Jest

Jest is a delightful JavaScript Testing Framework with a focus on simplicity. It works with projects using: Babel, TypeScript, Node, React, Angular, Vue, and more.

When to Use

• JavaScript & TypeScript Unit Testing: Standard, battery-included test runner for React, Node.js, and legacy frontend projects.
• Snapshot Testing: Freezing and asserting on large rendered component output, GraphQL responses, or JSON configurations.
• Comprehensive Mocking Engine: Spying on, mocking, and stubbing functions, timers, and entire modules with jest.mock().
• Code Coverage Reporting: Generating built-in Istanbul code coverage metrics without external plugins.

Quick Start

// sum.js
function sum(a, b) {
  return a + b;
}
module.exports = sum;