Functional Testing In this type of testing, the software is tested for the functional requirements. The tests are written in order to check if the application behaves as expected. Although functional testing is often done toward the end of the development cycle, it can—and should, —be started much earlier. Individual components and processes can be tested early on, even before it’s possible to do functional testing on the entire system. Functional testing covers how well the system executes the functions it is supposed to execute—including user commands, data manipulation, searches and business processes, user screens, and integrations. Functional testing covers the obvious surface type of functions, as well as the back-end operations (such as security and how upgrades affect the system).