How to test auto_now_add in django

Question

I have django 1.11 app and I want to write unit test for my solution.

I want to test registration date feature.

model.py:

class User(models.Model):
    first_name = models.CharField(max_length=30)
    last_name = models.CharField(max_length=30)
    registration_date = models.DateTimeField(auto_now_add=True)

    def get_registration_date(self):
        return self.registration_date

I'm using also django-boy for models factories: factories.py

  class UserFactory(factory.DjangoModelFactory):
        class Meta:
            model = models.User
        first_name = 'This is first name'
        last_name = 'This is last name'
        registration_date = timezone.now()

test.py

def test_get_registration_date(self):
    user = factories.UserFactory.create()
    self.assertEqual(user.get_registration_date(), timezone.now())

Problem is that I recived AssertionError:

AssertionError: datetime.datetime(2018, 4, 17, 9, 39, 36, 707927, tzinfo=<UTC>) != datetime.datetime(2018, 4, 17, 9, 39, 36, 708069, tzinfo=<UTC>)

Answer 1

The universal way to use Factory Boy with Django with DateTime with auto_now_add=True

1. Introduce custom DjangoFactory, with arg _fake_time to freeze time during object creation

from contextlib import suppress
from factory.django import DjangoModelFactory
from freezegun import freeze_time
from functools import partial

class CustomDjangoModelFactory(DjangoModelFactory):

    @classmethod
    def create(cls, _fake_time=None, **kwargs):
        wrapper = partial(freeze_time, time_to_freeze=_fake_time) if _fake_time else suppress
        with wrapper(_fake_time):
            return super().create(**kwargs)

2. Add/change your factory to be based on CustomDjangoModelFactory

import factory
from django.db import models

class MyModel(models.Model):
    name = models.CharField(max_length=255)
    created = models.DateTimeField(auto_now_add=True)

class MyModelFactory(CustomDjangoModelFactory):
    name = factory.Sequence(lambda n: "Model No. %03d" % n)

    class Meta:
        model = MyModel

3. Use it with _fake_time or without

my_model1 = MyModelFactory(name='first', _fake_time='2020-12-1')
my_model2 = MyModelFactory(name='second', _fake_time=datetime(2020, 11, 30))
my_model3 = MyModelFactory(name='third')

Answer 2

You can use mock:

import pytz
from unittest import mock

def test_get_registration_date(self):
    mocked = datetime.datetime(2018, 4, 4, 0, 0, 0, tzinfo=pytz.utc)
    with mock.patch('django.utils.timezone.now', mock.Mock(return_value=mocked)):
        user = factories.UserFactory.create()
        self.assertEqual(user.get_registration_date(), mocked)