'Assert adding an nonexistent tag yields an AJAX error.'

def test_add_async_nonexistent_tag(self):

    response = self.client.post(_add_async_tag_url(self.question.id), data={'tag-name': 'nonexistent    tag'}, HTTP_X_REQUESTED_WITH='XMLHttpRequest')
    self.assertContains(response, UNAPPROVED_TAG, status_code=400)
