Bug 27079: Unit tests

Bug 27079: Unit tests

Add a unit test to check for floating point errors in UpdateFine
relating to catching matching CalcFine amounts compared to DB amount
values.

Test plan
1/ Run the unit test and confirm it fails
2/ Apply the second patch in the series
3/ Run the unit test and confirm it passes

Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>