How to Prepare for a QA Engineer Interview: Complete Guide for Beginners

Everything you need to know to successfully pass a technical interview and start your career in testing

QA Interview

Are you preparing for a QA Engineer interview? Congratulations! You’ve chosen one of the most in-demand professions in IT. According to LinkedIn, demand for testing specialists has grown by 35% over the past year, and the average QA Engineer salary in 2026 ranges from $50,000 to $120,000 per year.

But to get this dream job, you need to pass the interview. And here many candidates face a problem: what exactly do you need to know?

Over my 5+ years in QA, I’ve been through dozens of interviews, conducted hundreds of interviews, and helped many colleagues prepare. In this article, I’ll share a structured preparation approach that really works.

📋 Table of Contents

  1. What They Ask in QA Interviews
  2. Testing Fundamentals: 7 Principles
  3. Types and Levels of Testing
  4. Test Design Techniques
  5. Defect Life Cycle
  6. Development Methodologies
  7. Practical Preparation Tips
  8. Questions to Ask the Interviewer

🎯 What They Ask in QA Interviews

A typical QA Engineer interview consists of several parts:

1. Theoretical Questions (40%)

  • Testing fundamentals
  • Types and levels of testing
  • Test design techniques
  • SDLC and methodologies

2. Practical Tasks (30%)

  • Writing test cases
  • Finding bugs on demo websites
  • Designing test scenarios
  • Live coding (for automation engineers)

3. Tools and Technologies (20%)

  • Bug tracking systems (JIRA)
  • Test management (Zephyr, TestRail)
  • Automation tools (Selenium, Playwright)
  • API testing (Postman)

4. Behavioral Questions (10%)

  • Teamwork
  • Conflict resolution
  • Examples from past experience

Important: 70% of candidates fail interviews specifically on theoretical questions. Knowledge of fundamentals is your foundation.

🧠 Testing Fundamentals: 7 Principles You Need to Know by Heart

These principles are the foundation. They’re asked at every interview.

Principle 1: Testing Shows the Presence of Defects, Not Their Absence

What this means: Even if you’ve run 1000 tests and found no bugs, it doesn’t mean bugs don’t exist. You can only reduce the probability of their presence.

Example for interview: “Imagine you tested the login function 100 times with different data and all tests passed. Can you guarantee bugs are absent? No, because there may be data combinations or scenarios you didn’t test.”

Principle 2: Exhaustive Testing is Impossible

What this means: It’s impossible to test all combinations of input data and scenarios. You need to use risk analysis and prioritization.

Real example: A 10-digit phone input field can have 10 billion combinations. Testing all combinations would take years. Instead, we use test design techniques (equivalence partitioning, boundary value analysis).

Principle 3: Early Testing Saves Time and Money

What this means: The earlier a bug is found, the cheaper it is to fix.

Statistics:

  • Bug found in requirements phase: fix cost = $1
  • Bug found in development phase: cost = $10
  • Bug found after release: cost = $100

What to do: Participate in requirements reviews, check design documents, write test cases before development starts.

Principle 4: Defect Clustering

What this means: 80% of bugs are usually found in 20% of modules (Pareto principle).

Practical application: If the payment module has already shown 15 bugs, and the profile module only 2, you should pay more attention to the payment module. It’s clearly more problematic.

Principle 5: Pesticide Paradox

What this means: If you constantly run the same tests, they stop finding new bugs. Like insects developing immunity to pesticides.

Solution:

  • Regularly update test cases
  • Add new scenarios
  • Use exploratory testing
  • Analyze bugs from production

Principle 6: Testing is Context Dependent

What this means: Testing approach depends on the type of application.

Examples:

  • E-commerce site: focus on UX, browser compatibility, performance
  • Medical software: strict security testing, regulatory compliance
  • Banking app: transaction security, calculation accuracy
  • Game: performance, graphics, usability

Principle 7: Absence of Errors Fallacy

What this means: Even if the product is 99% bug-free but doesn’t solve users’ needs — it’s a failure.

