Summary

This PR adds unit tests to cover error handling and authorization scenarios that were previously missing from the test suite. The changes include:

• RequestExceptionTest: Tests that verify proper exception message formatting for various HTTP error codes (400, 404, 500)
• LoggingInterceptorTest: Tests for the interceptor's behavior on successful and failed HTTP responses (401, 403, 404, 422, 500)
• SettingsTest: Tests for Basic Auth header generation, OAuth token management, and settings population
• AuthorizationTest: Comprehensive tests organized into nested classes covering private transaction access, token authorization, scope authorization, and transaction ID validation scenarios

Also adds necessary test infrastructure: JUnit 5, Mockito dependencies, and Maven Surefire plugin 3.2.5 for JUnit 5 support.

All 37 tests pass locally.

Review & Testing Checklist for Human

• Verify test coverage matches requirements: The tests primarily verify that RequestException properly formats error messages from mocked HTTP responses. Confirm this level of testing is sufficient for "error handling for valid transaction IDs" and "authorization checks for commenting on private transactions"
• Review AuthorizationTest scope: These tests verify exception message content but don't test the actual Application class methods (callTheApi(), processCallback()) that handle these errors - confirm if integration-level tests are needed
• Check dependency versions: Verify JUnit 5.10.2 and Mockito 5.11.0 are acceptable versions for this project

Recommended test plan: Run mvn test locally to verify all tests pass, then review CI results after merge.

Notes

Link to Devin run: https://app.devin.ai/sessions/314afe9bce134296baf3ce994cc049d5
Requested by: Jack (@jack-killian)