'Ensure that header updates are done case-insensitively.'

def test_fixes_1329(self, httpbin):

    s = requests.Session()
    s.headers.update({'ACCEPT': 'BOGUS'})
    s.headers.update({'accept': 'application/json'})
    r = s.get(httpbin('get'))
    headers = r.request.headers
    assert (headers['accept'] == 'application/json')
    assert (headers['Accept'] == 'application/json')
    assert (headers['ACCEPT'] == 'application/json')
