448: Other Uses for Tests

What It Covers

Stephanie and Joel explore how test suites serve purposes beyond verification: as learning tools for unfamiliar code, living documentation, code review aids, design feedback mechanisms, and accountability measures for shipping reliable features.

Key Questions Answered

• •Tests as learning tools: Writing tests for unfamiliar legacy code forces intimate understanding of edge cases and system behavior, making developers experts in complex areas teammates avoid. Backfilling test coverage reveals coupling issues faster than reading code alone.
• •Dependency graph decomposition: Break large features into leaf-node tasks with no blockers, ship each independently to production, then work backward to root. This approach transformed one risky multi-week initiative into 19 shippable PRs that maintained team velocity throughout.
• •Test-first code review: Reading test files before application code in pull requests provides context about intended behavior and edge cases, primes reviewers for what's coming, and increases confidence that last-minute changes didn't introduce breaking bugs before deployment.
• •Tests enable experimentation: A passing test suite acts as a safety net for trying multiple implementation approaches. Developers can discard entire code solutions while keeping tests, then attempt different designs knowing the specification remains constant and verifiable throughout iteration.