Add unit test for microsoft#148

Author: marcelwgn

dev/NavigationView/NavigationView_InteractionTests/NavigationViewTests.cs

@@ -2895,6 +2895,38 @@ public void KeyboardFocusToolTipTest() // Verify tooltips appear when Keyboard f
             }
         }
 
+        [TestMethod]
+        [TestProperty("TestSuite", "C")]
+        public void DisplayModeChangeSelectionEventTest()
+        {
+            var testScenarios = RegressionTestScenario.BuildLeftNavRegressionTestScenarios();
+            foreach (var testScenario in testScenarios)
+            {
+                using (var setup = new TestSetupHelper(new[] { "NavigationView Tests", "NavigationView Test" }))
+                {
+                    if (!PlatformConfiguration.IsOsVersionGreaterThanOrEqual(OSVersion.Redstone3))
+                    {
+                        Log.Warning("Test is disabled on RS2 and earlier because SplitView lacks the requisite events.");
+                        return;
+                    }
+
+                    ComboBox selectedItem = new ComboBox(FindElement.ById("SelectedItemCombobox"));
+                    selectedItem.SelectItemByName("Settings");
+
+                    ComboBox displayMode = new ComboBox(FindElement.ById("PaneDisplayModeCombobox"));
+                    displayMode.SelectItemByName("Top");
+                    Wait.ForIdle();
+
+                    TextBlock selectedItemWasNull = new TextBlock(FindElement.ById("SelectionChangedItemWasNull"));
+                    Verify.AreEqual("False", selectedItemWasNull.GetText());
+
+                    displayMode.SelectItemByName("Left");
+                    Wait.ForIdle();
+                    Verify.AreEqual("False", selectedItemWasNull.GetText());
+                }
+            }
+        }
+
         [TestMethod]
         [TestProperty("TestSuite", "C")]
         public void PaneOpenCloseEventsTest()

dev/NavigationView/TestUI/NavigationViewPage.xaml

@@ -1,4 +1,4 @@
-<!-- Copyright (c) Microsoft Corporation. All rights reserved. Licensed under the MIT License. See LICENSE in the project root for license information. -->
+<!-- Copyright (c) Microsoft Corporation. All rights reserved. Licensed under the MIT License. See LICENSE in the project root for license information. -->
 <local:TestPage
     x:Class="MUXControlsTestApp.NavigationViewPage"
     xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
@@ -177,6 +177,8 @@
                             <ComboBoxItem Content="LeftCompact" Tag="LeftCompact"/>
                             <ComboBoxItem Content="LeftMinimal" Tag="LeftMinimal"/>
                         </ComboBox>
+                        <TextBlock VerticalAlignment="Center">SelectedItem in SelectionChanged event was null: </TextBlock>
+                        <TextBlock VerticalAlignment="Center" x:Name="SelectionChangedItemWasNull" AutomationProperties.Name="SelectionChangedItemWasNull"/>
                     </StackPanel>
 
                     <StackPanel Orientation="Horizontal">

dev/NavigationView/TestUI/NavigationViewPage.xaml.cs

@@ -296,6 +296,7 @@ private void NavView_SelectionChanged(NavigationView sender, NavigationViewSelec
         {
             if (args.SelectedItem != null)
             {
+                SelectionChangedItemWasNull.Text = "False";
                 var itemdata = args.SelectedItem as NavigationViewItem;
                 if (itemdata != null)
                 {
@@ -309,6 +310,10 @@ private void NavView_SelectionChanged(NavigationView sender, NavigationViewSelec
                     }
                 }
             }
+            else
+            {
+                SelectionChangedItemWasNull.Text = "True";
+            }
         }
 
         private void MoviesEnabledCheckbox_Checked(object sender, RoutedEventArgs e)