@Test
public void testFetchAllActiveExecutorServerHosts() throws Exception {

  final Set<String> activeExecutorServerHosts = this.controller.getAllActiveExecutorServerHosts();
  assertThat(activeExecutorServerHosts.size()).isEqualTo(3);
  this.allExecutors.forEach(executor -> assertThat(
      activeExecutorServerHosts.contains(executor.getHost() + ":" + executor.getPort()))
      .isTrue());
}