Before even the best software application hits the market, it must be rigorously tested. All the cool concepts and nifty “bells and whistles” in the world mean nothing if the application fails to work correctly. That’s why developers need to put a new product through its paces before the public gets a hold of it.

So today, we’re discussing testing, specifically non-functional testing. This article defines non-functional testing, the characteristics of non-functional testing, its parameters, the various kinds of non-functional testing, and the differences between functional and non-functional testing.

Let’s get things started with a definition.

What Is Non-Functional Testing?

Non-functional testing is testing designed to check a software application's non-functional aspects such as performance, reliability, utility, etc. In addition, this testing is designed to test a system's readiness related to non-functional parameters typically never addressed by the functional testing process.

For instance, how many users can simultaneously log in to a software application? Or how easy or difficult is it to port the application to a different system? Or does the application behave differently in another operating system or environment?

So non-functional testing puts an application through its paces, testing aspects that functional testing doesn’t touch.

What Is Non-Functional Testing: The Objectives of Non-Functional Testing

The following are the objectives of non-functional testing:

  • First, to increase the product's efficiency, maintainability, usability, and portability
  • Optimize how the product is installed, set up, executed, managed, and monitored
  • To improve and enhance knowledge of the product's behavior and its technologies
  • To aid in reducing production risks and costs related to the product’s non-functional aspects
  • To gather and report product measurements and metrics for in-house research and development

What Is Non-Functional Testing: Characteristics of Non-Functional Testing

Non-functional testing possesses a unique set of characteristics:

  • Non-functional testing should be objective, quantifiable, and measurable and not use subjective characterization such as terms like “good,” “better,” and “best”
  • The exact numbers will probably be unknown at the beginning of the requirement process
  • Non-functional requirements must be prioritized
  • Testers must ensure that all quality attributes are correctly identified in software engineering

What Is Non-Functional Testing: Non-Functional Testing Parameters

These are the eleven parameters found in non-functional testing. Of course, there may be occasions where not all of them are brought into play. However, the parameters of Recovery, Reliability, Security, Stability, and Usability are the most essential and should never be left out.


This parameter defines how well a system is protected from sudden and deliberate attacks from within and without. This parameter is tested through Security Testing.


How well the software system continuously achieves the specific functions without failing. This condition is tested with Reliability Testing.


This parameter ensures that the software system keeps functioning and recovers itself in the event of system failure. This parameter is checked by Recovery Testing.


To what extent can a user depend on the system while operating? That’s what Stability Testing tells us.


How easy can users learn, operate, and prepare inputs and outputs through interaction with the system? Usability Testing checks this parameter.


To what extent can an application expand (or contract!) its processing ability to keep in synch with demand? That’s what Scalability Testing tells us.


How does the software in question interface with other software systems? Interoperability Testing measures this parameter.


How does the system handle capacity, quantity, and response time?


This parameter covers how easy it is for the application to work with different hardware and software configurations, such as CPU and RAM requirements.


How easy is it to migrate the software from its present hardware or software environment?


Some software apps have a degree of versatility that allows portions of the application to be converted for use in other applications.

The Types of Software Testing

Software testing has three distinct types: Functional, Non-Functional, and Maintenance. These primary types are further broken down into multiple testing levels, although these levels are typically referred to as “testing types,” despite the potential confusion.







Integration Testing












Unit Testing



User Acceptance



…and others

…and others


What Is Functional Testing?

We’ve mentioned functional testing already but haven’t taken any time to define it. Let’s remedy that.

Functional testing, typically performed manually, verifies that a program or app’s operational execution happens as set down by the business and technical requirements. Such an application passes functional testing only if every feature works correctly.

So, for example, if you’re running functional tests on an e-mail application, there could be a test that verifies that when an icon on a page gets clicked, it loads a new page.

