Question

Question:

Can anyone tell me why my unit test is failing with this error message?

CollectionAssert.AreEquivalent failed. The expected collection contains 1
occurrence(s) of . The actual
collection contains 0 occurrence(s).

Goal:

I’d like to check if two lists are identical. They are identical if both contain the same elements with the same property values. The order is irrelevant.

Code example:

This is the code which produces the error. list1 and list2 are identical, i.e. a copy-paste of each other.

[TestMethod]
public void TestListOfT()
{
    var list1 = new List<MyPerson>()
    {
        new MyPerson()
        {
            Name = "A",
            Age = 20
        },
        new MyPerson()
        {
            Name = "B",
            Age = 30
        }
    };
    var list2 = new List<MyPerson>()
    {
        new MyPerson()
        {
            Name = "A",
            Age = 20
        },
        new MyPerson()
        {
            Name = "B",
            Age = 30
        }
    };

    CollectionAssert.AreEquivalent(list1.ToList(), list2.ToList());
}

public class MyPerson
{
    public string Name { get; set; }
    public int Age { get; set; }
}

I’ve also tried this line (source)

CollectionAssert.AreEquivalent(list1.ToList(), list2.ToList());

and this line (source)

CollectionAssert.AreEquivalent(list1.ToArray(), list2.ToArray());

P.S.

Related Stack Overflow questions:

I’ve seen both these questions, but the answers didn’t help.

• CollectionAssert use with generics?
• Unit-testing IList with CollectionAssert

Answer 1

You are absolutely right. Unless you provide something like an IEqualityComparer<MyPerson> or implement MyPerson.Equals(), the two MyPerson objects will be compared with object.Equals, just like any other object. Since the objects are different, the Assert will fail.