ensure xsi:type can be used together with placeholders

see xmlunit/xmlunit#276

Author: bodewig

RELEASE_NOTES.md

@@ -2,6 +2,10 @@
 
 ## XMLUnit.NET 2.11.1 - /Not Released, yet/
 
+* PlaceholderDifferenceEvaluator would cause InvalidCastException for documents with
+  differences in `xsi:type` attributes.
+  Equivalent of XMLUnit Java Issue [#276](https://github.com/xmlunit/xmlunit/issues/276)
+
 * added readme files for the nuget packages.
   Issue [#46](https://github.com/xmlunit/xmlunit.net/issues/46).
 

src/main/net-placeholders/PlaceholderDifferenceEvaluator.cs

@@ -238,7 +238,10 @@ public ComparisonResult Evaluate(Comparison comparison, ComparisonResult outcome
                 return EvaluateConsideringPlaceholders(controlTarget.Value, testTarget.Value, outcome);
 
             // comparing textual content of attributes
-            } else if (comparison.Type == ComparisonType.ATTR_VALUE) {
+            }
+            else if (comparison.Type == ComparisonType.ATTR_VALUE && controlDetails.Value is string &&
+                     testDetails.Value is string)
+            {
                 return EvaluateConsideringPlaceholders((string) controlDetails.Value,
                     (string) testDetails.Value, outcome);
 

src/tests/net-placeholders/PlaceholderDifferenceEvaluatorTest.cs

@@ -446,5 +446,29 @@ public void IsDateTimePlaceholder_Element_IsDateTime_CustomFormat() {
 
             Assert.IsFalse(diff.HasDifferences());
         }
+
+        [Test]
+        public void CanCompareDocmentsWithXsiTypes() {
+            string control = "<element"
+                + " xmlns:myns=\"https://example.org/some-ns\""
+                + " xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\""
+                + " xsi:type=\"myns:some-type\" />";
+            string test = "<element"
+                + " xmlns:myns=\"https://example.org/some-ns\""
+                + " xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\""
+                + " xsi:type=\"myns:some-other-type\" />";
+
+            var diff = DiffBuilder.Compare(control).WithTest(test)
+                .WithDifferenceEvaluator(new PlaceholderDifferenceEvaluator().Evaluate).Build();
+
+            Assert.IsTrue(diff.HasDifferences());
+            int count = 0;
+            foreach (Difference difference in diff.Differences) {
+                count++;
+                Assert.AreEqual(ComparisonResult.DIFFERENT, difference.Result);
+                Assert.AreEqual(ComparisonType.ATTR_VALUE, difference.Comparison.Type);
+            }
+            Assert.AreEqual(1, count);
+        }
     }
 }