Add test for opening folder browser dialog

In order to make writing tests morepleasant I add shortcuts for operations inside form
That allow me express tests better then just counting tabs and pressing enter.

This currently catches issue in dotnet#5319

src/System.Windows.Forms/tests/IntegrationTests/System.Windows.Forms.IntegrationTests.Common/TestHelpers.cs

@@ -306,6 +306,18 @@ public static bool SendUpArrowKeyToProcess(Process process, bool switchToMainWin
             return SendKeysToProcess(process, "{UP}");
         }
 
+        /// <summary>
+        ///  Presses Alt plus choosen letter on the given process if it can be made the foreground process
+        /// </summary>
+        /// <param name="process">The process to send the Alt and key to</param>
+        /// <param name="letter">Letter in addition to Alt to send to process.</param>
+        /// <returns>Whether or not the Up key was pressed on the process</returns>
+        /// <seealso cref="SendKeysToProcess(Process, string, bool)"/>
+        public static bool SendAltKeyToProcess(Process process, char letter, bool switchToMainWindow = true)
+        {
+            return SendKeysToProcess(process, "%{" + letter + "}", switchToMainWindow);
+        }
+
         /// <summary>
         ///  Presses Tab any number of times on the given process if it can be made the foreground process
         /// </summary>

src/System.Windows.Forms/tests/IntegrationTests/System.Windows.Forms.IntegrationTests/WinformsControlsTest.cs

@@ -152,6 +152,25 @@ public void WinformsControlsTest_FileDialogTest()
             Assert.True(process.HasExited);
         }
 
+        [Fact]
+        public void WinformsControlsTest_OpenFolderBrowserDialogTest()
+        {
+            Process process = TestHelpers.StartProcess(_exePath);
+            TestHelpers.SendTabKeysToProcess(process, MainFormControlsTabOrder.DialogsButton);
+            TestHelpers.SendEnterKeyToProcess(process);
+            TestHelpers.SendEnterKeyToProcess(process, switchToMainWindow: false);
+
+            TestHelpers.SendAltKeyToProcess(process, 'b', switchToMainWindow: false);
+            TestHelpers.SendAltKeyToProcess(process, 'o', switchToMainWindow: false);
+
+            Assert.False(process.HasExited);
+
+            process.Kill();
+            process.WaitForExit();
+
+            Assert.True(process.HasExited);
+        }
+
         [Fact]
         public void DataBindings_remove_should_unsubscribe_INotifyPropertyChanged_PropertyChanged_event()
         {

src/System.Windows.Forms/tests/IntegrationTests/WinformsControlsTest/Dialogs.cs

@@ -23,10 +23,10 @@ public Dialogs()
             TypeDescriptor.AddProvider(new AssociatedMetadataTypeTypeDescriptionProvider(saveFileDialog1.GetType(), typeof(ExposedClientGuidMetadata)), saveFileDialog1);
             TypeDescriptor.AddProvider(new AssociatedMetadataTypeTypeDescriptionProvider(folderBrowserDialog1.GetType(), typeof(ExposedClientGuidMetadata)), folderBrowserDialog1);
 
-            _btnOpen = new("Open dialog")
+            _btnOpen = new("&Open dialog")
             {
                 Image = (System.Drawing.Bitmap?)(resources.GetObject("OpenDialog")),
-                Enabled = false
+                Enabled = false,
             };
 
             _btnOpen.Click += (s, e) =>