For Cards Vietnam payment method there aren’t any test data available, but you can see how it works with the payment flow given below.
Cards Vietnam Payment Flow
The customer enters his Email Address (the below page can be skipped by sending the parameter in the payment request).
The customer has to choose his preferred payment option from the given list.
The customer needs to enter the necessary credit card information and billing information. Then he needs to confirm the payment.
The customer receives a message that the payment was successfully processed.
Upon completion of the payment flow, the customer is redirected back to your ReturnURL.