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');
}