Introduction To Software Testing - A study of errors, defects & failures.
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Introduction
to Software
Testing.
A level of expectation is set the moment you walk in.
You would not expect to take delivery from the showroom with a scratch down the side of the vehicle. The car should have the right number of wheels, a steering wheel, an engine — and a spare for emergencies.
It should come with appropriate documentation, with all pre-sales checks completed and passed satisfactorily. The car you receive should be the car described in the sales literature.
Pre-sales
checks
passed.
Brochures, test drives, experience — all set a baseline. Deviation is the exception, not the rule.
Delivered
not working
— often.
Examples of software being delivered not working as expected, or not working at all, are common. No single cause, but inadequate testing is a major factor.
Software testing is neither complex nor difficult to implement, yet it is a discipline that is seldom applied with anything approaching the necessary rigour to provide confidence in delivered software.
It is costly in human effort, or in the technology that can multiply that effort — yet seldom implemented at a level that provides any assurance software will operate effectively, efficiently or even correctly.
Why does software fail?
Five real-world examples where inadequate testing or design flaws led to failures of varying scale — from financial loss to national security exposure.
A380
Returns
Wanted
App
Breach
Assembly
incompatibility.
After successful test flights and airworthiness accreditation, problems arose in the manufacture of the Airbus A380 aircraft. Assembly of the large sub-parts into the completed aircraft revealed enormous cabling and wiring problems.
The wiring of large sub-parts could not be joined together. The issue was quickly fixed and the aircraft entered into service within 18 months of the cabling difficulties being identified.
Privacy
breach.
When the UK Government introduced online filing of tax returns, a user could sometimes see the amount that a previous user earned.
This was regardless of the physical location of the two applicants — a session or data leakage defect with serious privacy implications for every citizen using the system.
Performance
collapse.
In November 2005, information on the UK's top 10 wanted criminals was displayed on a website. The publication was described in newspapers, on morning radio and television, and as a result many people attempted to access the site.
The performance of the website proved inadequate under this load and it had to be taken offline. The publicity created performance peaks beyond the capacity of the website.
Cartographic
errors.
A new smartphone mapping application was introduced in September 2012. Among many other problems, a museum was incorrectly located in the middle of a river, and Sweden's second city, Gothenburg, seemed to have disappeared from at least one map.
A high-profile launch with low-quality data undermined user trust within hours.
Personnel
exposure.
Security breaches at the US military resulted in the payment details of many personnel — perhaps even "all" — being compromised.
The exposed data included names, addresses, email addresses and bank details: the full financial identity of serving members of one of the world's most security-conscious organisations.
Of course they do. People are fallible.
To understand what's going on, we need to start at the beginning — with the people who design systems. Pressures bear down on designers and increase the likelihood of defects in specifications, designs and code.
From invisible thought to visible collapse.
Test results can lie — in both directions.
Looks broken.
Isn't.
The tester misunderstood what should happen in those precise circumstances. The application or system is actually performing correctly.
Looks fine.
Isn't.
A real failure exists, but is not identified as such — the test is seen as correct, and the defect slips through into production.
People. Companies.
The environment.
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