public void Test_IncludeUniqueArg()
{
var mail = BasicMailBuilder
.IncludeUniqueArg("key", "value")
.Build();
var message = new SendGridMessage();
message.AddUniqueArgs(new Dictionary <string, string>()
{
{ "key", "value" }
});
Assert.IsFalse(string.IsNullOrEmpty(message.Header.JsonString()));
Assert.AreEqual(message.Header.JsonString(), mail.Header.JsonString());
}