How to write unit tests for Inquirer.js?

I was wondering how to write unit tests for the npm package Inquirer.js, which is a tool to make CLI package more easily. I have read this post but I was't able to make it works.

Here is my code that needs to be tested:

const questions = [
                {
                    type: 'input',
                    name: 'email',
                    message: "What's your email ?",
                },
                {
                    type: 'password',
                    name: 'password',
                    message: 'Enter your password (it will not be saved neither communicate for other purpose than archiving)'
                }
            ];

            inquirer.prompt(questions).then(answers => {
                const user = create_user(answers.email, answers.password);
                let guessing = guess_unix_login(user);
                guessing.then(function (user) {
                    resolve(user);
                }).catch(function (message) {
                    reject(message);
                });
            } );

...and here is the test, written with Mocha:

describe('#create_from_stdin', function () {
            this.timeout(10000);
            check_env(['TEST_EXPECTED_UNIX_LOGIN']);
            it('should find the unix_login user and create a complete profile from stdin, as a good cli program', function (done) {
                const user_expected = {
                    "login": process.env.TEST_LOGIN,
                    "pass_or_auth": process.env.TEST_PASS_OR_AUTH,
                    "unix_login": process.env.TEST_EXPECTED_UNIX_LOGIN
                };
                let factory = new profiler();
                let producing = factory.create();
                producing.then(function (result) {
                    if (JSON.stringify(result) === JSON.stringify(user_expected))
                        done();
                    else
                        done("You have successfully create a user from stdin, but not the one expected by TEST_EXPECTED_UNIX_LOGIN");
                }).catch(function (error) {
                    done(error);
                });
            });
        });

I'd like to fill stdin with the process.env.TEST_LOGIN (to answer the first Inquirer.js question) and process.env.TEST_PASS_OR_AUTH (to answer the second Inquirer.js question) to see if the function create a valid profile (with the value unix_login guessed by the method create of the factory object).

I tried to understand how Inquirer.js unit tests itself, but my understanding of NodeJS isn't good enough. Can you help me with this unit test?

You simply mock or stub any functionality that you don't want to test.

• module.js - simplified example of a module you want to test

  const inquirer = require('inquirer')
  
  module.exports = (questions) => {
    return inquirer.prompt(questions).then(...)
  }
  

• module.test.js

  const inquirer = require('inquirer')
  const module = require('./module.js')
  
  describe('test user input' () => {
  
    // stub inquirer
    let backup;
    before(() => {
      backup = inquirer.prompt;
      inquirer.prompt = (questions) => Promise.resolve({email: 'test'})
    })
  
    it('should equal test', () => {
      module(...).then(answers => answers.email.should.equal('test'))
    })
  
    // restore
    after(() => {
      inquirer.prompt = backup
    })
  
  })
  

There are libraries to help with mocking/stubbing, like sinon.

Also it was easier to mock inquirer.prompt in this case because .prompt was just a property on the main export inquirer which will refer to the the same object in both module.js and module.test.js. For more complicated scenarios there are libraries that can help, like proxyquire. Or you can create your modules in a way that help you switch out the dependencies easily for testing. For example:

• module.js - make it a "factory" function which returns your main function with dependencies injected either automatically (via default arguments) or manually.

  module.exports = ({
    inquirer = require('inquirer'),
  } = {}) => (questions) => {
    return inquirer.prompt(questions).then(...)
  }
  

• module.test.js

  const module = require('./module.js')
  
  describe('test user input' () => {
  
    const inquirer = {prompt: () => Promise.resolve({email: 'test'})};
  
    it('should equal test', () => {
      module({inquirer})(...).then(answers => answers.email.should.equal('test'))
    })
  })