anchor.diff:  let
   
     cfg = config.libvirt.test;
  +
  +  ztail = pkgs.haskell.packages.ghc784.callPackage (
  +    { mkDerivation, array, base, containers, filepath, hinotify
  +    , old-locale, process, regex-compat, stdenv, time, unix
  +    }:
  +    mkDerivation {
  +      pname = "ztail";
  +      version = "1.1";
  +      sha256 = "11x6whwyfgdgda5bhdck0k12inzix8cjfm42hh09p703nalk07nq";
  +      isLibrary = false;
  +      isExecutable = true;
  +      executableHaskellDepends = [
  +        array base containers filepath hinotify old-locale process
  +        regex-compat time unix
  +      ];
  +      description = "Multi-file, colored, filtered log tailer";
  +      license = stdenv.lib.licenses.bsd3;
  +    }
  +  ) {};
   
     inherit (import ../lib.nix) hexByteToInt mkMAC;
   
  
positive.code:         ${concatStrings (mapAttrsToList (n: i: ''
            ln -sv "${i.libvirt.xmlFile}" "$out/dom-${n}.xml"
          '') cfg.instances)}
          ln -sv  "${libvirtNetwork}" "$out/net-test.xml"
        '';
  
        phases = [ "buildPhase" "installPhase" "fixupPhase" ];
  
negative.code: 
    config = {
  
      libvirt.test.instances.${cfg.test-driver.hostName} = {
        libvirt.name = mkForce "@testid@";
        nixos.modules = cfg.test-driver.extraModules ++ [{
          systemd.services.test-script = {
  