def test_sslChainLoads(self):
        """
        Specifying a chain file loads the contained certificates in the right
        order.
        """
        server = endpoints.serverFromString(
            object(),
            self.SSL_CHAIN_TEMPLATE % (escapedPEMPathName,
                                       escapedChainPathName,)
        )
        # Test chain file is just a concatenation of thing1.pem and thing2.pem
        # so we can check that loading has succeeded and order has been
        # preserved.
        expectedChainCerts = [
            Certificate.loadPEM(casPath.child("thing%d.pem" % (n,))
                                .getContent())
            for n in [1, 2]
        ]
        cf = server._sslContextFactory
        self.assertEqual(cf.extraCertChain[0].digest('sha1'),
                         expectedChainCerts[0].digest('sha1'))
        self.assertEqual(cf.extraCertChain[1].digest('sha1'),
                         expectedChainCerts[1].digest('sha1'))

        Specifying a chain file loads the contained certificates in the right
        order.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/internet/test/test_endpoints.py