Syntax Is All You Need: A Universal-Language Approach to Mutant Generation

While mutation testing has been a topic of academic interest for decades, it is only recently that “real-world” developers, including industry leaders such as Google and Meta, have adopted mutation testing. We propose a new approach to the development of mutation testing tools, and in particular the core challenge of generating mutants . Current practice tends towards two limited approaches to mutation generation: mutants are either (1) generated at the bytecode/IR level, and thus neither human readable nor adaptable to source-level features of languages or projects, or (2) generated at the source level by language-specific tools that are hard to write and maintain, and in fact are often abandoned by both developers and users. We propose instead that source-level mutation generation is a special case of program transformation in general, and that adopting this approach allows for a single tool that can effectively generate source-level mutants for essentially any programming language. Furthermore, by using parser parser combinators many of the seeming limitations of an any-language approach can be overcome, without the need to parse specific languages. We compare this new approach to mutation to existing tools, and demonstrate the advantages of using parser parser combinators to improve on a regular-expression based approach to generation. Finally, we show that our approach can provide effective mutant generation even for a language for which it lacks any language-specific operators, and that is not very similar in syntax to any language it has been applied to previously.