Manual API Testing Interview Questions

Manual API Testing Interview Questions

In this article, we will provide a comprehensive list of manual API testing interview questions along with answers to help you ace your interview. In the world of software development and quality assurance, Application Programming Interfaces (APIs) play a crucial role in enabling communication between different software components. To ensure the reliability, functionality, and security of APIs, manual API testing is a common practice. When preparing for an interview for a role in manual API testing, it’s essential to be well-prepared for questions that assess your knowledge and skills.

Manual API Testing Interview Questions

1. What is API Testing, and why is it important?

Answer: API Testing is the process of evaluating the functionality, reliability, security, and performance of an API. It is crucial because it ensures that different software components can communicate effectively, exchange data correctly, and function as intended.

2. Can you explain the key differences between UI testing and API testing?

Answer: UI testing focuses on the application’s user interface and involves testing the application’s look and feel, whereas API testing deals with the interaction between different software components and verifies data exchange and functionality.

3. What are some common HTTP methods used in API testing, and what do they represent?

Answer: Common HTTP methods include:

  • GET: Retrieve data from the server.
  • POST: Submit data to be processed to a specified resource.
  • PUT: Update a resource on the server.
  • DELETE: Remove a resource from the server.
  • PATCH: Apply partial modifications to a resource.

4. What is the purpose of the HTTP status code in API responses? Can you name a few common HTTP status codes and their meanings?

Answer: HTTP status codes indicate the outcome of an HTTP request. Common codes include:

  • 200 OK: Request succeeded.
  • 201 Created: Request resulted in a new resource.
  • 400 Bad Request: Invalid request data.
  • 401 Unauthorized: Authentication required or failed.
  • 404 Not Found: Resource not found.
  • 500 Internal Server Error: Server error.

5. Explain the term “Endpoint” in the context of API testing.

Answer: An endpoint is a specific URL or URI where an API can be accessed. Each endpoint represents a unique resource or functionality within the API.

6. What is the purpose of API documentation, and how does it assist in API testing?

Answer: API documentation provides detailed information about the API’s endpoints, parameters, request and response formats, and usage examples. It serves as a reference for testers to understand the API’s functionality and test it effectively.

7. What is the difference between request parameters and request headers in API testing?

Answer: Request parameters are used to send data or information as part of the API request (e.g., query parameters or data in the request body), while request headers carry metadata about the request (e.g., content type, authentication credentials).

8. How do you handle authentication in API testing, and what types of authentication mechanisms have you worked with?

Answer: Authentication in API testing involves using valid credentials to access protected resources. Common mechanisms include Basic Authentication, OAuth, API tokens, and API keys.

9. What is API mocking, and why is it useful in API testing?

Answer: API mocking is the process of creating simulated API responses for testing purposes. It allows testers to test API interactions without relying on the actual API, making it useful for early testing, development, and debugging.

10. Can you describe the typical steps involved in API testing?

Answer: The typical steps include:

  • Understanding the API’s functionality and documentation.
  • Planning test scenarios and designing test cases.
  • Sending API requests with various inputs.
  • Verifying the API responses and ensuring they match expected results.
  • Logging and reporting test results.

11. What is the purpose of API contracts or specifications, and how do you use them in testing?

Answer: API contracts or specifications (e.g., OpenAPI, Swagger) document the structure and behavior of an API. Testers use them to validate whether the API adheres to its defined contract, ensuring consistency and accuracy.

12. How do you handle API versioning in your testing efforts, and why is it important?

Answer: API versioning is crucial for maintaining backward compatibility. Testers can handle versioning by specifying the desired API version in their requests, ensuring that the correct version of the API is tested.

13. Can you explain the concept of API rate limiting and how it can impact testing?

Answer: API rate limiting restricts the number of API requests a client can make within a specified time frame. Testers must be aware of rate limits to avoid overloading the API during testing, which can lead to inaccurate results.

14. Describe the process of handling errors and exceptions in API testing.

Answer: Testers should intentionally send incorrect requests to the API to verify how it handles errors. Check for proper error codes, error messages, and appropriate HTTP status codes in the API responses.

15. What is the difference between positive testing and negative testing in API testing?

Answer: Positive testing validates that the API functions as expected under normal conditions, while negative testing evaluates how well the API handles unexpected or incorrect inputs and conditions.

16. How do you ensure data consistency in API testing when dealing with databases or external data sources?

Answer: Testers should have mechanisms to set up and clean up test data before and after API tests to maintain data consistency. This may involve database transactions, data rollback, or API data reset endpoints.

17. Can you explain the importance of API performance testing and share common performance metrics you monitor?

Answer: Performance testing evaluates how well an API performs under various load conditions. Common performance metrics include response time, throughput, and error rates.

