Chai

Chai is an assertion library. It pairs naturally with Mocha. It supports TDD (assert) and BDD (expect, should) styles.

When to Use

• BDD/TDD Assertion Library: Pairing with test runners like Mocha to write expressive, human-readable assertions in JavaScript/TypeScript.
• Expect / Should / Assert Syntax: Choosing between chainable BDD assertions (expect(foo).to.be.a('string')) and classical TDD assert.
• Deep Object & Array Equality: Comparing nested objects, array sets, and property structures effortlessly.
• Plugin Ecosystem (chai-as-promised, chai-http): Extending assertion vocabularies with async promises and HTTP response assertions.

Quick Start

import { expect } from "chai";

const foo = "bar";
const beverages = { tea: ["chai", "matcha", "oolong"] };