@AfterClass
  public static void tearDown() throws Exception {
    CONN.close();
    UTIL.shutdownMiniCluster();
    EXECUTOR_SERVICE.shutdownNow();
  }
Same as TestAsyncAggregationClient, except that {@link AsyncTableImpl} is involved in addition to
{@link RawAsyncTableImpl}. Exercises the code paths in {@link AsyncTableImpl#coprocessorService}.
hbase-endpoint/src/test/java/org/apache/hadoop/hbase/client/TestAsyncAggregationClientWithCallbackThreadPool.java