In the previous post, Lynn McKee recognized that, with respect to the Comparable Product oracle heuristic, “comparable” can be have several expansive interpretations, and not just one narrow one. I’ll emphasize: “comparable product”, in the context of the FEW HICCUPPS oracle heuristics, can mean any software product, any attribute of a software product, or even attributes of non-software products that we could use as a basis for comparison. (Since “comparable product” is a heuristic, it can fail us by not helping us to recognize a problem, or by fooling us into believing that there is a problem where there really isn’t one. For now, at least, I leave the failure modes for each example below as an exercise for the reader. That said…) Here are some examples of comparable products that we could use when applying this heuristic.
An alternative product. Our product is intended to help us accomplish a particular task or set of tasks. We compare the overall operation of our product to the alternative product and its behaviour, look and feel, output, workflow, and so forth. If our product is inconsistent with a product that helps people do the same thing, then we might suspect a problem in our product. This is the “Microsoft Word vs. OpenOffice” sense of “comparable product”.
A commercially competitive product. This is a special case of “alternative product”. People often hold commercial products to a higher standard than they hold freeware. If our product is inconsistent with another commercial product that is in the same market category (think “Microsoft Word vs. WordPerfect”), then we might suspect a problem in our product.
A product that’s a member of the same suite of products. Imagine being a tester on the enormous team that produces Microsoft Office. In places, Microsoft Outlook’s behaviour is inconsistent with the behaviour of Microsoft Word. We might recognize that a user could be frustrated or annoyed by inconsistencies between those products, because those products could reasonably be expected to have a consistent look and feel. I use both Word and Outlook. Sometimes I want to find a particular word or phrase in a long Outlook message that someone sent me. I press Ctrl-F. Instead of popping open the Find dialog, Outlook opens a copy of the message to be Forwarded. The appropriate key is to find something in Outlook is F4, which by default is assigned to “Redo or Repeat” in Word. (Note that Joel Spolsky’s Law of Leaky Abstractions starts to take effect here. This flavour of the comparable product heuristic starts to leak into territory covered by the “user expectations” heuristic. That’s okay; some overlap between oracle heuristics helps to reduce to chance that we’ll miss a problems if one heuristic misfires. Moreover, weighing information from a variety of oracles helps us to evaluate the signficance of a given problem. There’s another leaky abstraction here too: what is a product? Given that Word is a product and Outlook is a product, is Office a product?)
Two products that are subcomponents within the same larger product. As in the Office/Outlook/Word example just above, Outlook isn’t even consistent within itself. In the (incoming) message reading window, Ctrl-F triggers the Forward Message function. In the (outgoing) message editing window, Ctrl-F does bring up the Find dialog. That’s because I have Outlook configured to use Word’s editor as Outlook’s. (There’s a leaky abstraction here too: the “consistency within the product” heuristic, where similar behaviours and states within the product should be consistent with one another. It’s good when oracles overlap!)
An existing product whose sole purpose is comparable to a specific feature in our product. A very simple product might have a purpose that is directly comparable to a purpose, feature or function in our product. A command-line tool like wc (Unix’ command-line word-count program) isn’t comparable with Microsoft Word in the large, but it can be used as a point of comparison for a specific aspect of Word’s behaviour.
An existing product that is different, yet shares some comparable feature, function, or concept. Many non-testers (and, apparently, many testers too) would consider Halo IV and Microsoft Word to be in completely different categories, yet there are similarities. Both are pieces of computer software; both process data; both exhibit behaviour; both save and restore state; both may change their appearance depending on the display settings. If either one were to crash, respond slowly, or misrepresent something on the screen, we might recognize a problem, and recognizing or conceiving of a problem in one might trigger us to consider a problem in the other.
