WHEN To Use

Implementing E2E test automation for a web application
Debugging flaky tests that fail intermittently
Setting up CI/CD test pipelines with browser tests
Testing critical user workflows (auth, checkout, signup)
Choosing what to test with E2E vs unit/integration tests

Test Pyramid — Know Your Layer

        /\
       /E2E\         ← FEW: Critical paths only (this skill)
      /─────\
     /Integr\        ← MORE: Component interactions, API contracts
    /────────\
   /Unit Tests\      ← MANY: Fast, isolated, cover edge cases
  /────────────\

What E2E Tests Are For

E2E Tests ✓	NOT E2E Tests ✗
Critical user journeys (login → dashboard → action → logout)	Unit-level logic (use unit tests)
Multi-step flows (checkout, onboarding wizard)	API contracts (use integration tests)
Cross-browser compatibility	Edge cases (too slow, use unit tests)
Real API integration	Internal implementation details
Authentication flows	Component visual states (use Storybook)

Rule of thumb: If it would devastate your business to break, E2E test it. If it's just inconvenient, test it faster with unit/integration tests.

Core Principles

Principle	Why	How
Test behavior, not implementation	Survives refactors	Assert on user-visible outcomes, not DOM structure
Independent tests	Parallelizable, debuggable	Each test creates its own data, cleans up after
Deterministic waits	No flakiness	Wait for conditions, not fixed timeouts
Stable selectors	Survives UI changes	Use `data-testid`, roles, labels — never CSS classes
Fast feedback	Developers run them	Mock external services, parallelize, shard

Playwright Patterns

Configuration

// playwright.config.ts
import { defineConfig, devices } from "@playwright/test";

export default defineConfig({
  testDir: "./e2e",
  timeout: 30000,
  expect: { timeout: 5000 },
  fullyParallel: true,
  forbidOnly: !!process.env.CI,
  retries: process.env.CI ? 2 : 0,
  workers: process.env.CI ? 1 : undefined,
  reporter: [["html"], ["junit", { outputFile: "results.xml" }]],
  use: {
    baseURL: "http://localhost:3000",
    trace: "on-first-retry",
    screenshot: "only-on-failure",
    video: "retain-on-failure",
  },
  projects: [
    { name: "chromium", use: { ...devices["Desktop Chrome"] } },
    { name: "firefox", use: { ...devices["Desktop Firefox"] } },
    { name: "webkit", use: { ...devices["Desktop Safari"] } },
    { name: "mobile", use: { ...devices["iPhone 13"] } },
  ],
});

Pattern: Page Object Model

Encapsulate page logic. Tests read like user stories.

// pages/LoginPage.ts
import { Page, Locator } from "@playwright/test";

export class LoginPage {
  readonly page: Page;
  readonly emailInput: Locator;
  readonly passwordInput: Locator;
  readonly loginButton: Locator;
  readonly errorMessage: Locator;

  constructor(page: Page) {
    this.page = page;
    this.emailInput = page.getByLabel("Email");
    this.passwordInput = page.getByLabel("Password");
    this.loginButton = page.getByRole("button", { name: "Login" });
    this.errorMessage = page.getByRole("alert");
  }

  async goto() {
    await this.page.goto("/login");
  }

  async login(email: string, password: string) {
    await this.emailInput.fill(email);
    await this.passwordInput.fill(password);
    await this.loginButton.click();
  }
}

// tests/login.spec.ts
import { test, expect } from "@playwright/test";
import { LoginPage } from "../pages/LoginPage";

test("successful login redirects to dashboard", async ({ page }) => {
  const loginPage = new LoginPage(page);
  await loginPage.goto();
  await loginPage.login("user@example.com", "password123");

  await expect(page).toHaveURL("/dashboard");
  await expect(page.getByRole("heading", { name: "Dashboard" })).toBeVisible();
});

Pattern: Fixtures for Test Data

Create and clean up test data automatically.

