perdolique/playwright-e2e-testing

E2E testing with Playwright

This skill provides patterns and conventions for writing Playwright E2E tests for web applications, including SPA-specific techniques for routing, API mocking, and async navigation.

When to use this skill

• Writing E2E/browser tests for user flows
• Testing page routing and redirects
• Testing dialog/modal interactions
• Creating test data fixtures for a new feature
• Mocking API endpoints for E2E tests
• Debugging failing Playwright tests

Project configuration

When setting up or modifying playwright.config.ts, see references/configuration.md for conventions on web server setup, reporters, traces, screenshots, and CI behavior.

Test imports

If the project has a custom fixture file that extends Playwright's test object (common for API interception, shared setup, etc.), always import test and expect from that fixture — not from @playwright/test directly. Check the project's test directory for a fixtures/ folder or global.fixtures.ts.

// ✅ If project has custom fixtures — import from there
import { test, expect } from '../fixtures/global.fixtures.ts';

// ❌ Bypasses any project-level request interception or setup
import { test, expect } from '@playwright/test';

Standalone types are always fine to import directly:

import type { Page, Locator } from '@playwright/test';

Directory structure

Organize tests by feature domain. Each domain typically has its own fixture file:

tests/playwright/
├── constants.ts                     # Base URLs, shared constants
├── fixtures/
│   ├── global.fixtures.ts           # Extended test/expect (if project uses one)
│   ├── core-api.fixtures.ts         # Shared API mock helpers
│   └── {feature}.fixtures.ts        # Feature-specific test data
├── {feature-domain}/
│   └── {feature}.test.ts            # Test file
└── routing/
    └── redirects.test.ts            # Router/redirect tests

Writing test files

Basic structure

import type { Page } from '@playwright/test';
import { test, expect } from '../fixtures/global.fixtures.ts';
import { mockEndpoint } from '../fixtures/api.fixtures.ts';
import { baseFixture, variantFixture } from '../fixtures/{feature}.fixtures.ts';

// Helper functions (navigation, assertions)
async function openFeaturePage(page: Page): Promise<void> {
  await page.goto('/feature?id=test-id');
}

test.describe('Feature name', () => {
  test('description of expected behavior', async ({ page }) => {
    await mockEndpoint(page, baseFixture);
    await openFeaturePage(page);
    await expect(page.getByText('Expected text')).toBeVisible();
  });
});

Helper functions

Define helper functions at the top of the test file for repeated actions. Helpers improve readability and reduce duplication:

• Navigation helpers — openDialog(page), gotoProductPage(page)
• Assertion helpers — expectSummary(page, options), expectAvailability(page, from, to)
• Setup helpers — setupCommonMocks(page) for test-specific mock bundles
• Locator helpers — actionButtons(page) returning a Locator

Shared setup with beforeEach

When all tests in a describe block share identical mock setup:

test.describe('Router redirects', () => {
  test.beforeEach(async ({ page }) => {
    await setupCommonMocks(page);
  });

  test('redirects when resource is not found', async ({ page }) => {
    await page.goto('/resource?id=unknown');
    await expect(page).toHaveURL(/\/error\?id=unknown$/u);
  });
});

Multi-step flows with test.step()

For complex user flows (purchases, form submissions), use test.step() blocks. Playwright reports show which step failed, making debugging much faster.

test('completes purchase flow', async ({ page }) => {
  await test.step('prepare mocks', async () => {
    await mockProduct(page, productFixture);
    await mockCheckout(page);
  });

  const purchaseRequestPromise = page.waitForRequest(
    request => request.url().includes('/purchases') && request.method() === 'POST'
  );

  await test.step('open product page', async () => {
    await gotoProductPage(page);
  });

  await test.step('select option', async () => {
    await page.getByRole('button', { name: '14:00' }).click();
  });

  await test.step('verify confirmation page', async () => {
    await expect.poll(() => new URL(page.url()).pathname).toBe('/order-confirmation');
  });

  await test.step('submit order', async () => {
    await page.getByRole('button', { name: 'Confirm' }).click();
  });

  await test.step('verify purchase request', async () => {
    const request = await purchaseRequestPromise;

    expect(request.postDataJSON()).toEqual({
      items: [{ id: 'product-1', date: '2088-04-21T11:00:00.000Z' }]
    });
  });
});

Key patterns in multi-step flows:

• page.waitForRequest() — Set up BEFORE the action that triggers the request
• expect.poll() — Wait for async URL changes after SPA navigation
• satisfies — Type-check request payload expectations without losing literal types

localStorage setup via addInitScript

To set localStorage values before the page loads (e.g., saved state for routing tests):

async function setSavedState(page: Page, key: string, value: unknown): Promise<void> {
  await page.addInitScript(
    ({ storageKey, data }: { storageKey: string; data: string }) => {
      localStorage.setItem(storageKey, data);
    },
    { storageKey: key, data: JSON.stringify(value) }
  );
}

addInitScript runs before the page loads, so the app reads the correct localStorage values during initialization. page.evaluate runs after the page loads, which is too late for route guards.

