People interpret requirements and specifications in different ways, based on their models, and their past experiences, and their current context. When they hear or read something, many people tend to choose an interpretation that is familiar to them, which may close off their thinking about other possible interpretations. That’s not a big problem in simple, stable systems. It’s a bigger problem in software development. The problems we’re trying to solve are neither simple nor stable, and the same is true with the software that we’re developing.
The interpretation problem applies not only to software development and testing, but to the teaching of testing too. For example, in Rapid Software Testing, James Bach and I teach that an oracle is a way to recognize a problem, and one of the most important and powerful a broader set of oracle heuristics.
Here’s how the typical experiment went. We started by asking “We’re thinking of applying the comparable product oracle heuristic to a test of Microsoft Word. What product could we use for that?” Almost everyone suggested OpenOffice Writer, which seems to be the last remaining well-known full-featured word processing alternative to Microsoft Word. Some suggested WordPad, or Notepad, although almost everyone who did so suggested that WordPad (much less Notepad) wouldn’t be much use as comparable products. “Why not?” we asked. In general, the answer was that WordPad and Notepad were too simple, and didn’t reflect the complexity of Word.
Then we asked some follow-up questions. Is Word comparable with Unix’s command-line program wc? Most people said No (for some, we had to explain what wc is; it counts the words in a file that you provide as input). It was only when we asked, “What if we were testing the word count feature in Microsoft Word?” that the light began to dawn. When we asked if Word was comparable with Halo (the game), most people still said No. When we encouraged them to think more broadly about specific features of Word that we might compare with Halo, they started to get unstuck, and began to realize that while Word and Halo were dramatically different products in important respects, they were nonetheless comparable on some levels.
By contrast, here’s a conversation with Lynn McKee. The chat has been edited to de-Skypeify it (I’ve removed some typos, fixed some punctuation, and removed a couple of digressions not consequential to the conversation).
Michael: If you were asked, “We’re thinking of applying the comparable product oracle heuristic to a test of Microsoft Word. What product could we use for that?”, how would you answer?
Lynn: Hmmm. Certainly, we could use products such as “Open Office”, “Notepad” and others. Could you tell me more about what “we” are hoping to learn about the product under test to better assess which comparable products to use? Is this a brand new product? A version release? If so, what changed and what functions are we interested in comparing?
Michael: That’s a pretty good answer. A followup question: do you know the wc program, typically available under Unix?
Lynn: Sorry, I am not familiar with that product. Can you tell me more about it? How does it relate to your product? Is your product running on Unix?
Michael: Yes. wc is a command-line program. Its purpose is to count the words in a document. You supply the document as input; it returns the number of words in that document.
Lynn: While you were typing, I used my handy Google search to tell me a bit about Unix WC. Oh interesting, so are you looking to gather information about how capable, performant, etc the word count functionality is within MS Word? Can you tell me more about what functions of MS Word interest you the most? And why?
Michael: One more question: Halo IV — the game. Is that a comparable product to MS Word?
Lynn: Sheesh, I’ve only ever seen ads. Lemme think. It blows people’s brains out…sometimes I want to do that with MS Word. It would depend on what type of comparison we are hoping to draw. For example, Halo is a game and does require interaction with a user. From a UI perspective, there are menus and other forms of cause-and-effect type of interaction—that is, when I do X, I expect Y. There are also state comparisons I could draw. When I start a new game, save a game, reopen a game I have expectations about the state the game should be in. This is similar to how I may expect a document to behave with states. I may also expect certain behavior with pausing or crashing the game in terms of recovery that could be compared to MS Word. Conversely… if I am looking to compare the product’s ability to display fonts, images, format tables, etc. then I may find very low value in comparing the products. I think that you could compare any two products but you may find very different value in the comparison exercise, depending on what you hope to learn.
This is an answer that I would consider exemplary. I have related it here because it was outstanding in two ways: it was an extremely good answer, but it was also exceptional, in that most people didn’t consider wc or Halo to be even remotely comparable to Microsoft Word without a good deal of prompting. Lynn, on the other hand, recognized that “comparable” doesn’t necessarily mean “highly similar”; it can also mean “anything or any aspect of something that you might use as a basis for comparison“. She immediately questioned the question, to make sure that she understood the task at hand. She also did a bit of research on her own while I was answering the question, and asked some highly relevant questions about risks and particular concerns that I might have. Note that she’s doing important informal work—understanding the testing mission—before making too firm a commitment to what might or might not be considered “comparable” for the purposes of a particular question that we might have about the product.
I’ll have more to say about the Comparable Product heuristic tomorrow.