anchor.diff:      webserver = 
         {config, pkgs, ...}:
         {
  +        fileSystems = pkgs.lib.mkOverride 50 {} 
  +	[ 
  +	  { mountPoint = "/repos";
  +	    device = "storage:/repos"; } 
  +	];
  +      
           services = {
   	  portmap = {
   	    enable = true;
  
positive.code:         };
  	
  	environment = {
  	  extraPackages = [ pkgs.pythonPackages.trac ];
  	};
        };
        
  
negative.code:     ''
        startAll;
        
        $postgresql->waitForFile("/tmp/.s.PGSQL.5432");
        $postgresql->mustSucceed("createdb trac");
        
        $webserver->mustSucceed("mkdir -p /repos/trac");
        $webserver->mustSucceed("svnadmin create /repos/trac");
        
        $webserver->waitForFile("/var/trac");      
        $webserver->mustSucceed("mkdir -p /var/trac/projects/test");
        $webserver->mustSucceed("PYTHONPATH=${pkgs.pythonPackages.psycopg2}/lib/python2.5/site-packages trac-admin /var/trac/projects/test initenv Test postgres://root\@postgresql/trac svn /repos/trac");
        
        $client->waitForFile("/tmp/.X11-unix/X0");
        sleep 60;
        
        print STDERR $client->execute("su - alice -c 'DISPLAY=:0.0 konqueror http://webserver/projects/test &'");
        sleep 120;
        
        print STDERR $client->execute("DISPLAY=:0.0 scrot /hostfs/$ENV{out}/screen1.png");
      '';
  