mockito: Is there a way of capturing the return value of stubbed method?

Question

If I mock a method to return a new instance of some object, how can I capture the returned instance?

E.g.:

 when(mock.someMethod(anyString())).thenAnswe         


        

Answer 1

As an alternative to @JeffFairley's answer, you can leverage AtomicReference. It will act as a Holder, but I prefer this over real holders because it's defined in Java's base framework.

// spy our dao
final Dao spiedDao = spy(dao);
// instantiate a service that does some stuff, including a database find
final Service service = new Service(spiedDao);

// let's capture the return values from spiedDao.find()
AtomicReference reference = new AtomicReference<>();
doAnswer(invocation -> {
    QueryResult result = (QueryResult)invocation.callRealMethod();
    reference.set(result);
    return result;
}).when(spiedDao).find(any(User.class), any(Query.class));

// execute once
service.run();
assertThat(reference.get()).isEqualTo(/* something */);

/// change conditions ///

// execute again
service.run();
assertThat(result.get()).isEqualTo(/* something different */);

In my opinion: ResultCaptor is cool stuff that may be integrated in Mockito in the future, is widely reusable and short in syntax. But if you need that sporadically, then few lines of a lambda can be more concise