Nitro API Testing Patterns

Test Nitro API handlers with a real PostgreSQL database using transaction rollback isolation. Each test runs in a transaction that auto-rolls back, providing complete isolation without cleanup overhead.

When to Use This Skill

Use this skill when:

• Testing Nuxt 3 / Nitro API handlers
• Using Kysely or another query builder with PostgreSQL
• Need real database testing (not mocks)
• Want fast, isolated tests without truncation

Reference Files

• transaction-rollback.md - Core isolation pattern with Vitest fixtures
• test-utils.md - Mock events, stubs, and assertion helpers
• factories.md - Transaction-bound factory pattern
• vitest-config.md - Vitest configuration for Nitro
• ci-setup.md - GitHub Actions with PostgreSQL service
• async-testing.md - Testing background tasks and automations

Example Files

• test-utils-index.ts - Complete test utilities module
• global-setup.ts - Database reset and migration
• setup.ts - Per-file setup with stubs
• handler.test.ts - Example API handler test
• vitest.config.ts - Vitest configuration

Core Concept: Transaction Rollback

Instead of truncating tables between tests, each test runs inside a database transaction that rolls back at the end:

// Each test gets isolated factories and db access
test("creates user", async ({ factories, db }) => {
  const user = await factories.user({ email: "test@example.com" });

  // Test your handler
  const event = mockPost({}, { name: "New Item" });
  const result = await handler(event);

  // Verify in database
  const saved = await db.selectFrom("item").selectAll().execute();
  expect(saved).toHaveLength(1);
});
// Transaction auto-rolls back - no cleanup needed

Benefits:

• Fast: No DELETE/TRUNCATE between tests
• Isolated: Tests can't affect each other
• Real SQL: Catches actual database issues
• Simple: No manual cleanup

Quick Setup

1. Install Dependencies

yarn add -D vitest @vitest/coverage-v8

2. Create Test Utils Structure

server/
  test-utils/
    index.ts        # Factories, fixtures, mock helpers
    global-setup.ts # Runs once: reset DB, run migrations
    setup.ts        # Runs per-file: stub auto-imports

3. Configure Vitest

// vitest.config.ts
import { defineConfig } from "vitest/config";
import path from "path";

export default defineConfig({
  test: {
    globals: true,
    environment: "node",
    globalSetup: ["./server/test-utils/global-setup.ts"],
    setupFiles: ["./server/test-utils/setup.ts"],
  },
  resolve: {
    alias: {
      "~": path.resolve(__dirname),
    },
  },
});

4. Write Tests

// server/api/users/index.post.test.ts
import { describe, test, expect, mockPost, expectHttpError } from "~/server/test-utils";
import handler from "./index.post";

describe("POST /api/users", () => {
  test("creates user with valid data", async ({ factories: _, db }) => {
    const event = mockPost({}, {
      email: "new@example.com",
      name: "New User"
    });
    const result = await handler(event);

    expect(result.id).toBeDefined();
    expect(result.email).toBe("new@example.com");

    // Verify persisted
    const saved = await db
      .selectFrom("user")
      .where("id", "=", result.id)
      .selectAll()
      .executeTakeFirst();
    expect(saved?.name).toBe("New User");
  });

  test("throws 400 for missing email", async ({ factories: _ }) => {
    const event = mockPost({}, { name: "No Email" });
    await expectHttpError(handler(event), { statusCode: 400 });
  });
});

Key Patterns

Mock Event Helpers

// GET with route params and query
const event = mockGet({ id: 123 }, { include: "details" });

// POST with body
const event = mockPost({}, { name: "Test", status: "active" });

// PATCH with route params and body
const event = mockPatch({ id: 123 }, { status: "completed" });

// DELETE with route params
const event = mockDelete({ id: 123 });

Factory Pattern

test("lists user's projects", async ({ factories }) => {
  // Factories are transaction-bound - auto-rolled back
  const user = await factories.user();
  const project1 = await factories.project({ ownerId: user.id });
  const project2 = await factories.project({ ownerId: user.id });

  const event = mockGet({ userId: user.id });
  const result = await handler(event);

  expect(result).toHaveLength(2);
});

Testing with Related Data

test("returns task with job details", async ({ factories }) => {
  // Factories auto-create dependencies
  const job = await factories.job(); // Creates project automatically
  const task = await factories.task({ jobId: job.id });

  const event = mockGet({ id: task.id });
  const result = await handler(event);

  expect(result.job.id).toBe(job.id);
  expect(result.job.project).toBeDefined();
});

Testing Error Cases

test("returns 404 for non-existent resource", async ({ factories: _ }) => {
  const event = mockGet({ id: 999999 });
  await expectHttpError(handler(event), {
    statusCode: 404,
    message: "Not found",
  });
});

test("returns 400 for invalid input", async ({ factories: _ }) => {
  const event = mockPost({}, { invalidField: true });
  await expectHttpError(handler(event), { statusCode: 400 });
});

Auto-Import Stubs

The setup file stubs Nuxt/Nitro auto-imports:

Stub	Purpose
defineEventHandler	Unwraps to return handler directly
getUserSession	Returns test user (configurable)
useDatabase	Returns test transaction
createError	Creates H3-style errors
getValidatedQuery	Validates mock query params
readValidatedBody	Validates mock body
getRouterParam	Returns mock route params

Key Gotchas

1. Always destructure factories - Even if unused, it sets up the transaction:

   test("...", async ({ factories: _ }) => { ... });
   

2. Don't use top-level db imports - Use the db fixture instead:

   // ❌ Wrong - uses real db, not transaction
   import { db } from "../utils/db";
   
   // ✅ Right - uses test transaction
   test("...", async ({ db }) => { ... });
   

3. Nested transactions work - Code that calls db.transaction() works because we patch the prototype

4. Test file location - Co-locate with handlers: handler.ts → handler.test.ts

5. Separate test database - Always use a dedicated test DB (myapp-test, not myapp)

6. CI needs PostgreSQL service - See ci-setup.md for GitHub Actions config