void TestPermutations(int n, string[] expected)
        {
            List <string> valueList = new List <string>(16);

            Combinatorial.Permutations(n, x => {
                string s = string.Join(string.Empty, x);
                valueList.Add(s);
            });
            CollectionAssert.AreEqual(expected, valueList);
        }
 public void PermutationsGuardCase3Test()
 {
     Combinatorial.Permutations(1, null);
 }
 public void PermutationsGuardCase2Test()
 {
     Combinatorial.Permutations(-1, x => { });
 }