1. Role Expectations at 2 Years Experience (API Testing)
With 2 years of experience in API testing, interviewers expect you to be a strong functional/API tester, not just someone who sends requests in Postman. You should understand how APIs work, how systems interact, and how backend failures impact business flows.
What interviewers expect at this level
- Clear understanding of REST APIs and basic SOAP
- Ability to design API test scenarios independently
- Validate request/response, status codes, headers, and payloads
- Perform positive, negative, boundary, and security validations
- Use Postman / SOAPUI confidently
- Validate data using SQL queries
- Log high-quality API defects with RCA
- Understand STLC, SDLC, and Agile
- Support UI + API integrated testing
- Communicate defects clearly with developers
At 2 years, the focus is on practical API testing knowledge and real project experience, not just definitions.
2. Core API Testing Interview Questions & Structured Answers
Q1. What is API testing?
Answer:
API testing is the process of validating application programming interfaces to ensure they function correctly, return accurate responses, handle errors properly, and meet business requirements.
Unlike UI testing, API testing focuses on backend logic, data integrity, and system communication.
Q2. Why is API testing important?
Answer:
API testing is important because:
- It validates business logic early
- It is faster and more stable than UI testing
- It detects defects before UI is ready
- It ensures system-to-system integration works correctly
Q3. What types of APIs have you tested?
Answer:
- REST APIs
- Basic SOAP APIs (awareness level)
Q4. Difference between REST and SOAP APIs?
Answer:
| REST | SOAP |
| Lightweight | Heavy XML-based |
| JSON/XML | XML only |
| Uses HTTP methods | Uses WSDL |
| Faster | Slower |
Q5. What HTTP methods have you used?
Answer:
- GET – Fetch data
- POST – Create data
- PUT – Update data
- PATCH – Partial update
- DELETE – Remove data
Q6. What are common HTTP status codes?
Answer:
| Code | Meaning |
| 200 | OK |
| 201 | Created |
| 400 | Bad Request |
| 401 | Unauthorized |
| 403 | Forbidden |
| 404 | Not Found |
| 500 | Internal Server Error |
Q7. What validations do you perform in API testing?
Answer:
- Status code validation
- Response body validation
- Schema validation
- Header validation
- Authentication validation
- Data integrity validation
Q8. Difference between API testing and UI testing?
Answer:
API testing validates backend logic and data, while UI testing validates user interface and workflows.
API testing is faster, more reliable, and easier to automate.
Q9. What is idempotency?
Answer:
Idempotency ensures that multiple identical API requests produce the same result, preventing duplicate records.
Q10. What is pagination in APIs?
Answer:
Pagination limits the number of records returned per request to improve performance and manage large datasets.
3. STLC, SDLC & Agile (API Context)
Q11. Explain SDLC and your role as an API tester.
Answer:
| SDLC Phase | API Tester Role |
| Requirement Analysis | API spec review |
| Design | Request/response validation |
| Development | Early API testing |
| Testing | Functional & negative testing |
| Deployment | Smoke testing |
| Maintenance | RCA and monitoring |
Q12. Explain STLC in API projects.
Answer:
STLC includes requirement analysis, test planning, test case design, execution, and closure.
In Agile API projects, STLC runs continuously across sprints.
Q13. What is Agile testing in API projects?
Answer:
Agile API testing involves testing APIs early in sprint cycles, collaborating with developers, and validating endpoints continuously.
Q14. What Agile ceremonies do you attend?
Answer:
- Sprint planning
- Daily stand-ups
- Sprint review
- Retrospective
4. Scenario-Based API Interview Questions + RCA
Scenario 1: API Returns 200 but Data is Incorrect
RCA:
- Missing backend validation
- Incorrect business logic
Fix:
- Add business rule validation
- Update API response mapping
Scenario 2: Duplicate Records Created via API
RCA:
- No idempotency handling
- Retry mechanism without validation
Fix:
- Implement idempotency key
- Backend duplicate check
Scenario 3: API Accepts Invalid Payload
RCA:
- Missing schema validation
Fix:
- Add request schema validation
- Return 400 Bad Request
Scenario 4: API Performance Degrades Under Load
RCA:
- Inefficient database queries
- No caching
Fix:
- Optimize queries
- Introduce caching
Scenario 5: API Returns 500 Error Randomly
RCA:
- Unhandled exceptions
- Null pointer errors
Fix:
- Add exception handling
- Improve logging
5. API Test Case Examples (Detailed)
Sample API Test Case – POST API
| Field | Value |
| Test Case ID | API_TC_01 |
| Endpoint | /users |
| Method | POST |
| Scenario | Create user with invalid email |
| Payload | email=abc |
| Expected | 400 Bad Request |
| Priority | High |
GET API Test Case
- Validate response time
- Validate mandatory fields
- Validate pagination
Negative API Test Cases
- Missing mandatory fields
- Invalid data types
- Unauthorized access
6. Database Validation (API + SQL)
Why DB validation is required?
- To ensure API writes correct data
- To validate backend processing
Sample SQL Query
SELECT email, status
FROM users
WHERE user_id = 101;
7. Bug Reports & RCA (API Defects)
What makes a good API bug report?
- Endpoint and method
- Request payload
- Response body
- Status code
- Expected vs actual
- RCA if identified
Sample API Bug Report
| Field | Value |
| Summary | API returns 200 for invalid email |
| Endpoint | /users |
| Method | POST |
| Severity | High |
| Priority | High |
| RCA | Missing backend validation |
8. Tools Knowledge (Expected at 2 Years)
Postman
- Collections
- Environment variables
- Pre-request scripts (basic)
SOAPUI
- Basic SOAP requests
JIRA
- Defect logging
- Status tracking
TestRail
- API test case management
Selenium (Awareness)
- UI + API integration testing
SQL (Basic)
SELECT COUNT(*) FROM orders WHERE status=’FAILED’;
JMeter (Awareness)
- Load testing concepts
- Response time metrics
9. Domain Exposure (API Testing Examples)
Banking
- Account APIs
- Payment APIs
Insurance
- Policy and claims APIs
ETL / Data
- Data ingestion APIs
E-commerce
- Cart, order, payment APIs
10. Common Mistakes Candidates Make at 2 Years Experience
- Only knowing Postman UI
- No real defect examples
- Weak understanding of status codes
- Ignoring negative scenarios
- No RCA explanation
11. Quick Revision Cheat Sheet
- REST vs SOAP
- HTTP methods
- Status codes
- API validations
- Idempotency
- API defect lifecycle
12. FAQs + CTA
FAQ 1: Is automation required for API testing at 2 years?
Automation awareness is expected, but manual API testing is sufficient.
FAQ 2: Should I know SQL?
Yes. Basic SQL is mandatory for API validation.