Using mock object frameworks to teach object-oriented design principles

A well-designed reusable object-oriented software system adheres to two key object-oriented design principles -- i) program to an interface, not an implementation, and ii) favor object composition over class inheritance. Furthermore, the effect of unit testing (especially in the context of test-first or test-driven development) on quality of the resulting object-oriented software is undeniable. Teaching good object-oriented design principles in upper-level undergraduate courses in an effective way is challenging. We believe the use of mock object frameworks can help in teaching these object-oriented design principles in a pragmatic and hands-on manner. Using mock objects and mock object frameworks requires students to not only learn and understand the principles of good object-oriented design, but actively apply them in developing reusable object-oriented designs. This paper describes these broad object-oriented design principles and how to use mock object frameworks to teach object-oriented software design that is based on these principles.