Marius Liaaen

A practical guide to select quality indicators for assessing pareto-based search algorithms in search-based software engineering

Many software engineering problems are multi-objective in nature, which has been largely recognized by the Search-based Software Engineering (SBSE) community. In this regard, Pareto- based search algorithms, e.g., Non-dominated Sorting Genetic Algorithm II, have already shown good performance for solving multi-objective optimization problems. These algorithms produce Pareto fronts, where each Pareto front consists of a set of non- dominated solutions. Eventually, a user selects one or more of the solutions from a Pareto front for their specific problems. A key challenge of applying Pareto-based search algorithms is to select appropriate quality indicators, e.g., hypervolume, to assess the quality of Pareto fronts. Based on the results of an extended literature review, we found that the current literature and practice in SBSE lacks a practical guide for selecting quality indicators despite a large number of published SBSE works. In this direction, the paper presents a practical guide for the SBSE community to select quality indicators for assessing Pareto-based search algorithms in different software engineering contexts. The practical guide is derived from the following complementary theoretical and empirical methods: 1) key theoretical foundations of quality indicators; 2) evidence from an extended literature review; and 3) evidence collected from an extensive experiment that was conducted to evaluate eight quality indicators from four different categories with six Pareto-based search algorithms using three real industrial problems from two diverse domains.

Multi-objective test prioritization in software product line testing: an industrial case study

Test prioritization is crucial for testing products in a product line considering limited budget in terms of available time and resources. In general, it is not practically feasible to execute all the possible test cases and so, ordering test case execution permits test engineers to discover faults earlier in the testing process. An efficient prioritization of test cases for one or more products requires a clear consideration of the tradeoff among various costs (e.g., time, required resources) and effectiveness (e.g., feature coverage) objectives. As an integral part of the future Ciscos test scheduling system for validating video conferencing products, we introduce a search-based multi-objective test prioritization technique, considering multiple cost and effectiveness measures. In particular, our multi-objective optimization setup includes the minimization of execution cost (e.g., time), and the maximization of number of prioritized test cases, feature pairwise coverage and fault detection capability. Based on cost-effectiveness measures, a novel fitness function is defined for such test prioritization problem. The fitness function is empirically evaluated together with three commonly used search algorithms (e.g., (1+1) Evolutionary algorithm (EA)) and Random Search as a comparison baseline based on the Ciscos industrial case study and 500 artificial designed problems. The results show that (1+1) EA achieves the best performance for solving the test prioritization problem and it scales up to solve the problems of varying complexity.

A systematic test case selection methodology for product lines: results and insights from an industrial case study

In the context of product lines, test case selection aims at obtaining a set of relevant test cases for a product from the entire set of test cases available for a product line. While working on a research-based innovation project on automated testing of product lines of Video Conferencing Systems (VCSs) developed by Cisco, we felt the need to devise a cost-effective way of selecting relevant test cases for a product. To fulfill such need, we propose a systematic and automated test selection methodology using: 1) Feature Model for Testing (FM_T) to capture commonalities and variabilities of a product line; 2) Component Family Model for Testing (CFM_T) to model the structure of test case repository; 3) A tool to automatically build restrictions from CFM_T to FM_T and traces from CFM_T to the actual test cases. Using our methodology, a test engineer is only required to select relevant features through FM_T at a higher level of abstraction for a product and the corresponding test cases will be obtained automatically. We evaluate our methodology by applying it to a VCS product line called Saturn with seven commercial products and the results show that our methodology can significantly reduce cost measured as test selection time and at the same time achieves higher effectiveness (feature coverage, feature pairwise coverage and fault detection) as compared with the current manual process. Moreover, we conduct a questionnaire-based study to solicit the views of test engineers who are involved in developing FM_T and CFM_T. The results show that test engineers are positive about adapting our methodology in their current practice. Finally, we present a set of lessons learnt while applying product line engineering at Cisco for test case selection.

