LUTESS is a test data generator dedicated to synchronous software validation. The tool produces test with respect to an environment description. To check if this description is really as expected, we use mutation analysis. The key point of the approach is to select a subset of mutants which characterizes some kind of "interesting situations" that are supposed to be often produced thanks to environment description. Intuitively, if pre-selected mutants are killed "very often" during tests, environment description is as expected (with respect to these "interesting situations").