Bug 12001: Add tests

Bug 12001: Add tests

Yes, we need tests to make sure we understand what is going on in this
subroutine.
The different combination of HoldsInNoissuesCharge,
RentalsInNoissuesCharge and ManInvInNoissuesCharge are tested here with
the subroutine we are going to remove (GetMemberAccountBalance).
In one of the next patches the new methods will be used to make sure we
are not modifying the calculated values (except the formatting).

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>