Deep Link Handler Unit and Route Tests
epic-push-notification-delivery-engine-task-015 — Write unit tests for NotificationDeepLinkHandler covering: valid payload resolves correct go_router route, missing resource ID falls back to safe default route, unknown category falls back gracefully, cold-start payload is captured and applied after auth, and role guard violations redirect appropriately. Mock Supabase client and go_router for deterministic test execution.
Acceptance Criteria
Technical Requirements
Execution Context
Tier 5 - 253 tasks
Can start after Tier 4 completes
Implementation Notes
Implement NotificationDeepLinkHandler route resolution as a pure function (or a class with no side effects) that takes a NotificationPayload and a UserRole and returns a String route. This makes it trivially unit-testable without mocking a router at all for the core logic tests. Reserve the mocked GoRouter tests for the navigation-side-effect tests (verifying GoRouter.go() is called with the correct argument). Define a sealed class or enum NotificationRouteResult with variants: Resolved(String route), Fallback(String reason), and RoleViolation(String redirectRoute) so test assertions are type-safe rather than string comparisons.
Use const test data fixtures defined at the top of the test file for all payload variants.
Testing Requirements
Pure unit tests (flutter_test) with no widget tree or real routing. Use mockito or mocktail to create MockGoRouter and MockSupabaseClient. Organize tests into describe groups matching each acceptance criterion. Use fakeAsync for the cold-start deferred navigation test to control the async timing of auth state arrival.
Parameterize the route resolution tests using a table-driven approach (list of input payloads → expected output routes) to ensure all category/role combinations are covered without repetitive test code. Add a test that verifies the route resolution map is exhaustive — i.e., every NotificationCategory enum value has a corresponding route entry.
Flutter's background message handler for FCM must run in a separate Dart isolate. Incorrect dependency initialization in the isolate (e.g., attempting to access Riverpod providers or Supabase before initialization) will cause silent crashes on Android when the app is terminated, resulting in missed notifications that are invisible in crash reporting.
Mitigation & Contingency
Mitigation: Use a minimal top-level background handler function annotated with @pragma('vm:entry-point') that only stores the raw RemoteMessage payload to a platform channel or shared preferences. Process the payload in the main isolate on next app launch. Write an explicit test for terminated-state message handling on Android.
Contingency: If isolate crashes are observed, implement a native Android FirebaseMessagingService subclass that handles background messages without Flutter isolate complexity, falling back to a database-insert-only approach for terminated-state notifications.
Supabase Edge Functions can experience cold-start latency of 1–3 seconds after periods of inactivity. For high-frequency events like assignment creation, cumulative cold starts could cause dispatch delays exceeding the 30-second SLA, reducing the perceived reliability of the notification system.
Mitigation & Contingency
Mitigation: Configure the Edge Function with a keep-warm ping mechanism or use Supabase database webhooks that invoke the function directly on row insert to minimize cold-start frequency. Batch preference lookups within the function to reduce per-invocation Supabase round-trips.
Contingency: If latency SLA is consistently breached, move to a polling or Realtime-subscription architecture within the Edge Function, or pre-compute dispatch targets at preference-save time to eliminate per-dispatch preference queries.
If the deep link handler does not perform server-side role validation before rendering the target screen, a peer mentor who receives a mis-configured notification payload containing a coordinator-only route could access restricted data, violating the role-based access control invariants.
Mitigation & Contingency
Mitigation: The deep link handler must check the user's current role from the RoleStateManager before constructing the navigation route. Coordinator-only routes must be listed in a deny-list checked against the current role. The go_router route guard is a second line of defence.
Contingency: If a role bypass is discovered in testing, immediately add the affected route to the deep link handler deny-list and add a regression test. Audit all notification payload types for route targets that could expose cross-role data.
FCM v1 HTTP API enforces per-project send quotas. For large organisations with many active peer mentors receiving simultaneous assignment notifications, batch dispatch events (e.g., bulk coordinator assignments) could approach quota limits and result in dropped notifications with 429 errors logged silently.
Mitigation & Contingency
Mitigation: Implement exponential backoff retry logic in the Edge Function for 429 responses. Design bulk assignment flows to dispatch notifications in batches with a configurable delay between batches. Monitor FCM console quotas during load testing.
Contingency: If quota limits are hit, implement a notification queue table in Supabase and a separate Edge Function that processes the queue with rate limiting, ensuring eventual delivery without exceeding FCM quotas.