Compare two sets of a class without equals

Question

I have a class Something:

public class Something {
   public String a;
   public String b;
}

Suppose I can't write equals or compare method in class Something.

My test:

Set<Something> aSet;
Set<Something> otherSet;

assertEquals(aSet, otherSet);//Fails because it only compares references of elements and does not perform a deep comparision field by field

Is there any way to assert if both sets are equals comparing elements field by field (without writing equals method in Something class)?

This SO question also looks promising: https://stackoverflow.com/questions/5204082/is-it-possible-in-java-make-something-like-comparator-but-for-implementing-custo — markspace, Feb 02 '18 at 22:27
Please use only those tags that are really relevant to your question. Your question has **no** relation whatsoever to mocking frameworks! — GhostCat, Feb 05 '18 at 15:16
Well, what's the point in using a set when you don't have proper equals/hashcode methods in the class? Is there really "something" that adds instances multiple times? — Tom, Feb 05 '18 at 15:18

score 3 · Accepted Answer · answered Feb 03 '18 at 08:41

Give a try to AssertJ, it provides a way to compare element field by field recursively, example:

// the Dude class does not override equals
Dude jon = new Dude("Jon", 1.2);
Dude sam = new Dude("Sam", 1.3);
jon.friend = sam;
sam.friend = jon;

Dude jonClone = new Dude("Jon", 1.2);
Dude samClone = new Dude("Sam", 1.3);
jonClone.friend = samClone;
samClone.friend = jonClone;

assertThat(asList(jon, sam)).usingRecursiveFieldByFieldElementComparator()
                            .contains(jonClone, samClone);

Another possibility is to compare collections using a specific element comparator so SomethingComparator in your case, this requires a bit more work than the first option but you have full control of the comparison.

Hope it helps!

I chose this because is correct and really simple and fluent. It doesn't make sense to add code to classes only for testing. Thanks. — italktothewind, Feb 05 '18 at 19:58

pvpkiran · Answer 2 · 2018-02-02T22:25:41.497

1

You can use Hamcrest Library and do

assertThat( aSet, both(everyItem(isIn(otherSet))).and(containsInAnyOrder(aSet)));

edited Feb 02 '18 at 22:25

answered Feb 02 '18 at 22:13

pvpkiran

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How would this work without an equals method? – shmosel Feb 02 '18 at 23:18
I agree with @shmosel - I really doubt that this *answers* the question. Those hamcrest matchers ... will call equals() in the end. – GhostCat Feb 05 '18 at 15:15

score 0 · Answer 3 · answered Feb 03 '18 at 01:56

I had the similar situation when I couldn't implement equals/hashCode in the legacy code.

Let me share a solution based on the wrapper pattern. You wrap your legacy class and implement equals/hashCode there. In your tests you create a sets of wrapped objects and test it by regular way.

public class SomethingTest {
    class SomethingWrapper {
        private final Something value;

        SomethingWrapper(Something value) {
            this.value = value;
        }

        @Override
        public boolean equals(Object o) {
            if (this == o) return true;

            if (o == null || getClass() != o.getClass()) return false;

            SomethingWrapper that = (SomethingWrapper) o;

            return new EqualsBuilder()
                    .append(value.a, that.value.a)
                    .append(value.b, that.value.b)
                    .isEquals();
        }

        @Override
        public int hashCode() {
            return new HashCodeBuilder(17, 37)
                    .append(value.a)
                    .append(value.b)
                    .toHashCode();
        }
    }

    @Test
    public void compareSomethingSetsWithoutEquals() {
        final Set<Something> originalA = new HashSet<>();
        originalA.add(new Something("a1", "b1"));
        originalA.add(new Something("a2", "b2"));

        final Set<Something> originalB = new HashSet<>();
        originalB.add(new Something("a1", "b1"));
        originalB.add(new Something("a2", "b2"));

        final Set<SomethingWrapper> aWrappedSetA =
                originalA.stream().map(SomethingWrapper::new).collect(Collectors.toSet());

        final Set<SomethingWrapper> aWrappedSetB =
                originalB.stream().map(SomethingWrapper::new).collect(Collectors.toSet());

        assertEquals(aWrappedSetA, aWrappedSetB);
    }
}

Compare two sets of a class without equals

3 Answers3