Add unit tests

tests/Avalonia.Controls.UnitTests/SplitViewTests.cs

@@ -0,0 +1,66 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using Xunit;
+
+namespace Avalonia.Controls.UnitTests
+{
+    
+    public class SplitViewTests
+    {
+        [Fact]
+        public void SplitView_PaneOpening_Should_Fire_Before_PaneOpened()
+        {
+            var splitView = new SplitView();
+
+            bool handledOpening = false;
+            splitView.PaneOpening += (x, e) =>
+            {
+                handledOpening = true;
+            };
+
+            splitView.PaneOpened += (x, e) =>
+            {
+                Assert.True(handledOpening);
+            };
+
+            splitView.IsPaneOpen = true;
+        }
+
+        [Fact]
+        public void SplitView_PaneClosing_Should_Fire_Before_PaneClosed()
+        {
+            var splitView = new SplitView();
+            splitView.IsPaneOpen = true;
+
+            bool handledClosing = false;
+            splitView.PaneClosing += (x, e) =>
+            {
+                handledClosing = true;
+            };
+
+            splitView.PaneClosed += (x, e) =>
+            {
+                Assert.True(handledClosing);
+            };
+
+            splitView.IsPaneOpen = false;
+        }
+
+        [Fact]
+        public void SplitView_Cancel_Close_Should_Prevent_Pane_From_Closing()
+        {
+            var splitView = new SplitView();
+            splitView.IsPaneOpen = true;
+
+            splitView.PaneClosing += (x, e) =>
+            {
+                e.Cancel = true;
+            };
+
+            splitView.IsPaneOpen = false;
+
+            Assert.True(splitView.IsPaneOpen);
+        }
+    }
+}