1.5Trunk-Based Development in Detail

Trunk-based development takes GitHub Flow to its logical extreme. Feature branches live less than a day -- often less than a few hours. Developers commit to main frequently, often multiple times per day.

main ──****************************──── (continuous stream of small commits)
       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
       Very short-lived branches (hours, not days)

How Trunk-Based Development Works

1. main (the "trunk") receives commits continuously.
2. Short-lived branches exist only for the duration of a single code review, typically hours.
3. Feature flags replace feature branches. Incomplete features are deployed behind flags, not on separate branches.
4. Every commit must pass all tests. There is no stabilization period.

Implications for Testing

• Every commit must pass all tests: The pipeline must be fast and reliable. There is no "fix it later" window.
• Feature flags replace feature branches: Incomplete features are deployed behind flags, which means your tests must be flag-aware.
• Testing shifts left dramatically: QA reviews requirements and writes tests before development starts, because there is no time to catch up later.
• Flaky tests are existential threats: A flaky test that blocks main blocks the entire team. Fix flaky tests immediately, with the same urgency as a production incident.

When Trunk-Based Development Works

• The team has high test automation maturity (>90% of tests automated).
• CI pipeline completes in under 10 minutes.
• Feature flags are available and well-managed.
• The team has strong code review discipline.
• Engineers are experienced and disciplined about small, incremental commits.

Pro Tip: Trunk-based development is not "no branches." It is "very short-lived branches." The goal is to minimize divergence from main, not to eliminate branches entirely.