tdd-slice

name	tdd-slice
description	Use when implementing a feature or bugfix with test-first development and you want a disciplined red-green-refactor loop in small vertical slices.

TDD Slice

Write one failing behavior, make it pass with minimal code, then repeat. Tests should verify observable behavior through public interfaces.

Quick start

• Pick one behavior that matters now.
• Write one failing test for that behavior.
• Implement the smallest change that makes the test pass.
• Re-run the test immediately.
• Stop the slice with explicit proof before expanding scope.

Workflows

1. Use this skill when:
   • implementing a new feature with clear behavior targets
   • fixing a bug that should gain a regression test
   • changing logic-heavy code where fast feedback matters
2. Do not use it when the environment makes tests impossible and no practical feedback loop exists yet.
3. Choose the highest-value behavior to verify first.
4. Write exactly one failing test for that behavior.
5. Implement the smallest change that makes that test pass.
6. Re-run the relevant test or smallest proving test set.
7. Refactor only after green.
8. End the slice by stating:
   • behavior covered
   • proof run
   • next slice or stop condition

Hard gate

• Use vertical slices, not horizontal batches of tests.
• Prefer integration-style tests over implementation-coupled tests.
• Do not add speculative behavior for future tests.
• Name tests in the project's domain language when available.
• Do not call the slice complete without one failing-then-passing proof.

Further reading

• ../plan-griller/SKILL.md - use first when the change is too ambiguous to choose the next test safely
• ../diagnose-loop/SKILL.md - use when the test or runtime behavior is failing for reasons you cannot yet explain