As a rule, you test with an email that has already been confirmed. Here is the answer: if a contact has already completed the double opt-in, they cannot go through it a second time.
So if you want to test your email confirmation settings as well, set the email status of your test address to "unknown". You can then test the campaign completely.
Deleting the contact is not enough! When a contact is deleted from Quentn, the system remembers the status of the email address (using an anonymous hash value). If the contact registers again, it immediately gets its old status back. If this status is "unknown", the contact will also receive opt-in emails again.
This measure serves to protect us against fraud: If someone has unsubscribed or reported spam, for example, the admin of the system should not be able to change this status again - not even by deleting and re-creating the contact.