test: add exchange rate utility coverage

apps/web/__tests__/lib/currency/exchange-rates.test.ts

@@ -0,0 +1,87 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
+
+describe('exchange rate utilities', () => {
+  beforeEach(() => {
+    vi.resetModules();
+    vi.unstubAllGlobals();
+  });
+
+  afterEach(() => {
+    vi.restoreAllMocks();
+    vi.unstubAllGlobals();
+  });
+
+  it('returns API rates and caches them for subsequent calls', async () => {
+    const fetchMock = vi.fn().mockResolvedValue({
+      ok: true,
+      json: async () => ({
+        result: 'success',
+        rates: { USD: 1, EUR: 0.9, GBP: 0.8 },
+      }),
+    });
+    vi.stubGlobal('fetch', fetchMock);
+
+    const { getExchangeRates } = await import('@/lib/currency/exchange-rates');
+
+    const first = await getExchangeRates();
+    const second = await getExchangeRates();
+
+    expect(first).toEqual({ USD: 1, EUR: 0.9, GBP: 0.8 });
+    expect(second).toEqual(first);
+    expect(fetchMock).toHaveBeenCalledTimes(1);
+  });
+
+  it('falls back to static rates when the API is unavailable', async () => {
+    vi.stubGlobal('fetch', vi.fn().mockRejectedValue(new Error('network down')));
+
+    const { getExchangeRates } = await import('@/lib/currency/exchange-rates');
+    const rates = await getExchangeRates();
+
+    expect(rates.USD).toBe(1);
+    expect(rates.EUR).toBeGreaterThan(0);
+    expect(rates.JPY).toBeGreaterThan(0);
+  });
+
+  it('converts currencies using fetched rates', async () => {
+    vi.stubGlobal(
+      'fetch',
+      vi.fn().mockResolvedValue({
+        ok: true,
+        json: async () => ({
+          result: 'success',
+          rates: { USD: 1, EUR: 0.8, GBP: 0.5 },
+        }),
+      })
+    );
+
+    const { convertCurrency } = await import('@/lib/currency/exchange-rates');
+    const converted = await convertCurrency(80, 'EUR', 'GBP');
+
+    expect(converted).toBe(50);
+  });
+
+  it('returns the original amount for unknown currencies', async () => {
+    vi.stubGlobal(
+      'fetch',
+      vi.fn().mockResolvedValue({
+        ok: true,
+        json: async () => ({
+          result: 'success',
+          rates: { USD: 1, EUR: 0.9 },
+        }),
+      })
+    );
+
+    const { convertCurrency } = await import('@/lib/currency/exchange-rates');
+    await expect(convertCurrency(25, 'EUR', 'ZZZ')).resolves.toBe(25);
+  });
+
+  it('converts synchronously with pre-fetched rates', async () => {
+    const { convertToBase } = await import('@/lib/currency/exchange-rates');
+    const rates = { USD: 1, EUR: 0.8, GBP: 0.5 };
+
+    expect(convertToBase(80, 'EUR', 'USD', rates)).toBe(100);
+    expect(convertToBase(80, 'EUR', 'GBP', rates)).toBe(50);
+    expect(convertToBase(10, 'USD', 'USD', rates)).toBe(10);
+  });
+});