Basic API Testing Interview Questions with Answers

In this article, we will discuss the Basic API Testing Interview Questions that are frequently asked in interviews.

What are HTTP methods you have used in API Testing?

Generally we use the following HTTP methods in API Testing:

GET: used to fetch the data from the API
POST: used to create a new resource
PUT: used to update the existing resource
PATCH: used to update the partial resource
DELETE: used to delete the resource

But apart from these, there are other HTTP methods like

HEAD: used to fetch the headers of the resource
OPTIONS: used to fetch the supported methods of the resource
TRACE: used to fetch the path of the resource

What are the common status codes in API Testing?

Some of the common status codes in API Testing are:

200: OK - The request was successful and the response is returned
201: Created - The request was successful and a new resource was created
400: Bad Request - The request was invalid
401: Unauthorized - The request requires user authentication or the user is not authenticated
403: Forbidden - The request is not allowed because the user does not have permission
404: Not Found - The resource was not found
500: Internal Server Error - The server has encountered an error and cannot process the request

What is the difference between query param and path param?

Query param is sent as key-value pairs in the URL after the ? symbol. For example, in https://api.example.com/users?id=123, id is the query param. But the path param is sent as a part of the URL itself. For example, in https://api.example.com/users/123 123 is the path param.

How to make API accept XML and return XML?

To make an API accept XML and return XML, we need to set the Content-Type and Accept headers in the request and response.

For example, to make an API accept XML, we need to set the Content-Type header to application/xml in the request. And to make an API return XML, we need to set the Accept header to application/xml in the response.

What is the difference between Get and Post methods?

GET and POST are two different HTTP methods used in API Testing. The main differences between GET and POST are:

GET	POST
Data is sent as query parameters in URL	Data is sent in request body
Limited data can be sent due to URL length is limited	Large amount of data can be sent
Data is visible in browser URL	Data is not visible in browser URL instead sent in request body masked
Can be bookmarked	Cannot be bookmarked
Less secure as data is visible in URL	More secure as data is not visible in URL and sent in request body
Idempotent (multiple requests produce same result)	Non-idempotent (multiple requests may produce different results)

What is the difference between PUT and POST methods?

The main differences between PUT and POST are:

PUT	POST
Used to update the existing resource	Used to create a new resource
Requires the entire resource to be sent in the request	Requires only the fields to be updated to be sent in the request
Idempotent (multiple requests produce same result)	Non-idempotent (multiple requests may produce different results)

What is the difference between PUT and PATCH methods?

The main differences between PUT and PATCH are:

PUT	PATCH
Used to update the entire resource	Used to update the partial resource
Requires the entire resource to be sent in the request	Requires only the fields to be updated to be sent in the request
Idempotent (multiple requests produce same result)	Non-idempotent (multiple requests may produce different results)

What is an Idempotent method?

An Idempotent method is a method that if we call the same method multiple times, it will produce the same result. In other words, the result of the method does not change with multiple calls. For example, GET and PUT are idempotent methods.

What is a Non-idempotent method?

A Non-idempotent method is a method that if we call the same method multiple times, it will produce different results. In other words, the result of the method changes with multiple calls. For example, POST and DELETE are non-idempotent methods.

What is the difference between SOAP and REST?

SOAP (Simple Object Access Protocol) and REST (Representational State Transfer) are two different types of web services used for communication between client and server.

The main differences between SOAP and REST are:

SOAP	REST
SOAP is a protocol	REST is an architectural style
SOAP uses XML format	REST uses JSON, XML, or other formats
SOAP is more secure	REST is less secure
SOAP is more rigid	REST is flexible
SOAP requires more bandwidth	REST requires less bandwidth

What are headers in API Testing?

Headers are the meta information that is sent along with the request and response in API Testing. Some of the common headers are:

Content-Type: specifies the type of data in the request or response
Accept: specifies the type of data that the client can accept
Authorization: specifies the authentication information
User-Agent: specifies the information about the user agent
Cache-Control: specifies the caching information

What is the difference between Request and Response in API Testing?

Request is the data that is sent from the client to the server in API Testing. It contains the HTTP method, URL, headers, and body.

Whereas, Response is the data that is sent from the server to the client in API Testing. It contains the status code, headers, and body.

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