How do you write unit tests in Node.js?

Short answer: Unit tests check small, isolated pieces of your code (like functions) to make sure they work as expected.

Explain a bit more

Basic example using Mocha and Chai: // calculator.js function add(a, b) { return a + b; const { expect } = require('chai'); describe('add function', () => { it('should return the sum of two numbers', () => { const result = add(2, 3); expect(result).to.equal(5); }); }); Run tests with: mocha This test suite checks if add(2,3) equals 5 — simple and effective.

Example code

}
module.exports = add; // test/calculator.test.js const add = require('../calculator');

Real-world example (ShopNest)

A ShopNest BFF in Node.js aggregates catalog and price APIs for the React storefront.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.