java - Junit/Mockito - wait for method execution -

in application use observer pattern operations , want test them in unit tests. problem don't know how can test observers using junit/mockito/something else. help?

for example unit test:

@before public void setup() throws ioexception, exception {     observer = new gameinstanceobserver(); // observable (gameinstance) call update() method after every change     gameinstance.getinstance().addobserver(observer); // observable updated serverservice }  @test(expected = userdatadoesntexistexception.class) public void getroomuserdata_usingnullkey_shouldthrowuserdatadoesntexist() throws interruptedexception, userdatadoesntexistexception {     serverservice.createroom("exampleroom"); // operation asynchronous , updates gameinstance data (as wrote before gameinstance observable)     thread.sleep(400); // how in better way?      gameinstance gi = (gameinstance) observer.getobservable();     asserttrue(gi.getroom("exampleroom").getroomid().equals("exampleroom")); } 

i not use thread.sleep() , use in way (or similar):

@test(expected = userdatadoesntexistexception.class) public void getroomuserdata_usingnullkey_shouldthrowuserdatadoesntexist() throws interruptedexception, userdatadoesntexistexception {     serverservice.createroom("exampleroom"); // operation asynchronous , updates gameinstance data (as wrote before gameinstance observable)     waituntildatachange(gameinstance.getinstance()); // wait until observable changed know notified observer , can validate data      gameinstance gi = (gameinstance) observer.getobservable();     asserttrue(gi.getroom("exampleroom").getroomid().equals("exampleroom")); } 

if understand correctly, problem not test observer, test result of asynchronous method call. that, create observer blocks until update() method has been called. following:

public class blockinggameobserver extends gameinstanceobserver {     private countdownlatch latch = new countdownlatch(1);      @override     public void update() {         latch.countdown();     }      public void waituntilupdateiscalled() throws interruptedexception {         latch.await();     } } 

and in test:

private blockinggameobserver observer;  @before public void setup() throws ioexception, exception {     observer = new blockinggameobserver();     gameinstance.getinstance().addobserver(observer);  }  @test public void getroomuserdata_usingnullkey_shouldthrowuserdatadoesntexist() throws interruptedexception, userdatadoesntexistexception {     serverservice.createroom("exampleroom");        observer.waituntilupdateiscalled();     assertequals("exampleroom",                  gameinstance.getinstance().getroom("exampleroom").getroomid()); }