Dario Di Nucci

Software-based energy profiling of Android apps: Simple, efficient and reliable?

Modeling the power profile of mobile applications is a crucial activity to identify the causes behind energy leaks. To this aim, researchers have proposed hardware-based tools as well as model-based and software-based techniques to approximate the actual energy profile. However, all these solutions present their own advantages and disadvantages. Hardware-based tools are highly precise, but at the same time their use is bound to the acquisition of costly hardware components. Model-based tools require the calibration of parameters needed to correctly create a model on a specific hardware device. Software-based approaches do not need any hardware components, but they rely on battery measurements and, thus, they are hardware-assisted. These tools are cheaper and easier to use than hardware-based tools, but they are believed to be less precise. In this paper, we take a deeper look at the pros and cons of software-based solutions investigating to what extent their measurements depart from hardware-based solutions. To this aim, we propose a software-based tool named PETRA that we compare with the hardware-based MONSOON toolkit on 54 Android apps. The results show that PETRA performs similarly to MONSOON despite not using any sophisticated hardware components. In fact, in all the apps the mean relative error with respect to MONSOON is lower than 0.05. Moreover, for 95% of the analyzed methods the estimation error is within 5% of the actual values measured using the hardware-based toolkit.

A Developer Centered Bug Prediction Model

Several techniques have been proposed to accurately predict software defects. These techniques generally exploit characteristics of the code artefacts (e.g., size, complexity, etc.) and/or of the process adopted during their development and maintenance (e.g., the number of developers working on a component) to spot out components likely containing bugs. While these bug prediction models achieve good levels of accuracy, they mostly ignore the major role played by human-related factors in the introduction of bugs. Previous studies have demonstrated that focused developers are less prone to introduce defects than non-focused developers. According to this observation, software components changed by focused developers should also be less error prone than components changed by less focused developers. We capture this observation by measuring the scattering of changes performed by developers working on a component and use this information to build a bug prediction model. Such a model has been evaluated on 26 systems and compared with four competitive techniques. The achieved results show the superiority of our model, and its high complementarity with respect to predictors commonly used in the literature. Based on this result, we also show the results of a “hybrid” prediction model combining our predictors with the existing ones.

Landfill: an open dataset of code smells with public evaluation

Code smells are symptoms of poor design and implementation choices that may hinder code comprehension and possibly increase change- and fault-proneness of source code. Several techniques have been proposed in the literature for detecting code smells. These techniques are generally evaluated by comparing their accuracy on a set of detected candidate code smells against a manually-produced oracle. Unfortunately, such comprehensive sets of annotated code smells are not available in the literature with only few exceptions. In this paper we contribute (i) a dataset of 243 instances of five types of code smells identified from 20 open source software projects, (ii) a systematic procedure for validating code smell datasets, (iii) LANDFILL, a Web-based platform for sharing code smell datasets, and (iv) a set of APIs for programmatically accessing LANDFILLs contents. Anyone can contribute to Landfill by (i) improving existing datasets (e.g., Adding missing instances of code smells, flagging possibly incorrectly classified instances), and (ii) sharing and posting new datasets. Landfill is available at www.sesa.unisa.it/landfill/, while the video demonstrating its features in action is available at http://www.sesa.unisa.it/tools/landfill.jsp.

On the diffusion of test smells in automatically generated test code: an empirical study

The role of software testing in the software development process is widely recognized as a key activity for successful projects. This is the reason why in the last decade several automatic unit test generation tools have been proposed, focusing particularly on high code coverage. Despite the effort spent by the research community, there is still a lack of empirical investigation aimed at analyzing the characteristics of the produced test code. Indeed, while some studies inspected the effectiveness and the usability of these tools in practice, it is still unknown whether test code is maintainable. In this paper, we conducted a large scale empirical study in order to analyze the diffusion of bad design solutions, namely test smells, in automatically generated unit test classes. Results of the study show the high diffusion of test smells as well as the frequent co-occurrence of different types of design problems. Finally we found that all test smells have strong positive correlation with structural characteristics of the systems such as size or number of classes.

On the role of developer's scattered changes in bug prediction

The importance of human-related factors in the introduction of bugs has recently been the subject of a number of empirical studies. However, such factors have not been captured yet in bug prediction models which simply exploit product metrics or process metrics based on the number and type of changes or on the number of developers working on a software component. Previous studies have demonstrated that focused developers are less prone to introduce defects than non focused developers. According to this observation, software components changed by focused developers should also be less error prone than software components changed by less focused developers. In this paper we capture this observation by measuring the structural and semantic scattering of changes performed by the developers working on a software component and use these two measures to build a bug prediction model. Such a model has been evaluated on five open source systems and compared with two competitive prediction models: the first exploits the number of developers working on a code component in a given time period as predictor, while the second is based on the concept of code change entropy. The achieved results show the superiority of our model with respect to the two competitive approaches, and the complementarity of the defined scattering measures with respect to standard predictors commonly used in the literature.

