API Assured API Testing Interview Questions -

Introduction – Why API Testing Is Important in Interviews

With microservices, cloud platforms, and mobile applications dominating today’s software landscape, API testing has become a core skill for QA engineers and SDETs. That’s why interviewers frequently ask API Assured (Rest Assured) API testing interview questions to evaluate whether candidates can validate backend logic, automate APIs, and ensure data integrity without relying on UI layers.

In particular, Rest Assured is widely used in Java-based automation frameworks. Interviewers test your understanding of:

REST fundamentals

HTTP methods and status codes

API automation concepts

Real-time debugging and validation scenarios

This guide is designed for freshers to experienced professionals, covering theory, practical examples, and scenario-based questions in a simple, interview-focused manner.

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

Feature	REST	SOAP	GraphQL
Type	Architectural style	Protocol	Query language
Data format	JSON	XML	JSON
Performance	Fast & lightweight	Slower	Highly optimized
Flexibility	High	Low	Very high
Usage	Most modern apps	Legacy/enterprise	Modern frontend-driven apps

70+ API Assured API Testing Interview Questions and Answers

Basic API & Rest Assured Questions (Freshers)

What is API Assured (Rest Assured)?

API Assured, commonly known as Rest Assured, is a Java-based library used for automating REST API testing.

It provides easy-to-read syntax for:

Sending HTTP requests

Validating responses

Handling authentication

Parsing JSON/XML

Automating backend API workflows

Rest Assured is commonly integrated with:

TestNG

JUnit

Maven

Jenkins

CI/CD pipelines

Why Use Rest Assured for API Testing?

Rest Assured simplifies API automation by providing readable syntax for request and response validation.

Key Advantages

Easy API automation

Java integration

Strong assertion support

JSON and XML validation

Reusable automation frameworks

CI/CD integration support

Which Language is Used in API Assured?

Rest Assured is built using Java.

Candidates using Rest Assured are generally expected to have:

Basic Java knowledge

OOP concepts

Collections basics

Exception handling basics

REST API Fundamentals

What are the Main HTTP Methods?

REST APIs commonly use:

POST

PATCH

DELETE

GET

Used to retrieve data.

Example

GET /users/101

POST

Used to create resources.

Example

POST /users

PUT

Used to update or replace resources completely.

Example

PUT /users/101

PATCH

Used for partial updates.

Example

PATCH /users/101

DELETE

Used to remove resources.

Example

DELETE /users/101

What is an Endpoint?

An endpoint is the URL where an API receives requests.

Example

https://api.test.com/users/101

Endpoints represent API resources.

What is a Request Payload?

A request payload is the data sent to the server, usually in POST or PUT requests.

Example Payload

{
“email”: “test@example.com“,
“password”: “Test@123”
}

What is a Response Payload?

A response payload is the data returned by the server after processing the request.

Example Response

{
“id”: 501,
“message”: “User created successfully”
}

What is Statelessness in REST?

REST APIs are stateless.

This means:

Each request is independent

Server does not store client session information

Every request contains complete information

Benefits

Better scalability

Improved performance

Easier load balancing

What is Idempotency?

Idempotency means repeated identical requests produce the same result.

Common Idempotent Methods

DELETE

Example

GET /users/101

Calling this multiple times gives the same response without changing data.

What is the Base URI in Rest Assured?

The base URI is the root URL of the API being tested.

Example

RestAssured.baseURI = “https://api.test.com“;

This avoids repeating root URL in every request.

REST API Interview Questions

Difference Between POST and PUT

POST

Used to create new resources.

PUT

Used to update or replace existing resources.

Example

POST

POST /users

PUT

PUT /users/101

What is JSON?

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

JSON Example

{
“id”: 101,
“name”: “Srushti”,
“role”: “QA Engineer”
}

Why JSON is Popular

Lightweight

Easy to read

Easy to parse

Faster communication

What are Headers in API Testing?

Headers contain metadata about API requests and responses.

Common Headers

Content-Type

Authorization

Cache-Control

Example

Content-Type: application/json
Authorization: Bearer token123

What is Content-Type?

Content-Type specifies the format of request or response data.

Common Content Types

application/json

application/xml

multipart/form-data

What is API Versioning?

API versioning manages API changes across releases.

