We recommend that you test the email yourself before sending it to the actual recipients. For that purpose, we have provided a button to send test emails on the 'Schedule Via MassMailer' page for Salesforce campaigns. In order to send test emails you need to have at least one campaign member on the Campaign whose first name is 'Test'

'MasssMailer Mass Email Wizard' also supports Send Test Email feature. Here the 'Logged In User' receives the test email.