Due to increasing importance of test cases in software development, there is a need to verify and assure their quality. Mutation testing is an effective technique of checking if tests react properly to changes by introducing alterations to the original source code. A mutant which survives all test cases indicates insufficient or inappropriate testing assertions. The most onerous disadvantage of this technique is considerable time required to generate, compile mutants and then execute test cases against each of them. In the paper we propose an aspect-oriented approach to generation and execution of mutants, called response injection, which excludes the need for separate compilation of every mutant.

Along with growing popularity of agile methodologies and open source movement, unit testing has become one of the core practices in modern software engineering. It is particularly important in eXtreme Programming [1], which explicitly diminish the importance of other artifacts than source code and tests cases. In XP unit test cases not only verify if software meets functional requirements, but also enable refactoring, alleviate comprehension and provide guidance on how the production code should be used. Therefore, they contribute to many other important practices of XP, which explicitly or implicitly rely on their ability to effectively discover bugs.