Exploration Through Example

Example-driven development, Agile testing, context-driven testing, Agile programming, Ruby, and other things of interest to Brian Marick
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Sun, 11 Mar 2007

Vivid examples

"In the first part of the experiment, subjects read about a court case involving drunk driving. The defendant had run a stop sign while driving home from a party and collided with a garbage truck. No blood alcohol test had been done, and there was only circumstantial evidence to go on. The defendant was arguing that he was not drunk.

After reading a description of the case and the defendant, subjects were divided into two groups and given eighteen individual pieces of evidence to read: nine written by the prosecution about why the defendant was guilty, and nine written by the defense about why the defendant was innocent. Subjects in the first group were given prosecution evidence written in a pallid style and defense evidence written in a vivid style, while subjects in the second group were given the reverse.

For example, here is a pallid and vivid version of the same piece of prosecution evidence:

  • On his way out the door, Sanders [the defendant] staggers against a serving table, knocking a bowl to the floor.

  • On his way out the door, Sanders staggered against a serving table, knocking a bowl of guacamole dip to the floor and splattering guacamole on the white shag carpet.

And here's a pallid and vivid pair for the defense:

  • The owner of the garbage truck admitted under cross-examination that his garbage truck is difficult to see at night because it is grey in color.

  • The owner of the garbage truck admitted under cross-examination that his garbage truck is difficult to see at night because it is grey in color. The owner said his trucks are grey "because it hides the dirt," and he said, "What do you want, I should paint them pink?"

After all of this, the subjects were asked about the defendant's drunkenness level, his guilt, and what verdict the jury should reach.

The results were interesting. The vivid vs. pallid arguments had no significant effect on the subject's judgment immediately after reading them, but when they were asked again about the case 48 hours later -- they were asked to make their judgments as though they "were deciding the case now for the first time" -- they were more swayed by the vivid arguments. Subjects who read vivid defense arguments and pallid prosecution arguments were much more likely to judge the defendant innocent, and subjects who read the vivid prosecution arguments and pallid defense arguments were much more likely to judge him guilty.

The moral here is that people will be persuaded more by a vivid, personal story than they will by bland statistics and facts, possibly solely due to the fact that they remember vivid arguments better."

—Bruce Schneier, "The Psychology of Security"

This all seems to have some connection with tests-as-examples. It is probably useful for an example to be memorable. We want it to come to someone's mind at the moment it's relevant, not be something that has to be looked up.

That implication may clash with my usual advice to strip a test down so that each word that appears in it is essential to its purpose. (So, for example, the only tests that would mention a user's username and password would be tests about logging in.) It is the added detail in the stories above that make them memorable.

It may also clash with my advice to keep tests simple, at least at first. Complex, even humorous, soap opera tests (reg. required) like the following are more memorable partly because of the complexity.

"A customer named Marick hires a car for a three-day business trip. (This, by the way, gives him enough rental points to reach Preferred status.) Midway through the rental, he extends it for another week. Several days later, he calls to report the car has been stolen. He insists that the Preferred benefit of on-site replacement applies, even though he was not Preferred at the start of the rental. A new car is delivered to him. Two days after that, he calls to report that the "stolen" car has been found. It turns out he'd mis-remembered where he'd parked it. He wants one of the cars picked up and the appropriate transaction closed. Oh, and one other thing: the way he discovered the mislaid car was by backing into it with its replacement, so they're both damaged..."

It does support my habit of using real people (or personas of same) as test data. The above was partly inspired by my perennial inability to remember the make, model, or color of my rental car when I walk out of the hotel in the morning. My various veterinary clinic examples feature clinicians based either on real people or stereotypes (the impatient, judgmental surgeon).

(I should note the danger of using real people - by focusing always on a limited subset of the potential users, you become even more likely to overlook examples relevant to people outside that subset.)

In any case, I bring up Schneier's quote because this kind of thing will be important if tests ever take their place as a communication and discover tool, in addition to a bug-finding tool.

## Posted at 09:11 in category /examples [permalink] [top]

About Brian Marick
I consult mainly on Agile software development, with a special focus on how testing fits in.

Contact me here: marick@exampler.com.




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