We have our own REST API service which gives access to PayPal payments from different websites of our company. So our REST API communicates with PayPal REST API. Each time we want to release new version - we performing manual testing of our REST API against PayPal sandbox. It is not end-to-end testing since we have no web interface yet. We used Postman in order to send queries to our REST API which obviously is not handy and time consuming.
At some point we decided to automate those tests. And everything was easy before the moment when customer should login and confirm suggested payment. We automated that with our own Web Client which just simulates customer activity without opening site in the browser. It was working fine until PayPal changed UI for customers. We may fix code of our Web Client in order to support newest UI, but it doesn't sound as a good option since PayPal may change UI again and it is quite expensive to write such client.
So, my question is the following: is there effective way to login to PayPal sandbox website in order to confirm payment as customer (programmatically from full-integration tests, without opening site in browser)?
