public void AsLookup()
        {
            var a = new System.Collections.Specialized.NameValueCollection {
                { "1", "one" },
                { "1", "uno" },
            };
            var l = a.AsLookup();

            Assert.AreEqual(1, l.Count);
            Assert.AreEqual(2, l["1"].Count());
            Assert.AreEqual(0, l["2"].Count());
            a.Add("2", "dos");
            Assert.AreEqual(2, l.Count);
            Assert.AreEqual(1, l["2"].Count());
        }