Test Strategy and Coverage

3 Testing as Evidence for the Safety Case 16.3.1 Test Strategy and Coverage 

By tagging those controls which are safety-related one is able to derive a set of basic safety requirements. Safety requirements, when described in sufficient detail, are vital to testers tasked with formulating appropriate test cases. In this way solid traceability is created from the outset - simple but logical linkage between hazards, controls, requirements and test cases. Of course it is essential that the test cases created truly describe the expected system behaviour and that the integrity is not lost in traceability Chinese-whispers. It can therefore be useful for those formulating the hazard register to review the test cases and their validation criteria to ensure that the true nature of the test is correctly captured from a safety perspective. 

To some extent this process can also work in reverse. Reviewing test cases helps us to think about how validating parts of the system might evidence controls in ways we had previously not considered. Similarly one might ask whether failure of the scenario contained in the test case might lead to harm should it occur in the real-world. This might lead us to formulate new hazards or new causes of existing hazards. 

By examining the test plan and test cases early in the development lifecycle plenty of opportunity is afforded to get the assurance strategy right and to formulate this from the ground up based on the safety objectives. 

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