Hadi Hemmati

Assisting developers of big data analytics applications when deploying on hadoop clouds

Big data analytics is the process of examining large amounts of data (big data) in an effort to uncover hidden patterns or unknown correlations. Big Data Analytics Applications (BDA Apps) are a new type of software applications, which analyze big data using massive parallel processing frameworks (e.g., Hadoop). Developers of such applications typically develop them using a small sample of data in a pseudo-cloud environment. Afterwards, they deploy the applications in a large-scale cloud environment with considerably more processing power and larger input data (reminiscent of the mainframe days). Working with BDA App developers in industry over the past three years, we noticed that the runtime analysis and debugging of such applications in the deployment phase cannot be easily addressed by traditional monitoring and debugging approaches. In this paper, as a first step in assisting developers of BDA Apps for cloud deployments, we propose a lightweight approach for uncovering differences between pseudo and large-scale cloud deployments. Our approach makes use of the readily-available yet rarely used execution logs from these platforms. Our approach abstracts the execution logs, recovers the execution sequences, and compares the sequences between the pseudo and cloud deployments. Through a case study on three representative Hadoop-based BDA Apps, we show that our approach can rapidly direct the attention of BDA App developers to the major differences between the two deployments. Knowledge of such differences is essential in verifying BDA Apps when analyzing big data in the cloud. Using injected deployment faults, we show that our approach not only significantly reduces the deployment verification effort, but also provides very few false positives when identifying deployment failures.

Static test case prioritization using topic models

Software development teams use test suites to test changes to their source code. In many situations, the test suites are so large that executing every test for every source code change is infeasible, due to time and resource constraints. Development teams need to prioritize their test suite so that as many distinct faults as possible are detected early in the execution of the test suite. We consider the problem of static black-box test case prioritization (TCP), where test suites are prioritized without the availability of the source code of the system under test (SUT). We propose a new static black-box TCP technique that represents test cases using a previously unused data source in the test suite: the linguistic data of the test cases, i.e., their identifier names, comments, and string literals. Our technique applies a text analysis algorithm called topic modeling to the linguistic data to approximate the functionality of each test case, allowing our technique to give high priority to test cases that test different functionalities of the SUT. We compare our proposed technique with existing static black-box TCP techniques in a case study of multiple real-world open source systems: several versions of Apache Ant and Apache Derby. We find that our static black-box TCP technique outperforms existing static black-box TCP techniques, and has comparable or better performance than two existing execution-based TCP techniques. Static black-box TCP methods are widely applicable because the only input they require is the source code of the test cases themselves. This contrasts with other TCP techniques which require access to the SUT runtime behavior, to the SUT specification models, or to the SUT source code.

Automatic detection of performance deviations in the load testing of large scale systems

Load testing is one of the means for evaluating the performance of Large Scale Systems (LSS). At the end of a load test, performance analysts must analyze thousands of performance counters from hundreds of machines under test. These performance counters are measures of run-time system properties such as CPU utilization, Disk I/O, memory consumption, and network traffic. Analysts observe counters to find out if the system is meeting its Service Level Agreements (SLAs). In this paper, we present and evaluate one supervised and three unsupervised approaches to help performance analysts to 1) more effectively compare load tests in order to detect performance deviations which may lead to SLA violations, and 2) to provide them with a smaller and manageable set of important performance counters to assist in root-cause analysis of the detected deviations. Our case study is based on load test data obtained from both a large scale industrial system and an open source benchmark application. The case study shows, that our wrapper-based supervised approach, which uses a search-based technique to find the best subset of performance counters and a logistic regression model for deviation prediction, can provide up to 89% reduction in the set of performance counters while detecting performance deviations with few false positives (i.e., 95% average precision). The study also shows that the supervised approach is more stable and effective than the unsupervised approaches but it has more overhead due to its semi-automated training phase.

The MSR Cookbook: Mining a decade of research

The Mining Software Repositories (MSR) research community has grown significantly since the first MSR workshop was held in 2004. As the community continues to broaden its scope and deepens its expertise, it is worthwhile to reflect on the best practices that our community has developed over the past decade of research. We identify these best practices by surveying past MSR conferences and workshops. To that end, we review all 117 full papers published in the MSR proceedings between 2004 and 2012. We extract 268 comments from these papers, and categorize them using a grounded theory methodology. From this evaluation, four high-level themes were identified: data acquisition and preparation, synthesis, analysis, and sharing/replication. Within each theme we identify several common recommendations, and also examine how these recommendations have evolved over the past decade. In an effort to make this survey a living artifact, we also provide a public forum that contains the extracted recommendations in the hopes that the MSR community can engage in a continuing discussion on our evolving best practices.

Prioritizing Manual Test Cases in Traditional and Rapid Release Environments

Test case prioritization is one of the most practically useful activities in testing, specially for large scale systems. The goal is ranking the existing test cases in a way that they detect faults as soon as possible, so that any partial execution of the test suite detects maximum number of defects for the given budget. Test prioritization becomes even more important when the test execution is time consuming, e.g., manual system tests vs. automated unit tests. Most existing test case prioritization techniques are based on code coverage, which requires access to source code. However, manual testing is mainly done in a black- box manner (manual testers do not have access to the source code). Therefore, in this paper, we first examine the existing test case prioritization techniques and modify them to be applicable on manual black-box system testing. We specifically study a coverage- based, a diversity-based, and a risk driven approach for test case prioritization. Our empirical study on four older releases of Mozilla Firefox shows that none of the techniques are strongly dominating the others in all releases. However, when we study nine more recent releases of Firefox, where the development has been moved from a traditional to a more agile and rapid release environment, we see a very signifiant difference (on average 65% effectiveness improvement) between the risk-driven approach and its alternatives. Our conclusion, based on one case study of 13 releases of an industrial system, is that test suites in rapid release environments, potentially, can be very effectively prioritized for execution, based on their historical riskiness; whereas the same conclusions do not hold in the traditional software development environments.

