AssertEquals 2 Lists ignore order

Question

That should be really simple question I believe. But somehow I can't find answer in Google.

Assume that I have 2 Lists of Strings. First contains "String A" and "String B", second one contains "String B" and "String A" (notice difference in order). I want to test them with JUnit to check whether they contains exactly the same Strings.

Is there any assert that checks equality of Strings that ignore order? For given example org.junit.Assert.assertEquals throws AssertionError

java.lang.AssertionError: expected:<[String A, String B]> but was:<[String B, String A]>

Work around is to sort Lists firstly and then pass them to assertion. But I want my code to be as simple and clean as possible.

I use Hamcrest 1.3, JUnit 4.11, Mockito 1.9.5.

Answer 1

As you mention that you use Hamcrest,
So I would pick one of the collection Matchers

import static org.hamcrest.collection.IsIterableContainingInAnyOrder.containsInAnyOrder;
import static org.junit.Assert.assertThat;

public class CompareListTest {

    @Test
    public void compareList() {
        List<String> expected = Arrays.asList("String A", "String B");
        List<String> actual = Arrays.asList("String B", "String A");
        
        assertThat("List equality without order", 
            actual, containsInAnyOrder(expected.toArray()));
    }
    
}

Answer 2

You can use List.containsAll with JUnit's assertTrue to check that the first list contains every element from the second one, and vice versa.

assertEquals(expectedList.size(), actualList.size());
assertTrue(expectedList.containsAll(actualList));
assertTrue(actualList.containsAll(expectedList));

Hint:
This doesn't work with duplicates in the lists.

Answer 3

Here's a solution that avoids quadratic complexity (iterating over the lists multiple times). This uses the Apache Commons CollectionUtils class to create a Map of each item to a frequency count itself in the list. It then simply compares the two Maps.

Assert.assertEquals("Verify same metrics series",
    CollectionUtils.getCardinalityMap(expectedSeriesList),
    CollectionUtils.getCardinalityMap(actualSeriesList));

I also just spotted CollectionUtils.isEqualCollection that claims to do exactly what is being requested here...

https://commons.apache.org/proper/commons-collections/apidocs/index.html?org/apache/commons/collections4/CollectionUtils.html

Answer 4

With AssertJ, containsExactlyInAnyOrder() or containsExactlyInAnyOrderElementsOf() is what you need :

import org.assertj.core.api.Assertions;
import org.junit.jupiter.api.Test;

import java.util.Arrays;
import java.util.List;

public class CompareListTest {

    @Test
    public void compareListWithTwoVariables() {
        List<String> expected = Arrays.asList("String A", "String B");
        List<String> actual = Arrays.asList("String B", "String A");
        Assertions.assertThat(actual)
                  .containsExactlyInAnyOrderElementsOf(expected);
    }

    @Test
    public void compareListWithInlineExpectedValues() {
        List<String> actual = Arrays.asList("String B", "String A");
        Assertions.assertThat(actual)
                  .containsExactlyInAnyOrder("String A", "String B");
    }    
}

Answer 5

    Collections.sort(excepted);
    Collections.sort(actual);
    assertEquals(excepted,actual);

Answer 6

Im late to the party but here's my solution using Junit only. Any thoughts are welcome.

List<String> actual = new ArrayList<>();
actual.add("A");
actual.add("A");
actual.add("B");

List<String> expected = new ArrayList<>();
actual.add("A");
actual.add("B");
actual.add("B");

//Step 1: assert for size
assertEquals(actual.size(), expected.size());

//Step 2: Iterate
for(String e: expected){
    assertTrue(actual.contains(e));
    actual.remove(e);
}

Answer 7

For a quick fix I would check both ways:

assertTrue(first.containsAll(second));
assertTrue(second.containsAll(first));

And trying with a situation where the number of the same elements is different (e.g. 1, 1, 2 and 1, 2, 2) I didn't get false positives.

Answer 8

You can use ListAssert that comes in junit-addons jar.

ListAssert.assertEquals(yourList, Arrays.asList(3, 4, 5));

Answer 9

Note that solution by Roberto Izquierdo has quadratic complexity in general. Solution on HashSets always has linear complexity:

assertTrue(first.size() == second.size() &&
        new HashSet(first).equals(new HashSet(second)));

Answer 10

Looks like the other answers either reference 3rd party utils, are incorrect, or are inefficient.

Here's a O(N) vanilla solution in Java 8.

public static void assertContainsSame(Collection<?> expected, Collection<?> actual)
{
    assert expected.size() == actual.size();

    Map<Object, Long> counts = expected.stream()
        .collect(Collectors.groupingBy(
                item -> item,
                Collectors.counting()));

    for (Object item : actual)
        assert counts.merge(item, -1L, Long::sum) != -1L;
}

Answer 11

Using the updated hamcrest assertions

import org.junit.Test;

import java.util.Arrays;
import java.util.List;

import static org.hamcrest.collection.IsIterableContainingInAnyOrder.containsInAnyOrder;

import static org.hamcrest.MatcherAssert.assertThat;

public class TestCompareCollection {


    @Test
    public void compareList() {
        List<String> expected = Arrays.asList("String A", "String B");
        List<String> actual = Arrays.asList("String B", "String A");

        assertThat("List is not matching",
                actual, containsInAnyOrder(expected.toArray()));

    }

}