Testing conducted to verify the correct implementation of the design and compliance with program requirements for one software element (e.g. unit, module) or a collection of software elements. [IEEE Stds Glossary
Component Testing [aka: Unit Testing] is the process of examining individual hardware or software components or a set of related components in seclusion. This is derived from the developerâ€™s experience and intuition on how the components should operate in the system. Most plans of testing start with component testing and continue to system testing, where two or more components that system function or features and then testing this integrated system.