A chain of events in some product. We might choose to build simple test automation to aid us in comparing the output of comparable functions or algorithms in two products. (For example, if we were testing OpenOffice, we might use scripting to compare OpenOffice’s result of a sin(x) function with Microsoft Excel’s API result, or we could use a call to the Web to obtain comparable output from the sin(x) function in Wolfram Alpha.) Those comparisons may become much more interesting when we chain a number of functions together. Note that if we’re not modeling accurately, coding carefully, and logging diligently, comparisons of chains of events may be harder to analyze.
A product that we develop specifically to implement a comparable algorithm. While working at a bank, I developed an Excel spreadsheet and VBA code to model the business logic for the teller workstation application I was testing. I used the use cases for the application as a specification, which allowed me to predict and test the ways in which which general ledger accounts would be affected by each supported transaction. This was a superb way to learn about the application, the business rules, and the power of Excel.
A reference output or artifact. Those who use FIT or FitNesse develop tables of functions, inputs, and outputs that the tool compares to output from integration-level functions; those tables are comparable products. If our testing mission were to examine the font output of Word, the display from a font management tool could be comparable to Word’s output. The comparable product may not even be instantiated in software or in electronic form. For example, we could compare the fonts in the output of our presentation software to the fonts in a Letraset catalog; we could compare the output from a pocket calculator to the output of our program; we could compare aggregated output from our program to a graph sketched on paper by a statistician; we could compare the data in our mailing list to the data in the postal code book. (Well, we used to do that; now it’s much easier to do it with some scripting that gets the data from the postal service.) More than once I’ve found a bug by comparing the number posted on the “Contact Us” page to the number printed on our business cards or in our marketing material. We could also compare output produced by our program today (to output produced by our program yesterday (an idea that leaks into the “consistency with history” heuristic).
A product that we don’t like. I remember this joke from somewhere in Isaac Asimov’s work: “People compare my violin playing to Jascha Heifetz. They say, ‘A Heifetz he ain’t!’” A comparable product is not always comparable in a desirable way. If someone touts a music management product to me saying “it’s just like iTunes!”, I’m not likely to use it. If people have been known to complain about a product, and our product provides the same basis for a complaint, we suspect a problem with our product. (The Law of Leaky Abstractions applies here too, leaking into the “familiar problems” heuristic, in which a product should be inconsistent with patterns of problems that we’ve seen before.)
Patterns of behaviour in a range or sphere of products. We can compare our product against our experience with technology and with entire classes of relevant or interesting products, without immediately referring to a specific product. “It’s one thing from freeware, but I didn’t expect crashes this often from a professional product.” “Well, this would be passable on a Windows system, but you know about those finicky Mac users.” “Yikes! I didn’t expect this product to make my password visible on-screen!” “Aw geez; the on-screen controls here are just as confusing as they are on a real VCR—and there are no tooltips, either.” “The success code is 1? Non-zero return codes on command-line utilities usually represent errors, don’t they?”
All of these things point to a few overarching points.
- “Similar” and “comparable” can be interpreted narrowly or broadly. Even when products are dissimilar in important respects, even one point of similarity may be useful.
- Products can be compared by similarity or by contrast.
- We can make or prepare comparable products, in addition to referring to existing ones.
- A comparable product may or may not be computer software.
- Especially in reference to the few categories above, there is great value for a tester in knowing not only about technologies and functional aspects of products in the same product space, but also about user interface conventions, business or workplace domains, sources of background information, cultural and aesthetic characteristics, design heuristics, and all kinds of other things because…
- If the object of the exercise is to find problems in the product quickly, it’s a good idea to have access to a requisite variety of ideas about what we might use as bases for comparison. (I describe “requisite variety” here, and Jurgen Appello describes it even better here.
- Bugs thrive on overly narrow or overly broad interpretations of “comparable”. Know what you’re comparing, and why the comparison matters to your testing and to your clients.
The comparable product heuristic is an oracle principle, but in describing it here, I haven’t paid much attention to mechanisms by which we might make comparisons. We’ll get to that issue next.