Move tests to __tests__ folders, add unit tests for shared utils and services

Restructure tests into __tests__/ directories at package root so they can
be excluded from production builds. Add unit tests for dates, currency,
lookup service, payment method default logic, and tax exemption state
transitions.

packages/shared/__tests__/utils/currency.test.ts

@@ -0,0 +1,68 @@
+import { describe, it, expect } from 'bun:test'
+import { formatCurrency, roundCurrency, toCents, toDollars } from '../../src/utils/currency.js'
+
+describe('formatCurrency', () => {
+  it('formats whole dollars', () => {
+    expect(formatCurrency(100)).toBe('$100.00')
+  })
+
+  it('formats cents', () => {
+    expect(formatCurrency(49.99)).toBe('$49.99')
+  })
+
+  it('formats zero', () => {
+    expect(formatCurrency(0)).toBe('$0.00')
+  })
+
+  it('formats thousands with comma', () => {
+    expect(formatCurrency(1234.56)).toBe('$1,234.56')
+  })
+
+  it('formats negative amounts', () => {
+    expect(formatCurrency(-25.50)).toBe('-$25.50')
+  })
+})
+
+describe('roundCurrency', () => {
+  it('rounds to 2 decimal places', () => {
+    expect(roundCurrency(1.005)).toBe(1.01)
+    expect(roundCurrency(1.004)).toBe(1)
+  })
+
+  it('handles already-rounded values', () => {
+    expect(roundCurrency(10.50)).toBe(10.50)
+  })
+
+  it('handles zero', () => {
+    expect(roundCurrency(0)).toBe(0)
+  })
+})
+
+describe('toCents', () => {
+  it('converts dollars to cents', () => {
+    expect(toCents(1.00)).toBe(100)
+    expect(toCents(49.99)).toBe(4999)
+  })
+
+  it('rounds fractional cents', () => {
+    // 1.005 * 100 = 100.49999... in IEEE 754, so Math.round gives 100
+    // This is a known floating point limitation — use toCents(roundCurrency(x)) for precision
+    expect(toCents(1.005)).toBe(100)
+    expect(toCents(1.006)).toBe(101)
+  })
+
+  it('handles zero', () => {
+    expect(toCents(0)).toBe(0)
+  })
+})
+
+describe('toDollars', () => {
+  it('converts cents to dollars', () => {
+    expect(toDollars(100)).toBe(1.00)
+    expect(toDollars(4999)).toBe(49.99)
+  })
+
+  it('handles zero', () => {
+    expect(toDollars(0)).toBe(0)
+  })
+})

packages/shared/__tests__/utils/dates.test.ts

@@ -0,0 +1,79 @@
+import { describe, it, expect } from 'bun:test'
+import { isMinor, capBillingDay, todayISO } from '../../src/utils/dates.js'
+
+describe('isMinor', () => {
+  it('returns true for a child born 10 years ago', () => {
+    const dob = new Date()
+    dob.setFullYear(dob.getFullYear() - 10)
+    expect(isMinor(dob)).toBe(true)
+  })
+
+  it('returns false for an adult born 25 years ago', () => {
+    const dob = new Date()
+    dob.setFullYear(dob.getFullYear() - 25)
+    expect(isMinor(dob)).toBe(false)
+  })
+
+  it('returns true for someone turning 18 later this year', () => {
+    const dob = new Date()
+    dob.setFullYear(dob.getFullYear() - 18)
+    dob.setMonth(dob.getMonth() + 1) // birthday is next month
+    expect(isMinor(dob)).toBe(true)
+  })
+
+  it('returns false for someone who turned 18 earlier this year', () => {
+    const dob = new Date()
+    dob.setFullYear(dob.getFullYear() - 18)
+    dob.setMonth(dob.getMonth() - 1) // birthday was last month
+    expect(isMinor(dob)).toBe(false)
+  })
+
+  it('returns false on their 18th birthday', () => {
+    const dob = new Date()
+    dob.setFullYear(dob.getFullYear() - 18)
+    expect(isMinor(dob)).toBe(false)
+  })
+
+  it('accepts a string date', () => {
+    expect(isMinor('2000-01-01')).toBe(false)
+    expect(isMinor('2020-01-01')).toBe(true)
+  })
+
+  it('returns true for a newborn', () => {
+    expect(isMinor(new Date())).toBe(true)
+  })
+})
+
+describe('capBillingDay', () => {
+  it('caps at 28', () => {
+    expect(capBillingDay(31)).toBe(28)
+    expect(capBillingDay(29)).toBe(28)
+  })
+
+  it('floors at 1', () => {
+    expect(capBillingDay(0)).toBe(1)
+    expect(capBillingDay(-5)).toBe(1)
+  })
+
+  it('passes through valid days', () => {
+    expect(capBillingDay(15)).toBe(15)
+    expect(capBillingDay(1)).toBe(1)
+    expect(capBillingDay(28)).toBe(28)
+  })
+
+  it('floors fractional days', () => {
+    expect(capBillingDay(15.7)).toBe(15)
+  })
+})
+
+describe('todayISO', () => {
+  it('returns YYYY-MM-DD format', () => {
+    const result = todayISO()
+    expect(result).toMatch(/^\d{4}-\d{2}-\d{2}$/)
+  })
+
+  it('matches today', () => {
+    const expected = new Date().toISOString().split('T')[0]
+    expect(todayISO()).toBe(expected)
+  })
+})