01
What is contract testing?
Show answer
Verifying that a provider and consumer agree on request and response formats, using tools like Pact, to catch breaking changes early.
SDET (Software Development Engineer in Test) Interview Questions & Answers
40 questions for SDET (Software Development Engineer in Test) interviews — 4 easy, 34 medium, 2 hard.
About the SDET (Software Development Engineer in Test) role
A developer-minded tester who designs test frameworks, writes API and UI automation, adds tests to CI/CD pipelines and often contributes to testability of the product code. SDET interviews include Java coding rounds on strings and collections, framework design, API testing, mocking and pipeline questions, with a stronger focus on code quality than a typical automation role.
Java coding Framework design API automation CI/CD pipelines Mocking and contracts
Solved for this roleStart practicing
3 QUESTIONS FREESign up to unlock the full question bank and track your progress.Unlock every question and answer, then continue practising company-wise and package-wise.
3 questions free Unlock the rest in seconds
02
What is a quality gate in a CI/CD pipeline?
Show answer
A quality gate is a rule a build must pass before moving forward, such as all smoke tests passing, code coverage above a threshold, no critical static analysis issues, or no new high-severity vulnerabilities. If the gate fails, the pipeline stops and the change is not deployed. Gates make quality an automatic decision instead of a manual check.
03
Write a REST Assured PUT test that updates a resource using a POJO.
Show answer
@Test
public void updateUser() {
User update = new User("Ravi", "Lead QA");
given().spec(req)
.pathParam("id", 7)
.body(update)
.when()
.put("/users/{id}")
.then()
.statusCode(200)
.body("job", equalTo("Lead QA"));
}
04
POST vs PUT vs PATCH?
Show answer
POST creates a resource, PUT replaces the whole resource (idempotent) and PATCH updates part of it.
05
Your CI pipeline is blocked because a downstream service needed for API tests is often down. What do you do?
Show answer
Add a health check stage that pings dependencies before tests and marks the run as environment failure rather than test failure. For tests that do not need the real service, use stubs. Escalate with data on downtime frequency to the team owning the service. Keep a separate scheduled job for the real integration tests so pull requests are not blocked.
06
What is JsonPath and how do you use it for nested JSON?
Show answer
JsonPath (Groovy GPath syntax in REST Assured) navigates JSON with dot notation. For {"data":{"items":[{"price":10}]}} you use data.items[0].price. You can also filter: data.items.findAll { it.price > 5 }.name returns names of items costing more than 5. Use it inside body() assertions or via response.jsonPath().getList("data.items.name") to extract values for further checks.
07
Difference between ArrayList and LinkedList?
Show answer
ArrayList has fast random access and slower inserts in the middle; LinkedList has fast inserts and deletes but slow access by index.
08
How do you avoid page object classes becoming too large?
Show answer
Split pages into components for repeated or complex areas, keep only user actions as public methods, move generic helpers to BasePage or utilities, and avoid one method per element. If a page has distinct modes like view and edit, use separate classes. Review page classes during code review and refactor when they cross a few hundred lines.
09
Describe a time you improved the maintainability of an automation framework.
Show answer
Situation: our suite had duplicated locators across 200 tests and each UI release broke many of them. Task: reduce maintenance effort. Action: I introduced page objects and components for the top ten pages, added data-testid attributes with the developers and wrote a short guide. Result: fixing a UI change went from half a day to under an hour, and new joiners wrote tests faster.
10
What is a webhook and how do you test it?
Show answer
A callback where one system sends an HTTP request to another when an event occurs. Test with a mock receiver or tools such as webhook.site and verify the payload.
11
How do you validate an XML response in REST Assured?
Show answer
// REST Assured uses GPath for XML as well as JSON
given()
.accept(ContentType.XML)
.when()
.get("/orders/42")
.then()
.statusCode(200)
.contentType(ContentType.XML)
.body("order.@id", equalTo("42"))
.body("order.items.item.size()", equalTo(3))
.body("order.status", equalTo("SHIPPED"));
12
Tell me about a time you introduced BDD to a team. How did it go?
Show answer
Situation: requirements were often misread, causing rework late in sprints. Task: I proposed BDD for one module. Action: I ran short three-amigos sessions, wrote example scenarios with the BA, automated them with Cucumber and showed them in sprint review. Result: rework on that module dropped noticeably over two sprints, and the team adopted the practice for other complex stories.
13
How do you test API security basics as an automation tester?
Show answer
Check that endpoints reject missing or invalid tokens with 401, block users from other users' data with 403 or 404, validate input to prevent injection, do not leak stack traces or sensitive fields, enforce HTTPS and set security headers. Automate these as negative tests in the regression suite and work with the security team for deeper penetration testing.
