anchor.diff:  
   
     musicbrainzngs = buildPythonPackage rec {
  -    name = "musicbrainzngs-0.2";
  +    name = "musicbrainzngs-0.5";
   
       src = fetchurl {
         url = "http://pypi.python.org/packages/source/m/musicbrainzngs/${name}.tar.gz";
  -      md5 = "bc32aa1cf121f29c3ca1c06e9668865f";
  +      md5 = "9e17a181af72d04a291c9a960bc73d44";
       };
   
       meta = {
  
positive.code: 
  
    six = buildPythonPackage rec {
      name = "six-1.3.0";
  
      src = fetchurl {
        url = "http://pypi.python.org/packages/source/s/six/${name}.tar.gz";
        md5 = "ec47fe6070a8a64c802363d2c2b1e2ee";
      };
  
      # error: invalid command 'test'
  
negative.code: 
  
    mutagen = buildPythonPackage (rec {
      name = "mutagen-1.23";
  
      src = fetchurl {
        url = "http://pypi.python.org/packages/source/m/mutagen/${name}.tar.gz";
        sha256 = "12f70aaf5ggdzll76bhhkn64b27xy9s1acx417dbsaqnnbis8s76";
      };
      
      # one unicode test fails
      doCheck = false;
  
      meta = {
        description = "Python multimedia tagging library";
  