Software testing covers more than just verifying whether features work as expected. It also involves evaluating aspects like performance, security, and usability. This distinction is captured in two broad testing categories: functional and non-functional.
Overview
Functional testing verifies whether the system behaves as expected based on defined requirements, while non-functional testing evaluates how well the system performs in areas like speed, scalability, and reliability.
Functional Testing:
It involves validating features, user interactions, and system behavior to ensure each function delivers the expected output. Common types include unit testing, integration testing, and user acceptance testing.
Non-Functional Testing:
It evaluates how the software performs under various conditions, focusing on aspects like performance, scalability, security, and usability. Common types include performance testing, load testing, stress testing, and security testing.
Functional vs Non-functional Testing
| Aspect | Functional Testing | Non-Functional Testing |
|---|---|---|
| Objective | Validates what the system does | Evaluates how the system performs |
| Focus | Business logic and feature correctness | Performance, usability, security, and reliability |
| Test types | Unit, integration, system, acceptance tests | Load, stress, security, and performance tests |
| Execution method | Often manual or automated | Mostly automated with specialized tools |
This article explores the difference between functional and non-functional testing, detailing each type and its specific role in ensuring software quality.
Difference between Functional and Non Functional Testing
While Functional testing verifies that a software application performs its intended functions correctly, focusing on features and interactions, on the other hand, Non-functional testing assesses overall performance, usability, and quality attributes like speed and security.
While functional testing ensures feature correctness, non-functional testing guarantees broader standards of reliability and user experience.
| Parameters | Functional Testing | Non-Functional Testing |
|---|---|---|
| Focus | Validates specific functionalities of the software. | Assesses performance, usability, and other quality attributes. |
| Purpose | Ensures the software performs its intended functions. | Ensures the software meets performance, security, and usability standards. |
| Scope | Tests individual functions or features in isolation. | Tests overall system behavior and quality attributes. |
| Examples | Input validation, business logic, and user interactions. | Performance, load, security, and usability testing. |
| Testing Type | Generally includes unit, integration, and system testing. | Includes stress, scalability, and reliability testing. |
| Metrics | Measures correctness of output and feature functionality. | Measures speed, stability, and user experience. |
| Execution | Often automated and performed during development phases. | Often involves specialized tools and may require specific environments. |
| Outcome | Confirms that the software meets specified functional requirements. | Ensures the software can handle expected and unexpected conditions effectively. |
| Performance testing | Not a focus; performance is not tested | Primary focus; evaluates speed, responsiveness, and load handling |
What is Functional Testing?
Functional Testing verifies that a software application performs its intended functions correctly according to specified requirements. It focuses on testing user interactions, features, and outputs to ensure proper functionality.
Functional testing is a subset of software testing in which the QA tester ensures the software meets technical, business, and customer requirements. It’s a form of black-box testing in which each function of the application is validated against the requirements established during the planning stages.
Functional tests involve designing specific user input, monitoring the system’s output, and comparing the actual results with expected outcomes.
Scope of Functional Testing
The scope of functional testing includes the following key focus areas:
- Verifying that each function works as intended, based on business and technical requirements.
- Ensuring the application behaves correctly with each set of business logic to provide expected results.
- Covering both positive scenarios and tests to confirm that the application handles edge cases or non-ideal conditions appropriately.
Read More: Debunking Myths about Functional Testing
Types of Functional Testing
Different types of functional tests include:
- Unit Testing: It is the most granular level of testing in the software development life cycle. It involves developers writing and running tests for individual code units before integrating them into the larger codebase. Each test focuses on a single, isolated component to verify its correctness. Unit testing forms the foundation for more comprehensive testing later in development.
- Component Testing: This testing involves isolating and validating a single software module. It checks for bugs within a component and verifies that multiple units within that component work together as intended. Component testing requires more complex scripts and deeper test coverage at the module level than unit tests.
- Integration Testing: Once individual components are validated, integration testing checks how they function together. This type of testing is essential, especially when different team members develop different modules. In systems built with microservices, integration testing ensures that the interactions between services work smoothly and without conflict.
- System Testing: It evaluates the software as a whole, fully integrated system to ensure it meets all technical and business requirements. Also referred to as end-to-end (E2E) testing, it requires a test environment that closely mirrors real user conditions. This stage verifies that the software is ready for customer use.
- Regression Testing: This testing is performed after changes are made to the codebase, such as bug fixes or feature enhancements. The goal is to ensure that existing functionality remains unaffected and the application’s overall stability is preserved. It helps maintain the integrity of the software throughout continuous development.
- Sanity Testing: It focuses on verifying the correctness of recent software changes. It is typically conducted after receiving a new build, concentrating only on the modified or fixed areas. Sanity testing ensures the core functionality remains intact before the application proceeds to deeper testing stages.
- Smoke Testing: It is conducted once a build is completed to confirm that critical functions of the application are working. Often considered a preliminary check, it acts as a gatekeeper before more extensive testing begins, such as user acceptance testing or a production release. It helps identify major issues early in the QA cycle.
Read More: Sanity Testing vs Smoke Testing
Example of a Functional Test
The following examples show how different types of functional tests are applied in a real-world healthcare app scenario.
- Consider a healthcare app introducing a home delivery feature for medicines. One of the new functions is an “Add to Cart” button. A unit test would be run to verify that this button works as expected in isolation.
