public void ShoulBuildQueryString()
        {
            // arrange
            Transaction tx = new Transaction { Tx = "ABC", Amount = "123" };

            // act
            QueryString qs = tx.ToPdtQueryString();

            // assert
            Assert.AreEqual(7, qs.Count);
            Assert.AreEqual("?tx=ABC&st=&amt=123&cc=&cm=&item_number=&business=", qs.ToString());
        }