JUnit 4 compare Sets

Question

How would you succinctly assert the equality of Collection elements, specifically a Set in JUnit 4?

Answer 1

If you want to check whether a List or Set contains a set of specific values (instead of comparing it with an already existing collection), often the toString method of collections is handy:

String[] actualResult = calltestedmethod();
assertEquals("[foo, bar]", Arrays.asList(actualResult).toString());

List otherResult = callothertestedmethod();
assertEquals("[42, mice]", otherResult.toString());

This is a bit shorter than first constructing the expected collection and comparing it with the actual collection, and easier to write and correct.

(Admittedly, this is not a particularily clean method, and can't distinguish an element "foo, bar" from two elements "foo" and "bar". But in practice I think it's most important that it's easy and fast to write tests, otherwise many developers just won't without being pressed.)

Answer 2

You can assert that the two Sets are equal to one another, which invokes the Set equals() method.

public class SimpleTest {

    private Set<String> setA;
    private Set<String> setB;

    @Before
    public void setUp() {
        setA = new HashSet<String>();
        setA.add("Testing...");
        setB = new HashSet<String>();
        setB.add("Testing...");
    }

    @Test
    public void testEqualSets() {
        assertEquals( setA, setB );
    }
}

This @Test will pass if the two Sets are the same size and contain the same elements.

Answer 3

Using Hamcrest:

assertThat( set1, both(everyItem(isIn(set2))).and(containsInAnyOrder(set1)));

This works also when the sets have different datatypes, and reports on the difference instead of just failing.

Answer 4

Apache commons to the rescue again.

assertTrue(CollectionUtils.isEqualCollection(coll1, coll2));

Works like a charm. I don't know why but I found that with collections the following assertEquals(coll1, coll2) doesn't always work. In the case where it failed for me I had two collections backed by Sets. Neither hamcrest nor junit would say the collections were equal even though I knew for sure that they were. Using CollectionUtils it works perfectly.

Answer 5

A particularly interesting case is when you compare

   java.util.Arrays$ArrayList<[[name,value,type], [name1,value1,type1]]> 

and

   java.util.Collections$UnmodifiableCollection<[[name,value,type], [name1,value1,type1]]>

So far, the only solution I see is to change both of them into sets

assertEquals(new HashSet<CustomAttribute>(customAttributes), new HashSet<CustomAttribute>(result.getCustomAttributes()));

Or I could compare them element by element.

Answer 6

I like the solution of Hans-Peter Störr... But I think it is not quite correct. Sadly containsInAnyOrder does not accept a Collection of objetcs to compare to. So it has to be a Collection of Matchers:

assertThat(set1, containsInAnyOrder(set2.stream().map(IsEqual::equalTo).collect(toList())))

The import are:

import static java.util.stream.Collectors.toList;
import static org.hamcrest.Matchers.containsInAnyOrder;
import static org.junit.Assert.assertThat;