public void Test_EnablingClickTracking_true()
        {
            var mail = BasicMailBuilder
                       .EnableClickTracking(true)
                       .Build();

            var message = new SendGridMessage();

            message.EnableClickTracking(true);
            Assert.IsFalse(string.IsNullOrEmpty(message.Header.JsonString()));
            Assert.AreEqual(message.Header.JsonString(), mail.Header.JsonString());
        }