@BeforeClass
  public static void setUpClass() throws Exception {
    // Set RegionServer class and use default values for other options.
    UTIL.startMiniCluster(
      StartTestingClusterOption.builder().rsClass(PriorityRegionServer.class).build());
    TableDescriptor descriptor = TableDescriptorBuilder.newBuilder(TABLE_NAME)
      .setColumnFamily(ColumnFamilyDescriptorBuilder.of(FAMILY)).build();
    UTIL.getAdmin().createTable(descriptor);

    Configuration conf = new Configuration(UTIL.getConfiguration());
    conf.setClass(RpcControllerFactory.CUSTOM_CONTROLLER_CONF_KEY,
      PriorityRpcControllerFactory.class, RpcControllerFactory.class);
    CONN = ConnectionFactory.createConnection(conf);
    TABLE = CONN.getTable(TABLE_NAME);
  }
Tests that one can implement their own RpcControllerFactory and expect it to successfully pass
custom priority values to the server for all HTable calls.
hbase-server/src/test/java/org/apache/hadoop/hbase/TestCustomPriorityRpcControllerFactory.java