def test_verification(self):
        """
        Check certificates verification building custom certificates data.
        """
        clientDN = sslverify.DistinguishedName(commonName='client')
        clientKey = sslverify.KeyPair.generate()
        clientCertReq = clientKey.certificateRequest(clientDN)

        serverDN = sslverify.DistinguishedName(commonName='server')
        serverKey = sslverify.KeyPair.generate()
        serverCertReq = serverKey.certificateRequest(serverDN)

        clientSelfCertReq = clientKey.certificateRequest(clientDN)
        clientSelfCertData = clientKey.signCertificateRequest(
                clientDN, clientSelfCertReq, lambda dn: True, 132)
        clientSelfCert = clientKey.newCertificate(clientSelfCertData)

        serverSelfCertReq = serverKey.certificateRequest(serverDN)
        serverSelfCertData = serverKey.signCertificateRequest(
                serverDN, serverSelfCertReq, lambda dn: True, 516)
        serverSelfCert = serverKey.newCertificate(serverSelfCertData)

        clientCertData = serverKey.signCertificateRequest(
                serverDN, clientCertReq, lambda dn: True, 7)
        clientCert = clientKey.newCertificate(clientCertData)

        serverCertData = clientKey.signCertificateRequest(
                clientDN, serverCertReq, lambda dn: True, 42)
        serverCert = serverKey.newCertificate(serverCertData)

        onData = defer.Deferred()

        serverOpts = serverCert.options(serverSelfCert)
        clientOpts = clientCert.options(clientSelfCert)

        self.loopback(serverOpts,
                      clientOpts,
                      onData=onData)

        return onData.addCallback(
                lambda result: self.assertEqual(result, WritingProtocol.byte))

        Check certificates verification building custom certificates data.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_sslverify.py