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QA Engineer interview questions on manual testing, test case design, automation fundamentals, and bug lifecycle.
What is the difference between functional and non-functional testing?
Tip: Functional: tests WHAT the system does (login works, payment processes correctly). Non-functional: tests HOW WELL it does it (performance under load, security hardening, usability). Both are required.
What is the Software Testing Life Cycle (STLC)? List and explain each phase.
Tip: Phases: Requirement Analysis, Test Planning, Test Case Design, Environment Setup, Test Execution, Test Closure. QA is involved from requirements — not just at the end. Early defect detection is 10x cheaper than post-release fixes.
What is the difference between black-box and white-box testing?
Tip: Black-box: tester has no knowledge of internal code — tests against requirements (functional testing, UAT). White-box: tester knows the internal code — tests code paths, branches, and conditions (unit tests, code coverage).
What is regression testing and when is it run?
Tip: Regression testing: re-running existing test cases after a code change to ensure nothing that worked before is now broken. Run after every code change, especially before releases. Automated regression suites make this practical at scale.
What is Selenium WebDriver? What are its key limitations?
Tip: Selenium controls browsers via WebDriver protocol — ideal for simulating real user interactions. Limitations: flaky tests due to timing (use explicit waits, not Thread.sleep), no built-in test runner, slow compared to component tests. Playwright is the modern alternative.
What is the difference between TDD and BDD?
Tip: TDD (Test-Driven Development): write unit tests before code (red-green-refactor cycle). BDD (Behaviour-Driven Development): define behaviour in Given-When-Then language (Gherkin), bridging business and technical teams. TDD is a coding practice; BDD is a collaboration process.
How do you test a REST API? What aspects do you check and what tools do you use?
Tip: Check: status codes, response schema, error messages, edge cases (empty input, large payload), auth (unauthenticated gets 401, wrong role gets 403), performance (response time within SLA). Tools: Postman (manual), REST Assured (Java), pytest (Python), Newman (CI).
Tell me about the most critical bug you found. How did you find it and what was its impact?
Tip: Describe the bug discovery method: exploratory testing, edge case in test design, or automated test catching a regression. Quantify impact: "would have caused data loss for 12,000 users." Show you understand what made it critical.
You find a production-impacting bug 1 hour before a scheduled release. What do you do?
Tip: Immediately escalate to the release manager — do not try to fix it yourself in an hour. Assess severity and workaround availability. Document the bug clearly. The team decides: delay release, hotfix, or release with a known limitation.
What makes a good test case? List the essential attributes.
Tip: Essential attributes: unique ID, clear title, preconditions, step-by-step actions, expected result, actual result field, priority/severity. A good test case is: unambiguous, repeatable, traceable to a requirement, atomic (tests one thing), and maintainable.
How do you prioritise which bugs to test and report first?
Tip: Prioritise by: severity (data corruption > crash > functional failure > cosmetic) multiplied by frequency (how many users hit this). Align with the product manager on release goals.
When do you choose manual testing over automation? Give two concrete examples.
Tip: Manual is better for: exploratory testing (investigating unknown defects), short-lived features (automation ROI is negative if the feature ships once), usability testing (human judgement required). Automation wins for: regression, load testing, repetitive smoke tests.
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