anchor.diff:        users.users.alice.extraGroups = let
           inherit (config.virtualisation.virtualbox.host) enableHardening;
         in lib.mkIf enableHardening (lib.singleton "vboxusers");
  +      virtualisation.virtualbox.host.enableExtensionPack = useExtensionPack;
  +      nixpkgs.config.allowUnfree = useExtensionPack;
       };
   
       testScript = ''
  
positive.code:     "--hostonlyadapter2 vboxnet0"
    ];
  
    dhcpScript = pkgs: ''
      ${pkgs.dhcp}/bin/dhclient \
        -lf /run/dhcp.leases \
  
negative.code:         return join("\n", grep { $_ !~ /^UUID:/ } split(/\n/, $_[0]))."\n";
        }
  
        ${concatStrings (mapAttrsToList (_: getAttr "testSubs") vms)}
  
        $machine->waitForX;
  
  