Regression testing strategy

Regression testing is an indispensable part of software development, especially in rapidly iterating frontend projects where code changes are frequent. Regression testing effectively prevents defects introduced by new features from breaking existing functionality. A reasonable regression testing strategy requires a combination of automation tools, test scope selection, and team collaboration to efficiently ensure code quality.

Core Objectives of Regression Testing

The core of regression testing lies in verifying whether the system's original functions still work normally after code modifications. Common regression issues in frontend projects include:

• Style compatibility issues (e.g., CSS-in-JS dynamic styles overriding existing styles)
• Component interaction logic breakage (e.g., form validation rule conflicts)
• Data flow anomalies (e.g., unintended modifications to Redux state management)

// Typical regression case: Component props type change causing child component crashes  
// Before modification  
<Modal size="large" />  

// After type system adjustment  
interface ModalProps {  
  size?: 'sm' | 'md'; // 'large' option removed  
}  

Building an Automated Regression Testing System

Layered Testing Strategy

1. Unit Testing Layer: Use Jest/Vitest to ensure basic utility functions

// utils/formatDate.test.ts  
describe('formatDate', () => {  
  it('should handle UTC conversion', () => {  
    expect(formatDate('2023-01-01T00:00:00Z')).toBe('2023/01/01 08:00')  
  })  
})  

2. Component Testing Layer: Validate component behavior with Testing Library

// Button.test.jsx  
test('should trigger onClick', async () => {  
  const mockFn = jest.fn()  
  render(<Button onClick={mockFn} />)  
  fireEvent.click(screen.getByRole('button'))  
  expect(mockFn).toHaveBeenCalled()  
})  

3. E2E Testing Layer: Cover critical user journeys with Cypress/Playwright

// checkout.cy.js  
describe('Checkout Flow', () => {  
  it('should complete purchase', () => {  
    cy.visit('/products')  
    cy.get('[data-testid="add-to-cart"]').first().click()  
    cy.contains('Checkout').click()  
    cy.get('#email').type('test@example.com')  
    cy.contains('Place Order').should('be.enabled')  
  })  
})  

Intelligent Test Scope Selection

Test Filtering Based on Code Changes

1. Impact Map Analysis: Determine affected modules through dependency graphs

# Generate dependency graph with Madge  
npx madge --image graph.svg src/App.tsx  

2. Git Change Association Testing:

# Get files modified in this change  
git diff --name-only HEAD^ | grep '\.test\.'  

3. Strategy in Monorepo Environments:

# turbo.json configuration example  
{  
  "pipeline": {  
    "test": {  
      "dependsOn": ["^build"],  
      "outputs": ["coverage/**"],  
      "inputs": ["src/**/*.{js,ts}", "!__snapshots__"]  
    }  
  }  
}  

Regression Optimization in Continuous Integration

Parallel Test Execution Strategy

# GitHub Actions configuration example  
jobs:  
  test:  
    strategy:  
      matrix:  
        test-group: [1, 2, 3]  
    steps:  
      - run: jest --group=${{ matrix.test-group }}  

Visual Report Integration

// jest.config.js  
module.exports = {  
  reporters: [  
    'default',  
    ['jest-html-reporters', {  
      publicPath: './test-report',  
      filename: 'report.html'  
    }]  
  ]  
}  

Specialized Detection of Performance Regression

Rendering Performance Monitoring

// Using React Profiler API  
const onRender = (id, phase, actualDuration) => {  
  if (actualDuration > 100) {  
    trackSlowComponent(id)  
  }  
}  

<Profiler id="ProductList" onRender={onRender}>  
  <ProductList />  
</Profiler>  

Resource Loading Benchmark Testing

// Playwright performance test snippet  
test('should load under 2s', async ({ page }) => {  
  const start = Date.now()  
  await page.goto('/dashboard')  
  expect(Date.now() - start).toBeLessThan(2000)  
})  

Quality Gates in Team Collaboration

Regression Checklist in Code Review

1. Does the modification affect existing test cases?
2. Do snapshot tests need updating?
3. Have new boundary case tests been added?

Defect Prevention Mechanisms

// Type-safe API response handling  
interface LegacyResponse {  
  user: string;  
}  

interface NewResponse {  
  user: {  
    name: string;  
    id: number;  
  };  
}  

function isLegacyResponse(res: any): res is LegacyResponse {  
  return typeof res.user === 'string'  
}  

Version Management of Test Data

Mock Data Maintenance Strategy

// __mocks__/api.js  
const v1Responses = require('./fixtures/v1')  
const v2Responses = require('./fixtures/v2')  

module.exports = (url) => {  
  return url.includes('/v1/') ? v1Responses[url] : v2Responses[url]  
}  

Database Snapshot Technology

# Use Docker to manage test databases  
docker commit pg_test pg_snapshot_v2