Overview of Structured Testing - Software Testing: Testing Across the Entire Software Development Life Cycle - page 60

What happened to the Boeing Model 299 prototype? It is not hard to imagine how
quickly Boeing wanted an answer to that question. From an economics viewpoint,
losing the government contracts could force Boeing into bankruptcy because Boeing
was already in dire fi nancial straits. From an engineering point of view, an unseen
design fl aw could make Boeing a pariah of new aircraft designs for the government
and commercial markets alike.
Boeing did discover the cause of the Model 299 prototype crash after a very
intensive investigation. The good news was that the crash was caused neither by faulty
design nor by faulty construction. Review of the crash revealed no inappropriate
pilot action. The prototype's test pilots were the best in the industry.
The crash was caused by elevator (tail control) locks that were not removed before
takeoff. These control locks are normally placed on all control surfaces (ailerons,
rudder, elevators) when an aircraft is parked at an airport to prevent wind damage by
moving these hinged surfaces. At the time of the crash, there was no standard under-
standing among the ground crew and pilots as to who was responsible for removing
these control locks, either after landing or before the next takeoff. So, if both groups
assumed that the other group removed the control locks, the control locks remained
in place, thereby freezing the controls during takeoff with deadly consequences.
The solution to this problem was as profound as it was simple: the now ubiquitous
pilot's prefl ight checklist. The prefl ight checklist guarantees that if an experienced
pilot verifi es each action on the checklist has been accomplished before takeoff, the
takeoff can be successfully accomplished repeatedly with minimal safety risk.
3.2 CHECKLIST MENTALITY FOR
SOFTWARE TESTERS
Professional software testers have found the concept of a “prefl ight” checklist with
the same professional caveats to be an excellent way of ensuring a successful testing
project.
What are the professional caveats? Before you pick up a checklist either for a pilot
or a tester and attempt to fl y a plane or test software, consider the professional prereq-
uisites. The goal of the checklist is to be able to say “Yes, I have verifi ed that” to every
checklist question. For example, the following question does appear on aircraft prefl ight
checklists: “fl ight controls free and correct?” It is just one short question in the middle
of a list of 15 or 20 questions. If you hold a pilot's license, then your fl ight experi-
ence (2 weeks of ground school, 40 hours of fl ight instruction, pilot's license, and 100-
5000 hours of fl ight as pilot in command) tells you what stick to wiggle and what wing
surface movement to expect before you say to yourself, “Yes, I have verifi ed that.”
The following question appears on all professional software testing checklists:
“testing success defi ned?” It is just one short question in the middle of a list of 15-20
questions. If you have successfully completed several major testing projects, then
your testing experience tells you the importance of knowing how to tell when you
are done testing before you can plan a successful testing project so that you can say,
“Yes, I have verifi ed that.”