API vs UI Testing: Which One Should You Pick

June 5, 2024Yamini Priya
API vs UI Testing Which One Should You Pick

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In today’s fast-paced world of software development, it’s crucial to ensure that the products you build meet the needs and expectations of your users. This is where testing comes in, and there are various types of testing that you can perform to achieve this goal.

The two important types of testing are API and UI testing. Both play a vital role in ensuring the quality and reliability of products.

In this blog, we will dive deep into the world of API and UI testing, exploring their differences, advantages, and how they impact the quality of products.

Whether you’re a developer or QA tester, this blog will provide valuable insights into the world of software testing and help you ensure that your software is of the highest quality possible.

What is an API?

Before talking about API Testing, let us first understand what an API is and how an API works with an interesting example.

API stands for Application Programming Interface. API allows your application to communicate with another application easily. Simply put, two software applications can communicate with each other and also exchange data with API’s help.

For a better understanding, refer to the following image,

API Testing

  1. Consider you want to dine at a restaurant. To order your meal, you’ll need a waitperson to receive your order and pass it on to the chef, who will prepare your order.

  2. The chef then prepares your meal and gives it to the waitperson.

  3. Now, the waiter will deliver the meal they collected from the chef to you.

Here, you’re (the restaurant customer) the application, the waitperson is the API, and the chef is the server.

Likewise, an API collects a request from an application and passes it on to a server. The server processes the request and delivers the response to the API. Then, the API returns the response to the application.

How an API works

How does an API work?

API connects the world in various ways. We utilize API in our day-to-day activities while using various applications. Let’s take Lyft and Google Maps as an example to understand the working of an API.

Google Maps and Lyft API

If you regularly use Google Maps to commute from your location to the office, you must have noticed ride services offered by applications like Lyft on Google Maps. Refer to the below image to understand how Google Maps and Lyft’s API work,

API vs UI Testing

Now, let’s discuss in detail to understand how this works,

  1. The user searches for a destination on Google Maps and selects the ride-sharing option.

  2. Google Maps sends a request to Lyft’s API for ride information, like available ride options, estimated arrival time, and pricing.

  3. Lyft’s API processes the request and returns the ride information like ride price, travel time, and driver details to Google Maps in a structured format such as JSON.

  4. Now, Google Maps uses the returned information to display ride options and prices to the user.

  5. If the user selects a ride option, Google Maps sends a ride request to Lyft’s API with the user’s location and destination.

  6. Lyft’s API then processes the ride request and assigns a driver to the user.

  7. The driver’s location and ETA are sent back to Google Maps, which displays the information to the user.

  8. The user can track the driver’s progress on the map and receive notifications about the ride status.

Note – Lyft is available only in US and Canada

Swiggy and Google Maps API

In India, you can see how products like Swiggy and Google Maps communicate with each other using APIs. Let’s see how they work together with a clear explanation,

Swiggy uses Google Maps API to provide accurate and real-time tracking of their delivery partners to their customers. By integrating the Google Maps API into their platform, Swiggy shows the exact location of the delivery partner and their estimated time of arrival. Thus, they provide customers with a better and more transparent delivery experience.

Note – Swiggy is available only in India

What is API Testing?

API testing is a software testing technique that tests the APIs. It helps check if the APIs are working fine as expected in terms of functionality, performance, reliability, and security.Unlike UI testing, which tests the look and feel of the application, API testing focuses on the business logic of the application. Also, this testing requires software to send calls to the API.The software will send requests to API, receive output, and compare the actual responses with the expected responses. Thus, it helps check if the API is working correctly.

Benefits of API Testing

  • API testing is fast and consumes less time as no user interface is required for this testing.

  • It can improve the overall security of the application as it helps identify security vulnerabilities in the API.

  • API testing works at the business layer of an application beneath the presentation layer. This helps check the products in-depth, validating if all the system components are working as expected.

  • It also ensures that the databases are communicating correctly.

  • It requires low maintenance because changes to the API are mostly rare.

API Testing: Manual or Automation?

Though you can perform API testing manually, it is highly daunting as you need to process a large amount of data for testing. API testing offers fast and efficient results when automated. Top automation testing tools like Testsigma, Apache JMeter, Postman, and SoapUI can automate your API testing.

Benefits of Automating API Testing

  • Automating your API tests can save costs associated with manual testing, such as hiring additional testers, reducing testing time, and minimizing the risk of errors and bugs.

  • Automating API testing can significantly reduce the time required to test an application, allowing testers to focus on more complex test scenarios.

What is UI Testing?

UI stands for User Interface. The user interface is the application screen the user interacts with. In UI testing, the testers will test the design and layout of the application.It involves testing the individual components of the interface, such as button color, input fields, and menus, as well as how they interact with each other. UI testing aims to identify any defects, errors, or usability issues before the software is released to end users.

Why is UI Testing Important?

In today’s digital world, the importance of UI testing cannot be overstated. A good website with a good UI and a good user experience plays a critical role in driving traffic, customer retention, and conversions.

Websites are getting bigger in terms of size every year. Meaning they contain a large number of web pages and web elements. A recent survey stated that 21% of businesses have low website traffic due to issues with their website performance.

The performance of a website plays a significant role in user experience and user retention. The ideal loading time should be between 1-2 seconds for any website. A recent survey by Google revealed that over 53% of mobile site visitors leave the web page if it is taking more than three seconds to load.

You can identify all these issues and improve the website’s performance only when you perform comprehensive UI testing.

