anchor.diff:  
       services.xserver.enable = true;
       test-support.displayManager.auto.user = "alice";
  -    environment.systemPackages = [ pkgs.signal-desktop ];
  +    environment.systemPackages = with pkgs; [ signal-desktop file ];
       virtualisation.memorySize = 1024;
     };
   
  
positive.code:     machine.wait_for_text("Signal")
      machine.wait_for_text("File Edit View Window Help")
      machine.screenshot("signal_desktop")
    '';
  })
  
negative.code: {
    name = "signal-desktop";
    meta = with pkgs.lib.maintainers; {
      maintainers = [ flokli primeos ];
    };
  
    machine = { ... }:
  