chore: set up vitest and add zod

mvp/b2c/package.json

@@ -11,7 +11,10 @@
     "db:migrate": "drizzle-kit migrate",
     "db:push": "drizzle-kit push",
     "db:studio": "drizzle-kit studio",
-    "db:seed": "tsx src/db/seed.ts"
+    "db:seed": "tsx src/db/seed.ts",
+    "test": "vitest run",
+    "test:watch": "vitest",
+    "test:coverage": "vitest run --coverage"
   },
   "dependencies": {
     "@tailwindcss/postcss": "^4.3.0",
@@ -21,17 +24,20 @@
     "postgres": "^3.4.9",
     "react": "19.2.4",
     "react-dom": "19.2.4",
-    "tailwindcss": "^4.3.0"
+    "tailwindcss": "^4.3.0",
+    "zod": "^4.4.3"
   },
   "devDependencies": {
     "@types/node": "^20",
     "@types/react": "^19",
     "@types/react-dom": "^19",
+    "@vitest/coverage-v8": "^4.1.7",
     "dotenv": "^17.4.2",
     "drizzle-kit": "^0.31.10",
     "eslint": "^9",
     "eslint-config-next": "16.2.6",
     "tsx": "^4.22.3",
-    "typescript": "^5"
+    "typescript": "^5",
+    "vitest": "^4.1.7"
   }
 }

mvp/b2c/tests/smoke.test.ts

@@ -0,0 +1,7 @@
+import { describe, it, expect } from 'vitest';
+
+describe('vitest setup', () => {
+  it('runs', () => {
+    expect(1 + 1).toBe(2);
+  });
+});

mvp/b2c/vitest.config.ts

@@ -0,0 +1,17 @@
+import { defineConfig } from 'vitest/config';
+import { fileURLToPath } from 'node:url';
+
+export default defineConfig({
+  resolve: {
+    alias: { '@': fileURLToPath(new URL('./src', import.meta.url)) },
+  },
+  test: {
+    environment: 'node',
+    include: ['tests/**/*.test.ts'],
+    coverage: {
+      provider: 'v8',
+      include: ['src/budget/**'],
+      thresholds: { lines: 70, functions: 70, statements: 70, branches: 70 },
+    },
+  },
+});