E2E Testing Patterns

/e2e-testing-patterns

Build reliable, fast, and maintainable end-to-end test suites that provide confidence to ship code quickly and catch regressions before users do. Ask the user to paste failing tests, config files, or the flows they want covered; deliver test code, configs, and page objects as chat artifacts.

When to Use This Skill

• Implementing end-to-end test automation
• Debugging flaky or unreliable tests
• Testing critical user workflows
• Setting up CI/CD test pipelines
• Testing across multiple browsers
• Validating accessibility requirements
• Testing responsive designs
• Establishing E2E testing standards

For where E2E fits in an overall testing plan, use testing-strategy. For deep Playwright-specific tooling, use playwright-testing. For test-first development workflow, use test-driven-development.

Core Concepts

1. E2E Testing Fundamentals

What to Test with E2E:

• Critical user journeys (login, checkout, signup)
• Complex interactions (drag-and-drop, multi-step forms)
• Cross-browser compatibility
• Real API integration
• Authentication flows

What NOT to Test with E2E:

• Unit-level logic (use unit tests)
• API contracts (use integration tests)
• Edge cases (too slow)
• Internal implementation details

2. Test Philosophy

The Testing Pyramid:

        /\
       /E2E\         <- Few, focused on critical paths
      /-----\
     /Integr \       <- More, test component interactions
    /---------\
   /Unit Tests \     <- Many, fast, isolated
  /-------------\

Best Practices:

• Test user behavior, not implementation
• Keep tests independent
• Make tests deterministic
• Optimize for speed
• Use data-testid, not CSS selectors

Detailed patterns and worked examples

Detailed pattern documentation (Playwright config and page objects, fixtures, waiting strategies, network mocking, Cypress custom commands and intercepts, visual regression, sharding, accessibility testing) lives in references/details.md in this skill's directory. Read that file when the navigation tier above is insufficient.

Best Practices

1. Use Data Attributes: data-testid or data-cy for stable selectors
2. Avoid Brittle Selectors: Don't rely on CSS classes or DOM structure
3. Test User Behavior: Click, type, see - not implementation details
4. Keep Tests Independent: Each test should run in isolation
5. Clean Up Test Data: Create and destroy test data in each test
6. Use Page Objects: Encapsulate page logic
7. Meaningful Assertions: Check actual user-visible behavior
8. Optimize for Speed: Mock when possible, parallel execution

// Bad selectors
cy.get(".btn.btn-primary.submit-button").click();
cy.get("div > form > div:nth-child(2) > input").type("text");

// Good selectors
cy.getByRole("button", { name: "Submit" }).click();
cy.getByLabel("Email address").type("[email protected]");
cy.get('[data-testid="email-input"]').type("[email protected]");

Common Pitfalls

• Flaky Tests: Use proper waits, not fixed timeouts
• Slow Tests: Mock external APIs, use parallel execution
• Over-Testing: Don't test every edge case with E2E
• Coupled Tests: Tests should not depend on each other
• Poor Selectors: Avoid CSS classes and nth-child
• No Cleanup: Clean up test data after each test
• Testing Implementation: Test user behavior, not internals

Debugging Failing Tests

// Playwright debugging
// 1. Run in headed mode
npx playwright test --headed

// 2. Run in debug mode
npx playwright test --debug

// 3. Use trace viewer
await page.screenshot({ path: 'screenshot.png' });
await page.video()?.saveAs('video.webm');

// 4. Add test.step for better reporting
test('checkout flow', async ({ page }) => {
    await test.step('Add item to cart', async () => {
        await page.goto('/products');
        await page.getByRole('button', { name: 'Add to Cart' }).click();
    });

    await test.step('Proceed to checkout', async () => {
        await page.goto('/cart');
        await page.getByRole('button', { name: 'Checkout' }).click();
    });
});

// 5. Inspect page state
await page.pause();  // Pauses execution, opens inspector

Usage

When the user shares a flaky test, a suite to review, or a flow to cover, diagnose against the pitfalls above (waits, selectors, coupling, cleanup) and deliver corrected test code, page objects, fixtures, or configs as complete artifacts they can drop into their repo. Consult references/details.md for the full pattern library when writing non-trivial suites. Keep E2E coverage focused on critical user journeys; push edge cases down the pyramid. Defer to testing-strategy for what-to-test planning, playwright-testing for Playwright-specific depth, and test-driven-development for TDD workflow.

/e2e-testing-patterns $ARGUMENTS