The Beginner’s Guide to Unit and Integration Testing in JavaScript

| Updated on February 27, 2024

What is a Unit Test?

Unit tests verify that code in the codebase called “unit” (a small piece that can be isolated) behaves the way it is supposed to and the complete isolation approach is employed when testing the smallest component of an application against the expected behavior. As the term “complete isolation” is used here, it implies the developer requires the application to be isolated from external resources or dependencies such as databases, HTTP servers, or the files system. Unit tests become faster and more stable by not failing due to integration issues with these external services.

Best Practices for creating Unit Tests

The following are best practices for creating unit tests:

  • The test cases need to run at high speed for developers. Developers need quick and simple tests The development team will be unable to run test cases as often if they are slow.
  • Simple unit test cases also lead to more accurate test results.
  • It is not a good idea to duplicate implementation logic in test cases.
  • In order for test cases to be deterministic, they must exhibit the same behavior as long as the code remains unchanged and while doing deterministic testing, you must use real devices and browsers, not simulators and emulators. Without exposure to real production environments, test results are far from being accurate or deterministic.
  • An effective naming convention will help the test cases stand out.

Selenium JavaScript Frameworks for Unit Testing

Unit testing for JavaScript involves writing JavaScript code to verify all functionality of a web page or web application module. After adding the code to HTML as an inline event handler, it is then executed in the browser. Test suites are created by organizing unit tests.

For JavaScript unit testing, a variety of frameworks are available. Here are some of them:

Node.js: Node.js and browser-based assertion library for Javascript. There are a wide variety of test runners and unit testing frameworks that can be used with this framework, such as Protractor, Karma, Mocha, QUnit, Jasmine, etc.

Jasmine:  Using Jasmine, you can easily write tests for JavaScript code. It does not require a DOM or any other JavaScript framework, and it has an easy-to-understand syntax that makes writing tests simple.

Mocha: The framework runs both in the browser and in Node.js. Tests run serially in Mocha, providing flexibility and accuracy in reporting while catching uncaught exceptions and map them to the correct test case.

Jest: Often, unit tests cannot be very helpful when to run on the frontend application, so this open-source framework was built to work with React Native and React-based web applications. Configuring unit tests for the front-end can be time-consuming, but Jest makes this process much easier.

Karma: The main goal of Karma is to provide developers with a productive environment for conducting tests. In which developers don’t have to set up multiple configurations, but rather one where they can just write the code and get instant feedback. You can run your code on a headless PhantomJS instance or on a real browser on a real device such as a mobile phone, tablet, or desktop.

Cypress: A JavaScript-based framework based on Mocha for performing Cypress E2E testing. JavaScript tests can be run in the browser using Cypress, allowing for convenient and easy asynchronous testing. Unit tests in Cypress run without even needing a web server. Consequently, Cypress is ideally suited for testing JS/TS libraries intended for browser use.

Integration Testing – An Overview

Essentially, an integration test aims to check if the joint implementation of several program units that have been unit tested beforehand is functioning correctly. It is challenging to write integration tests in complex software systems due to a multitude of interconnections suitable for some specific functions.

Integration testing consists of several general components:

Develop Functions – Write Test Cases

Having developed your functions first, you can begin writing the test cases. The test cases are sent to the remote branch in order to perform the integration test.

Building the Original Integrated Test Environment

A dedicated environment is essential for testing because it can provide proper monitoring, resource management, and logging. Therefore, every integration test should begin in a clean environment.

Testing, Schedule, and Execution

Testing new business features are necessary, and testing should be integrated into the continuous integration server and triggered on development milestones such as a  pull-request merge. In addition, integration tests can be scheduled or executed after the completion of the code and tests.

Report on Integration Test Results

As a result of reporting test results, the development team will be updated on the progress so that if there is an issue, the development team can take immediate action. However, this reporting must be done through regular development tools channels like Slack or Jira to make the process seamless.

Integration tests: Why Should I Do Them?

