name: test-design description: > Test design and strategy skill for comprehensive testing. Use when: designing test cases, planning testing strategy, writing unit/integration/e2e tests, or improving test coverage. Triggers: test design, test strategy, unit test, integration test, e2e test, TDD, test coverage, test plan, test case design. Provides: testing pyramid guidance, test case templates, test categorization, mocking strategies, and test execution frameworks.

Test Design Skill

A structured approach to designing tests that give confidence without excessive maintenance burden.

Core Philosophy

Test behavior, not implementation. Tests that couple to internal implementation details become fragile and refactor-resistant. Aim to test what the code does, not how it does it.

The best test is the one that fails when something breaks, and passes when everything works. Perfect coverage means nothing if tests don't catch real bugs.

Testing Pyramid

        ┌─────────┐
        │   E2E   │  ← Few, slow, high confidence
       ┌┴─────────┴┐
       │ Integration│ ← Some, medium speed
      ┌┴───────────┴┐
      │    Unit     │ ← Many, fast, granular
      └─────────────┘

Unit tests form the base — fast, isolated, cover individual functions. Integration tests verify components work together. E2E tests validate complete user journeys.

Test Case Design

Arrange-Act-Assert (AAA) Pattern

def test_withdraw_amount_exceeds_balance():
    # Arrange
    account = Account(balance=Decimal("100.00"))

    # Act
    result = account.withdraw(Decimal("150.00"))

    # Assert
    assert result.is_failed()
    assert account.balance == Decimal("100.00")  # unchanged

Given-When-Then (GWT) Pattern

Feature: Account Withdrawal

  Scenario: Withdrawal amount exceeds balance
    Given an account with balance $100
    When I withdraw $150
    Then the withdrawal is rejected
    And the balance remains $100

Test Categories

🔴 Happy Path Tests

• Verify the main success scenario works
• At least one per feature/function

🟡 Edge Case Tests

• Boundary values (0, -1, max integer)
• Empty/null inputs
• Rare but possible conditions

🟡 Error Case Tests

• Invalid inputs
• Missing dependencies
• Permission denied scenarios

🟢 Edge/Extreme Cases

• Very large inputs
• Very small inputs
• Unicode/special characters
• Concurrent access

Test Doubles (Mocks/Stubs/Fakes)

Rule: Prefer real objects over mocks when practical. Mocks hide integration problems.

Test Naming Convention

test_<unit>_<scenario>_<expected_result>

Examples: - test_user_create_with_valid_input_succeeds - test_user_create_with_duplicate_email_fails - test_order_cancel_after_shipment_refunds_full_amount

Coverage Targets

Note: Coverage is a guide, not a goal. 100% coverage with shallow tests is worse than 70% with meaningful assertions.

Test Execution

Unit Tests

Run frequently during development (every save).

# Go
go test ./...

# Python
pytest tests/unit/ -v

# TypeScript
npm test -- --coverage

Integration Tests

Run before PR, after unit tests pass.

# Start dependencies
docker-compose up -d

# Run integration suite
pytest tests/integration/ -v
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E2E Tests

Run on CI against deployed environment.

# CI/CD pipeline
npm run test:e2e -- --specs=critical-paths

Test Data Management

Strategies

1. Factories/Fixtures — Create test data on demand
2. Seeded Data — Deterministic test datasets
3. Randomized Data — Fuzz testing with random inputs
4. Snapshot Testing — Verify serializable outputs

Best Practices

• Tests should be independent (no shared state)
• Each test should clean up after itself
• Use meaningful data, not magic values
• Avoid test interdependencies

File Structure

test-design/
├── SKILL.md
└── references/
    ├── test-case-templates.md
    ├── testing-pyramid.md
    ├── mocking-strategies.md
    ├── test-naming-conventions.md
    └── per-type/
        ├── unit-test-guide.md
        ├── integration-test-guide.md
        └── e2e-test-guide.md

这是一个质量不错的测试设计技能包，内容全面且实用。优点在于覆盖了从单元测试到端到端测试的核心知识点，提供了清晰的测试策略框架和多语言代码示例，Mocking 策略讲解尤为详细。不足之处是缺少图表等可视化辅助，文档中提到的一些文件实际不存在，部分内容略显重复。对于需要学习测试设计原则和实践的开发者来说，这是一个值得参考的资源。