We present in this paper a way to produce test suites for the POSIX mini-challenge, based on a formal model of a file system manager, written using a B machine. By this case study, we illustrate the limitations of a fully-automated testing process, which justifies the use of scenarios that complements the classical functional testing approach. Scenarios are expressed through schemas, focusing only on operation chaining. They are played on the model using a symbolic animation engine in order to automatically compute pertinent operation parameter values, based on model coverage criteria such as behavioral or data coverage. We concretize our experimentation by testing the POSIX conformance of two different file systems: a recent Linux distribution, and a customized Java implementation of POSIX used to evaluate the relevance of our approach.