will help you The test credentials are designed to be used in situations where using the live credentials would cost you money - sending an SMS, making a call, purchasing a phone number. They don't cover the entire Twilio API (yet). If you are only listing your messages, you should be able to do so safely with the live credentials, as retrieving messages does not cost anything. (Or am I missing a part of your question)?
wish helps you Twilio developer evangelist here. The test credentials won't deliver any SMS messages. Think of it as having the ability to exercise any requests, but not actually making them for real. Test credentials are useful for developing if you're concerned about making API requests.
Receiving SMS from Twilio sent with test credentials?
it fixes the issue If you want to send an actual SMS, then you are charged for sending the SMS. The test credentials are more for exercising the API. You cannot view the message log using the test credentials, ("message": "Resource not accessible with Test Account Credentials"). How To Use Twilio Test Credentials with Magic Phone Numbers