name: Testing Patterns description: This skill should be used when the user asks to "write tests", "test strategy", "coverage", "unit test", "integration test", or needs testing guidance. Provides testing methodology and patterns.

Testing Patterns and Strategy

Test Types

Test Structure

Arrange-Act-Assert (Technical)

// Arrange: Set up test data
user = User.new(name: "John")
cart = ShoppingCart.new(user)

// Act: Execute code under test
total = cart.calculate_total

// Assert: Verify outcomes
assert_equal 0, total

Given-When-Then (BDD)

given_a_user_with_an_empty_cart
when_the_user_calculates_total
then_the_total_should_be_zero

Test Doubles

Naming Conventions

Technical: test_[method]_[scenario]_[expected]

test_calculateTotal_withEmptyCart_returnsZero

BDD: [method]_should_[behavior]_when_[condition]

calculateTotal_should_returnZero_when_cartIsEmpty

Critical Practices

1. Test happy path first, then edge cases, then errors
2. Edge cases: Empty inputs, max values, nulls, zero, negatives
3. Error cases: Invalid inputs, network failures, timeouts
4. Isolate tests: Each test independent with setup/teardown
5. One assertion per concept: Single logical verification per test
6. Readable names: Tests serve as documentation

Coverage Guidelines

• 80%+ for critical code paths
• Branch coverage more thorough than line coverage
• High coverage does not guarantee bug-free code
• Prioritize meaningful tests over metrics

Anti-Patterns

• Testing implementation - Test behavior, not internals
• Excessive mocking - Use real implementations where practical
• Flaky tests - Control time, randomness, async operations
• Slow tests - Unit tests should run in milliseconds
• Test interdependence - Each test creates its own data