Here’s a small sample of the different available functional testing strategies (also referred to as “types”):

  • API Testing: If the application in question uses APIs, this test verifies that the third-party services won’t create issues such as memory drain or bugs.
  • Closed-box Testing: Also referred to as "black box testing," it focuses on the application's externally visible behavior and outputs, not the software's inner workings.
  • Integration Testing: This test shows whether multiple application components work well together as a single unit.
  • Regression Testing: This test verifies that recent updates or changes haven’t impacted the app’s existing functionality.
  • Sanity Testing: This test confirms that a bug was fixed, or a new bit of functionality was added successfully, and it didn’t raise new issues.
  • Unit Testing: This test checks the system’s individual components and units.
  • User Acceptance Testing: This test confirms that the accessibility, functionality, and quality of the application are good enough for real-life use.

Explaining the Difference Between Functional and Non-Functional Testing

Although these two testing methods occasionally overlap to one extent or the other, they have two distinct functions and check for different things.

The best way to sum up the difference between functional and non-function testing is functional testing shows that the application's functions are doing what they're supposed to do. In contrast, non-function testing verifies that the software conducts the processes correctly.

So, using our e-mail as an example, functional testing verifies that a user who registers on the site gets a confirmation e-mail. In contrast, non-functional testing measures how long it takes for the user to receive that e-mail.

As a rule, function testing questions can typically be answered with a “yes” or “no,” while non-functional questions elicit gradable answers.

What is Non-Functional Testing: A Guide to Non-Functional Testing Types

Since this article focuses on non-functional testing types, let's look closely at the testing levels or types that lie under the non-functional testing umbrella.

  • Performance Testing: Evaluates component or system compliance with the specified performance requirements.
  • Load Testing: Places demands on the device or system and measures its response.
  • Failover Testing: Verifies that, in the event of a system failure, the system has sufficient capabilities to handle extra resources such as servers.
  • Compatibility Testing: Tests how well the application performs within particular hardware, software, operating system, or network environments.
  • Usability Testing: Verifies how easy it is for the user to learn how to operate, prepare inputs for, and interpret outputs of the given component or system.
  • Stress Testing: It pushes a system or component up to or beyond its specified requirement limits.
  • Maintainability Testing: Tests the ability to handle issues that arise in the live environment or should the customer want an enhancement for an already live application.
  • Scalability Testing: Measures the application's ability to scale up, such as the number of transactions, data volume, user load support, etc.
  • Volume Testing: Confirms that a program can handle the values that can potentially grow over time (e.g., accumulated counts, logs, and data files) and the build-up will not crash the program or degrade its operation in any way.
  • Security Testing: Determines that an information system’s security measures work, protecting data and maintaining intended functionality.
  • Disaster Recovery Testing: Measures how well a system recovers from hardware failures, crashes, or other catastrophic problems.
  • Compliance Testing: Checks whether the system or software was developed following the established procedures, standards, and guidelines.
  • Portability Testing: Verifies that the product’s functionality won’t change if it’s installed on a different platform or system.
  • Efficiency Testing: Verifies that the application works efficiently and measures factors such as the number of required resources required, complexity, customer requirements, environment required, the time needed, project type, etc.
  • Reliability Testing: Proves that the application is reliable, producing the same expected output every time it’s used. This test is run for a specific period in a defined environment.
  • Baseline Testing: Also known as benchmark testing, it creates a new base to be used in subsequent testing.
  • Endurance Testing: Checks for memory leaks or other issues that may arise from extended execution.
  • Documentation Testing: Evaluates the product’s user manuals and related documents.
  • Recovery Testing: Evaluates how well the system recovers from crashes, hardware failures, or other catastrophic incidents. This test is also called disaster recovery testing.
  • Internationalization Testing: Verifies that the product’s functionality isn’t ruined, and all messages are properly externalized when the product is used in different languages and locales.
  • Localization Testing: Focuses on converting a globalized application to a particular region or culture.

Example Test Cases of Non-Functional Testing

Here’s what a group of non-function testing tasks for an application look like:

Test Case #

Test Case

Testing Domain


Does the software easily install on Windows and macOS platforms?

Compatibility Testing


Do all the web images have “alt tags?”

Accessibility Testing


Does the application's load time come in at less than five seconds even when 1,000 users access it simultaneously?

Performance Testing

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