| name | tdd-python |
| description | Python Test-Driven Development expertise with pytest, strict red-green-refactor methodology, domain-first modeling (DDD), principled DRY discipline, FastAPI testing patterns, and Pydantic model testing. Use when implementing Python features with TDD, writing pytest tests, testing FastAPI endpoints, developing with test-first approach, modeling domain concepts, refactoring duplication, or when user mentions 'Python TDD', 'pytest', 'FastAPI testing', 'red-green-refactor', 'Python unit tests', 'test-driven Python', 'domain modeling', 'value object', 'ubiquitous language', 'DRY', or 'Python test coverage'. |
| skills | ["code-style","api-design-standards","test-generation"] |
| allowed-tools | ["Read","Write","MultiEdit","Bash","Grep","Glob","TodoWrite"] |
TDD Python Skill
Python Test-Driven Development following strict red-green-refactor cycle with pytest — sharpened by DDD at Red (model the domain first) and DRY at Refactor (deduplicate same-concept repetition only).
Description
Systematic Python implementation using TDD methodology. Tests are written first and drive design; domain vocabulary drives the tests; duplication is removed only when the same concept repeats, not when syntax coincidentally looks alike.
Discipline Layering
- Before Red — Model the Domain: Name the entity, value object, or aggregate in the business's language. Decide entity vs. value object. Reject primitive obsession — wrap
str/int in EmailAddress, Money, NewType, or pydantic.BaseModel when they carry rules. Keep domain logic out of FastAPI routes.
- Red: Write a failing test. Name it in domain terms (
test_rejects_refund_when_amount_exceeds_daily_limit) — never mechanical (test_returns_false).
- Green: Minimal code to pass. No speculative abstractions.
- Refactor — DRY with discipline: Deduplicate only when the same domain concept appears ≥3 times with the same meaning. Three similar lines beats a premature abstraction. Promote recurring primitives to value objects. When uncertain, inline.
What's Included
- Examples: Python TDD cycles, FastAPI TDD, Pydantic model TDD, value-object modeling
- Reference: pytest patterns, Python testing best practices, branded-type idioms (
NewType, frozen=True)
- Templates: pytest templates, TDD workflows
Use When
- Implementing Python features with TDD
- Modeling domain concepts (entities, value objects, aggregates)
- FastAPI endpoint development (keeping domain rules out of routes)
- Pydantic model development
- Refactoring duplication after a green test
Related Agents
Skill Version: 1.1
