Key Difference between Functional and Non Functional Testing

Key Difference between Functional and Non-Functional Testing

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When it comes to software testing types, they can be broadly divided into Functional and Non Functional Testing. In this article, we will briefly introduce both testing types and try to understand the difference between functional and non functional testing!

Functional testing is a type of testing that focuses on evaluating the software’s functionality. This testing ensures that the software performs per the specifications and requirements outlined during the design phase. On the other hand, non functional testing evaluates the software’s non-functional aspects, such as performance, scalability, security, and usability.

Both types are important, and in this blog post, we’ll closely examine what makes each unique.

What is Functional Testing? Vs What is Non-Functional Testing?

Here are simple explanations for both testing types.

What is Functional Testing?

Functional testing is a type of software testing that involves verifying whether each function or feature of a software application operates correctly. This means that testers will typically try to determine if the system performs as expected when given specific inputs. Identify bugs, errors, or inconsistencies that might arise during normal use and determine whether the user input is valid or invalid.

You can conduct functional testing manually or through automated frameworks, often performing it alongside other tests like performance or security testing. Functional testing aims to ensure that a software product meets its intended purpose and works as expected so that users can complete their tasks efficiently and effectively.

What is Non Functional Testing?

Non functional testing evaluates a software application’s performance, reliability, security, and usability. It is carried out to ensure that the application meets non-functional requirements such as response time, scalability, data integrity, interoperability, and user experience. This testing simulates real-life scenarios to determine how the system behaves under different circumstances, such as high traffic or concurrent users.

This testing also helps to identify any potential bottlenecks in the system or uncover any security vulnerabilities that could put sensitive data at risk. Some common types of this tests include load testing, stress testing, security testing, and usability testing. By carrying out these tests, software developers can ensure that their applications perform optimally and deliver a great user experience.

Advantages of Functional Testing Vs Non Functional Testing

Let us look into the advantages .

Advantages of Functional Testing

Functional testing offers a range of advantages that make it one of the most effective methods for ensuring software quality. Some of the key benefits include:

  1. Complete coverage: Functional testing allows testers to evaluate whether an application meets all its stated requirements, giving developers and QA teams a detailed understanding of how well the software works.
  2. Improved accuracy: By carrying out functional tests in a controlled environment, errors can be isolated and addressed before they cause major issues. This helps reduce debugging time and ensures that bugs are caught during the development process rather than after release.
  3. Improved user experience: As functional testing focuses on ensuring that applications work as planned, it helps ensure users have positive experiences when using them. This includes ease of use, speed, responsiveness, and stability.

Functional testing thoroughly evaluates software performance across many areas and helps organizations build more reliable, high-quality products.

Advantages of Non Functional Testing

  1. The primary benefit of this testing is that it ensures the application’s reliability, scalability, and performance under different workloads and stress conditions.
  2. It also identifies user experience issues such as compatibility, accessibility, usability, and security.
  3. Performing this tests helps to identify weaknesses or areas for improvement in system components before they break down or become a bottleneck.
  4. Conducting this tests lowers the risk of financial loss due to system failure or downtime caused by inadequate network connectivity or hardware dependencies.
  5. Also, this results in better quality software with quicker releases and fewer post-release bugs, leading to happier customers and business owners.

How to Perform Functional Testing And Non functional Testing?

Functional testing and non functional testing are two different approaches used in software testing.

Regularly, functional testing is completed and integrated before releasing any software products into the market. Non functional testing is just as important as functional testing. Because it ensures that the application works correctly and meets the user’s performance, security, and usability expectations. Non functional testing helps identify potential issues when the application is used in real-world scenarios, such as slow response times or security vulnerabilities.

To perform functional and non functional testing, testers must deeply understand the software and the requirements to provide accurate results. You should automate the Functional and Non functional testing if you repeatedly execute the same tests and see an ROI on automating them.

With Testsigma, you can easily create and execute functional test cases for web, mobile, APIs, and Desktop without coding knowledge. Its intuitive interface allows you to easily manage your test cases, test data, and test reports. Testsigma’s AI-driven platform ensures that your tests are always up-to-date and relevant. It automatically detects changes in your application and updates your test cases accordingly. This saves you time and effort in maintaining your tests.

Whether you’re testing a web application, mobile app, or desktop software, Testsigma covers you. Its cross-platform capabilities allow you to automate tests across different devices and operating systems.

With the open-source version of Testsigma, you can access most of the tool’s features without cost. This makes it an ideal choice for small teams or individual testers who want to automate their testing without breaking the bank.

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How to Perform Functional Testing?

