Supertest for HTTP assertions in Express - Mini Project: Build & Apply

Supertest for HTTP assertions

📖 Scenario: You are building a simple web server using Express. You want to check that your server responds correctly to HTTP requests. This is like testing if a vending machine gives you the right snack when you press a button.

🎯 Goal: Build a small Express server and write tests using Supertest to check the server's responses. You will create the server, set up Supertest, write a test for the home page, and finally add a test for a JSON response.

📋 What You'll Learn

Create an Express app with a GET route at '/' that returns 'Hello World!'

Set up Supertest to test the Express app

Write a test that checks the '/' route returns status 200 and text 'Hello World!'

Add a GET route at '/data' that returns JSON { message: 'Hello JSON' }

Write a test that checks the '/data' route returns status 200 and the correct JSON

💡 Why This Matters

🌍 Real World

Testing web servers ensures they respond correctly before users see them. This prevents bugs and improves reliability.

💼 Career

Backend developers often write tests with Supertest to verify APIs work as expected, which is a key skill in web development jobs.

1

Create Express app with '/' route

Create an Express app in a variable called app. Add a GET route at '/' that sends the text 'Hello World!' as the response.

Express

// Your code here

Hint

Use express() to create the app. Use app.get to add the route. Use res.send to send the text.

2

Set up Supertest for the app

Import supertest and create a variable called request by calling supertest(app). This will let you test the app's routes.

Express

import express from 'express';
const app = express();
app.get('/', (req, res) => {
  res.send('Hello World!');
});

// Your code here

Hint

Import Supertest and call it with app to create request.

3

Write a test for '/' route

Write an async test function called testHomeRoute. Inside, use await request.get('/') to get the response. Check that response.status is 200 and response.text is 'Hello World!'.

Express

import express from 'express';
import supertest from 'supertest';
const app = express();
app.get('/', (req, res) => {
  res.send('Hello World!');
});
const request = supertest(app);

// Your code here

Hint

Use await request.get('/') to get the response. Check response.status and response.text with if statements.

4

Add '/data' route and test JSON response

Add a GET route at '/data' that sends JSON { message: 'Hello JSON' }. Then add an async test function called testDataRoute. Use await request.get('/data') and check that response.status is 200 and response.body.message is 'Hello JSON'.

Express

import express from 'express';
import supertest from 'supertest';
const app = express();
app.get('/', (req, res) => {
  res.send('Hello World!');
});

// Your code here

const request = supertest(app);

async function testHomeRoute() {
  const response = await request.get('/');
  if (response.status !== 200) throw new Error('Status is not 200');
  if (response.text !== 'Hello World!') throw new Error('Text is not Hello World!');
}

// Your code here

Hint

Add the route with app.get and send JSON with res.json. Write the test like the first one but check response.body.message.

Practice

1. What is the main purpose of using Supertest in Express applications?

easy

A. To create database connections automatically

B. To send fake HTTP requests and check server responses

C. To deploy the Express app to production

D. To style the Express server pages

Solution

1. Step 1: Understand Supertest's role

   Supertest is a tool used to simulate HTTP requests to your Express server without needing a browser.

2. Step 2: Identify its main use

   It helps test server responses like status codes and data returned, ensuring your server works as expected.

3. Final Answer:

   To send fake HTTP requests and check server responses -> Option B

4. Quick Check:

   Supertest = fake HTTP requests and response checks [OK]

Hint: Supertest sends fake requests to test server responses [OK]

Common Mistakes:

• Thinking Supertest styles pages
• Confusing Supertest with deployment tools
• Assuming it manages databases

2. Which of the following is the correct way to import Supertest in a Node.js Express test file?

easy

A. import request from 'supertest';

B. const supertest = import('supertest');

C. const request = require('supertest');

D. require('supertest').request;

Solution

1. Step 1: Identify import syntax

   In Node.js, the most common way to import Supertest is using CommonJS syntax: const request = require('supertest');.