A similarity-based approach for test case prioritization using historical failure data

Test case prioritization is a crucial element in software quality assurance in practice, specially, in the context of regression testing. Typically, test cases are prioritized in a way that they detect the potential faults earlier. The effectiveness of test cases, in terms of fault detection, is estimated using quality metrics, such as code coverage, size, and historical fault detection. Prior studies have shown that previously failing test cases are highly likely to fail again in the next releases, therefore, they are highly ranked, while prioritizing. However, in practice, a failing test case may not be exactly the same as a previously failed test case, but quite similar, e.g., when the new failing test is a slightly modified version of an old failing one to catch an undetected fault. In this paper, we define a class of metrics that estimate the test cases quality using their similarity to the previously failing test cases. We have conducted several experiments with five real world open source software systems, with real faults, to evaluate the effectiveness of these quality metrics. The results of our study show that our proposed similarity-based quality measure is significantly more effective for prioritizing test cases compared to existing test case quality measures.

Test case analytics: Mining test case traces to improve risk-driven testing

In risk-driven testing, test cases are generated and/or prioritized based on different risk measures. For example, the most basic risk measure would analyze the history of the software and assigns higher risk to the test cases that used to detect bugs in the past. However, in practice, a test case may not be exactly the same as a previously failed test, but quite similar. In this study, we define a new risk measure that assigns a risk factor to a test case, if it is similar to a failing test case from history. The similarity is defined based on the execution traces of the test cases, where we define each test case as a sequence of method calls. We have evaluated our new risk measure by comparing it to a traditional risk measure (where the risk measure would be increased only if the very same test case, not a similar one, failed in the past). The results of our study, in the context of test case prioritization, on two open source projects show that our new risk measure is by far more effective in identifying failing test cases compared to the traditional risk measure.

Model-Based Testing of Video Conferencing Systems: Challenges, Lessons Learnt, and Results

Model-Based Testing (MBT) is a well-established and intense field of research in academia. It has attracted attention of many industries as it can be seen from many industrial experiences of MBT reported in the literature and availability of commercial and open source tools in recent years. The thorough and methodical approach of MBT facilitates automated testing with the intention of improving the quality of software systems. Every industrial application of MBT faces varied challenges depending on the application domain, the current testing practices and tools, and the type of testing. Reporting such challenges, their solutions, and lessons learnt provides a body of knowledge, which can direct practitioners of MBT for their future applications of MBT. With such aim in our mind, we present results from an MBT project that is being carried out for testing embedded video conferencing systems developed by Cisco Systems, Inc. Norway for the last several years. We present challenges faced while conducting MBT, our solutions, some of the key results, and lessons learnt from our experience. Our experience showed that search algorithms provide an efficient solution for test case selection and test data generation. In addition, aspect-oriented modeling provides a scalable modeling solution for non-functional testing. Finally, we learned that model transformation offers an elegant solution for developing a model-based test case generation tool. All of our results are based on a large number of rigorous empirical evaluations.

Storm prediction in a cloud

Predicting future behavior reliably and efficiently is key for systems that manage virtual services; such systems must be able to balance loads within a cloud environment to ensure that service level agreements are met at a reasonable expense. In principle accurate predictions can be achieved by mining a variety of data sources, which describe the historic behavior of the services, the requirements of the programs running on them, and the evolving demands placed on the cloud by end users. Of particular importance is accurate prediction of maximal loads likely to be observed in the short term. However, standard approaches to modeling system behavior, by analyzing the totality of the observed data, tend to predict average rather than exceptional system behavior and ignore important patterns of change over time. In this paper, we study the ability of a simple multivariate linear regression for forecasting of peak CPU utilization (storms) in an industrial cloud environment. We also propose several modifications to the standard linear regression to adjust it for storm prediction.

Prioritizing manual test cases in rapid release environments

Test case prioritization is an important testing activity, in practice, specially for large scale systems. The goal is to rank the existing test cases in a way that they detect faults as soon as possible, so that any partial execution of the test suite detects the maximum number of defects for the given budget. Test prioritization becomes even more important when the test execution is time consuming, for example, manual system tests versus automated unit tests. Most existing test case prioritization techniques are based on code coverage, which requires access to source code. However, manual testing is mainly performed in a black‐box manner (manual testers do not have access to the source code). Therefore, in this paper, the existing test case prioritization techniques (e.g. diversity‐based and history‐based techniques) are examined and modified to be applicable on manual black‐box system testing. An empirical study on four older releases of desktop Firefox showed that none of the techniques were strongly dominating the others in all releases. However, when nine more recent releases of desktop Firefox, where the development has been moved from a traditional to a more agile and rapid release environment, were studied, a very significant difference between the history‐based approach and its alternatives was observed. The higher effectiveness of the history‐based approach compared with alternatives also held on 28 additional rapid releases of other Firefox projects – mobile Firefox and tablet Firefox. The conclusion of the paper is that test cases in rapid release environments can be very effectively prioritized for execution, based on their historical failure knowledge. In particular, it is the recency of historical knowledge that explains its effectiveness in rapid release environments rather than other changes in the process. Copyright