The software modules are each subjected to component testing, but they may still contain errors. And some of the well-known reasons are:

  • APIs contain instructions on how to communicate between different components. Having an excellent API for your business is critical as it makes developing computer programs easier. To incorporate a user-friendly look, modules usually interact with these APIs or third-party tools. But integration testing is highly valuable for making sure what’s received from the API is correct and meets expectations.
  • It is not uncommon for data to change when transferred from one module to another; the programmer may have designed the module differently compared to what was actually delivered. Because of such modifications, this causes issues in the integration of modules.
  • Manual testing is problematic because each aspect of a system is observed separately. For this reason, developers must employ integration testing to ensure that the end product is fault-free.

What is Mock Testing?

Mocking allows you to create a mock version of an external or internal service that can be served as a stand-in for the real one, which makes your tests run faster. In cases where you interact with an object’s properties rather than its behavior or function, mocking can be used.

What is Stub Testing?

In case your implementation is only interacting with a certain behavior of the object, you can use a stub to mock the behavior rather than the entire object.

Mocking and Stubbing in Unit Tests

If your program uses external dependencies, for example, system calls or access to a database, then mocking or stubbing is a good idea. You exercise the implementation whenever you run a test. Suppose when you use the delete/create function, you’re not letting the process be efficient, by allowing it to create or delete files, and the data it generates and deletes isn’t useful. Furthermore, you will have to go through the process of manually deleting something every time. And it is again expensive to clean up. Mocking/stubbing can help a lot in this case. 

Let’s use an example. Imagine the test writes a file to a .txt file, and then the system under the test deletes the file. This indicates that the real problem is not whether the test is independent, but rather the slowness of the system calls. In this case, you can stub the response from the file system call, which will take a lot less time since it would return immediately.

Mocking in Integration Testing

As part of integration testing, you assess relationships between services. One approach is to get all the dependent services up and running for the testing environment. However, this is not necessary. You may encounter multiple failure points due to services you cannot control, which adds to the complexity and time required for testing. You should write a few service integration tests with mocks and stubs to narrow down your scope. Integration testing follows different rules than unit testing. Here, you should only test functionality and implementations that you have control over. For this purpose, you can use mocks and stubs. Identify first which integrations are important. Next, decide which external or internal services can be mocked.

Tests: What Makes a Good One?

To launch a successful software product, thorough tests are essential. If your software doesn’t work properly, end-users won’t buy it or use it. Nonetheless, testing for bugs takes time. It is repetitive, costly, and prone to error. Prior to releasing your software to the public, you must devote enough time to testing every component.

The following are some tips. You cannot automate every test, so it’s important to decide which ones you want to automate first. Automating the following will benefit you most:

  • Testing often leads to operating errors.
  • Tests that require multiple records.
  • A test designed to identify frequently used functions that can lead to high-risk conditions.
  • Those tests require a lot of time and effort to run manually.

You should also test frequently and early. Launch your tests immediately and repeat them as frequently as necessary in order to capture the full potential of your product.

Closing Words

A faster go-to-market for your web app is possible if you perform unit tests during the development phase. Thus, a unit test framework that produces rapid unit tests, in addition to offering Selenium support, is crucial. 
As part of this article, we presented some unit test frameworks. You can use the discussed Unit testing frameworks to perform automated browser testing for your web app on cloud-based testing platforms like LambdaTest. It provides an online browser farm of 3000+ browsers and OS combinations for your test automation needs. In addition, it offers top-notch features like Cypress testing, Selenium testing, Appium testing, and HyperExecute to scale up your automation testing experience to the next level.

Adam Green

With more than 3 years of experience as a software and tech writer on Adam has been writing articles, blogs, and featured stories centered around the software and tech niche since he graduated from Virginia Tech University. He writes savvy articles, tutorials, and reviews that explain difficult concepts to readers of all levels. His expertise includes software development, cybersecurity, artificial intelligence, and emerging technologies. Through simple and engaging writing, Adam constantly delivers useful insights that enable readers to feel at ease in the ever-changing technological scene.

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