For PSE payment method there aren’t any test data available, but you can see how it works with the payment flow given below.
PSE Payment Flow
The customer enters his email address.
After selecting the payment method, the customer enters the required information and proceeds with the payment using the Pay button.
The customer enters his email address registered in PSE and completes the payment.
Upon completion of the payment flow, the customer is redirected back to your ReturnURL.