Mockito - Injecting a List of mocks

Question

I have the following code:

@Component  public class Wrapper {      @Resource      private List<Strategy> strategies;      public String getName(String id)     {     // the revelant part of this statement is that I would like to iterate over "strategies"         return strategies.stream()             .filter(strategy -> strategy.isApplicable(id))             .findFirst().get().getAmount(id);     }  } 

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@Component  public class StrategyA implements Strategy{...}  @Component  public class StrategyB implements Strategy{...} 

I would like to create a Test for it using Mockito. I wrote the test as follows:

@InjectMocks private Wrapper testedObject = new Wrapper ();  // I was hoping that this list will contain both strategies: strategyA and strategyB @Mock private List<Strategy> strategies;  @Mock StrategyA strategyA;  @Mock StrategyB strategyB;  @Test public void shouldReturnNameForGivenId() {   // irrevelant code...     //when     testedObject.getName(ID); } 

I am getting NullPointerException on line:

filter(strategy -> strategy.isApplicable(id)) 

, which states that the "strategies" list is initialized but is empty. Is there any way Mohito will behave in the same wasy as Spring? Adding automatically all instances implementing interface "Strategy" to the list?

Btw I do not have any setters in Wrapper class and I would like to leave it in that way if possible.

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); }