Testing Python

Python Testing

Target: $ARGUMENTS

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

Quick Reference

Full documentation: docs/best-practices/

• testing-strategy.md - Strategy, what to test, patterns to remove
• tdd-best-practices.md - TDD methodology
• bdd-best-practices.md - BDD methodology

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 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)

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)

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 testing-strategy.md → "Patterns to Remove")

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

Naming Convention

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

test_user_service_creates_new_user()
test_order_processor_validates_items()

Execution

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