Component testing, also known as module testing or program testing, is a software testing technique that focuses on evaluating individual modules or components of a larger software system. A component is the lowest unit of any application, and component testing aims to verify that each subsystem of a software application works as expected. Component testing is a form of closed-box testing, meaning that the test evaluates the behavior of the program without considering the details of the underlying code. It is done on the section of code in its entirety, after the development has been completed. Component testing examines use cases, so it could be considered a form of end-to-end (E2E) testing.

Component testing is performed on each individual component separately without integrating with other components. It is a kind of white box testing, and it looks for bugs and verifies the functioning of the modules/programs which are separately testable. Component testing is useful for identifying issues at the module level, so defects are captured at the early stage for each module and hence reduces the efforts of both developers and testers while testing the entire application. This testing eliminates the errors at the initial stage and builds confidence at the component level.

Component testing is conducted alongside other forms of testing, such as unit, integration, and system testing, and may be carried out manually or using automated testing tools. Defects may be found and fixed with less effort and expense if component testing is performed early in the development process. The main objective of component testing is to verify the input/output behavior of the test object, ensuring that the test object’s functionality is working correctly and completely fine as per the desired specification.

In summary, component testing is a software testing technique that focuses on evaluating individual modules or components of a larger software system. It is useful for identifying issues at the module level, and it aims to verify that each subsystem of a software application works as expected. Component testing is conducted alongside other forms of testing, and it may be carried out manually or using automated testing tools.