Testing authentication flows in Express - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the Express module correctly.

Express

const express = require([1]);

Drag options to blanks, or click blank then click option'

A"body-parser"

B"express-session"

C"express"

D"cookie-parser"

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong module name like 'express-session' or 'body-parser'.

Forgetting to put the module name in quotes.

You need to import the main Express module using require("express") to create an Express app.

2fill in blank

medium

Complete the code to set up a POST route for login at '/login'.

Express

app.[1]('/login', (req, res) => {
  // login logic
});

Drag options to blanks, or click blank then click option'

Aget

Bpost

Cput

Ddelete

Attempts:

3 left

💡 Hint

Common Mistakes

Using GET instead of POST for login routes.

Using PUT or DELETE which are not typical for login.

Login forms usually send data via POST, so use app.post to handle the login route.

3fill in blank

hard

Fix the error in the middleware usage to parse JSON bodies.

Express

app.use([1].json());

Drag options to blanks, or click blank then click option'

Aexpress

Bbody-parser

Ccookie-parser

Dexpress-session

Attempts:

3 left

💡 Hint

Common Mistakes

Using body-parser.json() without importing body-parser.

Using express-session or cookie-parser which are unrelated.

Express has a built-in json() middleware accessed via express.json() to parse JSON request bodies.

4fill in blank

hard

Fill both blanks to check if a user is authenticated and redirect if not.

Express

function ensureAuth(req, res, next) {
  if (req.[1]) {
    next();
  } else {
    res.[2]('/login');
  }
}

Drag options to blanks, or click blank then click option'

AisAuthenticated()

Bredirect

Csend

Dstatus

Attempts:

3 left

💡 Hint

Common Mistakes

Using res.send instead of res.redirect for navigation.

Checking a wrong property on req object.

The method req.isAuthenticated() checks if the user is logged in, and res.redirect() sends the user to the login page if not.

5fill in blank

hard

Fill all three blanks to create a test that sends a POST request to login and checks the response status.

Express

test('POST /login returns 200 on success', async () => {
  const response = await request(app)
    .[1]('/login')
    .send({ username: 'user', password: 'pass' });
  expect(response.[2]).toBe([3]);
});

Drag options to blanks, or click blank then click option'

Apost

Bstatus

C200

Dget

Attempts:

3 left

💡 Hint

Common Mistakes

Using get() instead of post() for login.

Checking response.statusCode instead of response.status.

Expecting a wrong status code like 404.

Use post() to send the login request, check response.status, and expect it to be 200 for success.

Practice

1. What is the main purpose of testing authentication flows in an Express app?

easy

A. To check if the server can handle large amounts of traffic

B. To verify users can log in and access protected routes correctly

C. To ensure the database schema is optimized

D. To test the styling of the login page

Solution

1. Step 1: Understand authentication flow testing

   Testing authentication flows means checking if users can log in and access parts of the app that require login.

2. Step 2: Identify the main goal

   The main goal is to verify correct login and access control, not performance or styling.

3. Final Answer:

   To verify users can log in and access protected routes correctly -> Option B

4. Quick Check:

   Authentication testing = verify login and access [OK]

Hint: Authentication tests check login and access only [OK]

Common Mistakes:

• Confusing authentication testing with performance testing
• Thinking styling or database optimization is tested here
• Assuming authentication tests check UI design

2. Which of the following is the correct way to import and use supertest for testing an Express app's authentication route?

easy

A. const request = require('supertest'); const app = require('./app');

B. const supertest = import('supertest'); const app = require('./app');

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

D. import * as request from 'supertest'; const app = require('./app');

Solution

1. Step 1: Identify CommonJS import syntax

   Most Express apps use CommonJS syntax with require, so const request = require('supertest'); is correct.

2. Step 2: Match import style for app

   Similarly, const app = require('./app'); is correct for CommonJS modules.

3. Final Answer:

   const request = require('supertest'); const app = require('./app'); -> Option A

4. Quick Check:

   Use CommonJS require for supertest and app [OK]

Hint: Use CommonJS require syntax for supertest and app [OK]

Common Mistakes:

• Mixing require() with import in CommonJS code
• Using dynamic import incorrectly
• Using namespace import when default import is expected

3. Given this test code snippet, what will be the status code returned when testing a protected route without authentication?

await request(app).get('/dashboard').expect(401);

medium

A. 401 (Unauthorized) - Access denied

B. 200 (OK) - Access granted

C. 404 (Not Found) - Route missing

D. 500 (Server Error) - Internal error

Solution

1. Step 1: Understand protected route behavior

   Protected routes require authentication; without it, the server should deny access.

2. Step 2: Identify correct HTTP status for unauthorized access

   HTTP status 401 means unauthorized access, which fits this case.

3. Final Answer:

   401 (Unauthorized) - Access denied -> Option A

4. Quick Check:

   Unauthenticated access to protected route = 401 [OK]

Hint: 401 means unauthorized access denied [OK]

Common Mistakes:

• Expecting 200 without authentication
• Confusing 401 with 404 or 500
• Assuming route is missing instead of protected

4. You wrote this test to check login failure:

await request(app).post('/login').send({ username: 'user', password: 'wrong' }).expect(401);

But the test fails even when the server returns 200. What is the likely mistake?

medium

A. The test should use GET instead of POST

B. The test is missing async/await keywords

C. The server does not properly check password and returns 200 anyway

D. The test should expect 404 instead of 401

Solution

1. Step 1: Analyze test expectation vs server behavior

   The test expects 401 for wrong password, but server returns 200, so server likely accepts wrong password.

2. Step 2: Identify root cause

   The server probably lacks proper password validation, causing incorrect success response.

3. Final Answer:

   The server does not properly check password and returns 200 anyway -> Option C

4. Quick Check:

   Wrong password but 200 means server validation missing [OK]

Hint: Check server password validation if test expects 401 but gets 200 [OK]

Common Mistakes:

• Assuming test syntax error without checking server logic
• Using wrong HTTP method for login
• Expecting wrong status code for authentication failure

5. You want to test that after a successful login, the user can access a protected route using the received token. Which sequence correctly tests this flow using supertest?

hard

A. Post login with wrong password, then get protected route with token

B. Get protected route first, then post login with token in body

C. Post login without saving token, then get protected route without headers

D. Post login, save token from response, then get protected route with Authorization header set to token

Solution

1. Step 1: Understand authentication token flow

   After login, server returns a token. This token must be sent in Authorization header to access protected routes.

2. Step 2: Identify correct test sequence

   First post login, save token from response, then use token in Authorization header for protected route request.

3. Final Answer:

   Post login, save token from response, then get protected route with Authorization header set to token -> Option D

4. Quick Check:

   Login -> save token -> use token in header for protected route [OK]

Hint: Save token after login, then use it in Authorization header [OK]

Common Mistakes:

• Trying to access protected route before login
• Not sending token in Authorization header
• Using wrong password in login step