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The Ultimate Feedback Loop: How We Decreased Customer Reported Defects by 80%

November 17, 2017

The Ultimate Feedback Loop: How We Decreased Customer Reported Defects by 80%

“In God we trust; all others bring data.” W. Edwards Deming

A defect reported by your customers is the most expensive one. Beyond pure money loss, those defects are an embarrassment for any organization. They passed all the quality gates. But the greatest cost that cannot be measured easily is the loss of reputation. It comes as a great surprise then, that almost no company investigates the defects reported by its customers. The companies try to quickly patch the problem and move forward. It’s a shame as a great deal knowledge can be gained about the system that produced those defects.

We’ve analyzed more than two years of customer reported defects. Even though we thought that each defect is unique, some obvious patterns emerged quickly. We were able to debunk widely believed software dogmas that were not working for us. We figured out which of the techniques were helping us or not to lower the defects count: Following the software testing pyramid guidelines? Switching the backend from dynamically typed language to static one? Writing a simple unit test, where there was none? Writing a simple integration test, where there was none? Focusing test engineers to use specific techniques? Using static code analysis? Determining the typical profile of a method that’s likely to contain an error? The end result: we decreased customer reported defects by 80%.

I’ll share Komfo's experience in building a simple framework for analyzing defects as well as tips and tricks so that you can build a similar program in your organization.


November 17, 2017

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  1. “If a tree falls in a forest and no one

    is around to hear it, does it make a sound?” If a defect goes unnoticed by customers, is it really a defect? @EmanuilSlavov
  2. Tester Defect Found Defect Resolved Defects found after this line

    are way more expensive to fix. Support Customer Developer All the defenses were bypassed The most expensive defects Reputation loss hard to measure Manager @EmanuilSlavov
  3. 38%of all the defects were regressions Any automated test would

    have alerted us before they reach production. @EmanuilSlavov
  4. 13%of the defects could have been caught if a simple

    unit test have been written @EmanuilSlavov
  5. With unit test defect detection “yield” so low, which methods

    should we test? 72%of the defects were in methods with complexity 3 and above 82%of the defects were in methods with more than 10 lines of code @EmanuilSlavov
  6. 36%of the defects could have been realistically caught on API

    level (and not on unit tests level) @EmanuilSlavov
  7. public function loadCursor($channel_id, $from, $to) { $collection = $this->getMongoCollection(); $this->applyChannelId($channel_id);

    $this->applyTimeRanges($from, $to); $this->cursor = $collection->find($this->filter); } public function loadCursor($channel_id, $from, $to) { $collection = $this->getMongoCollection(); $this->applyChannelId(urldecode($channel_id)); $this->applyTimeRanges($from, $to); $this->cursor = $collection->find($this->filter); } @EmanuilSlavov
  8. 30%of the defects can never be realistically detected in-house, only

    in the “real world” Edge Cases Configuration Issues Unintended Usage Incomplete Requirements Unit API UI @EmanuilSlavov
  9. 31% of the defects are detected less than one month

    after they are introduced in the codebase @EmanuilSlavov
  10. 51% of the defects are detected less than two months

    after they are introduced in the codebase @EmanuilSlavov
  11. 2.3%of the defects could be detected by custom static code

    analysis PHP: linter, HHVM, custom checks Java: The Sonar Suite, FindBugs JavaScript: ESLint @EmanuilSlavov
  12. 6%of the backend defects could be avoided by switching from

    PHP to Java. (but Java has hidden costs) @EmanuilSlavov
  13. 5% of the bugs were caused by me Developers should

    fix their defects and learn from the experience. @EmanuilSlavov
  14. At least one automated test written per method Manual sanity

    check even the smallest fixes Mandatory code reviews Test with boundary values @EmanuilSlavov
  15. Weird data generator for all automated tests Monitor exceptions after

    each automated tests run Fast interration tests - from 3 hours to 3 minutes Monitor and immediately fix errors in production @EmanuilSlavov
  16. 10 20 30 40 Q3/14 Q4/14 Q1/15 Q2/15 Q3/15 Q4/15

    Q1/16 Q2/16 Q3/16 Q4/16 Q1/17 Java Backend Fast Tests Monitor Java Code Reviews Monitor JS Weird Test Data Generator Check for exceptions after test Monitor PHP Lines of Code 35000 70000 105000 140000 Q3/14 Q4/14 Q1/15 Q2/15 Q3/15 Q4/15 Q1/16 Q2/16 Q3/16 Q4/16 Q1/17 Defects Count @EmanuilSlavov
  17. Allocate time Track customer reported defects Defect id in the

    commit message Investigate immediately Independent analysis Figure which metrics to track @EmanuilSlavov