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27 February 2024

9 Min. Read

API Testing vs UI Testing

API vs UI Testing: Why API Automation is better than UI Automation?

API vs UI Testing: Why API Automation is better than UI Automation?

Key Highlights

In this blog, we cover following key highlights:

  1. See a side-by-side comparison between API vs UI Testing

  2. Learn from Spotify’s example on how they achieved faster releases by focusing on API testing

  3. API testing targets backend logic; UI testing checks the front-end experience.

  4. Both are essential for full software quality assurance.

Proven Strategies to streamline your release processes, saving time and resources while enhancing accuracy.

In the fast-paced world of software development, efficiency and reliability in testing can significantly impact delivery times and product quality. While both UI and API testing play critical roles in the software development lifecycle, there's a growing consensus that API automation offers a strategic advantage in many scenarios.


This article delves into why API testing, with its speed, efficiency, and cost-effectiveness, is becoming the preferred choice for many developers and QA professionals. But not to sideline the fact that UI testing is also important, and UI along with API testing can play a significant role in software testing efforts of an organization.


A little background on API testing vs UI testing

UI Testing: User Interface (UI) testing focuses on interacting with the application's graphical interface to ensure it behaves as expected. This includes testing button clicks, text input, menu navigation, and other visual elements. While critical for ensuring a positive user experience, UI testing can be time-consuming and fragile, as minor changes in the UI can break tests.


Imagine clicking through an app's interface, verifying every action like a user would. That's UI testing—a crucial checkpoint for user satisfaction. However, it's akin to checking every window and door in a skyscraper; thorough but time-consuming.

API Testing: Application Programming Interface (API) testing involves direct testing of the application's logic layer, bypassing the UI. It's designed to verify that the API meets expectations regarding functionality, reliability, performance, and security. Since APIs serve as the building blocks of software applications, API testing can cover a broader range of application functionalities more efficiently than UI testing. Here’s a detailed article in case you want to dive deeper into the spectrum of API testing.

Think of API testing as checking the skyscraper’s plumbing and electrical systems directly, bypassing the need to enter each room. It's efficient, covers more ground, and identifies systemic issues early. API testing dives into the application's core, ensuring the components behave as expected under various conditions.

Advantages of API Testing Over UI Testing

Let’s have a side-by-side comparison of API vs UI testing to have a better understanding of the concepts involved within both these types.


Aspect

API Testing

UI Testing

Execution Speed

Fast

Slow

Development Cycle

Early

Later

Cost

Lower

Higher

Stability

High

Medium

Coverage

Comprehensive

Surface-level

➡️Speed and Efficiency

API tests interact directly with the application's backend, bypassing the UI. This direct approach means tests can run in milliseconds. For example, verifying a response code or the correctness of a response body with API testing is immediate and straightforward.


In contrast, UI tests involve loading graphical elements, which can take significantly longer. Automating a login process via the UI, for instance, requires loading the login page, entering credentials, submitting the form, and waiting for the next page to load. This process can take seconds or even minutes, depending on the application's complexity and performance.


➡️Earlier Testing in the Development Cycle

API testing can begin as soon as the API endpoints are defined and accessible, even if the UI is not yet developed. This allows for early detection of fundamental issues in the application's logic and behavior. For example, if an API responsible for user registration is tested early and found to improperly handle certain data, fixing it immediately saves time and resources.


UI testing requires a stable and accessible interface, which is usually developed after the core application logic. This means potential issues in the application's backend might not be discovered until later in the development cycle, making them more costly and time-consuming to resolve.


➡️Lower Cost

The speed and efficiency of API testing, coupled with the ability to detect issues early, contribute to its cost-effectiveness. Early bug detection typically results in lower costs associated with fixes, as changes in the backend are usually less expensive than redesigning the UI or adjusting the flow of interactions.


UI testing often identifies issues at a later stage, when they might be more integrated into the system and costly to fix. Additionally, the slower pace of UI testing increases the resource allocation for testing, which can inflate project budgets.


➡️Higher Test Stability

APIs are designed to be stable and backward compatible. Changes in the UI do not affect the API layer directly, making API tests less likely to break due to visual updates or frontend changes. For instance, an API endpoint returning user profile information will work the same way regardless of how the profile page's UI is redesigned.


UI tests are more fragile because they rely on the layout and elements of the interface, which can change frequently during development. A simple change, such as moving a button or changing an element's ID, can cause UI tests to fail, requiring regular maintenance to keep them up to date.


