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, 10 Jun 2004

Your heart as a squirming bag of worms

In response to my posting about the kludgy body, Pete TerMaat sent me some entertaining notes about how complex even a straightforward bodily function is. I'm really repeating these because they're cool, but I suppose I need some Grand Metaphorical Lesson, that being my schtick. How about "think of these next time you're tempted to whine about complex business rules"?

Even though it's simple in purpose, the heart is integrated in ways that are tough to duplicate.

Medtronic spends millions trying to come up with a hunk of metal that can replace just the electrical (pacemaking) aspects of the heart. The company's first pacemaker came about when the founder, Earl Bakken, grabbed a metronome circuit from a Popular Electronics magazine, and hooked it up to some leads so that the circuit would provide pacing pulses to the heart. Simple enough...

But not as sophisticated as the heart, which has some tight integration with the rest of the body. For example, when you merely *think* about running, your pulse starts to quicken in anticipation of greater demands on the heart. Also, when you go to sleep, your heart slows down.

How do pacemakers handle the problem of ramping up the pulse in reponse to exercise? They have motion detectors in them. One of the early models was fooled by a woman who knitted a lot. When she sat in her rocking chair and bobbed forward/backward, the motion detector figured she was out for a jog, and ramped up her heart rate.

There's another story about a rock climber. During an ascent he'd stop for a breather. As soon as he started climbing again, he needed his heart rate to increase. But the pacemaker lagged his needs. His solution was to pound his chest repeatedly, causing vibrations that were picked up by the pacemaker and interpreted as motion caused by exercise. This technique was a crude "remote control" for his pacemaker.

How do pacemakers know when you're sleeping? They check the time of day and compare it against the bedtime that your doc has programmed in for you. Again, not as nicely integrated as the real heart.


Another tidbit: the "rate response" feature of modern pacemakers, where they detect a person exercising and respond with a faster heart rate, was discovered by accident. Medtronic engineers put a vibration sensor in a pacemaker, hoping to to detect a particular condition--possibly ventricular fibrillation (where the heart quivers like a bag of worms), or ventricular tachychardia (an overly fast heartbeat). When they put the device in a canine for testing, it picked up a lot of "noise". They figured out that the "noise" happened when the dog moved. From that came the idea of interpreting the vibrations as body movement, corresponding to exercise.

(Posted with permission.)

## Posted at 09:47 in category /misc [permalink] [top]

Micro-techniques event

Apropos of my posting mentioning micro-techniques, Steve Freeman points to Joe Walnes's Personal Development Practices Map workshop at Agile Development Conference. Sounds rather like what I was asking for (depending on the granularity of the practices they consider).

## Posted at 08:14 in category /misc [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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Working your way out of the automated GUI testing tarpit
  1. Three ways of writing the same test
  2. A test should deduce its setup path
  3. Convert the suite one failure at a time
  4. You should be able to get to any page in one step
  5. Extract fast tests about single pages
  6. Link checking without clicking on links
  7. Workflow tests remain GUI tests
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