Moving program code that implements cross-cutting concerns into aspects can improve the maintainability of legacy systems. This kind of refactoring, called aspectualization, can also introduce faults into a system. A test driven approach can identify these faults during the refactoring process so that they can be removed. We perform systematic testing as we aspectualize commercial VLSI CAD applications. The process of refactoring these applications revealed the kinds of faults that can arise during aspectualization, and helped us to develop techniques to reduce their occurrences. Keywords: Aspect-oriented programming, refactoring, legacy systems, test driven development, regression testing, mock system, test coverage 1.

Aspect-based refactoring, called aspectualization, involves moving program code that implements cross-cutting concerns into aspects. Such refactoring can improve the maintainability of legacy systems. Long compilation and weave times, and the lack of an appropriate testing methodology are two challenges to the aspectualization of large legacy systems. We propose an iterative test driven approach for creating and introducing aspects. The approach uses mock systems that enable aspect developers to quickly experiment with different pointcuts and advice, and reduce the compile and weave times. The approach also uses weave analysis, regression testing, and code coverage analysis to test the aspects. We developed several tools for unit and integration testing. We demonstrate the test driven approach in the context of large industrial C++ systems, and we provide guidelines for mock system creation. Key words: mock systems, aspect oriented programming, legacy systems, refactoring, testing 1

The primary claimed benefits of aspect-oriented programming (AOP) are that it improves the understandability and maintainability of software applications by modularizing cross-cutting concerns. Before there is widespread adoption of AOP, developers need further evidence of the actual benefits as well as costs. Applying AOP techniques to refactor legacy applications is one way to evaluate costs and benefits. Aspect-based refactoring, called aspectualization, involves moving program code that implements cross-cutting concerns into aspects. Such refactoring can potentially improve the maintainability of legacy systems. Long compilation and weave times, and the lack of an appropriate testing methodology are two challenges to the aspectualization of large legacy systems. We propose an iterative test driven approach for creating and introducing aspects. The approach uses mock systems that enable aspect developers to quickly experiment with different pointcuts and advice, and reduce the compile and weave times. The approach also uses weave analysis, regression testing, and code coverage analysis to test the aspects. We developed several tools for unit