Story from practice: I worked on a banking application. After 3 months of testing, we released a version with zero critical bugs. But users complained that the money transfer process was too complex (8 steps instead of 3). The application was technically correct but useless.

Conclusion: QA should think not only about bugs but also about user experience.

🎨 Types and Levels of Testing

Testing Levels

Imagine a pyramid:

           /\
          /AT\      ← Acceptance Testing (Few, Slow, Expensive)
         /----\
        / ST   \    ← System Testing (Some)
       /--------\
      /   IT     \  ← Integration Testing (More)
     /------------\
    / Unit Tests  \ ← Unit Tests (Many, Fast, Cheap)
   /______________\

1. Unit Testing

  • What: Testing individual functions/methods
  • Who: Developers
  • Tools: JUnit, pytest, Jest
  • Example: Testing calculateDiscount(price, percentage) function

2. Integration Testing

  • What: Testing interaction between modules
  • Who: Developers or QA
  • Example: Authentication module interacts with database

3. System Testing

  • What: Testing the entire system as a whole
  • Who: QA team
  • Example: Testing complete flow: registration → login → purchase → payment

4. Acceptance Testing

  • What: Verifying business requirements compliance
  • Who: Clients, users, Product Owner
  • Types: UAT (User Acceptance Testing), Alpha, Beta

Functional Testing

Smoke Testing 🔥

  • When: After new build
  • Goal: Check that major functions work
  • Depth: Wide but shallow
  • Example: Can user login? Does homepage open? Are critical functions available?
  • Result: Go/No-Go for further testing

Sanity Testing 🧪

  • When: After bug fix or minor changes
  • Goal: Check specific functionality
  • Depth: Narrow but deep
  • Example: After fixing “Unable to reset password” bug — deeply test only password reset function

Regression Testing 🔄

  • When: After any code changes
  • Goal: Ensure new changes didn’t break existing functionality
  • Example: After adding new payment method, check that old methods still work

Exploratory Testing 🎭

  • When: In addition to planned tests
  • Goal: Find unexpected bugs through free exploration
  • Approach: No script, tester uses experience and intuition
  • Example: “What if I try entering emojis in the phone field?”

Non-Functional Testing

Performance Testing ⚡ Checking system performance under load.

Types:

  • Load Testing: Expected load (1000 concurrent users)
  • Stress Testing: Extreme load (10,000 users)
  • Spike Testing: Sudden spikes (0 → 5000 users in 1 minute)
  • Endurance Testing: Sustained load (1000 users for 24 hours)

Tools: JMeter, K6, Gatling, LoadRunner

Security Testing 🔒 Finding vulnerabilities and checking security.

What we check:

  • SQL Injection
  • XSS (Cross-Site Scripting)
  • CSRF (Cross-Site Request Forgery)
  • Authentication and authorization
  • Data encryption

Tools: OWASP ZAP, Burp Suite

Usability Testing 👤 Checking ease of use.

Criteria:

  • Can user achieve their goal?
  • How long does it take?
  • Is the interface intuitive?
  • Are users satisfied?

🛠 Test Design Techniques

This is gold for interviews. 90% of interviews include a practical test design task.

1. Equivalence Partitioning (EP)

Idea: Divide input data into partitions/classes where all values within the class behave the same.

Example: Age input field: Accepts 18-65

Classes:

  • Valid: 18-65 (test with 30)
  • Invalid 1: < 18 (test with 10)
  • Invalid 2: > 65 (test with 70)
  • Invalid 3: Non-numeric (test with “abc”)

Result: 4 test cases instead of 48!

2. Boundary Value Analysis (BVA)

Idea: Bugs most often occur at boundaries of ranges.

Rule: Test: min-1, min, min+1, max-1, max, max+1

Example: Age field accepts 18-65.

