Functional Testing is a testing technique which verifies that each function of the developed application operates in accordance with the requirement specification. This testing method primarily involves black-box testing and is not concerned about the source code of the application.
Functions of the application are tested by feeding them with input and analysing the output, and internal program structure is rarely considered. Basically, functional testing describes what the system does. It involves validating the user interface, databases, security, APIs, client/server apps as well as functionality of the application under test.
It helps to deliver a defect-free product.
It makes sure that all the end-users requirements are fulfilled.
It ensures the safety and security of the product.
It enhances the quality of the product.
It checks whether the product is working efficiently on all the platforms.
It focuses on the results produced by required inputs.