Software Testing in Safety Critical Systems
Abstract
Today, many safety-critical applications are controlled by computer software.
Therefore effective testing tools are required to provide a high degree of safety and to reduce severe failures to a minimum.
The paper examines existing regulating standards in safety-critical systems. By comparing different software testing methods the requirements and challenges in safety-critical software testing are being evaluated.
The IEC61508 standard serves as the main regulatory framework for all safetyrelated systems and provides the basis for the creation of application- and industryspecific standards. Moreover it defines certain safety integrity levels depending on the field of application and recommends testing methods according to these levels.
In model-based safety testing a usage model with restricted space state domain is used to generate representative test cases. Statistical testing is a mathematical approach that uses a high number of test cases to reach a significant result.
The main challenge of all safety-related testing methods is to reduce testing time and complexity without distorting the significance of the test. State domain restriction as well as importance sampling-based techniques can be used to overcome this problem. 3
Table of Contents
1 Introduction.................................................................................................................5
2 Definitions...................................................................................................................6
2.1 Reliability and Safety ....................................................................................................6
2.2 Safety-Critical System States........................................................................................6
2.3 Markov Chain Usage Model .........................................................................................7
3
Today, many safety-critical applications are controlled by computer software.
Therefore effective testing tools are required to provide a high degree of safety and to reduce severe failures to a minimum.
The paper examines existing regulating standards in safety-critical systems. By comparing different software testing methods the requirements and challenges in safety-critical software testing are being evaluated.
The IEC61508 standard serves as the main regulatory framework for all safetyrelated systems and provides the basis for the creation of application- and industryspecific standards. Moreover it defines certain safety integrity levels depending on the field of application and recommends testing methods according to these levels.
In model-based safety testing a usage model with restricted space state domain is used to generate representative test cases. Statistical testing is a mathematical approach that uses a high number of test cases to reach a significant result.
The main challenge of all safety-related testing methods is to reduce testing time and complexity without distorting the significance of the test. State domain restriction as well as importance sampling-based techniques can be used to overcome this problem. 3
Table of Contents
1 Introduction.................................................................................................................5
2 Definitions...................................................................................................................6
2.1 Reliability and Safety ....................................................................................................6
2.2 Safety-Critical System States........................................................................................6
2.3 Markov Chain Usage Model .........................................................................................7
3
Bibliography: https://noppa.oulu.fi/noppa/kurssi/811601s/luennot/811601S_lecture_11__vuori .pdf [accessed on 28.12.2013] 20 List of Figures List of Figures Figure 1: Three-state Markov Model for Safety-Critical Systems(Source: [2]).............7 Figure 2: IEC 61508-3 Verification and Validation Process(Source: [6])....................10 Figure 3: Model-based Safety Testing according Gang Yu et al. (Source: [2])..........12 Figure 4: Test Case Generation Framework according Gang Yu et al. (Source: [2]).14 21