Development of a software system from existing components can surely have various benefits, but can also entail a series of problems. One type of problems is caused by a limited exchange of information between the developer and user of a component. A limited exchange and thereby a lack of information can have various consequences, among them the requirement to test a component prior to its integration into a software system. A lack of information cannot only make test prior to integration necessary, it can also complicate this tasks. This paper proposes a new strategy to testing components and making components testable. The basic idea of the strategy is to merge components and testing tools in order to make components capable of testing their own methods. Such components allow their thorough testing without disclosing detailed information, such as source code. This strategy thereby fulfills the needs of both the developer and user of a component.