QA Notes | Mocha Chai

Chai is a assertions library, that can be paired with any testing framework based in JavaScript.

In this post we are going to review the following topics

• What is Chai, how to install?
• Assertion Styles
• Differences
• Adding Chai assertions to projects
• Centralizing assertions

Assertions

What is an assertion? Is an expression which encapsulates some testable logic specified about a target under test. - Is always True OR False.

Chai is clasified into two:

• BDD (expect, should)
• TDD (assert)

BDD - Behavior-driven development language, is an expressive language in a readable style. TDD - Test-driven development, more classical feel.

Pre-requisites for Mocha

1. NodeJS
2. Node Package Manager NPM

mkdir /path/to/newfolder
node -v #verify node version
npm -v #verify npm version
npm install chai -save-dev #install chai

Import Chai to project adding the following code

const chai = require('chai');

And run from the terminal

npm test/myfile.js

How to use Expect, Should and Assert

See code.

Expect vs Should vs Assert

• Expect supports Node.js and all modern browsers.
• Should doesn't support Internet Explorer.
• Should extends Object.Prototype

Manage undefined with should

// normal scenario
error.should.not.exist();
// given that error is undefined
should.not.exist(error);

Configurations

chai.config.showDiff = false; // turn off reported diff display
chai.config.truncateThreshol = 0; // disable truncating
chai.config.includeStack = true; // turn on stack trace

Adding Chai to your project

1. Install Chai using npm install chai -save-dev

2. Add Chai variables

const chai = require('chai');
const assert = chai.assert;
const expect = chai.expect;
const should = chai.should();

3. Use chai assertions

Thats the end of the introduction. You should be able to start working from here. Next step will be combining it with an automation framework, like Selenium.

• What is Chai, how to install?
• Assertion Styles
• Differences
• Adding Chai assertions to projects
• Centralizing assertions