Write unit tests for LocalAuthIntegration
epic-biometric-session-authentication-foundation-task-011 — Write flutter_test unit tests for LocalAuthIntegration using a mocked LocalAuthentication. Cover: isAvailable returns false when device has no biometrics, getAvailableBiometrics maps local_auth enums to domain BiometricType correctly, authenticate returns success on happy path, all LocalAuthException subtypes map to correct LocalAuthFailure domain codes, authenticate returns LocalAuthFailure.cancelled on user cancel.
Acceptance Criteria
Technical Requirements
Execution Context
Tier 3 - 413 tasks
Can start after Tier 2 completes
Implementation Notes
Because LocalAuthentication is a concrete class from a plugin (not an interface), mocking it directly with mockito requires @GenerateMocks([LocalAuthentication]) and running build_runner. An alternative that avoids codegen is to wrap LocalAuthentication behind a thin ILocalAuthPlugin interface with a real adapter — then the test can use a hand-written fake implementing ILocalAuthPlugin. This approach is recommended if the project does not already use build_runner for mockito. For the BiometricType mapping test, pass a list containing all known local_auth BiometricType values and assert the domain list matches exactly.
For the cancelled test: local_auth returns false (not an exception) when the user dismisses the dialog — the implementation should treat a false return as LocalAuthFailure.cancelled. Ensure this case is covered explicitly as it is easy to miss.
Testing Requirements
Pure unit tests with flutter_test. Group by method: isAvailable (3 cases), getAvailableBiometrics (4 cases), authenticate (7 cases). For PlatformException-based failures, construct PlatformException(code: 'NotEnrolled') etc. to simulate local_auth error codes — verify the LocalAuthFailure mapper produces the exact expected variant.
Use expect(result.isFailure, isTrue) and expect(result.failure, isA
iOS Keychain access requires correct entitlement configuration and provisioning profile setup. Misconfigured entitlements cause silent failures in CI/CD and on physical devices, where the plugin appears to work in the simulator but fails at runtime. This can delay foundation delivery and block all downstream epics.
Mitigation & Contingency
Mitigation: Add a dedicated integration test running on a physical iOS device early in the epic. Document required entitlements and provisioning steps in a developer runbook. Validate Keychain access in the CI pipeline using an iOS simulator with correct entitlements enabled.
Contingency: If Keychain entitlements cannot be resolved quickly, temporarily use in-memory storage behind the SecureSessionStorage interface to unblock downstream epics, then resolve the Keychain issue in a hotfix before release.
The Flutter local_auth plugin has a history of breaking API changes between major versions, and its Android implementation depends on BiometricPrompt which behaves differently across Android API levels (23-34). An incompatible plugin version or unexpected Android API behaviour can cause authentication failures on a significant portion of the target device fleet.
Mitigation & Contingency
Mitigation: Pin local_auth to a specific stable version in pubspec.yaml. Test against Android API levels 23, 28, and 33 in the CI matrix. Review the plugin changelog and migration guide before adopting any version bump.
Contingency: If the pinned version proves incompatible with target devices, evaluate flutter_local_auth_android as a replacement or fork the plugin adapter to isolate the breaking surface.
If users upgrade from a version of the app that stored session data in non-encrypted storage (SharedPreferences), a migration path is required. Failing to migrate silently leaves old tokens in plain storage, creating a security gap and potentially causing confusing authentication state on first launch of the new version.
Mitigation & Contingency
Mitigation: Audit existing storage usage across the codebase before writing SecureSessionStorage. If legacy plain storage keys exist, implement a one-time migration routine that reads from SharedPreferences, writes to Keychain/Keystore, and deletes the plain-text entry.
Contingency: If migration is discovered late, ship the migration as a mandatory patch release before the biometric feature is enabled for users, and add a startup check that blocks biometric opt-in until migration is confirmed complete.