Backend tests mock external services calls.

[ianliuwk1019]

Some backend tests, (especially the test_router_[xyz] router tests), depending on the setup scenarios, can indirectly calls external services during testing.

Other than the tests really are testing on external services integration, for other tests that are only for FAM system business rules, we should find a way to mock the external service calls and return expected mock objects depending on tests needs. That will improve testing speed, avoid coupling and relying on external services for test passing, and also avoid using real "number/id" or "user credential" for setting up tests (security and privacy reason).

So far the external services includes:

• integration/forest_client
• integration/idim_proxy
• integraiton/gc_notify (not being used yet)

Just a thought: This tasks might somewhat tricky or hidden on finding what external services is/are being used in tests scenarios, we can focus on just for mocking first the "forest_cliet" service.

Acceptance Criteria

• Mock the external service calls (indirectly) for tests so they don't call external services.

Additional context

• Add any other context about the task here.