01
How do you shard tests across machines?
Show answer
Use npx playwright test --shard=1/4 in each CI job and merge reports afterwards to reduce total run time.
Software Development Engineer in Test (SDET) Interview Questions & Answers
40 questions for Software Development Engineer in Test (SDET) interviews — 1 easy, 37 medium, 2 hard.
About the Software Development Engineer in Test (SDET) role
A developer-minded tester who writes automation code, test utilities and frameworks alongside product engineers. SDETs cover UI, API and integration testing and own quality in the pipeline. Interviews include data structures style coding in JavaScript or TypeScript, framework design questions, API testing, CI integration and discussions about test strategy, flakiness and code review. Expect to explain how your tests fit into the release process and how you work with developers.
TypeScript coding API test automation Framework design CI pipelines Code reviews
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02
How do you combine API and UI tests?
Show answer
Create test data through API calls, verify it in the UI and clean up via API, which makes UI tests faster and more reliable.
03
How do you share cookies between API login and UI?
Show answer
Log in with request.post, call request.storageState(), and create a browser context using that state.
04
Write a test that updates a user with PUT and verifies the change.
Show answer
test('update user', async ({ request }) => {
const res = await request.put('/api/users/12', {
data: { name: 'Neha', city: 'Jaipur' },
});
expect(res.status()).toBe(200);
const get = await request.get('/api/users/12');
expect(await get.json()).toMatchObject({ name: 'Neha', city: 'Jaipur' });
});
05
What does the reportSlowTests option do?
Show answer
reportSlowTests makes Playwright list test files that took longer than a threshold at the end of the run. You set max, the number of files to show, and threshold in milliseconds, for example { max: 5, threshold: 60000 }. It is a cheap way to find files worth splitting, because one slow file can hold up a worker or a whole shard.
06
What are generics in TypeScript?
Show answer
Placeholders for types that make reusable code type-safe, for example a helper function returning the same type of item that it receives.
07
What are template literals?
Show answer
Strings in backticks that allow embedded expressions like `Hello ${name}` and multi-line text, useful for building dynamic locators and URLs.
08
Write an API test with the request fixture.
Show answer
test('get user', async ({ request }) => {
const res = await request.get('/api/users/1');
expect(res.ok()).toBeTruthy();
expect((await res.json()).id).toBe(1);
});
09
How do you share one authenticated API context across all tests in a worker?
Show answer
Create a worker-scoped fixture that calls request.newContext with baseURL and an auth header, or logs in through the API and keeps the cookies. Pass it to use, and dispose it after use returns. Every test in that worker gets the same ready context, so login happens once per worker. Do not store per-test data on it, or tests start depending on each other.
10
How do you integrate Playwright with Allure or other reports?
Show answer
Install the allure-playwright reporter, add it in the config reporters array and generate the report from the allure-results folder in CI.
11
How do you validate response headers?
Show answer
Use response.headers() for an object of lower-cased header names, or headersArray() for duplicates. Assert content-type contains application/json, cache-control matches the policy, and security headers such as strict-transport-security are present. Also check that sensitive headers like server version are not exposed. Header checks catch configuration bugs that body checks miss.
12
How does this behave in arrow functions compared with regular functions?
Show answer
A regular function gets this from how it is called, so passing a class method as a callback can lose this. An arrow function has no own this and uses the value from the surrounding code. In page objects, arrow functions in callbacks such as map keep access to this.page, which avoids undefined errors.
13
How do you run Playwright in GitHub Actions?
Show answer
Workflow: checkout → setup-node → npm ci → npx playwright install --with-deps → npx playwright test → upload playwright-report as an artifact.
14
What does maxFailures do?
Show answer
maxFailures stops the run after a set number of test failures, for example maxFailures: process.env.CI ? 10 : undefined. If an environment is down and every test fails, the build stops early instead of burning an hour of CI time. Set it high enough that a few real failures still show their full picture.
