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TDD Implementation

This skill implements a feature using strict Test-Driven Development, based on the plan from /thorough:plan.

Step 1 — Locate the plan

Search the conversation history for the feature plan from /thorough:plan. Also read REQUIREMENTS.md for project context. If no plan exists, tell the user to run /thorough:plan [feature] first.

Step 2 — Implementation order

Break the plan into implementable units ordered by dependency:

1. Project setup (scaffold, dependencies, config)
2. Data model (schema, migrations, ORM setup)
3. Core business logic (one user story at a time)
4. API routes / server-side logic
5. UI components and pages
6. Integration between layers
7. Edge cases, error handling, empty states

Present this order and get confirmation before starting.

Step 3 — Red-Green cycle (for each unit)

1. Write failing tests that describe the expected behavior from the spec.
2. Run them. They must fail. If they pass, investigate — the test is wrong or the feature already exists.
3. Write minimal code to make tests pass.
4. Run tests again. All must pass.
5. Refactor if needed, keeping tests green.

Test quality rules

• Assert specific values, not just truthiness. expect(result.count).toBe(5) not expect(result).toBeTruthy().
• Test boundary conditions: if checking > 0, test with 0, 1, and -1.
• Verify side effects: don't just check return values — confirm state changes.
• Ensure operator sensitivity: a test should fail if > becomes >=.

Step 4 — Mid-implementation uncertainty

If something becomes unclear during coding: stop and ask. Use AskUserQuestion to resolve it. Do not guess, do not write a "basic version" to iterate on, do not add a TODO.

Step 5 — Verification

After all units are implemented:

1. Run the full test suite.
2. Verify against the success criteria from the plan.
3. List any deviations from the plan and explain why.
4. Present a summary of what was built.

Never consider implementation complete with failing tests.