Testing API routes in NextJS - Mini Project: Build & Apply

Testing API routes

📖 Scenario: You are building a Next.js app that has API routes to handle user data. To make sure your API routes work correctly, you want to write simple tests for them.

🎯 Goal: Create a test for a Next.js API route that returns a JSON response. You will set up the test data, configure the test environment, write the test logic, and complete the test file.

📋 What You'll Learn

Create a mock request and response object

Set a test configuration variable

Write a test function that calls the API route handler

Complete the test file with the necessary export or setup

💡 Why This Matters

🌍 Real World

Testing API routes ensures your backend logic works correctly before deploying your Next.js app.

💼 Career

Writing tests for API routes is a key skill for frontend and full-stack developers to maintain reliable web applications.

1

Set up mock request and response objects

Create two variables called req and res. Set req to an empty object {}. Set res to an object with a method json that is a jest mock function.

NextJS

# Create mock request and response objects
# Your code here

Need a hint?

Think of req as the request coming into your API, and res as the response you send back. Use jest.fn() to mock the json method.

2

Add a test configuration variable

Create a constant called testUserId and set it to the string 'user123'.

NextJS

const req = {};
const res = { json: jest.fn() };

# Create a test user ID
# Your code here

Need a hint?

This variable will be used to simulate a user ID in your test.

3

Write the test function calling the API handler

Write an async function called testApiRoute that calls the imported handler function with req and res. Then check that res.json was called.

NextJS

const req = {};
const res = { json: jest.fn() };

const testUserId = 'user123';

# Write the test function
# Your code here

Need a hint?

Use await to wait for the handler to finish. Use Jest's expect to check the mock function call.

4

Complete the test file with export

Export the testApiRoute function as the default export.

NextJS

const req = {};
const res = { json: jest.fn() };

const testUserId = 'user123';

async function testApiRoute() {
    await handler(req, res);
    expect(res.json).toHaveBeenCalled();
}

# Export the test function
# Your code here

Need a hint?

This makes the test function available for running by your test runner.