melikhanmutlu/testing-patterns

Testing Patterns

Principles for reliable test suites.

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1. Testing Pyramid

        /\          E2E (Few)
       /  \         Critical flows
      /----\
     /      \       Integration (Some)
    /--------\      API, DB queries
   /          \
  /------------\    Unit (Many)
                    Functions, classes

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2. AAA Pattern

| Step | Purpose | |------|---------| | Arrange | Set up test data | | Act | Execute code under test | | Assert | Verify outcome |

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3. Test Type Selection

When to Use Each

| Type | Best For | Speed | |------|----------|-------| | Unit | Pure functions, logic | Fast (<50ms) | | Integration | API, DB, services | Medium | | E2E | Critical user flows | Slow |

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4. Unit Test Principles

Good Unit Tests

| Principle | Meaning | |-----------|---------| | Fast | < 100ms each | | Isolated | No external deps | | Repeatable | Same result always | | Self-checking | No manual verification | | Timely | Written with code |

What to Unit Test

| Test | Don't Test | |------|------------| | Business logic | Framework code | | Edge cases | Third-party libs | | Error handling | Simple getters |

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5. Integration Test Principles

What to Test

| Area | Focus | |------|-------| | API endpoints | Request/response | | Database | Queries, transactions | | External services | Contracts |

Setup/Teardown

| Phase | Action | |-------|--------| | Before All | Connect resources | | Before Each | Reset state | | After Each | Clean up | | After All | Disconnect |

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6. Mocking Principles

When to Mock

| Mock | Don't Mock | |------|------------| | External APIs | The code under test | | Database (unit) | Simple dependencies | | Time/random | Pure functions | | Network | In-memory stores |

Mock Types

| Type | Use | |------|-----| | Stub | Return fixed values | | Spy | Track calls | | Mock | Set expectations | | Fake | Simplified implementation |

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7. Test Organization

Naming

| Pattern | Example | |---------|---------| | Should behavior | "should return error when..." | | When condition | "when user not found..." | | Given-when-then | "given X, when Y, then Z" |

Grouping

| Level | Use | |-------|-----| | describe | Group related tests | | it/test | Individual case | | beforeEach | Common setup |

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8. Test Data

Strategies

| Approach | Use | |----------|-----| | Factories | Generate test data | | Fixtures | Predefined datasets | | Builders | Fluent object creation |

Principles

• Use realistic data
• Randomize non-essential values (faker)
• Share common fixtures
• Keep data minimal

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9. Best Practices

| Practice | Why | |----------|-----| | One assert per test | Clear failure reason | | Independent tests | No order dependency | | Fast tests | Run frequently | | Descriptive names | Self-documenting | | Clean up | Avoid side effects |

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10. Anti-Patterns

| ❌ Don't | ✅ Do | |----------|-------| | Test implementation | Test behavior | | Duplicate test code | Use factories | | Complex test setup | Simplify or split | | Ignore flaky tests | Fix root cause | | Skip cleanup | Reset state |

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Remember: Tests are documentation. If someone can't understand what the code does from the tests, rewrite them.