Testing GET endpoints in Express - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the Express module.

Express

const express = require([1]);

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

A"express"

B"http"

C"path"

D"fs"

Attempts:

3 left

💡 Hint

Common Mistakes

Using other module names like 'http' or 'fs' instead of 'express'.

Forgetting to put quotes around the module name.

To use Express, you must import it with require('express').

2fill in blank

medium

Complete the code to create a new Express application.

Express

const app = [1]();

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

Ahttp

Bexpress

Crequire

Dapp

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to call require() instead of express().

Using http() which is not the Express app creator.

You create an Express app by calling the express() function.

3fill in blank

hard

Fix the error in the GET route handler to send a response.

Express

app.get('/hello', (req, res) => {
  res.[1]('Hello World');
});

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

Asend

Bjson

Cend

Dwrite

Attempts:

3 left

💡 Hint

Common Mistakes

Using res.write() without ending the response.

Using res.end() without sending data.

The res.send() method sends the response body to the client.

4fill in blank

hard

Fill both blanks to start the server on port 3000 and log a message.

Express

app.listen([1], () => {
  console.[2]('Server running on port 3000');
});

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

A3000

Blog

Cerror

Dinfo

Attempts:

3 left

💡 Hint

Common Mistakes

Using console.error or console.info instead of console.log.

Passing a string instead of a number as the port.

The app.listen method starts the server on the given port. console.log prints the message.

5fill in blank

hard

Fill all three blanks to test the GET /hello endpoint using supertest.

Express

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

test('GET /hello returns Hello World', async () => {
  const response = await request(app).[1]('/hello');
  expect(response.statusCode).toBe([2]);
  expect(response.[3]).toBe('Hello World');
});

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

Aget

B200

Ctext

Dbody

Attempts:

3 left

💡 Hint

Common Mistakes

Using post instead of get.

Checking response.text instead of response.body.

Expecting status code other than 200.

Use request(app).get('/hello') to send a GET request. The status code for success is 200. The response body contains the returned string.

Practice

1. What is the main purpose of testing GET endpoints in an Express app?

easy

A. To verify the server returns the correct data and status code

B. To check if the server can handle POST requests

C. To test database connection speed

D. To validate CSS styles on the page

Solution

1. Step 1: Understand GET endpoint testing

   Testing GET endpoints means checking if the server responds correctly when a client asks for data.

2. Step 2: Identify the goal of testing

   The goal is to confirm the server sends the right data and proper HTTP status code (like 200 for success).

3. Final Answer:

   To verify the server returns the correct data and status code -> Option A

4. Quick Check:

   Testing GET endpoints = verify data and status [OK]

Hint: GET endpoint tests check response data and status code [OK]

Common Mistakes:

• Confusing GET with POST request testing
• Testing unrelated features like CSS or database speed
• Ignoring status codes in tests

2. Which of the following is the correct way to start a test for a GET endpoint using supertest with Express?

easy

A. app.get('/path').send(200);

B. request(app).get('/path').expect(200, done);

C. supertest.get('/path').expect(200);

D. request.get(app, '/path').expect(200);

Solution

1. Step 1: Recall supertest syntax

   Supertest uses request(app).get('/path') to simulate a GET request to the Express app.

2. Step 2: Check the correct chaining

   Chaining .expect(200, done) checks the status code and signals test completion.

3. Final Answer:

   request(app).get('/path').expect(200, done); -> Option B

4. Quick Check:

   supertest GET syntax = request(app).get(path).expect(status) [OK]

Hint: Use request(app).get(path).expect(status, done) for GET tests [OK]

Common Mistakes:

• Calling app.get() instead of request(app).get()
• Missing the done callback in async tests
• Incorrect method chaining order

3. Given this Express GET endpoint and test code, what will the test output?

const express = require('express');
const app = express();
app.get('/hello', (req, res) => res.json({ message: 'Hi!' }));

const request = require('supertest');

test('GET /hello returns message', async () => {
  const response = await request(app).get('/hello');
  return response.body.message;
});

medium

A. "Hi!"

B. undefined

C. Error: No response

D. "hello"

Solution

1. Step 1: Analyze the endpoint response

   The GET /hello endpoint sends JSON { message: 'Hi!' } as response.

2. Step 2: Check the test return value

   The test awaits the GET request and returns response.body.message, which is 'Hi!'.

3. Final Answer:

   "Hi!" -> Option A

4. Quick Check:

   GET /hello returns message = "Hi!" [OK]

Hint: Response body message matches endpoint JSON key [OK]

Common Mistakes:

• Expecting response.body instead of response.body.message
• Forgetting to await the request
• Assuming string 'hello' instead of 'Hi!'

4. Identify the error in this test code for an Express GET endpoint:

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

test('GET /users returns 200', () => {
  request(app)
    .get('/users')
    .expect(200);
});

medium

A. Missing import of Express

B. Incorrect HTTP method used

C. Missing return or await to handle async test

D. Wrong path '/users' does not exist

Solution

1. Step 1: Check async test handling

   The test function is async but does not return or await the request promise, so Jest won't wait for it.

2. Step 2: Confirm correct fix

   Adding return before request(...) or making the test async and awaiting fixes the issue.

3. Final Answer:

   Missing return or await to handle async test -> Option C

4. Quick Check:

   Async test needs return or await [OK]

Hint: Always return or await supertest calls in tests [OK]

Common Mistakes:

• Not returning or awaiting async calls in tests
• Assuming path or method is wrong without checking
• Confusing import errors with test async errors

5. You want to test an Express GET endpoint that returns a list of users, but only those with active status true. Which test code correctly checks this filtering?

app.get('/active-users', (req, res) => {
  const users = [
    { id: 1, active: true },
    { id: 2, active: false },
    { id: 3, active: true }
  ];
  res.json(users.filter(u => u.active));
});

// Test code options:
A) await request(app).get('/active-users').expect(200).expect(res => {
  if (!res.body.every(u => u.active)) throw new Error('Inactive user found');
});

B) await request(app).get('/active-users').expect(200).expect(res => {
  if (res.body.length !== 3) throw new Error('Wrong number of users');
});

C) await request(app).get('/active-users').expect(404);

D) await request(app).get('/active-users').expect(200).expect(res => {
  if (!res.body.some(u => u.active === false)) throw new Error('Inactive user found');
});

hard

A. Incorrectly throws error when no inactive users found

B. Incorrectly expects all users, including inactive

C. Wrong status code expectation

D. Checks for inactive users but throws error if found

Solution

1. Step 1: Understand endpoint filtering

   The endpoint returns only users with active: true, so no inactive users should appear.

2. Step 2: Analyze test options

   Checks for inactive users but throws error if found uses every(u => u.active) and throws if any inactive, correctly verifying the filter.
   Incorrectly expects all users, including inactive expects length !== 3 (wrong, it's 2).
   Wrong status code expectation expects 404 (wrong).
   Incorrectly throws error when no inactive users found incorrectly throws error when no inactive users found.

3. Step 3: Verify A logic

   !every(u => u.active) detects any inactive user, matching the requirement.

4. Final Answer:

   Checks for inactive users but throws error if found -> Option D

5. Quick Check:

   Test filters out inactive users = no inactive found [OK]

Hint: Check response has no inactive users with some() or every() [OK]

Common Mistakes:

• Expecting all users instead of filtered active only
• Using wrong status code in test
• Confusing every() and some() logic in tests