Sasikumar Punnekkat

Feasibility analysis of fault-tolerant real-time task sets

Many safety critical real-time systems, employ fault tolerant strategies in order to provide predictable performance in the presence of failures. One technique commonly employed is time redundancy using retry/re-execution of tasks. This can in turn affect the correctness of the system by causing deadlines to be missed. This paper provides exact schedulability tests for fault tolerant task sets under specified failure hypothesis.

Analysis of Checkpointing for Real-Time Systems

Predictable performance in the event of failuresis of paramount importance in most safety critical real-timesystems. Various hardware as well as software fault-toleranttechniques are employed towards this goal among which checkpointingis a relatively cost-effective scheme. Since checkpointing schemesdepend on time redundancy, they could affect the correctnessof the system by causing deadlines to be missed. This paper providesexact schedulability tests for fault tolerant task sets undera specified failure hypothesis and employing checkpointing toassist in fault recovery. The effects of checkpointing strategieson task response time are analysed and some insights for optimalcheckpointing are provided. The emphasis here is on utilizingthis analysis as an off-line design support tool.

Response time analysis under errors for CAN

The Controller Area Network (CAN) is extensively used for timely communication in automotive and other applications. As timing analysis of CAN messages is emerging into industrial practice, and as the use of CAN in safety-critical applications is increasing, there is an apparent need to include the effects of transmission errors in the analysis of message latencies. The authors provide a general fault model and extend the timing analysis of CAN messages to cater for the effects of transmission errors on message latencies. This fault model helps us in composing the effects of interferences from multiple sources and to account for them in the calculation of message response times. We illustrate our model by applying it to derive the worst case latencies of a subset of messages selected from the frequently used SAE case study. We also discuss and illustrate the implications on message latencies for some realistic fault scenarios.

Sensitivity Analysis of Real-Time Task Sets

Though schedulability analysis has matured to the point where it is now possible to analyse realistic systems, there is still a lack of flexibility as far as the designer is concerned. Feasibility tests often provide little or no indication of the changes in task timing characteristics required to achieve a feasible system, nor any indication of the extent to which the worst case execution times of tasks may be increased without causing deadlines to be missed (in the case of a feasible system). In practice, however, it is useful to know how sensitive system feasibility is to changes in task timing characteristics. We give a general approach to the sensitivity analysis of task sets, which aids system developers in incorporating changes to the system whilst ensuring that the schedulability guarantees remain intact.

Factors Limiting Industrial Adoption of Test Driven Development: A Systematic Review

Test driven development (TDD) is one of the basic practices of agile software development and both academia and practitioners claim that TDD, to a certain extent, improves the quality of the code produced by developers. However, recent results suggest that this practice is not followed to the extent preferred by industry. In order to pinpoint specific obstacles limiting its industrial adoption we have conducted a systematic literature review on empirical studies explicitly focusing on TDD as well as indirectly addressing TDD. Our review has identified seven limiting factors viz., increased development time, insufficient TDD experience/knowledge, lack of upfront design, domain and tool specific issues, lack of developer skill in writing test cases, insufficient adherence to TDD protocol, and legacy code. The results of this study is of special importance to the testing community, since it outlines the direction for further detailed scientific investigations as well as highlights the requirement of guidelines to overcome these limiting factors for successful industrial adoption of TDD.

Flexible scheduling for adaptable real-time systems

Complex real time systems, such as those envisaged for autonomous vehicle control, are expected to exhibit: adaptive and dynamic behaviour, resilience to software/hardware failures and graceful degradation, under conditions of overload. Two objectives need to be met before such properties can be realised. First, critical services must be guaranteed to provide results of a minimum acceptable quality and reliability by their deadlines. Second, the utility of the system needs to be maximised. We present an approach to meeting the above objectives. This approach combines the benefits of both fixed priority preemptive and best effort scheduling: offline analysis is used to guarantee that critical timing requirements will be met, whilst at run time, a simple adaptive threshold policy arbitrates between competing optional components, enhancing the system utility obtained.