Selector patterns

Prefer user-facing selectors in this order:

1. page.getByRole('button', { name: 'Confirm' }) — Accessible role + name
2. page.getByText('Expected text') — Visible text content
3. page.getByTestId('action-button') — data-testid attribute
4. page.getByText('text', { exact: true }) — Exact match to avoid partial hits
5. page.getByText(/regex pattern/u) — Regex for dynamic content

Use .first() when multiple identical elements exist on the page (e.g., text duplicated for mobile/desktop viewports).

Assertion patterns

// Visibility
await expect(page.getByText('Welcome')).toBeVisible();

// Element count
await expect(page.getByRole('button', { name: /\d{2}:\d{2}/u })).toHaveCount(3);
await expect(page.getByText('Not present')).toHaveCount(0); // Assert absence

// URL matching
await expect(page).toHaveURL('http://localhost:5050/error?id=unknown');
await expect(page).toHaveURL(/\/order-success\?id=test-id$/u);

// Async URL change (SPA navigation)
await expect.poll(() => new URL(page.url()).pathname).toBe('/order-confirmation');

// Interactive state
await expect(page.getByRole('button', { name: 'Submit' })).toBeEnabled();
await expect(page.getByRole('button', { name: 'Submit' })).toBeDisabled();

// Regex with unicode flag (for apostrophes, special chars)
await expect(page.getByText(/^You.re all set!$/u)).toBeVisible();

Always use the /u (unicode) flag on regex patterns to correctly handle special characters.

API mocking with page.route()

Basic mock

async function mockProducts(page: Page, response: unknown): Promise<void> {
  await page.route('**/api/products**', async (route) => {
    await route.fulfill({ json: response });
  });
}

Mock with different HTTP methods

async function mockPurchase(page: Page, purchaseId: string, response: unknown): Promise<void> {
  // Mock POST (create)
  await page.route('**/api/purchases', async (route) => {
    await route.fulfill({ json: { id: purchaseId } });
  });

  // Mock GET (status poll)
  await page.route(`**/api/purchases/${purchaseId}`, async (route) => {
    await route.fulfill({ json: response });
  });
}

Block external requests

A common pattern is to block all external requests and only allow requests to the app itself:

await page.route('**/*', async (route) => {
  const url = new URL(route.request().url());

  if (url.origin === appBaseUrl) {
    await route.continue();
  } else {
    await route.abort();
  }
});

Override existing mocks

Playwright uses last-registered-wins for route matching. Register a new route for the same pattern to override an earlier mock:

// Global fixture mocks /api/properties with defaults
// Your test overrides with custom data:
await page.route('**/api/properties/**', async (route) => {
  await route.fulfill({ json: customPropertyData });
});

Mock third-party services

async function setupExternalMocks(page: Page): Promise<void> {
  await page.route('https://analytics.example.com/**', async (route) => {
    await route.fulfill({ status: 200, body: '' });
  });

  await page.route('https://cdn.example.com/**', async (route) => {
    await route.fulfill({ status: 200, body: '', contentType: 'image/jpeg' });
  });
}

Creating test data fixtures

See references/fixtures.md for detailed patterns.

Variant pattern (simple features)

Use a base const object + spread for variants. Each test gets exactly the data shape it needs, and you can see what differs from the base at a glance:

export const itemBase = {
  id: 'test-item-id',
  name: 'Test Item',
  status: 'active',
  items: []
} as const;

export const itemWithProducts = {
  ...itemBase,
  items: [{
    productId: 'test-product-id',
    status: 'confirmed'
  }]
} as const;

Factory pattern (complex features)

When fixtures need many permutations with computed fields:

function createAccessKey(options: {
  readonly id: string;
  readonly type: 'code' | 'remote';
  readonly name: string;
  readonly code?: string | null;
}) {
  return {
    id: options.id,
    type: options.type,
    name: options.name,
    code: options.code ?? null,
    validFrom: '2024-01-01T00:00:00.000Z',
    validTo: '2099-12-31T23:59:59.000Z'
  } as const;
}

Factory functions stay private to the fixture file. Exported variants compose them.

Fixture data conventions

| Convention | Why | | --- | --- | | Use as const on every exported object | TypeScript narrows the type, catches typos | | Use far-future dates in fixtures (e.g., year 2088) | Won't expire during test lifetime | | Use clearly fake IDs with consistent prefixes | Easy to grep, obviously not real data | | Spread from base, override only what matters | Makes test intent clear |

API request testing

For testing server-side API endpoints directly, use Playwright's APIRequestContext — no browser needed.

