mock_dates.py

import datetime

class FakeDateTime(datetime.datetime):
    def __eq__(self, instance):
        try:
            return (self.year, self.month, self.day, self.hour, self.minute, self.second) == (instance.year, instance.month, instance.day, instance.hour, instance.minute, instance.second)
        except:
            return False

    @classmethod
    def today(cls):
        return cls(2014, 12, 22, 17, 9, 48, 647196)


class FakeDate(datetime.date):
    def __eq__(self, instance):
        return (self.year, self.month, self.day) == (instance.year, instance.month, instance.day)

    @classmethod
    def today(cls):
        return cls(2014, 12, 22)

datetime.date = FakeDate
datetime.datetime = FakeDateTime

mock_dates_with_type.py

import datetime

class FakeDateType(type):
    def __instancecheck__(self, instance):
        return isinstance(instance, datetime.date)


class FakeDateTime(datetime.datetime):
    def __eq__(self, instance):
        try:
            return (self.year, self.month, self.day, self.hour, self.minute, self.second) == (instance.year, instance.month, instance.day, instance.hour, instance.minute, instance.second)
        except:
            return False

    @classmethod
    def today(cls):
        return cls(2014, 12, 22, 17, 9, 48, 647196)


class FakeDate(datetime.date):
    __metaclass__ = FakeDateType

    def __eq__(self, instance):
        return (self.year, self.month, self.day) == (instance.year, instance.month, instance.day)

    @classmethod
    def today(cls):
        return cls(2014, 12, 22)

datetime.date = FakeDate
datetime.datetime = FakeDateTime