private void injectEmptyFile(String suffix, boolean closeFile) throws IOException {
    Writer writer =
      WALFactory.createWALWriter(fs, new Path(WALDIR, WAL_FILE_PREFIX + suffix), conf);
    if (closeFile) {
      writer.close();
    }
  }
@param leaveOpen index to leave un-closed. -1 to close all.
@return the writer that's still open, or null if all were closed.
hbase-server/src/test/java/org/apache/hadoop/hbase/wal/TestWALSplit.java