public void Replace()
{
var a = new StringNode("a");
var b = new StringNode("b");
var c = new StringNode("c");
// a - b - c
a.AddFirst(b);
b.AddFirst(c);
b.Replace(new StringNode("d"));
string.Join("", a.DescendantsAndSelf().Select(n => n.Value)).Should().Be("ad");
}