My choices for refactoring the PaymentProcessor class includes;
By injecting the external dependencies through the constructor we decouple the business logic from specific implementations of infrastructure services.
Moved the data storage logic to PaymentRepository to avoid storing raw SQL queries in the processor.
Added PaymentCredentials to supply the API-key and user email to avoid having them hardcoded.
Made the SUCCESS and FAILURE messages into enums for limitation of status message options.
Improved robustness by adding input validation and using try-catch blocks to manage failures in external services.
By injecting dependencies, we can now easily provide "Mocks" or "Stubs" during testing.
This allows us to verify the behavior of PaymentProcessor without executing real payments or sending real emails.