Test all steps of registration as a participant. The best way to test the event website is to send an invitation to the test participant (see Send invitations) and then click on the registration button in the invitation. Then look at all the tabs, click on all links and finally on the login button. Answer all questions, perhaps leave the mandatory fields at the first time to see the reaction of the system. Verify that you have received a commitment or cancellation email and that they look as they had planned.
Then check that they can see the response as an administrator under Event Dashboard and let yve give you a detail report and summary under 'Event Dashboard -> Reports'.
Test your improvements
It is very likely that you noticed things when you were testing them, which they would like to have differently. Make the changes and start a new test. You will go through this loop several times, which is normal. It is important that you have tested all the changes.
If you have tested all the emails and the website, answered the questionnaire and everything looks as they want, you are ready to send the invitations.