E2E Testing

e2e-testing — drive a real browser, keep it deterministic

You write Playwright tests that walk a real browser through real user journeys — log in, fill a form, check out, navigate across pages — and you keep those tests deterministic enough to gate a merge. The whole game is one tension: e2e tests catch integration bugs nothing else can, and they are the slowest, flakiest layer you own. Every rule below exists to buy back determinism.

Pin @playwright/test and provision browsers with npx playwright install --with-deps. Current line is Playwright v1.60.x (v1.60.0 shipped 2026-05-11). The _react / _vue selector engines and the :light Shadow-DOM suffix were removed in v1.58.0 — at any version you should be pinning they are long gone, so do not reach for them.

Is this even an e2e test?

E2e is the most expensive layer. Spend it only on journeys that cross pages or services. Route the rest out.

Rule: if you can prove it without launching a browser, you should. Push logic down to testing-web.

Locators: the priority ladder

Pick the highest rung that uniquely identifies the element. Higher rungs track what the user perceives, so they survive markup churn.

1. getByRole('button', { name: 'Buy' }) — role + accessible name. Default choice; doubles as an a11y signal.
2. getByLabel('Email') / getByPlaceholder(...) — form fields.
3. getByText('Order confirmed') — visible copy that uniquely identifies content.
4. getByTestId('cart-total') — when nothing user-facing is stable; requires a deliberate data-testid.
5. CSS as a last resort, scoped and shallow.

Never XPath, never nth-child chains, never the removed _react/_vue/:light engines.

// Bad — couples the test to DOM structure; one wrapper div breaks it.
await page.locator('div.card > button:nth-child(2)').click();

// Good — finds the button the way the user reads it.
await page.getByRole('button', { name: 'Buy' }).click();

Strict mode. A locator that matches two nodes throws — that is the framework catching an ambiguous selector for you. Tighten the locator (getByRole(...).and(...), scope with page.getByRole('listitem').filter({ hasText: 'Pro' })). Reaching for .first() to silence the error hides the ambiguity and is the next flake.

Assertions: web-first only

// Bad — reads the DOM once, before the async update lands; races the render.
expect(await page.locator('#status').textContent()).toBe('Submitted');

// Good — re-polls the element until it says 'Submitted' or the timeout fires.
await expect(page.getByTestId('status')).toHaveText('Submitted');

expect(locator) assertions (toBeVisible, toHaveText, toHaveURL, toHaveCount) retry until the condition holds. A read-once value (await locator.textContent() then compare) captures a single frame and loses every race against a re-render. If you find expect(await in a test, it is a bug.

Auto-wait and the no-sleep rule

Locator actions (click, fill, check) already auto-wait: they block until the element is visible, stable, enabled, and receiving events. So waitForTimeout(2000) is never the right wait — it is either too short (flake) or too long (slow), and it waits for wall-clock time instead of the thing you actually care about.

The ordering trap: subscribe to a response (or register a page.route mock) before the action that triggers it, or you miss the event.

// Bad — handler registered after goto; the initial request already fired unmocked.
await page.goto('/orders');
await page.route('**/api/orders', route => route.fulfill({ json: [] }));

// Good — mock in place before navigation, so the first request is intercepted.
await page.route('**/api/orders', route => route.fulfill({ json: [] }));
await page.goto('/orders');

Fixtures and page objects

Fixtures give every test a fresh, isolated setup and kill copy-pasted boilerplate. Extend the base test with your own; the code before use(value) is setup, after it is teardown.

import { test as base } from '@playwright/test';
import { CheckoutPage } from './pages/checkout';

type Fixtures = { checkout: CheckoutPage };

export const test = base.extend<Fixtures>({
  checkout: async ({ page }, use) => {
    const checkout = new CheckoutPage(page); // setup: depends on the built-in `page`
    await use(checkout);                      // hand it to the test
    // teardown after the test goes here, if any
  },
});

Option fixtures (['default', { option: true }]) let a project or test.use() flip behavior without new fixtures. Keep page objects thin — locators and intent-named actions (checkout.placeOrder()), no assertions buried inside them. Full page-object recipe lives in references/config-and-ci.md.

Auth and storageState

Logging in through the UI on every test is slow and a flake surface. Log in once in a setup project, save the authenticated session to JSON, and load it via storageState in the projects that depend on it.

• A setup project runs the login spec and writes playwright/.auth/<role>.json.
• Real test projects declare dependencies: ['setup'] and use: { storageState: '…/<role>.json' }.
• One file per role (admin, member, anon) — never share one mutated session across roles.
• Regenerate every CI run; gitignore the .auth/ dir. Committed session state leaks secrets and goes stale.

The full multi-role setup-project wiring is in references/config-and-ci.md.