@BeforeClass
  public static void setUpBeforeClass() throws Exception {
    TEST_UTIL.getConfiguration().setClass(HConstants.REGION_IMPL, TestRegion.class, HRegion.class);
    StartTestingClusterOption.Builder builder = StartTestingClusterOption.builder();
    // 1 master is expected to be aborted with this test
    builder.numMasters(2).numRegionServers(3);
    TEST_UTIL.startMiniCluster(builder.build());
    SingleProcessHBaseCluster cluster = TEST_UTIL.getHBaseCluster();
    rs0 = cluster.getRegionServer(0).getServerName();
    TEST_UTIL.getAdmin().balancerSwitch(false, true);
  }
MasterRegion related test that ensures the operations continue even when Procedure state update
encounters retriable IO errors.
hbase-server/src/test/java/org/apache/hadoop/hbase/master/TestMasterRegionMutation1.java