This paper presents new techniques for specification based-testing of synchronous software with the Lutess tool. Lutess provides a framework consisting in automatically building generators which interact with the software under test and feed it with test input sequences. In the past few years, it has been established that operational profiles as well as scenarios are powerfull tools allowing for a better fault detection ability. As opposed to this last technique which relies on the ability of the human tester to specify scenarios, we propose an approach based on the sole software specification to automatically generate input sequences which may correspond to fault revealing scenarios.