@After
  public void shutdown() throws Exception {
    HMaster.setDisableBalancerChoreForTest(false);
    TEST_UTIL.shutdownMiniCluster();
  }
Make {@link BalancerChore} not run,so does not disrupt the test.
hbase-server/src/test/java/org/apache/hadoop/hbase/master/TestMasterBalancerNPE.java