public void TestStringWithDifferentCharacter()
        {
            const string s   = "ab";
            var          len = FindLongestSubstring.GetLengthOfLongestSubstring(s);

            Assert.IsTrue(len == 2, "length is {0}", len);
        }
        public void TestStringWithDuplicatedChar()
        {
            const string s   = "ababababababab";
            var          len = FindLongestSubstring.GetLengthOfLongestSubstring(s);

            Assert.IsTrue(len == 2, "length is {0}", len);
        }
        public void TestStringWithSameCharacter()
        {
            const string s   = "bbbbbbb";
            var          len = FindLongestSubstring.GetLengthOfLongestSubstring(s);

            Assert.IsTrue(len == 1, "length is {0}", len);
        }