Mockito - Injecting a List of mocks

Question

I have the following code:

@Component 
public class Wrapper
{ 
    @Resource 
    private List strategies;

    public String getName(String          


        

Answer 1

Annotate it with @Spy instead of @Mock. As Mockito cannot spy on an interface, use a concrete implementation, for example ArrayList. During test setup add the mocks to the List spy. This way you do not need to alter your test subject solely for test purposes.

@InjectMocks
private Wrapper testedObject = new Wrapper();

@Spy
private ArrayList<Strategy> mockedStrategies;

@Mock
private StrategyA strategyA;

@Mock
private StrategyB strategyB;

@Before
public void setup() throws Exception {
    mockedStrategies.add(strategyA);
    mockedStrategies.add(strategyB);
}

Answer 2

Mockito can not know that you want to put somthing in the List strategies.

You should rethink this an do something like this

@InjectMocks
private Wrapper testedObject = new Wrapper ();

private List<Strategy> mockedStrategies;

@Mock
StrategyA strategyA;

@Mock
StrategyB strategyB;

@Before
public void setup() throws Exception {
    mockedStrategies = Arrays.asList(strategyA, strategyB);
    wrapper.setStrategies(mockedStrategies);
}

Answer 3

You should not mock collections.

Create the mocks you need and put them into a list:

private List<Strategy> strategies; // not mocked!

@Mock
StrategyA strategyA;

@Mock
StrategyB strategyB;

@Before
public void setup(){
  strategies= Arrays.asList(strategyA,strategyB);
  testedObject.strategies= strategies;
}

@Test
public void shouldReturnNameForGivenId()
{   // irrevelant code...
    //when
    testedObject.getName(ID);
}

Answer 4

Why not just mock out your call to toStream()?

@InjectMocks
private Wrapper testedObject = new Wrapper();

private List<Strategy> mockedStrategies;

@Mock
StrategyA strategyA;

@Mock
StrategyB strategyB;

@Before
public void setup() {
    when(strategies.stream()).thenReturn(Stream.of(strategyA, strategyB));
}

To me this is far more elegant as it doesn't require you to add a helper method that is only relevant to testing to your code.

Answer 5

The solution from Erwin Dupont is nice but does not work when you need to inject the List of mocks in the constructor of the tested object.

Here's how I got round that. I've shown the solution for just 1 item in the list, but you could extend it to N items by putting a switch(index) into the get() method:

class Wrapper {
  private final List<Strategy> strategies;
  Wrapper(List<Strategy> strategies) { this.strategies = new ArrayList<>(strategies); }
  // ...
}

class WrapperTest {
  @InjectMocks
  private Wrapper testedObject;

  @Spy
  private List<Strategy> mockedStrategies new AbstractList<Strategy>() {
      @Override public Trigger get(int index) { return trigger; } // can get away without bounds-checking
      @Override public int size() { return 1; }
  };

  @Mock
  private Strategy strategy;

  @Test
  public void testSomething() {
    assertThat(testedObject).isNotNull();
    assertThat(testedObject.getStrategies()).hasSize(1);
  }
}