This is a sandbox account that you can create from here and login from here. This will create an account that behaves similar to the one you will use to make live transactions using the live API.
To make test transactions, you will need some Test Customer Accounts and Cards. This will help you to test for both success and failure scenarios.
To get these test customer accounts, you will need to call the sandbox API that returns the Payment Providers. Based on the response, test accounts will be included that work for the success and failure scenarios.