Unit test ApprovalWorkflowService FSM transitions
epic-expense-approval-workflow-core-logic-task-008 — Write exhaustive unit tests for all ApprovalWorkflowService state transitions using flutter_test and mocked repository/service dependencies. Cover: happy-path transitions for each state change, guard failures (wrong state, wrong role, double-export), auto-approval vs. manual-approval branching, and notification emission verification. Achieve 100% branch coverage on the FSM.
Acceptance Criteria
Technical Requirements
Execution Context
Tier 6 - 158 tasks
Can start after Tier 5 completes
Implementation Notes
Organise the test file as `approval_workflow_service_test.dart` mirroring the source file location. Create a shared `_buildService()` factory helper that wires up all mocks to reduce boilerplate across test cases. For the auto-approval branching tests, parameterise with `@TestParameters` or use a local test data table (Map of threshold values to expected outcomes) to avoid duplicated test code. Ensure all mocks are reset between tests using `reset(mock)` in tearDown().
The 100% branch coverage target is achievable because the FSM is a closed set of conditions — every if/switch branch must have an explicit test for both the true and false outcomes. Run `flutter test --coverage && genhtml coverage/lcov.info` locally to visualise gaps before committing.
Testing Requirements
This task IS the testing work. Use flutter_test with mocktail for all repository and service mocks. Structure tests in a describe-style group() hierarchy: one group per transition method, with sub-groups for happy paths and failure paths. Use setUp() to initialise the service and mocks before each test.
Use verify() and verifyNever() for notification assertion. Use throwsA(isA
The ThresholdEvaluationService is described as shared Dart logic used both client-side and in the Edge Function. Supabase Edge Functions run Deno/TypeScript, not Dart, meaning the threshold logic must be maintained in two languages and can diverge, causing the server to reject legitimate client submissions.
Mitigation & Contingency
Mitigation: Implement the threshold logic as a single TypeScript module in the Edge Function and call it via a thin Dart HTTP client wrapper for client-side preview feedback only. The server is always authoritative; the client version is purely for UX (showing the user whether their claim will auto-approve before they submit).
Contingency: If dual-language maintenance is unavoidable, create a shared golden test file (JSON fixtures with inputs and expected outputs) that is run against both implementations in CI to detect divergence immediately.
A peer mentor could double-tap the submit button or a network retry could trigger a duplicate submission, causing the ApprovalWorkflowService to attempt two concurrent state transitions from draft→submitted for the same claim, potentially resulting in two audit events or conflicting statuses.
Mitigation & Contingency
Mitigation: Implement idempotency in the ApprovalWorkflowService using a database-level unique constraint on (claim_id, from_status, to_status) per transition, combined with a UI-level submission lock (disable button after first tap until response returns).
Contingency: Add a deduplication check at the start of every state transition method that returns the existing state if an identical transition is already in progress or completed within the last 10 seconds.
Claims with multiple expense lines (e.g., mileage + parking) must have their combined total evaluated against the threshold. If individual lines are added asynchronously or the evaluation runs before all lines are persisted, the auto-approval decision may be computed on an incomplete set of expense lines.
Mitigation & Contingency
Mitigation: The Edge Function always fetches all expense lines from the database (not from the client payload) before computing the threshold decision. Define a clear claim submission contract that requires all expense lines to be persisted before the submit action is called.
Contingency: Add a validation step in ApprovalWorkflowService that counts expected vs. persisted expense lines before allowing the transition, returning a validation error if lines are missing.