E2e Testing Patterns

# e2e-testing-patterns — detailed patterns and worked examples

## Playwright Patterns

### Setup and Configuration

```typescript
// 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 1: Page Object Model

```typescript
// 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();
  }

  async getErrorMessage(): Promise<string> {
    return (await this.errorMessage.textContent()) ?? "";
  }
}

// Test using Page Object
import { test, expect } from "@playwright/test";
import { LoginPage } from "./pages/LoginPage";

test("successful login", 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();
});

test("failed login shows error", async ({ page }) => {
  const loginPage = new LoginPage(page);
  await loginPage.goto();
  await loginPage.login("invalid@example.com", "wrong");

  const error = await loginPage.getErrorMessage();
  expect(error).toContain("Invalid credentials");
});
```

### Pattern 2: Fixtures for Test Data

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

type TestData = {
  testUser: {
    email: string;
    password: string;
    name: string;
  };
  adminUser: {
    email: string;
    password: string;
  };
};

export const test = base.extend<TestData>({
  testUser: async ({}, use) => {
    const user = {
      email: `test-${Date.now()}@example.com`,
      password: "Test123!@#",
      name: "Test User",
    };
    // Setup: Create user in database
    await createTestUser(user);
    await use(user);
    // Teardown: Clean up user
    await deleteTestUser(user.email);
  },

  adminUser: async ({}, use) => {
    await use({
      email: "admin@example.com",
      password: process.env.ADMIN_PASSWORD!,
    });
  },
});

// Usage in tests
import { test } from "./fixtures/test-data";

test("user can update profile", async ({ page, testUser }) => {
  await page.goto("/login");
  await page.getByLabel("Email").fill(testUser.email);
  await page.getByLabel("Password").fill(testUser.password);
  await page.getByRole("button", { name: "Login" }).click();

  await page.goto("/profile");
  await page.getByLabel("Name").fill("Updated Name");
  await page.getByRole("button", { name: "Save" }).click();

  await expect(page.getByText("Profile updated")).toBeVisible();
});
```

### Pattern 3: Waiting Strategies

```typescript
// ❌ B