How to use the investigate.Investigate.BASE_URL function in investigate

def test_connectivity(self):
        """Connectivity Test which is used by resilient_circuits selftest.

        Calls http 'get' request against 'event_types' url.

        :return: Response
        """
        uri = self._uris["categories"]
        return self._session.get(urljoin(Investigate.BASE_URL, uri),
                                 params=None,
                                 headers=self._auth_header,
                                 proxies=self.proxies
                                 )
        return r