anchor.diff:      six
     ];
   
  -  # Fontconfig error: Cannot load default config file
  -  preCheck = ''
  +  # tests print “Fontconfig error: Cannot load default config file”
  +  preCheck = lib.optionalString withGraphviz ''
       export FONTCONFIG_FILE=${fontconfig.out}/etc/fonts/fonts.conf
     '';
  +
  +  # circular dependency anytree → graphviz → pango → glib → gtk-doc → anytree
  +  doCheck = withGraphviz;
   
     checkPhase = ''
       runHook preCheck
  
positive.code: , fetchpatch
  , nose
  , six
  , graphviz
  , fontconfig
  }:
  
negative.code:     sha256 = "05736hamjv4f38jw6z9y4wckc7mz18ivbizm1s3pb0n6fp1sy4zk";
    };
  
    patches = lib.optionals withGraphviz [
      (substituteAll {
        src = ./graphviz.patch;
        inherit graphviz;
  