More serialization test fixes (dotnet#20377)

Removes a couple more tests that depend on ISerializable implementations and fixes a diagnosability issue in DataContractSerializer tests

Author: morganbr

src/System.Runtime.Serialization.Xml/tests/DataContractSerializer.cs

@@ -1436,6 +1436,7 @@ public static void DCS_RootNameNamespaceAndKnownTypesThroughConstructorAsXmlDict
         Assert.StrictEqual(((SimpleKnownTypeValue)actual.SimpleTypeValue).StrProperty, "PropertyValue");
     }
 
+    [ActiveIssue(20361)]
     [Fact]
     public static void DCS_ExceptionObject()
     {
@@ -1450,6 +1451,7 @@ public static void DCS_ExceptionObject()
         Assert.StrictEqual(value.HelpLink, actual.HelpLink);
     }
 
+    [ActiveIssue(20361)]
     [Fact]
     public static void DCS_ArgumentExceptionObject()
     {
@@ -1464,6 +1466,7 @@ public static void DCS_ArgumentExceptionObject()
         Assert.StrictEqual(value.HelpLink, actual.HelpLink);
     }
 
+    [ActiveIssue(20361)]
     [Fact]
     public static void DCS_ExceptionMessageWithSpecialChars()
     {

src/System.Runtime.Serialization.Xml/tests/Utils.cs

@@ -283,6 +283,11 @@ private static bool CompareXElements(XElement baselineXElement, XElement actualX
         XElement[] deskChildElems = baselineXElement.Descendants().OrderBy(m => m.Name.NamespaceName).ToArray();
         XElement[] coreCLRChildElems = actualXElement.Descendants().OrderBy(m => m.Name.NamespaceName).ToArray();
 
+        if(deskChildElems.Length != coreCLRChildElems.Length)
+        {
+            return false;
+        }
+
         for (int i = 0; i < deskChildElems.Length; i++)
         {
             if (!CompareXElements(deskChildElems[i], coreCLRChildElems[i])) return false;

src/System.Runtime/tests/System/Reflection/StrongNameKeyPairTests.cs

@@ -17,16 +17,6 @@ public class SNKeyPairDerived : StrongNameKeyPair
         public SNKeyPairDerived(byte[] arr) : base(arr) {}
         public SNKeyPairDerived(FileStream keyPairFileStream) : base(keyPairFileStream) {}
         protected SNKeyPairDerived(SerializationInfo info, StreamingContext context) : base(info, context) {}
-
-        public SNKeyPairDerived SNKeyPairDerivedClone(ISerializable inter)
-        {
-            SerializationInfo info = new SerializationInfo(typeof(StrongNameKeyPair), new FormatterConverter());
-            StreamingContext context = new StreamingContext();
-
-            inter.GetObjectData(info, context);
-
-            return new SNKeyPairDerived(info, context);
-        }
     }
 
     public class StrongNameKeyPairTests
@@ -37,10 +27,8 @@ public class StrongNameKeyPairTests
         public void SNKeyPairDerivedTestPosTest()
         {
             var sKeyPairDerived = new SNKeyPairDerived(s_data);
-            var sKeyPair = sKeyPairDerived.SNKeyPairDerivedClone(sKeyPairDerived);
 
             RunActionWithDataFileStream(fileStream => sKeyPairDerived = new SNKeyPairDerived(fileStream));
-            sKeyPair = sKeyPairDerived.SNKeyPairDerivedClone(sKeyPairDerived);
         }
 
         [Fact]