TCS API Testing Interview Questions

Introduction – Why API Testing Is Important in TCS Interviews

In TCS (Tata Consultancy Services) interviews, API testing has become a core skill for QA, automation, and digital testing roles. Since most TCS projects involve banking, insurance, telecom, retail, and enterprise systems, APIs play a critical role in backend communication.

That’s why tcs api testing interview questions focus on:

• Strong understanding of API testing fundamentals
  
• Knowledge of REST APIs, HTTP methods, and status codes
  
• Ability to test APIs using Postman or SoapUI
  
• Awareness of real-time project scenarios
  
• Basic understanding of automation (Java/Python) for experienced candidates
  

This article is written in a TCS interview-oriented style—simple explanations, real examples, and scenario-based questions that match actual TCS technical interview patterns.

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What Is API Testing? (Simple & Interview-Friendly)

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

• Correct request handling
  
• Accurate response data
  
• Proper status codes
  
• Business rule validation
  
• Secure access and error handling
  

Unlike UI testing, API testing checks the backend directly, making it faster and more reliable.

Simple Example

For a Fund Transfer API:

• Valid request → 200 OK
  
• Insufficient balance → 422 Unprocessable Entity
  
• Invalid account → 404 Not Found
  

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REST vs SOAP vs GraphQL (TCS Project Context)

Feature	REST	SOAP	GraphQL
Data Format	JSON / XML	XML only	JSON
Performance	Fast	Slower	Optimized
TCS Usage	Very High	High (banking)	Low
Testing Tools	Postman, Rest Assured	SoapUI	Limited
Interview Focus	High	Medium	Low

👉 In tcs api testing interview questions, REST and SOAP are most important.

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TCS API Testing Interview Questions & Answers (100+)

Section 1: API & REST Basics (Q1–Q20)

1. What is API testing?
   API testing validates backend services by testing requests, responses, and business logic.
   
2. Why is API testing important in TCS projects?
   Because most TCS projects are backend-heavy enterprise systems.
   
3. What is a REST API?
   An API that follows REST principles and uses HTTP methods.
   
4. What does REST stand for?
   Representational State Transfer.
   
5. What are REST principles?
   Statelessness, client-server, cacheability, uniform interface.
   
6. What is an endpoint?
   A URL representing an API resource.
   
7. What is request payload?
   Data sent to the API.
   
8. What is response payload?
   Data returned by the API.
   
9. What is statelessness?
   Each API request is independent.
   
10. What is idempotency?
    Same request gives the same result.
    
11. Difference between PUT and PATCH?
    PUT updates full resource; PATCH updates partial resource.
    
12. What is authentication?
    Verifying user identity.
    
13. What is authorization?
    Verifying user permissions.
    
14. Common authentication methods used in TCS projects?
    Bearer Token, OAuth, Basic Auth.
    
15. What is JWT?
    JSON Web Token used for stateless authentication.
    
16. What is JSON?
    

{

  “id”: 101,

  “name”: “Arjun”

}

17. What is XML?
    

<user>

  <id>101</id>

  <name>Arjun</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?
    Describes how to use an API.
    

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HTTP Methods – Frequently Asked in TCS Interviews

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

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HTTP Status Codes – Must-Know for TCS API Interviews

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 access
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: API Validation & Tools (Q21–Q45)

21. Which tools are used for API testing in TCS?
    Postman, SoapUI, Rest Assured, Python requests.
    
22. Why is Postman widely used in TCS?
    Easy to use and suitable for manual API testing.
    
23. What validations are done in API testing?
    Status code, response body, headers, schema, response time.
    
24. Is validating status code enough?
    No, response data and business logic must be validated.
    
25. What is header validation?
    Validating headers like Authorization and Content-Type.
    
26. What is schema validation?
    Validating response structure.
    
27. What is response time testing?
    Checking API performance.
    
28. What is API smoke testing?
    Basic API health check.
    
29. What is API regression testing?
    Re-testing APIs after changes.
    
30. What is API chaining?
    Using one API’s response in another.
    
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 calls.
    
35. What is API security testing?
    Testing authentication and authorization.
    
36. What is environment testing?
    Testing across dev, QA, UAT, prod.
    
37. What is API contract testing?
    Validating client-server agreement.
    
38. What is data-driven API testing?
    Testing APIs with multiple datasets.
    
39. What is logging in API tests?
    Capturing request/response details.
    
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 REST Assured?
    Java library for API automation.
    
44. What is Python requests library?
    Python library for API calls.
    
45. Why API testing before UI testing?
    To catch backend issues early.
    

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Real-Time API Validation Example (TCS-Style)

Request

POST /api/login

{

  “username”: “tcsuser”,

  “password”: “password123”

}

Response

{

  “token”: “xyz123”,

  “expiresIn”: 3600

}

Validations

• Status code = 200
  
• Token is not null
  
• Token expiry is valid
  
• Token used for further API calls
  

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Automation Snippets (Common in TCS Projects)

Postman – Basic Test

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

  pm.response.to.have.status(200);

});

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Rest Assured (Java)

given()

.contentType(“application/json”)

.body(payload)

.when()

.post(“/login”)

.then()

.statusCode(200);

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Python Requests

import requests

res = requests.get(url)

assert res.status_code == 200

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Scenario-Based TCS API Testing Interview Questions (15)

1. API returns 200 but incorrect data – how do you detect?
   
2. Duplicate transaction created – how to test?
   
3. API accepts invalid input – defect?
   
4. Token expired but API still works – risk?
   
5. API returns 500 for invalid input – correct?
   
6. API slow under heavy load – what test?
   
7. Partial data saved after failure – how detect?
   
8. API works in Postman but fails in application – reason?
   
9. Same request gives different responses – why?
   
10. Unauthorized user accesses data – issue?
    
11. Schema change breaks consumer apps – prevention?
    
12. API fails only in production – possible causes?
    
13. Rate limiting not enforced – impact?
    
14. API timeout occurs – how to test?
    
15. Backend updated but UI shows old data – issue?
    

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How TCS Interviewers Evaluate API Testing Answers

TCS interviewers focus on:

• Clear understanding of API fundamentals
  
• Ability to explain real project scenarios
  
• Knowledge of Postman and basic automation
  
• Logical thinking and structured answers
  
• Awareness of enterprise-level testing challenges
  

👉 Simple, clear, and practical answers score higher than complex theory.

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TCS API Testing Interview Cheatsheet

• Know REST basics and status codes
  
• Practice Postman thoroughly
  
• Validate response body, not just status
  
• Prepare real-time examples
  
• Understand banking/enterprise scenarios
  

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FAQs – TCS API Testing Interview Questions

Q1. Is API testing mandatory for TCS QA roles?
Yes, basic API testing knowledge is expected.

Q2. Is Postman enough for TCS interviews?
Yes, for manual testing roles.

Q3. Do freshers need automation knowledge?
Not mandatory, but awareness is a plus.

Q4. Biggest mistake candidates make?
Only checking status codes.

Q5. How to prepare quickly for TCS API interviews?
Practice CRUD APIs daily using Postman.