Non-Functional Testing

In this section, we are going to study Non-Functional Testing in detail. Non-Functional testing is another type of software testing which concentrates on the testing of the non-functional behaviour of the application under test. In our previous tutorials, we studied types of software testing and got a basic understanding of non-functional testing. Here, we will cover all possible terms and information related to non-functional testing, such as what non-functional testing is, the need for non-functional testing, types of non-functional testing, parameters of non-functional testing, non-functional testing tools, advantages and disadvantages of non-functional testing, and more.

What is Non-Functional Testing?

A type of software testing that focuses on the non-functional aspects of the application under test (AUT) is known as Non-Functional Testing. It works in the opposite direction of functional testing. On the one hand, functional testing validates what software does, whereas non-functional testing validates how the software works. Non-functional testing usually validates the application/ software against its non-functional requirements and attributes such as usability, load, stress, etc. It keeps track of meeting the non-functional requirements of the system and contains all other modules which are not covered under the functional tests.

Like functional testing, non-functional testing is also essential for making the software 100% defect-free. It also plays a vital role in testing the performance quality of the software. The primary purpose of using non-functional tests is to enhance the end user's experience with the quality of the software. It comprises all the non-functional requirements, such as performance, security, usability, reliability, compatibility, etc. Hence, such requirements are also known as quality requirements. Non-functional requirements can be defined or captured in the following ways:

1. Artefacts/ Documents – Non-functional requirements should be captured in a separate document or artefact. It helps in quickly deciding what needs to be tested and how to conduct testing.
2. User stories or technical stories – Non-functional requirements can also be captured with the help of a user or technical story. A user story is an informal description of a module or feature of the software/ application from the user's perspective. It helps to understand the user’s requirements for the software under test.
3. Acceptance Criteria – Sometimes non-functional requirements are often captured in the acceptance criteria. However, the testing of those requirements is covered in the next iteration or sprint.

Non-functional testing is as necessary as functional testing to make the system competent and effective in the real world. Sometimes, the client and testing team only focuses on the functional attributes of the product, which creates a problem when the product is deployed in the market. Issues like the system being unable to take the load of multiple users, low performance while using, security-related concerns, compatibility issues with operating systems and browsers, and more. In that case, non-functional testing helps the system to operate and meet the non-functional requirements.

Need for Non-Functional Testing

As discussed above, non-functional testing is as necessary as functional testing in Software Testing Life Cycle. Non-functional testing is used to test the non-functional aspects of the software/ application under test to ensure the software is uniformly working from the user’s perspective. It is mainly performed to achieve customer satisfaction for all non-functional attributes of the system, such as performance, load, usability, reliability, configuration, globalization, etc.

Functional testing validates the system against all functional requirements and tests what the system does. In contrast, non-functional testing validates the system against the user's expectation and tests how the system works.

Below mentioned are the reasons for the requirement for non-functional testing:

• Non-functional tests are essential to cover all other attributes which are not covered in the functional tests to deliver a defect-free and high-quality standard product.
• To enhance productivity such as performance, usability, compatibility, efficiency, maintainability, portability, and other non-functional parameters of the system.
• To improve the process of installing, configuring, managing, controlling, and monitoring the system.
• To protect the system from the risk associated with the failure of non-functional aspects of the system.
• It also reduces the estimation cost of testing and maintenance of the non-functional aspects of the system in later stages of the testing process.
• It helps in enhancing and understanding the product’s knowledge and collecting the measurements and metrics of the system for future analysis.

Let’s understand the importance of non-functional testing with the help of an example:

Suppose an e-commerce application is developed by an organization, which completed tested from the functional aspects. However, non-functional testing still needs to be performed on the application. After functional testing, the application is moved to the production unit and deployed for real-time users. The application crashed after some time during the deployment into production as it was not prepared to handle the sudden load of multiple users simultaneously. The response time and performance of the application were not meeting the user’s expectations; therefore, it resulted in a system breakdown. Hence, non-functional testing is as crucial as functional testing for the product, and it must be addressed.

Some more examples of non-functional testing are mentioned below:

1. Usability testing – We can say that ‘Adding an item into a cart is an example of usability testing as this feature should be available for all users, and they can use it properly without any issues.
2. Load testing – Testing a 'Login' feature with multiple users simultaneously is an example of performance and load testing. Testing is done to check whether the application is working fine or not under a specific load.
3. Compatibility testing – Testing whether the system is compatible with different operating systems or not is an example of compatible testing.

