Type Sensitive Application of Mutation Operators for Dynamically Typed Programs

It is commonly accepted that strong typing is useful for revealing programmer errors and so the use of dynamically typed languages increases the importance of software testing. Mutation analysis is a demanding software testing criterion. Although mutation analysis has been applied to procedural languages, and object oriented languages, little work has been done on the mutation analysis of programs written in dynamically typed languages. Mutation analysis depends on the substitution and modification of program elements. In a strongly typed language, the declared type of the mutated element, a variable or operator, can be used to avoid generating type-incorrect substitutions or modifications. In a dynamically typed language, this type information is not available and so a much greater range of mutations are potentially applicable but many of the resulting mutants are likely to be incompetent (too easily killed). This paper describes a mutation analysis method in which the definition of mutants is performed at run-time when type information is available. The type information can be used to avoid generating incompetent mutants.