Common Approaches

/v1/users

/v2/users

Header-based versioning

Why Versioning is Important

Backward compatibility

Safer deployments

Controlled API evolution

What is Query Parameter?

Query parameters are passed after ? in the URL.

Example

GET /users?page=1&size=10

Common Uses

Pagination

Filtering

Sorting

Searching

What is Path Parameter?

Path parameters are dynamic values inside the endpoint URL.

Example

GET /users/101

Here, 101 is the path parameter.

What is Pagination?

Pagination splits large datasets into multiple pages.

Example

GET /users?page=2&size=20

Pagination Validations

Correct page size

Total records

Next/previous navigation

Empty page handling

What is Caching?

Caching stores API responses temporarily to reduce server load and improve performance.

Benefits

Faster responses

Reduced backend load

Better scalability

What is HATEOAS?

HATEOAS stands for Hypermedia As The Engine Of Application State.

It is a REST principle where API responses include navigation links.

Example

{
“id”: 101,
“links”: {
“self”: “/users/101”,
“orders”: “/users/101/orders”
}
}

SOAP & XML Questions

What is SOAP?

SOAP (Simple Object Access Protocol) is a protocol used for exchanging structured XML messages between systems.

SOAP Characteristics

XML-based

Strict standards

Enterprise security

Contract-based communication

What is WSDL?

WSDL (Web Services Description Language) is an XML document describing SOAP services.

WSDL Contains

Available operations

Request structures

Response structures

Endpoint details

What is SOAP Envelope?

SOAP Envelope is the root XML element in SOAP requests and responses.

Example

How Do You Validate XML Response?

XML responses are validated using XPath.

Example XML

<response>
<status>SUCCESS</status>
</response>

XPath Validation

/response/status = ‘SUCCESS’

SOAP vs REST – Which is Better?

Feature	REST	SOAP
Format	JSON	XML
Speed	Faster	Slower
Structure	Lightweight	Strict
Security	Moderate	Strong
Flexibility	High	Moderate

REST is generally preferred for modern lightweight applications, while SOAP is used in enterprise systems requiring strict security and contracts.

Status Codes – Interview Essentials

Code	Meaning
200	OK
201	Created
204	No Content
400	Bad Request
401	Unauthorized
403	Forbidden
404	Not Found
409	Conflict
500	Internal Server Error

API Validation Example (Real-Time)

Request

POST /api/users

Payload

{
“email”: “test@example.com“,
“password”: “Test@123”
}

Response

{
“id”: 501,
“message”: “User created successfully”
}

Validations

Status code = 201

id should not be null

message equals expected text

Response time within SLA

Automation Snippets (Mandatory for Interviews)

Rest Assured (Java – API Assured)

given()

.baseUri(“https://api.test.com”)

.header(“Content-Type”,”application/json”)

.when()

.get(“/users/101”)

.then()

.statusCode(200)

.body(“name”, equalTo(“Srushti”));

Postman (Manual Testing)

Postman is commonly used for:

Status code validation

Response body verification

Environment variables

Authentication testing

API collections

SoapUI Assertions

Common SoapUI assertions include:

JSONPath Match

XPath Match

Schema Compliance

Status Code Validation

Python (Requests Library)

import requests

res = requests.get(“https://api.test.com/users/101”)

assert res.status_code == 200

Scenario-Based REST API Testing Questions

API Returns 200 but Incorrect Data — What Do You Do?

Validate:

Business rules

Database consistency

Response schema

API mappings

If response data is incorrect, raise a functional defect with request and response evidence.

How Do You Test Token Expiration?

Steps

Generate token

Wait for expiry

Access secured API

Validate 401 Unauthorized response

How Do You Test Rate Limiting?

Send rapid consecutive requests and validate:

HTTP 429 returned

Rate limiting works correctly

How Do You Test Negative Scenarios?

Validate APIs using:

Invalid payloads

Missing headers

Wrong authentication

Invalid data types

Empty mandatory fields

Negative testing improves API reliability.

How Do You Test API Performance?

Validate:

Response time

SLA compliance

Backend processing

Server load

Database performance

How Do You Test File Upload APIs?

Validate:

File format

File size

Upload response

Invalid file handling

How Do You Test Dependent APIs?

Use API chaining.

Example

Generate token

Create user API

Fetch user API

Validate data consistency across APIs.

What if Backend is Unavailable?

