public void should_give_false_if_input_is_bad(string zip)
        {
            var z = new ZipCodeService();

            bool result = z.Validate(zip);

            Assert.AreEqual(false, result);
        }
        public void should_give_false_if_input_is_null()
        {
            var z = new ZipCodeService();

            bool result = z.Validate(null);

            Assert.AreEqual(false, result);
        }
        public void should_give_true_if_input_is_nnn_nn(string zipcode)
        {
            var z = new ZipCodeService();

            bool result = z.Validate(zipcode);

            Assert.AreEqual(true, result);
        }