Mocha

Mocha is a flexible JavaScript test framework. Unlike Jest, it does not come with an assertion library, mocking, or snapshotting built-in. It is a runner that allows you to choose your own tools (usually Chai + Sinon).

When to Use

• Flexibility: You want to pick your assertion library (Chai, Should.js).
• Node.js Backends: standard in many Express/NestJS (legacy) setups.
• Asynchronous Testing: Historically strong support for async (though standard now).

Quick Start

// npm install --save-dev mocha chai
const assert = require("chai").assert;