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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Thu, 20 Feb 2003

Don't confuse more exact with better

Ron Jeffries has a quote file. I'm in it for "Don't confuse more exact with better". I don't remember the conversation where I said that, but I sure do believe it. Here's an example of exactness that's worse, as recounted (in PDF) by James Bach:

"The screen control should respond to user input within 300 milliseconds." I once saw a test designer fret and ponder over this requirement. She thought she would need to purchase a special tool to measure the performance of the product down to the millisecond level. She worried about how transient processes in Windows could introduce spurious variation into her measurements. Then she realized something: With a little preparation, an unaided human can measure time on that scale to a resolution of plus or minus 50 milliseconds. Maybe that would be accurate enough. It further occurred to her that perhaps this requirement was specified in milliseconds not to make it more meaningful, but to make it more objectively measurable. When she asked the designer, it turned out that the real requirement was that the response time "not be as annoyingly slow as it is in the current version of this product."

Thus we see that the pragmatics of testing are not necessarily served by unambiguous specification, though testing is always served by meaningful communication.

I wasn't the designer James mentions, but I was at the lunch where the topic came up. I'm sorry to say that I got as caught up as the designer in the quest to satisfy - not question - the requirement. Exactness has that magic power.

That's one of the things that makes me worry about the generally good tendency in agile projects toward test automation. I know that agility is all about conversation. But people choose what to converse about. I believe that creating tests provokes many useful conversations as you strive to make ideas testable. But I also believe that having tests tends to foreclose future conversations. Wise people - like James - try to break free of the exactness of tests.

## Posted at 13:17 in category /testing [permalink] [top]