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[Charlie Poole <charlie@xxxxxxxxx>]

This fixes the problem of NUnit using an external comparer designed for
a particular type inappropriately.

In addition, it allows use of generic comparers when comparing lists and
other ienumerables. Multiple Using clauses may now appear, and will be
used on the appropriate types.

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https://bugs.launchpad.net/bugs/709062

Title:
  "System.ArgumentException : Cannot compare" when the element is a list

Status in NUnit V2 Test Framework:
  Fix Committed

Bug description:
  Relevant discussion can be found here.
  https://groups.google.com/forum/?pli=1#!topic/nunit-
  discuss/IgGiVyo3fKw

  
  This code throws me a System.ArgumentException : Cannot compare 2 exception. 

  
          public class IntListEqualComparer: IEqualityComparer<List<int>>
          {
              public bool Equals(List<int> x, List<int> y)
              {
                  return x.Count == y.Count;
              }

              public int GetHashCode(List<int> obj)
              {
                  return obj.Count.GetHashCode();
              }
          }

          [Test]
          public void IntListListTest()
          {
              var list1 = new List<int>() {2, 3};
              var list2 = new List<int>() {2, 3};

              var list11 = new List<List<int>>() {list1};
              var list22 = new List<List<int>>() { list2 };
              var comparer = new IntListEqualComparer();
              Assert.That(list11, new CollectionEquivalentConstraint(list22).Using(comparer));
          }

  It seems that Nunit can't compare if the elements are of the type
  List?

  Here's the complete stack trace:

  failed: System.ArgumentException : Cannot compare 2
  	at NUnit.Framework.Constraints.EqualityAdapter.EqualityComparerAdapter`1.ObjectsEqual(Object x, Object y)
  	at NUnit.Framework.Constraints.NUnitEqualityComparer.ObjectsEqual(Object x, Object y)
  	at NUnit.Framework.Constraints.NUnitEqualityComparer.CollectionsEqual(ICollection x, ICollection y)
  	at NUnit.Framework.Constraints.NUnitEqualityComparer.ObjectsEqual(Object x, Object y)
  	at NUnit.Framework.Constraints.CollectionItemsEqualConstraint.CollectionTally.ItemsEqual(Object expected, Object actual)
  	at NUnit.Framework.Constraints.CollectionItemsEqualConstraint.CollectionTally.TryRemove(Object o)
  	at NUnit.Framework.Constraints.CollectionItemsEqualConstraint.CollectionTally.TryRemove(IEnumerable c)
  	at NUnit.Framework.Constraints.CollectionEquivalentConstraint.doMatch(IEnumerable actual)
  	at NUnit.Framework.Constraints.CollectionConstraint.Matches(Object actual)

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