Test strategy and tools

TypeScript, as a superset of JavaScript, offers significant advantages in type safety and development efficiency. The choice of testing strategies and tools directly impacts a project's reliability and maintainability. From unit testing to end-to-end testing, the toolchain and design patterns at different levels need to be flexibly applied based on specific scenarios.

Unit Testing Strategy

Unit testing focuses on validating independent modules, typically implemented in TypeScript using frameworks like Jest or Mocha. Key strategies include:

1. Pure Functions First: Full coverage testing for side-effect-free utility functions

// utils.test.ts  
import { formatDate } from './dateUtils';  

test('formatDate returns ISO string', () => {  
  const date = new Date(2023, 0, 1);  
  expect(formatDate(date)).toBe('2023-01-01T00:00:00Z');  
});  

2. Module Isolation: Use jest.mock for dependency replacement

// userService.test.ts  
jest.mock('./apiClient');  
import { getUser } from './userService';  

test('getUser handles API error', async () => {  
  require('./apiClient').default.mockRejectedValue(new Error('Timeout'));  
  await expect(getUser(123)).rejects.toThrow('Fetch failed');  
});  

3. Type Testing: Use tools like tsd to validate type definitions

// types.test-d.ts  
import { expectType } from 'tsd';  
import { UserProfile } from './models';  

expectType<{ id: number }>({} as UserProfile); // Throws error on type mismatch  

Integration Testing Approach

Integration testing focuses on interactions between modules. Recommended strategies include:

• Testing Container Components: React Testing Library with TypeScript type checking

// UserCard.test.tsx  
import { render, screen } from '@testing-library/react';  
import UserCard from './UserCard';  

test('displays user name', () => {  
  const user = { name: 'John', age: 30 };  
  render(<UserCard user={user} />);  
  expect(screen.getByText(/John/)).toBeInTheDocument();  
});  

• API Contract Testing: Use Pact to validate interface specifications

// apiContract.test.ts  
import { Pact } from '@pact-foundation/pact';  

describe('User API', () => {  
  beforeAll(() => {  
    new Pact({  
      consumer: 'WebApp',  
      provider: 'UserService'  
    }).setup();  
  });  

  test('GET /users/{id} returns 200', async () => {  
    await expect(  
      fetch('/users/123').then(r => r.status)  
    ).resolves.toBe(200);  
  });  
});  

E2E Testing Implementation

End-to-end testing requires simulating real user scenarios. Common toolchain combinations include:

1. Cypress + TypeScript:

// userFlow.cy.ts  
describe('Checkout Process', () => {  
  it('completes purchase', () => {  
    cy.visit('/products');  
    cy.get('[data-testid="product-1"]').click();  
    cy.contains('Checkout').click();  
    cy.get('#email').type('test@example.com');  
    cy.intercept('POST', '/api/orders').as('order');  
    cy.contains('Place Order').click();  
    cy.wait('@order').its('response.statusCode').should('eq', 201);  
  });  
});  

2. Playwright Multi-Browser Testing:

// auth.test.ts  
import { test, expect } from '@playwright/test';  

test.describe('Authentication', () => {  
  test('login redirects to dashboard', async ({ page }) => {  
    await page.goto('/login');  
    await page.fill('#username', 'admin');  
    await page.fill('#password', 'secret');  
    await Promise.all([  
      page.waitForURL('/dashboard'),  
      page.click('button[type="submit"]')  
    ]);  
    expect(await page.title()).toContain('Dashboard');  
  });  
});  

Test Coverage Optimization

Improving coverage requires combining static analysis and dynamic detection:

• Istanbul Threshold Configuration (.nycrc):

{  
  "check-coverage": true,  
  "branches": 80,  
  "lines": 90,  
  "functions": 85,  
  "statements": 90  
}  

• Incremental Coverage Detection:

# Only check changed files  
nyc --reporter=lcov --extension=.ts jest --changedSince=main  

Performance Testing Integration

Include load testing in the testing pipeline:

// loadTest.ts  
import http from 'k6/http';  
import { check, sleep } from 'k6';  

export const options = {  
  vus: 100,  
  duration: '1m'  
};  

export default function () {  
  const res = http.get('https://api.example.com/products');  
  check(res, {  
    'status 200': (r) => r.status === 200,  
    'response time < 500ms': (r) => r.timings.duration < 500  
  });  
  sleep(0.5);  
}  

Test Data Management

Structured test data improves test case maintainability:

1. Factory Pattern for Test Data Generation:

// factories/user.ts  
interface User {  
  id: number;  
  name: string;  
  email: string;  
}  

export const createUser = (overrides?: Partial<User>): User => ({  
  id: Math.floor(Math.random() * 1000),  
  name: 'Test User',  
  email: 'test@example.com',  
  ...overrides  
});  

2. JSON Schema Validation:

// validateResponse.ts  
import Ajv from 'ajv';  

const validate = new Ajv().compile({  
  type: 'object',  
  properties: {  
    id: { type: 'number' },  
    title: { type: 'string' }  
  },  
  required: ['id', 'title']  
});  

export function assertValidProduct(data: unknown) {  
  if (!validate(data)) throw new Error('Invalid product schema');  
}  

Test Environment Containerization

Use Docker to ensure test environment consistency:

# test.Dockerfile  
FROM node:18  
WORKDIR /app  
COPY package*.json .  
RUN npm ci  
COPY . .  
CMD ["npm", "test:ci"]  

Configure GitHub Actions for matrix testing:

# .github/workflows/test.yml  
jobs:  
  test:  
    strategy:  
      matrix:  
        node-version: [16.x, 18.x]  
        os: [ubuntu-latest, windows-latest]  
    runs-on: ${{ matrix.os }}  
    steps:  
      - uses: actions/checkout@v3  
      - uses: actions/setup-node@v3  
        with:  
          node-version: ${{ matrix.node-version }}  
      - run: npm ci  
      - run: npm test