Introduction to Software Testing

“Wishful labeling”

• People tend to confuse an ideal with its implementation
• E.g., All you need is monitoring and a shutdown routine to have a safe system.
• Need a much greater understanding of the human element:
• cognition, politics, social factors, training, ...

Workmanship standards

• The early steam engines had low standards of workmanship, and engineers lacked proper training and skills.
• There were more jobs for highly-trained and experienced technologists than there were suitable people to fill them
• What do you think happened?

Safety engineering

• There exists a wealth of knowledge and experience outside the realm of software development/engineering.
• Safety engineering defines safety in terms of hazards:
• Attack problem of system safety by reducing or controlling hazards.

Basic approaches to safety engineering

• Avoidance: Stop hazards from occurring, or minimize their occurrence.
• E.g., If fire is a concern, use non-flammable materials and minimize chance of sparks.
• Disadvantages:
• cost
• performance

Basic approaches to safety engineering (Cont’d)

• Recovery: Control hazards if/when they do occur.
• E.g., sprinklers, fire doors, smoke detectors
• Advantages:
• cost, can be added after-the-fact
• Disadvantages:
• often less safe
• cost
• performance

Safety engineering (Cont’d)

• In practice, a combination of the two is used.
• Each system is different and requires careful analysis of:
• risk
• design
• cost
• performance

High-pressure steam engines and computer software

• “As Edison argued with respect to electricity, increased government regulation of our technology may not be to anyone’s benefit; but it is inevitable unless we, as the technology’s developers and users, take the steps necessary to ensure safety in the devices that are constructed and technical competence in those that construct them.”

• Thomas Edison (1847-1931)

You now know …

• … Historical analogies between steam engine reliability and software reliability
• … N-version programming
• … safety critical software
• … safety engineering