Designing Deletion Mutation Operators

As a test criterion, mutation analysis is known for yielding very effective tests. It is also known for creating many test requirements, each of which is represented by a "mutant" that must be "killed." In recent years, researchers have found that these test requirements have a lot of duplication, in that many test requirements yield the same tests. Put another way, hundreds of mutants can usually be killed by only a few dozen tests. If we could reduce this duplication without reducing mutation's effectiveness, mutation testing could become more cost-effective. One avenue of this research has been to use only one type of mutant, the statement deletion mutation operator. Researchers have found that statement deletion mutation has relatively few mutants, but yields tests that are almost as effective as using all mutants, with the significant benefit that fewer equivalent mutants are generated. This paper extends this idea by asking a simple question: if deleting statements is a cost-effective way to design tests, will deleting other program elements also be effective? This paper presents results from mutation operators that delete variables, operators, and constants, finding that indeed, this is an efficient and effective approach.