Testing authentication flows in Express - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main goal of testing authentication flows in an Express app?

To ensure that users can securely log in, access protected routes only when authenticated, and that invalid credentials are handled properly.

beginner

Which HTTP status code usually indicates a successful login in an authentication flow?

Status code 200 means success, but often 302 is used for redirect after login. For APIs, 200 with a token is common.

intermediate

Why do we test protected routes with and without authentication tokens?

To verify that protected routes deny access without valid tokens and allow access when tokens are valid, ensuring security.

beginner

What tool can you use to simulate HTTP requests when testing Express authentication flows?

Supertest is a popular tool to simulate HTTP requests and test Express routes including authentication.

beginner

How can you test that an Express app correctly handles invalid login credentials?

By sending a login request with wrong username or password and checking the response status and error message.

What should happen when a user tries to access a protected route without a valid token?

A The server should respond with a 401 Unauthorized status.

B The server should allow access.

C The server should crash.

D The server should redirect to a public page.

Protected routes require valid tokens; without them, the server responds with 401 Unauthorized.

Which library is commonly used to test HTTP requests in Express apps?

A React Testing Library

B Supertest

C Jest DOM

D Mocha UI

Supertest is designed to test HTTP endpoints in Node.js and Express apps.

What is a common way to test login success in an API authentication flow?

A Check for a 404 status code.

B Check if the server logs an error.

C Check if the page reloads.

D Check for a token in the response body.

A successful login usually returns a token that the client uses for future requests.

Why is it important to test both valid and invalid login attempts?

A To verify the app handles all cases securely and correctly.

B To ensure the app crashes gracefully.

C To speed up the login process.

D To make the UI look better.

Testing both cases ensures security and proper user feedback.

What status code usually indicates that login credentials are incorrect?

A 200 OK

B 500 Internal Server Error

C 401 Unauthorized

D 302 Found

401 Unauthorized means the credentials were rejected.

Explain how you would write a test to verify that a protected route in Express denies access without a token.

Think about what happens when someone tries to enter a locked door without a key.

Describe the steps to test a login endpoint for both successful and failed login attempts.

Imagine testing a door lock with the right and wrong keys.

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