There are many ways how you can test and preview your campaigns.
Sending a test email:
Open your campaign and navigate to Step 4: Content using the Campaign Wizard navigation bar.
Click on the Email Tests dropdown.
Choose the Send Test email option. This will open another window where you will be able to add up to 5 email addresses to which a test email will be sent.
When you're done, click on the Send Test Email button to send the test emails
Previewing your campaign:
Step 4 — The icons on the right-hand side, that display cell phone, a tablet, and a computer. You can see how your campaign will look on any of the devices and check the responsiveness.
Step 5 — Hover over the campaign preview and click on the email Email preview button. This will display your full campaign (With From: Name and Subject Line.
By clicking on the Show data button, all the merge tags that have been added to the campaign will be filled with information from your lists.