The logic for conversion of various objects that act like time (Time, AS::TimeWithZone, DateTime) to Date objects returned from Date fields is described in https://www.mongodb.com/docs/mongoid/master/reference/fields/#field-type-date.

mongoize should behave in the same manner when given string input for Date fields.

Test cases to check:

Date only: "2020-02-02"
Date with time: "2020-02-02 03:03:03"
Date with time and zone: "2020-02-02 03:03:03 +1000"

These cases should be tested with the following 3 possible environment settings as per https://www.mongodb.com/docs/mongoid/master/reference/configuration/#time-zones:

use_utc=true
use_utc=false, use_activesupport_time_zone=true
use_utc=false, use_activesupport_time_zone=false

This should also be done for Time and DateTime fields.