Interview Questions on REST API Automation Testing

Introduction – Why REST API Automation Testing Is Crucial in Interviews

In modern software development, applications are built using microservices and REST APIs. User interfaces change frequently, but backend APIs remain stable and critical to business functionality. Because of this, organizations strongly rely on REST API automation testing to ensure faster releases, better stability, and continuous delivery.

That’s why interview questions on REST API automation testing are asked in:

• Automation Testing interviews
  
• SDET roles
  
• Backend / API Testing roles
  
• CI/CD and DevOps-oriented QA positions
  

Interviewers want to assess whether you:

• Understand REST API fundamentals
  
• Can automate APIs using Java or Python
  
• Know HTTP methods and status codes
  
• Can validate business logic and data
  
• Have experience with real-time automation scenarios
  
• Can explain concepts clearly and practically
  

This article is a complete, SEO-optimised, interview-focused guide suitable for freshers, mid-level, and experienced QA professionals.

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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, without using the UI.

API testing ensures:

• Correct status codes
  
• Valid response data
  
• Proper business rule implementation
  
• Secure access
  
• Reliable performance
  

Simple Example

For a Create Order REST API:

• Valid request → 201 Created
  
• Missing mandatory field → 400 Bad Request
  
• Duplicate order → 409 Conflict
  

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REST vs SOAP vs GraphQL (Automation Interview Context)

Feature	REST	SOAP	GraphQL
Data Format	JSON / XML	XML only	JSON
Performance	Fast	Slower	Optimized
Automation Support	Excellent	Good	Limited
Popularity	Very High	Enterprise	Growing
Interview Focus	High	Medium	Low

👉 Most interview questions on REST API automation testing focus primarily on REST APIs.

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Interview Questions on REST API Automation Testing (100+)

Section 1: REST API Fundamentals (Q1–Q20)

1. What is REST API automation testing?
   Automating REST API test cases to validate backend functionality without UI.
   
2. Why automate REST APIs?
   They are faster, stable, and less flaky than UI tests.
   
3. What does REST stand for?
   Representational State Transfer.
   
4. What are REST principles?
   Statelessness, client-server, cacheability, uniform interface.
   
5. What is an endpoint?
   A URL representing an API resource.
   
6. What is a resource?
   An object or entity exposed via API.
   
7. What is request payload?
   Data sent to the API.
   
8. What is response payload?
   Data returned by the API.
   
9. What is statelessness in REST?
   Each request is independent.
   
10. What is idempotency?
    Same request produces the same result.
    
11. Difference between PUT and PATCH?
    PUT updates entire resource; PATCH updates partial fields.
    
12. What is authentication?
    Verifying user identity.
    
13. What is authorization?
    Verifying user permissions.
    
14. Common authentication methods?
    Bearer Token, OAuth, API Key, Basic Auth.
    
15. What is JWT?
    JSON Web Token used for stateless authentication.
    
16. What is JSON?
    

{

  “id”: 101,

  “name”: “Suresh”

}

17. What is XML?
    

<user>

  <id>101</id>

  <name>Suresh</name>

</user>

18. What is positive testing?
    Testing APIs with valid input.
    
19. What is negative testing?
    Testing APIs with invalid input.
    
20. What is API documentation?
    Details explaining API usage and structure.
    

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HTTP Methods – Core REST API Knowledge

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

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HTTP Status Codes – Frequently Asked in Interviews

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

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Section 2: REST API Automation Tools & Validations (Q21–Q50)

