Embedded systems are constrained and critical. They need to be validated before their development. They handle time constraints to model important aspects (delays, timeouts). This issue has to be taken into account in every step during its development life cycle, in particular in the testing step. This paper presents a methodology for the development of reliable embedded systems. A system is described as a timed automaton. It details an efficient derivation algorithm of test sequences able to identify controllable states on the system. Most of known errors of such systems are collected. They are automatically integrated on the derived sequences which are submitted to the implementation. If the system behaves correctly after this submission, the system is considered as robust.