You can test all your connections, and not just reservation connections by connecting to the Booking.com test entry points located at tls12-secure-supply-xml.booking.com.
Please test all endpoints from your system via this domain entry point to confirm that they work properly. Following the test, revert your system back to the original domain entry point as we will shut this entry point shortly after the deadline (30th of June 2018).
Please note that these test entry points connect to the normal production servers. Therefore all transactions (requests or updates) sent will be treated like real transactions.