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Safety Critical Systems 5 Formal Verification and Testing. T 79.5303 Safety Critical Systems. Requirements Model. Requirements Analysis. Test Scenarios. Test Scenarios. System Acceptance. Requirements Document. Functional / Architechural - Model. System

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Safety critical systems 5 formal verification and testing

Safety Critical Systems 5Formal Verification and Testing

T 79.5303 Safety Critical Systems


Formal verification testing

Requirements Model

Requirements

Analysis

Test Scenarios

Test Scenarios

System

Acceptance

Requirements

Document

Functional /

Architechural - Model

System

Integration & Test

Systems

Analysis & Design

Specification

Document

Knowledge Base *

Software

Design

Module

Integration & Test

Software

Implementation

& Unit Test

* Configuration controlled Knowledge

that is increasing in Understanding

until Completion of the System:

  • Requirements Documentation

  • Requirements Traceability

  • Model Data/Parameters

  • Test Definition/Vectors

Formal Verification/testing


Verification and validation
Verification and validation

  • Verification is the process of determining that a system or module meets its specification.

  • Validation is the process of determining that a system is appropriate for its purpose.

  • Testing is a process used to verify or validate system or its components.












Testing

Requirements Model

Requirements

Analysis

Test Scenarios

Test Scenarios

System

Acceptance

Requirements

Document

Functional /

Architechural - Model

System

Integration & Test

Systems

Analysis & Design

Specification

Document

Knowledge Base *

Software

Design

Module

Integration & Test

Software

Implementation

& Unit Test

* Configuration controlled Knowledge

that is increasing in Understanding

until Completion of the System:

  • Requirements Documentation

  • Requirements Traceability

  • Model Data/Parameters

  • Test Definition/Vectors

Testing


Testing in different stages of v

Testing in different stages of V

Testing is performed during various stage of system development.

Module testing – evaluation of a small function of the hardware/software.

System integration testing – investigates correct interaction of modules.

System validation testing – a complete system satisfies its requirements.


Forms of testing

Forms of Testing

Dynamic testing - execution of the system or component in the natural/simulated environment.

Functional – test all functions

Structural – test signal/test cases (glass-box)

Random – n-dimensional input space

Static testing - reviews, inspections and walkthroughs. Static code analysis for software.

Modelling - mathematical representation of the behaviour of a system or its environment.


Testing methods

Testing Methods

Black-box testing – requirements-based, no information of the system, what is inside.

White-box testing – more information about the system design to guide testing. Open view glass box.

Gray-box testing – open the internal structure, but not detailed information


Dynamic testing techniques

Dynamic testing techniques

Dynamic testing standards IEC1508, BCS (British Computer Society), Def STAN 00-55 and DO-178B.

- Process simulation

Error seeding/guessing

Timing and memory tests

Performance/stress testing

Probabilistic testing – values for failure rates


Test planning

Test planning

Lifecycle Phase Activity Safety case

Requirements Hazard identification Analysis results

Test planning Identify tests integrity Strategy for V/V

Req/Design/Test Trace hazards to specs. Risk reduction

Req/Design Define specs Design analysis

Safety Functional Requirements are the actual safety- related functions which the system, sub-system or item of equipments required to carry out. (CENELEC)


Simulator testing
Simulator testing

  • Safety critical standards e.g. Def STAN 00-551 recommend that if a simulator is used to validate a safety-critical system then the simulator should be properly validated.

  • In industry, simulators are validated using ad hoc techniques and no guidelines on simulator validation are available.


Simulator testing1
Simulator testing

  • Modified lifecycle model which illustrates the importance of environment simulation and helps to define the techniques which should be adopted.

  • This model expands the conventional ‘V’ model to form a ‘W’ model, where the left hand side represents the development of the product and the right hand side the development of the simulator used to test it.

  • The ‘W’ lifecycle model defines a similar set of phases for the development of the environment simulator to those used in the development of the product itself. This does not necessarily imply that the amount of effort required in the former is equal to that in the latter.



Statistical software testing
Statistical software testing

  • A type of random testing – input=>output

  • Provides quantifiable metric of software integrity = probability of failure and reliability figures

  • A proper environment simulation is needed

  • Statistical method(s) is needed to produce an estimate of probability of failure and a measure of the confidence in that estimate





Definitions of testability
Definitions of Testability

  • The degree to which a system or component facilitates the establishment of test criteria and the performance of tests to determine whether those criteria have been met.

  • The effort required to apply a given testing strategy to a system.

  • The ease with which faults in a system can be made to reveal themselves during testing.


Enough testing
Enough Testing

“How much testing do I need to do to prove that my system is safe?”.

  • An industrial project developed results which included the situation where failures were observed during testing. For example, a 99% confidence that the probability of failure on test demand is smaller than 0,001 requires about 5000 demands all of which are successful.

  • Safety critical system testing starts, when normal industrial testing procedures has passed without a single failure.


Testing1

Testing

Home assignment:

12.7 Describe the characteristics of the three major categories of dynamic testing and give examples of techniques that fall within each group. State whether each group corresponds to a black-box or a white-box approach.

Please email to [email protected] by

24 of April 2008

References: KnowGravity, I-Logix, Contesse project, Prover


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