Mockito: assertEquals on two lists, comparing object variables

Question

I want to use assertEquals() on the two lists list1 and list2.

The problem is, that I don't want to compare the lists like assertEquals(list1, list2). The elements are objects that can return their ids with a function getId(), and I want to check if the lists are equal in terms of the ids (ordered!).

How can I do that? Is functional programming a good idea?

score 3 · Answer 1 · answered Mar 11 '16 at 17:11

If you create the expected list with the ids of the objects in order, example

List<MyObject> expected = new ArrayList<>();
expected.add(myObject1); //with id = 1
expected.add(myObject2); //with id = 2
expected.add(myObject3); //with id = 3

assertEquals(expected, actual);

, then if the actual list has objects in different order of ids, it would fail.

score 2 · Accepted Answer · edited May 23 '17 at 10:29

2

You could transform the lists to lists of ids and then compare them:

return list1.stream().map(MyClass::getId).collect(Collectors.toList())
    .equals(list2.stream().map(MyClass::getId).collect(Collectors.toList()));

This question is very similar to this question, so you can take more ideas from there. In my answer you can see that in one of the options I proposed is creating a reusable utility method for lists comparison:

<T, U> boolean equal(List<T> list1, List<T> list2, Function<T, U> mapper) {
    List<U> first = list1.stream().map(mapper).collect(Collectors.toList());
    List<U> second = list2.stream().map(mapper).collect(Collectors.toList());
    return first.equals(second);
}

Then all you need to write is:

return equal(list1, list2, MyClass::getId);

edited May 23 '17 at 10:29

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answered Mar 11 '16 at 17:05

Dragan Bozanovic

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Good idea but what if list elements are in different order? – Andriy Kryvtsun Mar 11 '16 at 17:33
@AndriyKryvtsun Then they are not equal, of course, as described in the javadoc for `List`s, and that is in line with the requirements in the question. – Dragan Bozanovic Mar 11 '16 at 21:36
Thanks. I marked this one as correct since it is a one liner. Thanks to the other answers, too! – Yanick Nedderhoff Mar 14 '16 at 08:07

score 2 · Answer 3 · answered Mar 11 '16 at 17:44

2

You can use AssertJ fluent assertions library. Your comparison may looks like

// "id" need to be either a property or a public field
assertThat(list1).extracting("id").contains(list2);

answered Mar 11 '16 at 17:44

Andriy Kryvtsun

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This would incorrectly assert as true if list1 contains all of the same elements as list2, with some additional ones. If you made that same call one more time but flipping list1/list2 I think that would work as expected (although there are probably better ways to do this). – Mark Madej Nov 05 '20 at 21:24

score 0 · Answer 4 · edited May 23 '17 at 10:29

0

I see this question as a duplicate of this . If you want to compare the objects only with id , simpler way is to override the equals method , as frameworks use it to assert if two objects are equal.

edited May 23 '17 at 10:29

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answered Mar 11 '16 at 15:08

Raghavan

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In the future, please flag the question as a duplicate, rather than posting an answer saying it's a duplicate. – Rob Jun 30 '17 at 02:24

score 0 · Answer 5 · answered Jun 30 '17 at 01:05

0

I didn't do it directly but instead first compared list size, then compared each element.

answered Jun 30 '17 at 01:05

jwehrle

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Mockito: assertEquals on two lists, comparing object variables

5 Answers5