feat(domain): unit test infrastructure + expenses logic coverage

[LogenNineFingersIsAlive]

Summary

Adds unit testing infrastructure to the domain package with coverage reporting in CI.

What changed

New: expenses-logic.ts (pure logic extraction)

Extracted all pure business logic functions from expenses.service.ts into a separate, testable module:

• normalizeTransferDirection, normalizeExpenseKind, normalizeCounterpartyType
• assertPositiveAmountMinor, isTransferKind
• deriveExpenseKind — kind derivation from category + request
• computeRecoverableMinor — reimbursement recovery calculation
• deriveReimbursementStatus — state machine (none → expected → partial → settled / written_off)
• enrichExpensesWithReimbursements — batch enrichment
• resolveReimbursableDefaults — category mode → row reimbursable resolution
• validateAndResolveMyShareMinor — share validation with boundary checks

New: 72 unit tests (expenses-logic.test.ts)

Covers all extracted functions with edge cases:

• normalisation of invalid/null/undefined inputs
• positive amount validation (0, negative, float rejection)
• kind derivation across expense/income/transfer categories
• reimbursement status transitions through all states
• reimbursable default resolution across all category modes
• myShare validation boundaries

Coverage reporting

• expenses-logic.ts: 100% statements, branches, functions, lines
• Domain package baseline: ~5% overall (repositories + other services untested at unit level — covered by existing integration tests in tests/domain/)

CI changes

• Added Domain unit tests + coverage step after existing test step
• Coverage artifact uploaded per run (14-day retention)
• No hard coverage threshold yet — establishing baseline first

Files

• packages/domain/src/services/expenses-logic.ts (new)
• packages/domain/src/services/__tests__/expenses-logic.test.ts (new)
• packages/domain/src/services/expenses.service.ts (imports from logic module, no behaviour change)
• packages/domain/package.json (vitest + coverage deps)
• packages/domain/vitest.config.ts (new)
• .github/workflows/ci.yml (coverage step + artifact)
• pnpm-lock.yaml

Notes

• Existing CLI test accepts monzo sync --override syntax fails locally only due to live Monzo connection in dev DB — passes in CI (clean DB). Pre-existing, not caused by this PR.
• Existing integration tests in tests/domain/ continue to pass unchanged.

[Copilot]

Pull request overview

This pull request establishes unit testing infrastructure for the domain package by extracting pure business logic from expenses.service.ts into a separate testable module. This is the first instance of unit tests at the package level, with existing integration tests remaining in the tests/domain/ directory.

Changes:

• Extracted 8 pure business logic functions from expenses service into expenses-logic.ts for testability
• Added 72 comprehensive unit tests covering all edge cases including normalization, validation, kind derivation, and reimbursement state transitions
• Configured Vitest with coverage reporting in CI pipeline (14-day artifact retention)

Reviewed changes

Copilot reviewed 6 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
packages/domain/src/services/expenses-logic.ts	New module containing pure business logic functions extracted from expenses service - no I/O or database operations
packages/domain/src/services/__tests__/expenses-logic.test.ts	Comprehensive test suite with 72 tests achieving 100% coverage of the logic module
packages/domain/src/services/expenses.service.ts	Refactored to import functions from expenses-logic module, removing 264 lines of duplicated logic
packages/domain/vitest.config.ts	New Vitest configuration for domain package unit tests with v8 coverage provider
packages/domain/package.json	Added vitest and @vitest/coverage-v8 dev dependencies with test scripts
.github/workflows/ci.yml	Added domain unit test step with coverage artifact upload
pnpm-lock.yaml	Locked new testing dependencies including vitest 3.2.4 and coverage tooling

Files not reviewed (1)

• pnpm-lock.yaml: Language not supported

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