Selenium API Testing Interview Questions

Introduction – Why Selenium API Testing Is Important in Interviews

Many testers associate Selenium only with UI automation, but in real projects, API testing and Selenium often work together. Interviewers therefore ask selenium api testing interview questions to evaluate whether candidates understand end-to-end automation, not just browser actions.

In interviews, Selenium API testing questions help assess:

• Understanding of API testing fundamentals
  
• How APIs are tested independently and along with UI
  
• Knowledge of REST APIs, HTTP methods, and status codes
  
• Ability to use Postman, Rest Assured, or Python APIs alongside Selenium
  
• Real-time experience with hybrid automation frameworks
  

This article is written for freshers to experienced QA engineers, using simple explanations, real-time examples, code snippets, and scenario-based questions—perfect for interview preparation.

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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 contain valid data
  
• Business rules are enforced
  
• Errors and edge cases are handled properly
  

Unlike Selenium (UI testing), API testing does not involve browsers and is faster, more stable, and closer to backend logic.

Simple Example

For a Login API:

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

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REST vs SOAP vs GraphQL (Selenium Tester Perspective)

Feature	REST	SOAP	GraphQL
Data Format	JSON / XML	XML only	JSON
Performance	Fast	Slower	Optimized
Selenium Usage	With API tools	Rare	Limited
Automation	Rest Assured / Python	SoapUI	Specialized
Interview Focus	High	Medium	Low

👉 In selenium api testing interview questions, REST API testing is the most common focus.

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Selenium API Testing Interview Questions & Answers (100+)

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

1. What is Selenium?
   Selenium is a tool used for automating web applications.
   
2. Can Selenium be used for API testing?
   No, Selenium is for UI testing; APIs are tested using tools like Postman or libraries like Rest Assured.
   
3. Why do interviewers ask Selenium API testing 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 and UI rendering.
   
6. What is 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 produces same result.
    
13. What is authentication?
    Verifying user identity.
    
14. What is authorization?
    Verifying user access.
    
15. Common authentication methods?
    Bearer Token, API Key, OAuth.
    
16. What is JSON?
    

{ “id”: 101, “name”: “Rahul” }

17. What is XML?
    

<user><id>101</id><name>Rahul</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?
    Defines how to use an API.
    

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HTTP Methods – Must Know for Selenium API Interviews

Method	Purpose
GET	Retrieve data
POST	Create data
PUT	Update entire resource
PATCH	Update partial resource
DELETE	Remove data

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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: Selenium + API Integration (Q21–Q45)

21. How do Selenium and API testing work together?
    APIs prepare test data for Selenium UI tests.
    
22. Why use API calls before Selenium tests?
    To avoid slow UI steps like login or setup.
    
23. Can Selenium validate API responses?
    Indirectly, by calling APIs using Java/Python code.
    
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 for sending 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 changes.
    
38. What is API security testing?
    Testing auth and authorization.
    
39. What is environment testing?
    Testing across dev, QA, prod.
    
40. What is CI/CD integration?
    Running API tests in pipelines.
    
41. What is assertion?
    Validation of expected result.
    
42. What is TestNG/JUnit role?
    Test execution and reporting.
    
43. What is logging in API tests?
    Capturing request/response.
    
44. What is API contract testing?
    Validating client-server agreement.
    
45. Why is API testing important before UI testing?
    To catch backend issues early.
    

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Real-Time API Validation Example

Request

POST /api/login

{

  “username”: “testuser”,

  “password”: “pass123”

}

Response

{

  “token”: “abc123”,

  “expiresIn”: 3600

}

Validations

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

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Automation Snippets (Selenium + API)

Postman – Basic Test

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

  pm.response.to.have.status(200);

});

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Rest Assured (Java)

String token =

given()

.body(payload)

.when()

.post(“/login”)

.then()

.statusCode(200)

.extract().path(“token”);

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Using API Token in Selenium

driver.manage().addCookie(new Cookie(“auth”, 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 Selenium API Testing 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 UI still works – issue?
   
4. API fails but Selenium 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 validation fails but UI shows success – bug?
    
15. API schema change breaks UI tests – prevention?
    

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How Interviewers Evaluate Selenium API Testing Answers

Interviewers focus on:

• Understanding of UI vs API testing roles
  
• Ability to integrate APIs with Selenium
  
• Real-time problem-solving skills
  
• Knowledge of backend validation
  
• Clear explanation with examples
  

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

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Selenium API Testing Interview Cheatsheet

• Selenium ≠ API testing (but they complement)
  
• 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 – Selenium API Testing Interview Questions

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

Q2. Is API testing mandatory for Selenium roles?
Increasingly, yes.

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

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

Q5. What impresses interviewers most?
Ability to explain API + Selenium integration with examples.