How to do Unit Testing in NodeJS


Imagine you spent hours and hours developing a web application you have been planning to create for months. As you test your application, you find that it’s defective. With your heart shattered, you examine and troubleshoot only to find that the whole setup malfunctioned for a tiny little error on a unit of the application, which will now require you to rework it in its entirety. 

Devastating, right? This is every developer’s nightmare. 

What about a tool that helps you stay wary and descry errors in time and make your journey as a developer seamless? Node.JS is one such tool that isolates your application and helps catch errors in the early stages of development. It is one handy tool for developers in creating web applications. It allows you to pilot the server side and run Javascript, vastly simplifying your tasks. 

You may employ tools such as Jest, Mocha, or Ava to automate testing isolated components for errors and debug your application at the very beginning, repeating in intervals, ensuring a robust, reliable, and high-performing application as your outcome. 

Now, let us explore the depths of Node.JS. 
Before we do so, let us unravel its bedrock – Unit Testing. 

Unit Testing: Overview 

Chemicals are handled with extreme care in pharmaceutical laboratories, especially when developing a medicine. Each chemical component is thoroughly reviewed and tested for safety before undergoing the process. This ensures that the final product is of the desired outcome. 

In the tech world, when developing applications, it is similarly essential to test out each unit of code in isolation from the rest of the system. This critical technique is called Unit Testing. 

Unit Testing involves carefully investigating each unit or component of the application, typically at the beginning of the process, which is continued regularly to catch bugs and errors in the early stages. 

Unit Testing ensures that the entire code is error-free and ready to be integrated into a more complex system, eradicating the fear of inaccuracy. 

Importance of Unit Testing

Unit Testing is more than just the shield and armor to fight against software bugs. It is a powerful tool that plays a crucial role in many ways. Let us explore some of them. 

Guaranteed Accuracy 

By performing unit testing, you can rest assured that the entire code is functioning as it should, as it ensures that each unit of code is flawless in its execution at every situation and edge case it could encounter. 

Speedy Development 

Unit Testing helps detect any errors at the early stage of development. This quick fix accelerates the development process. 

Money-Saving Technique

Detecting and correcting defects before execution of the entire code thread into a larger system or establishing the application saves developers from unneeded worries and expenditures at a later stage. 

Improved Quality of the System

Besides correcting errors, Unit testing also helps developers understand how the code could be further optimized or reworked for an enhanced outcome. Subsequently, this results in a higher-quality application. 

Common Communication Language

Through its standard language and convention for understanding software systems, it improves the scope of collaboration between developers and testers. 

Unit testing is a highly constructive technique that can be implemented for a smooth-sailing development experience. Now, let us see how Node.JS harnesses unit testing to improve your productivity collectively. 

Node.JS and its Extensive Ecosystem

A lightweight, efficient tool that helps you build server-side web applications and desktop applications, APIs, and microservices, among others, on any platform sure is a jackpot of a tool. Node.JS is one such tool. It is an open-source JavaScript runtime environment built on the Google V8 JavaScript engine. 

The Node Package Manager (NPM) is a command-line tool home to various libraries, frameworks, and modules in the Node.JS ecosystem. It gives developers the ability to install and take control of the code. Moreover, both the front-end and back-end development of the system can be run using JavaScript on both sides, making it a sought-after option for developers. 

Node.JS: Fun Facts 

  • Top businesses such as Netflix, Amazon, LinkedIn, Reddit, Uber, GoDaddy, and Paypal have employed Node.JS for building their websites. It has been appraised as one of the best tools for its scalability. It is also widely considered to enhance the website/app performance.
  • It has been recorded that over 30 million websites worldwide use Node.JS, which included 6.3 million users from the US alone. 
  • Over 1 billion downloads have been recorded. 
  • Node.JS can reduce the loading time of your website by about 55%.
  • Node.JS is one of the most sought-after tools for establishing payment processing and e-commerce websites. For instance, AliExpresses uses Node to empower its website’s backend. 
  • Its libraries, frameworks, and modules are also highly sought-after by web developers, with nearly 35% statistically recorded. 

The global popularity of Node.JS speaks volumes regarding its advanced functionality and quality. 

Now that we know what Node.JS stands for, let us dig deeper into its execution. 

Node.JS Unit Testing & Techniques for Isolating Units

As we have learned already, the primary goal of Node.JS Unit Testing is to isolate a unit of code of a system to thoroughly test, correct, and optimize it for an adept execution of the code for final establishment. 

Now, developers choose one of the many frameworks offered by Node.JS, like Ava, Jest, or Jasmine, which provides many tools and APIs. Here, with the execution of a chosen technique, developers write and run test cases to derive the test report. These techniques, such as stubbing, mocking, and spying, are crucial in solitary testing of units detaching them from external dependencies and ensuring accuracy in test results. 

What are Spying, Stubbing, and Mocking?

