From Facebook Developer Wiki

Test Accounts for App Developers

One of the hard things about developing on Facebook Platform has been testing applications. Facebook's Terms of Service require that all accounts be linked to your real identity, so on the surface, you're not allowed to make fake accounts to test your applications.

To work around this roadblock, we formalized the concept of test accounts in a way that should be better for everyone. Here's how it works.

1. To make a test account, register a new account on Facebook as you normally would.
2. Have the test account become friends with your developer account (your own Facebook account).
3. From the test account, go to http://www.facebook.com/developers/become_test_account.php.

This will mark that account as a test account by adding an affiliation to the Facebook Platform Developer Test Accounts network. As long as the account is affiliated with that network, it will be considered a test account. If you accidentally make a real account a test account, you can remove its test account status by removing the affiliation with the Facebook Platform Developer Test Accounts Network from the Network Settings page.

A few important things to note:

• Test accounts can access your applications when they are in sandbox mode only if they are listed as developers of your application. Configure these settings in your application settings.
• Test accounts won't be able to see real Facebook users and vice versa. You can make an existing account a test account, but if that account is friends with a real account, each user will disappear from the other's list of friends.
• Our customer support team won't disable test accounts for being fake, but test accounts may be disabled for violating any other Terms of Service that would disable a real account.
• Only real accounts can administer and create applications. When a Facebook account becomes a registered test account, that account can no longer use the Facebook Developer application.

You can suggest ideas for ways to make test accounts better by submitting an enhancement idea into our public bug tracking system at: http://bugs.developers.facebook.com/enter_bug.cgi?product=Facebook%20Tools%20for%20developers.