Automated Test Case Selection Using Feature Model: An Industrial Case Study

Automated test case selection for a new product in a product line is challenging due to several reasons. First, the variability within the product line needs to be captured in a systematic way; second, the reusable test cases from the repository are required to be identified for testing a new product. The objective of such automated process is to reduce the overall effort for selection e.g., selection time, while achieving an acceptable level of the coverage of testing functionalities. In this paper, we propose a systematic and automated methodology using a Feature Model for Testing FM_T to capture commonalities and variabilities of a product line and a Component Family Model for Testing CFM_T to capture the overall structure of test cases in the repository. With our methodology, a test engineer does not need to manually go through the repository to select a relevant set of test cases for a new product. Instead, a test engineer only needs to select a set of relevant features using FM_T at a higher level of abstraction for a product and a set of relevant test cases will be selected automatically. We applied our methodology to a product line of video conferencing systems called Saturn developed by Cisco and the results show that our methodology can reduce the selection effort significantly. Moreover, we conducted a questionnaire-based study to solicit the views of test engineers who were involved in developing FM_T and CFM_T. The results show that test engineers are positive about adapting our methodology and models FM_T and CFM_T in their current practice.

Enhancing test case prioritization in an industrial setting with resource awareness and multi-objective search

Test case prioritization is an essential part of test execution systems for large organizations developing software systems in the context that their software versions are released very frequently. They must be tested on a variety of compatible hardware with different configurations to ensure correct functioning of a software version on a compatible hardware. In practice, test case execution must not only execute cost-effective test cases in an optimal order, but also optimally allocate required test resources, in order to deliver high quality software releases. To optimize the current test execution system for testing software releases developed for Videoconferencing Systems (VCSs) at Cisco, Norway, in this paper, we propose a resource- aware multi-objective optimization solution with a fitness function defined based on four cost-effectiveness measures. In this context, a set of software releases must be tested on a set of compatible VCS hardware (test resources) by executing a set of cost-effective test cases in an optimal order within a given test cycle constrained by maximum allowed time budget and maximum available test resources. We empirically evaluated seven search algorithms regarding their performance and scalability by comparing with the current practice (random ordering (RO)). The results show that the proposed solution with the best search algorithm (i.e., Random-Weighted Genetic Algorithm) improved the current practice by reducing on average 40.6% of time for test resource allocation and test case execution, improved test resource usage on average by 37.9% and fault detection on average by 60%.

Automated product line test case selection: industrial case study and controlled experiment

Automated test case selection for a new product in a product line is challenging due to several reasons. First, the variability within the product line needs to be captured in a systematic way; second, the reusable test cases from the repository are required to be identified for testing a new product. The objective of such automated process is to reduce the overall effort for selection (e.g., selection time), while achieving an acceptable level of the coverage of testing functionalities. In this paper, we propose a systematic and automated methodology using a feature model for testing (FM_T) to capture commonalities and variabilities of a product line and a component family model for testing (CFM_T) to capture the overall structure of test cases in the repository. With our methodology, a test engineer does not need to manually go through the repository to select a relevant set of test cases for a new product. Instead, a test engineer only needs to select a set of relevant features using FM_T at a higher level of abstraction for a product and a set of relevant test cases will be selected automatically. We evaluated our methodology via three different ways: (1) We applied our methodology to a product line of video conferencing systems called Saturn developed by Cisco, and the results show that our methodology can reduce the selection effort significantly; (2) we conducted a questionnaire-based study to solicit the views of test engineers who were involved in developing FM_T and CFM_T. The results show that test engineers are positive about adapting our methodology and models (FM_T and CFM_T) in their current practice; (3) we conducted a controlled experiment with 20 graduate students to assess the performance (i.e., cost, effectiveness and efficiency) of our automated methodology as compared to the manual approach. The results showed that our methodology is cost-effective as compared to the manual approach, and at the same time, its efficiency is not affected by the increased complexity of products.

UPMOA: An improved search algorithm to support user-preference multi-objective optimization

Multi-objective search algorithms (e.g., non-dominated sorting genetic algorithm II (NSGA-II)) have been applied extensively to solve various multi-objective optimization problems in software engineering such as problems in testing. However, existing multi-objective algorithms usually treat all the objectives with equivalent priorities and do not provide a mechanism to reflect various user preferences when guiding search. The need to have such a mechanism was observed in one of our industrial projects on applying search algorithms for test optimization of a product line of Videoconferencing Systems (VCSs) called Saturn, where user preferences must be incorporated into optimization objectives, based on domain knowledge of test engineers for VCS testing. To address this, we propose an extension to the most commonly-used multi-objective search algorithm NSGA-II, which has shown promising results with user preferences. We name the extension as User-Preference Multi-Objective Optimization Algorithm (UPMOA), which includes a user preference indicator p and is based on existing weight assignment strategies. We empirically evaluated UPMOA with two industrial problems focusing on optimizing the test execution system for Saturn in Cisco. To assess the performance and scalability of UPMOA, inspired by the two industrial problems, in total we created 64000 artificial problems with 128 different sets of user preferences. The evaluation includes two aspects: 1) Three weight assignment strategies together with UPMOA were empirically evaluated to identify a best weight assignment strategy for p. Results show that the Uniformly Distributed Weights (UDW) strategy can assist UPMOA in achieving the best performance; 2) UPMOA was compared with three representative multi-objective search algorithms (including NSGA-II) and results show that UPMOA significantly outperformed the others and has the ability to solve problems with a wide range of complexity.

