Jest

ELI5 — The Vibe Check

Jest is the most popular JavaScript testing framework. It does everything: runs your tests, provides expect() for assertions, mocks functions, generates coverage reports, and even has a watch mode. If you've done JS testing, you've probably used Jest.

Real Talk

Jest is a JavaScript testing framework developed by Meta. It provides a zero-config setup, built-in mocking, code coverage, snapshot testing, and parallel test execution. It works with Node.js, React, Vue, and most JS projects out of the box.

Show Me The Code

// jest.config.js
module.exports = { testEnvironment: 'node', coverageThreshold: { global: { lines: 80 } } };

// user.test.js
test('greets user by name', () => {
  expect(greet('Alice')).toBe('Hello, Alice!');
});

When You'll Hear This

"We use Jest for all our unit and integration tests." / "Jest's --watch mode is great for TDD."