Spying: It is typically used when you want to monitor and test the behavior of a module of a complex system. It records all the arguments sent to, values returned by the function, and the number of times it was called. This allows us to test whether the function was called as it was supposed to and to review all the arguments passed. 

Stubbing: A function that is used to set predefined values for the behavior of another function or module. Developers use this to simulate responses without connecting with its external dependencies. It is also used to remove the chances of its interaction with external dependencies, giving developers the ability to control the outcomes. 

Mocking: Mocking is a combination of both Stubs and Spies. When using external APIs, developers create predefined responses to specific arguments. It helps verify that the system returned the expected response. 

By employing and implementing these techniques, developers can ensure the tests’ reliability and move forward according to the reports. Programmers must understand the intricacies of running tests to deliver efficient outputs. 

Configuring and Running Unit Tests In Node.JS with Testing Frameworks

Node.JS unit testing offers the platform to vastly enhance a software system’s caliber and efficiency. On that account, developers must master the execution of Node.JS unit testing. 

Below, we will provide step-by-step guidance to configure and run unit tests in Node.JS with testing frames, such as Ava, Jest, or Mocha. Remember, the following steps might slightly contrast depending on the testing framework you work with. 

Step 1: Install and configure your choice of testing framework. 

Step 2: Run npm init in the command line to commence with the Node.JS project. 

Step 3: Store your test files in a test directory created in your project root directory.

Step 4: Run npm install and save your choice of a testing framework as its dev dependency. 

Step 5: Within the testing framework, use its syntax and API to write the test cases. 

Step 6: Create a configuration file for the chosen testing frame. Here, you can modify the settings and changes you require for the desired outcome. 

Step 7: Enter the chosen testing framework’s command in the command line to run the test successfully. 

Let us explore an example to see how it works. 

  1. Run npm unit in the command line to initialize a new Node.js project.
  1. Run npm install –save-dev jest to install Jest as a dev dependency.
  1. Create a test directory in your project root directory and create a test file, such as test/example.test.js.
  1. Write your test cases in the test file using Jest’s syntax and APIs.
  1. Create a jest.config.js file in your project root directory and configure Jest with options like test matches and environments.
  1. Run your tests by executing the npx jest command in the command line.

You can confidently type in your first unit test by following these steps. 

Writing Your First Unit Test

Let us write your first unit test with you. 

Step 1: Setup

First, let’s install Jest using npm:

Step 2: Writing a Unit Test

For this example, we’ll write a simple unit test for a function that returns the sum of two numbers. Create a new file called sum.test.js and add the following code:

Here, we import the sum function from another file (which we’ll define shortly) and write a test that expects the sum of 1 and 2 to equal 3. The test function is a global function provided by Jest that takes a description of the test and a callback function that contains the actual test logic. In this case, we’re using the expect function to check if the result of sum(1, 2) is equal to 3.

Step 3: Writing the Function to Test

Now that we have a unit test, let’s write the function it will test. Create a new file called sum.js and add the following code:

Here, we define a simple function that takes two arguments and returns their sum. We also export the sum function using the module.exports to be used in other files.

Step 4: Running the Unit Test

To run the unit test, simply run the following command in your terminal:

Jest will automatically find all test files in your project and run them. If everything is working correctly, you should see the following output:

Congratulations, you’ve just written and run your first unit test!

Different Types of Tests 

Integration and End-to-End Test

One primary thing to consider while testing unit codes in isolation is to test whether it works efficiently when conjoined with other codes and as a whole system. Luckily for us, Node.JS offers us a way to check for the same in a seamless method.

Here’s an example of an integration and end-to-end test. Again, let us consider the same function as we previously did. 

In the integration test, we define a test that checks if the sum function correctly adds two numbers together. Here, we’re testing the integration between the sum function and the variables a and b.

In the end-to-end test, we simulate a user interacting with a web page using the sum function to add two numbers. This test checks the end-to-end functionality of the application.

Test-Driven Development (TDD) 

Before writing code, we go for a software development process called Test-Driven Development (TDD) which involves various tests. The aim is to establish a foolproof and active codebase by thoroughly testing all code. First, let us explore an example to understand how TDD operates. For this, let us test the function of adding two numbers. Here, we commence with a failing test case to examine if the output is as expected. Once done, we write a minimum code to ensure all tests pass.   

Here’s an example code for the unit test for your reference: 

If you observe the code closely, you will find that the test checks if the function returns the result of addition of two numbers, if both the arguments are numbers while it returns NaN if one of the arguments are not numbers. 

Best Practices for Node.JS Testing

Node.JS in itself is a highly efficient tool. Regardless, there are a few measures you can take to ensure that your unit testing process is 100% effective in its execution. Employing these measures ascertains that the code you run is of excellent quality, giving you a green signal to proceed with your project. 

Keep it crisp. 

