feat: add MSW for integration test mocking

Install Mock Service Worker (MSW) and configure it for vitest.
Write one integration test for usePurchases hook using MSW.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

package.json

@@ -34,6 +34,7 @@
     "eslint-plugin-react-refresh": "^0.5.2",
     "globals": "^17.4.0",
     "jsdom": "^25.0.1",
+    "msw": "^2.12.14",
     "tailwindcss": "^4.0.0",
     "typescript": "^5.7.3",
     "typescript-eslint": "^8.56.1",

src/hooks/__tests__/useApi.test.tsx

@@ -0,0 +1,45 @@
+import { renderHook, waitFor } from '@testing-library/react'
+import { QueryClient, QueryClientProvider } from '@tanstack/react-query'
+import { usePurchases } from '../useApi'
+import { http, HttpResponse } from 'msw'
+import { server } from '../../test/mocks/server'
+
+function createWrapper() {
+  const queryClient = new QueryClient({
+    defaultOptions: { queries: { retry: false } },
+  })
+  return function Wrapper({ children }: { children: React.ReactNode }) {
+    return (
+      <QueryClientProvider client={queryClient}>
+        {children}
+      </QueryClientProvider>
+    )
+  }
+}
+
+describe('useApi hooks', () => {
+  describe('usePurchases', () => {
+    it('fetches and returns purchases', async () => {
+      const { result } = renderHook(() => usePurchases(), { wrapper: createWrapper() })
+
+      await waitFor(() => expect(result.current.isSuccess).toBe(true))
+
+      expect(result.current.data).toHaveLength(1)
+      expect(result.current.data![0]).toMatchObject({
+        id: 'pur_1',
+        storeName: 'Kroger',
+        total: 42.5,
+      })
+    })
+
+    it('returns an error when the endpoint fails', async () => {
+      server.use(
+        http.get('/api/v1/purchases', () => HttpResponse.error()),
+      )
+
+      const { result } = renderHook(() => usePurchases(), { wrapper: createWrapper() })
+
+      await waitFor(() => expect(result.current.isError).toBe(true))
+    })
+  })
+})

src/test/mocks/handlers.ts

@@ -0,0 +1,65 @@
+import { http, HttpResponse } from 'msw'
+import type { Purchase, Product, Coupon, PriceAlert } from '../../types/api.ts'
+
+const mockPurchases: Purchase[] = [
+  {
+    id: 'pur_1',
+    storeId: 'store_1',
+    storeName: 'Kroger',
+    date: '2024-01-15',
+    total: 42.5,
+    items: [
+      { id: 'item_1', productId: 'prod_1', name: 'Milk', quantity: 1, price: 3.99, unitPrice: 3.99 },
+      { id: 'item_2', productId: 'prod_2', name: 'Bread', quantity: 2, price: 5.98, unitPrice: 2.99 },
+    ],
+  },
+]
+
+const mockProducts: Product[] = [
+  {
+    id: 'prod_1',
+    name: 'Whole Milk',
+    brand: 'Kroger',
+    category: 'Dairy',
+    prices: [{ storeId: 'store_1', storeName: 'Kroger', price: 3.99, lastUpdated: '2024-01-15' }],
+  },
+  {
+    id: 'prod_2',
+    name: 'Whole Wheat Bread',
+    brand: 'Nature\'s Own',
+    category: 'Bakery',
+    prices: [{ storeId: 'store_1', storeName: 'Kroger', price: 2.99, lastUpdated: '2024-01-15' }],
+  },
+]
+
+const mockCoupons: Coupon[] = [
+  {
+    id: 'coupon_1',
+    productId: 'prod_1',
+    storeName: 'Kroger',
+    description: '$1 off milk',
+    discount: '$1.00',
+    expiresAt: '2024-12-31',
+    code: 'MILK1',
+  },
+]
+
+const mockAlerts: PriceAlert[] = [
+  {
+    id: 'alert_1',
+    productId: 'prod_1',
+    productName: 'Whole Milk',
+    targetPrice: 2.99,
+    currentPrice: 3.99,
+    triggered: false,
+  },
+]
+
+export const handlers = [
+  http.get('/api/v1/health', () => HttpResponse.json({ status: 'ok' })),
+  http.get('/api/v1/purchases', () => HttpResponse.json(mockPurchases)),
+  http.get('/api/v1/products', () => HttpResponse.json(mockProducts)),
+  http.get('/api/v1/products/prod_1', () => HttpResponse.json(mockProducts[0])),
+  http.get('/api/v1/coupons', () => HttpResponse.json(mockCoupons)),
+  http.get('/api/v1/price-alerts', () => HttpResponse.json(mockAlerts)),
+]

src/test/mocks/server.ts

@@ -0,0 +1,4 @@
+import { setupServer } from 'msw/node'
+import { handlers } from './handlers'
+
+export const server = setupServer(...handlers)

src/test/setup.ts

@@ -1 +1,6 @@
 import '@testing-library/jest-dom/vitest'
+import { server } from './mocks/server'
+
+beforeAll(() => server.listen())
+afterEach(() => server.resetHandlers())
+afterAll(() => server.close())