Object Comparison in Unit Testing

Question

I have two objects in my unit test, the actual and expected object. All properties on the object method are the exact same and if I run the following test:

Assert.AreEqual( expectedObject.Property1, actualObject.Property1);

the result passes as expected. However, when I try to run the following test it fails:

Assert.AreEqual (expectedObject, actualObject);

What am I missing? Can two objects not be compared and do I have to do a check on each property?

Answer 1

You need to override Equals for your object. Assert uses Object.Equals. By default, Object.Equals on objects of reference type performs a reference comparison. That is, two instances of a reference type are equal if and only if they refer to the same object. You want to override this so that instead of a reference comparison being performed a value comparison is performed. Here is a very nice MSDN article on the subject. Note that you also need to override GetHashCode. See MSDN fo the guidelines. Here is a simple example:

Before:

class Test {
    public int Value { get; set; }
}

Test first = new Test { Value = 17 };
Test second = new Test { Value = 17 };
Console.WriteLine(first.Equals(second)); // false

After:

class Test {
    public int Value { get; set; }
    public override bool Equals(object obj) {
        Test other = obj as Test;
        if(other == null) {
            return false; 
        }
        return this.Value == other.Value;
    }
    public override int GetHashCode() { 
        return this.Value.GetHashCode();
    }
}

Test first = new Test { Value = 17 };
Test second = new Test { Value = 17 };
Console.WriteLine(first.Equals(second)); // true

Answer 2

The second assert statement actually compares the references of the objects, not the content. Since the parameters of the AreEqual method are of type objects, there's not much information on how the unit test framework should compare these.

EDIT: check this question: http://stackoverflow.com/questions/318210/compare-equality-between-two-objects-in-nunit

Answer 3

For the above to work you need to override Equals and compare all properties there.