Write unit tests for AccessibilityAuditService
epic-screen-reader-support-core-services-task-013 — Write flutter_test widget tests using AccessibilityTestHarness for AccessibilityAuditService. Create test widget trees with known violations (unlabelled button, missing role, small touch target) and assert the audit report contains the expected violation entries. Also test clean trees produce zero violations. Verify report structure fields are correctly populated.
Acceptance Criteria
Technical Requirements
Execution Context
Tier 2 - 518 tasks
Can start after Tier 1 completes
Implementation Notes
AccessibilityAuditService likely traverses the semantics tree using SemanticsNode.visitChildren(). In tests, the semantics tree is only populated after tester.pumpAndSettle() + tester.ensureSemantics(). Create a reusable helper buildViolatingTree(type: ViolationType) that returns the minimal widget for each violation type — this makes tests readable and reduces duplication. For the touch target size test, be aware that Flutter's default minimum tap target enforcement (GestureBinding.instance.resamplingEnabled, or MaterialTapTargetSize) may automatically upscale some targets — use a raw GestureDetector inside a SizedBox to bypass this.
For the 'missing role' test, verify what AccessibilityAuditService considers a 'role' — it may be a Semantics(role: ...) property or a combination of flags. Align the test expectation with the actual service implementation rather than assumptions.
Testing Requirements
Pure flutter_test suite using testWidgets. Call tester.ensureSemantics() at the start of each test to activate the semantics tree. Build the minimum widget tree that reproduces the violation being tested — e.g., for the touch target test, use a SizedBox(width: 20, height: 20, child: GestureDetector(onTap: () {})). For the clean tree test, use a fully labelled, role-assigned, adequately sized widget.
Assert on typed fields of AuditViolation, not string matches. Group tests as: 'violation detection', 'clean tree', 'report structure', 'edge cases (ExcludeSemantics)'. Document the minimum touch target size constant (44dp) used in assertions as a shared const to keep tests in sync with the service implementation.
Flutter's build pipeline and SemanticsService.announce() operate asynchronously. Announcements triggered too early (before the semantic tree settles) may be swallowed silently on both platforms, causing acceptance criteria around the 500ms window to fail intermittently in CI and on device, which would block pilot launch.
Mitigation & Contingency
Mitigation: Implement the LiveRegionAnnouncer with a post-frame callback delay and an internal timing guard. Write integration tests using WidgetTester.pump() sequences that verify announcement delivery across multiple frame boundaries. Validate on physical devices at each sprint boundary, not only in CI.
Contingency: If consistent announcement timing cannot be achieved within Flutter's semantic pipeline, switch to a platform channel approach that calls native UIAccessibility.post (iOS) and AccessibilityManager.announce (Android) directly, bypassing Flutter's intermediary.
Flutter does not natively emit a focus-gain event to Dart code when VoiceOver or TalkBack moves focus to a specific widget. If the intercept mechanism for the SensitiveFieldWarningDialog relies on an unsupported or undocumented hook in the semantics tree, it may miss focus events for some field types or in some navigation contexts, leaving sensitive data unprotected.
Mitigation & Contingency
Mitigation: Prototype the focus-intercept mechanism during the first sprint of this epic, before building the dialog UI. Evaluate Flutter's SemanticsBinding.instance callbacks and custom SemanticsActions as intercept points. Document the chosen mechanism with platform compatibility notes.
Contingency: If no reliable focus-intercept is available, implement an alternative where sensitive fields show a static 'Screen reader active — tap to reveal' overlay instead of an OS dialog, which is less seamless but achieves equivalent privacy protection without relying on an unreliable event hook.
The AccessibilityTestHarness depends on internal flutter_test semantic tree APIs that can change between Flutter minor versions. If the project upgrades Flutter during this epic, the harness may break silently, causing CI accessibility tests to pass while actually skipping assertions.
Mitigation & Contingency
Mitigation: Pin the Flutter SDK version in pubspec.yaml for the duration of this epic. Document which flutter_test APIs are used and their stability tier. Add a canary test that explicitly fails if the semantic tree API surface changes.
Contingency: If a forced Flutter upgrade breaks the harness, prioritise patching the harness as a blocking task before any other epic work continues, using the canary test failure as the trigger.