public void PromptAdorner_RendersPrompt_WithoutError()
        {
            var editor  = new TextEditor();
            var adorner = new PromptAdorner(editor)
            {
                Visibility = Visibility.Visible
            };

            adorner.InvalidateArrange();

            // system under test
            adorner.Arrange(new Rect(new Size(100, 100)));
        }