'Assert the default headers are there upon initialization'

def test_has_default_headers(self):

    s = self.build_session()
    assert ('Accept' in s.headers)
    assert (s.headers['Accept'] == 'application/vnd.github.v3.full+json')
    assert ('Accept-Charset' in s.headers)
    assert (s.headers['Accept-Charset'] == 'utf-8')
    assert ('Content-Type' in s.headers)
    assert (s.headers['Content-Type'] == 'application/json')
    assert ('User-Agent' in s.headers)
    assert s.headers['User-Agent'].startswith('github3.py/')
