Book excerpt: Component-based software development regards software construction in terms of conventional engineering disciplines where the assembly of systems from readily-available prefabricated parts is the norm. Because both component-based systems themselves and the stakeholders in component-based development projects are different from traditional software systems, component-based testing also needs to deviate from traditional software testing approaches. Gross first describes the specific challenges related to component-based testing like the lack of internal knowledge of a component or the usage of a component in diverse contexts. He argues that only built-in contract testing, a test organization for component-based applications founded on building test artifacts directly into components, can prevent catastrophic failures like the one that caused the now famous ARIANE 5 crash in 1996. Since building testing into components has implications for component development, built-in contract testing is integrated with and made to complement a model-driven development method. Here UML models are used to derive the testing architecture for an application, the testing interfaces and the component testers. The method also provides a process and guidelines for modeling and developing these artifacts. This book is the first comprehensive treatment of the intricacies of testing component-based software systems. With its strong modeling background, it appeals to researchers and graduate students specializing in component-based software engineering. Professionals architecting and developing component-based systems will profit from the UML-based methodology and the implementation hints based on the XUnit and JUnit frameworks.