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The Comprehensive Guide to Non-Functional Testing

Head of Consulting and Architecture

Head of Consulting and Architecture

Non-Functional Testing: A Key Step In Software Development You Can’t Afford To Miss

User experience is paramount to successful software applications and goes far beyond mere functionality. Non-functional testing uncovers issues with trustworthiness, predictability, speed, and ease of use. Software that meets all expectations in terms of functionality but that is lacking in these areas will drive away customers and tarnish reputations. A typical example of this is an e-commerce platform that is unable to manage increased traffic on Black Friday and crashes, leading to loss of sales and reputational damage. This situation can be prevented by a type of non-functional testing called performance testing. Non-functional test parameters include response time, throughput, interoperability between different systems, internal links, and authentication, among others. These parameters do not influence the functionality of the software but its performance. Ideally, non-functional testing should be done far earlier in test cycles than it usually is as it is just as important as functional testing.


This guide covers nineteen types of non-functional tests that are vital to successful software development.


19 Non-functional Tests You Should Know About

Non-functional testing can take your app or website to the next level in terms of user experience. These assessments take a closer look behind the scenes at what makes for a great experience, all the aspects that the end user will never be aware of- except when it goes horribly wrong!


Performance Testing

Performance testing evaluates the application under a given workload: How would the system respond to expected and unexpected demands? Performance testing is an umbrella term encompassing many types of testing. Most organisations (including Inspired Testing) employ load testing, stress testing, endurance testing, and scalability testing as part of performance testing. Performance testing deals with issues with the system’s architecture and design and aims to test one of three key metrics: speed, scalability, and stability.


Load Testing

Load testing is a type of performance test that evaluates what load the software or website can manage before sacrificing reliability and performance. Load tests measure response time, throughput rates, and resource-utilisation levels. Load testing will identify easily overlooked issues like system lag, problematic page loads, and other difficulties that may develop due to high traffic. Load testing will enable you to leverage real-life data when identifying underlying problems. Just like performance tests in general, load tests are most valuable when integrated early in the development process.


Stress Testing

Stress testing is done to simulate the effect of an expected real-world load on a system. This is done to identify performance bottlenecks and break-points which can be solved with design tweaks, optimisation, and additional hardware.


The main purpose of stress testing is to determine the limit at which the application breaks, and if the system shows effective error management under such extreme conditions. Stress testing will also check other aspects of the system under extreme conditions like appropriate error message display


Endurance Testing

Endurance testing is used to determine if the system can cope with high processing requirements for a sustained period of time.


Spike Testing

Spike testing evaluates how the system responds to abrupt changes in demand. Unlike endurance testing, spike testing increases the workload for short periods of time to see if the system can respond to rapid significant changes.


Scalability Testing

Scalability testing determines the system’s ability to meet growing needs as the number of users scales up or down. It focuses on the behaviour of the application when put under excess load and measures the point at which it stops scaling and the reasons behind it. Scalability testing leads to improved user experience and customer satisfaction, lower infrastructure cost, and allows less expensive problem resolution while still in the testing phase. In addition to user/number-related performance, scalability testing also allows you to investigate response time, screen transition, memory usage, throughput, CPU and Network usage as users scale up and down.


Baseline Testing

Baseline testing establishes the documented baseline standard of an application as it goes through performance testing. This helps to set a baseline for maintaining software application performance over time. As changes are made to the application it goes through performance testing, the results of which can be compared to the documented baseline test results. This process helps to maintain the expected quality of an application.


Benchmark testing

Benchmark testing is used to assess performance test results against an organisational or industry standard. This assists in performance analysis when compared to competitors, ensure that all compliance and SLAs are met, and offers a way to ensure that best practices are followed with quantifiable results.


Failover Testing

Failover testing validates a system’s capacity to allocate resources toward recovery during an abrupt failure. The system will require additional resources to switch operations over to a backup system, and failover testing will determine its capacity to manage these additional resources. Failover testing will ensure minimal or no loss during downtime, a critical characteristic in certain applications such as banking, telecoms, and trading.


