If a ticket type is purchased for an event either as a test or actually purchased the ticket type cannot be deleted even if the ticket is refunded/deleted. You cannot delete a purchased ticket type, but you can hide it.  To ensure that constituents cannot see the ticket, assign a promotion code to the ticket using these steps:
  1. Go to Content > Events.
  2. Find the event that contains the ticket type you would like to hide.
  3. Click Edit.
  4. Go to step 6 (Configure Ticket Types) and click Edit for the ticket type you would like to hide.
  5. Go to step 7 (Promotion Code) and enter a promotion code.
Promotion codes restrict registration for the event to only those people who click a link that contains this code.  If you never share this link, no one will see this ticket.