Handling Test Length Bloat

The length of test cases is a little investigated topic in search-based test generation for object-oriented software, where test cases are sequences of method calls. While intuitively longer tests can achieve higher overall code coverage, there is always the threat of \emph{bloat} -- a complex phenomenon in evolutionary computation, where the length abnormally grows over time. In this paper, we show that bloat indeed also occurs in the context of test generation for object-oriented software. We present different techniques to overcome the problem of length bloat, and evaluate all possible combinations of these techniques using different search lengths. Experiments on a set of difficult search targets selected from several open source and industrial projects show that controlling bloat in the right way can significantly improve the search performance.