SOFTWARE TESTING, VERIFICATION AND RELIABILITY Softw. Test. Verif. Reliab. (2014) Published online in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/stvr.1542 MuRanker: a mutant ranking tool  Akbar Siami Namin * ,† , Xiaozhen Xue, Omar Rosas and Pankaj Sharma Computer Science Department, Texas Tech University, Lubbock, TX, USA SUMMARY Mutation testing is a fault-based software testing technique in which a large number of mutants are generated in order to assess the adequacy of test cases devised. One of the daunting problems in this area consists in determining whether a mutant can be killed by a test case or it cannot be killed easily because the mutant is semantically equivalent to the original programme. A possible solution, as proposed in this paper, is to measure the complexity of each mutant and prioritize them according to how easy or hard they are to be exposed. As a result, using a proper metric based on the mutants’ complexity, the tester may decide whether to focus on killing easy or hard mutants first. This paper introduces MuRanker, a mutation ranking tool that ranks mutants according to their predicted difficulty and complexity in being detected. The tool uses distance functions to decide the difficulty level of mutants. The computation of the distance function score is based on three representations, namely the control-flow-graph representation, the Jimple representation and the information captured through the code coverage data to differentiate the changes in the original and mutant programs. The tool generates a report that displays mutants in an ordered list based on their complexity. Using this tool, the tester can choose mutants and then devise appropriate test cases with the goal of killing them. The mutation ranking idea and the developed tool allow the software tester to save substantial time and effort on a task that, otherwise, would require the user to manually identify the difficult mutants. To our knowledge, MuRanker is the first mutation tool that proposes ranking mutants to facilitate mutation testing. Copyright © 2014 John Wiley & Sons, Ltd. Received 3 September 2012; Revised 25 May 2014; Accepted 14 June 2014 KEY WORDS: software testing; mutation testing; testing tools; distance functions 1. INTRODUCTION Mutation testing is the process of injecting faults into a programme. The act of inserting faults is referred to as mutating, and the programme obtained by mutating the original programme is known as a mutant. Mutation testing is based on the assumption that a programme is developed by a com- petent programmer [1] and is close to being correct, that is, all of the simple faults have been detected and removed. The competent programmer hypothesis states that a competent programmer may develop an incorrect programme, but the incorrect programme only needs a few simple correc- tions to be correct [2]. Mutation testing simulates the common mistakes programmers make during the software development process [3]. This fault-based testing technique is an iterative process in which developers insert faults into a programme to measure the effectiveness of a set of test cases and their ability to expose syntactic changes that can resemble faults. The test case adequacy is then measured using a mutation score, the ratio of the number of killed mutants over the total number of semantically non-equivalent mutants. *Correspondence to: Akbar Siami Namin, Computer Science Department, Texas Tech University, Lubbock, TX, USA. † E-mail: akbar.namin@ttu.edu ‡ The tool and its tutorial, and a video representing the tool can be downloaded through the tool Web page: http://www.depts.ttu.edu/cs/research/avesta/ Copyright © 2014 John Wiley & Sons, Ltd.