NavigableSet<byte[]> getCols(String... strCols) {
    NavigableSet<byte[]> cols = new TreeSet<>(Bytes.BYTES_COMPARATOR);
    for (String col : strCols) {
      byte[] bytes = Bytes.toBytes(col);
      cols.add(bytes);
    }
    return cols;
  }
This test tests whether parallel {@link StoreScanner#close()} and
{@link StoreScanner#updateReaders(List, List)} works perfectly ensuring that there are no
references on the existing Storescanner readers.
hbase-server/src/test/java/org/apache/hadoop/hbase/regionserver/TestStoreScannerClosure.java