Dynamic Selection of Classifiers in Bug Prediction: An Adaptive Method

In the last decades, the research community has devoted a lot of effort in the definition of approaches able to predict the defect proneness of source code files. Such approaches exploit several predictors (e.g., product or process metrics) and use machine learning classifiers to predict classes into buggy or not buggy, or provide the likelihood that a class will exhibit a fault in the near future. The empirical evaluation of all these approaches indicated that there is no machine learning classifier providing the best accuracy in any context, highlighting interesting complementarity among them. For these reasons ensemble methods have been proposed to estimate the bug-proneness of a class by combining the predictions of different classifiers. Following this line of research, in this paper we propose an adaptive method, named ASCI (Adaptive Selection of Classifiers in bug prediction), able to dynamically select among a set of machine learning classifiers the one which better predicts the bug-proneness of a class based on its characteristics. An empirical study conducted on 30 software systems indicates that ASCI exhibits higher performances than five different classifiers used independently and combined with the majority voting ensemble method.

Search-Based Testing of Procedural Programs: Iterative Single-Target or Multi-target Approach?

In the context of testing of Object-Oriented (OO) software systems, researchers have recently proposed search based approaches to automatically generate whole test suites by considering simultaneously all targets (e.g., branches) defined by the coverage criterion (multi-target approach). The goal of whole suite approaches is to overcome the problem of wasting search budget that iterative single-target approaches (which iteratively generate test cases for each target) can encounter in case of infeasible targets. However, whole suite approaches have not been implemented and experimented in the context of procedural programs. In this paper we present OCELOT (Optimal Coverage sEarch-based tooL for sOftware Testing), a test data generation tool for C programs which implements both a state-of-the-art whole suite approach and an iterative single-target approach designed for a parsimonious use of the search budget. We also present an empirical study conducted on 35 open-source C programs to compare the two approaches implemented in OCELOT. The results indicate that the iterative single-target approach provides a higher efficiency while achieving the same or an even higher level of coverage than the whole suite approach.

PETrA: a software-based tool for estimating the energy profile of Android applications

Energy efficiency is a vital characteristic of any mobile application, and indeed is becoming an important factor for user satisfaction. For this reason, in recent years several approaches and tools for measuring the energy consumption of mobile devices have been proposed. Hardware-based solutions are highly precise, but at the same time they require costly hardware toolkits. Model-based techniques require a possibly difficult calibration of the parameters needed to correctly create a model on a specific hardware device. Finally, software-based solutions are easier to use, but they are possibly less precise than hardware-based solution. In this demo, we present PETrA, a novel software-based tool for measuring the energy consumption of Android apps. With respect to other tools, PETrA is compatible with all the smartphones with Android 5.0 or higher, not requiring any device specific energy profile. We also provide evidence that our tool is able to perform similarly to hardware-based solutions.

Hypervolume-Based Search for Test Case Prioritization

Test case prioritization (TCP) is aimed at finding an ideal ordering for executing the available test cases to reveal faults earlier. To solve this problem greedy algorithms and meta-heuristics have been widely investigated, but in most cases there is no statistically significant difference between them in terms of effectiveness. The fitness function used to guide meta-heuristics condenses the cumulative coverage scores achieved by a test case ordering using the Area Under Curve (AUC) metric. In this paper we notice that the AUC metric represents a simplified version of the hypervolume metric used in many objective optimization and we propose HGA, a Hypervolume-based Genetic Algorithm, to solve the TCP problem when using multiple test criteria. The results shows that HGA is more cost-effective than the additional greedy algorithm on large systems and on average requires 36 % of the execution time required by the additional greedy algorithm.

Lightweight detection of Android-specific code smells: The aDoctor project

Code smells are symptoms of poor design solutions applied by programmers during the development of software systems. While the research community devoted a lot of effort to studying and devising approaches for detecting the traditional code smells defined by Fowler, little knowledge and support is available for an emerging category of Mobile app code smells. Recently, Reimann et al. proposed a new catalogue of Android-specific code smells that may be a threat for the maintainability and the efficiency of Android applications. However, current tools working in the context of Mobile apps provide limited support and, more importantly, are not available for developers interested in monitoring the quality of their apps. To overcome these limitations, we propose a fully automated tool, coined ADOCTOR, able to identify 15 Android-specific code smells from the catalogue by Reimann et al. An empirical study conducted on the source code of 18 Android applications reveals that the proposed tool reaches, on average, 98% of precision and 98% of recall. We made ADOCTOR publicly available.