SOAP and REST API Testing Interview Questions -

Introduction – Why API Testing Is Important in Interviews

In modern enterprise applications, SOAP and REST APIs are the backbone of system communication. Banking, insurance, telecom, healthcare, and e-commerce applications rely heavily on APIs to exchange data between systems.

Because of this, interviewers frequently ask SOAP and REST API testing interview questions to evaluate whether a candidate:

Understands both legacy SOAP and modern REST APIs

Can validate backend logic without relying on UI

Knows how to test XML and JSON responses

Can handle real-time API issues, failures, and edge cases

Has hands-on experience with tools like Postman, SoapUI, and ReadyAPI

This guide includes:

Clear explanations

Real-time examples

Request and response samples

Status codes

Automation snippets

Scenario-based interview questions

It is suitable for freshers as well as experienced API testers.

What Is API Testing? (Clear & Simple)

API testing is a type of software testing that validates the functionality, reliability, performance, and security of APIs (Application Programming Interfaces) by sending requests and verifying responses.

Instead of testing the graphical user interface (UI), API testing focuses on backend communication between systems. APIs act as intermediaries that allow different software applications to exchange data and communicate with each other.

API testing verifies whether APIs:

Return correct responses

Process requests accurately

Handle errors properly

Maintain security standards

Perform efficiently under load conditions

Why API Testing Is Important

Modern applications depend heavily on APIs for communication between:

Web applications

Mobile applications

Databases

Third-party services

Cloud platforms

If APIs fail, important business operations may stop functioning properly.

Areas Validated in API Testing

Functional Validation

Checks whether APIs work according to business requirements.

Data Validation

Ensures API responses contain accurate data.

Error Handling

Validates how APIs behave under invalid conditions.

Security Validation

Checks authentication and authorization mechanisms.

Performance Validation

Measures response time and scalability.

Example

Sending a GET request to:

/users/1

and validating whether the correct user details are returned in the response.

Real-Time Scenario

In a banking application, API testing verifies whether account balance APIs return accurate balance information after successful authentication.

REST vs SOAP vs GraphQL (Interview Comparison)

Feature	REST	SOAP	GraphQL
Protocol	HTTP	XML-based	HTTP
Payload	JSON / XML	XML only	JSON
Contract	OpenAPI	WSDL	Schema
Performance	Fast	Slower	Optimized
Common Usage	Modern apps	Banking / legacy	Modern microservices

Most soap and rest api testing interview questions focus on REST, but SOAP knowledge is mandatory for enterprise projects.

SOAP and REST API Testing Interview Questions & Answers (90+)

Section 1: API Basics (Q1–Q20)

1. What is an API?

An API (Application Programming Interface) allows two software systems to communicate with each other.

In modern applications, APIs act as intermediaries between:

Frontend and backend systems

Mobile apps and servers

Third-party integrations

Databases and services

For example:

A mobile banking app sends a request to an API

The API fetches account data from the backend

The response is returned to the mobile app

APIs are essential in microservices, cloud applications, e-commerce platforms, and enterprise systems.

2. What is API testing?

API testing validates:

API requests

API responses

Status codes

Headers

Authentication

Response schema

Business logic

Error handling

Unlike UI testing, API testing directly verifies backend functionality without relying on frontend screens.

Example:
For a login API, QA validates:

Valid credentials return token

Invalid credentials return proper error

Response time is acceptable

Sensitive data is protected

API testing improves reliability, integration quality, and backend stability.

3. Why is API testing important?

API testing is important because APIs are the backbone of modern applications.

One API failure can impact:

Web applications

Mobile apps

Payment systems

External integrations

Internal enterprise systems

Benefits of API testing:

Early defect detection

Faster execution compared to UI testing

Better backend coverage

Easier automation

Improved system reliability

In enterprise systems like banking and healthcare, API failures can cause major business impact.

4. Difference between API testing and UI testing?

API Testing	UI Testing
Validates backend logic	Validates frontend behavior
Faster execution	Slower execution
Stable and less UI-dependent	Affected by UI changes
Focuses on requests/responses	Focuses on user interactions
Easier to automate	More complex automation

API testing checks:

Data correctness

Business logic

Authentication

Integration behavior

UI testing checks:

Buttons

Forms

Layout

User workflows

Most modern QA teams perform both.