Here are the steps to perform functional testing:

  1. Application testing scope: Review the system requirements document to determine the application scope and the functions that must be tested.
  2. Designing test cases: Develop test cases that cover the system’s main functions under test.
  3. Execute test cases: To ensure the application’s functionality meets the accepted requirements and expected behavior.
  4. Analyze test results: Compare the results to the expected ones.
  5. Report and document defects: Document and report any defects found in the system.
  6. Repeat and refine tests: Repeat the tests until all defects have been fixed and all functions have been confirmed to work as expected. Refine the test cases and test scripts based on the feedback from the earlier tests.
  7. Perform a final test: After all the defects are fixed, perform a final test before releasing the application.

How to Perform Non Functional Testing?

Here are the steps to perform :

  1. Identify the Requirements: Identify the non-functional requirements that need to be tested, such as performance, usability, reliability, security, scalability, etc.
  2. Choose the Appropriate Testing Method: The appropriate testing techniques for the identified non-functional requirements such as performance and load testing, security testing, usability testing, scalability testing, etc.
  3. Set Performance & Load Benchmarks: Identify and set performance & load benchmarks for each requirement against which the tests can be compared.
  4. Prepare a Test Plan: Prepare a comprehensive test plan that contains the testing strategy, timeline, resources needed, etc.
  5. Execute the Tests: Execute the this tests per the test plan and compare the results against the benchmarks set.
  6. Analyze the Results: Analyze the results of the tests and look for any irregularities.
  7. Document the Results: Document the results of the tests and make the findings publicly available if relevant.
  8. Implement Changes: Implement any necessary changes to the software product and/or system configurations to improve performance and reliability.

Key Difference Between Functional Testing and Non Functional Testing

The below-given table will explain in detail a few criteria of the key differences.

CriteriaFunctional TestingNon-Functional Testing
PurposeTo test the functionality of the software application and ensure that it meets the specified requirements.To test the non-functional aspects of the software application, such as performance, usability, security, and reliability.
Testing TechniquesBlack box testing, White box testing, Unit testing, Integration testing, System testing, and Acceptance testing. Load testing, Stress testing, Usability testing, and Security testing.
Automated ExecutionAutomate the tests using tools like Testsigma, Selenium, Appium etcAutomate the test using  tools like Apache JMeter, LoadRunner, LoadUI, SoapUI, WebLoad
MetricsNumber of features tested, Pass/Fail rateTransaction success rate, Response time, Resource utilization rate
ExecutionTests are executed after the system is developed and is ready for testing.Tests are executed throughout the development lifecycle, from early requirements gathering to the final stages of deployment and testing.
Focus areaFocuses on the system’s functionality, i.e., whether the system is meeting the requirements.Focuses on the non-functional aspects of the system, such as performance, scalability, usability, security, and reliability.
RequirementBased on functional requirements, which describe what the system should do.Based on non-functional requirements, which describe how the system should perform.
UsageUsed to ensure that the system meets the functional requirements and is working as expected.Used to ensure that the system meets the non-functional requirements and performs well in performance, scalability, usability, security, and reliability.
ObjectiveTo find and fix defects in the system’s functionality.To find and fix bottlenecks and performance issues in the system, improve the system’s usability, and ensure that the system is secure and reliable.
Manual testingIt can be executed manually, but automation is becoming more common.For some types of testing, like performance and load testing, automated scripts are generally used.
FunctionalityTests the functional aspects of the system, such as adding a new customer, placing an order, or generating a report.Tests the non-functional aspects of the system, such as the system’s response time under load, the number of concurrent users that the system can support, and the ease of use of the system’s user interface.
Example Test CaseFunctional: Verify that a user can successfully add a new customer to the system.Non-functional: Verify that the system can handle 100 concurrent users without crashing.
Testing TypesUnit testing, integration testing, system testing, and acceptance testing.Performance testing, scalability testing, usability testing, security testing, and reliability testing.

Functional vs Non Functional Testing Examples

Let us take an example application and look at the examples.

Application: Image Uploader Functional Testing Test Cases:

  1. Verify the Upload button functionality
  2. Check allowed file types
  3. Validate image size limitation
  4. Test the drag-and-drop feature
  5. Verify File name with extensions

Non-Functional Testing Test Cases:

  1. Test responsiveness on various screen sizes
  2. Verify application performance
  3. Check the compatibility across web browsers
  4. Measure Upload time for large files
  5. Test the load tolerance capability of the application
An automated test case with Testsigma


So, whether you’re a developer, tester, or project manager, it’s important to remember the differences between functional and non functional testing to create high-quality software that meets the needs of your users.

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Frequently Asked Questions

Is API testing functional or nonfunctional?

API testing is functional testing, which tests how well the API performs its intended functions.

Is UI testing functional or nonfunctional?

UI Testing, also called GUI Testing, is a process designed to test that the components of any software a user interacts with functions as expected. This is a functional testing.


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