MS SQL Server Concepts and Programming Question:

To test a DML trigger defined on a table, you just need to execute several INSERT, UPDATE and DELETE statements on that table as shown in this tutorial example:

USE GlobalGuideLineDatabase;
GO

INSERT INTO ggl_users (name) VALUES ('GGL Admin');
GO
Records are inserted, updated, or deleted in ggl_users
(1 row(s) affected)

UPDATE ggl_users SET email='root@ggl'
WHERE name = 'GGL Admin';
GO
Records are inserted, updated, or deleted in ggl_users
(1 row(s) affected)

DELETE FROM ggl_users WHERE name = 'GGL Admin';
GO
Records are inserted, updated, or deleted in ggl_users
(1 row(s) affected)

The trigger, dml_message, is working as expected.