Unit, integration, and functional testing are crucial components of software application testing. Each of these employs a distinct and unique process to test the application. However, the most important remains functional testing and functional regression testing. Unit or integration testing cannot replace this, either by itself or collectively. While unit testing involves testing individual modules of an application, isolated integration testing checks if different modules are working together as a group. Finally, functional testing checks whether the system operates the way it is supposed to.
Together, these constitute an application that is bug-free and smooth for the end-user. Functionality is related to integration tests. The latter is performed only when the former has yielded desired results. However, successful automated functional testing signifies that the entire app is running smoothly.
