/db_dependent/Illrequests.t line 167.
    #          got: '3786'
    #     expected: '3787'
    ok 3 - after change, changed borrowernumber found in illrequests
    # Looks like you failed 1 test of 3.
not ok 4 - store borrowernumber change also updates holds

Signed-off-by: Magnus Enger <magnus@libriotech.no>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>