Why Assert.AreEqual<T> fails with identical objects?

Question

I have a class which contains this attributes:

public class Person
{
    public long Id { get; set; }

    public string Name { get; set; }

    public int? IdCountry { get; set; }
    public virtual Country Country { get; set; }
    public int? IdState { get; set; }
    public virtual State State { get; set; }
}

public class Country
{
    public int Id { get; set; }
    public string Name { get; set; }
}

public class State
{
    public int Id { get; set; }
    public string Name { get; set; }
    public int IdCountry { get; set; }
    public virtual Country Country { get; set; }
}

In a unit test I create 2 objects with the same values

Person expected = new Person()
{
    Name = "blablablbla",
    Id = 1
};
Person actual = PessoaFactory.Create(Name: "blablablbla", Id: 1);
Assert.AreEqual<Person>(expected, actual);

But the Assert.AreEqual throws an exception.

Answer 1

Because you need to override Equals and GetHashCode:

public override bool Equals(object o)
{
    if (!(o is Person)) { return false; }
    return ((Person)o).Id == this.Id;
}

public override int GetHashCode()
{
    return this.Id;
}

Assert.AreEqual<T> uses the default comparer for the type. The default comparer for that type is to compare hash codes. The hash codes aren't equal.