anchor.diff:        $machine->mustSucceed("echo hello");
         $machine->shutdown;
       '';
  +
   }
  
positive.code:           ../modules/testing/test-instrumentation.nix
            { key = "serial"; 
              boot.kernelParams = [ "console=tty1" "console=ttyS0" ];
              boot.loader.grub.timeout = pkgs.lib.mkOverride 0 {} 0; 
            }
          ];
      }).config.system.build.isoImage;
  
    testScript =
      ''
        createDisk("harddisk", 4 * 1024);
  
negative.code:       $machine->waitForJob("tty1");
        $machine->waitForJob("rogue");
        $machine->waitForJob("nixos-manual");
  
        # Test nix-env.
        $machine->mustSucceed("source /etc/profile");
        $machine->mustFail("hello");
        $machine->mustSucceed("nix-env -i hello");
        $machine->mustSucceed("hello") =~ /Hello, world/
            or die "bad `hello' output";
  
        # Partition the disk.
        $machine->mustSucceed(
  