[Core] Fix internal children clear logic (#820)

* Fix InternalChildren clear logic

* Improve InternalChildren clear logic

* Add test code to verify InternalChildren clear logic

* Add missing test cases

* Improve time complexity of clear logic

* Fix the test case where InvalidOperationException occurs.

* Correct the name casing of the test case

* Modify a wrong test code

1 files changed, 16 insertions, 1 deletions

diff --git a/Xamarin.Forms.Core.UnitTests/ContentViewUnitTest.cs b/Xamarin.Forms.Core.UnitTests/ContentViewUnitTest.cs
index 73bb531b..5d7dd651 100644
--- a/Xamarin.Forms.Core.UnitTests/ContentViewUnitTest.cs
+++ b/Xamarin.Forms.Core.UnitTests/ContentViewUnitTest.cs
@@ -388,6 +388,21 @@ namespace Xamarin.Forms.Core.UnitTests
 
 			Assert.AreEqual ("Foo", child.BindingContext);
 		}
-	}
 
+        [Test]
+        public void ContentView_should_have_the_InternalChildren_correctly_when_Content_changed()
+        {
+            var sut = new ContentView();
+            IList<Element> internalChildren = ((IControlTemplated)sut).InternalChildren;
+            internalChildren.Add(new VisualElement());
+            internalChildren.Add(new VisualElement());
+            internalChildren.Add(new VisualElement());
+
+            var expected = new View();
+            sut.Content = expected;
+
+            Assert.AreEqual(1, internalChildren.Count);
+            Assert.AreSame(expected, internalChildren[0]);
+        }
+    }
 }