An Industrial Survey on Contemporary Aspects of Software Testing

Software testing is a major source of expense in software projects and a proper testing process is a critical ingredient in the cost-efficient development of high-quality software. Contemporary aspects, such as the introduction of amore lightweight process, trends towards distributed development, and the rapid increase of software in embedded and safety-critical systems, challenge the testing process in unexpected manners. To our knowledge, there are very few studies focusing on these aspects in relation to testing as perceived by different contributors in the software development process. This paper qualitatively and quantitatively analyses data from an industrial questionnaire survey, with a focus on current practices and preferences on contemporary aspects of software testing. Specifically, the analysis focuses on perceptions of the software testing process in different categories of respondents. Categorization of respondents is based on safety-criticality, agility, distribution of development, and application domain. While confirming some of the commonly acknowledged facts, our findings also reveal notable discrepancies between preferred and actual testing practices. We believe continued research efforts are essential to provide guidelines in the adaptation of the testing process to take care of these discrepancies, thus improving the quality and efficiency of the software development.

A Framework for Comparing Efficiency, Effectiveness and Applicability of Software Testing Techniques

Software testing is expensive for the industry, and always constrained by time and effort. Although there is a multitude of test techniques, there are currently no scientifically based guidelines for the selection of appropriate techniques of different domains and contexts. For large complex systems, some techniques are more efficient in finding failures than others and some are easier to apply than others are. From an industrial perspective, it is important to find the most effective and efficient test design technique that is possible to automate and apply. In this paper, we propose an experimental framework for comparison of test techniques with respect to efficiency, effectiveness and applicability. We also plan to evaluate ease of automation, which has not been addressed by previous studies. We highlight some of the problems of evaluating or comparing test techniques in an objective manner. We describe our planned process for this multi-phase experimental study. This includes presentation of some of the important measurements to be collected with the dual goals of analyzing the properties of the test technique, as well as validating our experimental framework

Analysis of checkpointing for schedulability of real-time systems

Checkpointing is a relatively cost effective method for achieving fault tolerance in real-time systems. Since checkpointing schemes depend on time redundancy, they could affect the correctness of the system by causing deadlines to be missed. This paper provides exact schedulability tests for fault tolerant task sets under specified failure hypothesis and employing checkpointing to assist in fault recovery. The effects of checkpointing strategies on task response time are analysed and some insights for optimal checkpointing are provided. The emphasis here is on utilizing this analysis as an off-line design support tool.

Test case quality in test driven development: A study design and a pilot experiment

Background: Test driven development, as a side-effect of developing software, will produce a set of accompanied test cases which can protect implemented features during code refactoring. However, recent research results point out that successful adoption of test driven development might be limited by the testing skills of developers using it. Aim: Main goal of this paper is to investigate if there is a difference between the quality of test cases created while using test-first and test-last approaches. Additional goal of this paper is to measure the code quality produced using test-first and test-last approaches. Method: A pilot study was conducted during the master level course on Software Verification & Validation at Malardalen University. Students were working individually on the problem implementation by being randomly assigned to a test-first or a test-last (control) group. Source code and test cases created by each participant during the study, as well as their answers on a survey questionnaire after the study, were collected and analysed. The quality of the test cases is analysed from three perspectives: (i) code coverage, (ii) mutation score and (iii) the total number of failing assertions. Results: The total number of test cases with failing assertions (test cases revealing an error in the code) was nearly the same for both test-first and test-last groups. This can be interpreted as “test cases created by test-first developers were as good as (or as bad as) test cases created by test-last developers”. On the contrary, solutions created by test-first developers had, on average, 27% less failing assertions when compared to solutions created by the test-last group. Conclusions: Though the study provided some interesting observations, it needs to be conducted as a fully controlled experiment wit