Component testing is a part of the V-Model, which is a development life cycle model that shows the relationship between each phase of development and its corresponding phase of testing. In this model, each level of testing (unit testing, integration testing, system testing, acceptance testing) has a corresponding level of development (component design, component integration, system design, requirements analysis). Component testing is the process of testing individual components or units of software in isolation from other components or systems. Component testing verifies that the components meet their functional and non-functional requirements and work as expected in their intended environment. Component testing is usually done by developers who have access to the component design and code specifications. You can find more information about component testing and the V-Model in Software Testing Foundations: A Study Guide for the Certified Tester Exam, Chapter 22.