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Latest Refactor Was Always Where Compounding Lived

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Why TDD Matters More in the AI Era

The bar for "good tests" just moved. Agents made it non-optional.

  • Red and green were always the visible two thirds. Refactor produced no shippable artifact, so teams treated it as optional. That treatment was always wrong. The step with no green bar is the step that paid the rent.
  • Codebases that compound did the refactor pass. Codebases that accrete did not. The difference is invisible per PR and overwhelming over a year, which is why most teams never noticed it until a routine change cost three sprints.
  • Agents skip refactor by default. No deliverable, no green-bar reward, no prompt extension, context tokens spent elsewhere. The step humans cheated on under time pressure is the step the agent omits under context pressure.
  • Refactor decides the codebase's shape. Naming, abstraction, alignment with the domain. The decisions that matter are made in the rewrite, not in the original write. The first version is plausible. The third version is the design.

Read the argument: Refactor Was Always Where Compounding Lived

The Bar Moved

Old bar

Tests exist and pass. Good enough for humans with context.

New bar

Scenario names · builders · domain types · ubiquitous language. The test suite is the interface agents operate against.

Rich TDD isn't a style preference anymore. It's infrastructure for compressed-role, AI-augmented teams.

TDD Gears

Shift gears based on context, not habit

TDD Gears model showing Low, Medium, High, and Reverse gears for test-driven development

Low Gear

New territory. Build context. Small steps. Learn the shape of the problem before solving it.

Medium Gear

Patterns emerge. Apply design principles. Let the tests guide you toward better abstractions.

High Gear

Known patterns. Follow existing architecture. Move fast because the structure is already proven.

Reverse Gear

Wrong direction. Back up. Delete the test. Try a different approach. This isn't failure — it's steering.

Learn More About TDD Gears