How do you write unit tests for JavaScript code?

To write unit tests for JavaScript code, you typically use a testing framework like Jest or Mocha. First, you set up your testing environment by installing the necessary libraries. Then, you write test cases using functions like describe, it, or test to define your tests. Each test case should focus on a small, isolated piece of functionality. You use assertions to check if the output of your code matches the expected result.

Example using Jest:

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

// sum.test.js
const sum = require("./sum");

test("adds 1 + 2 to equal 3", () => {
  expect(sum(1, 2)).toBe(3);
});