Set up Istanbul and Mocha for Node.js code coverage with this guide. Learn to configure, run tests, and generate coverage reports seamlessly for your projects.

Configuring Istanbul and Mocha for Node.js Code Coverage

Introduction

Code coverage is an essential part of the software development process, allowing developers to determine which parts of their codebase are being tested. Istanbul is a popular JavaScript code coverage tool, while Mocha serves as a flexible test framework for Node.js applications. In this guide, we will walk through the steps to configure Istanbul and Mocha for effective code coverage reporting in your Node.js projects.

Prerequisites

Before we begin, ensure that you have Node.js and npm (Node Package Manager) installed on your machine. You can verify your installation by running the following commands in your terminal:

node -v
npm -v

Once verified, you can proceed to set up your project.

Setting Up Your Project

Start by creating a new directory for your project and initializing it with npm:

mkdir my-node-project
cd my-node-project
npm init -y

This command will create a package.json file, which will serve as the configuration file for your project.

Installing Mocha and Istanbul

Next, install Mocha and Istanbul as development dependencies. Run the following command in your terminal:

npm install --save-dev mocha nyc

Here, 'mocha' is the test framework, while 'nyc' is the command-line interface for Istanbul that provides code coverage reporting.

Creating Test Files

Now, let's create a simple test file. Create a directory named 'test' and add a test file called 'sample.test.js'. Use the following commands:

mkdir test
touch test/sample.test.js

Open 'sample.test.js' and add a simple test case:

const assert = require('assert');
const { add } = require('../src/sample');

describe('Sample Test', () => {
    it('should return the sum of two numbers', () => {
        assert.strictEqual(add(1, 2), 3);
    });
});

In this example, we assume there is a function 'add' in a sample module that we will test.

Writing Code to Test

Now, create a directory named 'src' and add a file called 'sample.js' with the following content:

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

module.exports = { add };

Configuring NYC

To configure NYC for code coverage, add a section in your package.json file. Include the following:

"nyc": {
    "reporter": ["text", "html"],
    "include": ["src/**/*.js"],
    "exclude": ["test/**/*.js"]
}

This will set up NYC to generate coverage reports in both text and HTML formats, including only files in the 'src' directory.

Running Tests with Coverage

Now, you can run your tests with code coverage by using the following command:

npx nyc mocha

After running the tests, NYC will generate coverage reports in the console and create an 'coverage' directory with an HTML report. You can open the HTML file in your browser to visualize the code coverage details.

Conclusion

By following these steps, you have successfully configured Istanbul (via NYC) and Mocha for code coverage in your Node.js application. This setup not only helps in maintaining code quality but also ensures that your code is thoroughly tested, leading to more reliable and maintainable applications.