Facebook – How to Get Rid of the New Message Layout on Facebook

This does indeed convert your "normal" account to a "test" account and it cannot be reversed

Take a look at this Article on Facebook:

We ensure that test users are exempt from Facebook spam or fake account detection systems to ensure that you can test your application without worrying about getting disabled.

Also, to ensure that using test user accounts to test various scenarios doesn't end up unintentionally creating spam, we enforce certain limitations on what test users can do.

• Test users can interact with other test users only and not with real users on site.
• Test users cannot fan a public Page or create public content on them like writing on a Page's wall. A Test user can however view and interact with the application tab on the Page if they are associated with that app.
• They can be accessed and used by any developer of the associated application.
• They only have test privileges on the associated application. This implies that they can use the app in live mode or sandbox mode but cannot edit any technical settings or access insights for that application.
• A test user is always a test user and cannot be converted to a normal user account.

Up until yesterday, creating a Test Account used to just add you to the Facebook Test Network. So to undo this, all you had to do previously was remove yourself from the Test Network. Unfortunately, this is no longer true due to recent changes made by Facebook.

There is a blog post here with further information about this.

UPDATE

The process of converting your own account to a test account is now redundant.

You can now create up to 50 developer test accounts to interact with your apps. Developers will be able to use the Graph API to create accounts, manage friends, test their apps, and build automated tests. These new tests accounts do not need to be verified, & each test user will receive a login URL that does not require a password. More detailed documentation of the APIs is available here.

Test accounts can now be created via the Graph API.

A test user is a user account associated with an app created for the purpose of testing the functionality of that app. You can use test users for manual or automated testing.

We allow you to access the test account via a login_url which allows you to directly login to the account. The login_url expires after one hour, but you easily refresh it to get a new login_url for the same test user. We also provide you an access_token for the test user so that you can take actions on behalf of the test user via the api.

An app can create up to 500 test users to start testing an app.

You can't deactivate Timeline once you've activated it.

As for Facebook’s help pages, there’s no reference given to turning off Timeline. In fact, the only conversion reference is if you accidentally switch your Timeline to a business page, something which requires contacting Facebook support to rectify.

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Facebook has confirmed to us that there is no way to return to the old-style profile once you have switched to Timeline.