Update ListProxyTest.WeakToWeak so it works in Release mode (#866)

* Update ListProxyTest.WeakToWeak so it works in Release mode

* Disable CS0414 for test

Xamarin.Forms.Core.UnitTests/ListProxyTests.cs

@@ -423,29 +423,31 @@ IEnumerator IEnumerable.GetEnumerator ()
 			}
 		}
 
+		// Need a member to keep this reference around, otherwise it gets optimized
+		// out early in Release mode during the WeakToWeak test
+#pragma warning disable 0414 // Never accessed, it's just here to prevent GC
+		ListProxy _proxyForWeakToWeakTest;
+#pragma warning restore 0414
+
 		[Test]
-		[Ignore()]
-		//TODO: Need to figure why this is failing on release 
 		public void WeakToWeak()
 		{
 			WeakCollectionChangedList list = new WeakCollectionChangedList();
-			var proxy = new ListProxy(list);
+			_proxyForWeakToWeakTest = new ListProxy(list);
 
-			Assert.True(list.AddObject());
+			Assert.True(list.AddObject(), "GC hasn't run");
 
 			GC.Collect();
 			GC.WaitForPendingFinalizers();
-			GC.Collect();
 
-			Assert.IsTrue(list.AddObject());
+			Assert.IsTrue(list.AddObject(), "GC run, but proxy should still hold a reference");
 
-			proxy = null;
+			_proxyForWeakToWeakTest = null;
 
 			GC.Collect();
 			GC.WaitForPendingFinalizers();
-			GC.Collect();
 
-			Assert.IsFalse(list.AddObject());
+			Assert.IsFalse(list.AddObject(), "Proxy is gone and GC has run");
 		}
 
 		public class WeakCollectionChangedList : List<object>, INotifyCollectionChanged
@@ -467,7 +469,7 @@ public bool AddObject()
 			{
 				bool invoked = false;
 				var me = new object();
-
+				Console.WriteLine($"Handler count is {handlers.Count}");
 				foreach (var handler in handlers.ToList())
 				{
 					if (handler.IsActive)
@@ -477,6 +479,7 @@ public bool AddObject()
 					}
 					else
 					{
+						Console.WriteLine($"Handler is inactive");
 						handlers.Remove(handler);
 					}
 				}