Mock an async method with Handler<AsyncResult<>> argument

[vahid....@industrieit.com]

Sorry if it's a newbie question but I could not find any example for it out there. I think best I could explain it through an example. 

I have this data access interface:

public interface UserDao {

   void loadUsers(Handler<AsyncResult<List<User>>> handler);

}

It is used in a service like this:

public class UserService {

  private UserDao userDao;

  public UserService(UserDao UserDao) {
    this.userDao = userDao;
  }

  public void getUsers(Future<List<User>> future) {
    userDao.loadUsers( ar ->{
      if (ar.succeeded()){
        List<User> users = ar.result();
        // process users
        future.complete(users);
      }else {
        // handle the error
      }
    });
  }
}

Now my intention is to unit test my service and mock the data access layer. I want to return a fixed set of results every time getUsers method of UserDao class is called. 

@Test
public void testGetUsers(TestContext context) {

  Async async = context.async();

  UserDao mockUserDao = Mockito.mock(UserDao.class);

  UserService userService = new UserService(mockUserDao);
  List<User> mockResult = Arrays.asList(new User(), new User());

  /* (?) How to make mockUserDao return mockResult through its Handler argument? */

  Future<List<User>> future = Future.future();
  userService.getUsers(future);
  future.setHandler(ar -> {
    assertEquals(2, ar.result().size());
    async.complete();
  });

  async.awaitSuccess();

}

How can I do that? It does not fit the normal Mockito pattern when(serviceMock.method(any(Argument.class))).thenAnswer(new Result()) as mockResult is not returned from the method per say but through the handler.

[Thomas SEGISMONT]

Try:

when(mockUserDao.loadUsers(any(XXX.class)).thenAnswer(Future.<List<User>>succeededFuture(mockResult));

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[vahid....@industrieit.com]

Thanks Thomas but it won't work because the Future/Handler is NOT returned from the loadUsers() method. That's actually the point of this question.

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[John Warner]

Mockito provides a couple of ways of doing what you want. One is the:

Mockito.doAnswer(invocation->{invocation.getArgument(0).doSomething}).when(mockDao).loadUsers(any());

structure. You can grab what is passed into your mock's method from the invocation and then do whatever you like with it. I know it's called doAnswer, but it's not actually returning anything. 

The other is to use an ArgumentCaptor and Mockito verify. So something like:

@ArgumentCaptor
ArgumentCaptor<AsyncResult<Handler<List<User>>> asyncResultCaptor;
...
Mockito.verify(mockDao).loadUsers(asyncResultCaptor.capture());
AsyncResult<Handler<List<User>>> result = asyncResultCaptor.getValue();

Then you can do whatever you like with it. 

Sorry I don't have time to put together proper examples of this, but hopefully this makes sense.

[Thomas SEGISMONT]

Ha I see now. Sorry I totally missed the point...

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