BPEL (Business Process Execution Language) is an emerging standard language to describe web service composition behaviour. The advanced features of BPEL such as concurrency and hierarchy make it challenging to verify BPEL models. Previously, we proposed WSA (web service automata) to be the formal models for BPEL. Based on WSA, this paper presents a model checking based test case generation framework for BPEL. We apply SPIN and NuSMV model checkers as the test generation engine, and we encode the conventional structural test coverage criteria into LTL and CTL temporal logic. State coverage and transition coverage are used for BPEL control flow testing, and all-du-path coverage is used for BPEL data flow testing. Two levels of test cases can be generated to test whether the implementation of web services conforms to the BPEL behaviour and WSDL interface models. The generated test cases are executed on the JUnit test execution engine.