데이터베이스 연결 테스트

Fatal error:  Uncaught Error: Undefined constant "DEBUG_MODE" in C:\xampp\htdocs\video_make_pdf\first_dev_mp4towordtopdf\src\Database.php:23
Stack trace:
#0 C:\xampp\htdocs\video_make_pdf\first_dev_mp4towordtopdf\src\Database.php(32): Database->__construct()
#1 C:\xampp\htdocs\video_make_pdf\first_dev_mp4towordtopdf\database\test_connection.php(15): Database::getInstance()
#2 {main}
  thrown in C:\xampp\htdocs\video_make_pdf\first_dev_mp4towordtopdf\src\Database.php on line 23