Tests for Django model that uses columns with auto_now

test_auto_now_example.py

""" A way to test columns with auto_now

Columns with auto_now auto update with the current time when
the model is saved - this patches function django uses to
get the current time when the model is saved to use whatever
time you want.

Base on answers on SO: https://stackoverflow.com/questions/49874923/how-to-test-auto-now-add-in-django
"""
from contextlib import contextmanager
from unittest.mock import patch
from django.test import TestCase
from django.utils import timezone
from .models import MyModel # model w/ auto_now col

@contextmanager
def freeze_time(at: dt.datetime):
  with patch.object(timezone, 'now', return_value=at): # patch django.utils.timezone.now()
    yield

class TestMyApp(TestCase):

  def test_create_model_that_uses_autonow(self):

    # this one will have the current time
    my_obj = MyModel.objects.create(...)
    
    # some time other than now that you want to use
    at = dt.datetime(...) 
    with freeze_time(at):
      my_obj_freeze = MyModel.objects.create(...)
      
      # do testy stuff...