Everything You Need to Know About Non-functional Testing in One Comprehensive Guide

Testing is a crucial part of every software development process as it helps to ensure that not only customer satisfaction is guaranteed, but the software itself matches all standards and requirements. While testing was traditionally limited to the functional requirements, the concept of non-functional testing has gradually come under the spotlight. Its growing importance could be attributed to the fact that modern applications and their ecosystems have both undergone drastic transformations.

The older applications usually used to run in closed, largely undistributed environments where everything was generally within control. However, the arrival and widespread utilization of cloud computing and microservices have changed the face of the applications and their ecosystems. Non-functional requirements (NFRs) have become as important as their functional counterparts, and the need and importance of testing these NFRs have consequently become equally important.

What is Non-Functional Testing?

Non-functional testing refers to the testing of those aspects of a software application which are not connected in any way with a defined user action or a function.

As the name suggests, it concentrates on an application’s non-functional aspects such as performance, usability, security, compatibility, and all other aspects that are not tested under functional testing. Non-functional testing is performed to verify these NFRs and if the system’s behavior is in accordance with them.

The following are some of the significant non-functional aspects of an application that are considered and tested under non-functional testing:

• How does the application behave and perform under normal circumstances?

• How does it behave when a large number of users log in simultaneously?

• How much stress could the application handle?

• How secure is the application?

• Is the application robust enough to recover from a disaster?

• Does the application show similar behavioral patterns in a different environment or OS?

• Are the documents accompanying the application easy to understand?

The singular purpose of NFR testing is to ensure that the application works well with regards to the non-functional aspects.

Ultimately, the motive of non-functional testing is to test all characteristics of an application that would help to provide an application which meets the business expectations.

The Importance of Non-functional Testing

Consider an application that is developed and wholly tested for functional requirements, but non-functional testing is not performed. Now imagine what would happen when the application goes live and is immediately subjected to a massive load.

In the absence of non-functional testing, you would be very unsure of the application’s ability to handle massive traffic. The application may become slow or even crash in the worst case scenario. What an embarrassment that would be! In another scenario, imagine if the application is not tested for security, if that is the case then an unauthorized party could easily crack the data entered by the app users.

Non-functional testing is as important as functional testing. It ensures security and establishes the reliability of the application. It ensures that the application developed is robust enough to work under duress. The application’s compatibility with various devices, its user-friendliness, its endurance and a host of other vital parameters are established and verified through NFR testing.

Functional vs. Non-functional Testing: What Differentiates the Two?

Though both functional and non-functional testing is performed with the objective of delivering an application in line with the demands of the business, there are many differences between the two.

A detailed analysis of functional vs non-functional testing throws up the following points as the major differentiators between the two.

• Functional testing is concerned with how well the system works, but non-functional testing is concerned with how well the system responds. For instance, functional testing may test the mechanism for inputting data, but non-functional testing may test the speed at which a document is saved.

• Functional testing is largely based on the customer’s requirements, but its counterpart is based on the customer’s expectations. Unlike previously, modern businesses differentiate between the customer’s requirement and expectation and the growing emphasis placed on the customer’s expectation has made non-functional testing a non-negotiable.

• Customer feedback has far greater utility for non-functional testing. Even though functional testing also benefits from this feedback (as it helps reduce the risk factors of the product), non-functional testing stands to gain (and lose, if customer feedback is not provided) a lot more because it lets the testers know what the customer expects and helps them improve the product.

• It is hard to conduct a thorough and efficient non-functional testing process in the absence of appropriate tools. This is not a problem with functional testing which could also be done manually with the same efficiency.

• Functional testing is performed only before the application goes live. Certain types of non-functional testing such as maintenance testing and documentation testing are required to be performed once the application has gone live.

• Another key difference lies in the very nature of the requirements on which the tests are based. While functional requirements specify which functionality needs to be tested, non-functional requirements define how it needs to be tested. Also, the implementation plan for both types of requirements are described in separate places; the one for functional requirements is defined in the system design document while that of the non-functional requirements is defined in the system architecture.

• The functional vs non-functional testing comparison could be better explained through its examples. Under functional testing, you may test if providing the username and password on the login screen allows users to log in to the site. Under non-functional testing, for example, you check if the user can login to the site within 3 seconds by providing the username and password.

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