14
What are the Actions class use cases?
Show answer
Mouse and keyboard actions such as hover, drag and drop, double click, right click and key combinations, built with moveToElement(...).perform().
15
What is the difference between static and non-static members?
Show answer
Static members belong to the class and are shared by all instances; non-static members belong to each object.
16
How do you pass authentication in an API test?
Show answer
Use headers such as Bearer tokens, basic auth, API keys or OAuth flows; fetch a token in a setup step and reuse it.
17
What are page components or page fragments in POM?
Show answer
Components are classes for UI parts that repeat across pages, such as the header, search bar, date picker or a data table. A page object then has-a component: homePage.header().search("laptop"). This follows composition over inheritance, avoids duplicate locators and matches modern component-based frontends. Components are usually scoped to a root WebElement so locators search only inside that element.
18
How do you handle a component that appears inside many different pages, like a modal dialog?
Show answer
Create a ModalComponent class scoped to the modal root element, with methods like title(), confirm() and cancel(). Pages that open modals return the component, such as cartPage.removeItem() returning ConfirmModal. The component waits for itself to appear and disappear. This keeps modal logic in one place and avoids copying locators into every page.
19
How do you validate a response against a JSON schema in REST Assured?
Show answer
Add the json-schema-validator dependency, place the schema file in src/test/resources, and assert with then().body(matchesJsonSchemaInClasspath("user-schema.json")). Schema validation checks field types, required fields and structure, so it catches contract changes that value checks might miss. It complements, not replaces, assertions on business values like status or totals.
20
What is the Page Object Model?
Show answer
A design pattern where each page is a class holding its locators and actions, so tests stay readable and a locator change is fixed in one place.
21
What are try-with-resources and why use them?
Show answer
A try block that automatically closes resources such as file readers or streams, preventing leaks without a finally block.
22
An API returns a list in random order and your assertion on the first element fails intermittently. How do you fix it?
Show answer
Do not assert on positions when the API does not guarantee order. Use order-independent Hamcrest matchers such as hasItem, hasItems or containsInAnyOrder on the extracted field, for example body("name", hasItems("Pen", "Book")). Or use GPath filtering like find { it.id == 42 } to pick the right item before checking its fields. If order matters for the feature, raise it as a requirement and request a sort parameter.
23
Tell me about a time you had to explain a technical test failure to a non-technical manager.
Show answer
Situation: a release was blocked by failing tests and the manager wanted to know if it was safe to ship. Task: explain the risk without jargon. Action: I separated the failures into one real bug, where customers could be charged twice, and three environment issues. I showed the bug with a short screen recording. Result: the manager delayed the release by one day, the bug was fixed and the environment issues were assigned to DevOps.
24
Write a REST Assured test that deserializes a response into a POJO.
Show answer
@Test
public void getUserAsPojo() {
User user = given()
.pathParam("id", 2)
.when()
.get("/users/{id}")
.then()
.statusCode(200)
.extract().as(User.class);
Assert.assertEquals(user.getId(), 2);
Assert.assertNotNull(user.getEmail());
}
25
Explain your CI/CD pipeline for tests.
Show answer
Code pushed to Git → Jenkins job triggers (webhook or schedule) → mvn clean test with the suite XML → reports and screenshots published → notifications on Slack/email → failures triaged before release.
26
What are filters in REST Assured?
Show answer
Filters intercept requests and responses, similar to middleware. They implement the Filter interface and can add headers, refresh tokens, log traffic, or attach request and response details to Allure reports with AllureRestAssured. You add them with given().filter(myFilter) or globally in a RequestSpecification. Filters keep cross-cutting concerns out of individual tests.
27
What are wrapper classes in Java?
Show answer
Classes such as Integer and Double that wrap primitive types as objects, needed for collections and for parsing text from web elements.
28
A developer changed the UI and 40 tests failed with NoSuchElementException. How does POM help here?
Show answer
Because locators live only in page classes, I check which page object methods fail, update the changed locators in those few classes, and rerun. Usually 40 failures map to two or three locators. I would also ask developers to add stable data-testid attributes and review UI changes with QA early, so future changes do not break tests unexpectedly.
29
Your code review shows a test class with 30 copy-pasted lines in every method. How do you refactor it with Java features?
Show answer
Extract repeated steps into private helper methods or a page object, move common setup into @BeforeMethod, and use a DataProvider when only data differs. If the repeated code differs only in a small action, pass that action as a lambda, such as a Consumer<WebDriver>. Rerun the tests after each small refactor to confirm behaviour is unchanged.
30
What is the difference between SOAP and REST?
Show answer
SOAP is a strict XML protocol with WSDL and WS-Security; REST is a lighter architectural style using HTTP and usually JSON.