Worker-scoped fixtures for authentication

Use worker-scoped fixtures instead of beforeAll + shared mutable let variables. Worker scope creates the context once per worker thread (same performance), eliminates shared mutable state, and integrates cleanly with Playwright's teardown lifecycle.

// tests/playwright/fixtures.ts
import { test as base, type APIRequestContext } from '@playwright/test'
import { appBaseUrl } from './constants'

interface WorkerFixtures {
  authedRequest: APIRequestContext;
}

export const test = base.extend<Record<never, never>, WorkerFixtures>({
  authedRequest: [
    async ({ playwright }, use) => {
      const request = await playwright.request.newContext({ baseURL: appBaseUrl })
      await request.post('/api/auth/create-session')
      await use(request)
      await request.dispose()
    },
    { scope: 'worker' },
  ],
})

Import test from this file in API test files. The fixture is available as { authedRequest } in the test callback.

Type-safe JSON parsing

APIResponse.json() returns Promise<any> (Playwright's Serializable = any). Assigning any directly to a typed variable triggers no-unsafe-assignment. Use unknown as the intermediate type, then parse with a validation library:

// ✅ Correct — breaks out of any safely
const raw: unknown = await response.json()
const body = v.parse(mySchema, raw)  // Valibot accepts unknown, returns typed result

// ❌ Wrong — casting any → specific type bypasses runtime check
const body = await response.json() as MyResponseType

// ❌ Wrong — no-await-expression-member: don't chain .json() onto an await
const raw: unknown = await (await request.get('/api/items')).json()

When using Valibot, split request and parse onto separate lines — Valibot's parse throws a descriptive error if the shape doesn't match, which makes test failures easy to diagnose.

What to assert in API tests

When a validation schema already enforces response shape, shape assertions add zero value — the schema throws before assertions are even reached. Focus on assertions TypeScript and schemas can't verify:

// ❌ Redundant when v.parse(schema, raw) already validates the shape
expect(body).toMatchObject({ id: expect.any(Number), name: expect.any(String) })

// ✅ Tests actual behavior — HTTP contract, correct data, filter logic, auth
expect(response.status()).toBe(200)
expect(body.name).toBe('MSR')
expect(body.items.length).toBeGreaterThan(0)
expect(filteredBody.items.every(item => item.category.slug === 'sleeping-pads')).toBe(true)

High-value API assertions: status codes, specific values (names, slugs, IDs confirming correct record), filter correctness, pagination boundaries, auth enforcement (401 without session).

Testing 401 / unauthenticated responses

Create an anonymous context inline — never reuse the authenticated fixture for negative auth tests:

test('returns 401 without session cookie', async ({ playwright }) => {
  const anonRequest = await playwright.request.newContext({ baseURL: appBaseUrl })
  const response = await anonRequest.get('/api/equipment/groups')

  expect(response.status()).toBe(401)

  await anonRequest.dispose()
})

# Run all Playwright tests
npx playwright test

# Run a specific test file
npx playwright test tests/playwright/product/checkout.test.ts

# Run with UI mode for debugging
npx playwright test --ui

# Run with headed browser
npx playwright test --headed

# Run with Playwright inspector/debug mode
npx playwright test --debug

# Open the last HTML report
npx playwright show-report

Check the project's package.json for available test scripts — many projects define shortcuts like test:playwright, test:e2e, or similar.

Validation checklist

Before considering an E2E test complete, verify:

• [ ] test and expect imported from the project's fixture file (if one exists)
• [ ] Only types imported from @playwright/test (e.g., type Page, type Locator)
• [ ] Feature-specific fixtures use as const on all exported objects
• [ ] Future dates used in fixture data
• [ ] test.describe() groups related tests
• [ ] Helper functions extracted for repeated navigation/assertion patterns
• [ ] Multi-step flows use test.step() blocks
• [ ] page.waitForRequest() set up BEFORE the triggering action
• [ ] Regex patterns use /u flag
• [ ] .first() used when multiple matching elements exist
• [ ] No external services left unmocked (check console for blocked request warnings)
• [ ] API tests: const raw: unknown = await response.json() — never assign any directly
• [ ] API tests: Schema validation (Valibot/Zod) used; shape-only toMatchObject assertions removed
• [ ] API tests: Auth tests use inline anonymous context, not the authenticated fixture
• [ ] API tests: Worker-scoped fixtures used for authentication (not beforeAll + let)
• [ ] Test runs successfully

Reference files

• references/configuration.md — Playwright config setup: web server, reporters, traces, screenshots, CI behavior
• references/fixtures.md — Complete fixture patterns, factory functions, variant pattern details