testing-strategy

Testing Strategy Skill

Covers unit, integration, and e2e test patterns for all supported frameworks.

Test File Organization

Folder Structure

• Unit tests: co-locate with source files
  • src/services/user.ts → src/services/__tests__/user.test.ts (Jest/Vitest)
  • src/services/user.ts → src/services/test_user.py (pytest)
• Integration tests: separate tests/ directory at project root
  • tests/integration/auth.test.ts
  • tests/integration/database.test.ts
• E2E tests: separate e2e/ or tests/e2e/ directory
  • e2e/flows/login.test.ts
  • e2e/flows/checkout.test.ts

File Naming Convention

• Unit: <module>.test.ts or <module>_test.py
• Integration: <feature>.integration.test.ts or test_<feature>.py
• E2E: <flow>.e2e.test.ts or test_<flow>_e2e.py

Test Structure: Arrange-Act-Assert

All tests MUST follow AAA pattern:

describe('UserService', () => {
  describe('createUser', () => {
    it('should create a user with valid email and name', () => {
      // ARRANGE: Setup test data, mocks, fixtures
      const email = '[email protected]';
      const name = 'Alice Chen';
      
      // ACT: Call the function under test
      const user = service.createUser(email, name);
      
      // ASSERT: Verify the result
      expect(user.email).toBe(email);
      expect(user.name).toBe(name);
      expect(user.id).toBeDefined();
    });
  });
});

Golden rule: One logical assertion per test (one reason to fail).

Test Naming: Descriptive, Not Clever

❌ BAD:

it('works', () => { ... });
it('user creation 1', () => { ... });

✅ GOOD:

it('should create a user with valid email and return user object with id', () => { ... });
it('should reject email without @ symbol', () => { ... });
it('should hash password before storing in database', () => { ... });

Pattern: should [what happens] [given conditions if not obvious]

Framework-Specific Setup

Node.js / TypeScript (Jest / Vitest)

// jest.config.js
module.exports = {
  preset: 'ts-jest',
  testEnvironment: 'node',
  roots: ['<rootDir>/src', '<rootDir>/tests'],
  testMatch: ['**/__tests__/**/*.ts', '**/*.test.ts'],
  collectCoverageFrom: [
    'src/**/*.ts',
    '!src/**/*.d.ts',
    '!src/index.ts'
  ],
  coverageThreshold: {
    global: {
      branches: 80,
      functions: 80,
      lines: 80,
      statements: 80
    }
  }
};

// tsconfig.test.json
{
  "extends": "./tsconfig.json",
  "compilerOptions": {
    "jsx": "react",
    "types": ["jest", "node"]
  }
}