@BeforeClass
  public static void beforeClass() throws Exception {
    // Default in ZookeeperMiniCluster is 1000, setting artificially low to trigger exhaustion.
    // need min of 7 to properly start the default mini HBase cluster
    UTIL.getConfiguration().setInt(HConstants.ZOOKEEPER_MAX_CLIENT_CNXNS, 10);
    UTIL.startMiniCluster();
  }
Spark creates many instances of TableOutputFormat within a single process. We need to make sure
we can have many instances and not leak connections. This test creates a few TableOutputFormats
and shouldn't fail due to ZK connection exhaustion.
hbase-mapreduce/src/test/java/org/apache/hadoop/hbase/mapred/TestTableOutputFormatConnectionExhaust.java