Understanding why a defect existed.
WHY IT MATTERS
Fixing a defect prevents that defect; understanding the cause prevents the class.
WHAT TO ASK
How was it introduced? Why did it reach this stage undetected? What would have caught it earlier?
WHY THE SECOND QUESTION MATTERS MOST
The escape is frequently more informative than the defect.
WHAT COMMON CAUSES ARE
Requirements ambiguous or missing A case nobody considered A change with unforeseen effect Insufficient testing of that area Environment differences Time pressure
WHAT TO DO ABOUT EACH
- Ambiguity: improve requirement review
- Unconsidered cases: improve test design
- Unforeseen effect: improve regression coverage
- Environment: reduce differences
WHAT TO ADD AFTER EVERY SIGNIFICANT DEFECT
A test that would have caught it.
WHY
It prevents recurrence, and it grows the suite where defects actually occur.
WHAT TO TRACK
Causes, categorised, over time.
WHAT PATTERNS REVEAL
Where the process is weak.
WHAT TO AVOID
Analysis assigning blame.
WHY
It produces defensiveness and concealment, which prevents learning.
WHAT TO FOCUS ON
The conditions that allowed it.