STIPI: Using Search to Prioritize Test Cases Based on Multi-objectives Derived from Industrial Practice

The importance of cost-effectively prioritizing test cases is undeniable in automated testing practice in industry. This paper focuses on prioritizing test cases developed to test product lines of Video Conferencing Systems (VCSs) at Cisco Systems, Norway. Each test case requires setting up configurations of a set of VCSs, invoking a set of test APIs with specific inputs, and checking statuses of the VCSs under test. Based on these characteristics and available information related with test case execution (e.g., number of faults detected), we identified that the test case prioritization problem in our particular context should focus on achieving high coverage of configurations, test APIs, statuses, and high fault detection capability as quickly as possible. To solve this problem, we propose a search-based test case prioritization approach (named STIPI) by defining a fitness function with four objectives and integrating it with a widely applied multi-objective optimization algorithm (named Non-dominated Sorting Genetic Algorithm II). We compared STIPI with random search (RS), Greedy algorithm, and three approaches adapted from literature, using three real sets of test cases from Cisco with four time budgets (25 %, 50 %, 75 % and 100 %). Results show that STIPI significantly outperformed the selected approaches and managed to achieve better performance than RS for on average 39.9 %, 18.6 %, 32.7 % and 43.9 % for the coverage of configurations, test APIs, statuses and fault detection capability, respectively.

Exploring Model-Based Repositories for a Broad Range of Industrial Applications and Challenges

Nowadays, systems are becoming increasingly complex and large and the process of developing such large-scale systems is becoming complicated with high cost and enormous effort required. Such a complicated process has a prominent challenge to ensure the quality of delivered artifacts. Therefore there is clearly a need to facilitate reuse of developed artifacts (e.g., requirements, architecture, tests) and enable automated analyses such as risk analyses, prioritizing test cases, change impact analysis, with the objective to reduce cost, effort and improve quality. Model-based engineering provides a promising mechanism to facilitate reuse and enable automation. The key idea is to use models as the backbone of structuring repositories that contain reusable artifacts (e.g., test cases, requirements). Such a backbone model is subse-quently used to enable various types of automation such as model-based testing and automated rule verification. In this paper, we report 12 industrial projects from five different industry domains that all require the construction of model-based repositories to enable various types of automation. We believe using models as the backbone to structure repositories for the purpose of enabling different types of automation in different contexts is a new and non-conventional model-based development research approach. This exploratory paper will serve the basis for future research to derive a generic model-based repository.

CBGA-ES: A Cluster-Based Genetic Algorithm with Elitist Selection for Supporting Multi-Objective Test Optimization

Multi-objective search algorithms (e.g., non-dominated sorting genetic algorithm II (NSGA-II)) have been frequently applied to address various testing problems requiring multi-objective optimization such as test case selection. However, existing multi-objective search algorithms have certain randomness when selecting parent solutions for producing offspring solutions. In the worse case, suboptimal parent solutions may result in offspring solutions with bad quality, and thus affect the overall quality of the next generation. To address such a challenge, we propose a cluster-based genetic algorithm with elitist selection (CBGA-ES) with the aim to reduce such randomness for supporting multi-objective test optimization. We empirically compared CBGA-ES with random search, greedy (as baselines) and four commonly used multi-objective search algorithms (e.g., NSGA-II) using two industrial and one real world test optimization problem, i.e., test suite minimization, test case prioritization, and test case selection. The results showed that CBGA-ES significantly outperformed the baseline algorithms (e.g., greedy), and the four selected search algorithms for all the three test optimization problems. CBGA-ES managed to outperform more than 75% of the objectives for all the four algorithms in each test optimization problem. Moreover, CBGA-ES was able to improve the quality of the solutions for an average of 32.5% for each objective as compared to the four algorithms for the three test optimization problems.