CDDSO-326 fix calendar initialisation in qc validators

[piotr-florek-mohc]

just a simple fix plus some unit tests

[matthew-mizielinski]

LGTM and tests pass

[mo-jareddrayton]

One thing that we might need to be careful of is the state of the isodatetime Calendar singleton. As it stands it will be changed to "gregorian" when calling .date_validator but not switched back. This could cause problems if any validation code that needs the "360_day" calendar is added or moved to after this change of calendar.

[piotr-florek-mohc]

One thing that we might need to be careful of is the state of the isodatetime Calendar singleton. As it stands it will be changed to "gregorian" when calling .date_validator but not switched back. This could cause problems if any validation code that needs the "360_day" calendar is added or moved to after this change of calendar.

Good catch, I forgot that the default() method returns a singleton. Will fix that asap.

[mo-jareddrayton]

Normally quite handy to set and forget but in cases like this it's kind of awkward to handle! I'd probably opt to use cf_time or datetime for this validator rather than set and then reset the Calendar in isodatetime.