5. What types of APIs have you tested?

Commonly tested APIs include:

REST APIs

SOAP APIs

REST APIs

Use JSON mostly

Lightweight

Widely used in modern applications

SOAP APIs

Use XML

WSDL-based

Common in enterprise systems

Some projects may also use:

GraphQL APIs

Microservices APIs

6. What are HTTP methods?

HTTP methods define the type of action performed on resources.

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

These methods are heavily used in REST APIs.

7. What is GET request?

GET request retrieves data from the server.

Characteristics:

Read-only operation

Should not modify data

Parameters usually passed in URL

Example:

/customers/101

Used for:

Fetching user details

Viewing orders

Retrieving account information

8. What is POST request?

POST request creates new resources.

Example:
Creating a new customer account.

POST requests usually contain request payloads:

{
“name”: “Ravi”,
“balance”: 5000
}

POST is commonly used for:

Registration

Order creation

Payment submission

9. Difference between PUT and PATCH?

PUT

Used for full resource update.

Entire object is replaced.

Example:

{
“name”: “Ravi”,
“balance”: 7000
}

PATCH

Used for partial update.

Only specific fields are modified.

Example:

{
“balance”: 7000
}

PATCH is more efficient when only small updates are required.

10. What is DELETE request?

DELETE request removes a resource from the system.

Example:
Deleting a customer account.

Expected validations:

Resource removed successfully

Correct status code returned

No orphan data remains

DELETE operations should also validate authorization and rollback behavior.

11. What is an endpoint?

An endpoint is a URL representing a specific API resource.

Example:

/customers/101

Where:

/customers = resource

101 = specific customer ID

Endpoints are used by applications to interact with backend services.

12. What is request payload?

Request payload is the data sent to the API in the request body.

Example:

{
“username”: “testuser”,
“password”: “pass123”
}

Payloads are mainly used in:

POST requests

PUT requests

PATCH requests

QA validates:

Mandatory fields

Data types

Invalid inputs

Boundary values

13. What is response body?

Response body is the data returned by the API after processing the request.

Example:

{
“token”: “abc.def.xyz”,
“status”: “SUCCESS”
}

QA engineers validate:

Correct values

Data structure

Schema

Business rules

Sensitive information exposure

14. What is stateless API?

Stateless API means each request is independent.

The server does not remember previous requests automatically.

Each request must include:

Authentication

Headers

Required parameters

REST APIs are generally stateless.

Benefits:

Scalability

Simplicity

Better performance

15. What is idempotency?

Idempotency means repeating the same request multiple times produces the same result.

Example:
Deleting the same resource repeatedly should not create different outcomes after initial deletion.

Idempotency is important in:

Payment systems

Retry mechanisms

Distributed systems

GET, PUT, and DELETE are generally idempotent.

16. What is authentication?

Authentication verifies user identity.

Common methods:

Basic Authentication

Bearer Token

OAuth

API Keys

Example:
User logs in using credentials and receives access token.

Authentication ensures only valid users access the API.

17. What is authorization?

Authorization verifies user permissions after authentication.

Example:

Admin can delete accounts

Regular user cannot access admin APIs

Authentication = who the user is
Authorization = what the user can access

18. What authentication methods have you used?

Common authentication methods:

Basic Auth

Bearer Token

OAuth 1.0

OAuth 2.0

Basic Auth

Uses username and password.

Bearer Token

Uses access token in Authorization header.

OAuth

Widely used for secure enterprise authentication.

19. What is API versioning?

API versioning manages API changes without breaking existing consumers.

Example:

/api/v1/users
/api/v2/users

Benefits:

Backward compatibility

Controlled upgrades

Safer deployments

20. What is negative API testing?

Negative testing validates API behavior with invalid inputs.

Examples:

Invalid credentials

Missing headers

Invalid payload

Expired token

Special characters

Goal:
Ensure APIs fail gracefully without crashing.

