public void AddWithOverwrite()
{
XFastTrie<string> trie = new XFastTrie<string>();
string temp;
trie.Add(1, "1");
Assert.Throws<ArgumentException>(() => trie.Add(1, "2"));
Assert.AreEqual("1", trie[1]);
Assert.DoesNotThrow(() => trie[1] = "one");
Assert.AreEqual("one", trie[1]);
}