How can I solve "ReferenceError: expect is not defined" error message?

Question

I am trying to test Javascript with mocha. I've this snippet of code:

describe('Array', function() {
    describe('indexOf()', function() {
        it("dovrebbe tornare -1 quando l'elemento non è presente", function() {
            expect([1,2,3].indexOf(4)).to.equal(-1)
        })
    })
})

and a test/array.js file. Mocha was installed with

$ npm install -g mocha

When I run

$ mocha

I get this error:

$ mocha
․ 

0 passing (5ms)
1 failing

1) Array indexOf() dovrebbe tornare -1 quando l'elemento non è presente:
 ReferenceError: expect is not defined
  at Context.<anonymous> (/Users/simonegentili/Desktop/Javascipt Best Practice/test/array.js:4:4)
  at Test.Runnable.run (/usr/local/lib/node_modules/mocha/lib/runnable.js:211:32)
  at Runner.runTest (/usr/local/lib/node_modules/mocha/lib/runner.js:358:10)
  at /usr/local/lib/node_modules/mocha/lib/runner.js:404:12
  at next (/usr/local/lib/node_modules/mocha/lib/runner.js:284:14)
  at /usr/local/lib/node_modules/mocha/lib/runner.js:293:7
  at next (/usr/local/lib/node_modules/mocha/lib/runner.js:237:23)
  at Object._onImmediate (/usr/local/lib/node_modules/mocha/lib/runner.js:261:5)
  at processImmediate [as _immediateCallback] (timers.js:317:15)

score 105 · Accepted Answer · edited Mar 24 '18 at 16:57

105

Mocha is a test framework; you need to provide your own assertion lib as https://mochajs.org/#assertions states. Thus, expect is indeed undefined because you never defined it.

(I recommend chai)

npm install chai

then

(see Amit Choukroune's comment pointing out to actually require chai)

then

var expect = chai.expect;

edited Mar 24 '18 at 16:57

starcwl

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answered Oct 04 '13 at 21:57

Dan Heberden

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20

you should use `var expect = require('chai').expect,` – Amit Choukroun Nov 12 '14 at 21:40
1

or `const chai = require('chai')` above it. – chovy Jan 17 '17 at 04:42
4

Or `var expect = (typeof require === 'undefined') ? chai.expect : require('chai').expect;` if you wish to run test in mocha on a page in the browser. – Michiel Roos Feb 16 '17 at 10:25
Or `let { expect } = require('chai')` – Gershom Maes Feb 05 '21 at 20:22

score 12 · Answer 2 · edited Feb 11 '17 at 17:39

12

Try

First, in the terminal

npm install expect.js

And in your code:

var expect = require('expect');

edited Feb 11 '17 at 17:39

Keatinge

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answered Oct 04 '13 at 21:56

Paul Rad

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dmchk · Answer 3 · 2019-10-23T04:00:07.737

10

After you install Chai as other posts suggest, with the es6 syntax you should put the import at the top

import {expect} from 'chai';

edited Oct 23 '19 at 04:00

answered Apr 17 '17 at 15:41

dmchk

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score 4 · Answer 4 · answered Sep 17 '21 at 11:40

4

In my case i was using JEST Test Cases. and i put all test.js file inside pages/ folder of next file structure.

So solve my issue by move all test.js file from pages folder of next file structure to inside __test__ folder outside or root of the folder

answered Sep 17 '21 at 11:40

Krishna Jangid

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score 3 · Answer 5 · edited Oct 23 '18 at 06:30

3

let chai = require('chai');

var assert = chai.assert;

describe('Array', function() {
  describe('#indexOf()', function() {
    it('should return -1 when the value is not present', function() {
      assert.equal(-1, [1, 2, 3].indexOf(4));
    });
  });
});

edited Oct 23 '18 at 06:30

AntonioGarcía

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answered Oct 23 '18 at 05:52

shael

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score 3 · Answer 6 · answered Aug 27 '19 at 21:30

3

In order to expose expect globally, while using chai, following should be loaded by means of configuration for your prefered testing library:

require('chai/register-assert');  // Using Assert style
require('chai/register-expect');  // Using Expect style
require('chai/register-should');  // Using Should style

For example:

npx mocha --config .mocharc.js *.spec.js

answered Aug 27 '19 at 21:30

micrub

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And from the CLI just use `mocha --require chai/register-expect` – Brett Zamir Oct 21 '19 at 02:39

score 1 · Answer 7 · answered May 17 '16 at 19:11

In my use case, I was running a mocha spec through karma. The solution was to install the karma integrations for my test framework libs:

npm install karma-mocha --save-dev
npm install karma-sinon-chai --save-dev

...and also to add the frameworks to my karma.conf.js:

module.exports = function(config) {
    config.set({
        browsers: ['Chrome'],
        frameworks: ['mocha', 'sinon-chai'],
        files: [
            '.tmp/**/*.spec.js'
        ],
        client: {
            chai: {
                includeStack: true
            },
            mocha: {
                reporter: 'html',
                ui: 'bdd'
            }
        }
    })
}

Hope this helps someone else.

score 0 · Answer 8 · edited Apr 05 '16 at 10:56

0

Install Expect.js or Chai.js if you are using Mocha for TDD

So, do npm install expect or npm install chai

edited Apr 05 '16 at 10:56

John Slegers

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answered Apr 05 '16 at 10:49

ALoK VeRMa

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score 0 · Answer 9 · answered May 28 '19 at 18:41

0

Either add this script tag in html file

<script src="https://unpkg.com/expect@%3C21/umd/expect.min.js"></script>

or install package

npm install chai or expect

answered May 28 '19 at 18:41

ASHISH R

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score 0 · Answer 10 · answered Dec 18 '19 at 10:43

Create a file chaiexpections.js and declare expect as global

'use strict';

// Configure chai
global.expect = require('chai').expect;

Now pass it in config file under cucumberopts, require

cucumberOpts: {
    require: ['./testsuites/*.js','./chaiexpections.js','./commons/hooks.js']
    //tags: [],
    strict: true,    
    format: [],  
    'dry-run': false,           
    compiler: [],
    format: 'json:results.json',   
  },

This prevents the overhead of having to declare chai exception in each stepdefinition

score 0 · Answer 11 · answered May 07 '23 at 11:29

In my case I was importing setupTests.ts file inside index.tsx so when react app starts the development server it couldn't find the test related dependencies .

setupTests.ts

import "@testing-library/jest-dom";

I did solve this issue the easiest way possible providing jest a config file named jest.config.js and removed import "setupTests"; from index.tsx file .

module.exports = {
  setupFilesAfterEnv: ["./src/setupTests.ts"],
};

How can I solve "ReferenceError: expect is not defined" error message?

11 Answers11

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