API Testing Interview Questions for 2 Years Experience

Introduction – Why API Testing Is Important in Interviews

Once you reach around 2 years of experience, interviewers no longer test you only on definitions. They expect you to explain how you actually test APIs in real projects.

In interviews, api testing interview questions for 2 years experience are designed to check whether you can:

• Validate backend logic beyond UI
  
• Understand REST APIs, HTTP methods, and status codes
  
• Use tools like Postman / SoapUI confidently
  
• Handle real-time issues such as wrong data, failures, and edge cases
  
• Write basic automation scripts or at least explain them
  

This article is a complete, mid-level interview guide with clear explanations, real-time examples, JSON/XML samples, status codes, Postman tests, and scenario-based questions.

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What Is API Testing? (Clear & Simple)

API testing is the process of verifying that Application Programming Interfaces work as expected by checking:

• Requests and responses
  
• Status codes
  
• Response body data
  
• Headers and authentication
  
• Business rules
  

Simple Example

For a login API:

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

At 2 years experience, interviewers expect you to say:
👉 “I validate status code, response body, token, and error message.”

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REST vs SOAP vs GraphQL (Interview Comparison)

Feature	REST	SOAP	GraphQL
Protocol	HTTP	XML-based	HTTP
Data Format	JSON / XML	XML only	JSON
Performance	Fast	Slower	Optimized
Flexibility	High	Low	Very High
Usage	Most modern apps	Banking/Legacy	Modern systems

👉 For 2 years experience, strong REST API knowledge is mandatory; basic SOAP understanding is enough.

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API Testing Interview Questions for 2 Years Experience (80+ Q&A)

Section 1: Core API Basics (Q1–Q20)

1. What is an API?

An API allows different software systems to communicate with each other.

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2. What is API testing?

API testing validates backend services by checking requests, responses, status codes, headers, and business logic.

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3. Why is API testing important?

Because APIs are used by multiple applications, one API defect can impact many systems.

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4. Difference between API testing and UI testing?

API testing validates backend logic; UI testing validates frontend behavior.

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5. Which APIs have you tested in your project?

Mostly REST APIs using Postman; some exposure to SoapUI.

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6. What HTTP methods have you used?

GET, POST, PUT, PATCH, DELETE.

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7. Difference between PUT and PATCH?

• PUT → Full update
  
• PATCH → Partial update
  

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8. What is an endpoint?

A specific URL that represents an API resource, e.g. /users/101.

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9. What is request payload?

Data sent to the API in the request body.

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10. What is response body?

Data returned by the API after processing the request.

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11. What is a stateless API?

Each request is independent and contains all required information.

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12. What is idempotency?

Repeating the same request multiple times gives the same result.

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13. What is API versioning?

Managing changes using versions like /v1, /v2.

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14. What is authentication?

Verifying identity using token, API key, or credentials.

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15. What is authorization?

Verifying whether a user has permission to access a resource.

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16. What authentication types have you tested?

Bearer Token, Basic Auth, API Key.

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17. What is JWT?

JSON Web Token used for secure API authentication.

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18. What is API schema?

Defines structure and data types of request and response.

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19. What is API chaining?

Using response data from one API as input for another API.

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20. What is negative API testing?

Testing API behavior with invalid or unexpected inputs.

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HTTP Status Codes – Must Know for 2 Years Experience

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	Invalid URL
409	Conflict	Duplicate record
422	Unprocessable	Business rule violation
500	Server Error	Backend failure

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Section 2: API Validation & Testing Types (Q21–Q45)

21. What validations do you perform in API testing?

• Status code
  
• Response body
  
• Headers
  
• Schema
  
• Response time
  

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22. Is validating only status code enough?

No. Response data and business rules must also be validated.

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23. What is positive API testing?

Testing APIs with valid input data.

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24. What is negative API testing?

Testing APIs with invalid data.

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25. What is boundary value testing?

Testing minimum and maximum allowed values.

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26. What is API regression testing?

Re-testing APIs after code changes.

