Quality Up FrontHow to spend less time debuggingLars Jarnbo Pedersen Co-founder Switch-Gears ApS

About me

Partner at Switch-Gears ApS● Transitioning companies from old

development tools to modern Open Source ones

Been working for Nokia 2001-2012● Release manager for S40 software for many

years● Part of a small team that introduced Git,

Gerrit and Jenkins to S40 development resulting in BIG productivity gains

Pain in SW Development

50%of developer time is spent finding and fixing bugs*

*http://www.businessweekly.co.uk/hi-tech/14898-software-bugs-cost-more-than-double-eurozone-bailout

COST OF BUGS

Why?

Programming is hard…● you have to map the problem domain to

the programming language in use● its usually a collaborative effort● time pressure● best practises are not shared

Bugs are discovered late…● context is lost● often it is not the programmer who

introduced the bug, who is fixing it

Luckily

90%of the bugs can be

caught during development*

*http://www.codinghorror.com/blog/2006/01/code-reviews-just-do-it.html

COST OF BUGS

Because

Average defect detection rate is 25 percent for unit testing, 35 percent for function testing, and 45 percent for integration testing. [McConnell93]

Furthermore, the average effectiveness of design and code inspections are 55 and 60 percent. [McConnell93]

How?

Peer Code Review

● Beneficial for “quality of review” if the author pre-reviews and leaves comments for subsequent reviewers [Cohen2006]

● The longer a reviewer spends on the initial read-through, the more defects will ultimately be found [Uwano2006]

● Defect detection drops dramatically after ~60 minutes, to zero after ~90 minutes [Dunsmore2000]

Peer Code Review

● Long methods and loops are very time consuming to understand [Uwano2006]

● Review 100 to 300 LOC at a time, in 30-60 minutes chunks, with a break between each sitting [Cohen2006]

● Spend at least 5 minutes reviewing a single line of code [Cohen2006]

● Limit reviewing to 1 hour per day [Ganssle2009]

Mental Model

Development Process

Platform Quality

Platform Knowledge

+

=

Increase Platform Knowledge

Write Readable Code!!!● You spend much more time reading code than

writing it - so make it nice to read!● Refactor if necessary● Include test-code

Commit changes in logical units● Always commit working code● Never mix error-fixes and feature implementations

Write descriptive commit messages● Make sure the reason for the change is clearly

explained

Optimize Development Process

Make it simple on the developers,● allow multiple workflows at the developers

desk● don’t let the release/integration process

stop the development flow● minimize manual process steps

while keeping a strict process● automatically build and test all commits● require code-review of all commits

This is NOT rocket science!

So why don’t we do it already?● Waterfall development● Code Reviews are perceived expensive● Last generation of tools do not support

this easilyWhat is enabling it now?

● Agile development● New breed of Open Source tools

Git / Gerrit / Jenkins

Git (DVCS) changes everything!

Git is NOT subversion++● all operations except for push/pull are

local => well suited for continuous integration

● allows for multiple workflows○ development○ integration / releasing

● is a first class citizen during development AND debugging!○ gitk for code analysis○ git bisect for debugging

Gerrit

A developer codes - and asks for feedback

Peer Code Review

Another developer reviews and comments

Continuous Integration

Actually you saw it in action already!Good tools help you without getting in the way

Our experiences - Low Gain Example

[Anonymized and obscured]

Our experiences - High Gain Example

[Anonymized and obscured]

References

Books● Code Complete: A Practical Handbook of Software Construction, Second

Edition by Steve McConnell (Jun 16, 2004)● Clean Code: A Handbook of Agile Software Craftsmanship by Robert C.

Martin (Aug 11, 2008)

Articles● SCM Ranking (Switch-Gears)● CI Ranking (Switch-Gears)● Best Kept Secrets of Peer Code Review (Smartbear)● The Cost of Software Bugs (Business Weekly)● Code Review - Just Do It (Coding Horror)

Videos● Linus Torvalds on Git (Google TechTalk) ● Development at the Speed and Scale of Google (InfoQ)