How could the concept of Zero Defect improve the quality of the software that is developed and deployed to customer.

1. Bugs first,
even before new Features?
or
Zero Defect
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2. What is “Bugs first”?
 Alternative one: Fix bugs immediately
 “Fix all bugs before starting next user story.”
 Sprint: “User story can be closed only when all bugs have been fixed.”
 Kanban: “Work in progress (WIP) can only be closed when all bugs have been fixed.”
 Alternative two: Fix bugs in sprint
 “No bugs at end of sprint.”
“No bugs as done-done criteria.”
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3. Potentially shippable product
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4. Why?
 Bug-free, stable software makes a tremendous impression, especially when
you demonstrate intermediate versions.
 Closer to full product quality in each sprint
Higher Product quality
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5. Why?
 Each unsolved bug is a piece of work that need to be done “later”
 Reducing bugs leads to less “later work”
 The need of stabilization sprints after “end of development” decrease
 Velocity measurements become more true
 In sum: Release planning becomes much more reliable!
Higher predictability
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6. Finding Bugs early
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7. Finding Bugs early
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8. Zero Defect
 Maintain the software at highest quality during the development
 Improving quality actually reduces development time
 Programmer writes between eight and twenty lines of code a day;
 the rest of the day is usually spent on debugging
 Studies done at e.g. NASA, IBM, have shown that better QA leads to shorter
schedules.
 An IBM study concluded that software projects that make quality a top
priority typically have the shortest schedules, the highest productivity, and
even the best sales.
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17. Ten basic rules – (1-5)
 Test your product every day as you develop it, and fix defects as soon as you find them.
 Gated checkin, 20 minute build, Daily Build
 Once you find a defect, fixing it becomes your number one priority, and you avoid writing any new code until the defect is 100%
eliminated.
 Review your code regularly.
 Code inspections are far more effective than testing
 Code reading detected almost twice as many defects per hour as testing
 Rewrite poor-quality modules.
 Typically you find that 20% of your routines are responsible for 80% of your errors
 Assume full responsibility for every bug.
 95% of all software defects are caused by the programmer. Only 1% of defects are hardware errors, and the remaining 4% are
caused by the compiler, the OS, or other software
 Never dismiss a potential bug; find out the exact cause of any anomaly, especially if irregular
 Handle change effectively.
 Carefully consider how each change will impact your pre-existing code. Poor integration of unanticipated features is a major cause
of defects
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18. Ten basic rules – (6-10)
 Rewrite all prototyping code from scratch.
 Rapidly prototyped features that slip into the final product are a major source of bugs because they are not subject to the same
quality standards as the rest of the code.
 Set QA objectives at the beginning of every project.
 Set QA goals, e.g. performance, quality standards, coding guidelines
 Don't rush debugging work.
 50% of all bug fixes are done incorrectly the first time, often introducing new bugs in the process.
 Take the time to understand the source of the bug.
 Write UT first to verify your correction.
 Treat the quality of your code at the same level of importance as the quality of your product.
 Rate your code on a scale of one to ten for overall quality.
 Are you sure that it is above 8, if not rewrite it.
 Learn from every bug; each one represents a mistake that you made.
 Learn why you made each mistake
 Adopt simple coding conventions to avoid common bugs, e.g. initialize each variable, release memory, try/catch, comment your code
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19. Accumulation of “Undone”
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preparation development
Undone Undone
Undone
Stabilization
Iterations
Planned
Release
Actual
Release
Undone
Unknown amount
of undone work !
(Ken Schwaber)

20. Open Bugs Compared
 Waterfall compared to “Bugs First”
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21. Why? - Faster Learning
 Fast feedback enables fast learning
 Improve coding practices
 Improve system knowledge
 Improve domain knowledge
 Additional bugs can be avoided
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22. Why? - Less total effort
 The earlier a bug is fixed, the less is the administrative cost
 Fix bugs as long as the code is still fresh in mind – is faster
 Fix bugs before the code has developed further – is easier
 A lot of time can be saved in system integration and test – expensive test environments
can be better used
 Each sprint provides a stable platform for the next one
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23. If you see a problem  fix it!
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24. Questions?
If (unclear == true) then askme();
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