You can get the MasterCard test card number from your project dashboard. Log in to your dashboard and on the left of the dashboard, click on the test data on the left panel and you you can select Visa DIrect (PullFunds Transactions POST, PushFunds Transactions POST, and Transaction Query). PAAI (General Inquiry and Funds Transfer Inquiry).
Real payment methods must be used in the production environment. Test values from the sandbox testing page will not work. This means that every test transaction that you allow to settle in your production account will debit funds from the associated payment method and fees will be assessed.