API Testing Interview Questions for Intermediate

16. What is API versioning, and why is it important in API testing?

API versioning involves specifying a version number in the API endpoint or headers to ensure the backward compatibility. It manages the changes in the API over time.

• It ensures the correct version of the API is being tested.
• It ensures that the changes in the API do not break the existing client applications.

17. What is the purpose of HTTP status codes in API testing?

HTTP status codes indicate whether a specific request successfully completed or not. These are embedded in the HTTP header of a page to tell the browser the result of its request.

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

The request body is used to send and receive data such as input parameters, or data to create/ update resources via the REST API. The response body is the data API send to the client.

19. What is the purpose of the request and response headers in API testing?

The request headers are used to specify a content type, caching, authentication, etc. The response header can provide information about the server, caching, etc.

20. What is API mocking?

API mocking is practice of simulating the behavior of an API endpoint during testing without actually invoking the real API. It is beneficial during the development stage.

21. Why API Mocking is used in API Testing?

• Mock APIs are useful when applications have dependencies with external APIs.
• Mock APIs are useful for testers to plan and validate test executions and for developers to do unit testing and identify the initial development stages.
• Mock APIs are useful in situations where the complete API needs to be made available for consumer testing before committing it to development stage.

22. What are the advantages of using API mocking in API testing?

• Development stage: API mocking is useful to simulate external dependencies and unexpected behavior.
• Functional stage: API mocking is useful to prepare the API to handle extreme cases detect potential failures and verify whether the API works as expected or not.
• Non-functional stage: API mocking makes it possible to evaluate the performance and response times of APIs in various scenarios.
• Allows API demonstration: API mocking allows developers to demonstrate an API to clients before deploying the software.

23. What is API security testing, and why is it important?

API security testing is the process of testing the vulnerabilities in the API. This is done through penetration testing or manual scanning of the APIs. API security testing is important:

• Cloud-based applications rely on APIs to exchange data and interact with each other. Any security vulnerabilities can have far-reaching consequences.
• Online operations and businesses rely on APIs to integrate different systems and services. This causes potential security risks.
• Organizations rely on security solutions that are built for web apps to detect and secure from API threats. Such solutions cannot detect unique vulnerabilities and gaps in the APIs.

24. How do you ensure the security of APIs in your tests?

• Use secure communication protocols like HTTPs to encrypt data transmitted between client and server.
• It is important to properly implement authentication and authorization mechanisms to ensure that only authorized users can access the API endpoints and perform the authorized actions.
• Ensure that all the input data in the API requests are properly authorized, validated, and sanitized to prevent injection attacks and cross-site scripting attacks.

25. What are the different types of error responses in API testing?

• Validation errors: Validation errors occur when the API request does not meet the validation criteria defined by the API.
• HTTP error status codes: These can be client-side status codes or server-side status codes. There are standard HTTP status codes like 4xx or 5xx that indicate errors in the API request or response.
• Custom error messages: These are the customer error messages that are returned by the API in case of errors or exceptions.

26. How do you handle error responses in your API tests?

• Clear error messages: One of the best practice to handle error responses is to provide clear and helpful error messages that explain the cause of the error and the solution to the error.
• Error logging: Best practice is to implement error logging and monitoring tools that can help track, analyze, and resolve errors in API testing.
• Use consistent error codes: It is important to use consistent and meaningful error messages that indicate the type and severity of the error.

27. What is input validation?

Input validation is the process of analyzing the inputs and disallowing the inputs that are considered unsuitable. It ensures that all input data in API requests are properly sanitized and validated to prevent injection attacks.

28. Why input validation is important in API testing?

Input validation is important in API testing as it prevents malicious data from entering the system. It is important to prevent injection attacks and other malicious activities. This can be done manually or using automated tools.

29. What is cross-site request forgery (CSRF)?

Cross-site request forgery is an attack that forces user top execute unwanted action in the web application in which they are authorized to perform actions. This attack exploits the trust the web application has in an authenticated user.

API testing is a type of software testing that involves testing application programming interfaces (APIs) directly and as part of integration testing to determine if they meet expectations for functionality, reliability, performance, and security. Unlike UI testing, which focuses on the graphical interface of an application, API testing focuses on the business logic layer of the software architecture. With the increasing reliance on APIs in modern software architecture, mastering API testing has become indispensable for quality assurance professionals. Top companies like Google, Facebook, Amazon, Microsoft, and many others prioritize API testing to maintain their high standards of software quality.

In this article, we will provide Top API Testing Interview Questions tailored for both beginners and experienced professionals with 3, 5, and 8 years of experience. Here, we cover everything, including core API concepts, REST and SOAP protocols, testing tools, authentication methods, performance testing, error handling, and more, that will surely help you to crack API testing interviews.

The questions are divided into three categories:

• API Testing Interview Questions For Freshers
• API Testing Interview Questions For Intermediate
• API Testing Interview Questions For Experienced

The article also provides answers to each question, along with explanations and practical Example with PostMan. This will help you to understand the concepts behind the questions and to prepare for your interview.