Abstract: Software testing plays an important role to assure the quality of software and can be highly effective if performed rigorously. Studies found that testing can benefit from formal specification as it provides precise description of expected software behavior and most importantly, it is in a form that it can be manipulated easily for automation purpose. Grey-box testing approach usually based on knowledge obtains from specification and source code while seldom the design specification is concerned. In this study, an approach was described with an example of circular queue for testing a module with internal memory from its formal specification based on grey-box approach. However, in this research, we proposed a grey-box testing approach that uses the knowledge of design specification instead of source code. We utilized formal specifications that were documented using Parnas’s Module Documentation (MD) method to generate test oracle and to execute the test. The MD provides the information of external and internal view of a module that is useful in our testing approach. Key words: Specification-based testing, grey-box testing, testing tool, test oracle generator