Some (not all) recommendations:
1 You may save packages as Visual basic files and search for the production server string if it completely absent. There will be text like this:
oConnection.ConnectionProperties("Data Source") = "MyServerName"
2. If the source are only text files on a local machine then plug off the network cable on the test server and run each package to make sure it would not give you an error message that it is trying to connect to the production server.
3. (Wild!) put an entry in HOSTS file on the Test server (ask your sysadmin first!)
This will re-direct connections to productionServerName to the local host (test server) I just tested it, it works! The only thing that happened when looped back to the test server it lost my Windows credentials, so I had to specify SQL Credentials for the connection.