REST vs SOAP – Interview-Focused Differences

Aspect	REST	SOAP
Data format	JSON/XML	XML only
Protocol	HTTP	HTTP/SMTP
Security	OAuth, JWT	WS-Security
Performance	Faster	Slower
Contract	Optional	Mandatory WSDL

HTTP Status Codes – Must Know

Code	Meaning	Example
200	OK	Successful GET
201	Created	Successful POST
204	No Content	Successful DELETE
400	Bad Request	Invalid input
401	Unauthorized	Invalid credentials
403	Forbidden	Access denied
404	Not Found	Invalid endpoint
409	Conflict	Duplicate record
422	Unprocessable Entity	Business rule failure
500	Server Error	Backend crash

21. What validations do you perform in REST API testing?

Common validations:

Status code validation

Response body validation

Header validation

Schema validation

Authentication validation

Response time validation

Business logic validation

Strong QA engineers validate both technical and business behavior.

22. Is status code validation enough?

No.

Even if status code is 200:

Response data may be wrong

Business rules may fail

Schema may change

Null values may exist

Interviewers expect validation beyond status codes.

23. What is JSON?

JSON (JavaScript Object Notation) is a lightweight data-interchange format widely used in REST APIs.

Example:

{
“id”: 101,
“name”: “Ravi”,
“balance”: 5000
}

Benefits:

Human-readable

Lightweight

Easy parsing

Faster transmission

24. What is schema validation?

Schema validation ensures API response structure matches expected contract.

Checks include:

Required fields

Data types

Nested objects

Field formats

Schema validation helps detect backend contract changes quickly.

25. What is pagination testing?

Pagination testing validates APIs returning large datasets page by page.

Validations:

Correct page size

Total records count

No duplicate data

Correct navigation between pages

Important in:

Search APIs

E-commerce listings

Reporting systems

26. What is filtering testing?

Filtering testing validates query parameter behavior.

Example:

/users?status=active

Expected:
Only active users returned.

27. What is sorting testing?

Sorting testing validates response ordering.

Example:

Ascending by name

Descending by date

QA checks:

Correct order

Consistent results

Stable sorting

28. What is API rate limiting?

Rate limiting restricts number of requests within time period.

Purpose:

Prevent abuse

Protect servers

Maintain performance

Example:
100 requests per minute.

29. What is API regression testing?

Regression testing re-validates APIs after changes.

Performed after:

Bug fixes

Feature updates

Deployments

Ensures existing functionality still works.

30. What is API smoke testing?

Smoke testing validates basic API health.

Checks:

APIs accessible

Core functionality working

Authentication functioning

Usually executed before detailed testing.

31. What is API security testing?

Security testing validates:

Authentication

Authorization

Data protection

Vulnerability handling

Common issues tested:

SQL injection

Unauthorized access

Sensitive data exposure

32. What is API performance testing?

Performance testing measures:

Response time

Throughput

Stability under load

Helps identify bottlenecks and scalability issues.

33. What is API mocking?

API mocking simulates API responses without real backend.

Useful when:

Backend unavailable

Third-party APIs expensive

Frontend development continues independently

34. What is API caching?

Caching stores responses temporarily for faster retrieval.

Benefits:

Improved performance

Reduced server load

Faster response times

QA validates cache consistency and expiration behavior.

35. What is content-type validation?

Content-type validation ensures APIs return expected formats.

Examples:

application/json

application/xml

Important for integration compatibility.

36. What is header validation?

Header validation checks important headers such as:

Authorization

Content-Type

Cache-Control

Headers are critical in secured APIs.

37. What is API rollback?

Rollback ensures no partial data remains after failure.

Example:
Payment deducted but order creation failed.

Expected:
Entire transaction reverts safely.

38. What is API concurrency testing?

Concurrency testing validates API behavior under simultaneous requests.

Checks:

Race conditions

Duplicate records

Data corruption

System stability

Very important for banking and ticket-booking systems.

39. What is data consistency testing?

Data consistency testing ensures same data appears correctly across systems.

Example:
Order data should match:

Database

API response

UI display

40. What is contract testing?

Contract testing validates agreement between API provider and consumer.

Checks:

Request structure

Response schema

Field expectations

Prevents integration failures between teams.

