diff --git a/tests/HeadlessTest.Ursa/Controls/DateTimePicker/CalendarViewHelper.cs b/tests/HeadlessTest.Ursa/Controls/DateTimePicker/CalendarViewHelper.cs
index b351389..a2ecc09 100644
--- a/tests/HeadlessTest.Ursa/Controls/DateTimePicker/CalendarViewHelper.cs
+++ b/tests/HeadlessTest.Ursa/Controls/DateTimePicker/CalendarViewHelper.cs
@@ -11,44 +11,44 @@ internal static class CalendarViewHelper
     {
         var previousButton = calendarView.GetTemplateChildren()
                                          .FirstOrDefault(a => a.Name == CalendarView.PART_PreviousButton);
-        Assert.IsType<Button>(previousButton);
-        var button = (Button)previousButton;
-        button.RaiseEvent(new RoutedEventArgs(Button.ClickEvent));
+        Assert.IsAssignableFrom<Button>(previousButton);
+        var button = previousButton as Button;
+        button?.RaiseEvent(new RoutedEventArgs(Button.ClickEvent));
     }
     
     internal static void ClickNext(this CalendarView calendarView)
     {
         var nextButton = calendarView.GetTemplateChildren()
                                      .FirstOrDefault(a => a.Name == CalendarView.PART_NextButton);
-        Assert.IsType<Button>(nextButton);
-        var button = (Button)nextButton;
-        button.RaiseEvent(new RoutedEventArgs(Button.ClickEvent));
+        Assert.IsAssignableFrom<Button>(nextButton);
+        var button = nextButton as Button;
+        button?.RaiseEvent(new RoutedEventArgs(Button.ClickEvent));
     }
     
     internal static void ClickFastNext(this CalendarView calendarView)
     {
         var nextButton = calendarView.GetTemplateChildren()
                                      .FirstOrDefault(a => a.Name == CalendarView.PART_FastNextButton);
-        Assert.IsType<Button>(nextButton);
-        var button = (Button)nextButton;
-        button.RaiseEvent(new RoutedEventArgs(Button.ClickEvent));
+        Assert.IsAssignableFrom<Button>(nextButton);
+        var button = nextButton as Button;
+        button?.RaiseEvent(new RoutedEventArgs(Button.ClickEvent));
     }
     
     internal static void ClickFastPrevious(this CalendarView calendarView)
     {
         var previousButton = calendarView.GetTemplateChildren()
                                          .FirstOrDefault(a => a.Name == CalendarView.PART_FastPreviousButton);
-        Assert.IsType<Button>(previousButton);
-        var button = (Button)previousButton;
-        button.RaiseEvent(new RoutedEventArgs(Button.ClickEvent));
+        Assert.IsAssignableFrom<Button>(previousButton);
+        var button = previousButton as Button;
+        button?.RaiseEvent(new RoutedEventArgs(Button.ClickEvent));
     }
     
     internal static void ClickHeaderButton(this CalendarView calendarView)
     {
         var headerButton = calendarView.GetTemplateChildren()
                                        .FirstOrDefault(a => a.Name == CalendarView.PART_HeaderButton);
-        Assert.IsType<Button>(headerButton);
-        var button = (Button)headerButton;
-        button.RaiseEvent(new RoutedEventArgs(Button.ClickEvent));
+        Assert.IsAssignableFrom<Button>(headerButton);
+        var button = headerButton as Button;
+        button?.RaiseEvent(new RoutedEventArgs(Button.ClickEvent));
     }
 }
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