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By James Bach
Paul Gerrard believes there are irrefutable testing axioms. This is not surprising, since all axioms are by definition irrefutable. To call something an axiom is to say you will cover your ears and hum whenever someone calls that principle into question. An axiom is a fundamental assumption on which the rest of your reasoning will be based.
They are not universal axioms for our field. Instead they are articles of Paul’s philosophy. As such, I’m glad to see them. I wish more testing authors would put their cards on the table that way.
I think what Paul means is that not that his axioms are irrefutable, but that they are necessary and sufficient as a basis for understanding what he considers to be good testing. In other words, they define his school of software testing. They are the result of many choices Paul has made that he could have made differently. For instance, he could have treated testing as an activity rather than speaking of tests as artifacts. He went with the artifact option, which is why one of his axioms speaks of test sequencing. I don’t think in terms of test artifacts, primarily, so I don’t speak of sequencing tests, usually. Usually, I speak of chartering test sessions and focusing test attention.
Sometimes people complain that declaring a school of testing fragments the craft. But I think the craft is already fragmented, and we should explore and understand the various philosophies that are out there. Paul’s proposed axioms seem a pretty fair representation of what I sometimes call the Chapel Hill School, since the Chapel Hill Symposium in 1972 was the organizing moment for many of those ideas, perhaps all of them. The book Program Test Methods, by Bill Hetzel, was the first book dedicated to testing. It came out of that symposium.
The Chapel Hill School is usually called “traditional testing”, but it’s important to understand that this tradition was not well established before 1972. Jerry Weinberg’s writings on testing, in his authoritative 1961 textbook on programming, presented a more flexible view. I think the Chapel Hill school has not achieved its vision, it was largely in dissatisfaction with it that the Context-Driven school was created.
One of his axioms is “5. The Coverage Axiom: You must have a mechanism to define a target for the quantity of testing, measure progress towards that goal and assess the thoroughness in a quantifiable way.” This is not an axiom for me. I rarely quantify coverage. I think quantification that is not grounded in measurement theory is no better than using numerology or star signs to run your projects. I generally use narrative and qualitative assessment, instead.
For you context-driven hounds out there, practice your art by picking one of his axioms and showing how it is possible to have good testing, in some context, while rejecting that principle. Post your analysis as a comment to this blog, if you want.
In any social activity (as opposed to a mathematical or physical system), any attempt to say “this is what it must be” boils down to a question of values or definitions. The Context-Driven community declared our values with our seven principles. But we don’t call our principles irrefutable. We simply say here is one school of thought, and we like it better than any other, for the moment.


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