Bug 10644: add unit tests for ClassSource.pm

Bug 10644: add unit tests for ClassSource.pm

The tests are wrapped in a database transaction.

To test:
prove t/db_dependent/ClassSource.t
t/db_dependent/ClassSource.t .. 1/24 prepare_cached(SELECT * FROM `class_sort_rules` WHERE `class_sort_rule` = ?) statement handle DBI::st=HASH(0x92dbedc) still Active at C4/ClassSource.pm line 249
prepare_cached(SELECT * FROM `class_sources` WHERE cn_source = ?) statement handle DBI::st=HASH(0x926876c) still Active at C4/ClassSource.pm line 137
attempting to use non-existent class sorting routine routine1
prepare_cached(SELECT * FROM `class_sort_rules` WHERE `class_sort_rule` = ?) statement handle DBI::st=HASH(0x92dbedc) still Active at C4/ClassSource.pm line 249
prepare_cached(SELECT * FROM `class_sources` WHERE cn_source = ?) statement handle DBI::st=HASH(0x926876c) still Active at C4/ClassSource.pm line 137
t/db_dependent/ClassSource.t .. ok
All tests successful.
Files=1, Tests=24,  0 wallclock secs ( 0.02 usr  0.00 sys +  0.12 cusr  0.01 csys =  0.15 CPU)
Result: PASS

Signed-off-by: Srdjan <srdjan@catalyst.net.nz>
Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>
(cherry picked from commit 5de06b87e29f12250a35df3239372a7ed0754811)
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>