The answer is in the civicrm_uf_match table in your Civicrm database. Each Drupal user is connected to its corresponding Civi contact record there.
- The uf_id column is the Drupal user ID.
- The uf_name column is the email address associated with the Drupal user and Civi contact record.
- The contact_id column is the Civi contact record ID.
I don't know the ramifications of deleting the row which contains Drupal user 1, but you could certainly create a new Civi contact record (not yourself), and put that new contact ID in the row with uf_id 1 (replacing whatever value is in the contact_id column currently). Once that is done, you could delete your test contact record safely.
Our Drupal user 1 is associated with a contact record named [myorg] Tech and the email address is tech@[myorg].org. Thus our default address for mailings come from that address with no problems.
Hope that helps!