Lutess: A testing environment for synchronous software We present Lutess, a tool for testing synchronous reactive software. Lutess provides a formal framework based on the use of the Lustre language. It embodies several testing techniques: random testing with or without operational profiles, specification-based testing and behavioral pattern oriented testing. Section 2 introduces the issue of testing reactive software and presents Lutess from the tester’s viewpoint. Section 3 describes Lutess functional generation methods, while section 4 presents their formal definitions and section 5 gives some aspects about their implementation. Section 6 shortly considers Lutess applicability through its actual experimentation