15
How do you structure environment-specific configs in Playwright?
Show answer
Use dotenv files per environment, read them in playwright.config and set baseURL and credentials from variables, selecting with an ENV flag.
16
What are interfaces and types in TypeScript?
Show answer
Both describe the shape of data. Interfaces are extendable and suit object contracts; type aliases can also model unions and primitives.
17
How do retries work?
Show answer
Set retries in the config or CLI and failed tests re-run in a fresh context, with trace recorded on first retry to diagnose flakiness.
18
How do you override options like baseURL or viewport for one file?
Show answer
Call test.use at the top of the file or inside a describe block, for example test.use({ viewport: { width: 375, height: 812 }, locale: 'hi-IN' }). The options apply only to tests in that scope. Options you can set this way include baseURL, storageState, colorScheme and extraHTTPHeaders. Global defaults stay in the use block of playwright.config.
19
How do you test that duplicate POST requests do not create duplicate orders?
Show answer
If the API supports an idempotency key header, send the same POST twice with the same key and assert one order exists and both responses return the same id. Send it with different keys and expect two orders. Also try concurrent requests with Promise.all to check race conditions. Without a key, document the risk to the team.
20
Tell me about a time you introduced component tests to a frontend team.
Show answer
Situation: our end-to-end suite took 40 minutes and most failures were in form validation. Task: speed up feedback. Action: I set up Playwright component tests for the form library, wrote ten examples and a short guide, and paired with two developers on their first tests. Result: validation checks moved to component level, the end-to-end suite dropped to 25 minutes and developers began writing component tests themselves.
21
How do you use test.step and test annotations?
Show answer
test.step groups actions into named steps in reports; annotations such as test.skip, test.fixme and test.slow communicate intent and adjust behaviour.
22
How do you attach a screenshot or log to the report from inside a test?
Show answer
test('report', async ({ page }, testInfo) => {
await page.goto('/reports');
await testInfo.attach('report page', {
body: await page.screenshot(),
contentType: 'image/png',
});
await testInfo.attach('meta', { body: 'build 42', contentType: 'text/plain' });
});
23
What are closures?
Show answer
A function that remembers variables from its outer scope even after that scope has finished. They are used for private state and factory helpers.
24
How do you publish the Playwright HTML report from a CI pipeline?
Show answer
Keep the html reporter in the config. After the test step, add an upload-artifact step that runs even when tests fail, using a condition like always(), and upload the playwright-report folder with a retention period. Team members download and open it with npx playwright show-report. Some teams also publish it to static hosting for direct links.
25
What is testInfo and what can you do with it?
Show answer
testInfo is passed as the second argument to tests and hooks. It gives the test title, project name, retry number, status and output path. You can attach files, add annotations, change the timeout with testInfo.setTimeout, or skip conditionally. For example, attach extra logs only when testInfo.status differs from testInfo.expectedStatus.
26
Tell me about a time an accessibility check caught a real issue before release.
Show answer
Situation: a new checkout redesign was ready for release. Task: I had just added an axe scan to our Playwright smoke tests. Action: the scan flagged that the payment form inputs had placeholder text but no labels, and a keyboard test showed the pay button was unreachable with Tab. I raised it with screenshots and the rule links. Result: the developer fixed both in a day and the release went out on time.
27
How do you organise tests with page object model in Playwright?
Show answer
Create a class that takes a page, defines locators as properties and exposes action methods; instantiate it in a fixture for clean tests.
28
How do you filter a list of locators by text or by a child element?
Show answer
// pick one product card from many
const card = page.getByRole('listitem')
.filter({ hasText: 'Wireless Mouse' })
.filter({ has: page.getByRole('button', { name: 'Add to cart' }) });
await card.getByRole('button', { name: 'Add to cart' }).click();
// hasNotText and hasNot exclude matches
29
Promise.all vs Promise.allSettled vs Promise.race?
