API Testing Interview Questions and Answers for experienced

1. What is API testing and why is it important?

   • Answer: API testing is a type of software testing that focuses on verifying the Application Programming Interfaces (APIs) of a software system. It involves sending requests to the API and validating the responses to ensure that the API functions as expected. It's crucial because it allows for testing the backend logic independently of the UI, leading to earlier detection of bugs, improved security, better performance, and faster overall testing cycles.

2. Explain the difference between REST and SOAP APIs.

   • Answer: REST (Representational State Transfer) and SOAP (Simple Object Access Protocol) are both architectural styles for building APIs, but they differ significantly. REST is lightweight, uses various data formats (like JSON), and is stateless, relying on HTTP methods (GET, POST, PUT, DELETE). SOAP, on the other hand, is more complex, typically uses XML, and is often stateful, requiring more overhead. REST is generally preferred for its simplicity and flexibility, while SOAP is chosen when robust security and interoperability are paramount.

3. What are the different types of API testing?

   • Answer: Several types of API testing exist, including:
     • Unit Testing: Testing individual components of the API.
     • Integration Testing: Testing the interaction between different components or APIs.
     • Contract Testing: Verifying that the API adheres to its defined contract.
     • Functional Testing: Checking if the API performs its intended functions correctly.
     • Load Testing: Assessing the API's performance under various load conditions.
     • Security Testing: Identifying vulnerabilities and ensuring the API's security.
     • UI Testing (indirectly): Although not strictly API testing, verifying the UI interacts correctly with the API is important.

4. Describe the API testing lifecycle.

   • Answer: The API testing lifecycle typically includes:
     • Planning and Analysis: Defining the scope, objectives, and test cases.
     • Test Design: Creating test cases based on the API specifications.
     • Test Development: Writing the automation scripts for executing the tests.
     • Test Execution: Running the tests and recording the results.
     • Test Reporting: Generating reports that summarize the test results.
     • Test Maintenance: Updating and maintaining the test cases and scripts as the API evolves.

5. What tools are commonly used for API testing?

   • Answer: Popular API testing tools include Postman, REST-assured (Java), Swagger/OpenAPI tools, SoapUI, JMeter (for load testing), and Karate DSL.

6. How do you handle API authentication in your tests?

   • Answer: API authentication methods vary, including API Keys, OAuth 2.0, JWT (JSON Web Tokens), Basic Authentication, and others. My approach involves using the appropriate method within my chosen testing tool; for example, setting headers in Postman or using specific libraries in Java for OAuth 2.0 flows.

7. Explain how you would test for different HTTP status codes.

   • Answer: I would assert the HTTP status code returned by the API call against the expected status code. For example, a successful GET request should return a 200 OK, while a 404 indicates a resource not found. My testing framework would include checks to validate the status code and handle different responses accordingly.

8. How do you handle error scenarios during API testing?

   • Answer: Error handling is critical. I would design test cases to specifically trigger error conditions (e.g., invalid input, missing parameters). The tests should then verify that the API returns appropriate error messages, error codes (HTTP status codes like 400 Bad Request or 500 Internal Server Error), and potentially handles the error gracefully without crashing.

9. What are some common challenges faced during API testing?

   • Answer: Common challenges include handling authentication and authorization correctly, managing large datasets and varied input parameters, dealing with asynchronous operations, testing complex dependencies between APIs, and ensuring thorough test coverage without overwhelming the system.

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