While I would also be quite irate if I was in your position, it does not sound like this can be blamed entirely on FB. My first parsing of "Make <your name> a Test Account" is that it means "the FB account with <your name> will be converted from a real account in to a test account".
Also,
> "To make a test account, register on Facebook as you normally would. Then, when logged in to the test account, go to this URL"
That also seems quite clear to me:
Create a test account
Log in to the test account
Click "Make <your name> a Test Account"
That being said, I do agree - this should have required more confirmation. This could have been avoided with a simple message box saying "Hold up, are you sure? <Your name> will no longer be a normal FB user. All <Your name's> friends will be deleted, and you will not be able to admin any apps. If you want a test account in addition to your normal account, you need to..."