Getting Started with Cucumber.js | The Behavior-Driven Testing Framework for JavaScript

Modern software teams strive to bridge the gap between developers, testers, and product owners. One of the best ways to achieve that collaboration is through Behavior-Driven Development (BDD), and the Cucumber testing framework makes it seamless. In this guide, we’ll explore Cucumber.js, the JavaScript implementation of Cucumber, understand how it works, and see how tools like Keploy can enhance your testing workflow.

🧠 What Is the Cucumber Testing Framework?

Cucumber is an open-source testing framework built around the principles of Behavior-Driven Development (BDD). It allows writing test cases in plain English using Gherkin syntax, so both technical and non-technical stakeholders can understand the expected system behavior. Instead of focusing on how something is implemented, Cucumber focuses on what the software should do using natural-language statements like:

Feature: User Login

  Scenario: Successful login with valid credentials

    Given the user is on the login page

    When they enter valid credentials

    Then they should be redirected to the dashboard

Cucumber then maps these steps to executable code written in your preferred language such as JavaScript, Java, or Python.

⚙️ What Is Cucumber.js?

Cucumber.js is the JavaScript implementation of the Cucumber testing framework. It enables developers to write and run BDD tests directly in Node.js environments. You can install it easily using npm:

npm install --save-dev @cucumber/cucumber

Once installed, you can create a test setup that connects Gherkin feature files with your JavaScript test definitions.

📁 Understanding the Cucumber JS File Structure

A typical Cucumber.js file structure looks like this:

project/

 ├── features/

 │   ├── login.feature

 │   └── signup.feature

 ├── step_definitions/

 │   ├── login.steps.js

 │   └── signup.steps.js

 ├── support/

 │   ├── hooks.js

 │   └── world.js

 ├── cucumber.js

 └── package.json

Key Components

Feature Files (.feature) describe the behavior in plain English (Gherkin).\
Step Definitions (.js) contain the JavaScript code implementing each step.\
Support Files include hooks, global configurations, and shared logic.\
cucumber.js file defines Cucumber configuration (paths, formatters, and options).

🧩 Example: Using Cucumber with JavaScript

Here’s a simple example of Cucumber with JavaScript for login validation.

login.feature

Feature: Login Functionality

  Scenario: Successful login

    Given the user is on the login page

    When they submit valid credentials

    Then they should see the dashboard

login.steps.js

import { Given, When, Then } from '@cucumber/cucumber';

import assert from 'assert';

import { login } from '../src/app.js';

 

Given('the user is on the login page', function () {

  this.page = 'login';

});

 

When('they submit valid credentials', function () {

  this.result = login('user\@example.com', 'password123');

});

 

Then('they should see the dashboard', function () {

  assert.strictEqual(this.result, 'dashboard');

});

Run the test

npx cucumber-js

This runs your Cucumber.js test suite and outputs readable results describing the scenario’s success or failure.

🤝 Using Keploy with Cucumber.js for API Testing

While Cucumber.js excels in functional and behavioral testing, Keploy can automate your API test generation alongside it, making your testing process faster and more comprehensive.

Here’s how they work together:

Task	Cucumber.js	Keploy
Define expected behavior	✅ (via Gherkin)	❌
Execute step definitions	✅	✅ (for APIs)
Auto-generate test data	❌	✅
Record & replay API calls	❌	✅
CI/CD integration	✅	✅

Keploy automatically records real API interactions during manual or BDD testing and converts them into test cases with mocks, ensuring consistent API validation across environments.

👉 Try it here: Keploy.io

🔍 Why Use Cucumber with JavaScript

Readable Tests: Stakeholders can easily understand requirements.\
Reusable Steps: Define once, use across multiple features.\
Integration with Frameworks: Works well with Playwright, Cypress, and Jest.\
Seamless Automation: Combine with Keploy for API-based test generation.

🧠 Best Practices for Cucumber.js

Keep scenarios short and clear — each scenario should test one behavior.\
Use reusable step definitions to avoid duplication.\
Integrate with CI/CD pipelines using tools like GitHub Actions or Jenkins.\
Leverage Keploy to add automatic test recording and mocking for API endpoints.

 How to Test AI Models

Testing AI models requires a slightly different approach compared to traditional software testing. Instead of verifying fixed outputs, AI testing focuses on evaluating accuracy, bias, and consistency across various data sets and predictions.

Here are some best practices:

1. Define expected behavior in plain English using BDD-style scenarios with Cucumber.js, such as “Given the model receives image data, When it predicts, Then accuracy should exceed 90%.”
2. Automate API-level validation with Keploy, which can record and replay API calls to test model inference endpoints.
3. Use data-driven testing to evaluate model performance against multiple datasets.
4. Monitor model drift and bias through regression test cases that validate ongoing performance.

Keploy can help automate the API layer of your AI workflows, ensuring that your model predictions and endpoints behave consistently across releases while Cucumber helps describe expected model outcomes in a human-readable format.

Final Thoughts

Cucumber.js makes testing more human-readable, collaborative, and maintainable, while Keploy adds automation intelligence to your QA workflow. Together, they create a powerful test ecosystem where BDD meets AI-driven automation. Whether you’re just starting with Cucumber and JavaScript or looking to improve automation and test AI models, combining these tools can help you ship quality software faster and with confidence.

Learn more about AI-driven and open-source test automation at Keploy.io.