Test values:

  • 17 (min-1) ❌
  • 18 (min) ✅
  • 19 (min+1) ✅
  • 64 (max-1) ✅
  • 65 (max) ✅
  • 66 (max+1) ❌

3. Decision Table Testing

When to use: When result depends on combination of conditions.

Example: Login Testing

ConditionTest 1Test 2Test 3Test 4
Valid UsernameYesYesNoNo
Valid PasswordYesNoYesNo
ResultLogin SuccessErrorErrorError

4. State Transition Testing

When to use: When system can be in different states.

Example: Order Status

New → Paid → Shipped → Delivered
  ↓     ↓       ↓         ↓
Cancelled ← ← ← ← ← ← ← Cancelled

Test each valid transition and invalid transitions (e.g., Delivered → Paid should fail)

5. Use Case Testing

When to use: Derives test cases from use cases.

Example: Use Case: User purchases product

  1. User logs in
  2. User searches product
  3. User adds to cart
  4. User proceeds to checkout
  5. User makes payment
  6. System confirms order

Create test cases for each step and variations

6. Error Guessing

When to use: Uses tester’s experience to guess potential errors.

Example: Common errors to guess:

  • Divide by zero
  • Null pointer
  • Empty string
  • Special characters in input
  • Maximum integer overflow

🐛 Defect/Bug Life Cycle

Interview question: “Describe the bug life cycle from discovery to closure.”

Main States:

1. New Bug just discovered and logged in the system.

2. Assigned Bug assigned to specific developer for fixing.

3. Open Developer started working on the fix.

4. Fixed Developer claims bug is resolved. Code changes committed.

5. Retest QA re-tests the bug to verify if fix works.

6. Verified / Closed QA confirms bug is fixed. Bug is closed.

7. Reopened Bug still reproduces after fix attempt or reappears later.

Additional States:

Rejected

  • Not a valid bug
  • Cannot reproduce
  • Working as designed

Duplicate

  • Same bug already reported

Deferred

  • Valid bug but low priority
  • Will be fixed in future release

Severity vs Priority: What’s the Difference?

This is one of the most popular interview questions!

Severity — impact of bug on system functionality Priority — urgency of fixing the bug

Examples:

BugSeverityPriorityReason
Logo misaligned on homepageLowHighLow impact but visible to all users
Payment processing failsCriticalCriticalMajor functionality, affects revenue
Admin panel crashCriticalLowCritical issue but affects few users
Typo in footerLowLowMinimal impact, nobody notices

Golden rule:

  • Severity determined by QA (technical aspect)
  • Priority determined by Product Owner / business (business aspect)

🔄 Development Methodologies

Waterfall

Characteristics:

  • Sequential approach
  • Each phase completes before next begins
  • Testing at end of cycle

Phases: Requirements → Design → Development → Testing → Release

Pros: ✅ Simple and understandable structure ✅ Good documentation ✅ Works well for projects with clear requirements

Cons: ❌ Inflexible to changes ❌ Testing too late ❌ Expensive bug fixes

Agile / Scrum

Characteristics:

  • Iterative approach
  • Short development cycles (sprints 1-4 weeks)
  • Testing throughout entire cycle
  • Fast feedback

Key Ceremonies:

  • Sprint Planning: Planning work for sprint
  • Daily Standup: Daily 15-minute sync
  • Sprint Review: Demo of completed work
  • Sprint Retrospective: Process analysis and improvement

QA Role in Agile:

  • Testing from day 1 of sprint
  • Writing test cases parallel to development
  • Automation is critical
  • Close collaboration with developers
  • Participation in all ceremonies

Pros: ✅ Flexibility to changes ✅ Early bug detection ✅ Constant feedback ✅ Regular releases

Cons: ❌ Requires experienced team ❌ Less documentation ❌ Difficult to estimate timelines

V-Model

Characteristics:

  • Extension of Waterfall
  • Each development phase has corresponding testing phase

Structure:

