Application token is not required to test in sandbox environment.
http://code.google.com/apis/adwords/docs/developer/adwords_api_sandbox.html
developerToken
A string that identifies you as an authorized user of the sandbox.
Must be the same login_id used in the email header, followed by ++ and
the currency code used by the account.
Example:
j...@gmail.com++USD
applicationToken
Ignored in sandbox
A string that identifies an application as being authorized to call
the AdWords API web services.