Sunday, August 25, 2013

On the Trail of the White-Tailed Defect

Recently, I read an article about evolutionary biologist Dirk Semmann of the Universtity of Göttingen in Germany. His research suggests that the white tails on rabbits is a defense mechanism. Simply put, a predator will focus on the bright tail instead of the animal. As a result, when the rabbit turns sharply the predator momentarily loses sight of the rabbit and it is better able to get away.

Now apply that concept to defects in complex systems. You (the predator) are on the hunt for defects (the rabbits) in the system to prevent release bugs (☼). Some of the defects are slow, some are fast, some are camouflaged, and some are very, very, sneaky. This article deals with one of the most elusive defects in wild - the White-Tailed Defect. This defect gets you to focus on an obvious trait that always appears to identify it. It is such an obvious target that you decide it is a perfect candidate for automation. You can then spend your limited time finding those pesky camouflaged defects you know are still hiding in the system.

Everything runs smoothly until release day, when the developers decide to make a small improvement in the application that should have no real impact. Then the White-Tail Defect strikes and deftly slips by your well-designed defenses.

Here is one example White-Tail Defect. You are testing for field overruns on the string fields and find that the developers have implemented a standardized GUI check that displays a dialog warning to the operator when the field is overrun. It is built into the GUI framework and reliably provides the same dialog when the check is run. You automate the check for the dialog and all is well. Then, a field is modified by a coder that is new to the team and forgets to add the GUI overflow check. It just so happens that your automation never checks the actual value stored in the database or checks the database error logs.  It isn't until after release that the system error shows up in the customer database (☼).

So, how do you hunt a White-Tail Defect? The key is to understand your prey and adjust your tactics to compensate. The white-tail defense is a cognitive trick that plays on the mind's need to see patterns in things. By suddenly breaking out of that pattern, the defect can escape detection. Here are two tactics for making that less likely:

  • Hunt In Packs - You can fool some of the testers some of the time, but a well-coordinated team can catch most of the White-Tail Defects out there. Communication, coordination, and open dialog on changing up your test approaches in a session-based format leave few places to hide.
  • Layer Your Attacks - The White-Tail Defect can slip by at the GUI, or at the database, or at the unit level, but that trick it pulls is not as effective when facing multiple strategies. Mix up tours, steel threads, sessions, quick tests, and automated checks to place multiple barriers in the way of the defect.
Good hunting!

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