31
What is method overriding and where is it useful in frameworks?
Show answer
A subclass redefines a parent method. Frameworks use it to customise base behaviour, such as overriding a wait or click method in a base page class.
32
How do you run Selenium tests in Docker containers in CI?
Show answer
Use official Selenium images, either standalone-chrome for simple runs or a Grid with hub and node containers via Docker Compose. The test container or Jenkins agent points RemoteWebDriver to http://selenium-hub:4444. Containers give the same browser version everywhere and are cleaned after each run. Add shm_size for Chrome stability and record videos for failed tests if needed.
33
How does HashMap work internally?
Show answer
It uses the key's hashCode to find a bucket and equals to resolve collisions, giving O(1) average lookups; Java 8 converts long buckets into trees.
34
Tell me about a time you moved from web automation to mobile automation.
Show answer
Situation: my team needed Android regression tests and I only knew Selenium. Task: deliver a smoke suite in one month. Action: I learned Appium 2 setup, used Appium Inspector to find locators, asked developers to add accessibility ids, and reused our TestNG, POM and reporting structure with a new driver factory. Result: twenty smoke tests ran nightly on emulators within four weeks, and release smoke testing dropped from half a day to forty minutes.
35
What are generics in Java and how do they help in a test framework?
Show answer
Generics let classes and methods work with a type parameter while keeping compile-time type safety, such as List<String> or a method <T> T readJson(String path, Class<T> type). In a framework they let you write one reusable helper for many types, for example a generic API client that deserializes responses into any POJO, or a BasePage method that returns the correct page type for chaining. They remove casts and catch type errors at compile time.
36
Your API tests started failing with SSL handshake errors on a new test server. What do you do?
Show answer
First confirm the server uses a self-signed or internal certificate. The proper fix is to import the company CA certificate into a truststore and configure REST Assured with trustStore(path, password). As a temporary measure in a test environment only, relaxedHTTPSValidation() skips checks. Never use relaxed validation against production, and raise the certificate issue with the infra team.
37
What is the use of the this and super keywords?
Show answer
this refers to the current object; super refers to the parent class, used to call parent constructors and methods.
38
Write a REST Assured test using RequestSpecBuilder and ResponseSpecBuilder.
Show answer
RequestSpecification req = new RequestSpecBuilder()
.setBaseUri(Config.baseUrl())
.setContentType(ContentType.JSON)
.addHeader("Authorization", "Bearer " + token)
.build();
ResponseSpecification ok = new ResponseSpecBuilder()
.expectStatusCode(200)
.expectContentType(ContentType.JSON)
.build();
given().spec(req).when().get("/orders").then().spec(ok);
39
You see ConcurrentModificationException in your test utility. What causes it and how do you fix it?
Show answer
It occurs when a collection is modified while being iterated with a for-each loop, for example removing items from an ArrayList inside the loop. Fix by using Iterator.remove(), removeIf(), collecting items to remove separately, or using CopyOnWriteArrayList or ConcurrentHashMap when threads share the collection. In parallel tests, shared lists are a common source.
40
What is the LoadableComponent pattern in Selenium?
Show answer
LoadableComponent is a Selenium support class that standardises how a page object ensures it is loaded. You extend it and implement load(), which navigates to the page, and isLoaded(), which throws an Error if the page is not ready. Calling get() checks isLoaded and calls load only if needed, then checks again. It gives a consistent, self-verifying way to open pages and fails fast with a clear message.
Frequently asked questions
What does a SDET (Software Development Engineer in Test) do?
A developer-minded tester who designs test frameworks, writes API and UI automation, adds tests to CI/CD pipelines and often contributes to testability of the product code. SDET interviews include Java coding rounds on strings and collections, framework design, API testing, mocking and pipeline questions, with a stronger focus on code quality than a typical automation role.
Which skills are tested in a SDET (Software Development Engineer in Test) interview?
Expect questions on Java coding, Framework design, API automation, CI/CD pipelines, Mocking and contracts. Most rounds also ask you to explain a project and solve one practical problem live.
How do I prepare for a SDET (Software Development Engineer in Test) interview?
Revise Core Java for Testers, API Testing and CI/CD, REST Assured, Page Object Model first using the topic sheets, practise the questions on this page aloud, then do one full mock interview to practise timing.
Topic sheets for this role
Other roles
More ways to practise
Company-wise Automation Testing questionsPackage-wise Automation Testing questionsExperience-wise Automation Testing questionsRole-wise Automation Testing questionsCity-wise Automation Testing questionsMost asked Automation Testing questionsScenario-based questionsPractical / hands-on questionsHR & behavioural questionsAutomation Testing mock interviewOnline assessment questionsTechnical round questionsManagerial round questionsAutomation Testing topic sheets