Can I make test bookings on my portal first to check everything works before I let real customers on it?

Yes, in almost every case you can test your portal before you open it to the public. A new white label portal is usually set up in a test mode first, where searches and bookings run against the supplier test systems rather than their live ones. That means you can walk through a whole booking from search to confirmation without anything really being ticketed and without any money moving.

How realistic that test feels does depend on the supplier and on what is included in your plan. Some suppliers give a proper test environment that behaves much like the live one. Others give test data that is made up or out of date, so you may see strange availability or odd results that would never appear once you are live. And a few suppliers do not offer a test environment at all, so the only honest way to check them is a small real booking that you cancel yourself afterwards, which can mean a cancellation or ticketing cost depending on the fare rules.

When you do test, try to cover the whole journey rather than just a search. Check that your markup is applied the way you expect, that the payment page works with your own payment setup, that the confirmation email and the voucher carry your company name, that a customer can log in and see the booking, and that you can cancel or amend it from your agent side. Mistakes nearly always show up at those later steps, not in the search.

Before you go live, ask which of the suppliers on your plan have a working test environment and which ones will need a real booking to prove, then write a short list of the scenarios you want to see pass and keep it until every one of them is signed off.