Test with confidence, code with clarity

Your home for mastering Test-Driven Development through real-world katas and expert guidance.

Browse Katas Learn TDD Fundamentals
TDD Buddy Logo
Latest The Visible Test Suite Is the Ceiling on What the Next Agent Can Deliver

Kata Catalog

Practice TDD with a curated set of real-world katas, each with clear requirements and test cases.

Browse Katas

Guides & References

Learn best practices, naming conventions, and advanced TDD techniques from industry experts.

Explore Guides

Interactive Learning

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

Learn More

Why TDD Matters More in the AI Era

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

  • The verification horizon showed up in the measurements. Two 2026 papers arrived at the same finding from opposite ends: the discrimination power of the visible test suite bounds what any search process converges on. The horizon is real and readable in the numbers.
  • Stronger models widen the gap between visible pass and actually correct. Coincidence-passes cluster on tasks whose suites underspecify the requirement. Model strength that outruns the suite exploits the discrimination gap; it does not close it.
  • Building to the test is what search processes do, not a failure mode to fix. Agents deliver what you check, not what you requested. That is the shape of a reward loop. The lever is the check.
  • Raising the ceiling is suite work. Named scenarios in the domain, property tests where invariants exist, contract tests at every seam the agent cannot author both sides of. The ceiling is a design property, not a dashboard number.

Read the argument: The Visible Test Suite Is the Ceiling on What the Next Agent Can Deliver

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