Introduction to TDD in Node.js

  • Node.js
  • Gabriele Romanato

Test-Driven Development (TDD) is a software development methodology that involves writing tests before the application code. In the Node.js environment, this practice is very common thanks to the availability of testing frameworks like Mocha, Chai, and Jest.

Why use TDD

  • Encourages more modular and maintainable software design
  • Helps prevent bugs from the early stages of development
  • Makes code refactoring safer

Common tools

To implement TDD in Node.js, the most common tools are:

  • Mocha: test framework
  • Chai: assertion library
  • Jest: complete framework with built-in support for assertions and mocking

Installing Mocha and Chai

npm install --save-dev mocha chai

Add a test script to your package.json:

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

Practical example: sum function

Let's write a test for a function that adds two numbers:

const { expect } = require('chai');
const sum = require('../sum');

describe('sum', () => {
  it('should return the sum of two numbers', () => {
    expect(sum(2, 3)).to.equal(5);
  });
});

Now let's implement the sum function:

function sum(a, b) {
  return a + b;
}

module.exports = sum;

Running the tests

Run the tests with:

npm test

Conclusion

TDD is a powerful practice to improve code quality and reliability. In Node.js, thanks to the simplicity of the available tools, it's easy to get started and quickly see tangible benefits.

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