@BeforeClass
  public static void before() throws Exception {
    TESTING_UTIL.getConfiguration().setInt(HConstants.HBASE_BALANCER_PERIOD, 60000);
    StartTestingClusterOption option = StartTestingClusterOption.builder()
      .masterClass(MyMaster.class).numRegionServers(NB_SERVERS).numDataNodes(NB_SERVERS).build();
    TESTING_UTIL.startMiniCluster(option);
  }
The below tests are testing split region against a running cluster
hbase-server/src/test/java/org/apache/hadoop/hbase/regionserver/TestSplitTransactionOnCluster.java