Requirements ←───────→ Acceptance Testing
    ↓                        ↑
System Design ←──────→ System Testing
    ↓                        ↑
Architecture ←───────→ Integration Testing
    ↓                        ↑
Detail Design ←──────→ Unit Testing
    ↓                        ↑
         Coding

Pros: ✅ Testing planned early ✅ Clear correspondence between development and testing

Cons: ❌ Inflexible like Waterfall ❌ Not suitable for complex projects

💡 Practical Preparation Tips

2 Weeks Before Interview:

Week 1: Theory

  • Day 1-2: Study 7 testing principles
  • Day 3-4: Types and levels of testing
  • Day 5-6: Test design techniques
  • Day 7: Review + practical tasks

Week 2: Practice

  • Day 1-2: Write 20-30 test cases for real website
  • Day 3-4: Find bugs on public sites (e.g., demo e-commerce)
  • Day 5: Prepare answers to behavioral questions (STAR method)
  • Day 6: Study company and product
  • Day 7: Final review + Mock interview

Day Before Interview:

✅ Check tech

  • Stable internet connection?
  • Camera and microphone working?
  • Zoom/Teams installed and working?

✅ Prepare environment

  • Quiet place
  • Good lighting
  • Neutral background
  • Water nearby

✅ Prepare materials

  • Copy of resume
  • List of questions for interviewer
  • Notebook for notes

✅ Light review

  • Review 7 principles
  • Review differences: Smoke vs Sanity, Regression vs Retesting
  • Refresh knowledge of methodologies

❌ Don’t:

  • Don’t try to learn new topics
  • Don’t stay up late
  • Don’t stress (easier said than done, but try!)

During Interview:

STAR Method Structure:

  • Situation: Describe the context
  • Task: What was the task?
  • Action: What did you do?
  • Result: What was the outcome?

Example:

Question: “Tell me about a complex bug you found”

Bad answer: “I found a bug in login. Developer fixed it.”

Good answer: “Situation: On an e-commerce project, we were preparing for Black Friday release.

Task: During final regression testing, I discovered users couldn’t login if their email contained special characters (e.g., user+test@example.com).

Action: I immediately:

  1. Documented the bug with clear reproduction steps
  2. Showed live demonstration to team
  3. Conducted analysis: ~15% of our users use such emails
  4. Marked as Critical priority as it blocked access

Result: Developer fixed within 4 hours. We avoided losing 15% of users on the most important sales day. I also created a new category of test cases for checking special characters in all input fields.”

❓ Questions for the Interviewer

Never end an interview without questions. It shows disinterest.

About Processes:

  1. “What development methodology does the team follow?”
  2. “How is the testing process organized?”
  3. “What percentage of tests are automated?”
  4. “How often do releases happen?”

About Team:

  1. “What is the QA team structure?”
  2. “Who will I work most closely with?”
  3. “How is collaboration between QA and developers structured?”

About Growth:

  1. “What opportunities for learning and development?”
  2. “What does success look like in this role at 3, 6, 12 months?”
  3. “Is there budget for courses and certifications?”

About Technologies:

  1. “What technology stack does the team use?”
  2. “What testing tools do you use?”
  3. “Are you planning to implement new tools?”

About Product:

  1. “What are the most challenging aspects of the product from testing perspective?”
  2. “How do you ensure quality with fast releases?”

Closing:

  1. “What do you enjoy most about working here?”
  2. “What are the next steps in the interview process?”

🎓 Top 20 Questions from Real Interviews

Basic Concepts:

  1. What is software testing and why is it needed?

    • Process of checking software compliance with requirements
    • Finding defects before release
    • Improving product quality

  2. What’s the difference between verification and validation?

    • Verification: “Are we building the product right?” (compliance with specs)
    • Validation: “Are we building the right product?” (meeting user needs)

  3. What’s the difference between QA and QC?

    • QA: Proactive, process-oriented, prevents defects
    • QC: Reactive, product-oriented, detects defects

