@Test
  public void testIndexOnlyLruBlockCache() {
    CacheConfig cc = new CacheConfig(this.conf);
    conf.set(BlockCacheFactory.BLOCKCACHE_POLICY_KEY, "IndexOnlyLRU");
    BlockCache blockCache = BlockCacheFactory.createBlockCache(this.conf);
    assertTrue(blockCache instanceof IndexOnlyLruBlockCache);
    // reject data block
    long initialBlockCount = blockCache.getBlockCount();
    BlockCacheKey bck = new BlockCacheKey("bck", 0);
    Cacheable c = new DataCacheEntry();
    blockCache.cacheBlock(bck, c, true);
    // accept index block
    Cacheable indexCacheEntry = new IndexCacheEntry();
    blockCache.cacheBlock(bck, indexCacheEntry, true);
    assertEquals(initialBlockCount + 1, blockCache.getBlockCount());
  }
Assert that when BUCKET_CACHE_COMBINED_KEY is false, the non-default, that we deploy
LruBlockCache as L1 with a BucketCache for L2.
hbase-server/src/test/java/org/apache/hadoop/hbase/io/hfile/TestCacheConfig.java