// fixtures/test-data.ts
import { test as base } from "@playwright/test";

export const test = base.extend<{ testUser: TestUser }>({
  testUser: async ({}, use) => {
    // Setup: Create user
    const user = await createTestUser({
      email: `test-${Date.now()}@example.com`,
      password: "Test123!@#",
    });

    await use(user);

    // Teardown: Clean up
    await deleteTestUser(user.id);
  },
});

// Usage — testUser is created before, deleted after
test("user can update profile", async ({ page, testUser }) => {
  await page.goto("/login");
  await page.getByLabel("Email").fill(testUser.email);
  // ...
});

Pattern: Smart Waiting

Never use fixed timeouts. Wait for specific conditions.

// ❌ FLAKY: Fixed timeout
await page.waitForTimeout(3000);

// ✅ STABLE: Wait for conditions
await page.waitForLoadState("networkidle");
await page.waitForURL("/dashboard");

// ✅ BEST: Auto-waiting assertions
await expect(page.getByText("Welcome")).toBeVisible();
await expect(page.getByRole("button", { name: "Submit" })).toBeEnabled();

// Wait for API response
const responsePromise = page.waitForResponse(
  (r) => r.url().includes("/api/users") && r.status() === 200
);
await page.getByRole("button", { name: "Load" }).click();
await responsePromise;

Pattern: Network Mocking

Isolate tests from real external services.

test("shows error when API fails", async ({ page }) => {
  // Mock the API response
  await page.route("**/api/users", (route) => {
    route.fulfill({
      status: 500,
      body: JSON.stringify({ error: "Server Error" }),
    });
  });

  await page.goto("/users");
  await expect(page.getByText("Failed to load users")).toBeVisible();
});

test("handles slow network gracefully", async ({ page }) => {
  await page.route("**/api/data", async (route) => {
    await new Promise((r) => setTimeout(r, 3000)); // Simulate delay
    await route.continue();
  });

  await page.goto("/dashboard");
  await expect(page.getByText("Loading...")).toBeVisible();
});

Cypress Patterns

Custom Commands

// cypress/support/commands.ts
declare global {
  namespace Cypress {
    interface Chainable {
      login(email: string, password: string): Chainable<void>;
      dataCy(value: string): Chainable<JQuery<HTMLElement>>;
    }
  }
}

Cypress.Commands.add("login", (email, password) => {
  cy.visit("/login");
  cy.get('[data-testid="email"]').type(email);
  cy.get('[data-testid="password"]').type(password);
  cy.get('[data-testid="login-button"]').click();
  cy.url().should("include", "/dashboard");
});

Cypress.Commands.add("dataCy", (value) => {
  return cy.get(`[data-cy="${value}"]`);
});

// Usage
cy.login("user@example.com", "password");
cy.dataCy("submit-button").click();

Network Intercepts

// Mock API
cy.intercept("GET", "/api/users", {
  statusCode: 200,
  body: [{ id: 1, name: "John" }],
}).as("getUsers");

cy.visit("/users");
cy.wait("@getUsers");
cy.get('[data-testid="user-list"]').children().should("have.length", 1);

Selector Strategy

Priority	Selector Type	Example	Why
1	Role + name	`getByRole("button", { name: "Submit" })`	Accessible, user-facing
2	Label	`getByLabel("Email address")`	Accessible, semantic
3	data-testid	`getByTestId("checkout-form")`	Stable, explicit for testing
4	Text content	`getByText("Welcome back")`	User-facing
❌	CSS classes	`.btn-primary`	Breaks on styling changes
❌	DOM structure	`div > form > input:nth-child(2)`	Breaks on any restructure

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

// ✅ GOOD: Stable selectors
page.getByRole("button", { name: "Submit" }).click();
page.getByLabel("Email address").fill("user@example.com");
page.getByTestId("email-input").fill("user@example.com");

