Interview Questions and Answers to get every answer ready

Before acting on an element, Playwright automatically waits until it is attached, visible, stable, enabled and able to receive events. Web-first assertions such as expect(locator).toBeVisible() also retry until the condition is met or a timeout occurs, so you rarely need manual sleeps.

User-facing locators first: getByRole, getByLabel, getByPlaceholder, getByText, then getByTestId for stable test IDs. CSS and XPath are supported but more brittle.

await page.getByRole('button', { name: 'Login' }).click();

Start waiting for the event before the click that opens it:

const [newPage] = await Promise.all([
  page.waitForEvent('popup'),
  page.getByText('Open report').click()
]);
await newPage.waitForLoadState();

Playwright runs test files in parallel using worker processes by default. Set the number with workers in playwright.config, and set fullyParallel: true to also parallelise tests inside a single file. Keep tests independent so they can run in any order.

Use the built-in request fixture (APIRequestContext):

test('get user', async ({ request }) => {
  const res = await request.get('/api/users/1');
  expect(res.ok()).toBeTruthy();
  expect((await res.json()).id).toBe(1);
});

It is also useful to set up test data or log in via API before UI tests.

An implicit wait is a global setting: the driver polls for up to N seconds whenever it looks for any element. An explicit wait (WebDriverWait + ExpectedConditions) waits for a specific condition on a specific element, such as clickable or visible. Prefer explicit waits, and don't mix the two.

A design pattern where each page or component gets its own class holding its locators and actions (e.g. LoginPage.login(user, pass)). Tests call these methods instead of raw locators, so a UI change is fixed in one place, which makes the suite easier to maintain and read.

Retesting re-runs the specific failed test cases after a bug fix to confirm the fix. Regression testing checks that the fix or a new change has not broken existing, previously working features, which makes it ideal for automation.

Smoke testing is a broad, shallow check that a new build's critical paths work and it is stable enough to test further. Sanity testing is a narrow, focused check of a specific feature or fix after a minor change.

A lightweight in-memory copy of the real DOM. When state changes, React builds a new virtual tree, compares it with the previous one (diffing) and applies only the minimum changes to the real DOM.

Props are read-only inputs passed from a parent component. State is data a component owns and can change with useState; changing state triggers a re-render. Data flows down through props; changes flow up through callback functions.

useEffect runs side effects after render: API calls, subscriptions, timers. The dependency array controls when it re-runs: [] runs it once after the first render; [id] re-runs when id changes. Return a function to clean up.

A function with access to req, res and next that runs between the request and the route handler, for logging, authentication, parsing JSON, error handling and so on. It must call next() to pass control on, or send a response.

app.use((req, res, next) => {
  console.log(req.method, req.url);
  next();
});

PUT replaces the whole resource with the data sent and is idempotent: sending it twice gives the same result. PATCH updates only the fields sent and is not guaranteed to be idempotent, for example a patch that increments a counter. POST creates and is not idempotent.

MongoDB stores flexible JSON-like documents, suits changing or nested data, and scales horizontally easily. SQL databases suit structured data with strong relationships and complex joins and transactions, such as banking. Many real systems use both.

Authenticate with JWT or sessions and check authorisation on every route; hash passwords with bcrypt; validate and sanitise all input; use HTTPS; configure CORS narrowly; add rate limiting; keep secrets in environment variables; and never return stack traces to clients.