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Differences Between Functional and Non-functional Testing

By Shreya Bose, Community Contributor -

What is Functional Testing?

Functional Testing is a sub-set of software testing in which the QA/tester tries to verify that the software works (“functions”) is accordance with technical, business and customer requirements. It is a form of black-bos testing in which each function of the website/app is checked so that it aligns with corresponding requirements (from the brainstorming and planning stages). 

Functional tests are run by designing and feeding specific user input data, monitoring the system’s output in response to this data, and comparing the actual results with expected ones. 

A few common examples of the kind of “function” that a functional test verifies:

  • Can users easily and seamless log into the site/app with the correct credentials?
  • When a user clicks “Buy Now”, does the UI take them directly to the next required page?
  • If a user enters special characters in a field where they are not allowed, does the system throw up an error message and refuse to proceed?

If you need more clarify, don’t worry. We’ll discuss the differences between functional and non functional testing later in this piece. 

Scope of Functional Testing 

  • Testing every function to verify if each one does what it is meant to, especially in the light of business and technical requirements. 
  • Investigating that an application correctly works with each set of business logic specifications to provide expected output. 
  • Comprises positive, happy path tests AND tests to ensure that the application acts differently (and accordingly) in non-ideal conditions to keep functioning.

Types of Functional Testing 

  • Unit Testing: Developers create and run unit tests to test every code block they craft, before pushing it to the larger codebase. Each unit test verifies a single component, and is the most granular test in the SDLC. It is also the base for more expansive an layered tests down the line.
  • Component/module testing: Like unit testing, component testing isolates a single software module and checks it for bugs. However, module tests require more complex scripts than unit tests.
  • Integration testing: Once components are verified, the must be integrated and then again tested for collective functionality — integration testing. This is also important because different modules are often built by different devs in a team.
    Don’t forget that microservices have become a fixture in modern software design. Testing their interactions is an essential part of integration tests.
  • System testing: The software is tested as a fully integrated ecosystem to check that it satisfies all requirements emerging from all stakeholders. It’s also commonly known as End-to-End Testing.At this point, you need access to a test environment that replicates real user conditions. The software must be verified for usage in the hands of real customers.

Tools like BrowserStack give you access to a real device cloud comprising 3000+ real browsers & devices, where you test software on completely real browsers, devices and operating systems – including desktop & mobile variants of each. You basically upload your software to every browser-device-OS combination in your target user base, and ensure that any bugs in your apps are caught before they even hit the market. Sign Up for Free

  • Regression Testing: For every iteration to a software’s architecture, there is a risk that changes with interfere with existing functions and features. Regression tests are triggered after every alteration to the software to verify that its stability and efficiency is intact.
  • Sanity Testing: Sanity tests check for the stability of a build after it has gone bug fixes or new code. It’s similar to regression tests, except that it doesn’t check the whole system but only the changed/fixed code.
  • Smoke Testing: Once the build it completed, QAs take over and test critical functions in smoke tests. This is the last layer of testing before the software goes onto User Acceptance tests and the production release cycle. 

Example of a Functional Test

  • A healthcare app wants to add home delivery of medicines to its app. One of the features is an “Add to Cart” button. A unit test will be run to verify the individual button’s validity.
  • 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

What is Non-Functional Testing?

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: 

As is obvious from the name, performance testing check that the software is literally performing at optimal levels. A few markers of performance are page/app loading speed, software crash rates, memory, latency time, throughput, CPU interrupts per second, etc.

Ideal tools for performance testing: BrowserStack Live & App Live (for manual testing), Automate & App Automate (for automated testing), and SpeedLab (for testing page load speed). 

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  • Load Testing:

Load tests check how well a system handles increased load, such as from too many users logging in and shopping at the same time. 

Ideal tools for load testing: BrowserStack Live & App Live (for manual testing), Automate & App Automate (for automated testing), and SpeedLab (for testing page load speed).

  • Security Testing:

Security tests check the software’s weaknesses and vulnerabilities to external attacks. Conducted from the POV of a hacker/attacker, it scans the software’s system design and looks for gaps that could be exploited for data theft or for making unauthprized changes.

Ideal tools for security tests: ImmuniWeb, Vega, Wapiti

  • Visual Testing

Visual tests examine if all UI elements are rendering as expected, with every element showing up with the proper shape, size, color, font, and placement. It’s intent is to verify the accuracy of your software’s visual output, and compare it against the expected output as set down in the requirements.

Ideal tools for visual tests: Percy and App Percy by BrowserStack allows you to run automated visual tests for Web and Mobile Applications.

Differences Between Functional and Non-functional Testing

  • Portability Testing

Can the software run on different operating systems, including multiple versions of each OS? That is the question portability tests set out to answer. It is a part of software compatibility testing.

Ideal tools for compatibility tests: BrowserStack Live & App Live (for manual testing), Automate & App Automate (for automated testing).

  • Reliability Testing:

These tests verify that software operates seamlessly, sans bugs or errors, under different predetermined conditions. Think about geolocation testing, localization testing, and network throttling – all reliability tests aimed at checking software efficacy in different/difficult real user conditions.

Ideal tools for reliability tests: BrowserStack Live & App Live (for manual testing), Automate & App Automate (for automated testing)

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  • Efficiency Testing:

These tests check how many resources are consumed for said software to accomplish its required tasks.

Ideal tools for efficiency tests: WebLOAD, LoadNinja

  • Volume Testing

Also known as flood testing, these tests check how the software responds when bombarded with excessive data (for example, when too many users sign up by entering their information).

Ideal tools for volume tests: HammerDB, JdbcSlim

  • Recovery Testing

Recovery tests verify how fast and well a site/app can bounce back to peak functionality after crashes, hardware failures, or any unpredictable predicaments. You break the software by exposing it to different conditions and then monitor how quickly it recovers under each set of parameters.

Ideal tools for recovery tests: Box Backup, Bacula.

  • Responsive Testing

Responsive tests monitor and evaluate if an app/site renders well on screen sizes and resolutions offered by different devices, mobile, tablets, desktops, etc. A site’s responsiveness is an essential contributor to its success. Most people access the internet from their mobile devices, and expect to find software that works perfectly on their hand-held/desktop endpoints.

Ideal tools for responsive tests: BrowserStack Live and BrowserStack Responsive Design Tester (free tool).

Free Responsive Test on Commonly Used Resolutions

Try testing the responsiveness of your website on real devices.

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. 

Difference between Functional and Non Functional Testing

Functional TestingNon-Functional Testing
Evaluates the state of a software’s functions in real user conditions. Evaluates the non-functional attributes of software, essentially everything not covered in functional tests. 
Can be manual or automated.Is usually automated. 
Intended to ensure software meets both business and technical requirements. Intended to ensure that the released software is stable, maintainable, secure and high performing. 
Checks to ensure that software is free of bugs. Checks that software performs at high levels. 
Designed on the basis of requirements documentation. Designed on the basis of requirements as well as research on customer expectations. 

In Conclusion

The differences in functional vs. non functional testing operate at the fundamental level. Understanding these differences is central to shaping and executing the right tests to judge the right features and facets of the software under development. So, it’s a great idea to start with “What is functional and non functional testing?”

At the risk or becoming a broken record, allow us to reiterate that running functional and non-functional tests in real user conditions. Either you purchase/acquire all the browsers, devices and OSes as well as automation frameworks (plus the people who can actually use them) required for comprehensive test suites, or you use a real device cloud that lets you run the same same suite without breaking the bank. 

Try BrowserStack. Sign up for free, run tests on 3000+ real browsers and devices, and you’ll see it all for yourself. 

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