Removed duplicate TestRoot.

Use the one in Avalonia.UnitTests.

tests/Avalonia.Visuals.UnitTests/TestRoot.cs

@@ -1,39 +0,0 @@
-// Copyright (c) The Avalonia Project. All rights reserved.
-// Licensed under the MIT license. See licence.md file in the project root for full license information.
-
-using System;
-using Avalonia.Platform;
-using Avalonia.Rendering;
-
-namespace Avalonia.Visuals.UnitTests
-{
-    public class TestRoot : TestVisual, IRenderRoot
-    {
-        public Size ClientSize { get; }
-        
-        public IRenderTarget CreateRenderTarget()
-        {
-            throw new NotImplementedException();
-        }
-
-        public void Invalidate(Rect rect)
-        {
-            throw new NotImplementedException();
-        }
-
-        public IRenderer Renderer
-        {
-            get { throw new NotImplementedException(); }
-        }
-
-        public Point PointToClient(Point p)
-        {
-            throw new NotImplementedException();
-        }
-
-        public Point PointToScreen(Point p)
-        {
-            throw new NotImplementedException();
-        }
-    }
-}

tests/Avalonia.Visuals.UnitTests/VisualTests.cs

@@ -5,6 +5,7 @@ using System;
 using System.Collections.Generic;
 using System.Linq;
 using Avalonia.Controls;
+using Avalonia.UnitTests;
 using Avalonia.VisualTree;
 using Xunit;
 
@@ -66,8 +67,8 @@ namespace Avalonia.Visuals.UnitTests
         [Fact]
         public void Adding_Children_Should_Fire_OnAttachedToVisualTree()
         {
-            var child2 = new TestVisual();
-            var child1 = new TestVisual { Child = child2 };
+            var child2 = new Decorator();
+            var child1 = new Decorator { Child = child2 };
             var root = new TestRoot();
             var called1 = false;
             var called2 = false;
@@ -84,8 +85,8 @@ namespace Avalonia.Visuals.UnitTests
         [Fact]
         public void Removing_Children_Should_Fire_OnDetachedFromVisualTree()
         {
-            var child2 = new TestVisual();
-            var child1 = new TestVisual { Child = child2 };
+            var child2 = new Decorator();
+            var child1 = new Decorator { Child = child2 };
             var root = new TestRoot();
             var called1 = false;
             var called2 = false;
@@ -104,11 +105,11 @@ namespace Avalonia.Visuals.UnitTests
         {
             var root1 = new TestRoot();
             var root2 = new TestRoot();
-            var child = new TestVisual();
+            var child = new Canvas();
 
-            root1.AddChild(child);
+            root1.Child = child;
 
-            Assert.Throws<InvalidOperationException>(() => root2.AddChild(child));
+            Assert.Throws<InvalidOperationException>(() => root2.Child = child);
             Assert.Equal(0, root2.GetVisualChildren().Count());
         }
     }