41. What is API monitoring?

API monitoring tracks:

Uptime

Failures

Response times

Availability

Helps identify production issues early.

42. What is throttling?

Throttling limits traffic temporarily to protect backend systems.

Different from rate limiting because it dynamically controls load during spikes.

43. What is API chaining?

API chaining uses output from one API in another API request.

Example:

Token used in profile API

Profile ID used in orders API

Simulates real workflows.

44. What is negative testing?

Negative testing validates invalid scenarios.

Examples:

Missing mandatory fields

Invalid tokens

Unsupported methods

Invalid formats

Ensures robust error handling.

45. What is boundary value testing?

Boundary testing validates minimum and maximum values.

Example:
If quantity allowed is 1–100:

Test 0

Test 1

Test 100

Test 101

Helps identify edge-case failures.

Section 3: SOAP API Testing Interview Questions (Q46–Q70)

46. What is SOAP?

SOAP (Simple Object Access Protocol) is an XML-based messaging protocol used for communication between applications over a network.

SOAP is commonly used in enterprise applications because it provides:

Standardized communication

Strong security

Reliable messaging

Structured contracts

SOAP APIs usually communicate through:

HTTP

HTTPS

SMTP

SOAP is heavily used in industries such as:

Banking

Insurance

Telecom

Healthcare

Unlike REST APIs, SOAP follows strict standards and uses XML for all request and response messages.

47. What is WSDL?

WSDL stands for Web Services Description Language.

It is an XML document that defines the SOAP web service contract.

WSDL contains:

Available operations

Request formats

Response formats

Endpoints

Data types

Protocol details

In SOAP testing, WSDL acts like a blueprint for the API.

Tools like:

SoapUI

ReadyAPI

can automatically generate SOAP requests using WSDL.

48. What is SOAP envelope?

SOAP Envelope is the root element of a SOAP message.

It defines:

Start of SOAP message

XML namespaces

Structure of the message

Example:

<soapenv:Envelope>
  <soapenv:Header/>
  <soapenv:Body>
  </soapenv:Body>
</soapenv:Envelope>

Every SOAP request and response must contain an envelope.

49. What are SOAP headers?

SOAP headers carry:

Security information

Authentication tokens

Metadata

Transaction details

Headers are optional but commonly used in enterprise applications.

Examples:

WS-Security tokens

Session information

Correlation IDs

SOAP headers help manage enterprise-level security and communication.

50. What is SOAP body?

SOAP Body contains the actual request or response data.

Example:

<soapenv:Body>
  <getBalance>
     <accountId>101</accountId>
  </getBalance>
</soapenv:Body>

The body contains business-related information exchanged between systems.

51. What is SOAP fault?

SOAP Fault is an error response returned by a SOAP service.

It provides detailed error information such as:

Invalid request

Authentication failure

Server processing issues

Missing fields

Example:

<soap:Fault>
<faultcode>SOAP-ENV:Client</faultcode>
<faultstring>Invalid account ID</faultstring>
</soap:Fault>

SOAP Faults are application-level errors.

52. What is WS-Security?

WS-Security is a security standard used in SOAP web services.

It provides:

Message encryption

Digital signatures

Authentication

Message integrity

WS-Security is commonly used in:

Banking APIs

Healthcare systems

Enterprise integrations

It provides stronger enterprise-level security than typical REST implementations.

53. What tools are used for SOAP testing?

Common SOAP testing tools include:

SoapUI

ReadyAPI

These tools support:

WSDL import

XML validation

XPath assertions

SOAP Fault handling

Security testing

54. How do you validate SOAP responses?

SOAP responses are validated using:

XPath assertions

XML schema validation

SOAP Fault validation

Header validation

Example XPath validation:

//balance > 0

QA engineers validate:

Correct XML nodes

Proper schema structure

Business values

No SOAP faults

55. What is XML?

XML (Extensible Markup Language) is a markup language used for structured data exchange.

SOAP APIs primarily use XML.

Example:

XML is:

Structured

Hierarchical

Human-readable

Extensible

56. What is schema validation in SOAP?

Schema validation checks whether XML responses match the expected XSD schema.