Attributes or Parameters of Non-Functional Testing

As we all know, there are multiple parameters and attributes of non-functional testing available in the software testing process. Some of the important parameters are listed below:

• Security – Testing the system’s security is one of the essential attributes of non-functional testing. It defines how secure the system is from sudden and unwanted security attacks such as viruses, phishing attacks, malicious software, etc. Security attribute is covered under Security testing.
• Availability – Another parameter of non-functional testing is Availability, and it specifies the user's dependency on the software or system under test. In other words, it defines the stability of the system while operating, and it is covered under Stability testing.
• Efficiency – Another parameter of non-function testing is Efficiency. It specifies the ability of the system to handle the response time, capacity, power, rely on variations, quantity, etc., and it is covered under Performance and Usability testing.
• Portability – Another attribute of non-functional testing is Portability. It specifies the ability of the system to relocate or shift from its existing hardware/software environment to another, and this attribute is covered under Portability testing.
• Load capacity - Another attribute of non-functional testing is its loading capacity. It specifies the system’s capability of handling a sudden or unwanted load on the system, and it is covered under Load testing.
• Reliability – Another attribute of non-functional testing is Reliability. It specifies the system's consistency for performing and completing a task without errors and issues, and it is covered under Reliability testing.
• Performance – Another attribute of non-functional testing is Performance. It specifies the behaviour and nature of the system while working on an assigned task, and it is covered under Performance testing.
• Usability – Another attribute of non-functional testing is Usability. It specifies the user's convenience for using, operating, understanding, learning, and interacting with the system, and it is covered under Usability testing.
• Scalability – Another attribute of non-functional testing is Scalability. It specifies the system's ability to expand or extend its processing capacity and computing power to satisfy an urgent demand, and it is covered under Scalability testing.
• Interoperability - Another attribute of non-functional testing is Interoperability. It specifies the interaction and relationship of the system with other software or systems according to the user's requirements, and it is covered under Interoperability testing.
• Survivability - Another attribute of non-functional testing is Survivability. It specifies the system’s ability to run smoothly and recovers itself in the situation of failure or malfunction, and it is covered under Recovery testing.
• Flexibility - Another attribute of non-functional testing is Flexibility. It specifies the system’s ability to configure and integrate with other software/ hardware systems such as RAM, CPU, and more. It is covered under Compatibility testing.

Types of Non-Functional Testing

Like functional testing, it also uses black-box testing techniques. Non-functional testing is further classified into various types of testing, which are mentioned below:

1. Performance testing
2. Security testing
3. Usability testing
4. Accessibility testing
5. Compatibility testing
6. Reliability testing
7. Portability testing
8. Failover testing
9. Recovery testing
10. Localization testing
11. Internationalization or Globalization testing
12. Interoperability testing

Performance Testing

A type of non-functional testing that tests the system's performance by adding some workload to it is known as Performance testing. It helps to test the run-time performance, speed, and response time of the application under numerous test conditions. For creating standard quality software, performance testing is executed as it validates how software and its components are working.

Through performance testing, we can quickly identify and remove the bottlenecks behind the slow performance of the application. This will result in stable and fast-performing software, and performance testing experts will perform it.

Performance testing is further classified into various testing types:

1. Load testing – It is used to test the software's behaviour under certain load conditions. It tests the loading capacity of the system by running multiple applications simultaneously and verifies how the system behaves in such situations.
2. Stress testing – It is used to test the software's stability when abnormal or extreme conditions are applied to it. It identifies the breaking point of the software under the heavy and unexpected workload.
3. Scalability testing - It is used to test the software’s scalability and response time under multiple user requests. It validates the software's capability, whether it can scale up or down depending on the increased traffic or users.
4. Volume testing – It is used to test the software's behaviour and performance when a massive volume of data is transferred to the database, and it is also known as flood testing.
5. Endurance testing – It is used to test the software's behaviour by applying heavy and unexpected workloads continuously over a long period. Endurance testing is also referred to as Soak testing.

Security Testing

A type of non-functional testing that tests the system's security to identify all the hidden vulnerabilities and threats is known as Security testing. In other words, security testing is performed to determine the security faults or flaws of the system, which may result in massive data loss. Security testing ensures that the system or application is secure from all kinds of threats and viruses which could enter the system internally or externally. The primary focus is to verify the authentication and authorization of the system to prevent and secure it from malicious attacks, hacking, etc.

Like performing testing, security testing is also served by expert teams. There is one subset of security testing, which is known as Penetration testing or Pen testing.

Usability Testing

A type of non-functional testing that tests the software's usability for its end users is known as Usability testing. In simple words, usability testing is used to examine and test the software from the customer's point of view, which evaluates the system's user-friendliness. It helps a user to test the application's usability in various ways like testing the look and feel of the software, the application should be easy to use and understand, and the GUI of the application should be user-friendly. It also helps us to discover and improve the software's design as per the requirements.

