public void FindFirstRecurringCharNullTests()
        {
            var result = FirstRecurringChar.FindFirstChar("ABC");

            Assert.Null(result);
        }
        public void FindFirstRecurringCharTests()
        {
            var result = FirstRecurringChar.FindFirstChar("ABCA");

            Assert.AreEqual('A', result);
        }
        public void FindFirstRecurringCharMultipleReccuringTests()
        {
            var result = FirstRecurringChar.FindFirstChar("BCABA");

            Assert.AreEqual('B', result);
        }