Validation checks:

Mandatory fields

Data types

XML structure

Element order

Schema validation helps identify:

Contract changes

Missing nodes

Incorrect formats

57. What is SOAP authentication?

SOAP authentication verifies user or system identity.

Methods include:

Username/password

Security tokens

Certificates

WS-Security headers

Enterprise SOAP services often use certificate-based authentication for enhanced security.

58. Difference between SOAP fault and HTTP error?

SOAP Fault	HTTP Error
Application-level error	Protocol-level error
Returned inside SOAP XML	Returned as HTTP response
Business/service issue	Communication/request issue

Example:

SOAP Fault → Invalid business data

HTTP 404 → Endpoint not found

59. What is SOAP version?

The two major SOAP versions are:

SOAP 1.1

SOAP 1.2

Differences include:

Content-Type handling

Fault structure

Processing rules

SOAP 1.2 provides improved standards and error handling.

60. What is SOAP action?

SOAP Action defines the intent of the SOAP request.

It tells the server:

Which operation to execute

Which service action is requested

Example:

SOAPAction: “getBalance”

Incorrect SOAP action values may cause request failures.

61. What is document vs RPC style?

These are two SOAP message styles.

Document Style

XML document-oriented

More flexible

Commonly used today

RPC Style

Function/method-oriented

Simulates remote procedure calls

Document style is preferred in modern enterprise services.

62. What is message-level security?

Message-level security protects the SOAP message itself.

Security applies directly to XML content.

Benefits:

End-to-end encryption

Secure intermediaries

Message integrity

This differs from transport-level security like HTTPS.

63. What is SOAP performance testing?

SOAP performance testing measures:

Response time

Throughput

Scalability

Stability under load

Enterprise SOAP services can become slow due to XML processing overhead.

Performance testing helps identify bottlenecks.

64. What is SOAP regression testing?

SOAP regression testing ensures existing functionality still works after:

Bug fixes

Enhancements

Deployments

Regression testing is important because enterprise SOAP systems are often interconnected.

65. What is SOAP data-driven testing?

SOAP data-driven testing runs the same SOAP request using multiple XML datasets.

Example:
Testing balance API with:

Valid accounts

Invalid accounts

Closed accounts

High-volume accounts

This improves test coverage significantly.

66. What is SOAP mocking?

SOAP mocking simulates SOAP service behavior without actual backend dependency.

Useful when:

Backend unavailable

Third-party services costly

Integration incomplete

Mock services help continue frontend and QA testing independently.

67. What is SOAP endpoint?

SOAP endpoint is the URL where SOAP service is hosted.

Example:

https://bankapi.com/services/accountService

Clients send SOAP requests to the endpoint.

68. What is SOAP binding?

SOAP binding defines:

Communication protocol

Message format

Encoding style

Bindings describe how SOAP messages are transmitted between systems.

Common bindings:

HTTP binding

HTTPS binding

69. What is SOAP transport?

SOAP transport defines how SOAP messages travel across the network.

Most common transports:

HTTP

HTTPS

SMTP

HTTPS is preferred for secure enterprise communication.

70. What is SOAP logging?

SOAP logging captures:

Request XML

Response XML

Headers

Fault messages

Logging helps:

Debug failures

Analyze transactions

Troubleshoot integrations

SOAP logs are very important during production issue analysis.

Real-Time API Validation Examples

REST API Example

POST /api/login

{
“username”: “user1”,
“password”: “pass123”
}

Validations

Status code = 200

Token exists

Token expiry > 0

SOAP API Example

<soapenv:Envelope>
  <soapenv:Body>
     <getBalance>
        <accountId>101</accountId>
     </getBalance>
  </soapenv:Body>
</soapenv:Envelope>

Validations

No SOAP fault

Balance node exists

Balance > 0

Postman / SoapUI / Automation Snippets

Postman Test Script

pm.test(“Status code 200”, () => {

pm.response.to.have.status(200);

});

SoapUI XPath Assertion

//balance > 0

Rest Assured (Java)

given().when().get(“/users/1”).then().statusCode(200);

Python Requests

import requests

res = requests.get(url)

assert res.status_code == 200

Scenario-Based SOAP and REST API Testing Questions

REST API returns 200 but wrong data – what do you check?

