def METHOD_NAME(self):
    s = self.ChannelSerializer(
        data=dict(
            name="New test channel",
            description="This is the best test channel",
            content_defaults=dict(author="Buster"),
        )
    )
    self.assertTrue(s.is_valid())
    c = s.save()
    defaults = DEFAULT_CONTENT_DEFAULTS.copy()
    defaults.update(author="Buster")
    self.assertEqual(defaults, c.content_defaults)