API Testing Using Selenium Interview Questions

Introduction – Why API Testing Using Selenium Is Asked in Interviews

Many candidates assume Selenium is only for UI testing, but in real-world automation projects, API testing and Selenium are used together to build faster, more reliable end-to-end test frameworks. Because of this, interviewers frequently ask api testing using selenium interview questions to check whether you understand how backend APIs and UI automation complement each other.

Interviewers want to know:

• Do you understand API testing fundamentals, not just Selenium clicks?
  
• Can you use APIs to prepare test data for Selenium tests?
  
• Do you know REST concepts, HTTP methods, and status codes?
  
• Can you explain real-time project scenarios where API + Selenium are combined?
  
• Do you understand basic automation using Java/Python with APIs?
  

This article is written in an interview-focused, simple, and technical style, suitable for freshers to experienced automation engineers.

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What Is API Testing? (Clear & Simple)

API testing is the process of validating Application Programming Interfaces to ensure that:

• Requests are processed correctly
  
• Responses return valid data
  
• Business rules are enforced
  
• Errors and edge cases are handled properly
  

API testing works at the backend/service layer and does not require a browser, making it:

• Faster than UI testing
  
• More stable
  
• Easier to debug
  

Simple Example

For a Login API:

• Valid credentials → 200 OK + token
  
• Invalid password → 401 Unauthorized
  
• Missing field → 400 Bad Request
  

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REST vs SOAP vs GraphQL (Selenium Automation Perspective)

Feature	REST	SOAP	GraphQL
Data Format	JSON / XML	XML only	JSON
Performance	Fast	Slower	Optimized
Selenium Usage	High (with API tools)	Limited	Rare
Automation Tools	Rest Assured, Python	SoapUI	Special libs
Interview Focus	Very High	Medium	Low

👉 In api testing using selenium interview questions, REST API testing is the main focus.

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API Testing Using Selenium Interview Questions & Answers (100+)

Section 1: Selenium + API Basics (Q1–Q20)

1. What is Selenium?
   Selenium is an automation tool used for testing web applications.
   
2. Can Selenium be used directly for API testing?
   No, Selenium is for UI testing; APIs are tested using tools or libraries.
   
3. Why do interviewers ask API testing using Selenium questions?
   To check understanding of end-to-end automation.
   
4. What is API testing?
   Testing backend services without UI.
   
5. Why is API testing faster than Selenium testing?
   Because it avoids browser interaction.
   
6. What is a REST API?
   An API that follows REST principles and uses HTTP methods.
   
7. What does REST stand for?
   Representational State Transfer.
   
8. What is an endpoint?
   A URL representing an API resource.
   
9. What is request payload?
   Data sent to the API.
   
10. What is response payload?
    Data returned by the API.
    
11. What is statelessness?
    Each request is independent.
    
12. What is idempotency?
    Same request gives the same result.
    
13. What is authentication?
    Verifying user identity.
    
14. What is authorization?
    Verifying user permissions.
    
15. Common authentication methods?
    Bearer Token, API Key, OAuth.
    
16. What is JSON?
    

{ “id”: 101, “name”: “Kiran” }

17. What is XML?
    

<user><id>101</id><name>Kiran</name></user>

18. What is positive testing?
    Testing with valid input.
    
19. What is negative testing?
    Testing with invalid input.
    
20. What is API documentation?
    Details on how to use an API.
    

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HTTP Methods – Must Know for API + Selenium Interviews

Method	Purpose
GET	Fetch data
POST	Create data
PUT	Update full resource
PATCH	Update partial resource
DELETE	Remove resource

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HTTP Status Codes – Interview Favorites

Code	Meaning	Example
200	OK	Successful GET
201	Created	Successful POST
204	No Content	Successful DELETE
400	Bad Request	Invalid input
401	Unauthorized	Invalid token
403	Forbidden	No permission
404	Not Found	Resource missing
409	Conflict	Duplicate data
422	Validation error	Business rule issue
500	Server Error	Backend failure

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Section 2: API + Selenium Integration Concepts (Q21–Q50)

