Java8 stream of iterator is not mockable?

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Felix Gao

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Aug 12, 2016, 4:50:52 AM8/12/16
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Hi all I am trying to mock an iterator 
@Test
public void scratch(){
    List<String> testlist = new ArrayList<String>(){{
        add("1");
    }};

    Iterator<String> iter = mock(Iterator.class);
    when(iter.hasNext()).thenReturn(true, false);
    when(iter.next()).thenReturn("1");

    List<String> resultList = StreamSupport.stream(
            Spliterators.spliteratorUnknownSize(iter, Spliterator.ORDERED), false)
            .collect(Collectors.toList());

    assertThat(resultList.size(), is(1));
    assertThat(resultList.get(0), is("1"));
}


this code will not work but
@Test
public void scratch(){
    List<String> testlist = new ArrayList<String>(){{
        add("1");
    }};

    List<String> resultList = StreamSupport.stream(
            Spliterators.spliteratorUnknownSize(testlist.iterator(), Spliterator.ORDERED), false)
            .collect(Collectors.toList());

    assertThat(resultList.size(), is(1));
    assertThat(resultList.get(0), is("1"));
}

will work just fine

any help?

Thanks,

Felix












Malte Finsterwalder

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Aug 12, 2016, 5:36:08 AM8/12/16
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I can't help you directly, but here is what I would so.

1) Do not mock Iterator! Do you really want to test the interaction between Streams and Iterator? I don't think so. The Java lib is tested and works fine. ;-) Use a Collection or Stream and you are done with it. 

2) Should you really, really, really need to mock an Iterator, then you need to read the code what streams will do with the iterator. And you need to mock everything correctly, that it works as expected.

Greetings,
   Malte

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Brice Dutheil

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Aug 12, 2016, 6:09:22 AM8/12/16
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I agree with Malte on this type of things. Don’t mock types you don’t own.

Technically the reason is that the Stream that uses the created Spliterator does not invoke hasNext() or next() directly ; instead it invokes the default method forEachRemaining, which is not mocked thus do nothing as it is a mock.

Adding this stub make the test work (mockito 2 beta) : 


doAnswer(CALLS_REAL_METHODS).when(iter).forEachRemaining(any());

But in the end this behaviour is subject to JDK implementation which is not under your or our control. For that reason the preferred way would be to use a concrete type.

Cheers,
— Brice

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Eric Lefevre-Ardant

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Aug 12, 2016, 3:20:18 PM8/12/16
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Not sure why that function might be a problem.
Just make sure that 'iter' is initialised to an appropriate, fully instantiated, iterator, and you're fine.

On 12 August 2016 at 19:27, Felix Gao <guoh...@gmail.com> wrote:
Thank Brice and Malte on the do not mock iterator, but unfortunately, I need to test this function. 

List<UserRole> getUserRolesWithWildcardAppName(
        UserInfo.Username userID,
        Application.Name applicationName
) {
    List<UserRole> resultList;
    try {
        Result<com.intuit.wasabi.repository.cassandra.pojo.UserRole> result =
                userRoleAccessor.getUserRolesByUserIdWithWildcardAppName(userID.getUsername());
        resultList = StreamSupport.stream(
        Spliterators.spliteratorUnknownSize(iter, Spliterator.ORDERED), false)
        .collect(Collectors.toList());    } catch (ReadTimeoutException | UnavailableException | NoHostAvailableException e) {
        throw new RepositoryException("Could not retrieve permissions for user \"" + userID + "\" and application "
                + "\"" + applicationName + "\"", e);
    }
    return resultList;
}
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Malte Finsterwalder

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Aug 12, 2016, 4:47:29 PM8/12/16
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I can't see where "iter" comes from.Where is it passed in or defined?
And even if you need to test a method that uses an iterator, why not just fill a collection in your test and hand the real iterator from the collection to the code under test? Like Eric said.

Greetings,
   Malte

On 12 August 2016 at 19:27, Felix Gao <guoh...@gmail.com> wrote:
Thank Brice and Malte on the do not mock iterator, but unfortunately, I need to test this function. 

List<UserRole> getUserRolesWithWildcardAppName(
        UserInfo.Username userID,
        Application.Name applicationName
) {
    List<UserRole> resultList;
    try {
        Result<com.intuit.wasabi.repository.cassandra.pojo.UserRole> result =
                userRoleAccessor.getUserRolesByUserIdWithWildcardAppName(userID.getUsername());
        resultList = StreamSupport.stream(
        Spliterators.spliteratorUnknownSize(iter, Spliterator.ORDERED), false)
        .collect(Collectors.toList());    } catch (ReadTimeoutException | UnavailableException | NoHostAvailableException e) {
        throw new RepositoryException("Could not retrieve permissions for user \"" + userID + "\" and application "
                + "\"" + applicationName + "\"", e);
    }
    return resultList;
}




On Friday, August 12, 2016 at 3:09:22 AM UTC-7, Brice wrote:
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Felix Gao

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Aug 12, 2016, 5:40:56 PM8/12/16
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Thanks Eric and Malte, I will just create the collection like you guys mentioned.
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