Improves UI test reliability

Adds retry logic to clear button click in date picker test; captures a screenshot of the split button popup during UI test.

Author: Keboo

tests/MaterialDesignThemes.UITests/WPF/DatePickers/DatePickerTests.cs

@@ -76,12 +76,14 @@ public async Task OnDatePicker_WithClearButton_ClearsSelectedUncommittedText()
         await datePickerTextBox.SendKeyboardInput($"invalid date");
         await Assert.That(await datePickerTextBox.GetText()).IsEqualTo("invalid date");
 
-        // Act
-        await clearButton.LeftClick();
-        await Task.Delay(50, TestContext.Current!.CancellationToken);
+        // Act & Assert
+        await Wait.For(async () => {
+            await clearButton.LeftClick();
+            await Task.Delay(50, TestContext.Current!.CancellationToken);
 
-        // Assert
-        await Assert.That(await datePickerTextBox.GetText()).IsNull();
+            string? text = await datePickerTextBox.GetText();
+            await Assert.That(text).IsNull();
+        });
 
         recorder.Success();
     }

tests/MaterialDesignThemes.UITests/WPF/SplitButtons/SplitButtonTests.cs

@@ -93,15 +93,16 @@ public async Task SplitButton_WithButtonInPopup_CanBeInvoked()
         //NB: give the popup some time to show
         await Wait.For(async () => await popupContent.GetIsVisible());
         await Wait.For(async () => await popupContent.GetActualHeight() > 10);
+
+        await recorder.SaveScreenshot("PopupOpen");
+
         await popupContent.LeftClick();
         await Task.Delay(50, TestContext.Current!.CancellationToken);
 
         // Assert
-        await Wait.For(async () =>
-        {
-            var invocations = await clickEvent.GetInvocations();
-            await Assert.That(invocations).HasSingleItem();
-        });
+        var invocations = await clickEvent.GetInvocations();
+        await Assert.That(invocations).HasSingleItem();
+
         recorder.Success();
     }