private BlockCache initCombinedBlockCache(final String l1CachePolicy) {
    Configuration that = HBaseConfiguration.create(conf);
    that.setFloat(BUCKET_CACHE_SIZE_KEY, 32); // 32MB for bucket cache.
    that.set(BUCKET_CACHE_IOENGINE_KEY, "offheap");
    that.set(BLOCKCACHE_POLICY_KEY, l1CachePolicy);
    BlockCache bc = BlockCacheFactory.createBlockCache(that);
    Assert.assertNotNull(bc);
    Assert.assertTrue(bc instanceof CombinedBlockCache);
    return bc;
  }
Test case for HBASE-22127 in LruBlockCache.
hbase-server/src/test/java/org/apache/hadoop/hbase/io/hfile/TestHFile.java