Question

I have a unit test for a method which gets an object from a collection. This keeps failing and I cannot see why, so I have created a very simple test below to create 2 supplier object and test they are equal to see if I can spot the problem in my test of my code. But this test again is failing. Can anyone see or explain why?

    [TestMethod()]
    public void GetSupplierTest2()
    {
        Supplier expected = new Supplier();
        expected.SupplierID = 32532;
        expected.SupplierName = "Test 1"

        Supplier actual = new Supplier();
        actual.SupplierID = 32532;
        actual.SupplierName = "Test 1"

        Assert.AreEqual(expected, actual);
    }

But if I test the individual properties of the objects the test passes…

    [TestMethod()]
    public void GetSupplierTest2()
    {
        Supplier expected = new Supplier();
        expected.SupplierID = 32532;
        expected.SupplierName = "Test 1"

    Supplier actual = new Supplier();
        actual.SupplierID = 32532;
        actual.SupplierName = "Test 1"

        Assert.AreEqual(expected.SupplierID , actual.SupplierID );
        Assert.AreEqual(expected.SupplierName , actual.SupplierName );
    }

Answer 1

If you want to compare two different instances of Supplier, and want them to be considered equal when certain properties have the same value, you have to override the Equals method on Supplier and compare those properties in the method.

You can read more about the Equals method here: http://msdn.microsoft.com/en-us/library/bsc2ak47.aspx

Example implementation:

public override bool Equals(object obj)
{
    if (obj is Supplier)
    {
        Supplier other = (Supplier) obj;
        return Equals(other.SupplierID, this.SupplierID) && Equals(other.SupplierName, this.SupplierName);
    }
    return false;
}

Note that you’ll also get a compiler warning that you have to implement GetHashCode as well, that could be as simple as this:

public override int GetHashCode()
{
    return SupplierID;
}