MSTest: CollectionAssert.AreEquivalent failed. The expected collection contains 1 occurrence(s) of

It works if I add an IEqualityComparer<T> as described on MSDN and if I use Enumerable.SequenceEqual. Note however, that now the order of the elements is relevant.

In the unit test

//CollectionAssert.AreEquivalent(list1, list2); // Does not work
Assert.IsTrue(list1.SequenceEqual(list2, new MyPersonEqualityComparer())); // Works

IEqualityComparer

public class MyPersonEqualityComparer : IEqualityComparer<MyPerson>
{
    public bool Equals(MyPerson x, MyPerson y)
    {
        if (object.ReferenceEquals(x, y)) return true;

        if (object.ReferenceEquals(x, null) || object.ReferenceEquals(y, null)) return false;

        return x.Name == y.Name && x.Age == y.Age;
    }

    public int GetHashCode(MyPerson obj)
    {
        if (object.ReferenceEquals(obj, null)) return 0;

        int hashCodeName = obj.Name == null ? 0 : obj.Name.GetHashCode();
        int hasCodeAge = obj.Age.GetHashCode();

        return hashCodeName ^ hasCodeAge;
    }
}

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.

I was getting this same error when testing a collection persisted by nHibernate. I was able to get this to work by overriding both the Equals and GetHashCode methods. If I didn't override both I still got the same error you mentioned:

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

I had the following object:

public class EVProjectLedger
{
    public virtual long Id { get; protected set; }
    public virtual string ProjId { get; set; }
    public virtual string Ledger { get; set; }
    public virtual AccountRule AccountRule { get; set; }
    public virtual int AccountLength { get; set; }
    public virtual string AccountSubstrMethod { get; set; }

    private Iesi.Collections.Generic.ISet<Contract> myContracts = new HashedSet<Contract>();

    public virtual Iesi.Collections.Generic.ISet<Contract> Contracts
    {
        get { return myContracts; }
        set { myContracts = value; }
    }

    public override bool Equals(object obj)
    {
        EVProjectLedger evProjectLedger = (EVProjectLedger)obj;
        return ProjId == evProjectLedger.ProjId && Ledger == evProjectLedger.Ledger;
    }
    public override int GetHashCode()
    {
        return new { ProjId, Ledger }.GetHashCode();
    }
}

Which I tested using the following:

using (ITransaction tx = session.BeginTransaction())
{
    var evProject = session.Get<EVProject>("C0G");

    CollectionAssert.AreEquivalent(TestData._evProjectLedgers.ToList(), evProject.EVProjectLedgers.ToList());

    tx.Commit();
}

I'm using nHibernate which encourages overriding these methods anyways. The one drawback I can see is that my Equals method is based on the business key of the object and therefore tests equality using the business key and no other fields. You could override Equals however you want but beware of equality pollution mentioned in this post:

CollectionAssert.AreEquivalent failing... can't figure out why