If you're doing this for an e-commerce site, you'll be using payments options.
All payment options that I know offer a "sandbox mode" that allows you to use fake info, although some of them provide you that info in a very specific way, like not any CC number, but very specific credit card numbers for testing purposes.
So there you have your answer: whatever payment option you need to test, will give you fake info to use in sandbox mode, so using fake info is OK. Furthermore, you already say that the payment info will be fake.
Now, a very different scenario is if you want to test usability and consumer behavior. Let's say, you want to test your form to see if they are clear and your target understands what it is required. For example, the format you use to input name, or phone, or address, or whatever. To be more specific: It's not the same to use something like askdjhakjsdhkash than to use Beverly Hills, Los Angeles, CA . If you need to test the user behavior when faced with your form, I'd use real info.
Finally, you can read more on the subject at http://www.measuringu.com/blog/credit-usability.php , some of the tips might be of use for you