Integration tests for aggregation, BLoC, and screen assembly

Structure the test file into three sections matching the three layers under test: (1) AggregationService tests — pure unit tests with no Flutter framework, using dart:test group(); (2) BLoC tests — using bloc_test's blocTest() macro with act/expect; (3) Widget tests — using flutter_test's testWidgets() with pumped widget trees. For AggregationService parallel failure tests, use Completer objects to simulate delayed repository responses and verify that Future.wait([...]) error semantics are handled correctly (i.e., a single failure does not cancel other in-flight fetches if using Future.wait(eagerError: false) or a custom gather utility). For widget navigation tests, inject a MockGoRouter via a Provider override and assert the push method was called with the expected arguments — avoid relying on real navigation stack changes in widget tests. Define a shared buildTestWidget(BLoC bloc) helper that wraps PeerMentorDetailScreenWidget with all required Providers (BlocProvider, GoRouter, localization) to reduce boilerplate across test cases.

Use the bloc_test package for all BLoC state transition tests — do not use raw StreamController mocking. Use mocktail for repository mocks (preferred over mockito for null-safety ergonomics). For widget tests, inject the BLoC via BlocProvider with a MockBLoC created using bloc_test's MockBloc. Use whenListen to pre-seed BLoC states for widget rendering tests.

For navigation tests, use GoRouter's testing overrides or a custom NavigatorObserver to capture push calls. For the aggregation service parallel fetch tests, use Future.wait with mocked async delays to verify partial failure handling. Run all tests with flutter test --coverage and assert >= 85% line coverage on BLoC and screen widget files.