Code coverage basics in Node.js - Mini Project: Build & Apply

Code coverage basics

📖 Scenario: You are working on a small Node.js project. You want to check how much of your code is tested by your tests. This helps you find parts of your code that need more testing.

🎯 Goal: Set up a simple Node.js function and a test file. Then configure a code coverage tool to measure how much of your function is tested.

📋 What You'll Learn

Create a Node.js function in a file called math.js

Create a test file called math.test.js that tests the function

Add a configuration to enable code coverage using nyc

Run the tests with coverage and verify the coverage report

💡 Why This Matters

🌍 Real World

Code coverage is used in real projects to check how much code is tested. This helps developers find untested parts and improve test quality.

💼 Career

Many software jobs require writing tests and using coverage tools like nyc to ensure code quality and reliability.

1

Create the function to test

Create a file called math.js and write a function named add that takes two parameters a and b and returns their sum.

Node.js

// Your code here

Need a hint?

Define a function named add with parameters a and b. Return their sum. Export the function using module.exports.

2

Write a test for the function

Create a file called math.test.js. Import the add function from math.js. Write a test using test that checks if add(2, 3) returns 5.

Node.js

const { add } = require('./math');

// Your test code here

Need a hint?

Import add from math.js. Use test to check if add(2, 3) equals 5.

3

Configure code coverage with nyc

Create a file called .nycrc in your project root. Add JSON content with { "all": true } to enable coverage for all files. Also, add a script in package.json called test:coverage that runs nyc --reporter=lcov --reporter=text npm test.

Node.js

{
  "all": true
}

// Add the following script to package.json:
// "test:coverage": "nyc --reporter=lcov --reporter=text npm test"

Need a hint?

Create a .nycrc file with { "all": true }. Add a test:coverage script in package.json to run tests with coverage using nyc.

4

Run tests with coverage and check report

Run the command npm run test:coverage in your terminal. This runs your tests and shows a coverage report in text format. Verify that the coverage report shows 100% coverage for statements, branches, functions, and lines.

Node.js

// Run the command below in your terminal
// npm run test:coverage

// Check the coverage report output

Need a hint?

Run npm run test:coverage in your terminal. Look for the coverage summary showing 100% coverage.