Functional Testing and Non-functional Testing – What’s the Difference?

Artem Golubev

Functional Testing vs. Non-functional Testing

How do you ensure delivering a flawless software application to your customers? It is the comprehensive combination of the application’s functional and non-functional testing coverage.

In functional testing, verification is done for each feature or function of the software application in conformance with the user requirements specification. Functional testing concentrates on the result, not the process itself. On the flip side, the targets of non-functional testing are parameters focusing on the application’s process (performance, security, usability, etc.). The goal of these two types of testing is to ensure the seamless working of the software product as per the given user requirements and par excellence customer satisfaction.

Both subject testing types are equally important if you want to provide a safe and highly appealing user experience. However, some startup companies might initially focus their efforts primarily on functional testing – if they are constrained to afford both.

It is important to note that the functional testing is designed to be performed prior to the non-functional testing. Doing so develops an efficient understanding of the QA team about how the system executes its functions so that the non-functional testing part can become more productive. These testing types complement each other, and both are deemed critical for successful software delivery. Ideally, the two testing types under discussion here must go hand in hand, especially when defect-free software delivery is your goal.

In this article, we will cover functional and non-functional testing types in detail, which will help you develop a thorough understanding of their concepts.

The big picture in software testing often outshines the necessary individual details. Novice software testers must understand the different types of functional testing to maximize the testing efforts output. The goal is to validate the software actions using black-box testing techniques. Meaning the software’s source code is out of the concern here. The given user requirements serve as the baseline. The QA testers are required to write test cases under each of its types (described below), where the functional test suite is supposed to cover the entire functionality of the software application.

The following is a brief description of the most relevant functional testing types:

Smoke Testing

The goal of smoke testing (also sometimes called build verification) is to ensure that the critical functionality of the application is working as expected. The purpose of smoke testing is to be brief and validate that the build isn’t severely broken – since if it is, you’ll have to wait for a new one and start testing from scratch.

Sanity Testing

Once you’ve established having a stable software build, sanity testing is the next step. This type of testing is quite similar to smoke testing, as both assure that the build is ready for further testing. This testing aims to ensure that the prior bugs have been resolved, as well as no new issues have been introduced due to newly introduced code changes.

Integration Testing

Just as the name suggests, integration testing is performed when two or more software application components are integrated to form a system. This type of testing aims to ensure the desired functioning of the application when the components or modules of the system work together as a single unit. Integration testing also covers validating data accepted by the API, whether it’s with your own product or a third-party tool.

Regression Testing

Regression testing is typically the last step to be done before QA gives the green light to the release. It is also the broadest and the most substantial one. The ultimate target here is to ascertain that any update or change in the code didn’t accidentally impact any other feature or functionality of the software in a negative way. Apart from code changes, regression testing should be applied whenever a new requirement or feature is added, or configuration changes are made.

Localization Testing

The localization testing is performed to check that the software application offers extensive usability and full functionality in a specific locale. This is where the product is customized to serve the needs of a targeted region, culture, or language. An example of localization testing will be a region-specific date/time format or displaying amounts and symbols in a local currency.

Once you’ve completed the functional testing round, the non-functional testing comes into play. Here the primary focus is the customer’s expectations. It can be challenging to define some of these requirements and simulate them, so there are designated automated tools to execute this type of testing. The subject testing is carried out through the performance specifications, and the target is to ensure that the software application meets or exceeds customers’ expectations. An example of a non-functional test case is the expectation of the end-user to have the landing page of a website load within 2 seconds.

Let’s look into the most critical non-functional testing types below:

Performance Testing

It is the practice of evaluating how a software application performs in terms of its stability and responsiveness under a given workload. The performance testing is typically done to examine the robustness, speed, and reliability of the product under test. The following are the major subtypes of performance testing:

• Load Testing – models the usage of a software application by simulating users accessing the app concurrently.
• Stress Testing – performed to test the ability of a software program to work effectively under unfavorable conditions by simulating a certain number of users simultaneously.
• Volume Testing – this type of performance testing is done on high volumes of data to see how effectively the database handles it.
• Endurance Testing – endurance tests are executed to evaluate the performance of the software product under normal workload conditions over an extended period.

Usability Testing

Usability testing can be employed to evaluate a software application through representative users. During the execution of this testing type, the participating users will try to accomplish typical tasks while the observers would listen, watch and take notes. The goal of this testing is to collect quantitative and qualitative data while determining the satisfaction of the participants with the product.

Security Testing

The primary aim of security testing is to uncover the vulnerabilities of the software system. It ascertains that the software data and other resources are protected from any possible intruders. Moreover, it ensures that the developed product is free from any risk or threat that could lead to a loss.

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As a final step, let’s summarize the main key points regarding both types of testing discussed in this article.