Abstract: The rise of component-based software development poses the problem of components trustability. To know whether a given component can be used within a certain context, there must be a way of telling what the component is supposed to do (its contract) without entering into the details of the how. Based on this idea, we have proposed a general Design-for-Trustability methodology ("DfT"), starting from simple self-testing of individual classes to optimized integration testing, This paper describes the "DfT" methodology, the self-testable class model that supports it and the associated tools for java development.