@Override
    public String toString() {
      StringBuilder buffer = new StringBuilder();
      buffer.append("mockFs{files:[");
      for(int i=0; i < files.size(); ++i) {
        if (i != 0) {
          buffer.append(", ");
        }
        buffer.append(files.get(i));
      }
      buffer.append("]}");
      return buffer.toString();
    }
WARNING: detele(Path...) don't actually delete
ql/src/test/org/apache/hadoop/hive/ql/io/orc/TestInputOutputFormat.java