Usability testing is also known as User experience testing (UX). There are mainly two techniques used to perform usability testing, i.e., Laboratory Usability testing and Remote Usability testing.

Accessibility Testing

There is one subset of Usability testing, which is known as Accessibility Testing. It is a type of non-functional testing that ensures the system is accessible by all types of users, such as ordinary and disabled people having disabilities such as colour blindness, hearing problem, physical impairments, learning impairments, etc. The primary purpose of accessibility testing is to test whether the system is uniformly working for regular and physically challenged users. It covers both usability and accessibility testing of the system simultaneously. We have special software, such as Speech recognition software, Smart keyboard software, Screen reader software, Screen magnifier software, etc., available in the market to provide assistance to physically challenged users.

Compatibility Testing

A type of non-functional testing that tests the software’s compatibility with other devices, applications, and systems is known as Compatibility testing. It is used to verify that the application under test must be compatible with multiple software and hardware devices, web browsers, operating systems, databases, etc. It ensures that the application should meet all the compatibility checks and delivers the best user experience to its users. It also tests the application’s compatibility with max and min configurations.

Through compatibility testing, we can also test the different versions of the same application. It is further classified into two categories, i.e., Forward Compatibility testing and Backward Compatibility testing.

Reliability Testing

The process of testing the reliability of the software is known as Reliability testing. It tests whether the software is reliable or not. It ensures that the software works as per the user's requirements for a specific period under certain conditions to check its reliability. It should come up with the same results without any errors or defects while testing the application continuously for hours and hours. It also helps in testing the consistency of the application.

Portability Testing

Testing the portable behaviour of the software is known as Portability testing. In other words, portability testing is done to quickly identify whether the software or application can be moved from one environment to other. It determines all the hurdles a software faces while porting it to other systems. With the help of portability testing, we can verify whether the system is performing or working as expected after installing it in another environment. Hence, the system's functionality should be unaffected due to environmental change.

Failover testing

A type of non-functional testing that focuses on the system's ability to handle crucial situations, such as system failure, is known as Failover testing. In other words, failover testing is used to validate the system’s capability of automatically switching the system to a reliable backup and allocate extra resources when a sudden failure occurs. The testing ensures that the system must be capable of handling sudden loads in a system failure or slowdown to pass failover testing successfully. Some of the failover testing examples are Banking applications or websites, Government websites, Trading applications and websites, etc.

Recovery testing

A type of non-functional testing that focuses on testing the system’s ability to recover from a system failure is known as Recovery testing. In other words, recovery testing ensures that the system is capable enough to recover from any critical situation, such as system failure, hardware or software crashes, network failures, etc. With the help of recovery testing, testers can examine and improve the ability of the system to recover quickly from a system crash or disaster. To perform recovery testing, first, we need to make a system failure and then validate the system's behaviour against that failure.

Localization testing

A type of non-functional testing which focuses on testing the system’s localization quality for a specific region, culture, or target is known as Localization testing. In other words, localization testing verifies the system's behaviour and quality for a specific locale, culture, region, etc., to meet the localization requirements. It is performed on the local version of the software/ application to ensure the version meets the cultural and linguistic aspects of the software. Testing mainly covers the User Interface and content of the application. An example of localization testing is, testing a social media platform which is specifically designed for French people and only supports the French language and related stuff.

Internationalization testing

A type of non-functional testing which focuses on testing the system’s consistency across various cultures and regions is known as Internationalization testing. In other words, internationalization testing verifies the adaptability of the software to perform uniformly across multiple regions, languages, and cultures without any changes in the source code. It works in the opposite direction of localization testing. Testing is done to ensure that there shouldn’t be any discrepancies and breakage of functionality which may cause data loss during the conversion of one language into other. It is also termed as Globalization Testing.

Interoperability Testing

Another type of non-functional testing is Interoperability testing which validates the relationship and functionality of the software under test with other software systems as per the user requirements. In other words, it ensures that the system can interact and communicate with other systems or devices without having any issues. It tests the end-to-end relationship between two systems according to the client's requirements. The objective of interoperability testing is to exchange data between two communicating systems or devices uniformly and to avoid issues while transferring data from one system to another. Interoperability testing is further divided into five categories, as mentioned below:

1. Data Type Interoperability Testing – It focuses on transferring data types from one type to another.
2. Physical Interoperability Testing – It focuses on validating the connections between two or more connecting devices/ systems.
3. Semantic Interoperability Testing – It focuses on data semantics and algorithms used in data transferring between two or more systems.
4. Protocol Interoperability Testing – It focuses on testing the protocol used in data transferring between two or more systems.
5. Data Format Interoperability Testing – It focused on testing the data format of the sent and received data.

