private void Clone_Clicked(object source, RoutedEventArgs e)
        {
            Button btn = (Button)source;

            if (btn != null)
            {
                ITestCase testCase = btn.DataContext as ITestCase;
                if (testCase != null)
                {
                    ITestCase clone_case = testCase.Clone() as ITestCase;
                    if (clone_case != null)
                    {
                        TestCases.Add(clone_case);
                        Document.AddTestCase(clone_case);
                        Document.TestSuiteSaver.SaveSuite();
                    }
                }
            }
        }