Question

using System;
using System.Collections.Generic;
using System.Linq;
using NUnit.Framework;

namespace UnitTest.Model
{
[TestFixture]
public class SampleEquatableObjectTest
{
    [Test]
    public void TwoIdenticalUsersComparedEqualTrue()
    {
        var user1 = new SampleObject { Id = 1, Name = "Test User" };
        var user2 = new SampleObject { Id = 1, Name = "Test User" };

        Assert.IsTrue(user1.Equals(user2));
    }

    [Test]
    public void TwoDifferentUsersComparedEqualFalse()
    {
        var user1 = new SampleObject { Id = 1, Name = "Test User 1" };
        var user2 = new SampleObject { Id = 2, Name = "Test User 2" };

        Assert.IsFalse(user1.Equals(user2));
    }

    [Test]
    public void CollectionOfUsersReturnsDistinctList()
    {
        var userList = new List<SampleObject>
                           {
                               new SampleObject {Id = 1, Name = "Test User"},
                               new SampleObject {Id = 1, Name = "Test User 1"},
                               new SampleObject {Id = 2, Name = "Test User 2"}
                           };

        Assert.AreEqual(userList.Count, 3);

        var result = userList.Distinct();

        Assert.AreEqual(result.Count(), 2);

        var multipleTest = (from r in result group r by new { r.Id } into multGroup where multGroup.Count() > 1 select multGroup.Key).Any();

        Assert.IsFalse(multipleTest);
    }

    public class SampleObject : IEquatable<SampleObject>
    {
        public int Id { get; set; }
        public string Name { get; set; }

        public bool Equals(SampleObject other)
        {
            if (ReferenceEquals(this, other))
                return true;
            if (ReferenceEquals(other, null) || ReferenceEquals(this, null))
                return false;

            return Id.Equals(other.Id);
        }
    }
}

}

The distinct method in this test case does not return a distinct list. The assert for count will fail. I looked at other similar questions and Microsoft examples but they look exactly like the code I have in the test. Any input?

Answer 1

You also need to override the GetHashCode() and Equals methods from the Object class. For more information see this corresponding FXCOP violation.

Then your tests will work like expected.

public class SampleObject : IEquatable<SampleObject>
{
    public int Id { get; set; }
    public string Name { get; set; }

    public bool Equals(SampleObject other)
    {
        if (ReferenceEquals(this, other))
            return true;
        if (ReferenceEquals(other, null) || ReferenceEquals(this, null))
            return false;

        return Id.Equals(other.Id);
    }

    public override int GetHashCode() 
    {
        return Id;
    }

    public override bool Equals(object obj) 
    {
        return Equals(obj as SampleObject);
    }
}