private void Cb3_SelectionChanged(object sender, SelectionChangedEventArgs e)
 {
     using (Repos rep = new Repos())
     {
         TempList3 = rep.Testjes(TempList[Cb3.SelectedIndex]);
         foreach (Test t in TempList3)
         {
             Testen.Add(t.TestNaam);
         }
     }
     Cb4.ItemsSource = Testen;
 }