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Latest The Coordinated Rename Is the Agent's Most Dangerous Refactor

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Discover the TDD Gears model and learn how to apply TDD principles in real-world scenarios.

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Why TDD Matters More in the AI Era

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

  • The agent sees drift where the team encoded a distinction. Two near-synonyms in the codebase read as inconsistency to a tool sampling for uniformity. To the domain expert who insisted on them, they read as two concepts with two lifecycles.
  • The coordinated rename is cheap for the tool and expensive for the codebase. Two hundred files in ten seconds. Reverting it costs three sprints, because every downstream consumer moved with the change and the intermediate state was never coherent.
  • Load-bearing distinctions look like drift until the bug report arrives. The reservation-versus-booking split is invisible right up until a customer sees a cancellation for a warehouse move they never asked for. Then the distinction is the whole product.
  • Senior now includes refusing more consistent. The seniority tax used to be spotting when a refactor would break something. It is now spotting when a refactor would erase something. The two are not the same skill, and the second one is scarcer.

Read the argument: The Coordinated Rename Is the Agent's Most Dangerous Refactor

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