@Test
public void topicChangedShouldUpdateTopicAndShowTopicRemovedMessageWhenTopicIsNull() {

    final Topic topic = new Topic();
    when(controller.getTopic()).thenReturn(topic);
    when(chatState.isLogonCompleted()).thenReturn(true);
    final long time = System.currentTimeMillis();
    responder.topicChanged(300, null, "Harry", time);
    verify(messageController).showSystemMessage("Harry removed the topic");
    verify(userInterface).showTopic();
    verifyTopic(topic, "", "", time);
}