@Test
public void enqueu_event() {

    // prepare
    Event e = mock(Event.class);
    // run
    handlerExecutor.execute(e);
    // verify
    ArgumentCaptor<Runnable> captor = ArgumentCaptor.forClass(Runnable.class);
    verify(executor).execute(captor.capture());
    captor.getValue().run();
    verify(e).visit(any(EventVisitor.class));
}