Visual Regression Testing

// Playwright visual comparisons
test("homepage looks correct", async ({ page }) => {
  await page.goto("/");
  await expect(page).toHaveScreenshot("homepage.png", {
    fullPage: true,
    maxDiffPixels: 100,
  });
});

test("button states", async ({ page }) => {
  const button = page.getByRole("button", { name: "Submit" });

  await expect(button).toHaveScreenshot("button-default.png");

  await button.hover();
  await expect(button).toHaveScreenshot("button-hover.png");
});

Accessibility Testing

// npm install @axe-core/playwright
import AxeBuilder from "@axe-core/playwright";

test("page has no accessibility violations", async ({ page }) => {
  await page.goto("/");

  const results = await new AxeBuilder({ page })
    .exclude("#third-party-widget")  // Exclude things you can't control
    .analyze();

  expect(results.violations).toEqual([]);
});

Debugging Failed Tests

# Run in headed mode (see the browser)
npx playwright test --headed

# Debug mode (step through)
npx playwright test --debug

# Show trace viewer for failed tests
npx playwright show-report

// Add test steps for better failure reports
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("Complete checkout", async () => {
    await page.goto("/checkout");
    // ... if this fails, you know which step
  });
});

// Pause for manual inspection
await page.pause();

Flaky Test Checklist

When a test fails intermittently, check:

Issue	Fix
Fixed `waitForTimeout()` calls	Replace with `waitForSelector()` or expect assertions
Race conditions on page load	Wait for `networkidle` or specific elements
Test data pollution	Ensure tests create/clean their own data
Animation timing	Wait for animations to complete or disable them
Viewport inconsistency	Set explicit viewport in config
Random test order issues	Tests must be independent
Third-party service flakiness	Mock external APIs

CI/CD Integration

# GitHub Actions example
name: E2E Tests
on: [push, pull_request]

jobs:
  e2e:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-node@v4
      - run: npm ci
      - run: npx playwright install --with-deps
      - run: npm run build
      - run: npm run start & npx wait-on http://localhost:3000
      - run: npx playwright test
      - uses: actions/upload-artifact@v4
        if: failure()
        with:
          name: playwright-report
          path: playwright-report/

NEVER Do

NEVER use fixed waitForTimeout() or cy.wait(ms) — they cause flaky tests and slow down suites
NEVER rely on CSS classes or DOM structure for selectors — use roles, labels, or data-testid
NEVER share state between tests — each test must be completely independent
NEVER test implementation details — test what users see and do, not internal structure
NEVER skip cleanup — always delete test data you created, even on failure
NEVER test everything with E2E — reserve for critical paths; use faster tests for edge cases
NEVER ignore flaky tests — fix them immediately or delete them; a flaky test is worse than no test
NEVER hardcode test data in selectors — use dynamic waits for content that varies

Quick Reference

Playwright Commands

// Navigation
await page.goto("/path");
await page.goBack();
await page.reload();

// Interactions
await page.click("selector");
await page.fill("selector", "text");
await page.type("selector", "text");  // Types character by character
await page.selectOption("select", "value");
await page.check("checkbox");

// Assertions
await expect(page).toHaveURL("/expected");
await expect(locator).toBeVisible();
await expect(locator).toHaveText("expected");
await expect(locator).toBeEnabled();
await expect(locator).toHaveCount(3);

Cypress Commands

// Navigation
cy.visit("/path");
cy.go("back");
cy.reload();

// Interactions
cy.get("selector").click();
cy.get("selector").type("text");
cy.get("selector").clear().type("text");
cy.get("select").select("value");
cy.get("checkbox").check();

// Assertions
cy.url().should("include", "/expected");
cy.get("selector").should("be.visible");
cy.get("selector").should("have.text", "expected");
cy.get("selector").should("have.length", 3);

e2e-testing-patterns

E2E Testing Patterns

Installation

OpenClaw / Moltbot / Clawbot

WHAT This Skill Does