2. Step 2: Check other options

   import request from 'supertest'; uses ES module syntax which requires specific setup and may not work by default. const supertest = import('supertest'); uses invalid syntax. require('supertest').request; accesses a non-existent property.

3. Final Answer:

   const request = require('supertest'); -> Option C

4. Quick Check:

   CommonJS require syntax = const request = require('supertest'); [OK]

Hint: Use CommonJS require syntax for Supertest in Node.js [OK]

Common Mistakes:

• Using ES module import without setup
• Trying to destructure or access wrong properties
• Using invalid import syntax

3. Given the following test code, what will be the status code of the response?

import request from 'supertest';
import express from 'express';

const app = express();
app.get('/hello', (req, res) => res.status(200).send('Hi'));

test('GET /hello returns status 200', async () => {
  const response = await request(app).get('/hello');
  expect(response.status).toBe(201);
});

medium

A. 200

B. 404

C. 201

D. 500

Solution

1. Step 1: Analyze the Express route

   The route /hello sends a response with status code 200 and body 'Hi'.

2. Step 2: Check the test assertion

   The test expects status 201, but the actual response status is 200, so the test will fail if expecting 201.

3. Final Answer:

   200 -> Option A

4. Quick Check:

   Route sends 200, test expects 201, actual = 200 [OK]

Hint: Match expected status with route's actual status code [OK]

Common Mistakes:

• Confusing expected and actual status codes
• Assuming 201 is default success code
• Ignoring route's explicit status

4. Identify the error in this Supertest test code snippet:

import request from 'supertest';
import app from './app';

test('POST /data returns 201', async () => {
  const res = await request(app).post('/data')
    .send({ name: 'Alice' })
    .expect(201);
  expect(res.body.name).toBe('Alice');
});

medium

A. No error, code is correct

B. Missing await before request call

C. Using .expect() and then checking res.body without await

D. POST method should not have a body

Solution

1. Step 1: Review async/await usage

   The await is correctly used before request(app).post(...), so the promise resolves before assertions.

2. Step 2: Check .expect and body assertions

   Using .expect(201) is valid and chaining expect(res.body.name).toBe('Alice') is correct after awaiting the response.

3. Final Answer:

   No error, code is correct -> Option A

4. Quick Check:

   Await + .expect + body check = correct usage [OK]

Hint: Await the request before assertions to avoid errors [OK]

Common Mistakes:

• Forgetting await causing unresolved promises
• Misusing .expect without awaiting
• Assuming POST cannot have a body

5. You want to test an Express route that returns JSON only if a query parameter type=admin is present, otherwise it returns 403 Forbidden. Which Supertest code snippet correctly tests the 403 response when the query parameter is missing?

hard

A. await request(app).get('/secret').query({ type: 'user' }).expect(403);

B. await request(app).get('/secret?type=admin').expect(403);

C. await request(app).post('/secret').send({ type: 'admin' }).expect(403);

D. await request(app).get('/secret').expect(403);

Solution

1. Step 1: Understand route behavior

   The route returns JSON only if query type=admin is present; otherwise, it returns 403 Forbidden.

2. Step 2: Identify test for missing query parameter

   To test 403 when the parameter is missing, send a GET request without any query parameters.

3. Step 3: Evaluate options

   await request(app).get('/secret').expect(403); sends GET without query, expecting 403, which matches the requirement. await request(app).get('/secret').query({ type: 'user' }).expect(403); sends type=user, which is not missing but wrong type, so may or may not return 403 depending on implementation. await request(app).post('/secret').send({ type: 'admin' }).expect(403); uses POST instead of GET. await request(app).get('/secret?type=admin').expect(403); sends type=admin which should return success, not 403.

4. Final Answer:

   await request(app).get('/secret').expect(403); -> Option D

5. Quick Check:

   Missing query param = GET without query = expect 403 [OK]

Hint: Test missing query by omitting .query() in GET request [OK]

Common Mistakes:

• Sending wrong HTTP method (POST instead of GET)
• Including wrong query parameters instead of missing
• Expecting 403 when query param is present