protected override List <T> SortTestHelper <T>(ImmutableTrieList <T> list, Comparison <T> comparison)
 {
     return(list.Sort(comparison).ToList());
 }
 protected override List <T> SortTestHelper <T>(ImmutableTrieList <T> list, int index, int count, IComparer <T> comparer)
 {
     return(list.Sort(index, count, comparer).ToList());
 }
 protected override List <T> SortTestHelper <T>(ImmutableTrieList <T> list)
 {
     return(list.Sort().ToList());
 }