The Stream X-machine (SXM) is a form of extended finite state machine that describes a system as a finite set of states, an internal memory and a number of transitions between the states. One of the strengths of using a SXM to specify a system is that, under certain well defined conditions, it is possible to produce a test suite that is guaranteed to determine the correctness of the implementation under test. This paper shows how SXM based testing techniques can be applied to generate test suites at class level from state diagrams. Furthermore, a technique for constructing test suites for a hierarchical SXM without flattening the diagram, by reusing the test suites for the components, is given.