public void Test_DisablingUnsubscribe()
{
var mail = BasicMailBuilder
.DisableUnsubscribe()
.Build();
var message = new SendGridMessage();
message.DisableUnsubscribe();
Assert.IsFalse(string.IsNullOrEmpty(message.Header.JsonString()));
Assert.AreEqual(message.Header.JsonString(), mail.Header.JsonString());
}