DEV Community

Cover image for Mocha/Chai with TypeScript
Matteo Bruni
Matteo Bruni

Posted on • Edited on

Mocha/Chai with TypeScript

#tutorial #typescript #javascript #webdev

Introduction

I wanted to create some tests for tsParticles (leave a star if you want 🌟, it's free 👀), and I didn't know anything about them.

GitHub logo tsparticles / tsparticles

tsParticles - Easily create highly customizable JavaScript particles effects, confetti explosions and fireworks animations and use them as animated backgrounds for your website. Ready to use components available for React.js, Vue.js (2.x and 3.x), Angular, Svelte, jQuery, Preact, Inferno, Solid, Riot and Web Components.

View on GitHub

I started searching and I found some informations about Mocha and Chai for writing tests in Javascript and in TypeScript but I had to read multiple articles at once because they were incomplete.

If you need to unit test your TypeScript code you're in the right place.

Let's start!

Requirements

Before starting writing tests we need some libraries added to our project.

I will use npm but you can use yarn too (obvious, thanks).



npm install chai mocha ts-node @types/chai @types/mocha --save-dev
Enter fullscreen mode Exit fullscreen mode

Once the installation is complete we are almost ready.

Add a test key to your package.json scripts, like this



"test": "env TS_NODE_COMPILER_OPTIONS='{\"module\": \"commonjs\" }' mocha -r ts-node/register 'tests/**/*.ts'"
Enter fullscreen mode Exit fullscreen mode

This will set the right flag for module, if you have commonjs already you can skip everything until mocha, for ts-node that supports only commonjs modules then it runs tests using mocha.

This is a bit outdated, check out the updated article for a simpler installation.

matteobruni

Mocha/Chai with TypeScript (2023 update)

Matteo Bruni ・ Aug 13 '23

#typescript #tutorial #javascript #webdev

I prefer using a tests folder than some .test.ts files. This will require an exclude key in your tsconfig (if you have one, obviously).

This is a sample taken from my config



"exclude": [
  "./tests/",
  "./node_modules/",
  "./dist/"
],
Enter fullscreen mode Exit fullscreen mode

Once everything is set we can start writing tests.

Tests

Writing a test with chai is really easy, I started writing almost immediately.

Let's see a sample, it's faster than all words I can write.



import { Options } from '../src/Classes/Options/Options'; // this will be your custom import
import { expect } from 'chai';

describe('Options tests', () => { // the tests container
    it('checking default options', () => { // the single test
        const options = new Options(); // this will be your class

                /* detect retina */
        expect(options.detectRetina).to.be.false; // Do I need to explain anything? It's like writing in English!

        /* fps limit */
        expect(options.fpsLimit).to.equal(30); // As I said 3 lines above

        expect(options.interactivity.modes.emitters).to.be.empty; // emitters property is an array and for this test must be empty, this syntax works with strings too
        expect(options.particles.color).to.be.an("object").to.have.property("value").to.equal("#fff"); // this is a little more complex, but still really clear
    });
});
Enter fullscreen mode Exit fullscreen mode

You can see the simplicity of the syntax, chai is a really simple test writing library.

If you want to start writing your own tests that's all you need. Super easy.

If you want to read every function available in chai you can find all of them here.

Running Tests

Once the test is completed we can try it with the command we prepared at the beginning



npm test
Enter fullscreen mode Exit fullscreen mode

and if you did everything right the output will be something like this



> tsparticles@1.13.0-alpha.0 test /path/to/your/project/
> env TS_NODE_COMPILER_OPTIONS='{"module": "commonjs" }' mocha -r ts-node/register 'tests/**/*.ts'



  Options tests
    ✓ checking default options
    ✓ check default preset options


  2 passing (16ms)
Enter fullscreen mode Exit fullscreen mode

If something is not working you'll get a message like this



> tsparticles@1.13.0-alpha.0 test /path/to/your/project/
> env TS_NODE_COMPILER_OPTIONS='{"module": "commonjs" }' mocha -r ts-node/register 'tests/**/*.ts'



  Options tests
    1) checking default options
    ✓ check default preset options


  1 passing (48ms)
  1 failing

  1) Options tests
       checking default options:
     AssertionError: expected undefined not to be undefined
      at Context.<anonymous> (tests/Options.ts:19:45)
      at processImmediate (internal/timers.js:456:21)



npm ERR! Test failed.  See above for more details.
Enter fullscreen mode Exit fullscreen mode

An error blocking any future command, so you can run the tests before the build script, like this



"build": "npm test && tsc",
Enter fullscreen mode Exit fullscreen mode

and with the command below you can now test and build



npm run build
Enter fullscreen mode Exit fullscreen mode

If the tests will pass the build will proceed as expected, otherwise the tests failing will stops the process.