Show answer
all waits for every promise and rejects on the first failure; allSettled waits for all and reports each outcome; race settles with the first one to finish.
30
How do you keep API tests independent of environment data?
Show answer
Do not depend on records that happen to exist in a shared environment. Each test or fixture creates what it needs through the API and cleans up after. Read environment-specific values such as base URL and credentials from config. For reference data that must exist, seed it in a setup project and verify it before tests run.
31
How do you debug a test in VS Code with the Playwright extension?
Show answer
Install the Playwright Test for VS Code extension. Open the Testing panel to see tests, then set a breakpoint in the test file and click Debug Test. Execution stops at the breakpoint with the browser open, so you can inspect variables. Turn on Show browser to watch runs, and use Pick locator or Record at cursor to add steps.
32
How do you test file upload via API?
Show answer
Use request.post with multipart: { file: { name, mimeType, buffer } } and assert the response and stored file details.
33
Tell me about a bug you found through API testing that UI tests missed.
Show answer
Situation: the UI hid a delete button for normal users, so UI tests passed. Task: check permissions properly. Action: I called the delete endpoint directly with a normal user's token and it returned 204. Result: the team fixed the server-side permission check, and I added role-based API tests for every admin endpoint.
34
A beforeAll creates one user and tests in the same file fail randomly in parallel mode. Why?
Show answer
With fullyParallel, the file's tests run in different workers, so each worker creates its own user, or tests in one worker share one user and change its state. Shared mutable data causes random failures. Give each test its own data through a test-scoped fixture, or create a unique user per worker with workerInfo.workerIndex in the name.
35
How do you mock an API response?
Show answer
await page.route('**/api/users', route =>
route.fulfill({ status: 200, json: [{ id: 1, name: 'Test' }] })
);
36
How do you validate an API response in Playwright?
Show answer
Assert the status with expect(res.status()).toBe(200), parse res.json() and check fields, using schema validation for the structure.
37
Explain the event loop.
Show answer
JavaScript runs one call stack and uses queues for async work; the event loop pushes callbacks from the microtask (promises) and task queues when the stack is empty.
38
How do you read environment variables safely in a TypeScript test project?
Show answer
Load a .env file with a package like dotenv in playwright.config, then read process.env.BASE_URL. Values are string | undefined, so validate them early and throw a clear error if a required one is missing. Keep .env out of git and commit an .env.example instead. In CI, set the same names as secret variables.
39
What happens if you forget an await?
Show answer
The action runs without waiting, so the next step may run first — causing flaky failures or 'Target closed' errors. The @typescript-eslint/no-floating-promises rule catches it.
40
Test data is left behind when tests fail midway. How do you guarantee cleanup?
Show answer
Create the data inside a fixture and delete it after await use(). Fixture teardown runs even when the test fails or times out, so cleanup is reliable. Avoid cleanup steps at the end of the test body, because they never run after a failed assertion. As a safety net, tag test data with a prefix and run a nightly cleanup job.
Frequently asked questions
What does a Software Development Engineer in Test (SDET) do?
A developer-minded tester who writes automation code, test utilities and frameworks alongside product engineers. SDETs cover UI, API and integration testing and own quality in the pipeline. Interviews include data structures style coding in JavaScript or TypeScript, framework design questions, API testing, CI integration and discussions about test strategy, flakiness and code review. Expect to explain how your tests fit into the release process and how you work with developers.
Which skills are tested in a Software Development Engineer in Test (SDET) interview?
Expect questions on TypeScript coding, API test automation, Framework design, CI pipelines, Code reviews. Most rounds also ask you to explain a project and solve one practical problem live.
How do I prepare for a Software Development Engineer in Test (SDET) interview?
Revise JavaScript and TypeScript, API Testing, Framework Design and CI/CD, Fixtures and Hooks first using the topic sheets, practise the questions on this page aloud, then do one full mock interview to practise timing.
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