NUnit comparing two lists

Question

OK so I'm fairly new to unit testing and everything is going well until now. I'm simplifying my problem here, but basically I have the following:

[Test]
public void ListTest()
{
    var expected = new List<MyClass>();
    expected.Add(new MyOtherClass());
    var actual = new List<MyClass>();
    actual.Add(new MyOtherClass());
    Assert.AreEqual(expected,actual);
    //CollectionAssert.AreEqual(expected,actual);
}

But the test is failing, shouldn't the test pass? what am I missing?

Use CollectionAssert like in your comment, then implement the IComparable interface on MyOtherClass. NUnit has no idea how to compare those objects unless they conform to an equality interface. — vcsjones, Nov 08 '13 at 14:40
@vcsjones I think you mean `IEquatable` not `IComparable` or overriding Equals method — Sriram Sakthivel, Nov 08 '13 at 14:42
@SriramSakthivel you are right IEquatable is the right way to go, if you add it as an answer I will accept it. Thanks. — SOfanatic, Nov 08 '13 at 14:51

score 73 · Answer 1 · answered Nov 08 '13 at 14:59

73

If you're comparing two lists, you should use test using collection constraints.

Assert.That(actual, Is.EquivalentTo(expected));

Also, in your classes, you will need to override the Equals method, otherwise like gleng stated, the items in the list are still going to be compared based on reference.

Simple override example:

public class Example
{
    public int ID { get; set; }

    public override bool Equals(object obj)
    {
        return this.ID == (obj as Example).ID;
    }
}

answered Nov 08 '13 at 14:59

matth

6,112
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5

If you override `Equals` you should also override `GetHashCode`. – Daniel Lidström Feb 06 '15 at 10:43
https://github.com/nunit/docs/wiki/CollectionContainsConstraint documents NUnit 3's way of handling collection constraints. – Mike Grove aka Theophilus Mar 15 '17 at 19:38
2

Note `EquivalentTo` compares collections. If order/sequence matters, use [SequenceEqual](https://stackoverflow.com/a/19861846/569302) – Jesus is Lord Jul 20 '18 at 22:55

score 15 · Answer 2 · answered Nov 08 '13 at 14:51

A very simple way to get this test to work is to only create the MyOtherClass instance once. That way, when comparing the item in the two lists they will be "equal" (because they reference the same object). If you do this, CollectionAssert will work just fine.

[Test]
public void ListTest()
{
    var thing = new MyOtherClass();

    var expected = new List<MyClass>();
    expected.Add(thing);

    var actual = new List<MyClass>();
    actual.Add(thing);

    CollectionAssert.AreEqual(expected,actual);
}

If you don't this though, you'll need to implement IEquatable<MyOtherClass> in MyOtherClass or override Equals to define what makes two instances of that class the "same".

score 10 · Answer 3 · answered Nov 08 '13 at 14:49

10

Try to be a bit more specific about what you are trying to achieve. Explicitly telling that you want to compare entire sequence will solve the problem. I personally wouldn't rely on NUnit fancy features for determining what you meant by says AreEqual. E.g.

Assert.IsTrue(actual.SequenceEqual(expected));

answered Nov 08 '13 at 14:49

Klark

8,162
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if you want more informations in your IDE, you should rely on NUnit fancy features – aloisdg Feb 19 '20 at 11:01

score 9 · Accepted Answer · answered Nov 08 '13 at 15:00

I convert my comment to answer on request.

Well, this fails because AreEqual uses reference comparison. In order to make it work you need value comparison(your own custom comparison).

You can pretty much do that by implementing IEquatable interface. and keep in mind when you're implementing this interface you must override Object.Equals and Object.GetHashCode as well to get consistent results.

.Net framework supports doing this without implementing IEquatable you need IEqualityComparer that should do the trick, but nunit should have a method which takes this as a overload. Am not certain about "nunit" though.

score 4 · Answer 5 · edited May 23 '17 at 12:25

From Nunit documentation:

Starting with version 2.2, special provision is also made for comparing single-dimensioned arrays. Two arrays will be treated as equal by Assert.AreEqual if they are the same length and each of the corresponding elements is equal. Note: Multi-dimensioned arrays, nested arrays (arrays of arrays) and other collection types such as ArrayList are not currently supported.

You have a list of objects ... so it's not the same as comparing 2 ints. What you should do is probably compare all the objects inside the list ... (Try converting your list to an array ... might actually work :) )

As I said (and most others as well), you'll probably need to override Equals. Here's MSDN page about how to do it (Covers Equals, == operator, and GetHashCode).

Similar with more info : [compare-equality-between-two-objects-in-nunit]
(Compare equality between two objects in NUnit)

It won't, unless Equals is overridden – Sriram Sakthivel Nov 08 '13 at 14:46 — Sriram Sakthivel, Nov 08 '13 at 14:46

score 2 · Answer 6 · answered Jun 09 '15 at 18:15

If you can't modify a class then this example can be helpful:

[Test]
public void Arrays_Should_Be_Equal()
{
    MyClass[] array1 = GetTestArrayOfSize(10);
    MyClass[] array2 = GetTestArrayOfSize(10);

    // DOESN'T PASS
    // Assert.That(array1, Is.EquivalentTo(array2));

    Func<MyClass, object> selector = i => new { i.Property1, i.Property2 };
    Assert.That(array1.Select(selector), Is.EquivalentTo(array2.Select(selector)));
}

private MyClass[] GetTestArrayOfSize(int count)
{
    return Enumerable.Range(1, count)
        .Select(i => new MyClass { Property1 = "Property1" + i, Property2 = "Property2" + i }).ToArray();
}

score 2 · Answer 7 · answered Jan 30 '23 at 21:26

Option 1: AreEquivalent

CollectionAssert.AreEquivalent(expectedList, actualList);

Option 2: IEqualityComparer - for custom equality comparisons

Assert.That(expectedList, Is.EqualTo(actualList).Using(new IEqualityComparerImplementation()));

        private class IEqualityComparerImplementation: IEqualityComparer<T>
        {
            public bool Equals(GeometricPlane plane1, GeometricPlane plane2)
            {
                // obviously add in your own implementation
                throw new NotImplementedException();
            }

            public int GetHashCode(GeometricPlane obj)
            {
                throw new NotImplementedException();
            }
        }

NUnit comparing two lists

7 Answers7

Option 1: AreEquivalent

Option 2: IEqualityComparer - for custom equality comparisons

Linked