public void FibonacciSequence_Next()
{
var fs = new FibonacciSequence(new FibonacciState(0));
Assert.That(fs.Next(fs.Next(fs.Next(fs.Next(new FibonacciState(1))))).Value, Is.EqualTo(5));
Assert.That(fs.Previous.Value, Is.EqualTo(3));
}