Question

如果我模拟一个方法来返回某个对象的新实例，我该如何捕获返回的实例？

E.g：

 when(mock.someMethod(anyString())).thenAnswer(new Answer() {
     Object answer(InvocationOnMock invocation) {
         Object[] args = invocation.getArguments();
         Object mock = invocation.getMock();
         return new Foo(args[0])
     }
 });

显然，我可以有一个Foo类型的字段，在answer里面将它设置为新实例，但有更好的方法吗？像ArgumentCaptor？

Answer 1

我想做类似的事情，但是使用间谍对象而不是模拟。具体来说，给定一个间谍对象，我想捕获返回值。根据{{3}}的回答，这就是我想出的内容。

public class ResultCaptor<T> implements Answer {
    private T result = null;
    public T getResult() {
        return result;
    }

    @Override
    public T answer(InvocationOnMock invocationOnMock) throws Throwable {
        result = (T) invocationOnMock.callRealMethod();
        return result;
    }
}

预期用途：

// 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()
final ResultCaptor<QueryResult> resultCaptor = new ResultCaptor<>();
doAnswer(resultCaptor).when(spiedDao).find(any(User.class), any(Query.class));

// execute once
service.run();
assertThat(resultCaptor.getResult()).isEqualTo(/* something */);

/// change conditions ///

// execute again
service.run();
assertThat(resultCaptor.getResult()).isEqualTo(/* something different */);

Answer 2

看起来您希望观察然后Answer个实例并在每次调用answer方法时接收notfications（这会触发创建新的Foo ）。那么为什么不发明一个ObservableAnswer类：

public abstract class ObservableAnswer implements Answer {
  private Listener[] listeners; // to keep it very simple...

  public ObservableAnswer(Listener...listeners) {
    this.listeners = listeners;
  }

  @Override
  public Object answer(InvocationOnMock invocation) {
    Object answer = observedAnswer(invocation);
    for (Listener listener:listeners) {
       listener.send(answer);
    }
    return answer;
  }

  // we'll have to implement this method now
  public abstract Object observedAnswer(InvocationOnMock invocation);
}

预期用途：

Listener[] myListenerns = getListeners();  // some magic (as usual)
when(mock.someMethod(anyString())).thenAnswer(new ObservableAnswer(myListeners) {
     Object observedAnswer(InvocationOnMock invocation) {
         Object[] args = invocation.getArguments();
         Object mock = invocation.getMock();
         return new Foo(args[0])
     }

 });

Answer 3

作为@JeffFairley答案的替代方法，您可以利用AtomicReference<T>。它将充当Holder<T>，但我更喜欢它，而不是真正的持有人，因为它是在Java的基本框架中定义的。

// 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<QueryResult> 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 */);

我认为：ResultCaptor是很酷的东西，将来可能会集成到Mockito中，可以广泛使用并且语法短。但是，如果您偶尔需要它，那么lambda的几行会更简洁

Answer 4

调用doAnswer，然后调用真正的方法并将返回值添加到一个列表中，如下：

final var capturedValues = new ArrayList<Integer>();
final var myObjectList = spy(new MyObject());
doAnswer(invocation -> {
  final var r = invocation.callRealMethod();
  capturedValues.add((Integer) r);
  return r;
})
.when(myObjectList)
.mySuperMethod;

一个完整的例子：

@Test
public void test() {

  // arrange
  final var capturedValues = new ArrayList<Integer>();
  final var myObjectList = spy(new ArrayList<>());
  doAnswer(invocation -> {
    final var r = invocation.callRealMethod();
    capturedValues.add((Integer) r);
    return r;
  })
      .when(myObjectList)
      .size();

  // act
  myObjectList.size();
  myObjectList.add("one");

  myObjectList.size();
  myObjectList.add("two");

  myObjectList.size();

  // assert
  assertEquals(3, capturedValues.size());
  assertEquals("[0, 1, 2]", capturedValues.toString());
}

mockito：有没有办法捕获存根方法的返回值？

4 个答案: