How to Unit test with different settings in Django?

Is there any simple mechanism for overriding Django settings for a unit test? I have a manager on one of my models that returns a specific number of the latest objects. The number of objects it returns is defined by a NUM_LATEST setting.

This has the potential to make my tests fail if someone were to change the setting. How can I override the settings on setUp() and subsequently restore them on tearDown()? If that isn't possible, is there some way I can monkey patch the method or mock the settings?

EDIT: Here is my manager code:

class LatestManager(models.Manager):
    """
    Returns a specific number of the most recent public Articles as defined by 
    the NEWS_LATEST_MAX setting.
    """
    def get_query_set(self):
        num_latest = getattr(settings, 'NEWS_NUM_LATEST', 10)
        return super(LatestManager, self).get_query_set().filter(is_public=True)[:num_latest]

The manager uses settings.NEWS_LATEST_MAX to slice the queryset. The getattr() is simply used to provide a default should the setting not exist.

EDIT: This answer applies if you want to change settings for a small number of specific tests.

Since Django 1.4, there are ways to override settings during tests: https://docs.djangoproject.com/en/stable/topics/testing/tools/#overriding-settings

TestCase will have a self.settings context manager, and there will also be an @override_settings decorator that can be applied to either a test method or a whole TestCase subclass.

These features did not exist yet in Django 1.3.

If you want to change settings for all your tests, you'll want to create a separate settings file for test, which can load and override settings from your main settings file. There are several good approaches to this in the other answers; I have seen successful variations on both hspander's and dmitrii's approaches.

You can do anything you like to the UnitTest subclass, including setting and reading instance properties:

from django.conf import settings

class MyTest(unittest.TestCase):
   def setUp(self):
       self.old_setting = settings.NUM_LATEST
       settings.NUM_LATEST = 5 # value tested against in the TestCase

   def tearDown(self):
       settings.NUM_LATEST = self.old_setting

Since the django test cases run single-threaded, however, I'm curious about what else may be modifying the NUM_LATEST value? If that "something else" is triggered by your test routine, then I'm not sure any amount of monkey patching will save the test without invalidating the veracity of the tests itself.