def METHOD_NAME(self, requests_post):
    url = 'http://callback-target.com'
    payload = {'data': 'value'}
    callback = self.build.callbacks.create(url=url, event=self.event, payload=json.dumps(payload), payload_is_json=False)
    callback.dispatch()
    self.assertTrue(requests_post.called)
    self.assertTrue(callback.is_sent)
    requests_post.assert_called_with(url, data=payload)