anchor.diff:        $machine->mustSucceed("echo hello");
         $machine->shutdown;
       '';
  +
   }
  
positive.code:           "mount LABEL=nixos /mnt",
        );
  
        $machine->shutdown;
  
        # Now see if we can boot the installation.
  
negative.code:           ../modules/testing/test-instrumentation.nix
            { key = "serial"; 
              boot.kernelParams = [ "console=tty1" "console=ttyS0" ];
              boot.loader.grub.timeout = pkgs.lib.mkOverride 0 {} 0;
              # The test cannot access the network, so any sources we
              # need must be included in the ISO.
              isoImage.storeContents = [ pkgs.hello.src ];
            }
          ];
      }).config.system.build.isoImage;
  
    # The test script boots the CD, installs NixOS on an empty hard
    # disk, and then reboot from the hard disk.
    testScript =
      ''
        createDisk("harddisk", 4 * 1024);
  