public void Concat()
        {
            var a = new System.Collections.Specialized.NameValueCollection {
                { "1", "one" }
            };
            var b = new System.Collections.Specialized.NameValueCollection {
                { "2", "two" }
            };
            var c = a.Concat(b);

            b.Add("2", "dos");
            Assert.AreEqual("one", c["1"]);
            Assert.AreEqual("two", c["2"]);
            Assert.AreEqual("two,dos", b["2"]);
        }