Enhancement: ArgumentCaptor.captureIf(ArgumentMatcher)

Assume we have the following test.

 @Mock
 private Consumer<Collection<?>> consumer;

 @Test
 public void test() throws Exception {

    consumer.accept(new HashSet<>());
    consumer.accept(new ArrayList<>());

    ArgumentCaptor<ArrayList<?>> captor = ArgumentCaptor.forClass(ArrayList.class);
    verify(consumer).accept(captor.capture());
 }

The test fails with:

org.mockito.exceptions.verification.TooManyActualInvocations:
consumer.accept(<Capturing argument>);
Wanted 1 time:
-> at foo.TestClass.testName(TestClass.java:64)
But was 2 times. Undesired invocation:
-> at agh.TestClass.testName(TestClass.java:61)

    at foo.TestClass.test(TestClass.java:64)
    [..]

The test fails because the ArgumentCaptor stores every type, because the type information is erased a runtime. How can we capture the type that is specified in the captor, in this case ArrayList? It is possible to implement an Answerthat stores the argument, and use Matchers.isA(ArrayList.class)but thats ugly->

doAnswer(captureArg1).when(consumer).accept(isA(ArrayList.class));

Maybe it is a good idea to create a pull req and extend the ArgumentCaptor API by adding a method like <T> T captureIf(ArgumentMatcher<? extends T>)?

Then we could write: verify(consumer).accept(captor.captureIf(isA(ArrayList.class)));

[ChristianSchwarz]

@terebesirobert thank you for being open minded and considering my “hints”, good style of cooperation !

[ChristianSchwarz]

I have some questions about the user experience/expectation of the captureIf(..) API.

Use Case 1:

ArgumentCaptor<Collection> captor = ...
Consumer<Collection> consumer = mock(Consumer.class)

consumer.consume(new ArrayList());
consumer.consume(new HashSet());

verify(consumer).consume(captor.captureIf(instanceOf(List.class)));
verify(consumer).consume(captor.captureIf(instanceOf(Set.class)));

List<Collection> values = captor.getValues(); 

What should be the content of values here?

• I would expect values contains an ArrayListand a HashSetinstance.

---

Use Case 2:

ArgumentCaptor<Number> captor = ...
Consumer<Number> consumer = mock(Consumer.class)

consumer.consume(1);
consumer.consume(-2);

verify(consumer).consume(captor.captureIf(gt(0))); //greater than 2
verify(consumer).consume(captor.capture());

List<Collection> values = captor.getValues(); 

What should be the content of values here?

• I would expect valuescontains 1 and -2 cause both arguments will be covered by capture() (equivalent to captureIf(any())) and 1 will be covered by gt(0)

---

Use Case 3:

ArgumentCaptor<Number> captor = ...
Consumer<Number> consumer = mock(Consumer.class)

consumer.consume(1);
consumer.consume(null);

verify(consumer).consume(captor.captureIf(isNotNull()));
verify(consumer).consume(captor.captureIf(isNull()));

List<Collection> values = captor.getValues(); 

What should be the content of values here?

• I would expect valuescontains 1 and null cause the arguments matchers a combined with or (isNull or isNotNull)