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[Charlie Poole <charlie@xxxxxxxxx>]

Nice! Passing the responsibility to the non-null object seems like a good
strategy.

It would need to be extended to cover cases where the non-null object
implements IEquatable as well. And we should look at every special case in
NUnitEqualityComparer and make sure that they will handle null correctly.
Most likely, this will lead to some refactoring too.

Charlie


On Tue, Mar 26, 2013 at 5:09 AM, Meg Gotshall <natraj@xxxxxxx> wrote:

> >From what I recall, the logic for the null checks at the beginning of
> the method is something like:
>
> if (a == null && b == null)
>   return true;
>
> if (a == null || b == null)
>   return false;
>
>
> Could that be safely replaced with:
>
> if (a == null && b == null)  // or ReferenceEquals if you switch for
> clarity
>   return true;
>
> if (a == null)
>   return b.Equals(null);
> else if (b == null)
>   return a.Equals(null);
>
> ?
>
> I don't have the code in front of me, but off the top of my head, I
> can't think of any cases where you would still need to do any of the
> type-specific comparisons that come before the call to a.Equals(b).  It
> seems like a relatively safe way to fix the issue without affecting any
> existing calls.
>
> --
> You received this bug notification because you are subscribed to NUnit
> Extended Testing Platform.
> https://bugs.launchpad.net/bugs/1157828
>
> Title:
>   EqualityComparer does not respect value-equality for null
>
> To manage notifications about this bug go to:
> https://bugs.launchpad.net/nunitv2/+bug/1157828/+subscriptions
>

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https://bugs.launchpad.net/bugs/1157828

Title:
  EqualityComparer does not respect value-equality for null

Status in NUnit V2 Test Framework:
  New

Bug description:
  I am using a third-party library that includes Null Objects with value
  comparisons that return true for null.  However, the NUnit equality
  comparer uses reference equality (via the == operator with
  System.Object references) to check for null and returns false if only
  one input is the null pointer.  This means that the value-equality
  comparison for the custom type is never reached.

  The following is a quick & dirty implementation of a Null Object with
  a few tests that demonstrate the problem:

  public class MyObject
  {
      public static MyObject NullObject = new MyObject(-1);

      public int Value { get; set; }

      public MyObject(int value)
      {
          this.Value = value;
      }

      public static bool operator ==(MyObject left, MyObject right)
      {
          if (ReferenceEquals(left, NullObject) || ReferenceEquals(left, null))
              return (ReferenceEquals(right, NullObject) || ReferenceEquals(right, null));

          else if (ReferenceEquals(right, NullObject) || ReferenceEquals(right, null))
              return false;

          return Equals(left, right);
      }

      public static bool operator !=(MyObject left, MyObject right)
      {
          return !(left == right);
      }
      public override bool Equals(object obj)
      {
          if (ReferenceEquals(obj, NullObject) || ReferenceEquals(obj, null))
              return (ReferenceEquals(this, NullObject));

          else if (ReferenceEquals(this, NullObject))
              return false;

          MyObject myobj = obj as MyObject;
          if (myobj == null)
              return false;

          return this.Value == myobj.Value;
      }

      public override int GetHashCode()
      {
          return base.GetHashCode();
      }

  }

  [TestFixture]
  public class TestNullObject
  {
      // TEST PASSES
      [Test]
      public void TestIsTrue()
      {
          Assert.IsTrue(MyObject.NullObject == null);
          Assert.IsTrue(null == MyObject.NullObject);
      }

      // TESTS FAIL
      [Test]
      public void TestIsNull()
      {
          Assert.IsNull(MyObject.NullObject);
      }

      [Test]
      public void TestAreEqual1()
      {
          Assert.AreEqual(MyObject.NullObject, null);
      }

      [Test]
      public void TestAreEqual2()
      {
          Assert.AreEqual(null, MyObject.NullObject);
      }
  }

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