These instructions are meant for the new edition of MassMailer. 

In the MassMailer Outreach Wizard's final step, 'Review and Send' you can click on the button, 'Send Test Email' in the 'Template Information' section.

It opens up a dialogue box in which you can enter comma separated emails to receive the test emails, select any merge record (even if you don't use any merge field in the template) and click on the 'Send Now' button.