The Difference Between Functional and Non-Functional Testing

Within the realm of software development, there are a wide variety of ways that quality assurance teams can evaluate their applications and ensure that they are delivering the best products possible. For agile testing methodologies in particular, teams can leverage numerous different kinds of testing approaches to examine their code and reveal defects. All of these practices can become fairly chaotic for QA teams to keep up with and track across projects due to the sheer density of test cases that can be leveraged.

Luckily, there are two main umbrellas that all tests fall under, which QA management can use to prioritize their strategies. Functional and non-functional testing are two sides of the testing coin, and it's critical for organizations to understand the differences between these two categories in order to utilize them to their fullest extent.

Functional Testing

QA teams often refer to functional testing as blackbox testing, where cases are set to evaluate the app against business requirements. Manual testing is often more beneficial for these tests, but automation can still be used in these cases. Software Testing Class noted that functional testing is concerned with sanity, interface, integration, unit and regression tests, among others. These all are focused on running functions to follow their outputs, then comparing actual results to the ones that were expected.

Functional testing helps to ensure that business specifications are being met and that any major changes in these areas are dealt with quickly. In a LinkedIn post, TestingWhiz consultant Pratik Patel noted that functional testing puts the requirements coverage as the priority, and teams must carefully evaluate user commands, searches, navigation, integration and data manipulation. This amount of scrutiny will ensure that the app directly meets organizational goals and can bolster its success.

Non-functional Testing

On the other side of the coin is non-functional testing, which mainly focuses on the readiness of a system. Not only can it take place after functional testing, but it also can significantly benefit from test automation integration, since many of these test cases are repeatable across projects. Non-functional testing concentrates on the quality of the product and its suitability from the perspective of its users. Test cases under this category can include performance, usability, stress, scalability, baseline, compliance, load, security and maintainability testing, as well as numerous others. These non-functional testing types can directly impact the user experience, so it will be critical to get it right for the sake of active engagement and project success.

"Non-functional testing has a great influence on customer and user satisfaction with the product," Software Testing Class stated. "Non-functional testing should be expressed in a testable way, not like 'the system should be fast' or 'the system should be easy to operate' which is not testable."

Do You Need Both?

Testing itself takes a lot of effort, and teams actively look for ways to shave time off their packed schedules. In this vein, it may be easy to think that a team could go all-in for one type of testing over another, and still produce quality software. While the application may come out fitting one area's requirements, it'll invariably be missing out on other parts that would improve overall usability and capabilities. For example, functional testing mainly zeros in on business requirements and defect mitigation, but may not be conducive to ensuring that users are getting what they really want. At the same time, sticking only to non-functional testing could verify that parts of the application are working, but could potentially introduce vulnerabilities that break the overall functionality.

Non-functional and functional testing are two sides of the same coin, and as a result, teams cannot afford to use one without the other. However, the amount of focus and methods used to carry out each will vary from project to project. It will be important for QA professionals to understand the key differences between these two categories and how they rely upon each other to create the best product possible with an agile test plan. With this knowledge, testers can create solid testing strategies with cases that directly fit their needs and can prioritize tests according to these divisions.