public void Test_Merge()
        {
            TokenCollection a = Create(new[] { "mouse", "mouse", "mouse" });
            TokenCollection b = Create(new[] { "mouse", "chicken", "chicken" });

            TokenCollection merge = TokenCollection.Merge(a, b);

            Assert.AreEqual(6, merge.Sum);
            Assert.AreEqual(4, merge.get("mouse"));
            Assert.AreEqual(2, merge.get("chicken"));
        }