  4. Explain the difference between bug, defect, error, and failure

    • Error: Mistake in code made by developer
    • Bug/Defect: Deviation from expected behavior
    • Failure: System’s inability to perform function

  5. Name the 7 testing principles

    • [List all 7 principles we covered above]

Types of Testing:

  1. What’s the difference between Smoke and Sanity testing?

    • Smoke: Wide and shallow, on new build
    • Sanity: Narrow and deep, after fixes

  2. What’s the difference between Regression and Retesting?

    • Regression: Check new changes didn’t break existing functionality
    • Retesting: Check specific fixed bug

  3. What is exploratory testing?

    • Simultaneous learning, test design, and execution
    • No pre-written test cases
    • Based on tester’s experience

  4. Explain the difference between Black Box, White Box, and Gray Box testing

    • Black Box: No code knowledge, focus on functionality
    • White Box: Full code knowledge, focus on logic
    • Gray Box: Partial knowledge, combined approach

Practical Questions:

  1. How do you write a good test case?

    • Clear preconditions
    • Detailed steps (reproducible)
    • Specific expected results
    • Test data
    • Unique ID

  2. How do you prioritize testing?

    • Risk analysis
    • Functionality criticality
    • Usage frequency
    • Complexity
    • Business priorities

  3. What would you test in an input field?

    • Valid data
    • Boundary values
    • Invalid data
    • Special characters
    • Empty field
    • Maximum/minimum length
    • SQL injection / XSS

  4. How do you test a button?

    • Clickability
    • Visual state (enabled/disabled)
    • Text and localization
    • Positioning
    • Keyboard navigation (Tab, Enter)
    • System response to click

Life Cycle:

  1. Describe defect life cycle

    • New → Assigned → Open → Fixed → Retest → Verified/Closed
    • Or: Rejected, Duplicate, Deferred, Reopened

  2. What’s the difference between Severity and Priority?

    • Severity: Impact on system (technical)
    • Priority: Fix urgency (business)
    • Example: Misaligned logo = Low Severity, High Priority

Methodologies:

  1. What is Agile/Scrum? QA role in Agile?

    • Iterative development in short sprints
    • QA: testing from day 1, automation, close collaboration

  2. What are entry and exit criteria?

    • Entry Criteria: Conditions to start testing
    • Exit Criteria: Conditions to stop testing

Tools:

  1. What tools have you used?

    • Be honest, list only those you’ve actually worked with
    • For each, tell specific usage example

  2. What’s Test Plan vs Test Strategy?

    • Test Strategy: High-level, long-term approach (organizational)
    • Test Plan: Detailed plan for specific project/release

Behavioral:

  1. Tell me about a complex bug you found
    • Use STAR method
    • Show your analytical approach
    • Mention business impact

🚀 Conclusion: Your Pre-Interview Checklist

✅ Theory (memorize):

  • 7 testing principles
  • Verification vs Validation
  • QA vs QC
  • 4 testing levels
  • Smoke vs Sanity vs Regression vs Retesting
  • Severity vs Priority
  • Defect life cycle
  • Agile/Scrum basics

✅ Practice:

  • Wrote 20+ test cases
  • Found real bugs on demo sites
  • Practiced test design techniques
  • Prepared 3-5 STAR stories

✅ Preparation:

  • Studied company and product
  • Prepared questions for interviewer
  • Checked tech (camera, microphone, internet)
  • Well-rested and positively minded

💪 Final Advice

The most important thing in an interview is not knowing everything, but showing the ability to learn and think like QA.

If you don’t know the answer:

  1. Don’t panic — it’s normal
  2. Be honest — “I don’t know exactly, but here’s my hypothesis…”
  3. Show thinking — explain how you would find the answer
  4. Express interest — “That’s an interesting question, I’ll definitely study it”

Remember: Companies hire people who can grow, not those who already know everything.

Good luck on your interview! 🍀

If this article was helpful, give it a 👏 and share with friends who are also preparing for QA interviews.

Questions? Comments? Leave them below, I’ll be happy to answer!