@Override public void onServerStart(Server server) {
    if (scheduler != null) {
      scheduler.startScheduling();
    }
  }
@Test
  public void when_scheduler_should_start_on_server_start() {
    var scheduler = mock(TokenExpirationNotificationScheduler.class);
    var underTest = new TokenExpirationNotificationInitializer(scheduler);
    underTest.onServerStart(mock(Server.class));
    verify(scheduler, times(1)).startScheduling();
  }