Seite - 156 - in The Future of Software Quality Assurance

156 A. L.Smith I askedMarkushowheoptimizesmutation testing to reduceequivalentmutants, andhe disagreedwith themetric: This cannot be answered as is, the reality is more difficult. The question implies that equivalent mutations are a real world problem, but they are not. The question also implies the toolproducesmutationsof“lowinformationalvalue”andnoteverymutationthatcomes back alive contains value for the human who reads a report. Both assumptions are false in my world. Equivalent mutants almost never show up, and lowvalue mutationsdo notexist, hence everything must be killed.—Markus Schirp To understandwhatMarkusmeant, let’s lookat anequivalentmutation: Pseudo Code def foo(i): return i + 1 + 0 An example of a potentially equivalent mutant would be to remove the “+ 0”. While thiswouldchangethesoftwareunder testing, it doesn’tchangetheoutput,as adding zero to a number has no actual effect anyway. That is exactly the point, the code is irrelevantandshouldbe removed. 5 Mutation TestingTools Mutation testing tools are numerous in nature, this is in part, because they are intrinsically linked with the programming languages used in the implementation. Youcan’tgenerallyusea tooldesignedforC++withJava. It is crucial topicka tool thatsupports theunderlyingtechnologystack,hassupport toallowyoutoconfigure the mutation heuristics you want, integrates with your development environment well, and supports parallel and distributed execution.Wikipedia [8] has a good list ofmutationenginesthatyoucanusewithyourcode.Gettingstartedwiththesetools canbeas simpleas injectinga dependencyintoyourbuildconfiguration. Selecting and evaluating tools that suit you is actuallymore important than with traditionaltoolselection.Onereasonisthat thetoolswillcomewithdifferentdefault operators and strategies built in. As outlined earlier, these operators and strategies effectively dictate the technical approach and directly affect the results. The tool also may determinehow you can scale the run-timeexecution, and choosing a tool with such limitedsupportmayresult in impractical execution timelines. Tools and libraries also exist for mutating data structures rather than code, for instance,applyingheuristicoperatorsagainststandarddatastructuressuchasXML.