18. How do you ensure that API testing is repeatable and maintainable over time?

Answer: Test automation is key to making API testing repeatable and maintainable. Automation scripts can be reused and updated as needed, reducing manual effort and ensuring consistency.

19. What is the significance of API testing in a continuous integration/continuous deployment (CI/CD) pipeline?

Answer: API testing in a CI/CD pipeline ensures that new code changes do not break existing API functionality. It helps maintain software quality throughout the development and deployment process.

20. Can you share an example of a challenging API testing scenario you’ve encountered and how you resolved it?

Answer: In your response, describe a specific testing challenge, such as complex authentication requirements or handling large datasets, and detail your problem-solving approach and the outcome.

21. What is the role of POSTMAN in API testing, and how does it assist in the testing process?

Answer: POSTMAN is an API testing tool that simplifies the testing process by providing an intuitive graphical user interface (GUI) to create, send, and validate API requests and responses. It supports various HTTP methods and authentication methods, making it a popular choice for testers.

22. Explain the concept of API test data management. How do you manage and maintain test data for API testing?

Answer: API test data management involves creating, storing, and maintaining test data that is used during API testing. Testers can manage test data through various methods, including using databases, data files, or API calls to generate or reset data as needed.

23. What is the purpose of API token-based authentication, and how do you include tokens in API requests?

Answer: API token-based authentication is a method where an API expects a token in the request header to authenticate the client. Testers include tokens by adding an “Authorization” header with the token value in API requests.

24. Can you describe the concept of API test environment setup and its importance in testing?

Answer: API test environment setup involves preparing the necessary infrastructure, configurations, and dependencies to facilitate API testing. It is essential for ensuring that tests are conducted in an isolated and controlled environment, mimicking production conditions as closely as possible.

25. How do you handle API versioning and backward compatibility when changes are made to the API?

Answer: When changes are made to the API, versioning is essential to maintain backward compatibility. Testers can specify the API version in their requests and thoroughly test the new version without impacting existing clients relying on older versions.

26. What is API contract testing, and how does it differ from functional testing?

Answer: API contract testing focuses on validating that the API complies with its documented contract or specification. It ensures that the API adheres to the defined standards, whereas functional testing verifies the functionality and behavior of the API under various conditions.

27. Can you explain the significance of load testing in API testing?

Answer: Load testing assesses an API’s performance under expected and peak loads. It helps identify performance bottlenecks, scalability issues, and the API’s ability to handle concurrent requests, ensuring optimal performance in production.

28. What are the benefits of using API testing frameworks, and can you name a few popular API testing frameworks?

Answer: API testing frameworks provide a structured approach to writing, organizing, and executing API tests. Popular frameworks include Postman, RestAssured (for Java), and Karate DSL (for web service testing).

29. How do you approach testing for API security vulnerabilities, such as SQL injection, Cross-Site Scripting (XSS), or authentication bypass?

Answer: Testers use techniques like input validation, parameterization, and boundary value analysis to assess and identify security vulnerabilities. They intentionally attempt to exploit these vulnerabilities to verify the API’s security measures.

30. What is the role of API documentation in API testing, and how can incomplete or unclear documentation impact testing efforts?

Answer: API documentation serves as a reference for testers to understand the API’s functionality, request and response formats, and expected behavior. Incomplete or unclear documentation can lead to misunderstandings and hinder testing efforts, emphasizing the importance of thorough and accurate documentation.

31. What is the difference between SOAP and RESTful APIs, and how does it impact the testing approach for each?

Answer: SOAP is a protocol with strict standards for messaging and communication, while REST is an architectural style with a more flexible approach. Testing SOAP APIs may involve XML-based requests and responses, while REST APIs typically use JSON or XML. Testing SOAP APIs often requires more comprehensive tools and XML knowledge, while REST is simpler and more accessible.

32. How do you ensure that API test cases are maintainable and can be easily updated as the application evolves?

Answer: To maintain API test cases effectively, it’s essential to use clear and descriptive test names, utilize variables for dynamic data, and create reusable functions for common tasks. Regularly review and update test cases as the application evolves and changes.

33. Describe the importance of test data preparation for API testing, and what strategies do you employ to create realistic test data?

Answer: Test data preparation is crucial to simulate real-world scenarios. Strategies include using data generators, setting up test databases, and using production-like data to ensure test data is representative and relevant.

34. Can you explain the concept of API request headers and provide examples of commonly used headers in API testing?

Answer: API request headers contain additional information about the request. Common headers include:

  • Content'-Type: Specifies the format of the request body (e.g., application/json).
  • Accept: Defines the expected response format (e.g., application/json).
  • Authorization: Contains authentication credentials or tokens.
  • User-Agent: Identifies the client making the request.

