Write unit tests for SessionResumeManager lifecycle and routing logic
epic-biometric-session-authentication-ui-and-lifecycle-task-013 — Write unit tests for SessionResumeManager covering: lifecycle observer registration and teardown, debounce prevents duplicate prompts within the debounce window, expired session routes to credential login, valid session with biometrics available routes to BiometricPromptOverlay, valid session without biometrics routes to BiometricUnavailableBanner, and revocation flow clears all credentials atomically.
Acceptance Criteria
Technical Requirements
Execution Context
Tier 3 - 413 tasks
Can start after Tier 2 completes
Implementation Notes
SessionResumeManager should accept its dependencies (SecureStorage, CredentialStore, AppRouter, BiometricStatusChecker, clock/ticker for debounce) through constructor injection — not via service locator — to make unit testing straightforward. The debounce timer should use a Ticker or a clock abstraction rather than calling DateTime.now() directly, so fake_async can control time. For atomicity in the revocation flow, wrap deleteAll() and clear() in a try/catch that rolls back or surfaces an error before calling navigate(). Avoid catching broad Exception types — be explicit about storage-layer exceptions.
Testing Requirements
Pure Dart unit tests using flutter_test (no widget pump needed). Use fake_async package to control time for debounce assertions — never use real Future.delayed or sleep in tests. Mock WidgetsBinding using a FakeWidgetsBinding or pass the observer management methods as injectable callbacks to avoid tight coupling with the Flutter engine. Verify call order on mocks (e.g., deleteAll before navigate) using mocktail's verifyInOrder.
Each test case should be isolated with setUp/tearDown creating fresh manager instances. Target 100% line and branch coverage for SessionResumeManager.
Flutter's AppLifecycleState.resumed event fires in scenarios beyond simple user-initiated app-switching: it also fires when the native biometric dialog itself dismisses and returns control to Flutter, when system alerts (low battery, notifications) temporarily cover the app, and when the app is foregrounded by a deep link. Without careful debouncing and state tracking, SessionResumeManager can trigger multiple overlapping biometric prompts or prompt immediately after a just-completed authentication, creating a confusing loop.
Mitigation & Contingency
Mitigation: Implement a state machine inside SessionResumeManager with explicit states (idle, prompting, authenticated, awaiting-fallback) and guard all prompt triggers with a state check. Add a minimum inter-prompt interval of 3 seconds. Write widget tests that simulate rapid lifecycle event sequences and verify only one prompt is shown.
Contingency: If the state machine approach proves difficult to test or maintain, replace it with a simple boolean isPromptActive flag with a debounce timer, accepting slightly less precise semantics in exchange for simpler reasoning about concurrent lifecycle events.
The BiometricPromptOverlay appears on top of the existing app content when the app resumes. If focus is not correctly transferred to the overlay and returned to the underlying screen after authentication, screen reader users (VoiceOver/TalkBack) will either be unable to interact with the prompt or will lose their navigation position in the app after authentication completes, violating WCAG 2.2 focus management requirements and creating a broken experience for Blindeforbundet users.
Mitigation & Contingency
Mitigation: Use Flutter's FocusScope and FocusTrap utilities to capture focus within the overlay on presentation and restore the previous FocusNode after dismissal. Add a live region announcement (using the accessibility live region announcer component) when the overlay appears. Include dedicated VoiceOver and TalkBack test cases in the acceptance criteria.
Contingency: If FocusTrap behaviour proves unreliable across Flutter versions, implement the overlay as a full Navigator push to a modal route rather than an overlay widget, which gives Flutter's built-in modal semantics and focus management automatic WCAG-compliant behaviour.
The BiometricUnavailableBanner needs to deep-link to biometric enrollment settings on both iOS and Android. iOS uses a single URL scheme (app-settings:) that opens the app's settings page. Android has no universal URL for biometric settings — the correct Intent action (Settings.ACTION_BIOMETRIC_ENROLL) was introduced in API 30, with different fallback actions required for API 23-29. Using the wrong action on older Android devices either crashes or navigates to an unrelated settings screen.
Mitigation & Contingency
Mitigation: Build an Android API version check into LocalAuthIntegration that selects the correct Intent action based on the runtime SDK version. Test against Android API 23, 28, and 30+ in the CI matrix. For iOS, validate that the app-settings: URL scheme is correctly declared.
Contingency: If the Android settings Intent fragmentation cannot be resolved reliably for all target API levels, fall back to navigating to the top-level Settings screen (Settings.ACTION_SETTINGS) with an overlay instruction telling the user to navigate to 'Security > Biometrics' manually, ensuring the user always has a path to resolve the issue even if the deep link is imprecise.