Unit test filter service and read state service

For testing the optimistic update emission sequence, use a StreamController or a fake repository that delays resolution. Emit from the service, capture emitted values in a list via stream.listen(), then resolve the fake repository — assert the optimistic value appeared before the repository resolved. For rollback, use mocktail's when().thenThrow() to simulate repository failure, then verify the service emits the rollback signal. For role scope tests, construct NotificationFilter predicates for each role and assert that notifications outside the role's scope are excluded.

Use const constructors for test notification fixtures to keep tests readable. Group tests with descriptive group() labels: 'role scope filtering', 'type predicate', 'read-state predicate', 'optimistic update', 'rollback', 'mark-all-read'. Use setUp() to reset mocks between tests.

Pure unit tests using flutter_test and mocktail. No widget or integration tests in this task. Test structure: one test file per service class, grouped with group() blocks per scenario category. For Role-Aware Notification Filter Service: test each role scope independently, test type filters (assignment_reminder, certification_expiry, pause_status, scenario_prompt), test read-state filters (all/unread/read), test combined type+read-state predicates, test empty input list.

For Notification Read State Service: test optimistic stream emission ordering using StreamController fakes, test rollback on mock repository .throws(), test read_at extraction from mock response, test mark-all-read with list of 0, 1, and N items. Use lcov or flutter test --coverage to verify 90%+ line coverage.