➡️Better Test Coverage

Because API testing focuses on the business logic layer, it can more comprehensively test the application's functionality. API tests can easily send various combinations of inputs to test edge cases and error conditions. For example, testing an API endpoint that retrieves a user's order history can involve testing with different user IDs, including non-existent ones, to ensure the API handles all scenarios gracefully.


While UI testing is essential for ensuring the application is user-friendly and behaves as expected from a user's perspective, it's inherently limited in its ability to test backend logic extensively. Certain logic paths or error conditions might be difficult or impossible to trigger through the UI alone.


By focusing on these advantages, we can appreciate why API testing is often considered a more efficient and effective approach compared to UI testing, especially in early development stages and for ensuring the robustness and reliability of the application's core logic.

Build API tests without writing or maintaining scripts

Set up an API testing suite in a day!

How Spotify’s API testing practice helped them release faster?

Spotify's Agile Testing Strategy, particularly their emphasis on API testing over UI testing, is a key element of their ability to achieve faster releases and efficiently meet user demands for new features. This strategy is shaped by their overall Agile and engineering culture, which prioritizes rapid iteration, continuous integration, and a strong focus on automated testing to ensure quality and speed in development.


Agile Testing Strategy at Spotify

Squad Model

Spotify organizes its development teams into autonomous "squads" that focus on specific areas of the product. Each squad is responsible for the full lifecycle of their features, from design to deployment, which includes testing. This model encourages ownership and allows for faster decision-making and development cycles.


Continuous Integration and Deployment

A core component of Spotify's strategy is the use of continuous integration (CI) and continuous deployment (CD) practices. By integrating code changes into a shared repository several times a day, teams can detect and fix integration errors quickly. Continuous deployment allows them to release new changes to users rapidly after passing automated tests.


Automated Testing Pyramid

Spotify follows the testing pyramid strategy, emphasizing a greater number of lower-level unit tests, a moderate number of service tests (including API tests), and fewer high-level UI tests. This approach ensures that most testing is fast and can be automated, leading to quicker feedback loops.


Spotify’s Emphasis on API Testing Over UI Testing

Faster Feedback and Iteration

API tests run much faster than UI tests, providing quicker feedback to developers. This speed is crucial for Agile development, where the goal is to iterate rapidly. By catching issues at the API level, developers can address problems before they propagate to the more complex and slower-to-test UI layer.


Stability and Reliability

APIs tend to have more stable interfaces than UIs, which can change frequently with new designs or user interactions. Testing at the API level ensures that the core functionality works correctly, regardless of UI changes, leading to more reliable tests that do not need to be rewritten as often as UI tests.


Scalability and Integration Testing

API testing allows Spotify to test the integration between different services and components of their architecture efficiently. As Spotify's system is built on a microservices architecture, ensuring that these services communicate and work together correctly is critical. API tests validate this integration without the overhead of UI tests, which are more concerned with the user interface rather than the internal workings of the system.


Continuous Deployment

By focusing on API testing, Spotify can more confidently and frequently deploy new features and updates. API tests are integral to their CI/CD pipeline, allowing for automated validation of changes at the integration level. This automation supports continuous deployment by ensuring that new deployments do not break existing functionality.


Spotify's Agile Testing Strategy, with its emphasis on API testing, supports their goals of rapid iteration, high-quality releases, and the ability to quickly respond to user demands. By prioritizing automated, fast, and reliable API tests over more brittle and slower UI tests, Spotify ensured that their core functionalities remain robust and that they can continuously deliver new and updated features to their users with confidence.


Tools for API Testing

Popular tools for API testing include HyperTest, an automated autonomous tool that generates API tests on its own and makes sure it covers end-to-end scenarios, leaving no bug to leak in the production. It has helped teams at Nykaa, Porter, Fyers, Groww etc in achieving:


✔️Coverage: Close to 90% coverage in under a sprint i.e. 2 weeks

✔️Speed: Regression time brought down from hours or days to < 30 mins


Types of regressions reported by hypertest

Other tools include Postman, which offers a user-friendly interface for sending requests to APIs and analyzing responses; Swagger, which provides tools for designing, building, and documenting APIs; and SoapUI, designed for testing SOAP and REST APIs.


These tools support automation and can be integrated into CI/CD pipelines, making them valuable assets for teams looking to enhance their API testing practices. Here’s a detailed article on the top performing API testing tools for 2024, make sure to give it go to help you narrow down your choices smartly.


