Hi there,
you do not need to be current, neither you need a current medical in order to take the FAA ATP knowledge test.
The only thing you need to bring to the test is a proper identification (i.e. current passport ideally including a photograph of yourself) and sufficient money to pay the testing fee.
An endorsement is not required to take the FAA ATPL written test!
Minimum passing score is 70% and the test is valid for a period of 24 month (meaning the check ride should be taken within this time frame, otherwise the written test needs to be re-taken).
See ATP Test Guide:
http://www.faa.gov/training_testing/...-G-8082-1E.pdf
FAA Knowledge Test Guides - in general:
Airman Knowledge Test Guides
In order to take the FAA ATPL check ride an applicant (pilot) must have at least 1500 hrs total flying time and hold an FAA CPL with an instrument rating (IR). For further details see link below:
Electronic Code of Federal Regulations:
In Europe there are only two locations where FAA testing is provided, Paris (Le Bourget Airport) and London (Farnborough Airport) the tests are given by Flight Safety International (see my previous post above #3).