Testing

Testing

Announce at start: "Following the testing skill for test design."

Core Rule

Test behavior, not implementation. Tests must survive refactoring.

Test Pyramid

Write tests in this ratio:

Writing Tests

1. Structure: Arrange-Act-Assert

Every test follows AAA:

def test_order_total_includes_tax():
    # Arrange
    order = Order(items=[Item(price=100)])
    tax = TaxCalculator(rate=0.08)

    # Act
    total = order.calculate_total(tax)

    # Assert
    assert total == 108.00

2. Naming: Describe Behavior

3. Data: Explicit, Not Magic

• Use explicit test data in each test
• Avoid shared fixtures with hidden setup
• Use builder patterns for complex objects

Coverage Priorities

Critical paths (payments, auth, data mutations) always require 100% coverage.

AI-Specific Rules

• Verify AI-generated tests actually assert something meaningful
• Check that tests fail when the code is wrong (not just pass when right)
• Use fakes over mocks where possible — more realistic behavior
• Never test private methods directly
• Never share mutable state between tests

Bug Fix Tests

Every bug fix must include a regression test that:

1. Fails before the fix (proves the bug)
2. Passes after the fix (proves the fix)
3. Prevents recurrence

Related Skills

Deep Reference

For principles, rationale, anti-patterns, and examples:

• guides/testing-strategy/testing-strategy.md
• guides/testing-ai-code/testing-ai-code.md

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