35. What is regression testing in the context of API testing, and why is it important?

Answer: Regression testing in API testing involves retesting API endpoints after changes or updates to ensure that new code modifications do not introduce defects or break existing functionality. It’s important to maintain the stability and reliability of the API.

36. How do you handle API testing for scenarios involving file uploads and downloads?

Answer: Testing file uploads and downloads typically involves sending and validating binary data in API requests and responses. Testers need to ensure that the API can handle various file types and sizes, and verify that files are uploaded and downloaded correctly.

37. Can you describe the concept of API mocking frameworks, and why might you use them in API testing?

Answer: API mocking frameworks allow testers to simulate API behavior for endpoints that are not yet implemented or for third-party APIs that cannot be directly accessed in a test environment. This enables testing to proceed independently of the actual API’s availability.

38. What strategies do you employ for API test data cleanup and ensuring the test environment remains in a consistent state?

Answer: Test data cleanup can involve executing cleanup scripts or using API endpoints specifically designed for data reset. The goal is to return the environment to a known state before running subsequent tests to maintain data consistency.

39. How do you verify and validate API responses for pagination or large datasets?

Answer: For pagination or large datasets, testers need to verify that the API correctly handles pagination parameters and returns the expected number of results per page. They may also validate the correctness of links or next/previous page tokens.

40. Can you explain the concept of API load balancing and its role in API testing?

Answer: API load balancing distributes incoming API requests across multiple servers to ensure high availability and performance. Testers should verify that the load balancing mechanism evenly distributes requests and that APIs remain responsive under load.

41. What is the purpose of API versioning, and can you name different versioning approaches used in API development?

Answer: API versioning ensures that changes to the API do not disrupt existing clients. Different versioning approaches include URI versioning (e.g.,/v1/resource), custom headers (e.g., Accept-Version: v1), and query parameters (e.g.,/resource?version=v1).

42. Explain the concept of API contract testing. How does it differ from functional testing, and why is it valuable?

Answer: API contract testing focuses on verifying that the API adheres to its documented contract, including request and response formats. Unlike functional testing, it doesn’t emphasize the API’s functionality but ensures it meets its specifications, which is crucial for maintaining consistency and compatibility.

43. What are the key components of an API request, and how do you ensure they are correctly configured during testing?

Answer: Key components include the endpoint URL, HTTP method, headers, parameters, and request body (if applicable). Testers should meticulously configure each component according to the API’s documentation to ensure correct testing.

44. Can you explain the concept of API load testing and share examples of scenarios where it is particularly important?

Answer: API load testing evaluates how an API performs under expected and peak loads. It is essential for APIs that handle a large number of concurrent requests, such as e-commerce checkout, social media feeds, and online gaming.

45. How do you handle scenarios in API testing where there are dependencies on external systems, databases, or third-party APIs?

Answer: To handle dependencies, testers may use mock services to simulate the behavior of external systems or stubs for third-party APIs. This allows testing to proceed independently of the actual dependencies.

46. What role does test data management play in API testing, and how can you ensure data privacy and security in testing?

Answer: Test data management involves generating, storing, and managing test data. To ensure data privacy and security, testers should use sanitized or anonymized data and avoid using real production data in tests.

47. Describe your approach to testing APIs with asynchronous operations or long-running processes.

Answer: For APIs with asynchronous operations, testers must account for delays in responses and verify that asynchronous tasks complete successfully. They may use polling mechanisms or callback notifications for such testing.

48. What are the advantages of using scripting languages like Python or JavaScript for API testing, and can you provide examples of test automation frameworks for these languages?

Answer: Scripting languages like Python and JavaScript are popular for API testing due to their ease of use and extensive libraries. Examples of test automation frameworks include requests(Python) and axios (JavaScript).

49. How do you perform API testing for webhooks, and what challenges might you encounter in webhook testing?

Answer: Webhook testing involves verifying that an API correctly processes incoming webhook notifications. Testers need to simulate webhook events and ensure that the API responds appropriately. Challenges may include ensuring the webhook endpoint remains accessible and secure.

50. Can you share your approach to ensuring comprehensive test coverage in API testing?

Answer: To achieve comprehensive test coverage, testers should create test scenarios that cover various use cases, including positive and negative testing, edge cases, and boundary testing. They should also consider authentication, error handling, and performance aspects in their test coverage.


These manual API testing interview questions and answers cover essential concepts and practices in API testing. Be sure to review these questions and prepare responses tailored to your experience and the specific job requirements to showcase your expertise during the interview. With proper preparation, you can confidently demonstrate your API testing skills and land your desired role.

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