You can send a test message directly from the dashboard without have a contact or mobile number assigned to a group.
The Send a Test is located on the right hand side of the 'Send campaign' page. The Quick Send takes the From and Message template and constructs a test SMS.
How to send a test message
Edit the 'From' and 'Message Template' in the main section (left handside).
When finished setting the 'Message Template' and 'From' enter a mobile number in full international format in the Send a Test 'Send to' field.
Then press 'Send a test'.