API Testing interview questions

First of all, web development is the process of designing, developing, and updating websites. This approach also entails managing technological elements like capacity and performance.

1. What is an API?

API: Application Programming Interface.  It is a procedure which enables software components to communicate and transfer data and it allows communication between two applications. When the UI is absent postman tool is used as a client to test the application.

2. What are the types of API testing?

 Soap: Simple Object Access Protocol, we can communicate with any server. This uses http methods, XML based protocol, and uses xml format only. Response time is more and not best for CRUD operations.

Rest: Representational state protocol. Rest API is popular nowadays. It uses XML, JSON, HTML, Text, JavaScript. Response time is less. Best for CRUD operations.

3 . What is API Testing?

API testing validates Application Programming  Interfaces. It is used to check the      functionality, performance and security of the programming interfaces. It mainly focuses on the business logic in applications, where UI is absent. GUI is mainly focused on look n feel, but API focuses on response time security and business logic.

4. What is a RESTful API?

This is a simpler and quite easy API. When we automate rest api it is called restful services. When a request is sent from the client, an appropriate response is sent back from the server.   To automate rest api  we need rest assured libraries. Usually contains a json body. To create, read, update and delete information restful service uses  http methods like get,post,put and delete.

5. What are the advantages of API testing?
  • API provides the security.
  • API checks the authentication and the data that we are passing.
  • We can hit lots of APIs in less time, so time effective.
  • API helps to avoid data breaching.
  • We can use the response of one API to another API.

Easy navigation and menu item accessibility on every page are hallmarks of a successful website. Additionally, intuitive navigation makes it easier for visitors to navigate a website.
Intuitive: It should be able to foresee your visitor’s thoughts and provide for their immediate wants. Furthermore, it’s critical that your website has a landing page specifically tailored to your visitors’ searches.

6. What is an API endpoint?

End points are the different service urls which are used to hit the URL with domain uri. It’s a way for different systems and applications to communicate with each other , by sending and receiving information via the endpoint.

7. Mention common HTTP methods used in API testing
  • GET-     used to get the data
  • POST-   used to create data
  • PUT-      used to update the data
  • DELETE –  used to delete the data
  • PATCH – used to update partial data
8. What is the purpose of HTTP status codes in API testing?

Status codes represent the response, whether the http request has been successfully completed. These are successful responses (200-299), server-side error responses (500 -599) and client side error responses (400-499). Redirection messages (300-399), Informational responses (100-199).

9. What is JSON, and why is it commonly used in API testing?

We pass the data in Rest API testing in the form of JSON format. This is language independent. JSON data is in the form of key n value pairs separated by a colon.

JSON data can be easily sent between computers, and used by any programming language. We can send a JavaScript object in pure text format.

10. What is the purpose of authentication in API testing?

Authentication involves confirming the identity of the client sending a request. some APIs require auth details . It will be more robust and stronger. In market different types of autherisation  avilable.  

11. What is the purpose of query parameters in API testing?

Represents the Query parameter. This query parameter helps us to query    based     on certain criteria. We can filter the data.  We can limit the results by giving query parameters. We can filter the result by giving this. In the params tab we can give a query parameter.

12. What is the purpose of the request and response body in API testing?

 API is used to communicate between two systems. We pass the http request, Json body, header and auth details  to send the request. It’s used to send data to the server. By sending various request bodies we can test the application behaviour.

Response body contains the data sent by the server. It contains the status codes, time duration and errors . if any errors are there it will give the details. 

13. What are the principles of API Testing?

Reusability, reduce the complexity, open close principle – it  says that don’t change the old functionality to add new functionality.  single responsibility principle -improves the reusability and efficiency.

14. What do we actually verify in API testing?
  • We verify the application behaviour as expected and actuval deviation.
  • Verify the status codes. 
  • Verify the schema format. Time taken (response time).
  • Size of the response body. And error handling details.
15. What is the 3 layer architecture of API

All web applications come under 3 layer architecture .In this we will have a client layer that can be called as presentation layer Database  layer  in between these two we will have business logic layer  or middle layer.

When we send the request from client layer , corresponding business logic will be executed  business logic layer contain  business logic in the form  of programs depends upon your type of request corresponding business logic will be triggered and that will pass your request to the server which is database server and again business logic will get the data and provide the response to the client.

Business layer will act as the mediator between client and server.

16. What is the relationship between client and server?

Client is a  machine from which we can initiate the request and it’s  a physical computer, we can just pass the request from the client.

A server is the storage area which is also a physical computer which contains actual data. Whenever we send the request  to the server there will be some service which will actually fetch the data and provide a response.

Server means physical machine where  actual web pages , data , record  and everything is available on the server.

We can send requests through the browser or  postman tool. They act like clients.

In another word Client is a place where we can initiate a request and see the response and server is a place where exactly all the data and pages will be stored  and from where we get the response  to the request. 


Finally, API testing interview questions are essential to examine a candidate’s knowledge of API ideas, testing procedures, and problem-solving abilities. These questions examine the candidate’s ability to work effectively with APIs by delving into subjects such as REST, SOAP, authentication, and error handling. Successful candidates will have a strong understanding of both theoretical ideas and practical application, demonstrating their ability to ensure the dependability, security, and usefulness of APIs in a variety of circumstances. Overall, well-crafted API testing interview questions assist organisations in identifying people who possess the necessary ability for success in API testing roles. 

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