Software Engineering at Google
Fergus Henderson (PDF, via Hacker News):Write access to the repository is controlled: only the listed owners of each subtree of the repository can approve changes to that subtree. But generally any engineer can access any piece of code, can check it out and build it, can make local modifications, can test them, and can send changes for review by the code owners, and if an owner approves, can check in (commit) those changes. Culturally, engineers are encouraged to fix anything that they see is broken and know how to fix, regardless of project boundaries.
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Most larger teams also have a “build cop” who is responsible for ensuring that the tests continue to pass at head, by working with the authors of the offending changes to quickly fix any problems or to roll back the offending change. (The build cop role is typically rotated among the team or among its more experienced members.) This focus on keeping the build green makes development at head practical, even for very large teams.
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All code used in production is expected to have unit tests, and the code review tool will highlight if source files are added without corresponding tests. Code reviewers usually require that any change which adds new functionality should also add new tests to cover the new functionality.
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Most software at Google gets rewritten every few years.