Use mock services to simulate backend behavior.

Mock services help continue testing when actual backend systems are unavailable.

How Do You Test Concurrency?

Send parallel requests and validate:

No duplicate records

Proper transaction handling

Data consistency

Concurrency testing is critical in banking and e-commerce applications.

How Do You Test Backward Compatibility?

Validate older API versions continue working after new releases.

Validation Areas

Old endpoints still accessible

Existing fields remain stable

No breaking changes

How Interviewers Evaluate Your Answers in API Assured (Rest Assured) Interviews

Introduction

In API testing interviews, especially for Rest Assured and API automation roles, interviewers do not evaluate candidates only on theoretical definitions.

They mainly assess whether the candidate can:

Understand backend API behavior

Explain real-time testing scenarios

Validate APIs logically

Debug issues effectively

Think like a tester and automation engineer

Strong communication and practical understanding often matter more than memorized answers.

Core Understanding of API Concepts

Interviewers first check whether candidates have strong API fundamentals because API testing is now a critical part of modern QA and automation roles.

Important Areas Interviewers Expect Candidates to Understand

What APIs are

REST architecture

Client-server communication

Request and response flow

Endpoints and resources

HTTP methods

Headers and payloads

Authentication and authorization

JSON and XML basics

Common Beginner Questions

What is REST API?

REST (Representational State Transfer) is an architectural style used for communication between systems over HTTP.

What is an Endpoint?

An endpoint is the URL where an API receives requests.

Example

GET /users/101

What is Payload?

Payload refers to the request or response body exchanged between systems.

JSON Example

{
“id”: 101,
“name”: “Srushti”
}

What Interviewers Actually Evaluate

Interviewers want to verify whether candidates truly understand:

How APIs work

Why APIs are tested

What validations matter

What risks APIs can introduce

Candidates who explain concepts practically usually perform better.

Knowledge of Rest Assured Syntax

For Rest Assured interviews, interviewers often check whether candidates understand the basic automation structure and syntax.

They may not always expect perfect coding syntax from freshers, but they do expect logical understanding.

Basic Rest Assured Structure

given()

.when()

.get(“/users/101”)

.then()

.statusCode(200);

What Interviewers Expect You to Know

given()

Used for request setup.

Common Usage

Headers

Authentication

Query parameters

Request payload

when()

Used to send API request.

then()

Used for validations and assertions.

Real-Time Validation Example

given()

.header(“Content-Type”,”application/json”)

.when()

.get(“/users/101”)

.then()

.statusCode(200)

.body(“name”, equalTo(“Srushti”));

Why Syntax Understanding Matters

Interviewers use syntax questions to check whether candidates can:

Automate APIs

Read framework code

Debug automation failures

Understand request/response validation

Even basic syntax understanding creates strong impression.

Usage of Status Codes

Status codes are one of the most important interview topics in API testing.

Interviewers expect candidates to understand both:

Technical meaning

Real-time usage scenarios

Important Status Codes

Code	Meaning
200	OK
201	Created
204	No Content
400	Bad Request
401	Unauthorized
403	Forbidden
404	Not Found
409	Conflict
500	Internal Server Error

Common Interview Questions on Status Codes

Difference Between 401 and 403

401 Unauthorized

Authentication failed.

403 Forbidden

User is authenticated but lacks permission.

Why Does API Return 400?

Possible reasons:

Invalid payload

Missing mandatory fields

Invalid data type

Validation failure

When is 204 Used?

When request succeeds but no response body is returned.

What Interviewers Evaluate Through Status Code Questions

They assess whether candidates can:

Debug issues logically

Understand backend behavior

Identify API failures correctly

Explain business impact

Ability to Explain Real-Time Scenarios

Modern API interviews are heavily scenario-based.

Interviewers prefer candidates who explain concepts using real-world examples rather than textbook definitions.

Common Real-Time Scenarios

API Returns 200 but Incorrect Data

Expected approach:

Validate business rules

Check response schema

Verify database consistency

Raise functional defect

Token Expired During Execution

Expected solution:

Regenerate token dynamically

Retry request

Handle authentication gracefully

API Response is Slow

Expected checks:

Response time

SLA compliance

Backend processing

Database queries

Server load

File Upload API Testing

Expected validations:

File size

File format

Upload success response

Invalid file handling

Why Real-Time Scenarios Matter

Real-time examples show that candidates can:

Think practically

Debug issues

Understand workflows

Handle production-like situations

This is extremely valuable in enterprise projects.