Tools for UI Testing

To conduct effective UI testing, developers and QA teams rely on various tools and frameworks. Here are some popular ones:


  1. Selenium: Selenium is an open-source tool widely used for web application testing. It supports multiple programming languages and browsers, making it versatile for cross-browser testing.

  2. Appium: Appium is an open-source tool for mobile application testing. It allows you to test both Android and iOS apps using the same API, making it a valuable choice for mobile UI testing.

  3. Katalon Studio: Katalon Studio is a comprehensive test automation tool designed for web, mobile, and API testing. It offers a user-friendly interface with built-in test recorder and test case management.

  4. Playwright: Playwright is a modern automation library for web and browser automation. It supports multiple programming languages, offers cross-browser compatibility, and has a focus on reliability.


Why are both API testing and UI testing important?

Even though we strongly believe API testing can’t be skipped when planning a testing suite for your software, it’s equally true that UI testing is also important. No amount of backend testing can bring out the errors UI testing can point out in the front-end.


Both API testing and UI testing play critical roles in the software development lifecycle, serving complementary purposes that ensure the overall quality and user satisfaction of applications. These testing methodologies address different layers of the application architecture, targeting specific aspects of functionality, performance, and user experience.


API Testing: Ensuring Backend Functionality and Integration

API testing focuses on the middle layer of the application, where the core business logic and data management occur. This type of testing is crucial for several reasons:


  1. Integration Verification: API testing validates the interaction between different software components and external systems, ensuring that they communicate and function together as expected.

  2. Functionality Assurance: It checks the logic of the business processes conducted at the API level. This includes sending requests to the API and getting the expected responses, ensuring that the API behaves as intended under various conditions.

  3. Performance Evaluation: API tests assess the response time, reliability, and scalability of the backend, identifying performance bottlenecks that could impact the overall application performance.

  4. Security Testing: APIs are often exposed to the internet, making them vulnerable to attacks. API testing includes evaluating authentication, encryption, and access control mechanisms to safeguard sensitive data.


UI Testing: Validating User Experience and Interface

UI (User Interface) testing, on the other hand, focuses on the front-end of the application, ensuring that the user interface is intuitive, responsive, and functions correctly across different devices and browsers. This form of testing is essential for:


  1. User Experience: UI testing verifies that the application is user-friendly, aesthetically pleasing, and provides feedback to the user's actions as expected, leading to higher user satisfaction.

  2. Cross-Platform Compatibility: It checks the application's appearance and functionality across various devices, screen sizes, and browsers, ensuring a consistent user experience.

  3. Functional Correctness: UI tests simulate user interactions with the application, verifying that all UI elements function correctly, including buttons, menus, forms, and other interactive components.

  4. Accessibility Compliance: This ensures that the application is accessible to users with disabilities, adhering to legal and ethical standards for inclusivity.


Complementary Nature of API and UI Testing

Both API and UI testing are integral to a comprehensive testing strategy:

  • API testing allows teams to isolate and diagnose issues at the backend level, ensuring that the application's core functionality and integration points work correctly without the influence of the front-end.


  • UI testing ensures that the end-user's interaction with the application is as designed, covering the look, feel, and overall experience of the application.


Incorporating both testing types into the development process enables teams to identify and resolve issues more effectively, leading to a robust, user-friendly application that meets both functional requirements and user expectations. This dual-focus approach ensures that both the backend logic and the frontend presentation work in harmony, providing a seamless experience for the user.


Conclusion

As we've seen, API testing offers compelling advantages over UI testing, including speed, efficiency, and the ability to test earlier in the development cycle. While challenges exist, the benefits of API testing, especially when integrated with UI testing, can lead to more reliable, cost-effective, and efficient development processes.


We encourage teams to explore API testing further—whether by experimenting with tools like HyperTest or Postman, participating in a webinar on API testing best practices, or simply integrating more API tests into your existing test suites. By embracing API testing, you can take a significant step towards more agile, resilient, and high-quality software development.

Frequently Asked Questions (FAQs)

1. What is the difference between UI testing and API testing?

UI testing focuses on the user interface, ensuring visual elements work correctly. API testing checks the communication between software components.

2. Which has more scope API or UI testing?

API testing generally has a broader scope as it covers backend functionality and integration points, while UI testing is more focused on the frontend.

3. Is API testing manual or automated?

API testing can be manual or automated, but automation is commonly preferred for efficiency and thoroughness. UI testing is also often automated for comprehensive coverage.
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