CODEWITHSUNDEEP
javamockingmockito
feeblefakie
feeblefakie

Reputation: 620

How to mock forEach behavior with Mockito

I want to make the following work, but I don't know how to mock forEach behavior properly. (The code is taken from a related question Testing Java enhanced for behavior with Mockito )

@Test
public void aa() {
  Collection<String> fruits;
  Iterator<String> fruitIterator;

  fruitIterator = mock(Iterator.class);
  when(fruitIterator.hasNext()).thenReturn(true, true, true, false);
  when(fruitIterator.next()).thenReturn("Apple")
      .thenReturn("Banana").thenReturn("Pear");

  fruits = mock(Collection.class);
  when(fruits.iterator()).thenReturn(fruitIterator);
  doCallRealMethod().when(fruits).forEach(any(Consumer.class));

  // this doesn't work (it doesn't print anything)
  fruits.forEach(f -> {
    mockObject.someMethod(f); 
  });

  // this works fine
  /*
  int iterations = 0;
  for (String fruit : fruits) {
    mockObject.someMethod(f); 
  }
  */

  // I want to verify something like this
  verify(mockObject, times(3)).someMethod(anyString());
}

Any help will be very appreciated.

Upvotes: 14

Views: 33494

Answers (3)

Martin Bamford
Martin Bamford

Reputation: 404

You can use org.mockito.Mockito.doAnswer as follows

Assume we are mocking a class that extends java.lang.Iterable and we have created a Mockito mock for that class, and this mock is named iterable

and that we have created a collection called pages which is the results you want the iterable class to return when the forEach method is returned (ie you want each invocation of forEach is to return the next element in the list pages

then you can program the iterable mock as follows:

doAnswer((Answer<Void>) invocation -> {
            Object[] args = invocation.getArguments();
            Consumer<Page<Alert>> consumer = (Consumer<Page<Alert>>) args[0];
            pages.forEach(consumer);
            return null;
        }).when(iterable).forEach(any());

Upvotes: 1

patrio2
patrio2

Reputation: 219

Iterator mockIterator = mock(Iterator.class);
doCallRealMethod().when(fruits).forEach(any(Consumer.class));
when(fruits.iterator()).thenReturn(mockIterator);
when(mockIterator.hasNext()).thenReturn(true, false);
when(mockIterator.next()).thenReturn(mockObject);

Upvotes: 13

Alexandre Dupriez
Alexandre Dupriez

Reputation: 3036

The method forEach of the Collection interface is a "defender" method; it does not use Iterator but call the Consumer passed to the method.

If you are using Mockito version 2+ (*), you can ask the default method forEach of the Collection interface to be called:

Mockito.doCallRealMethod().when(fruits).forEach(Mockito.any(Consumer.class));

Note that the "defender" method is actually going to request an Iterator to traverse the collection, hence will use the Iterator you mocked in your test. It wouldn't work if no Iterator was provided by the mocked collection, as with when(fruits.iterator()).thenReturn(fruitIterator)

(*): Mockito has added the possibility to support Java 8 default ("defender") method since version 2 - you can check the tracking issue here.

Upvotes: 9

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