Plagues aren’t just for blog posts

Vibrio cholerae with a Leifson flagella stain ...
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For the past couple of months, James Whittaker has been writing about the “plagues of testing.” As he’s been posting, I’ve been reading through a book about a real plague.

As software testers, we see a system from a perspective that developers and business types rarely and may never see.  We know our tests, we know how well they ran.  We know our system under test and which components are picky.  If you are like me, and have access to the code base, you also know the code.  In the case of both the system and it’s code you know what should be better.  Sometimes this is not a big deal, but sometimes it is a warning that it’s time to polish the resume. I have not seen this, personally, but I know that there are testers who find themselves in this position.

John Snow was a doctor in this position. He was an expert in the new art of anesthesiology in 1850’s London. He was also deeply involved in the study of cholera and concluded that it was a water born illness. This was very much counter to the prevailing theory of the time that cholera was passed through a sheer volume of stench or miasma (I can hear Dr. Evil saying this word). Health authorities in London, were so convinced that miasma, or extreme smellyness, was the reason for disease that they passed a law in 1848 requiring Londoners to drain their waste into a sewage system that would deposit into the Thames river. Unfortunately, the Thames was also a main source of drinking water for the city. Snow knew all of this and could see a health crisis in the making.

In 1854 when a major outbreak of cholera erupted in a neighborhood very close to where Snow lived, he conducted a thorough investigation in order to prove this theory that cholera was passed through water. He had a list that detailed the names and addresses of 83 people who had died from cholera.  He also had an invaluable resource of detailed information about the neighborhood’s residents in the form of local clergyman Henry Whitehead.  While Whitehead tracked down and questioned everyone he possibly could about their drinking habits, Snow analyzed this data to form patterns of who had been drinking the water, who had died and, just as importantly, who had NOT died.  Not only were Snow and Whitehead able to convince the local parish board to remove the handle of a contaminated water pump, they knew their data so well that they were able to figure out the index, or original, case that had started the outbreak.

John Snow Map

After the outbreak had subsided, Snow put the analysis from his investigation together with a very famous map into a monograph that circulated among London’s health professionals.  His monograph slowly but effectively turned the tide of thinking among health professionals away from the miasma theory.  This and a very smelly Thames convinced authorities to build a new sewer system that drained into the sea.

Frequently, when I talk to people about data visualization, they always ask me how I know what to visualize.  The Ghost Map, by Steven Johnson, illustrates this perfectly.  John Snow went from having a theory to proving his theory with visualization in a convincing way.  There’s no wizard or easy-button for this one.  It takes knowing what you are trying to say and knowing the data, inside and out, you are using to prove your theory.  For testers, this means digging into test runs and testcase organization.  Where are the tests that failed?  How many times did they fail? How are they grouped together?  Does an object that make 1 test fail make others fail as well?  If you know which tests are failing, what do you know about the code you were excercising?  How complex is it?  I know this awful, but I would so go here if I thought it made a difference…who coded it and do I respect their coding talent? Even if I think they are solid, did they know what they were supposed to be doing? You have to know exactly why you are telling the PM you think there is a serious problem and have a way to show it. I lump business people in with having the same short attention span as doctors and politicians. My blog post probably lost them at “James Whittaker.”

Johnson and Whitehead could not drag the dead people’s relatives in front of London’s public health community and force the doctors to listen.  These days doctor’s short attention span is because of insurance, but I’m sure there were other reasons back in the day.  A good visualization does not take a long time for the viewer to process.  That is their special power.  Snow’s map is much more concise than a table of 83 names and addresses along with their individual stories.  Visualization can quickly show your groups of tests that are failing.  It can show that severe defects are increasing, and not decreasing, over time.  Business may drive the ship/do not ship decision, but a good tester will know why a seriously ailing system is in so much trouble.  A great tester can effectively communicate this to a business team.

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