You must execute the tester with some GET params in the url:
modelId: ID of the model room (must be online).
userNick: The username that you want to use in the room. (must be available)
Example: http://localhost:8888/tester.php?modelId=XXXXX&userNick=XXXX
Don´t forget add your SECRET, PARTNER_ID and APP_ID in the tester.php file