Testing your dynamic content and merge fields works exactly the same as testing a normal email.

Once you have inserted your content, go to the Send Test tab of the campaign that it is attached to. Select which contact you are wishing to mimic in the "Contact Field". The dynamic content will be tested depending on whether there is the corresponding data in that specific contact record.

For example, if you have used Dear #[Person/FirstName]#, and you are mimicking the contact John Smith, the test will pull through Dear John.

To see a step by step tutorial on testing your content, please read the following article.