With the rise of mobile devices and a vast array of browsers and operating systems, ensuring that your product works seamlessly across all platforms is crucial. You can accomplish that by performing responsiveness testing, mobile testing, and cross-browser testing. These testing methods will help verify that your application is responsive, mobile-friendly, and compatible with a wide range of devices and browsers.

Manual UI testing can be tedious as you might want to check every web element, like buttons, images, links, and font, manually for every screen size. Therefore, it is best to automate your UI testing using Testsigma, which can test your application for any device, screen size, and platform.

Benefits of UI Testing

Running user interface tests can be beneficial for your applications in many ways, including:

  • UI testing helps to ensure that users have a positive experience while using your product. By identifying and resolving UI issues, developers can ensure the user interface is intuitive and user-friendly.

  • It also helps to ensure that the code behind the user interface is quality. By testing the user interface and its associated code, developers can easily identify and resolve code-related problems before they become major issues.

  • Improves your application’s quality and stability as UI testing helps find and fix bugs in the UI.

UI Testing: Manual or Automation?

Manual UI testing is preferred only in the case of small websites that consists of a minimum number of web pages and UI elements. But it is highly inefficient and complex for large websites that might have thousands of UI elements to validate.

For example, consider you have a page with 15 input fields. For this scenario, the tester will have to validate all the input fields with different sets of values, which is time-consuming. Hence, automated UI testing is considered the best for fast and efficient results. You can automate your UI testing using Testsigma for quick and efficient results.

Benefits of Automating UI Testing

  • Automated UI testing is faster and more affordable than manual UI testing.

  • Faster debugging and a wider test coverage when you automate your UI testing.

API vs UI Testing: The Core Differences

Both testing types play a major role in assuring a product’s quality. Let’s take a quick look at the API vs UI testing differences to understand these concepts better.

table,td { border: 1px solid; padding: 10px; } table { width: 100%; border-collapse: collapse; }
UI TestingAPI Testing
Testers perform itDevelopers and testers perform it
Functionality of the application is testedThe Business Logic of the application is validated
Testing is between the user and front-end of the applicationTesting is between back-end of one application and back-end of another application
It is performed on the presentation layer, i.e., the front-endIt is performed on the business layer, i.e., the back-end
Slow execution timeFast execution time
Testers can automate UI testsTesters can automate API tests

API vs UI Testing: Which is Better?

API and UI testing serve different purposes, but both are important for testing software applications thoroughly. Let’s take a quick glimpse at how these testing could help create a great quality product. API testing focuses on testing an API’s functionality and behavior. Once the functionality of the APIs is thoroughly tested, it is best to automate those tests to ensure faster and more efficient testing.

On the other hand, UI testing focuses on testing the user interface of the application. Here, the QA will test the web UI elements like button color, font size, and style. In general, UI testing is more time-consuming than API testing, as UI testing involves testing every visual aspect of the application. So, once the UI of an application is stable, it is advised to automate the UI tests.

If you are trying to determine which testing is better than the other, then that is unlikely to result in a successful outcome. You need to perform both these testing to ensure the quality and reliability of a software application. Also, they both need to be automated.

Automating API and UI Testing With Testsigma

Though there are different tools available to automate these testing, Testsigma is one tool that will let you automate both from the same place. It is a cloud-based test automation tool that allows you to create and execute tests for your web and mobile applications.

Let’s discuss how it supports each test and the benefits it offers,

API Testing In Testsigma

Using Testsigma, you can easily create API test cases by specifying the request and response parameters and validating the response using assertions. It supports RESTful API Testing. It lets you easily add the REST API in test steps with just a tap. To start your API testing, select the project type as “REST APIs” from the dropdown and proceed to add the API test steps.

API Testing in Testsigma

Automating API testing with Testsigma offers a ton of benefits, including,

  • You don’t need to learn code. Testsigma is a no-code test automation tool that lets you create your tests in plain English.

  • No installation or setup is required. You can simply execute your API tests on the cloud.

  • The ability to customize and automate all the API call sequences.

  • Validate your API using various REST API methods like GET, POST, DELETE, PUT, and HEAD via one integrated test or separate tests for each method.

  • Perform both API and functional UI tests using a single platform.

  • Easily send multiple API requests to test whether the communication channels are working properly.

API Testing in Testsigma

For more information, refer to our detailed documentation on automating your REST API testing with Testsigma.

Automate API tests 10x faster, build and validate API’s using Testsigma. No setup or coding required.

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UI Testing In Testsigma

For UI testing, Testsigma provides an intuitive test recorder that allows you to automatically record your interactions with the application and generate test scripts.

UI Testing In Testsigma

It allows you to run tests simultaneously on 3000+ real devices and 1000+ desktop browsers and OS combinations.

It also provides detailed test reports that highlight any failures or errors and provide insights into the performance of your application.

Now you can avoid the hassle of installing different tools. With Testsigma, you can easily test the UI of your web and mobile applications in one place.

You can also install Testsigma Recorder, the Chrome extension that lets you easily record the web interactions and store them as test steps in plain English which you can directly run on the cloud.

You can signup for a free trial of Testsigma Cloud and start automating your API and UI testing in minutes.


It is worth noting that both API testing and UI testing are equally important and complement each other. Both help ensure that an application is working as expected and that it meets the desired quality standards.

With Testsigma, you can avoid the hassle of installing and setting up multiple tools. Testsigma provides a comprehensive test automation platform that allows you to perform both API as well as UI testing in one place, making it easier to manage and maintain your test suite.

Testsigma is also available as an open source and free version.

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I hope this article helped you understand the differences between API vs UI testing, and now you know which testing needs to be done when. Do let me know your thoughts in the comments section.


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