private void btnStartTest_Click(object sender, RoutedEventArgs e)
{
List <string> wordstest = new List <string>();
Random rnd = new Random();
for (int i = 0; i < sliTestWordsNum.Value; i++)
{
wordstest.Add(test[rnd.Next(test.Count)]);
}
TestWindow twin = new TestWindow(wordstest);
twin.Show();
//btnStartTest.IsEnabled = false;
}