public void Indexer_Test()
        {
            var sequence = new StringCharacterSequence("abcdefg");
            var buffer   = sequence.CreateBuffer();

            buffer[0].Should().Be('a');
            buffer[1].Should().Be('b');
            buffer[2].Should().Be('c');
            buffer[3].Should().Be('d');
            buffer[4].Should().Be('e');

            var result = buffer.Capture(3);
            var str    = new string(result);

            str.Should().Be("abc");

            sequence.Peek().Should().Be('d');
        }