def test_constructorDoesNotAllowExtraChainWithoutPrivateKey(self):
        """
        A C{extraCertChain} without C{privateKey} doesn't make sense and is
        thus rejected.
        """
        self.assertRaises(
            ValueError,
            sslverify.OpenSSLCertificateOptions,
            certificate=self.sCert,
            extraCertChain=self.extraCertChain,
        )

        A C{extraCertChain} without C{privateKey} doesn't make sense and is
        thus rejected.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_sslverify.py