Non-Functional Testing tools

Some of the most popular non-functional testing tools available in the market are listed below:

• LoadRunner – One of the best and most popular performance testing tools is LoadRunner, as it provides accurate testing results and can also be used for Unit and Integration testing. It is designed by Micro Focus to validate the performance aspects of the system, such as load, stress, scalability, volume, endurance, etc. The objective of LoadRunner is to test the behaviour and performance of a system under a particular load. LoadRunner is a licensed tool, but it allows several trials for free. It also supports the integration with Selenium for functional testing.
• JMeter – It is one of the most popular open-source testing tools available. It is an Apache product mainly used for automation, performance (load), and reliability testing. JMeter is an easy-to-use tool used for analyzing the load and performance of the system. It is fully designed and developed in Java programming language. Like LoadRunner, JMeter also supports integration with Selenium and can be used as a functional and unit-testing tool.
• NeoLoad – It is an automation testing tool developed in Java programming language for performance, stress, and load testing of web applications. It is mainly used by enterprise organizations for testing APIs, web applications, etc. It is a Neotys product that offers features like automatic test design and maintenance, pre-defined integrations with SDLC tools, and quick analysis of root causes to both developers and testers. It also supports a variety of web, mobile, and native applications for testing purposes. Like LoadRunner, NeoLoad is also a commercial testing tool.
• LoadStorm Pro - It is one of the cheapest load and performance testing tools available in the market. LoadStorm Pro is one of the powerful cloud-based load testing tools which provides a set of hybrid features to test mobile and web applications efficiently. It helps in determining the scalability of the application, creating browser recordings, and uploading the recording to the cloud. It provides graphs and reports for measuring the performance, average response time, number of users, error rates, etc., as per the performance testing aspects. Like LoadRunner, it provides a couple of free trials, and we need to purchase it for further testing.
• CloudTest – It is a cloud-based testing platform used for testing websites, APIs, and mobile applications comprehensively. In other words, CloudTest is mainly designed for performing load and stress testing on applications and websites. It can also be used as a virtual testing platform by users and developers. It offers a variety of features, such as a globally distributed environment, visual playback editor and test creation, real-time feedback, a customizable dashboard, a dynamic ramp, and more. CloudTest is a product of the SOASTA software association (a subsidiary of Akamai) and is available on the internet as an open-source tool.
• Loader.io – It is an open-source cloud-based performance, load, and scalability testing tool used to test APIs and web applications. Like CloudTest, it is also an open-source and straightforward testing tool. In other words, Loader.io (a product of SendGrid) is designed for monitoring and managing data and application during the process of testing APIs and web apps. It provides a simple and interactive display/dashboard with graphs and reports which can be accessed from any location at any time. It also supports integration with PaaS (Platform as a Service) providers, web browsers, and CI/CD tools.
• WireShark – WireShark (formerly known as Ethereal) is a free and open-source security testing tool. It is a packet analyzer mainly used for analyzing, troubleshooting, educating, and developing communication and network protocols. It is a cross-platform tool, hence, supports multiple operating systems like Windows, Mac, Linux, Unix, and other systems. Some of the essential features of WireShark are Packet monitoring and importing packets from a capture file.
• W3af – W3af stands for Web Application Attack and Audit Framework. It is one of the most popular and widely used security testing tools available in the market. It is an open-source security scanner that scans vulnerabilities and security-related issues in websites and web applications. It can identify over 200 errors and vulnerabilities in the application, such as guessable credentials, buffer overflow, SQL injections, unhandled application issues, cross-site scripting, misconfigurations, etc. The purpose of W3af is to protect the application or website from all kinds of malicious elements such as viruses, threats, cyber-attacks, etc. It offers an interactive graphical user interface and a command-line interface.
• LambdaTest - It is one of the most powerful cloud-based platforms mainly used for cross-browser testing of websites and web applications. LambdaTest can also be used for Accessibility testing, Responsive Testing, and Localization Testing. It offers us to test all websites and web applications consistently over more than 2000 desktop and mobile web browsers, device emulators, and operating systems with manual, automated, and visual testing. It also provides a feature of one-click defect reporting, i.e., a tester can directly log a bug from the LambdaTest tool to different defect management tools such as JIRA, Mantis, GitHub, Trello, etc. Some of the essential features of LambdaTest are integration with various CI/CD tools such as Jenkins, AWS, GitLab, etc., execution performed on a secure, scalable, and reliable cloud-based platform, allows integration with Selenium for automation testing, and more.
• Functionize – It is a cloud-based AI-powered automation testing platform mainly used for performance, functional, and load testing. It makes the testing process quick and faster with the help of big data and machine learning approaches. It is mainly used by enterprise organizations to speed up their testing process. One of the primary features of Functionize is Smart Element Recognition, which helps in quickly recognizing the element on a webpage, and it doesn't use a single locator to locate or find elements of a webpage. It also allows its user to diagnose test failures with the help of a one-click feature (SmartFix). Functionize comes upon a 14 days trial basis. After that user can subscribe to its packages.
• Loadster – It is a hybrid cloud-based testing tool mainly used for performance, load, and stress testing of a web application, websites and APIs. It performs load testing on the product to identify hidden bottlenecks and blockers, optimizes the user experience, and improves the quality of the products in terms of performance. Some critical features of Loadster are browser-based testing, quick script recording and feedback, automatic test reports, live streaming of test results, full diagnostic of test results, and more. Like other load testing tools, Loadster is also an enterprise testing tool.
• SonarQube – It is a code quality assurance tool mainly used for security testing. In other words, SonarQube is used for analyzing and verifying the quality of code with the help of static code analysis and generates the quality report of the code. It combines both static and dynamic code analysis to improve the entire workflow with continuous code security and code quality. It also helps in quickly identifying the bugs to prevent system failures and disasters which reduces the risk of software development. SonarQube automatically identifies defects in the source code and sends an alert to the developer to fix bugs before moving the product into production. It is an open-source testing tool available in the market.

