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tdd-python

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'.

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greyhaven-ai/claude-code-config
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April 18, 2026 at 01:43
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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 - `tdd-python-implementer` **Skill Version**: 1.1
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