21. Which tools are used for REST API automation testing?
    Rest Assured, Postman + Newman, Python requests, SoapUI.
    
22. What is Rest Assured?
    A Java library for REST API automation.
    
23. What is Python requests library?
    A Python library to send HTTP requests.
    
24. What is Newman?
    A CLI tool to run Postman collections.
    
25. What validations are done in REST API automation?
    Status code, response body, headers, schema, response time.
    
26. Is validating status code enough?
    No, response data and business logic must be validated.
    
27. What is schema validation?
    Validating response structure.
    
28. What is response time testing?
    Checking API performance.
    
29. What is API chaining?
    Using one API’s response in another.
    
30. What is data-driven REST API testing?
    Testing APIs with multiple datasets.
    
31. What is API mocking?
    Simulating API responses.
    
32. What is rate limiting?
    Restricting number of API calls.
    
33. What is concurrency testing?
    Testing multiple users simultaneously.
    
34. What is backend validation?
    Validating database after API execution.
    
35. What is API security testing?
    Testing authentication and authorization.
    
36. What is environment testing?
    Testing APIs in dev, QA, UAT, prod.
    
37. What is CI/CD integration?
    Running API automation in pipelines.
    
38. What frameworks are used with Rest Assured?
    TestNG, JUnit, Maven.
    
39. What is assertion in API automation?
    Validation of expected results.
    
40. What is logging in API automation?
    Capturing request and response logs.
    
41. What is pagination testing?
    Validating page size and page number.
    
42. What is filtering testing?
    Validating query parameters.
    
43. What is sorting testing?
    Validating sorted responses.
    
44. What is caching?
    Temporary storage of API responses.
    
45. What is cache invalidation?
    Refreshing outdated data.
    
46. What is API smoke testing?
    Basic API health check.
    
47. What is API regression testing?
    Re-testing APIs after changes.
    
48. What is API contract testing?
    Validating client-server agreement.
    
49. What is error handling testing?
    Validating correct error responses.
    
50. Why REST API automation before UI automation?
    It is faster and more reliable.
    

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Real-Time REST API Automation Example

Request

POST /api/login

{

  “username”: “autoUser”,

  “password”: “pass123”

}

Response

{

  “token”: “abc789”,

  “expiresIn”: 3600

}

Validations

• Status code = 200
  
• Token is not null
  
• Expiry time > 0
  
• Token usable for secured APIs
  

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REST API Automation Code Snippets

Rest Assured – Java

given()

.contentType(“application/json”)

.body(payload)

.when()

.post(“/login”)

.then()

.statusCode(200);

Extract Token – Rest Assured

String token =

given()

.body(payload)

.when()

.post(“/login”)

.then()

.extract().path(“token”);

Python Requests

import requests

response = requests.get(url)

assert response.status_code == 200

Postman Test Script

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

  pm.response.to.have.status(200);

});

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Scenario-Based Interview Questions on REST API Automation Testing (15)

1. API returns 200 but incorrect data – how do you catch it?
   
2. Token expired but API still works – security issue?
   
3. Duplicate records created – how do you prevent this?
   
4. API returns 500 for invalid input – correct behavior?
   
5. Same request gives different responses – why?
   
6. API slow under heavy load – what test is needed?
   
7. Partial data saved after failure – how test rollback?
   
8. API works locally but fails in CI pipeline – reason?
   
9. Authorization missing but API accessible – defect?
   
10. Schema change breaks automation – how handle?
    
11. API works in Postman but fails in automation – why?
    
12. Rate limiting not implemented – impact?
    
13. Backend updated but response unchanged – issue?
    
14. Bulk API partially succeeds – how validate?
    
15. Random API timeouts – how debug?
    

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How Interviewers Evaluate REST API Automation Answers

Interviewers typically check:

• Understanding of REST fundamentals
  
• Strong automation approach
  
• Validation beyond status codes
  
• Real-time project experience
  
• Logical and confident explanations
  

👉 Practical explanations with examples score higher than theoretical definitions.

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REST API Automation Testing – Quick Revision Cheatsheet

• Master REST principles
  
• Memorize HTTP methods & status codes
  
• Validate response data thoroughly
  
• Practice Rest Assured or Python
  
• Understand CI/CD basics
  

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FAQs – Interview Questions on REST API Automation Testing

Q1. Is REST API automation mandatory for automation roles?
Yes, in most modern QA and SDET roles.

Q2. Is Postman enough for automation interviews?
For basics yes, but Rest Assured or Python is preferred.

Q3. Do freshers need REST API automation knowledge?
Basic understanding is expected.

Q4. Biggest mistake candidates make?
Only validating HTTP status codes.

Q5. How to prepare quickly for REST API automation interviews?
Practice CRUD APIs and scenario-based questions.