Mutant-Kraken: A Mutation Testing Tool for Kotlin

Kotlin, a Java Virtual Machine (JVM) based language, offers modern features, such as concise syntax and enhanced null safety, and was adopted by Google as the preferred language for Android development. Despite the rise in popularity, there is a notable absence of comprehensive mutation testing tools for Kotlin developers. The lack of specialized mutation operators and developer-friendly tools for Kotlin poses challenges to developers and testers, impacting the overall reliability and quality of Kotlin codebases. This paper aims to fill this gap by introducing Kotlin-specific mutation operators and a flexible, open-source, developer-friendly tool, Mutant-Kraken. Mutant-Kraken leverages traditional mutation testing concepts while tailoring new mutation operators based on Kotlin’s unique programming features. The tool’s four-phase process includes gathering files, generating mutants, building and testing, and producing HTML-based analysis results. The approach emphasizes configurability, enabling developers to customize settings such as ignored files, timeout, and mutation operators, making it adaptable to diverse Kotlin projects. Mutant-Kraken includes seven, novel Kotlin-specific mutation operators, addressing features like null checks and functional programming. In an experimental study on three open-source Kotlin projects, Mutant-Kraken has been evaluated to be feasible, efficient, and effective.