Sun, 11 Mar 2007
"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
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
It may also clash with my advice to keep tests simple, at least at
first. Complex, even
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