Basic Survival Guide to Functional vs. Non-Functional Testing

Madigan Johnson

Software testing is and will continue to become one of the most influential components of the software development process. If done correctly, testing will help catch costly mistakes and ensure high-quality products are being delivered to the customers. There are multitudes of testing practices that are implemented on a daily basis, but these methodologies are usually divided into two testing groups; functional testing and non-functional testing. We will be giving you the low-down on both. 

What is functional testing?

Functional testing is a type of testing that focuses entirely on the requirements of the software. It requires the tester to verify that each component of the software works in accordance with the specifications that the client has laid out. It is a type of black-box testing that does not require focus on the source code of the application. 

During the functional testing process, each functionality is tested by inputting an appropriate input, checking the output, and then cross-examining that against the expected results that are produced by the clients and identifies the domains where the performance did not meet the expected results. Functional testing can be accomplished either through manual or automated testing. 

What is non-functional testing?

Non-functional testing is where the focus of testing is on the non-functional aspects of the system such as reliability, performance, usability, and more. The focus here is more on how the software application will deal when forced to cope with challenging situations. If only focused on functional testing during the testing process, large issues might escape unnoticed. 

Non-functional testing helps provide the user with the best experience possible as it focuses on how competent and effective the program is during certain loads and situations. It defines the way the system operates rather than the specific functions. Enabling non-functional testing allows for businesses to guarantee that the software is sturdy and reliable for its users. 

Types of functional testing

  • Unit testing: the individual components of the software system are tested, usually by developers. It does not check the overall functionality of the software, but rather units to validate that they perform as designed.
  • Integration testing: the individual units are now combined and tested as a whole. This is to check if there are any faults of defects in the interactions between the smaller components of the software system.
  • System testing: where the complete and unified software system is tested. This is conducted to see if the system complies with the requirements set forth. 
  • User acceptance testing: This type of testing looks at the acceptability rate of the system. It checks the compliance with the requirements and ensures that it is acceptable to release to the public and can handle real-world situations and problems.
  • Smoke testing: are quick functional tests that focus on the build of the software and if it is stable enough to continue on or needs further improvement.
  • Regression testing: verifies that if there are any new features or functionalities that it does not change or impact any of the already existing features. 
  • Sanity testing: is performed on an already stable software system that has undergone minor changes in the code or functionalities. It is conducted to establish that previous bugs or issues were fixed and this did not result in the creation of any new ones. 

Types of non-functional testing

  • Performance tests are used to provide assurance that software applications will work appropriately under the expected workloads. It can be broken down into these further types: 
  1. Load tests- this is used to test the behavior of a system that that has an increasing workload
  2. Stress tests- a form of performance testing that is used to evaluate the behavior of a system at or beyond the limits of its foreseen workload
  3. Endurance tests- used to test when the system is given a continuous increased workload
  4. Scalability tests- checks the performance of the software system with the minimum and maximum load
  5. Volume tests- analyzes the response time and behavior of the system when it is repeatedly overwhelmed with a large amount of data 
  6. Spike tests- investigates the behavior of a system when the load is suddenly increased
  • Reliability tests: this checks if the system can maintain the performance level over time indicated by the requirements of the system under certain conditions.
  • Robustness tests: this test is conducted to ensure that all systems will continue to operate as intended, even when there is certain unanticipated events.
  • Usability tests: these are used to secure that the user experience is fantastic and that the end product can be used easily.
  • Localization tests: this helps with the assurance that the system will function properly and as intended in the country or locality in which it is based. 
  • Security tests: by conducting these types of tests, you are ensuring that the software system is secure and not exposed to any outside threats 

Differences between Functional and Non-Functional Testing

So now that we have an idea of what the two types of testing look like, it is important to gain clarity on what the differences between the two are and when to use them. While both of these are designed to give the user the best experience possible, the main difference between the two is that functional testing focuses on the software meeting particular requirements while non-functional testing focuses on how well the system works. 

Functional testing has an increased concentration on finding and fixing bugs, whereas non-functional testing is more concerned with the usability of and overall experience of the user with less focus on the bug searching. 

The main difference between these types of testing is that functional testing focuses on the what where non-functional testing focuses on the how. With that being said, you must always conduct functional testing before you can do any sort of non-functional testing. 

In conclusion…

There is no testing without functional and non-functional testing. All of the testing techniques fall under these two. Bad quality software can be avoided when implementing both testing types as it eliminates the bugs and ensures that the user experience is actually viable. Using this testing will allow companies to save time and money.

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