feat(WHE-18): implement money, billing period, and typed domain ids

packages/domain/src/billing-period.test.ts

@@ -0,0 +1,39 @@
+import { describe, expect, test } from 'bun:test'
+
+import { DOMAIN_ERROR_CODE, DomainError } from './errors'
+import { BillingPeriod } from './billing-period'
+
+describe('BillingPeriod', () => {
+  test('parses canonical YYYY-MM format', () => {
+    const period = BillingPeriod.fromString('2026-03')
+
+    expect(period.year).toBe(2026)
+    expect(period.month).toBe(3)
+    expect(period.toString()).toBe('2026-03')
+  })
+
+  test('rejects malformed format', () => {
+    expect(() => BillingPeriod.fromString('2026/03')).toThrow(
+      new DomainError(
+        DOMAIN_ERROR_CODE.INVALID_BILLING_PERIOD,
+        'Billing period must match YYYY-MM: 2026/03'
+      )
+    )
+  })
+
+  test('navigates next and previous correctly', () => {
+    const december = BillingPeriod.from(2026, 12)
+
+    expect(december.next().toString()).toBe('2027-01')
+    expect(december.previous().toString()).toBe('2026-11')
+  })
+
+  test('compares periods', () => {
+    const left = BillingPeriod.from(2026, 3)
+    const right = BillingPeriod.from(2026, 4)
+
+    expect(left.compare(right)).toBe(-1)
+    expect(right.compare(left)).toBe(1)
+    expect(left.compare(BillingPeriod.from(2026, 3))).toBe(0)
+  })
+})