Bug 29476: Correct soonest renewal date calculation for checkouts with auto-renewal

Bug 29476: Correct soonest renewal date calculation for checkouts with auto-renewal

If a checkout with auto-renewal enabled doesn't have a
"norenewalbefore" circulation rule set the code in CanBookBeRenewed()
falls back to using due date (to verify this please look for the
string "auto_too_soon" in C4/Circulation.pm), the calculation result
of GetSoonestRenewDate() however didn't do this, though luckily it was
not used in CanBookBeRenewed so we didn't get any issues
there. However, GetSoonestRenewDate() is used for displaying the
soonest renewal date in the staff interface on the circ/renew.pl page
so you would have gotten wrong results there.

This patch moves additionally the tests made for Bug 14395 under a new
subtest for GetSoonestRenewDate() as they should have been like that
already before.

To test:
  1) prove t/db_dependent/Circulation.t

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>