The complexity of distributed systems is a problem when designers want to evaluate their safety and liveness. Often, they are built by integration of existing components with newly developed ones. Actually it is valuable to handle the integration of external pieces of software in the specification and testing activities. However it is difficult to validate them formally unless doing reverse-engineering (which is a heavy procedure). The paper proposes to use structured formal specifications to generate a reasonable set of tests that evaluate behavior of software components in order to get an answer to both questions. To do so, the authors use the description of components external behavior and express it using the OF-Class formalism (an encapsulation of colored Petri nets). Test patterns are generated using an appropriate formalism, HML logic, and they exploit various hypotheses corresponding to a user's testing procedure.