testing-strategy

Testing Strategy

This skill provides comprehensive guidance for implementing effective testing strategies across your entire application stack.

Test Pyramid

The Testing Hierarchy

        /\
       /  \
      /E2E \       10% - End-to-End Tests (slowest, most expensive)
     /______\
    /        \
   /Integration\  20% - Integration Tests (medium speed/cost)
  /____________\
 /              \
/   Unit Tests   \ 70% - Unit Tests (fast, cheap, focused)
/__________________\

Rationale:

• 70% Unit Tests: Fast, isolated, catch bugs early
• 20% Integration Tests: Test component interactions
• 10% E2E Tests: Test critical user journeys

Why This Distribution?

Unit tests are cheap:

• Run in milliseconds
• No external dependencies
• Easy to debug
• High code coverage per test

Integration tests are moderate:

• Test real interactions
• Catch integration bugs
• Slower than unit tests
• More complex setup

E2E tests are expensive:

• Test entire system
• Catch UX issues
• Very slow (seconds/minutes)
• Brittle and hard to maintain

TDD (Test-Driven Development)

Red-Green-Refactor Cycle

1. Red - Write a failing test:

describe('Calculator', () => {
  test('adds two numbers', () => {
    const calculator = new Calculator();
    expect(calculator.add(2, 3)).toBe(5); // FAILS - method doesn't exist
  });
});

2. Green - Write minimal code to pass:

class Calculator {
  add(a: number, b: number): number {
    return a + b; // Simplest implementation
  }
}
// Test now PASSES

3. Refactor - Improve the code:

class Calculator {
  add(a: number, b: number): number {
    // Add validation
    if (!Number.isFinite(a) || !Number.isFinite(b)) {
      throw new Error('Arguments must be finite numbers');
    }
    return a + b;
  }
}

TDD Benefits

Design benefits:

• Forces you to think about API before implementation
• Leads to more testable, modular code
• Encourages SOLID principles