anchor.diff:        };
   
       webcheck = 
  +      { tarball ? jobs.tarball {}
  +      }:
         let
           services = pkgs.fetchsvn {
             url = https://svn.nixos.org/repos/nix/services/trunk;
  
positive.code:       in
          with import "${nixos}/lib/testing.nix" {inherit nixpkgs services; system = "i686-linux";} ;
          runInMachineWithX {
            drv = pkgs.lib.overrideDerivation (build {}) (oldAttrs: { configureFlags = ""; buildInputs = oldAttrs.buildInputs ++ [pkgs.firefox] ; }) ;
          };
  
    };
  
negative.code: { nixpkgs ? ../nixpkgs
  }:
  
  let
  