🔍 How to Mock the inquirer NPM Package in Jest (The Right Way)

When writing tests for a Node.js CLI app, chances are you’re using inquirer for interactive prompts. But when it comes to unit testing, you don’t want your tests waiting for manual input. That’s where mocking inquirer with Jest comes in.

In this quick guide, we’ll show you how to mock inquirer with Jest like a pro—no hacks, no headaches.

📦 What is inquirer?

inquirer is a popular Node.js library used to build command-line interfaces with interactive prompts. It’s widely adopted for tools, generators, and CLI wizards.

npm install inquirer

Example usage:

const inquirer = require('inquirer');

async function askUser() {
  const answers = await inquirer.prompt([
    { type: 'input', name: 'username', message: 'Enter your name:' },
  ]);
  console.log(`Hello, ${answers.username}!`);
}

Cool, right? But now let’s make it testable.

🎯 The Goal: Mock inquirer.prompt() in Jest

We want to replace inquirer.prompt() with a mock function that returns predefined answers.

🧪 Step-by-Step: Mocking inquirer with Jest

1. Project Setup

Make sure jest is installed:

npm install --save-dev jest

In your package.json, define:

"scripts": {
  "test": "jest"
}

2. Example CLI Code (askUser.js)

const inquirer = require('inquirer');

async function askUser() {
  const answers = await inquirer.prompt([
    { type: 'input', name: 'username', message: 'Enter your name:' },
  ]);
  return `Hello, ${answers.username}!`;
}

module.exports = { askUser };

3. Writing the Jest Test (askUser.test.js)

jest.mock('inquirer');

const inquirer = require('inquirer');
const { askUser } = require('./askUser');

describe('askUser', () => {
  it('should return greeting with mocked username', async () => {
    inquirer.prompt.mockResolvedValue({ username: 'TestUser' });

    const result = await askUser();
    expect(result).toBe('Hello, TestUser!');
  });
});

🧠 Pro Tip: Avoid Real Prompts in CI/CD

Mocking inquirer is essential if you're running tests in CI/CD pipelines. Nothing ruins a build like a prompt waiting for input!

🚫 Common Mistake: Forgetting mockResolvedValue

inquirer.prompt() returns a Promise. If you use mockReturnValue, it won’t work correctly. Always use mockResolvedValue for async mocks.

✅ Correct:

inquirer.prompt.mockResolvedValue({ username: 'Jane' });

❌ Incorrect:

inquirer.prompt.mockReturnValue({ username: 'Jane' }); // Won’t await!

🧼 Clean Mocks After Each Test (Optional)

If your test suite is large:

afterEach(() => {
  jest.clearAllMocks();
});

📚 TL;DR

🔚 Final Thoughts

Mocking inquirer in Jest is simple, powerful, and essential for test automation. As a senior developer, you don’t want flaky tests—or worse, manual prompts slowing things down.

By mocking properly, you keep your test suite fast, reliable, and CI-friendly.