Testing Strategies & Methodologies

Test Pyramid

        UI/E2E Tests
       /            \
      /              \
   Integration Tests
    /                \
  /                  \
Unit Tests

• Unit Tests: Fast, isolated, low-level (60%)
• Integration Tests: Component interactions (30%)
• E2E Tests: Full system workflows (10%)

Testing Types

Unit Testing

• Test individual functions/methods
• Mocking dependencies
• Fast execution
• Examples: Jest, Pytest, Mocha

Integration Testing

• Test component interactions
• With real databases/services
• Slower than unit tests
• Examples: Postman, Supertest

End-to-End Testing

• Complete user workflows
• Browser automation
• Slowest but most realistic
• Examples: Cypress, Selenium, Playwright

Property-Based Testing

• Generate random inputs
• Verify invariants hold
• Find edge cases
• Examples: Hypothesis, QuickCheck

Contract Testing

• Verify API contracts between services
• Consumer and provider sides
• Microservices testing
• Examples: Pact, Spring Cloud Contract

Chaos Engineering

• Inject failures intentionally
• Test system resilience
• Find weak points
• Tools: Chaos Toolkit, Gremlin

Best Practices

1. Test Behavior, Not Implementation - Focus on what, not how
2. Keep Tests Fast - Run frequently
3. Isolate Dependencies - Mock external systems
4. Clear Test Names - Describe what's being tested
5. DRY Tests - Eliminate duplication
6. Test Edge Cases - Boundaries, nulls, errors
7. Use Test Fixtures - Consistent setup
8. Automate Testing - CI/CD integration

Test Naming Convention

test_[function]_[scenario]_[expected_outcome]

Example:
test_calculateDiscount_withValidCode_returnsDiscountedPrice
test_loginUser_withInvalidPassword_throwsAuthenticationError

Example Test Patterns

AAA Pattern (Arrange-Act-Assert)

test('calculateTotal with items', () => {
  // Arrange
  const cart = new Cart();
  cart.addItem({ price: 10 }, 2);
  
  // Act
  const total = cart.getTotal();
  
  // Assert
  expect(total).toBe(20);
});

BDD (Behavior-Driven Development)

Feature: User Authentication
  Scenario: Login with valid credentials
    Given a user with email "test@example.com"
    When the user logs in with correct password
    Then they should see the dashboard

Metrics

• Code Coverage: % of code executed by tests (aim for 80%+)
• Test Pass Rate: % of tests passing
• Test Execution Time: How long tests take to run
• Mutation Score: % of introduced bugs caught

Common Pitfalls to Avoid

• Over-testing trivial code
• Not testing error paths
• Flaky tests (non-deterministic)
• Testing implementation details
• Ignoring performance in tests
• Not testing concurrency

References

• Test Driven Development (Kent Beck)
• Growing Object-Oriented Software, Guided by Tests
• Working Effectively with Legacy Code (Michael Feathers)
• Testing Strategies for Microservices
• Chaos Engineering (whitepaper)