Identifying The Most Important Parts Of A Codebase

In this video, we explore how a strong test plan benefits not just the immediate code review process but also long-term codebase understanding and team efficiency. As engineers join new teams or revisit legacy code, test plans become invaluable guides for understanding and validating past changes.

Key Takeaways:

• We use test plans to unlock team knowledge: In large codebases, no one fully understands every part of the system. A clear test plan helps future engineers (and our future selves) grasp what a change does and why it was made.

• We prioritize hotspots over ancient code: When onboarding to a team, we focus on recent changes in active areas of the codebase—not the 1,000 untouched lines at the top. Test plans tied to recent diffs help us make sense of these hotspots quickly.

• We support testability with repeatable artifacts: Whether it’s a video, screenshot, or command-line script, we include a way to replicate and verify our changes. This ensures others can validate functionality easily and efficiently.

• We aim for speed and clarity: For front-end work, visual demos (videos or GIFs) help reviewers instantly see the impact. For backend or logic-heavy changes, unit tests and integration scripts are more scalable and maintainable.

• We build infrastructure for long-term velocity: Investing early in test infrastructure—like command-line test runners—makes it easier to validate changes quickly and helps teams move faster as the codebase grows.

Ultimately, we think of test plans not just as review aids, but as living documentation and a key onboarding tool for future engineers working in our code.