- The app wants to show users nearby healthcare centers based on their GPS data. Verifying this function requires a module test, as it requires multiple units to work together to get the expected result.
- The app offers users the ability to directly transfer money from their bank account to the app’s own “wallet” for faster purchases. At this point, two modules come into play and tests must be run to check how well they integrate to get the job done. Cue the integration tests.
BrowserStack enables teams to run functional tests across a wide range of real browsers and devices. This helps ensure every feature works seamlessly in real user conditions without the overhead of maintaining in-house test infrastructure.
What is Non Functional Testing?
Non Functional Testing assesses the performance, usability, and other attributes of a software application beyond its core functions. It ensures the software meets quality standards like speed, security, and scalability.
As the name suggests, non-functional testing covers non-functions attributes of any software. It tests everything not already verified by functional tests.
These non-functional software elements include performance, usability, stability, efficiency, maintainability, and portability, though non-functional tests can include some aspects if the project requires it. Like functional tests, this form of QA verification also uses SRS (Software Requirements Specification) documents to create test scenarios, suites, and scripts.
Its final goal is to optimize all non-functional elements so that the software under test can offer the best possible user experience.
Scope of Non Functional Testing
- Identifying gaps in product usability, maintainability, effectiveness, stability and portability.
- Reducing the risk of bugs (and consequently user disapproval and monetary loss) emerging in production when software is actually used by end-users.
- To simplify and debug mechanisms related to installation, configuration, management and monitoring the software.
- Identifying (based on expected real-world usage) the metrics that must be tracked and studied to gauge product success.
- Creating or adding to the repository of knowledge (internal or open-source) about the specific product and the larger technology that powers it.
Types of Non Functional Testing
- Performance Testing: It evaluates how efficiently a software application performs under expected conditions. Performance testing focuses on key metrics such as loading speed, crash frequency, memory usage, response time, and CPU consumption. This type of testing ensures the application runs smoothly and meets performance expectations.
BrowserStack App Performance allows you to test mobile apps on real devices under real-world scenarios. Track key metrics, debug with session replays, detect regressions, and generate shareable performance reports to ensure a smooth user experience.
- Load Testing: It includes measuring how a system handles increased user activity or demand, such as multiple logins or simultaneous transactions. This type of testing helps identify performance bottlenecks and ensures the application remains stable and responsive under typical and peak usage scenarios.
- Security Testing: This testing examines the software for vulnerabilities that malicious actors could exploit. It involves scanning the system for weak points in authentication, data handling, and access control to ensure data protection and application integrity.
- Visual Testing: It checks the accuracy of UI elements, including layout, font, color, and positioning. It ensures that the application’s appearance is consistent across devices and browsers, and that the user interface matches the design specifications.
- Stress Testing: This testing pushes the system beyond normal operating limits to assess its behavior under extreme conditions. It helps identify the application’s breaking point and ability to recover from crashes or failures.
- Scalability Testing: This type of testing evaluates how well the application can grow to accommodate more users, data, or transactions. It ensures that performance remains consistent even as demand increases, making it essential for long-term system planning.
- Responsive Testing: It ensures that the application displays and functions properly across different screen sizes and devices. This includes testing mobile phones, tablets, and desktops to guarantee a seamless user experience regardless of the device used.
Pro Tip: Leverage BrowserStack’s Responsive Testing to effortlessly test and ensure your website’s compatibility across a wide range of devices and screen sizes. This helps guarantee a seamless user experience on mobile, tablet, and desktop platforms, enhancing overall accessibility and performance.
Ideal tools for responsive tests: BrowserStack Live and BrowserStack Responsive Design Tester (free tool).
Examples of Non-Functional Tests
- An eCommerce app must be optimized to handle heavy user traffic for the upcoming Black Friday. Load tests, recovery tests, and volume tests must be run to ensure that it does not buckle and bend under a wildly increased inflow of users.
- Your software has been released, and a week after, so has the new iPhone. Responsive tests and portability tests are required to ensure that it is rendering well on the new iPhone’s screen, and is compatible with the iOS version the phone is running on.
- Your website homepage has a big green button with CTA text on it. Visual tests are needed to check if the button shows up clearly, unobstructed, and center screen on different browsers, devices, and OSes.
Conclusion
Both functional and non-functional testing play vital roles in ensuring software quality. While functional testing verifies that each feature operates correctly according to specifications, non-functional testing assesses the software’s performance, security, and usability under various conditions.
A comprehensive testing strategy that includes both approaches is essential for delivering a reliable, high-performing application that meets both user expectations and business requirements. By understanding and applying these testing methodologies, developers and QA teams can address both the functional and operational aspects of software, ultimately leading to a more robust and user-friendly product.
For effective functional testing, BrowserStack offers two powerful tools: BrowserStack Live and BrowserStack Automate. BrowserStack Live enables real-time manual testing on a wide range of real devices and browsers, allowing you to verify user interactions and interface elements in various environments.
BrowserStack Automate provides scalable automated testing across multiple platforms, running extensive test suites without manual intervention. Together, these tools ensure comprehensive functional validation, helping you deliver a seamless and high-quality user experience across different devices and browsers.
BrowserStack Percy simplifies non-functional testing by automating visual tests across web and mobile apps. It captures and compares screenshots to detect UI discrepancies, ensuring visual consistency and performance across devices and browsers. Integrate Percy to maintain your software’s visual integrity and enhance user experience efficiently.
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