Sending a test email to yourself is the closest measure of accuracy to test rendering, but even so it's not 100% guaranteed. Bear in mind that email clients vary from subscriber to subscriber and may have custom display settings in place that are beyond your control and ours.
You can view a live preview, or send a preview email to yourself, so that you can see the email as your recipients will. The View Preview and Send Preview functions are available in the composition step for emails and SMSes. There's also a Compatibility tool that gives you an idea of what your email will look like in specific email clients.
We advise all users to set up a test list with email accounts from a variety of service providers (versions of Microsoft Outlook, Gmail, Hotmail etc.). This will allow you to see how the email renders in the different email clients. Read our articles on importing contacts if you need to brush up on these functions.