private static ByteBuff getOverwriteByteBuff(BucketEntry bucketEntry) {
    int byteSize = bucketEntry.getLength();
    byte[] data = new byte[byteSize];
    Arrays.fill(data, (byte) 0xff);
    return ByteBuff.wrap(ByteBuffer.wrap(data));
  }
Overwrite 0xff to the {@link BucketEntry} content to simulate it would be overwrite after the
{@link BucketEntry} is freed.
hbase-server/src/test/java/org/apache/hadoop/hbase/io/hfile/bucket/TestBucketCacheRefCnt.java