AssertEquals 2 Lists ignore order

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.

Solution 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()));
    }
    
}

Solution 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.

Solution 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

Solution 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");
    }    
}