anchor.diff:          environment.systemPackages = [ ${optionalString testChannel "pkgs.rlwrap"} ];
   
           nix.binaryCaches = [ http://cache.nixos.org/ ];
  +        ${replaceChars ["\n"] ["\n  "] extraConfig}
         }
       '';
   
  
positive.code:       $machine->succeed("cat /mnt/etc/nixos/hardware-configuration.nix >&2");
  
        $machine->copyFileFromHost(
            "${ makeConfig { inherit testChannel grubVersion grubDevice grubIdentifier; } }",
            "/mnt/etc/nixos/configuration.nix");
  
        # Perform the installation.
  
negative.code:       $machine = createMachine({ ${hdFlags} qemuFlags => "${qemuFlags}" });
        $machine->waitForUnit("multi-user.target");
        $machine->copyFileFromHost(
            "${ makeConfig { inherit testChannel grubVersion grubDevice grubIdentifier extraConfig; readOnly = false; forceGrubReinstallCount = 2; } }",
            "/etc/nixos/configuration.nix");
        $machine->succeed("nixos-rebuild boot >&2");
        $machine->shutdown;
  