[test] Extend Refund Regression Tests
This adds regression tests around various refund paths. It does not yet cover add/withdraw when affiliate is set, but I will add those in a subsequent pass after this is merged.
As of 2024-05-14 a change has been implemented to enforce access token expiry. If you see higher numbers of HTTP 401 responses, please check tokens that may have expired. For more details, including how to mitigate disruption, please check our docs guide on Expired Access Tokens. If you have a support contract, you may open a support ticket for additional assistance.
This adds regression tests around various refund paths. It does not yet cover add/withdraw when affiliate is set, but I will add those in a subsequent pass after this is merged.