### Question:
VoiceCallEngine { public static VoiceCallEngine getInstance() { if(instance == null) { instance = new VoiceCallEngine(); } return instance; } private  VoiceCallEngine(); static VoiceCallEngine getInstance(); RtcEngine getmRtcEngine(); void joinChannel(String channelID, EventHandler handler); void leaveChannel(); void muteMic(); void unmuteMic(); void useSpeaker(); void useEarpiece();  }### Answer:
@Test public void testGetInstance() { assertNotNull(VoiceCallEngine.getInstance()); assertNotNull(VoiceCallEngine.getInstance().getmRtcEngine()); }