Compatibility Testing

Compatibility testing determines if the application can operate in different environments. There are many types of compatibility tests to check if an application can run on different hardware, operating systems, software, networks, browsers, devices, and across versions. Both backward and forward compatibility testing can be performed. Backward compatibility testing verifies the behaviour of an application with its older versions of hardware or software. Forward compatibility testing validates the behaviour and compatibility of the application with newer versions of hardware or software and is harder to perform.


Usability Testing

Usability testing determines how user-friendly the application is, the overall user experience, and identifies areas that users may struggle with. It investigates how easy it is to learn how to use and understand the application to perform the desired task by taking into account aspects like navigation, design, embedded search, and content quality. Other traits that usability testing will take into account include how intuitive the interface is, performance, information hierarchy, efficiency, accuracy, and recall.


Maintainability Testing

Maintainability testing indicates how easy it is to fix problems in the system, make improvements, adapt to a changing environment, and prevent future maintenance. These processes ensure that the same quality can be achieved throughout the lifetime of the application. Maintainability has four attributes: analysability, changeability, stability, and testability. Maintenance costs can form a significant part of a project’s costs therefore it is important to do maintainability testing.


Volume Testing

Volume testing verifies the performance of the application against a large volume of data in the database. Where other types of testing focus on the number of users, volume testing focuses on data and the database. The impact of a high volume of data on the response time and system behaviour can be tested with volume testing. Volume testing will identify the point at which the system stability will degrade as well as the capacity of the system in terms of normal and heavy volume. Volume testing will lead to the early detection of bottlenecks and assist with scalability plans.


Security Testing

Security testing identifies any threats in the system as well as potential vulnerabilities. This is incredibly important as it ensures that no confidential information is leaked. Types of security testing include vulnerability scanning, security scanning, penetration testing, risk assessment, security auditing, ethical hacking, and posture assessment. The core security principles are confidentiality, integrity, availability, authentication, authorization, and non-repudiation. The major focus areas in security testing include network security, system software security, client-side application security, and server-side application security.


Disaster Recovery Testing

Disaster recovery testing assesses the application’s ability to recover from failures such as software or hardware crashes, network failure, and more. This type of testing is done to determine if the operation can continue after integrity loss by reverting to a point before the loss where integrity was intact. Disaster recovery testing will also provide information on the time it will take for the operation to resume if lost data can be recovered completely or not, and the percentage of scenarios in which the system can recover.


Compliance Testing

Compliance testing determines if an application meets a predefined set of standards before it is released into production. These standards include internal standards – those set by an organization. External standards are industry or regulatory standards. Compliance testing done throughout the development cycle will ensure that the deliverables of each phase meet internal and external standards. It is also valuable to evaluate the project’s documentation for completeness.


Portability Testing

Portability testing determines the ease with which a component or application can be moved between environments such as browsers, operating systems, and database versions. There are four attributes of portability testing: adaptability, compatibility/co-existence, installability, and interoperability testing. Adaptability testing verifies that the application can perform all intended behaviour in the different environments. Compatibility testing confirms that multiple unrelated systems can co-exist without conflict in the same environment. Installability testing tests the software’s ability to install in different environments. Interoperability tests the functional relationship between two software systems.


Reliability Testing

Reliability testing checks that an application can perform without failure within a specific environment for a specified period. It is key to improved software quality and is used to ensure that the application is reliable and without bugs for its expected purpose. Reliability testing may reveal many design and functionality problems and must be performed at several levels. It includes feature testing, load testing, and regression testing. Reliability testing is used to determine the number of failures in a specific period, the perpetual structure of repeating failure, and the main cause of failure.


Static testing

Static testing is the validation of the documents and specifications on which test cases will be designed. This ensures that the base of the project is set correctly before development starts and serves as a fixed point of reference for future comparison purposes. Most issues can be resolved through static testing. Static testing is incredibly important as an error in the baseline will carry through to the rest of the project.


Non-Functional Testing In A Nutshell

Non-functional testing is arguably just as important as functional testing in successful software development. It should be incorporated early in the development lifecycle to find and address bugs as soon as possible. It is far less expensive to fix problems early in the lifecycle of an application than when it is in the production phase already. Non-functional testing ensures that an application works in any environment, under various loads, and along with other software. It is an essential part of any software development lifecycle.


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