Cypress Core Knowledge

Deep Knowledge: Use mcp__documentation__fetch_docs with technology: cypress for comprehensive documentation.

When NOT to Use This Skill

• Unit Testing - Use vitest or jest for isolated tests
• Multi-Tab Scenarios - Cypress doesn't support multiple tabs
• Native Mobile Apps - Use Appium or Detox
• Multi-Browser Testing - Limited browser support compared to Playwright
• Performance Testing - Use k6, Lighthouse, or dedicated tools

Basic Test

describe('Login', () => {
  beforeEach(() => {
    cy.visit('/login');
  });

  it('should login successfully', () => {
    cy.get('[data-testid="email"]').type('user@example.com');
    cy.get('[data-testid="password"]').type('password123');
    cy.get('button[type="submit"]').click();

    cy.url().should('include', '/dashboard');
    cy.contains('Welcome back').should('be.visible');
  });

  it('should show error for invalid credentials', () => {
    cy.get('[data-testid="email"]').type('wrong@example.com');
    cy.get('[data-testid="password"]').type('wrong');
    cy.get('button[type="submit"]').click();

    cy.contains('Invalid credentials').should('be.visible');
  });
});

Commands

// Selection
cy.get('.class');
cy.get('#id');
cy.get('[data-testid="element"]');
cy.contains('text');
cy.find('.child');

// Actions
cy.click();
cy.type('text');
cy.clear();
cy.check();
cy.select('option');
cy.scrollIntoView();

// Navigation
cy.visit('/page');
cy.go('back');
cy.reload();

Assertions

cy.get('element')
  .should('be.visible')
  .should('have.text', 'Hello')
  .should('have.class', 'active')
  .should('have.attr', 'href', '/home')
  .should('have.length', 3)
  .should('contain', 'text')
  .should('not.exist');

// Chained
cy.get('input').should('have.value', 'test').and('be.disabled');

Custom Commands

// cypress/support/commands.ts
Cypress.Commands.add('login', (email: string, password: string) => {
  cy.visit('/login');
  cy.get('[data-testid="email"]').type(email);
  cy.get('[data-testid="password"]').type(password);
  cy.get('button[type="submit"]').click();
});

// Usage
cy.login('user@example.com', 'password');

Intercept API

cy.intercept('GET', '/api/users', { fixture: 'users.json' }).as('getUsers');
cy.visit('/users');
cy.wait('@getUsers');

cy.intercept('POST', '/api/users', { statusCode: 201 }).as('createUser');

Production Readiness

Configuration

// cypress.config.ts
import { defineConfig } from 'cypress';

export default defineConfig({
  e2e: {
    baseUrl: 'http://localhost:3000',
    viewportWidth: 1280,
    viewportHeight: 720,
    video: true,
    screenshotOnRunFailure: true,
    retries: {
      runMode: 2,      // CI retries
      openMode: 0,     // Local retries
    },
    env: {
      apiUrl: 'http://localhost:3000/api',
    },
  },
  component: {
    devServer: {
      framework: 'react',
      bundler: 'vite',
    },
  },
});

Authentication

// cypress/support/commands.ts
Cypress.Commands.add('login', (email: string, password: string) => {
  // Programmatic login (faster than UI)
  cy.request({
    method: 'POST',
    url: '/api/auth/login',
    body: { email, password },
  }).then(({ body }) => {
    window.localStorage.setItem('token', body.token);
  });
});

// Preserve auth between tests
Cypress.Commands.add('preserveAuth', () => {
  cy.getCookie('session').then(cookie => {
    if (cookie) {
      Cypress.Cookies.preserveOnce('session');
    }
  });
});

// Usage
beforeEach(() => {
  cy.login(Cypress.env('TEST_USER'), Cypress.env('TEST_PASS'));
});

API Testing & Mocking

// Intercept and mock
cy.intercept('GET', '/api/users', { fixture: 'users.json' }).as('getUsers');
cy.intercept('POST', '/api/users', (req) => {
  req.reply({
    statusCode: 201,
    body: { id: '123', ...req.body },
  });
}).as('createUser');

// Wait for API calls
cy.wait('@getUsers').its('response.statusCode').should('eq', 200);

// Spy without mocking
cy.intercept('GET', '/api/users').as('getUsers');
cy.wait('@getUsers').then((interception) => {
  expect(interception.response.body).to.have.length.greaterThan(0);
});

CI Configuration

# GitHub Actions
- name: Cypress run
  uses: cypress-io/github-action@v5
  with:
    build: npm run build
    start: npm start
    wait-on: 'http://localhost:3000'
    record: true
  env:
    CYPRESS_RECORD_KEY: ${{ secrets.CYPRESS_RECORD_KEY }}

- name: Upload screenshots
  uses: actions/upload-artifact@v3
  if: failure()
  with:
    name: cypress-screenshots
    path: cypress/screenshots

Network Handling

// Handle slow networks
cy.intercept('/api/**', (req) => {
  req.on('response', (res) => {
    res.setDelay(1000); // Simulate slow response
  });
});

// Handle offline
cy.intercept('/api/**', { forceNetworkError: true });

// Retry failed requests
cy.request({
  url: '/api/data',
  retryOnStatusCodeFailure: true,
  retryOnNetworkFailure: true,
});

Monitoring Metrics

Best Practices

// Use data-testid for stable selectors
cy.get('[data-testid="submit-btn"]').click();

// Avoid arbitrary waits
// BAD: cy.wait(5000)
// GOOD: cy.get('[data-testid="result"]').should('be.visible')

// Chain assertions
cy.get('form')
  .should('be.visible')
  .find('input')
  .should('have.length', 3);

// Custom assertions
cy.get('@createUser')
  .its('request.body')
  .should('deep.include', { name: 'John' });

Checklist

• Programmatic login (not UI)
• API interception for isolation
• Retry configuration for CI
• Video recording enabled
• Screenshots on failure
• data-testid for selectors
• No arbitrary cy.wait()
• Custom commands for reuse
• CI/CD with Cypress Dashboard
• Environment variables secured

Anti-Patterns

Quick Troubleshooting

Reference Documentation

• Commands
• Fixtures