@Override
        public void doAnAction() throws Exception {
          ByteArrayCacheable returned =
            (ByteArrayCacheable) toBeTested.getBlock(key, false, false, true);
          if (returned != null) {
            assertArrayEquals(buf, returned.buf);
          } else {
            Thread.sleep(10);
          }
          totalQueries.incrementAndGet();
        }
Just checks if heapsize grows when something is cached, and gets smaller when the same object
is evicted
hbase-server/src/test/java/org/apache/hadoop/hbase/io/hfile/CacheTestUtils.java