self = 
def test_extra_headers(self):
    import requests


  from google.cloud import _http as base_http


tests/unit/test__http.py:73:

"""Shared implementation of connections to API servers."""

import json
import platform
import warnings

from pkg_resources import get_distribution


from six.moves.urllib.parse import urlencode

E   ModuleNotFoundError: No module named 'six'

.nox/unit-3-7/lib/python3.7/site-packages/google/cloud/_http.py:22: ModuleNotFoundError