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27. What is API smoke testing?

Basic health check of APIs.

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28. What is API security testing?

Testing authentication and authorization.

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29. What is API performance testing?

Testing response time and throughput.

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30. What is API rate limiting?

Restricting number of requests per user.

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31. What is pagination testing?

Validating page-wise data.

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32. What is filtering testing?

Validating query parameters.

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33. What is sorting testing?

Validating order of data in response.

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34. What is schema validation?

Ensuring response structure matches API contract.

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35. What is API mocking?

Simulating API responses when backend is unavailable.

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36. What is API rollback?

Reverting operations if failure occurs.

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37. What is data consistency testing?

Ensuring same data across systems.

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38. What is API concurrency testing?

Testing multiple requests at the same time.

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39. What is API caching?

Storing responses temporarily to improve performance.

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40. What is content-type validation?

Ensuring response is JSON/XML as expected.

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41. What is header validation?

Validating headers like Authorization and Content-Type.

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42. What is response time SLA?

Maximum acceptable API response time.

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43. What is contract testing?

Validating agreement between API provider and consumer.

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44. What is API monitoring?

Tracking API availability and failures.

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45. What is API throttling?

Limiting traffic to protect backend systems.

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Real-Time API Validation Example

Sample Request

POST /api/login

Content-Type: application/json

{

  “username”: “testuser”,

  “password”: “pass123”

}

Sample Response

{

  “token”: “abc.def.xyz”,

  “expires_in”: 3600,

  “userId”: 101

}

Validations

• Status code = 200
  
• Token is not null
  
• expires_in > 0
  
• userId is numeric
  

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Postman / Automation Basics (Expected at 2 Years Level)

Postman Test Script

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

  pm.response.to.have.status(200);

});

pm.test(“Token exists”, function () {

  var json = pm.response.json();

  pm.expect(json.token).to.not.be.undefined;

});

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Rest Assured (Basic – Java)

given()

  .contentType(“application/json”)

  .body(payload)

.when()

  .post(“/login”)

.then()

  .statusCode(200);

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Python Requests (Basic)

import requests

response = requests.post(url, json=payload)

assert response.status_code == 200

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Scenario-Based API Testing Interview Questions (15)

These are very common for 2 years experience:

1. API returns 200 but wrong data – what do you check?
   
2. Login API works, profile API fails – possible reasons?
   
3. Token expired but API still accessible – defect type?
   
4. API works in Postman but not in UI – why?
   
5. API slow only in production – possible causes?
   
6. Duplicate records created – what validation missed?
   
7. Unauthorized user accesses secured API – issue?
   
8. API crashes for special characters – what testing?
   
9. Same request returns different responses – why?
   
10. Payment deducted but order not created – what testing?
    
11. API returns null fields – how do you handle?
    
12. API response schema changes suddenly – impact?
    
13. API fails only in CI pipeline – reason?
    
14. API returns XML instead of JSON – issue?
    
15. Partial data saved after failure – what testing missed?
    

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How Interviewers Evaluate Answers (2 Years Experience)

Interviewers look for:

• Clear understanding of API basics
  
• Validation beyond status code
  
• Real project examples
  
• Logical debugging approach
  
• Tool knowledge (Postman mandatory)
  

👉 Practical thinking matters more than theory.

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API Testing Interview Cheatsheet (2 Years)

• Always validate response body
  
• Never trust only 200 status
  
• Test negative scenarios
  
• Check headers and schema
  
• Understand authentication clearly
  
• Be ready with real examples
  

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FAQs – API Testing Interview Questions for 2 Years Experience

Q1. Is Postman enough for 2 years experience?
Yes, Postman is mandatory; basic automation is a plus.

Q2. Do interviewers expect automation knowledge?
Basic understanding is expected, not advanced coding.

Q3. REST or SOAP – which is more important?
REST is more important.

Q4. Biggest mistake candidates make?
Validating only status codes.

Q5. How to prepare quickly?
Practice real APIs using Postman.