SOAP service returns fault – how do you debug?

Token expired but API still accessible – defect?

API works in Postman but fails in app – why?

Duplicate records created – what validation missed?

SOAP response missing mandatory tag – impact?

REST API slow only in production – reason?

Same request returns different responses – why?

Unauthorized user accesses secured API – issue?

XML schema changes – what breaks?

API returns null fields – how to catch?

Payment deducted but order not created – what testing?

SOAP security header missing – impact?

API fails only in CI pipeline – reason?

Partial data saved after failure – what testing missed?

How Interviewers Evaluate Your Answers

Interviewers usually look for:

Clear understanding of SOAP and REST

Real-time project examples

Validation beyond status codes

Logical debugging skills

Tool knowledge using:

Postman

SoapUI

Strong candidates explain:

What they tested

Why they tested it

How they validated results

SOAP & REST API Testing Interview Cheatsheet

Validate status + data + business rules

Understand JSON and XML properly

Know SOAP faults and REST errors

Test negative scenarios carefully

Practice real project examples

Use Postman and SoapUI regularly

FAQs – SOAP and REST API Testing Interview Questions

Q1. Is SOAP still relevant?
Yes, SOAP is still very relevant, especially in large enterprise industries.

Even though REST APIs are more popular for modern web and mobile applications, many critical enterprise systems still rely heavily on SOAP APIs.

Where SOAP Is Still Commonly Used

SOAP is widely used in industries like:

Banking

Insurance

Healthcare

Telecom

Government systems

Enterprise ERP systems

These industries prefer SOAP because of:

Strong security

Strict contracts

Reliability

Transaction support

Compliance requirements

Q2. REST or SOAP – which is more important?
For most modern API testing interviews and real-world projects, REST is much more important than SOAP.

Today, most applications use REST APIs because they are:

Lightweight

Faster

Easier to integrate

Easier to automate

Better suited for web and mobile applications

However, basic SOAP knowledge is still useful because some enterprise and legacy systems continue using SOAP services.

Why REST Is More Important Today

REST APIs are heavily used in:

Web applications

Mobile applications

Microservices architecture

Cloud platforms

SaaS applications

Third-party integrations

Most modern backend systems are REST-based.

That is why interviewers focus heavily on REST concepts during API testing interviews.

Q3. Do interviewers expect automation?
Yes — but the level of automation expected depends heavily on the QA role.

For Manual QA Roles

Usually, interviewers expect:

Basic API testing knowledge

Postman usage

Request/response validation

Status codes

Authentication

Negative testing

Automation is often considered a bonus, not mandatory.

You may still get questions like:

“Have you worked on API automation?”

“Do you know any automation tools?”

Even basic awareness helps.

Q4. Biggest mistake candidates make?
The biggest mistake candidates make in API testing interviews is focusing only on tools and status codes instead of understanding real business behavior and backend validation.

Many candidates think:

“I sent the request in Postman and got 200 OK, so the API works.”

But interviewers expect much deeper analysis, especially for candidates with around 2 years of experience.

1. Trusting Only 200 OK

This is the most common mistake.

Candidates often validate only:

Status code = 200

But APIs can still return incorrect business data.

Example

{
“total”: -500
}

The API technically succeeded, but the business logic is wrong.

Interviewers expect validation of:

Response body

Business calculations

Database updates

Schema

Headers

Workflow behavior

Not just status codes.

2. Knowing Only Basic Postman Usage

Many candidates only know:

Sending requests

Checking response

Viewing status code

But at 2 years experience, interviewers expect more advanced usage such as:

Assertions

API chaining

Dynamic variables

Pre-request scripts

Environment variables

Collection Runner

Negative testing

Example

pm.expect(r.total).to.eql(r.subtotal – r.discount + r.tax);

This demonstrates business validation thinking.

3. Ignoring Business Logic

API testing is not only technical testing.

Interviewers expect candidates to validate:

Discounts

Tax calculations

Order workflows

Payment handling

Access permissions

Duplicate prevention

Example Questions

Can duplicate orders happen?

