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.

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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) 

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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) 

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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?

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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

Here's a method you can use that doesn't require altering your non-test code. Just patch the default attributes of the fields you want to affect. For example--

field = User._meta.get_field('timestamp') mock_now = lambda: datetime(2010, 1, 1) with patch.object(field, 'default', new=mock_now):     # Your code here 

You can write helper functions to make this less verbose. For example, the following code--

@contextmanager def patch_field(cls, field_name, dt):     field = cls._meta.get_field(field_name)     mock_now = lambda: dt     with patch.object(field, 'default', new=mock_now):         yield 

would let you write--

with patch_field(User, 'timestamp', dt):     # Your code here 

Similarly, you can write helper context managers to patch multiple fields at once.

Answer 2

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())