While editing a newsletters You can send newsletter at the last tab Step 5: Send newsletter. The upper part is to send to the selected mailing lists/user groups, the lower part is for sending for testing.
The test sending is designated to look at the newsletter at a mail client and check the look-and-feel and the content. It is important to especially look at the HTML version of the newsletter at various mail clients, because for HTML mails there is no standard unlike web sites with HTML and so nearly each mail client goes its own way. That means that the newsletter may look different at the mail client than at the editor or the preview.
Caution:
At test sending the links to edit or delete a subscription are not replaced! There only are placeholders. This behaviour is wanted. At real sending the links are replaced according to the subscriber naturally.