def test_constructorWithOnlyCertificate(self):
        """
        C{privateKey} and C{certificate} make only sense if both are set.
        """
        self.assertRaises(
            ValueError,
            sslverify.OpenSSLCertificateOptions, certificate=self.sCert
        )

        C{privateKey} and C{certificate} make only sense if both are set.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_sslverify.py