Can unauthorized users access APIs?

Are invalid transactions blocked?

Does rollback work properly?

Business logic validation is one of the most important interview areas.

4. No Negative Testing Mindset

Many candidates test only happy paths.

Strong candidates always test:

Invalid payloads

Missing fields

Expired tokens

Invalid authentication

Boundary values

Special characters

Empty requests

Negative testing shows deeper understanding of API behavior.

5. Weak Debugging Approach

Weak answer:

“I will report the defect.”

Strong answer:

Check logs

Verify request payload

Compare database records

Validate headers

Analyze backend logic

Reproduce the issue

Check dependent services

Interviewers heavily evaluate troubleshooting ability at this level.

6. No Real-Time Scenario Thinking

Many candidates memorize definitions but struggle with practical questions.

Common interview scenarios:

API returns 200 but wrong data — what do you do?

Payment deducted but order not created — what testing applies?

Retry creates duplicate records — how prevent it?

Interviewers prefer practical thinking over memorized theory.

7. Weak Understanding of Authentication

Candidates commonly confuse:

Authentication

Authorization

JWT tokens

Bearer tokens

401 vs 403

These are among the most frequently asked API interview topics.

You should clearly understand:

How tokens work

How tokens expire

How tokens are passed

Role-based access control

8. No Automation Awareness

Some candidates think API testing means only manual testing in Postman.

But modern projects increasingly expect:

Basic automation knowledge

Assertions

API automation awareness

CI/CD basics

Even simple knowledge of:

Rest Assured

Python requests

Newman

creates a stronger profile.

9. Weak Assertions

Some candidates validate only:

pm.response.to.have.status(200);

Interviewers expect stronger validations such as:

Schema validation

Field validation

Business rule validation

Header validation

Range validation

Assertions should validate meaningful behavior, not just technical success.

10. Explaining “What” but Not “Why”

Weak answer:

“I validated response fields.”

Better answer:

“I validated totals and discounts because incorrect calculations may cause financial defects.”

Interviewers value reasoning and risk awareness.

Q5. How to prepare quickly?
If your goal is to become interview-ready fast, focus on practical understanding, not memorizing hundreds of definitions.

You do NOT need to master everything.
You need strong basics + real examples + confidence.

Step 1: Learn Core API Fundamentals (1–2 Days)

Focus on these topics first:

Must Know Concepts

What is an API?

REST vs SOAP

HTTP methods:

POST

PATCH

DELETE

Status codes:

JSON basics

Request vs response

Headers

Authentication vs authorization

These questions are asked in almost every interview.

Step 2: Practice in Postman (2–3 Days)

This is the fastest way to gain confidence.

Practice:

Sending requests

Adding headers

Passing tokens

Validating responses

Testing positive and negative cases

Practice APIs

Use free public APIs like:

JSONPlaceholder

ReqRes

Dummy REST APIs

Practice:

CRUD operations

Invalid inputs

Missing headers

Step 3: Learn Basic ReadyAPI Concepts (1–2 Days)

If your interview involves ReadyAPI, focus on:

Important Topics

TestSuite

TestCase

TestStep

Assertions

Property Transfer

Environment setup

Data-driven testing

SOAP vs REST

JSONPath/XPath assertions

You do not need advanced Groovy initially.

Step 4: Prepare Real-Time Scenarios

This is where most candidates fail.

Practice answering questions like:

API returns 200 but wrong data

Token expired but API still works

Duplicate records created

API slow in production

Payment successful but order failed

Interviewers care a lot about logical thinking.

Step 5: Learn Basic Assertions

Know how to validate:

Status code

Response body

Headers

Schema

Response time

Example:

pm.response.to.have.status(200);

And conceptually:

$.status == “CREATED”

Step 6: Understand Authentication Clearly

Very important topic.

Learn:

Bearer token

Basic Auth

OAuth basics

API keys

Many interviews include token-related scenarios.

Step 7: Practice Explaining Your Testing Approach

Do not just say:

“I tested the API.”

Say:

“I validated status codes, response body, authentication, business logic, negative scenarios, and database consistency.”

Introduction – Why API Testing Is Important in Interviews

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