In order to run a test transaction, you have to access your pay-me-now account. Once you login with your account id, and password, you have to create sub-id's or sub-accounts. There should be a menu option on the pay-me-now screen "Available Services". Ensure that the sub-id's option is Activated. Once this is confirmed, return to the menu options and select "Add Sub-id's". The Sub-id name can be any 5-characters. Once this is completed, you should see a window at the very top of the pay-me-now screen labeled: Sub ID:
Enter the sub-id that you just created in the window and hit the change button. This should bring up a new screen with the sub-id configurations. At the top, you should see a pull-down window with the status of your account ie. "active"
Now you can select the pull-down window and change your status to "testing"
The last thing that you have to do is enter the correct info into the OSCommerce payment module setup screen. Go to ADMIN within OSCommerce, Select Modules, Select Payment, Select Merchant Partners Credit Card. Enter the correct info as well as the correct test parameters. Enable merchant partners, Enter your Account ID and Sub ID. As far as test parameters, I would strongly recommend that you download the contribution for merchant partners instead of using the files from the pay-me-now website. If you use the files from the contribution, the test parameters are as follows: cc# 5454545454545454 exp date: 12/2005 ccv: 123
Let me know if any of this is unclear or if you require additional info.
Goodluck!