Bytecode Testability Transformation

Abstract

Bytecode as produced by modern programming languages is well suited for search-based testing: Different languages compile to the same bytecode, bytecode is available also for third party libraries, all predicates are atomic and side-effect free, and instrumentation can be performed without recompilation. However, bytecode is also susceptible to the flag problem; in fact, regular source code statements such as floating point operations might create unexpected flag problems on the bytecode level. We present an implementation of state-of-the-art testability transformation for Java bytecode, such that all Boolean values are replaced by integers that preserve information about branch distances, even across method boundaries. The transformation preserves both the original semantics and structure, allowing it to be transparently plugged into any bytecode-based testing tool. Experiments on flag problem benchmarks show the effectiveness of the transformation, while experiments on open source libraries show that although this type of problem can be handled efficiently it is less frequent than expected.