Functional testing ensures that functions and features of the application work properly. Nonfunctional testing examines other aspects of how well the application works.
Functional testing tests the functionality of an app. Nonfunctional testing tests the performance of these functions.
Some examples of functional testing include unit testing, integration testing, API testing., exploratory testing, and critical business flows testing, These all test functional aspects of the website or mobile app.
Nonfunctional testing makes applications more usable and more reliable. Unfortunately, it can often be rushed in an effort to meet release deadlines.
When nonfunctional testing is overlooked, performance and UX defects can leave users with a bad experience and cause brand damage. Worse, applications could crash with an influx of users. Accessibility defects can result in compliance fines. And their security could be at risk.