For UOB Online payment method there aren’t any test data available, but you can see how it works with the payment flow given below.
UOB Online Payment Flow
The customer enters his email address, name and phone number.
The customer is shown the details of his payment and proceeds to pay with UOB Online.
The customer logs in to his UOB account by entering his User ID and password, and completes the payment.
Upon completion of the payment flow, the customer is redirected back to your ReturnURL.