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Nonfunctional Testing: an Introductory Guide

Tests represent an extremely important step in the software development process, as they aim to validate if an application is…

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By Shawn J,

Tests represent an extremely important step in the software development process, as they aim to validate if an application is working correctly and if it meets the specified requirements.

In this context, we can apply several techniques at different times and in different ways to validate the main aspects of the software.
To prevent testing from being a mere step in the development cycle, implementing a process related to this ensures greater control of testing activities and, consequently, more quality of the software.

What Are Nonfunctional Tests?

We use nonfunctional tests to verify nonfunctional application requirements and also check whether the system behavior complies with the requirements or not. They test all aspects that are not tested in functional testing.

Software testing that examines a software application’s nonfunctional features is known as nonfunctional testing. It’s intended to assess a system’s readiness in relation to nonfunctional criteria that are never tested during functional testing. Both functional and non-functional testing are important to validating a software program’s quality.

Nonfunctional tests such as load and stress tests are typically performed using automation tools. In addition to performance tests, types of nonfunctional tests include installation tests, reliability tests, and security tests.

Contrary to what many imagine, testing software goes far beyond running tests exploring the features of an already-developed system. In fact, in order to move forward in the face of this stigma, the first obstacle we face is to make the test process, and the development process run in parallel from the beginning of the software life cycle.

Types of Nonfunctional Tests

1. Accessibility Testing

Accessibility tests are assessment exams that software must pass. Their objective is to evaluate the ease with which people with some type of disability or limitation have to interact with certain software. On a personal note, my son has special needs, and I appreciate companies that test their software for accessibility.

In this way, they ensure that the program is properly prepared and adapted to be used by people with different types of special needs.

Accessibility tests are similar to tests done to verify the usability of programs. The first analyzes only how easy it is for users to use a given tool. The second assesses the ease with which any user profile has to interact with the tool.

2. Security Testing

In search of broader coverage of the tests, executing the security test can be fundamental to reaching a safer operational environment, besides guaranteeing a correct application of the security assumptions defined for the software.

Nowadays, with the advancement of software testing and, consequently, with the greater experience and qualification of professionals in the area, the activities aimed at testing are more extensive, making a series of techniques and types of testing increasingly more explored.

We can divide these testing techniques between functional and structural, and the functional test, or black box test, is the one that aims to verify if the implementation is in accordance with what was specified.

The structural test, also called white box test, seeks to ensure that the developed software is well structured internally and, therefore, working correctly.

The combination of these techniques provides more detailed planning of the tests, allowing the discovery of different types of errors in the software. It also provides more confidence to the application by enabling a considerable reduction in the number of problems presented by the customer.

3. Scalability Testing

This is a kind of nonfunctional test in which we assess a software application’s, system’s, network’s, or process’s capacity to increase or reduce the number of user requests or other performance aspects. We can perform it at the hardware, software, or database level.

We can define scalability testing as the ability of a network, system, application, product, or process to function correctly when the volume of the system changes or when we increase the amount of data traffic. This ensures that a software product can manage the scheduled increase in user traffic, data volume, frequency of transaction counts, and many other things. It tests the ability of the system, processes, or databases to meet a growing need.

4. Performance Testing

We can divide performance tests into types according to their purpose. One very useful is a performance test that aims to verify the performance of a system when it has to deal with variable loads of users or transactions.

For example, we can run a load test on a simple web application, starting with 100 concurrent users and adding new users every five minutes, totaling 1,000 users at the end of the test.

It’s possible to analyze how the entire application ecosystem behaved during this period, if there was any slowdown at any point in the test, and if the CPU and memory usage of the servers was within the established limit, among other performance indicators.

5. Ability Test

Similar to the load test, this type of test aims to identify the limits of the applicationthat is, how many simultaneous users or calls per second the application is able to support within the defined quality parameters.

6. Stress Test

The objective of this test is to verify the performance of a system when we subject it to loads at or above the initially specified limit. If it’s specified that the application must support 1,000 simultaneous users, the stress test applies loads from this value.

In this way, it’s possible to collect information on how the application behaves under extreme conditions, often with few available computing resources, and identify if there’s unavailability on the server or if there’s slowness that can harm the end-user experience.

Nonfunctional Testing Vs. Functional Testing

The major difference between functional and nonfunctional testing is that functional testing checks whether the application is able to perform the function it has to do. This ensures that the software product is working properly.

Nonfunctional testing is the type of test that checks nonfunctional aspects, such as performance, usability, reliability, etc.

In other words, functional testing is testing that verifies what the system does, and nonfunctional testing is testing that verifies how the system behaves.

Suppose we’re testing a cashier system in a clothing store, and we must verify that when scanning a shirt that costs $20 and a pair of pants that costs $40, the final value will be $60. Functional testing verifies what is intended for the system to do and what is described in the requirements.

As for the nonfunctional test, we can see it as a slightly more subjective evaluation, more focused on the behavior of the software.

A good example would be to understand how the system behaves if there’s an intrusion attempt using any given technique. This is an example of a nonfunctional test type: security. Evaluating how the system behaves if a certain number of people connect simultaneously and perform a certain type of transaction is a kind of nonfunctional performance test.

Why Nonfunctional Testing Is Important

We often worry so much about functional tests that we don’t reserve time for nonfunctional tests such as security, performance, and usability, among others.

Nonfunctional tests are always very important, but what happens is that some companies have not yet realized the importance of software quality in their development process.

Nonfunctional testing is important because when we don’t pay attention, our systems can often be vulnerable to unforeseen failures during development and unexpected behavior both by users and by a possible malicious agent.

Usability is also a key factor in modern applications, and developers often end up not giving due importance to this aspect. The result is an application that’s difficult to use and does not retain the user.


Software testing is important to ensure that the software is working perfectly and that each of the configuration units is able to work alone and together in search of the best possible experience for users. In this sense, software testing is a fundamental tool both for the software to work and for it to be safe.

We can see in this post that nonfunctional tests are as important as functional tests, as nonfunctional tests deal with extremely relevant issues that are crucial for the system to be reliable, capable of withstanding high loads of data and traffic, and safe, as the number of attack techniques only increases daily.

If you are interested in trying out some market-leading performance testing software, check out Tricentis NeoLoad. And, if you want the best AI-powered progressive testing software on the market for your commercial-facing app, give Testim a try.