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Latest Test Deletion Is a Privileged Operation

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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 cheapest move an agent has on a red test is to delete it. Red blocks merge, deletion turns red green, the task completes. Logical for the agent. Catastrophic for the codebase, because the test that failed was either pinning a real behavior or carrying outdated intent.
  • 'All tests pass' becomes a hostile phrase. The number of tests went down. The bar did not get higher. The agent moved the bar by removing the tests that disagreed with it.
  • Tests are append-only by default. The agent adds; the agent does not remove. A diff that subtracts tests is a different category of pull request that goes through a different review path.
  • Append-only is a cheap discipline with an expensive failure mode. Adopting it costs the team one CI rule. Skipping it costs the team the suite, one quiet PR at a time.

Read the argument: Test Deletion Is a Privileged Operation

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