How to mock.patch a plain dictionary in python?

How do I mock.patch a plain dictionary {} ?

I would like to check if the headers is set to {'Content-Type': 'application/json’}.

def get(self):
    result = Spider.get_news_urls()
    for k, v in result.iteritems():
        response = requests.get(v)
        xml = response.text()
        headers = {'Content-Type': 'application/json'}
        data = ''
        taskqueue.Task(url='/v1/worker', headers=headers, payload=json.dumps(data)).add(queue_name='itagnewstasks')
    return 'success', 200

The following unit test seems to successfully patch dict. But I have a {}, which I need to patch.

@mock.patch('__builtin__.dict')
@mock.patch('requests.get')
def test_header_is_set_to_json(self, req_get, x):
    gen = Generator()
    gen.get()
    x.assert_called_with()

I suppose an alternative way would be to mock patch taskqueue.Task() and compare if it was called with headers= {'Content-Type': 'application/json'} as a parameter.