Published January 22, 2023
by Doug Klugh

The Need for Speed

Should your software development team use feature branches to isolate changes from each developer or leverage Trunk-Based Development (TBD) to integrate small batches of code frequently as part of everyone’s daily work?  In other words, should you optimize for individual productivity or team productivity?  If you want to deliver software faster and with higher quality, the answer should be obvious.  TBD enables continuous integration, simplifies code merges, and shortens the feedback cycle through frequent automated testing.  Feature branching promotes Continuous Isolation while TBD promotes Continuous Integration.  Although TBD is a new approach for many teams, it is a key component to achieving frequent and continuous delivery.

Feature Branching

Feature branching is an effective method for optimizing individual productivity by isolating each developer's work from the rest of the team.  Each developer works independently without other team members stepping on their toes (or on their code).  However, when it comes time to merge that branch with everyone else's code, it can be difficult — even unmanageable at times.  When that happens, developers tend to do it less often — further compounding the problem.  Infrequent code merges also lengthen the feedback cycle and impede collaboration within the team.  This fosters nothing more than a group of individuals focusing on their own isolated piece.

Trunk-Based Development

Trunk-Based Development optimizes team productivity by integrating everyone's changes frequently, shifting the feedback loop earlier in the development lifecycle.  With continuous integration, code merges are much smaller and, hence, much easier.  Frequent integration enables us to Shift Left (i.e., fail fast) by catching merge conflicts and test failures for the entire codebase much earlier than with feature branches. 

« Without automated testing, continuous integration is the fastest way to get a big pile of junk that never compiles or runs correctly. »

- Gary Gruver, Director of Engineering, HP LaserJet Firmware Division

Supporting Activities

Following are some fundamental practices that facilitate Trunk-Based Development:

Feature Toggleslaunch

Feature toggles are a necessity for Trunk-Based Development.  They enable developers to integrate incomplete code with production code by encapsulating features and infrastructure changes inside switchable software modules.  These switches can be used to easily turn features on or off within any environment.  This will ensure that incomplete features will not break existing functionality and will not be accessible to users until they are ready for primetime.

Unit Testslaunch

Unit tests are also a must-have for Trunk-Based Development.  It is critical that all code changes are verified prior to integrating them with production code.  Not only should the code be verified locally before merging to the trunk, but unit tests should also compose most of the Commit Tests, serving as the entry gate to the deployment pipeline. 

Acceptance Testslaunch

Automated acceptance tests will help to validate the entire system to ensure that new functionality isn't breaking the production build.  And because developers are integrating small batches of code, most failures will be quick to locate and easy to fix. These tests will maintain confidence that the software is fulfilling its purpose, while guarding against wide-spread changes to the system.

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