I am using the same login on a test app and it works. Also the email from USPS says contact them when you are finished testing.
Your Web Tools User ID, shown above, is required to test and integrate USPS Web Tools APIs. With this ID, you may begin sending calls to the test server. Depending on the API, the address to the test server is either
http://production.shippingapis.com/ShippingAPITest.dll or
https://secure.shippingapis.com/ShippingAPITest.dll. Use this information in combination with your User ID and your XML string to send a request to the USPS servers. For more details, refer to the programming guides (located at
http://www.usps.com/webtools) for the specific API you are integrating.
A sample test request would look like: "http://production.shippingapis.com/ShippingAPITest.dll?API=[API_Name]&XML=[XML_String_containing_User_ID]"
When you have completed your testing, email the USPS Internet Customer Care Center (ICCC). They will switch your profile to allow you access to the production server and will provide you with the production URLs.
The ICCC is staffed as follows:
Monday through Friday from 8:00AM to 8:30PM Eastern Time
Saturday from 8:00AM to 6:00PM Eastern Time
Sunday and Postal Holidays - Closed except for the following Holidays: Martin Luther King; President's Day; Columbus Day; & Veteran's Day with hours from 9:00AM to 6:00PM Eastern Time