Payrexx Direct

In this article you can find a list of test credit cards for Payrexx Direct:
https://support.payrexx.com/de/support/solutions/articles/11000078221

Postfinance, Ogone, Concardis, Viveum

Stripe

A list of credit cards for testing, you can find on: https://stripe.com/docs/testing

Paypal

A list of credit cards for testing, you can find on: https://developer.paypal.com/docs/classic/payflow/payflow-pro/payflow-pro-testing/

Paymill

A list of credit cards for testing, you can find on: https://developers.paymill.com/guides/reference/testing.html