anchor.diff:      rotated = map (i: "${logfile}.${toString i}") (range 1 9);
       all = concatMapStringsSep " " (f: "\"${f}\"") ([logfile] ++ rotated);
       logcmd = "tail -F ${all} 2> /dev/null | logger -t \"${tag}\"";
  -  in optionalString debug "$machine->execute(ru '${logcmd} & disown');";
  +  in if debug then "machine.execute(ru('${logcmd} & disown'))" else "pass";
   
     testVM = vmName: vmScript: let
       cfg = (import ../lib/eval-config.nix {
  
positive.code:     };
  
      testScript = ''
        sub ru ($) {
          my $esc = $_[0] =~ s/'/'\\${"'"}'/gr;
          return "su - alice -c '$esc'";
        }
  
        sub vbm {
          $machine->succeed(ru("VBoxManage ".$_[0]));
        };
  
        sub removeUUIDs {
          return join("\n", grep { $_ !~ /^UUID:/ } split(/\n/, $_[0]))."\n";
        }
  
        ${concatStrings (mapAttrsToList (_: getAttr "testSubs") vms)}
  
        $machine->waitForX;
  
        ${mkLog "$HOME/.config/VirtualBox/VBoxSVC.log" "HOST-SVC"}
  
        ${testScript}
      '';
  
      meta = with pkgs.stdenv.lib.maintainers; {
  
negative.code: 
  assert use64bitGuest -> useKvmNestedVirt;
  
  with import ../lib/testing-python.nix { inherit system pkgs; };
  with pkgs.lib;
  
  let
  