Before your event begins, you may like to test the event app, including features such as Messaging in order to get a feel of how the event app would be like for the event attendees.
In order to test the Messaging feature, you would first have to be added as a tester in the Attendee module. Refer to this article to learn how to add attendees in the CMS.
While adding your test account, you would have to mark yourself as a tester. In order to so do, click on the toggle button next to Tester.
As a tester, you will be able to view the full attendee list, however you will only be able to connect with and message other event app testers only. Events attendees will not be able to view the testers in the attendee list.