API Automation Testing Using Selenium Interview Questions

Introduction – Why API Testing Is Important in Interviews

In modern test automation roles, interviewers expect candidates to understand both UI automation and API automation. That’s why api automation testing using selenium interview questions are increasingly common in QA, SDET, and automation engineer interviews.

While Selenium is mainly used for UI testing, real-world frameworks combine Selenium with API tools to:

• Validate backend data before UI checks
  
• Speed up test execution
  
• Reduce flaky UI tests
  
• Ensure end-to-end test coverage
  

Interviewers test your ability to integrate API automation with Selenium, validate REST responses, handle authentication, and design efficient frameworks.

This article is written for freshers to experienced professionals, with clear explanations, real-time examples, scenario-based questions, and automation snippets.

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What Is API Testing? (Clear & Simple)

API testing is the process of testing application programming interfaces directly by sending requests and validating responses for correctness, performance, security, and reliability.

In one line:

API testing ensures backend logic works correctly without relying on the UI.

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REST vs SOAP vs GraphQL

Feature	REST	SOAP	GraphQL
Type	Architectural style	Protocol	Query language
Data format	JSON	XML	JSON
Performance	Fast & lightweight	Heavy	Optimized
Flexibility	High	Low	Very high
Usage	Most modern apps	Legacy systems	Modern apps

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60+ API Automation Testing Using Selenium Interview Questions & Answers

Selenium + API Basics (Freshers)

1. Can Selenium be used for API testing?
   Selenium itself is not used for API testing, but it is commonly integrated with API tools for end-to-end automation.
   
2. Why combine API testing with Selenium?
   To validate backend data before or after UI actions and reduce dependency on UI flows.
   
3. Which tools are commonly used with Selenium for API testing?
   Postman, SoapUI, Rest Assured, Python requests.
   
4. What is REST API?
   An architectural style that uses HTTP methods to access resources.
   
5. What is an endpoint?
   A URL that accepts API requests.
   
6. What is request payload?
   Data sent to the server in POST/PUT requests.
   
7. What is response payload?
   Data returned by the server.
   
8. What is statelessness in REST?
   Each request is independent and contains all required information.
   
9. What is idempotency?
   Multiple identical requests return the same result.
   
10. What is API automation?
    Automating API requests and validations using code.
    

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REST API Interview Questions

11. Which HTTP methods are most common?
    GET, POST, PUT, PATCH, DELETE.
    
12. Difference between POST and PUT?
    POST creates resources; PUT updates/replaces them.
    
13. What is JSON?
    Lightweight data-interchange format.
    

{

  “userId”: 101,

  “name”: “Srushti”,

  “role”: “QA”

}

14. What are headers in API testing?
    Metadata such as Content-Type and Authorization.
    
15. What is Content-Type header?
    Specifies request/response format (application/json).
    
16. What is query parameter?
    Parameters passed after ? in a URL.
    
17. What is path parameter?
    Dynamic value inside endpoint path.
    
18. What is pagination?
    Dividing large responses into pages.
    
19. What is API versioning?
    Managing changes using /v1, /v2, etc.
    
20. What is caching?
    Storing responses to reduce server load.
    

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Selenium + API Framework Questions

21. How do you use API calls in Selenium tests?
    Use API automation to set up test data before UI steps.
    
22. Give a real-time example of Selenium + API usage.
    Create a user via API → Login via UI → Validate profile.
    
23. What are benefits of API-first testing?
    Faster tests and stable automation.
    
24. How do you validate API response in Selenium framework?
    Use assertions in API layer before UI execution.
    
25. What is test data management in API automation?
    Creating and cleaning test data using APIs.
    

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Status Codes – Interview Must-Know

Status Code	Meaning
200	OK
201	Created
204	No Content
400	Bad Request
401	Unauthorized
403	Forbidden
404	Not Found
409	Conflict
500	Internal Server Error

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API Validation Example (Real-Time)

Request

GET /api/users/101

Response

{

  “id”: 101,

  “name”: “Srushti”,

  “email”: “srushti@test.com”

}

Validations

• Status code = 200
  
• id exists
  
• Email format is valid
  

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API Automation Tools & Code Snippets

Postman (Manual + Collection Runs)

Using Postman:

• Validate response body
  
• Verify status codes
  
• Use environment variables
  

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SoapUI (API Assertions)

Using SoapUI:

• JSONPath assertion
  
• XPath assertion
  
• Schema compliance
  

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Rest Assured (Java – With Selenium)

Using Rest Assured:

given()

  .baseUri(“https://api.test.com”)

.when()

  .get(“/users/101”)

.then()

  .statusCode(200)

  .body(“name”, equalTo(“Srushti”));

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Python API Automation

import requests

response = requests.get(“https://api.test.com/users/101”)

assert response.status_code == 200

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Scenario-Based REST API Testing Questions (10+)

31. API returns 200 but incorrect data – what do you do?
    Validate business logic and raise a defect.
    
32. How do you use API testing to reduce Selenium execution time?
    Prepare test data using APIs instead of UI steps.
    
33. How do you test authentication APIs?
    Validate valid, invalid, and expired tokens.
    
34. How do you test rate limiting?
    Send multiple requests and expect 429.
    
35. How do you test negative scenarios?
    Invalid payloads, missing headers, wrong data types.
    
36. How do you test file upload APIs?
    Validate file size, format, and response message.
    
37. How do you test dependent APIs?
    Chain requests and validate outputs.
    
38. How do you test concurrency?
    Send parallel requests and validate consistency.
    
39. How do you test backward compatibility?
    Validate older API versions still work.
    
40. How do you test API performance?
    Measure response time and SLA limits.
    

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How Interviewers Evaluate Your Answer

Interviewers look for:

• Understanding of API fundamentals
  
• Ability to integrate API automation with Selenium
  
• Knowledge of status codes
  
• Real-time framework usage examples
  
• Clear explanation of why APIs are tested
  

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API Automation Testing Cheat Sheet (Quick Revision)

• Use APIs to create test data
  
• Validate status + response body
  
• Cover positive & negative cases
  
• Handle authentication dynamically
  
• Reduce UI dependency
  
• Log defects with request/response
  

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FAQs – API Automation Testing Using Selenium

Q1. Is Selenium enough for API testing?
No. Selenium is for UI; API tools are required for backend testing.

Q2. Do interviewers expect API automation knowledge?
Yes, especially for automation and SDET roles.

Q3. Can freshers learn API automation easily?
Yes, basics are simple and highly valuable.

Q4. Which API tool is best with Selenium?
Rest Assured (Java) is most commonly used.