API Testing Interview Questions and Answers
Freshers / Beginner level questions & answers
Ques 1. What are the common HTTP methods used in API testing?
Common HTTP methods include GET (retrieve data), POST (create data), PUT (update data), DELETE (remove data), and PATCH (partially update data).
Ques 2. What is the purpose of status codes in HTTP responses?
HTTP status codes indicate the outcome of an HTTP request. For example, 200 OK indicates success, 404 Not Found indicates a resource was not found, etc.
Ques 3. What is Postman, and how is it used in API testing?
Postman is an API testing tool that allows testers to send HTTP requests and receive responses. It simplifies the process of testing APIs by providing a user-friendly interface.
Ques 4. What is the difference between unit testing and API testing?
Unit testing focuses on testing individual components or functions in isolation, while API testing involves testing the interactions and behavior of the entire API.
Intermediate / 1 to 5 years experienced level questions & answers
Ques 5. What is API testing?
API testing involves testing the application programming interfaces (APIs) to ensure they meet functional and performance requirements.
Ques 6. Explain the difference between SOAP and RESTful APIs.
SOAP (Simple Object Access Protocol) is a protocol for exchanging structured information, while REST (Representational State Transfer) is an architectural style based on a set of constraints. RESTful APIs are generally simpler and use standard HTTP methods.
Ques 7. Explain the concept of endpoint in API testing.
An endpoint is a specific URL where an API can be accessed. It represents the location where the resource can be found or manipulated.
Ques 8. What is the importance of authentication in API testing?
Authentication ensures that the API is accessed by authorized users only. Common authentication methods include API keys, OAuth, and JWT.
Ques 9. Explain the term 'Swagger' in the context of API testing.
Swagger is a tool that helps document and test APIs. It provides a standard way to describe RESTful APIs using a JSON or YAML format.
Ques 10. What is the role of the 'Authorization' header in API requests?
The 'Authorization' header is used to send credentials (such as API keys or tokens) with an HTTP request, allowing the server to authenticate the user.
Ques 11. How do you handle pagination in API testing?
Pagination is often handled using parameters like 'page' and 'per_page' in API requests to retrieve a specific subset of data. Testers need to ensure that pagination works correctly.
Ques 12. What is the purpose of the 'Content-Type' header in an HTTP request?
The 'Content-Type' header specifies the media type of the resource being sent or requested. Common values include 'application/json' and 'application/xml'.
Ques 13. Explain the term 'Mocking' in the context of API testing.
Mocking involves creating simulated responses from an API to test the behavior of an application without making actual calls to the real API. It helps in isolating the testing environment.
Ques 14. What are the advantages of automated API testing over manual testing?
Automated API testing offers faster execution, repeatability, broader coverage, and the ability to detect issues early in the development process.
Ques 15. What is the purpose of the 'Cache-Control' header in an HTTP response?
The 'Cache-Control' header specifies caching directives for both requests and responses. It controls how caching is applied to the resource.
Ques 16. Explain the concept of 'Rate Limiting' in API testing.
Rate limiting restricts the number of API requests a client can make in a given time period. It is used to prevent abuse, ensure fair usage, and maintain system stability.
Ques 17. What is the purpose of the 'Accept' header in an HTTP request?
The 'Accept' header indicates the media types that the client can understand. It helps the server provide an appropriate response format, such as JSON or XML.
Ques 18. Explain the term 'Webhooks' in the context of APIs.
Webhooks are HTTP callbacks that allow external systems to be notified in real-time when certain events occur. They are often used for event-driven architectures.
Ques 19. What is the purpose of the 'Location' header in an HTTP response?
The 'Location' header is used in the HTTP response to provide the URL of the newly created or modified resource, especially in the case of a successful POST request.
Ques 20. How do you handle API versioning to ensure backward compatibility?
API versioning is often done using URL versioning, custom headers, or request parameters. Testers need to ensure that changes in versions do not break existing functionality.
Ques 21. What is the purpose of the 'OPTIONS' HTTP method?
The 'OPTIONS' method is used to describe the communication options for the target resource. It is often used to support cross-origin resource sharing (CORS).
Ques 22. What is the purpose of the 'ETag' header in an HTTP response?
The 'ETag' header provides a mechanism for caching and conditional requests. It represents a unique identifier for a specific version of a resource.
Ques 23. How do you handle testing for paginated APIs?
Testing paginated APIs involves verifying that the pagination parameters work correctly, ensuring that the correct number of items is returned per page, and testing the behavior of pagination links.
Ques 24. How can you ensure data integrity in API testing?
Data integrity in API testing can be ensured by validating the correctness and consistency of data returned by the API. This includes checking data types, formats, and values.
Ques 25. What is the purpose of the 'HEAD' HTTP method?
The 'HEAD' method is similar to GET but returns only the headers and no message body. It is often used to check the status and headers of a resource without fetching the entire content.
Ques 26. Explain the concept of 'Swagger Codegen' in API development.
Swagger Codegen is a tool that automatically generates server stubs and client libraries from an OpenAPI Specification. It helps in accelerating API development.
Ques 27. What is the purpose of the 'Retry-After' header in an HTTP response?
The 'Retry-After' header indicates how long the client should wait before making another request. It is often used in the context of rate limiting or when a server is temporarily unavailable.
Experienced / Expert level questions & answers
Ques 28. How do you handle security testing for APIs?
Security testing for APIs involves checking for vulnerabilities such as injection attacks, data exposure, and unauthorized access. It often includes using tools like OWASP ZAP.
Ques 29. Explain the term 'Load Testing' in the context of API testing.
Load testing involves assessing the performance of an API by subjecting it to a specific load, often by simulating multiple concurrent users or requests. It helps identify performance bottlenecks.
Ques 30. What is the role of the 'Pre-flight request' in the context of CORS?
A pre-flight request is an HTTP OPTIONS request sent by the browser before the actual request. It checks if the server allows the actual request to be made from the specific origin.
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