JavaScript:
Writing tests

How to:

Native Approach (using Jest)

Jest is a popular testing framework that provides a friendly API for writing unit tests in JavaScript. It requires minimal configuration and comes with features like mock functions, timers, and snapshot testing.

1. Installation:

npm install --save-dev jest

2. Writing a simple test:

Create a file named sum.test.js:

const sum = require('./sum'); // Assume this function simply adds two numbers

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

3. Running your test:

npx jest

Sample Output:

PASS  ./sum.test.js
✓ adds 1 + 2 to equal 3 (5ms)

Testing Asynchronous Code

Jest makes it easy to test promises and async/await syntax:

// asyncSum.js
async function asyncSum(a, b) {
  return Promise.resolve(a + b);
}

// asyncSum.test.js
test('async addition works', async () => {
  await expect(asyncSum(1, 2)).resolves.toBe(3);
});

Using Third-Party Libraries (Mocha & Chai)

Mocha is another popular testing framework, often used with the assertion library Chai for more expressive tests.

1. Installation:

npm install --save-dev mocha chai

2. Writing a test with Mocha and Chai:

Create calculate.test.js:

const chai = require('chai');
const expect = chai.expect;

const calculate = require('./calculate'); // A simple calculation module

describe('Calculate', function() {
  it('should sum two values', function() {
    expect(calculate.sum(5, 2)).to.equal(7);
  });
});

3. Running your tests with Mocha:

Add a script in your package.json:

"scripts": {
  "test": "mocha"
}

Then execute:

npm test

Sample Output:

  Calculate
    ✓ should sum two values


  1 passing (8ms)

These examples illustrate basic test writing and execution in JavaScript. Adopting a testing framework like Jest or Mocha with Chai can provide a solid foundation for robust application testing, helping to ensure your code functions as intended across updates and refactorings.