Code Review as a Great Tool in the Agile Toolbox Matthias Sohn, Stefan Lay

Agenda How we became agile What we learned from Open Source Why we embraced Code Review How we scale up agile with Open Source processes

Agile Feedback cycles Source:

Agile Feedback cycles Pair Programming Ralph and Karsten hacking on E4

Agile Feedback cycles Test Driven Development

Agile Feedback cycles Continuous Integration Q: Who is who?

Agile Feedback cycles Code Review? Sometimes formal Code Review (Fagan style inspection) Pair Programming is considered to be more agile Higher bandwidth (Faster feedback) Leads to faster integration than Code Review Individuals and interactions over processes and tools

Agile Software Engineering Engineering practices are key SAP trained its developers > 4000 participants 1 week training 3 weeks coaching Focus on Scrum Pair programming Test Driven Development Continuous Integration Acceptance Tests

Code Review in Open Source Maintainer Hierarchy / Contributors Public peer review on mailing list Committer / Contributor model Public peer review Patch in Bugzilla Gerrit Github

Code Review vs. Pair Programming

Code Review leads to small, self-contained increments ensures that ideas can be understood from code leads to review discussions visible to everybody leaves room to develop alternative solutions Ideal complement to Pair Programming which is great to explore unknown terrain onboard new developer combine complementary skills

Code Review is asynchronous Can be done when there is time The whole team can review (also external reviewers) Review takes time, but also leaves time This leads to parallel workflow Git perfectly supports this Some aspects can be automated Rule checking Build and test Deployment to staging environment All checks happen before submit

Code Review Best Practices Small changes are much easier to review A change should logically do one thing (not many) No change shall break build or tests Split big changes into series of digestible changes - These changes depend on each other - Last change should switch the new feature on Commit message should explain Why - The What should be obvious from the code change

Code Review and Scrum Successful code review required for a task to be finished Many Done Criteria already checked during code review Make review visible on Scrum Board Reserve time for review Everybody should review

Code Review and Scrum Scrum Board StoryBug FixReviewStory AStory BStory C … Open In Progress In Review Done

Code Review with Git and Gerrit Gerrit is a Code Review system based on JGit Also serves as a Git server Adding access control and workflow Used by Android Eclipse Google, QualComm, SAP, WikiMedia…

Code Review with Git and Gerrit

Gerrit usage at SAP started 2010 Projects: > Users: > Changes: > Run by a small team of developers (us) Training is important (> 400 developers) Recently Git and Gerrit were approved as standard infrastructure

Scaling Agile with Open Source Processes Agile processes work great for small teams Collaboration between teams of a large project? High level planning of cross team topics still necessary Open Source like processes can replace detailed top- down planning Contribute to components owned by other teams Review relevant changes of other teams Scale up Pair Programming -> Hackathons

Contributions between teams Find project information easily Standardized infrastructure Contributor Guide

Finding project info

Finding project info - Skalli

Standardized infrastructure git clone mvn clean install Eclipse CBI:

Project specific Standardized Contributor Guide Where to get the sources How to setup the project How to build Review process Communication channels Correction Process Coding conventions How to test Review rules …

Conclusion Code Review brings additional value to agile teams Git and Gerrit help a lot Improves collaboration within and between teams Standardization helps to scale

Questions & Answers

Agile Manifesto Individuals and interactions over processes and tools Working software over comprehensive documentation Customer collaboration over contract negotiation Responding to change over following a plan In a complex and changing environment feedback is key!