function addServerCertificateToTrustedCertificateInDiscoveryServer(server, callback) {

        const filename = server.certificateFile;
        fs.existsSync(filename).should.eql(true);
        const certificate = readCertificate(filename);
        discovery_server.serverCertificateManager.trustCertificate(certificate, callback);

    }
                setTimeout(function () {

                    callback(null, {
                        process: server_exec,
                        pid_collected: pid_collected,
                        endpointUrl: "opc.tcp://" + os.hostname() + ":" + port + "/UA/SampleServer",
                        serverCertificate: crypto_utils.readCertificate(serverCertificateFilename)
                    });

                }, 100);
                // create a first channel (client1) with
                function (callback) {
                    //xx console.log(" creating initial channel with some certificate");
                    const certificateFile1 = m("certificates/client_cert_2048.pem");
                    const privateKeyFile1 = m("certificates/client_key_2048.pem");
                    client1 = OPCUAClient.create({
                        certificateFile: certificateFile1,
                        privateKeyFile: privateKeyFile1,
                        securityMode: opcua.MessageSecurityMode.Sign,
                        securityPolicy: opcua.SecurityPolicy.Basic128Rsa15,
                        serverCertificate: serverCertificate
                    });

                    const certificate = readCertificate(certificateFile1);
                    test.server.serverCertificateManager.trustCertificate(certificate,callback);

                },
                // create a second channel (client2)
                // with a different certificate ....
                function (callback) {

                    // creating second channel with different credential
                    console.log(" creating second channel with different certificate");
                    const certificateFile2 = m("certificates/client_cert_3072.pem");
                    const privateKeyFile2 = m("certificates/client_key_3072.pem");
                    client2 = OPCUAClient.create({
                        certificateFile: certificateFile2,
                        privateKeyFile: privateKeyFile2,
                        securityMode: opcua.MessageSecurityMode.Sign,
                        securityPolicy: opcua.SecurityPolicy.Basic256,
                        serverCertificate: serverCertificate
                    });
                    const certificate = readCertificate(certificateFile2);
                    test.server.serverCertificateManager.trustCertificate(certificate,callback);

                },