Logical Debugging Approach

Interviewers often evaluate how candidates investigate failures.

They want testers who can analyze problems systematically instead of randomly guessing.

Example Debugging Flow

API Fails with 500 Error

A strong debugging approach:

Check request payload

Validate headers

Verify authentication

Review response body

Check backend logs

Validate database dependencies

Weak Interview Answer

“API failed.”

Strong Interview Answer

“I would first validate request payload, headers, and authentication. Then I would analyze response logs, verify backend dependencies, and identify whether the issue is caused by validation failure, server logic, or database behavior.”

This demonstrates strong analytical thinking.

Communication Skills Matter

Interviewers strongly evaluate communication clarity.

Even technically correct answers may sound weak if poorly explained.

Strong Candidates Usually:

Explain clearly

Use practical examples

Structure answers logically

Mention validations and business impact

Weak Answer Example

“I validated status code.”

Strong Answer Example

“I validated the status code to ensure the API successfully processed the request and returned expected backend behavior according to business requirements.”

This sounds much more professional.

API Assured API Testing Cheat Sheet

Validate Status Code and Response Body

Always validate:

Status code

Response body

Headers

Business rules

Response time

Example

{
“id”: 101,
“message”: “Success”
}

Validation should confirm:

Correct status code

Correct response message

Required fields exist

Cover Positive and Negative Cases

Positive Testing

Validate APIs using valid inputs.

Example

Valid login credentials

Correct payload

Negative Testing

Validate APIs using invalid inputs.

Example

Wrong token

Missing headers

Invalid payload

Empty fields

Negative testing improves API reliability and security.

Parameterize Test Data

Avoid hardcoded values.

Benefits

Reusability

Easier maintenance

Better scalability

Data-driven execution

Example

.queryParam(“page”,1)

Handle Authentication Dynamically

Modern APIs use tokens and authentication extensively.

Candidates should understand:

Token generation

Token reuse

Token refresh handling

Example

.header(“Authorization”,”Bearer token123″)

Dynamic token handling is very important in enterprise automation.

Use Assertions Effectively

Assertions validate API behavior automatically.

Common Assertions

Status code validation

JSON response validation

Header validation

Schema validation

Response time validation

Example Assertion

.then()

.statusCode(200)

.body(“name”, equalTo(“Srushti”));

Log Defects with Request and Response

Strong API testers log detailed and meaningful defects.

Good API Defect Reports Include

Endpoint URL

Request payload

Response payload

Headers

Status code

Steps to reproduce

Expected result

Actual result

FAQs – API Assured API Testing

Q1. Is API Assured same as Rest Assured?
Yes, API Assured and Rest Assured Are the Same

API Assured is commonly referred to as Rest Assured in modern API automation testing.

Both terms point to the same Java-based library used for automating REST API testing.

However, in the industry and official documentation, the tool is primarily known as:

Rest Assured

Q2. Is API automation mandatory for testers?
API Automation is Becoming Increasingly Important

Modern applications rely heavily on:

REST APIs

Microservices

Cloud platforms

Mobile integrations

CI/CD pipelines

Because of this, API automation has become a highly valuable skill for testers.

While it may not be strictly mandatory for every QA role, companies increasingly prefer testers who understand API automation concepts.

Q3. Can freshers learn API Assured?
Yes, Freshers Can Definitely Learn Rest Assured

Rest Assured is beginner-friendly for candidates who already know:

Basic API concepts

HTTP methods

JSON structure

Basic Java

Freshers do not need advanced programming knowledge initially.

Many companies expect freshers to have at least basic awareness of API automation concepts, and Rest Assured is one of the most used tools for this purpose.

Q4. Is Postman enough for interviews?
Yes, Postman Can Be Enough for Many Fresher Interviews

For fresher QA and API testing interviews, Postman is often sufficient if you can confidently explain:

API fundamentals

HTTP methods

Status codes

Request and response validation

Authentication

Real-time testing scenarios

Many companies primarily evaluate whether candidates understand how APIs work rather than expecting advanced automation expertise.

Introduction – Why API Testing Is Important in Interviews

Leave a Comment Cancel Reply