Mocking default=timezone.now for unit tests

Question

I'm trying to write unit tests for a django app that does a lot of datetime operations. I have installed mock to monkey patch django's timezone.now for my tests.

While I am able to successfully mock timezone.now when it is called normally (actually calling timezone.now() in my code, I am not able to mock it for models that are created with a DateTimeField with default=timezone.now.

---

I have a User model that contains the following:

from django.utils import timezone
...
timestamp = models.DateTimeField(default=timezone.now)
modified = models.DateTimeField(default=timezone.now)
...
def save(self, *args, **kwargs):
    if kwargs.pop('modified', True):
        self.modified = timezone.now()
    super(User, self).save(*args, **kwargs)

---

My unit test looks like this:

from django.utils import timezone

def test_created(self):
    dt = datetime(2010, 1, 1, tzinfo=timezone.utc)
    with patch.object(timezone, 'now', return_value=dt):
        user = User.objects.create(username='test')
        self.assertEquals(user.modified, dt)
        self.assertEquals(user.timestamp, dt)

---

assertEquals(user.modified, dt) passes, but assertEquals(user.timestamp, dt) does not.

How can I mock timezone.now so that even default=timezone.now in my models will create the mock time?

---

Edit

I know that I could just change my unit test to pass a timestamp of my choice (probably generated by the mocked timezone.now)... Curious if there is a way that avoids that though.

Answer 1

I just ran into this issue myself. The problem is that models are loaded before mock has patched the timezone module, so at the time the expression default=timezone.now is evaluated, it sets the default kwarg to the real timezone.now function.

The solution is the following:

class MyModel(models.Model):
    timestamp = models.DateTimeField(default=lambda: timezone.now())