Test account details will vary between payment service providers - they each have their own set of test details, though there are some "common" ones used across providers. Most PSPs have pages online where they supply such test details.
See below links to pages with test details for some of the PSPs
Authorize.net: https://developer.authorize.net/hello_world/testing_guide/
Braintree: https://developers.braintreepayments.com/guides/credit-cards/testing-go-live/php
CyberSource: https://developer.cybersource.com/hello-world/testing-guide-v1.html
Global Payments: https://developer.globalpay.com/resources/test-card-numbers
GoCardless: https://developer.gocardless.com/resources/test-bank-details
https://developer.gocardless.com/developer-tools/scenario-simulators
Moneris: https://developer.moneris.com/More/Testing/Testing%20a%20Solution
SagePay/ Opayo: https://www.sagepay.co.uk/support/12/36/test-card-details-for-your-test-transactions
Stripe: https://stripe.com/docs/testing
Worldpay: http://support.worldpay.com/support/kb/bg/testandgolive/tgl5103.html