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senior
strategy

How do you design a testing strategy for a large application?

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test-pyramid
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coverage
Quick Answer

A testing strategy defines what to test, how much, and when. Use the testing trophy/pyramid as a guide: prioritize integration tests, supplement with unit tests for complex logic, and use E2E for critical paths. Consider cost, speed, and confidence.

Detailed Explanation

Testing Trophy Approach:

  1. Static Analysis (TypeScript, ESLint)
  2. Unit Tests (isolated logic)
  3. Integration Tests (most value)
  4. E2E Tests (critical flows)

Strategy Components:

  • Test boundaries: What to test
  • Coverage targets: How much
  • Test environments: Where to run
  • CI/CD integration: When to run

Prioritization:

  1. Revenue-critical paths
  2. Frequently changing code
  3. Complex business logic
  4. Integration points
  5. Edge cases with history of bugs

Cost-Benefit Analysis:

  • Test maintenance cost
  • Execution time
  • Confidence provided
  • Flakiness risk

Code Examples

Testing strategy example
// E-commerce app testing strategy

/**
 * CRITICAL PATH TESTS (E2E)
 * - Checkout flow end-to-end
 * - User authentication
 * - Payment processing
 * 
 * INTEGRATION TESTS
 * - Cart operations with API
 * - Product search and filtering
 * - User profile updates
 * - Order history display
 * 
 * UNIT TESTS
 * - Price calculation logic
 * - Discount application rules
 * - Form validation functions
 * - Data transformation utilities
 */

// jest.config.js - Different configs for different test types
module.exports = {
  projects: [
    {
      displayName: 'unit',
      testMatch: ['<rootDir>/src/**/*.unit.test.{js,jsx}'],
      testEnvironment: 'node'
    },
    {
      displayName: 'integration',
      testMatch: ['<rootDir>/src/**/*.integration.test.{js,jsx}'],
      testEnvironment: 'jsdom',
      setupFilesAfterEnv: ['<rootDir>/test/setupIntegration.js']
    }
  ],
  coverageThreshold: {
    global: { branches: 80, functions: 80, lines: 80 },
    './src/utils/pricing/': { branches: 95, functions: 95 }, // Critical
    './src/components/': { branches: 70, functions: 70 }  // Lower for UI
  }
};

Resources

Testing Trophy

article

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