public void Test_SetCategories()
{
var categories = new List <string>()
{
"test", "email"
};
var mail = BasicMailBuilder
.SetCategories(categories)
.Build();
var message = new SendGridMessage();
message.SetCategories(categories);
Assert.IsFalse(string.IsNullOrEmpty(message.Header.JsonString()));
Assert.AreEqual(message.Header.JsonString(), mail.Header.JsonString());
}