@BeforeClass
  public static void setUp() throws Exception {
    // Set up the integration test util
    if (util == null) {
      util = new IntegrationTestingUtility();
    }

    // Make sure there are three servers.
    util.initializeCluster(3);

    // Set up the load test tool.
    loadTool = new LoadTestTool();
    loadTool.setConf(util.getConfiguration());

    // Create executor with enough threads to restart rs's,
    // run scans, puts, admin ops and load test tool.
    executorService = Executors.newFixedThreadPool(8);

    // Set up the tables needed.
    setupTables();

    // Set up the actions.
    sleepTime = util.getConfiguration().getLong(SLEEP_TIME_KEY, SLEEP_TIME_DEFAULT);
    setupActions();
  }
The load test tool used to create load and make sure that WALs aren't empty.
hbase-it/src/test/java/org/apache/hadoop/hbase/mttr/IntegrationTestMTTR.java