assert post worked Django

I just wrote some tests case about my forms, here is one :

def test_department_admin_creation(self):

    nb = Department.objects.count()
    response = self.client.post(self.url, {"name" : 'department', "organization" : self.organization})
    self.assertEqual(response.status_code, 200)
    self.assertEqual(nb+1,Department.objects.count())

And I'm wondering why the last assertion doesn't work while the status_code's one did.

Thank you !