If you want to see my configuration you can find everything here.

Happy Testing 😏

Top comments (14)

Collapse
 
devtronic profile image
Julian Finkler •

Great tutorial, thank you!

Collapse
 
raqhael profile image
Raphael •

I tried for like 3 Hours to test my simple typescript code with karma+jasime (because angular is using it so how hard can it be)...

Looked 2mins on this guide and it works like a charme thank you!

Collapse
 
wesleymconner profile image
WesMC •

Thanks @matteobruni quite helpful.

I was able to test APIs with minor adjustments.

For context: My source is in src/ts including tests under src/ts/test. My compiles produce one js (under src/js-tmp) per source ts (under src/ts). My dists cherry-pick from js-tmp (i.e., exclude tests, ...).

=== test-whatever.ts ===
import chai, { expect } from 'chai'
import chaiHttp from 'chai-http'
chai.use(chaiHttp);
import mocha from 'mocha'
const { describe, before, beforeEach, it, after } = mocha
  :
import { ..stuff to test.. } from '../index.js'


=== package.json ===
{ ..
  "type": "module",
  "source": "src/js-tmp/index.js",
  "main": "src/js-tmp/index.js",
..}

=== tsconfigBase.json ===
{ ..
  "esModuleInterop": true,
  "module": "es2022",
  "moduleResolution": "node",
  "target": "es2022"
.. }

=== tsconfig.json ===
{
  "extends": "../../tsconfigBase.json",
  "compilerOptions": {
    "baseUrl": ".",
    "rootDir": "src/ts",
    "outDir": "src/js-tmp"
  },
  "include": [ "src/ts/**/*.ts" ]
}
Enter fullscreen mode Exit fullscreen mode


`

Collapse
 
tequilacat profile image
tequilacat •

OMG finally. I tried to add chai testing to my first typescript app instead of karma, all examples inevitable ended with 'Cannot use import statement outside a module'. Tried babel and configured all jsons possible with no luck.

This one finally highlighted the critical part I needed, and because the example is simple and concise it wasn't lost - env TS_NODE_COMPILER_OPTIONS='{"module": "commonjs" }'

many thanks

Collapse
 
angelincalu profile image
Angelin Calu •

'env' is not recognized as an internal or external command,

Collapse
 
matteobruni profile image
Matteo Bruni •

If you are on Windows env needs to be replaced with set, at least this is what I've read googling around.
That command is related to ts-node as you can read here

Collapse
 
belingheri profile image
Belingheri • • Edited

Yes, but i had to add &&.
set TS_NODE_COMPILER_OPTIONS={\"module\": \"commonjs\" } && mocha -r ts-node/register 'tests/**/*.ts'

Thread Thread
 
brainafesoh profile image
brainafesoh •

Damn windows, I just wasted the last 24hrs just because of this😩!
Thanks a lot.

Collapse
 
johanneshayry profile image
johanneshayry •

I have been using npmjs.com/package/cross-env for cross platform support

Collapse
 
mlp1802 profile image
Mikkel Petersen • • Edited

Error [ERR_UNSUPPORTED_DIR_IMPORT]: Directory import '/home//node_modules/ts-node/register not supported resolving ES modules imported from /home/mikkel/src//node_modules/mocha/lib/esm-utils.js
Did you mean to import ts-node/register/index.js?

Is pretty much what I get no matter what tutorial I follow.

Collapse
 
oli8 profile image
Olivier •

Thanks, was very helpful on a project of mine.

Collapse
 
pandzic1989 profile image
Ivan Pandžić •

Is env TS_NODE_COMPILER_OPTIONS='{\"module\": \"commonjs\" }' equivalent of adding this to your tsconfig.json

"ts-node": {
    "compilerOptions": {
      "module": "commonjs"
    }
},
Enter fullscreen mode Exit fullscreen mode
Collapse
 
matteobruni profile image
Matteo Bruni •

It depends if you need that in your tsconfig, which was not my case

Collapse
 
ojuliomiguel profile image
Júlio Miguel •

Very helpful article.

View full discussion (14 comments)

Read next

rose_michelle profile image

Beginner-Friendly Python Projects with Source Code

Namubiru Rose -

michael_mazzone_87d595a97 profile image

Modular React architecture

Michael Mazzone -

farouk_ profile image

Task manger app

Farouk -

testbhai profile image

Guys I am facing this problem Please help me to out this situation: "Not able to send UDP message to Virtual Device Emulator."

Test -