codeburn/tests/currency-rounding.test.ts
2026-06-03 10:45:39 +08:00

105 lines
4 KiB
TypeScript

import { describe, it, expect, beforeEach, afterEach } from 'vitest'
import { convertCost, roundForActiveCurrency, getFractionDigits } from '../src/currency.js'
import { CurrencyState } from '../src/currency.js'
import * as currencyMod from '../src/currency.js'
// We poke the module-level state directly via switchCurrency for these tests.
// Each test restores USD afterwards so it doesn't bleed.
async function setActive(code: string, rate: number): Promise<void> {
// switchCurrency does network + persistence; for unit tests we set the
// active state directly via the module's internal state. Since the module
// doesn't expose a setter, we go through getCurrency()'s state and patch.
// Instead use the public switchCurrency only when offline: nope, just
// exploit the fact that the module exports `getCurrency` which returns a
// ref. We can't easily mock fetch. So we test only convertCost (which uses
// active.rate) and rounding helpers — both pure functions of the state.
const state = currencyMod.getCurrency()
// @ts-expect-error — directly mutating for test
state.code = code
// @ts-expect-error
state.rate = rate
// @ts-expect-error
state.symbol = code
}
beforeEach(async () => {
await setActive('USD', 1)
})
afterEach(async () => {
await setActive('USD', 1)
})
describe('convertCost — no rounding contract', () => {
it('returns unrounded float for USD (rate=1)', () => {
expect(convertCost(1.234567)).toBe(1.234567)
expect(convertCost(0.001)).toBe(0.001)
})
it('returns unrounded float for non-USD currencies', async () => {
await setActive('JPY', 150)
// 1 USD * 150 = 150, but a fractional input must NOT be rounded by convertCost.
expect(convertCost(0.123456)).toBeCloseTo(18.5184, 4)
expect(convertCost(1.5)).toBe(225)
})
it('rounding is the caller\'s responsibility (display vs export)', async () => {
// Regression guard: previously convertCost did its own rounding which
// produced ¥412.37 in CSV exports while the dashboard rendered ¥412.
// Confirm we now return the raw value and the caller decides.
await setActive('JPY', 150)
const raw = convertCost(2.7491)
expect(raw).toBe(412.365) // unrounded
expect(roundForActiveCurrency(raw)).toBe(412) // currency-aware rounding for export
})
})
describe('roundForActiveCurrency', () => {
it('USD rounds to 2 decimals', async () => {
await setActive('USD', 1)
expect(roundForActiveCurrency(1.2345)).toBe(1.23)
expect(roundForActiveCurrency(1.235)).toBeCloseTo(1.24, 2)
expect(roundForActiveCurrency(0.005)).toBe(0.01)
})
it('JPY rounds to whole numbers', async () => {
await setActive('JPY', 150)
expect(roundForActiveCurrency(412.37)).toBe(412)
expect(roundForActiveCurrency(412.5)).toBe(413)
expect(roundForActiveCurrency(0.4)).toBe(0)
})
it('KRW rounds to whole numbers', async () => {
await setActive('KRW', 1300)
expect(roundForActiveCurrency(15999.7)).toBe(16000)
})
it('EUR rounds to 2 decimals like USD', async () => {
await setActive('EUR', 0.92)
expect(roundForActiveCurrency(1.2345)).toBe(1.23)
})
it('matches the display contract: roundForActiveCurrency(convertCost(x)) is what users see', async () => {
await setActive('JPY', 150)
// Dashboard displays via formatCost which uses getFractionDigits=0 for JPY.
// CSV exports must produce the same integer value, not a 2-decimal float.
expect(roundForActiveCurrency(convertCost(2.75))).toBe(413)
expect(roundForActiveCurrency(convertCost(2.745))).toBe(412)
})
})
describe('getFractionDigits', () => {
it('returns 0 for zero-fraction currencies', () => {
expect(getFractionDigits('JPY')).toBe(0)
expect(getFractionDigits('KRW')).toBe(0)
expect(getFractionDigits('CLP')).toBe(0)
})
it('returns 2 for typical currencies', () => {
expect(getFractionDigits('USD')).toBe(2)
expect(getFractionDigits('EUR')).toBe(2)
expect(getFractionDigits('GBP')).toBe(2)
expect(getFractionDigits('INR')).toBe(2)
expect(getFractionDigits('CNY')).toBe(2)
})
})