public void addCallback(Callback cb) {
    this.callbacks.add(cb);
  }
@Test(timeout=15000)
  public void testCallbackThrowsRTE() throws Exception {
    hm.addCallback(new Callback() {
      @Override
      public void enteredState(State newState) {
        throw new RuntimeException("Injected RTE");
      }
    });
    LOG.info("Mocking bad health check, waiting for UNHEALTHY");
    svc.isHealthy = false;
    waitForState(hm, HealthMonitor.State.HEALTH_MONITOR_FAILED);
  }