@BeforeClass
  public static void setUpBeforeClass() throws Exception {
    UTIL.getConfiguration().setClass(HConstants.MASTER_IMPL, MockHMaster.class, HMaster.class);
    StartTestingClusterOption option =
      StartTestingClusterOption.builder().numMasters(2).numRegionServers(2).numDataNodes(2).build();
    UTIL.startMiniCluster(option);
    UTIL.waitUntilAllSystemRegionsAssigned();
  }
Test to confirm that we will not hang when stop a backup master which is trying to become the
active master. See HBASE-19838
hbase-server/src/test/java/org/apache/hadoop/hbase/master/TestShutdownBackupMaster.java