Difference between Non-Functional and Functional Testing

Non-Functional Testing – It is a type of software testing which tests the non-functional attributes and aspects of a system and ensures that the system is meeting and working as per the expected non-functional requirements of the system. It includes attributes like performance, load, stress, usability, reliability, portability, compatibility, efficiency, etc.

Functional Testing – Another type of software testing is Functional testing which works on validating the functional aspects of the system. It validates the system's functionality by testing all smaller units and components of the system and ensuring each function/feature is working as per the expected functional requirements. It works in the opposite direction of non-functional testing.

Following are the differences between functional and non-functional testing:

Parameters/ Attributes	Functional Testing	Non-Functional Testing
Purpose	Functional testing is performed to validate the functional requirements and behaviour of the application under test.	Non-functional testing is performed to validate the non-functional requirements and attributes of the system.
Functionality	It mainly focuses on testing what the system does.	It mainly focuses on testing how the system works.
Requirements	Functional test requirements are defined by the clients, and testing is performed based on the business specifications.	Non-functional test requirements are based on the end-users and performance specifications.
Focus area	It helps the team to test the system based on the customer's expectations.	It helps to test the system based on the customer’s expectations.
Execution	Functional tests are performed before non-functional testing.	Similarly, non-functional tests are executed after the completion of functional tests.
How to test	Functional testing can be done by manual as well as automation testing.	Non-functional testing is challenging to perform manually and, therefore, primarily performed via automation testing.
Types	Functional testing is further divided into various testing types: Unit testing Smoke testing Sanity testing Regression testing Integration testing Database testing	Non-functional testing is further divided into different testing types: Performance testing Security testing Usability testing Reliability testing Compatibility testing Portability testing
Example	Example of functional testing: Testing the login functionality of the application.	Example of non-functional testing: We test the performance and load when multiple users are accessing the website.

Advantages of Non-Functional Testing

The following are the benefits of non-functional testing:

• One of the major benefits of non-functional testing is that it covers the testing which is not covered in functional testing, such as portability, reliability, security, and many more.
• It enhances the capability and performance of the developed software so that multiple users can access the software simultaneously.
• Like functional testing, it ensures the system is defect free and working as per the non-functional requirements.
• Non-functional testing is performed from real-time and end-user perspectives.
• It enhances the security of the product to prevent it from malicious attacks.
• It also improves the usability, reliability, and accessibility of the software under test.
• Non-functional testing is always performed via automation. Hence, it consumes less time compared to functional testing.

Disadvantages of Non-Functional Testing

The following are the disadvantages of non-functional testing:

• Non-functional testing is performed every time the software gets updated to ensure the non-functional aspects of the software are working as expected.
• During the software maintenance, client or users have to pay again for re-examining the software, which makes the maintenance testing and software expensive.
• For non-functional testing, we need skilled and experienced testers to perform different types of non-functional tests.
• As non-functional tests are always automated and cannot be performed manually, it increases the cost of testing.
• It is always done after functional testing, so non-functional testers must wait for functional testing to be completed.