NUnit的Is.EqualTo对于从泛型类派生的类是否不能可靠地工作?

今天我遇到了NUnit的以下问题。

我开始做一些序列化测试,并使用NUnit的Is.EqualTo()函数测试是否相等。

当一个本该失败的测试通过时,我开始怀疑出了什么问题。当我使用obj1.Equals(obj2)时,它失败了。

namespace NUnit.Tests

{

using Framework;

    public class ThatNUnit
    {
        [Test]
        public void IsNotEqualTo_ClientsNotEqual_Passes()
        {
            var client1 = new DerrivedClient();
            var client2 = new DerrivedClient();

            client1.Name = "player1";
            client1.SomeGenericProperty = client1.Name;
            client2.Name = "player2";
            client2.SomeGenericProperty = client2.Name;

            Assert.That(client1.Equals(client2), Is.False);
            Assert.That(client1, Is.Not.EqualTo(client2));
        }

        [Test]
        public void IsNotEqualTo_ClientsAreEqual_AlsoPasses_SomethingWrongHere()
        {
            var client1 = new DerrivedClient();
            var client2 = new DerrivedClient();

            client1.Name = "player1";
            client1.SomeGenericProperty = client1.Name;
            client2.Name = client1.Name;
            client2.SomeGenericProperty = client1.Name;

            Assert.That(client1.Equals(client2), Is.True);
            Assert.That(client1, Is.Not.EqualTo(client2));
        }
    }

    public class DerrivedClient : Client<string>
    {
    }

    public class Client<T>
    {
        public string Name { get; set; }

        public T SomeGenericProperty { get; set; }

        public override bool Equals(object obj)
        {
            if (ReferenceEquals(null, obj))
            {
                return false;
            }
            if (ReferenceEquals(this, obj))
            {
                return true;
            }
            if (obj.GetType() != typeof(Client<T>))
            {
                return false;
            }
            return Equals((Client<T>)obj);
        }

        public bool Equals(Client<T> other)
        {
            if (ReferenceEquals(null, other))
            {
                return false;
            }
            if (ReferenceEquals(this, other))
            {
                return true;
            }
            return Equals(other.Name, Name) && Equals(other.SomeGenericProperty, SomeGenericProperty);
        }

        public override int GetHashCode()
        {
            unchecked
            {
                return ((Name != null ? Name.GetHashCode() : 0) * 397) ^ SomeGenericProperty.GetHashCode();
            }
        }

        public override string ToString()
        {
            return string.Format("{0}, {1}", Name, SomeGenericProperty);
        }
    }
}

第二个测试中的两个(实际冲突的断言)表明了问题:

Assert.That(client1.Equals(client2), Is.True);
Assert.That(client1, Is.Not.EqualTo(client2));

因此,我深入研究了NUnit的源代码,结果发现,在对某些特殊条件执行了一些if()之后,ObjectsReequal(object x,object y)方法(最终通过Assert.that(x,Is.EqualTo(y))调用)来到了以下代码行:

return x.Equals(y);

我发现这非常令人困惑,因为我现在必须思考,也就是说.EqualTo()只需要走更长的路,但基本上应该和x.Equals(y)一样

这里是感兴趣的人的完整方法(在NUNit.Framework.Constraints命名空间中):

  public bool ObjectsEqual(object x, object y)
    {
        this.failurePoints = new ArrayList();

        if (x == null && y == null)
            return true;

        if (x == null || y == null)
            return false;

        Type xType = x.GetType();
        Type yType = y.GetType();

        if (xType.IsArray && yType.IsArray && !compareAsCollection)
            return ArraysEqual((Array)x, (Array)y);

        if (x is ICollection && y is ICollection)
            return CollectionsEqual((ICollection)x, (ICollection)y);

        if (x is IEnumerable && y is IEnumerable && !(x is string && y is string))
            return EnumerablesEqual((IEnumerable)x, (IEnumerable)y);

        if (externalComparer != null)
            return externalComparer.ObjectsEqual(x, y);

        if (x is string && y is string)
            return StringsEqual((string)x, (string)y);

        if (x is Stream && y is Stream)
            return StreamsEqual((Stream)x, (Stream)y);

        if (x is DirectoryInfo && y is DirectoryInfo)
            return DirectoriesEqual((DirectoryInfo)x, (DirectoryInfo)y);

        if (Numerics.IsNumericType(x) && Numerics.IsNumericType(y))
            return Numerics.AreEqual(x, y, ref tolerance);

        if (tolerance != null && tolerance.Value is TimeSpan)
        {
            TimeSpan amount = (TimeSpan)tolerance.Value;

            if (x is DateTime && y is DateTime)
                return ((DateTime)x - (DateTime)y).Duration() <= amount;

            if (x is TimeSpan && y is TimeSpan)
                return ((TimeSpan)x - (TimeSpan)y).Duration() <= amount;
        }

        return x.Equals(y);
    }

那么这里发生了什么,如何修复呢?

我希望能够信任我的测试,因此必须再次尝试。

提前谢谢。

与此同时,我进一步努力解决这个问题,发现了一个类似的问题 here 并发布了一个可能的 workaround