Backblaze India SDET Interview: Rounds, Questions and Preparation

What the job involves

SDETs at global tech product companies build and maintain automated test frameworks, write code to validate APIs and UIs, and integrate tests into CI/CD pipelines. They work closely with developers to catch regressions early, improve test reliability, and ship high-quality software at speed. Day to day involves writing test code, debugging failures, and reviewing test coverage for new features.

Role and Technical Knowledge

1. 1

   What is the difference between a manual test case and an automated test script? When would you choose one over the other?

   Explain that manual tests are good for exploratory, usability, and one-time checks, while automation suits repetitive regression, smoke, and data-driven tests. Mention cost, maintenance, and frequency of execution.

2. 2

   How do you test a REST API endpoint that returns a list of files with pagination?

   Cover status codes, response schema, pagination parameters like limit and offset, boundary values, invalid tokens, and empty results. Mention using Rest Assured or Postman and validating JSON with JSON Schema.

3. 3

   What is the Page Object Model in Selenium and why is it useful?

   Explain that POM separates page locators and actions from test logic, improving readability and reducing duplication. Mention how it makes maintenance easier when UI changes.

4. 4

   How would you test a file upload feature that supports large files and multiple file types?

   Discuss valid and invalid file types, size limits, concurrent uploads, network interruptions, and checking the file integrity after upload. Mention both UI and API level validation.

Practical Scenarios and Debugging

1. 5

   Your automated test suite passes locally but fails in CI. How do you debug this?

   Check environment differences, timing issues, headless mode, test data setup, and CI logs. Suggest adding screenshots, video recording, and retry logic for flaky tests.

2. 6

   A test you wrote is flaky and passes only 70 percent of the time. What steps do you take?

   Identify root cause such as waits, dynamic locators, or shared state. Replace implicit waits with explicit waits, use stable selectors, and isolate test data. Mention running the test in a loop to reproduce.

3. 7

   How would you design a test strategy for a new feature that lets users share files via a public link?

   Cover functional tests for link generation, access control, expiry, and revocation. Include security tests for unauthorized access, performance tests for concurrent downloads, and negative cases like invalid links.

4. 8

   You find a critical bug just before a release. What do you do?

   Report it immediately with clear steps, logs, and impact. Discuss severity versus priority, suggest a workaround if possible, and recommend whether to delay the release based on risk.

Coding and Automation Fundamentals

1. 9

   Write a function to find the first non-repeating character in a string. Explain your approach and its time complexity.

   Use a hashmap to count frequencies in one pass, then iterate to find the first character with count 1. Mention O(n) time and O(1) space for a fixed character set.

2. 10

   How do you handle dynamic web elements in Selenium when IDs change on every page load?

   Use relative XPath or CSS selectors based on stable attributes, text, or parent-child relationships. Mention avoiding absolute XPaths and using explicit waits for element visibility.

3. 11

   What is the difference between implicit wait, explicit wait, and fluent wait in Selenium?

   Implicit wait applies globally for a fixed time. Explicit wait waits for a specific condition on an element. Fluent wait polls at intervals and ignores specific exceptions. Explain when to use each.

4. 12

   How do you connect to a database from your test code and verify that a record was inserted?

   Use JDBC or a similar library to run a SELECT query after the insert operation. Mention using a test database, cleaning up data, and avoiding hardcoded credentials.

Behavioural and HR Questions

1. 13

   Tell me about a time you found a bug that others missed. How did you handle it?

   Use the STAR method. Describe the bug, how you discovered it, its impact, and how you communicated it to the team. Show attention to detail and ownership.

2. 14

   Why do you want to work as an SDET instead of a developer or a manual tester?

   Talk about enjoying both coding and quality advocacy. Mention building tools, automating repetitive tasks, and preventing bugs early. Avoid saying you dislike development or testing.

3. 15

   Describe a situation where you had to learn a new tool or technology quickly for a project.

   Pick a real example like learning Selenium or Postman for a college project or internship. Explain your learning approach, resources used, and the outcome.

4. 16

   How do you handle feedback or criticism about your test cases or code?

   Show openness to feedback, ask clarifying questions, and iterate. Give an example where feedback improved your work. Emphasize collaboration over defensiveness.