When writing test cases, your unit tests must be precise and short. This works by enhancing the speed and accuracy of your tests tenfold. It also ascertains no bumps in your testing journey, allowing you to attain fast and accurate results. 

Implement Mocking and Stubbing 

By using unit testing techniques such as mocking and stubbing, you can ensure the reliability and accuracy of your tests. 

Create concise test cases 

The more concise your codes are, the more value it retains in the long run. The readability of the code ascertains that even with the evolution of your codebase, the test case remains intact and continues providing accurate outputs.

Repeat testing for expected results

Every once in a while, running the tests to review the generation of expected results ensures the reliability of your code. It also helps remove bugs in the early stages which vastly saves time. 

Use relevant test names.

Using relevant test names helps you keep track of test cases further down the road when the system may need to get more complex. Again, this saves a lot of time and haste. 

Eliminate the risk of test pollution.

You must avoid frequent faulty testing that inherently fails. Also, ensuring that your test cases do not affect other test cases enhances the performance of your system. 

By following these guidelines, you get one step closer to becoming a seasoned developer. 

Efficient Testing & Reporting for Node.JS Applications

Efficient Testing in Node.JS: Running Tests & Analyzing Results 

  1. Utilize a package manager, such as NPM to install your choice of testing framework and dependencies. 
    Example: npm install –save-dev jest
  2. Write down a list of test cases for all possible scenarios and edge cases. 
  3. The tests are to be executed using the command line of the testing frame, say Jest. 
    Example: npm test
  4. Examine the derived output of the success and failures encountered by the testing framework. 
  5. Work on the failed outputs till they pass the test. 
  6. Keep track of the amount of code covered by the testing framework. Now run a test on uncovered codes. 
  7. Optimize your code in accordance with the result to ensure its quality and maintenance. 

Following these steps, you are assured that all your codes have been efficiently tested and are ready for execution. 

Improving your Node.JS Testing with Code Coverage Reports 

Code Coverage Reports are used as an extra line of defense against any probable errors or missed codes. In addition, code Coverage Report Tools such as Jest ensure that you have tested each unit of code of the project. 

  1. Install Jest and the Istanbul code coverage tool as a development dependency in your Node.js project using npm. For example, run npm install –save-dev jest Istanbul.
  2. Configure Jest to generate code coverage reports by adding the –coverage flag to the Jest CLI command in the package.json file. This can be done by adding “scripts”: { “test”: “jest –coverage” } to your package.json file.
  3. Run the tests using Jest by running the npm test command. Jest will generate a code coverage report and save it in the coverage directory in your project.
  4. Open the index.html file in the coverage/lcov-report directory to view the code coverage report in your browser. The report will show which lines of code are covered by tests and which are not.
  5. Analyze the code coverage report to identify parts of your code that are not being tested. Then, refactor your code and tests to increase code coverage and improve the effectiveness of your tests.

Streamline Node.js Testing with Automated Continuous Integration (CI) using Jenkins or Travis CI.

Why strain your fingers when automated testing tools such as Jenkins or Travis CL exist? These tools use Continuous Integration (CI). These tools help evaluate your code and pick up errors while you drink your regular cup of coffee.

  1. Set up a CI server like Jenkins or Travis CI to automatically build and test your Node.js project whenever changes are made to the code.
  2. Configure the CI server to install any necessary dependencies and run the tests using the testing framework.
  3. Create a pipeline or job on the CI server to automate the testing process. The pipeline should fetch the latest code from your version control system, install dependencies, run the tests, and generate code coverage reports.
  4. Configure the CI server to notify you of any failures or errors in the testing process. You can use email notifications, Slack notifications, or other methods.
  5. Monitor the automated testing process results and analyze the code coverage reports to identify any parts of your code that are not being tested. Then, refactor your code and tests to increase code coverage and improve the effectiveness of your tests.

It’s time to say NO to manual testing and implement automated testing tools. These not only save time and effort, but they also ascertain a higher quality code for your perfect codebase. 


Want your code to be fault-free? There’s Node.JS. 

Need your code to run fast and efficiently? Node.JS 

Want your code to retain its quality even with the evolution of your codebase? Node.JS got you! 

Want to code like a pro and ditch the fears of a novice? Node.JS is your buddy. 

Empowering Node.JS and its unit testing ability gives you the liberty to work on minor projects to large-scale projects confidently. 

Incorporating these techniques into your Node.js development process allows you to create robust, reliable, high-quality Node.js applications. 
Alternatively, you can also use’s Chrome extension to make your life much easier. Download our google chrome extension to run extensive tests without much effort. 

So, start implementing these techniques and be a fearless Node.js developer today!

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Sagar Soni

Sagar is the co-founder and CTO of Requestly. When he's not busy architecting the next big thing in software development, you'll likely find him behind the wheel, cruising the streets and enjoying the thrill of the drive. For Sagar, it's all about the code by day and the open road by night.