21. How are APIs used with Selenium in real projects?
    For test data setup and teardown.
    
22. Why use API calls before Selenium tests?
    To avoid slow UI actions like registration or login.
    
23. How do you bypass UI login using APIs?
    By generating a token via API and injecting it into browser session.
    
24. What tools are used with Selenium for API testing?
    Postman, Rest Assured, Python requests.
    
25. What is Rest Assured?
    A Java library for REST API automation.
    
26. What is Python requests library?
    A Python library to send HTTP requests.
    
27. What is API chaining?
    Using one API’s response in another.
    
28. What is header validation?
    Validating headers like Authorization.
    
29. What is schema validation?
    Validating response structure.
    
30. What is response time testing?
    Validating API performance.
    
31. What is API smoke testing?
    Basic API health check.
    
32. What is API regression testing?
    Re-testing APIs after changes.
    
33. What is data-driven API testing?
    Testing APIs with multiple datasets.
    
34. What is API mocking?
    Simulating API responses.
    
35. What is rate limiting?
    Restricting API calls.
    
36. What is concurrency testing?
    Testing multiple users simultaneously.
    
37. What is backend validation?
    Validating database after API calls.
    
38. What is API security testing?
    Testing authentication and authorization.
    
39. What is environment testing?
    Testing across dev, QA, prod.
    
40. What is CI/CD integration?
    Running API + Selenium tests in pipelines.
    
41. What is assertion?
    Validation of expected results.
    
42. What role does TestNG/JUnit play?
    Test execution and reporting.
    
43. What is API contract testing?
    Validating client-server agreement.
    
44. Why validate APIs before UI?
    To catch backend defects early.
    
45. What is token-based authentication?
    Using tokens instead of sessions.
    
46. What is cookie-based authentication?
    Using browser cookies for auth.
    
47. How do APIs reduce Selenium flakiness?
    By avoiding unstable UI steps.
    
48. What is teardown using APIs?
    Deleting test data after tests.
    
49. Can Selenium validate API responses?
    Indirectly, via Java/Python code.
    
50. Why API testing is mandatory for automation roles?
    Because modern frameworks combine API + UI.
    

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Real-Time API Validation Example

Request

POST /api/login

{

  “username”: “autoUser”,

  “password”: “pass123”

}

Response

{

  “token”: “xyz789”,

  “expiresIn”: 3600

}

Validations

• Status code = 200
  
• Token is not null
  
• Token used in Selenium UI session
  

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Automation Snippets (API + Selenium)

Postman – Basic Test

pm.test(“Status code is 200”, function () {

  pm.response.to.have.status(200);

});

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Rest Assured – Extract Token

String token =

given()

.body(payload)

.when()

.post(“/login”)

.then()

.statusCode(200)

.extract().path(“token”);

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Inject Token into Selenium

driver.manage().addCookie(new Cookie(“authToken”, token));

driver.navigate().refresh();

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Python Requests

import requests

res = requests.get(url)

assert res.status_code == 200

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Scenario-Based API Testing Using Selenium Interview Questions (15)

1. UI login is slow – how can API help?
   
2. API returns 200 but wrong data – how detect?
   
3. Token expired but Selenium test still works – issue?
   
4. API fails but UI test passes – risk?
   
5. Same request gives different responses – why?
   
6. API accepts invalid input – defect?
   
7. Selenium test flaky due to backend issue – solution?
   
8. API works in Postman but fails in automation – reason?
   
9. Duplicate records created – how prevent?
   
10. API returns wrong status code – impact?
    
11. Data setup via UI vs API – which is better?
    
12. API slow under load – what test to run?
    
13. Unauthorized user accesses UI data – API issue?
    
14. Backend updated but UI shows success – bug?
    
15. API schema change breaks UI tests – how to prevent?
    

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How Interviewers Evaluate Your Answers

Interviewers look for:

• Clear understanding of API vs UI testing
  
• Knowledge of REST fundamentals
  
• Ability to integrate APIs with Selenium
  
• Real-time automation experience
  
• Logical explanations, not memorized definitions
  

👉 They want end-to-end automation thinkers, not just Selenium script writers.

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API Testing Using Selenium – Quick Revision Cheatsheet

• Selenium ≠ API testing (but they work together)
  
• Use APIs for test data setup
  
• Know REST basics & status codes
  
• Validate business logic, not just UI
  
• Be ready with real project examples
  

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FAQs – API Testing Using Selenium Interview Questions

Q1. Can Selenium test APIs directly?
No, Selenium is for UI; APIs are tested via libraries/tools.

Q2. Is API knowledge mandatory for Selenium roles?
Yes, in most modern automation roles.

Q3. Which is more important: API or UI testing?
Both; API testing is faster and more stable.

Q4. Do freshers need API testing knowledge?
Basic REST understanding is expected.

Q5. What impresses interviewers most?
Clear explanation of API + Selenium integration with examples.