Checkout.com India SDET Interview: Rounds, Questions and Preparation

What the job involves

SDETs at global tech companies design, build, and maintain automated test suites and test infrastructure for high-scale products, often working closely with developers in CI/CD pipelines. Day to day they write code to test APIs, UIs, and backend services, investigate flaky tests, and improve release confidence. At fintech employers like Checkout.com India, this includes testing payment flows, idempotency, and data consistency under load.

Role and technical knowledge

1. 1

   What is the difference between a manual tester and an SDET?

   A strong answer explains that an SDET writes production-quality automation code, builds test frameworks, and contributes to CI/CD, not just executes test cases. Mention coding, debugging, and ownership of test infrastructure.

2. 2

   How would you test a payment checkout flow end to end?

   Cover happy path, failed payments, retries, idempotency, currency rounding, webhook delivery, and database state after each step. Show that you think about both UI and backend validation.

3. 3

   Explain the Page Object Model and why it is used in Selenium.

   Describe separating page locators and actions from test logic to reduce duplication and improve maintenance. Mention how it helps when UI changes frequently.

4. 4

   What is idempotency in APIs and how would you test it?

   Explain that repeating the same request with the same idempotency key should not create duplicate side effects. Testing involves sending the same request twice and verifying only one transaction or record is created.

Practical scenarios and automation

1. 5

   You have a flaky test that passes locally but fails in CI. How do you debug it?

   Check environment differences, timing issues, test data, and parallel execution. Suggest adding logs, retries with reporting, and isolating the test to reproduce consistently before fixing the root cause.

2. 6

   How would you validate an API response that returns a list of transactions with pagination?

   Verify status code, schema, page size, total count, sorting, and boundary pages. Also test invalid page numbers, empty results, and consistency between page links and returned data.

3. 7

   Write a SQL query to find duplicate payment IDs in a transactions table.

   Use GROUP BY on payment_id with HAVING COUNT(*) > 1. Explain that you would then inspect the duplicates to decide if they are valid retries or data integrity bugs.

4. 8

   How do you decide what to automate versus what to test manually?

   Automate stable, high-value, repetitive checks like regression and API tests. Keep exploratory, visual, and one-off checks manual. Mention risk, frequency, and maintenance cost as factors.

Coding and problem solving

1. 9

   Given a string, find the first non-repeating character.

   Use a hash map to count characters in one pass, then scan again for the first count of one. Discuss time and space complexity.

2. 10

   How would you reverse a linked list iteratively?

   Walk through pointer manipulation with prev, current, and next. Mention edge cases like empty list and single node, and state O(n) time and O(1) space.

3. 11

   Write a function to check if a string is a valid palindrome, ignoring non-alphanumeric characters.

   Use two pointers moving inward, skipping non-alphanumeric characters and comparing case-insensitively. Mention handling empty strings and Unicode if relevant.

Behavioural and HR

1. 12

   Tell me about a time you found a critical bug. How did you handle it?

   Use STAR format: describe the bug, its impact, how you reproduced and reported it, and how you verified the fix. Show ownership and clear communication.

2. 13

   Why do you want to work as an SDET in a fintech company?

   Connect interest in quality, automation, and payments or financial systems. Mention learning opportunities, scale, and the importance of correctness in money movement.

3. 14

   Describe a situation where you disagreed with a developer about a bug.

   Show that you rely on evidence like logs, steps to reproduce, and expected versus actual behavior. Emphasize respectful resolution and focus on user impact.

4. 15

   Where do you see yourself in three years as an SDET?

   Talk about deepening automation and framework skills, learning performance or security testing, and eventually mentoring juniors. Align growth with the company's engineering needs.