To test a web form multiple times on the same computer, you must enable 'kiosk' mode. To turn on this setting Edit campaign > go to Opt-In Channels > Fields tab > switch On - Allow multiple people to fill out web form using the same computer (kiosk mode).
This is because the system blocks duplicates. You need to delete your subscriber record, then re-subscribe, to get a new set of your auto-responder messages. Subscribers are deleted from the Subscriber tab of campaign dashboard or the "Unsubscribe" link found in the message.