Testing aims to enhance the quality of the software under test. This is achieved through finding and removing errors which, if they were present, would detract from the operational efficiency or accuracy of the product and therefore detract from the product's quality. Black box testing is based on knowledge of the specified functionality of a product, whereas white box testing makes use of knowledge of the program code. Regardless of the testing technique employed, the main objective is to derive a set of test cases that will uncover defects in the code. In this thesis my testing approach focuses on an object-oriented model of a software system. The model is constructed through "reverse engineering" a rigorous description of claimed functionality from the user documentation of the product. The model is represented in the form of objects, attributes and operations. The operations are perceived by the user as being the functionality of the system. My approach uses an object-oriented black box testing technique to exercise the functionality of the model. This is achieved through deriving test cases from the model (which is represented at a different level of abstraction using graph theory notation). The test cases consist of the valid sequences of operations that are allowed, along with the expected output for each such sequence. My objective is to completely exercise the functionality of the model using a minimum set of valid test cases.