git:20260404.9bec903 to git:20260404.d174eb3

---

name: testing-python

description: Writes tests following TDD (using pytest and Hypothesis) and BDD best practices. Use when writing unit tests, integration tests, or BDD scenarios.

compatibility: Designed for Claude Code

metadata:

allowed-tools: Read, Grep, Glob, Edit, Write, Bash

argument-hint: [test-scope or component-name]

stability: stable

last-verified-cc-version: 1.0.34

---

# Python Testing

**Target**: $ARGUMENTS

Writes **focused, behavior-driven tests** following project testing strategy.

## Quick Reference

**TDD methodology** (language-agnostic): See `tdd-core` plugin (`testing-tdd` skill)

**Python-specific documentation**: `references/`

- `references/testing-strategy.md` - Python tools (pytest, Hypothesis, inline-snapshot, pytest-bdd)

- `references/tdd-best-practices.md` - Python TDD examples (extends tdd-core)

- `references/bdd-best-practices.md` - BDD methodology with pytest-bdd

## Quick Decision

**TDD (default)**: Use pytest for known cases, Hypothesis for edge cases. Works at unit/integration/acceptance levels.

**BDD (optional)**: Use Given-When-Then for stakeholder collaboration on acceptance criteria.

See `references/testing-strategy.md` for full methodology comparison.

## TDD Essentials (Quick Reference)

**Cycle**: RED (failing test) → GREEN (minimal pass) → REFACTOR (clean up)

**Structure**: Arrange-Act-Assert (AAA)

```python

def test_order_processor_calculates_total():

# ARRANGE

items = [Item(price=10.00, qty=2), Item(price=5.00, qty=1)]

processor = OrderProcessor()

# ACT

total = processor.calculate_total(items)

# ASSERT

assert total == 25.00

```

## Hypothesis Priorities (Edge Cases within TDD)

| Priority | Area | Example |

| ---------- | ------ | --------- |

| CRITICAL | Math formulas | Scores always in bounds |

| CRITICAL | Loop termination | Never hangs |

| HIGH | Input validation | Handles any text |

| HIGH | Serialization | Always valid JSON |

## What to Test (KISS/DRY/YAGNI)

**High-Value**: Business logic, integration points, edge cases, contracts

**Avoid**: Library behavior, trivial assertions, implementation details, default constants, stale fixture patches (see `references/testing-strategy.md` → "Patterns to Remove")

See `references/testing-strategy.md` → "Patterns to Remove" for full list.

## Naming Convention

**Format**: `test_{module}_{component}_{behavior}`

```python

test_user_service_creates_new_user()

test_order_processor_validates_items()

```

## Execution

```bash

make test # All tests

make test_rerun # Rerun failed tests (fast iteration)

make validate # Full pre-commit validation

pytest tests/ -v # Verbose

pytest -k test_user_ # Filter by name

```

## Quality Gates

- [ ] All tests pass (`make test`)

- [ ] TDD Red-Green-Refactor followed

- [ ] Arrange-Act-Assert structure used

- [ ] Naming convention followed

- [ ] Behavior-focused (not implementation)

- [ ] No library behavior tested

- [ ] Mocks for third-party types use spec=RealClass