@Override
      public boolean accept(Path p) {
        if (WALSplitUtil.isSequenceIdFile(p)) {
          return false;
        }
        return true;
      }
@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