API Testing Interview Questions

Top 55 API Testing Interview Questions: A Complete Guide

Are you prepared to excel in your API testing interview? This article serves as your comprehensive guide to mastering common API testing interview questions. We cover key topics including API concepts, API testing tools, Postman, and Rest Assured, providing insightful answers to help you stand out.

Whether you’re a fresher or an experienced professional, these interview questions empower you to showcase your expertise and leave a lasting impression.

Don’t hesitate; immerse yourself in this guide and elevate your API testing interview preparation. Your success is just a read away! This resource is tailored to support your journey, ensuring you’re well-prepared to tackle any API testing interview that comes your way.

Lastly, stay confident and composed during your interview. Your knowledge and preparation will shine through, making a strong impression on your potential employers. Best of luck in your API testing interview – you’ve got this

API Testing Interview Questions for Freshers

Here are most frequently Asked API Interview Questions For Freshers: 

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

API testing is the process of validating the functionality, reliability, performance, and security of application programming interfaces (APIs). It ensures that APIs perform as intended and interact seamlessly with other software components. 

API testing is an integral part of modern software development problems and solutions

API testing is crucial as it helps detect defects early in the development lifecycle, ensures the stability of software applications, and enhances the user experience.

2. Explain the difference between SOAP and RESTful APIs.

SOAP (Simple Object Access Protocol) is a protocol that uses XML for message exchange and relies heavily on request-response interactions. 

REST (Representational State Transfer), on the other hand, is an architectural style that uses various HTTP methods and focuses on resource-based interactions. 

RESTful APIs are generally more lightweight, easier to implement, and widely adopted for web services.

3. How do you handle authentication in API testing?

Authentication in API testing is often managed through various methods such as Basic Authentication (username/password), API keys, OAuth, or tokens. These mechanisms validate the identity of the user or application accessing the API. 

Testers simulate these authentication methods to ensure secure access and data protection.

4. What are the key components of an API request?

An API request consists of an HTTP method (GET, POST, PUT, DELETE), endpoint URL, headers (including authentication), parameters, and request body (if applicable). 

These components collectively define the action, data, and scope of the API call.

5. What is the purpose of status codes in API responses?

Status codes indicate the outcome of an API request. For instance, a 200 status code signifies a successful request, while a 404 status code indicates that the resource wasn’t found. 

Status codes help developers and testers understand the outcome of an API call and take appropriate actions.

6. How do you ensure data security in API testing?

Data security in API testing involves verifying that sensitive information is transmitted securely using encryption protocols (e.g., HTTPS). 

Testers also validate that access controls and authorization mechanisms are in place to prevent unauthorized access to data.

7. What is endpoint testing?

Endpoint testing involves testing individual API endpoints (URLs) to ensure they respond correctly to specific HTTP methods and return the expected data. It ensures that each endpoint behaves as intended and handles different scenarios effectively.

8. How can you parameterize requests in API testing?

Parameterization involves substituting dynamic values (variables) in API requests. Testers achieve this by using data-driven testing approaches, test data from external sources (such as spreadsheets or databases), or by using environment-specific values.

9. How do you handle API versioning?

API versioning is the practice of maintaining multiple versions of an API to support backward compatibility while introducing new features. 

Testers verify that API versions are correctly specified in requests and that changes between versions don’t adversely affect existing functionality.

10. Explain the concept of payload in API requests.

The payload is the data sent in the request body of an API call. It could be in various formats like JSON, XML, or other data structures. Testers ensure that payloads are correctly structured, valid, and include all required information for the API call to succeed.

11. What are Postman collections and environments?

Postman collections are sets of saved API requests that can be organized, executed, and shared. 

Environments store variables and configurations that can be used across multiple requests within a collection, facilitating parameterization and testing in different scenarios.

12. How do you automate API tests in Postman?

API tests can be automated in Postman using test scripts. These scripts are written in JavaScript and executed after making an API call. 

They enable assertions to validate responses, manipulate data, and perform complex validations during automated testing.

13. Explain the purpose of Pre-request Scripts and Tests in Postman.

Pre-request Scripts are executed before sending a request and can be used to set dynamic values or perform calculations on variables. 

Tests are executed after receiving a response and help validate the response data against expected values, status codes, and more.

14. What is the significance of API documentation?

Api documentation helps developers and testers understand how to interact with the API correctly and facilitates seamless integration.

Optimizing API documentation provides comprehensive details about an API’s endpoints, methods, parameters, response formats, authentication requirements, and usage examples. 

15. How do you log a request and response in case of API validation failure?

Logging requests and responses during API validation failures is crucial for debugging. In tools like Postman, you can use the log() function to log detailed information about both the request and response, aiding in identifying the cause of failures.

API Testing Interview Questions for Experienced

Here are some tricky API testing interview questions along with their answers:

16. How do you handle dynamic values in API responses, such as timestamps or unique identifiers?

To handle dynamic values, you can use data validation techniques like regular expressions or custom validation scripts. You can also capture the dynamic values during the test execution and use them for assertions in subsequent requests.

17. Explain the concept of OAuth 2.0 flows and when each flow is used.

OAuth 2.0 defines several authorization flows, including Authorization Code, Implicit, Resource Owner Password Credentials, and Client Credentials. 

Each flow is used in different scenarios, such as web applications, single-page applications, mobile apps, and server-to-server communication.

18. How can you simulate API responses with delayed or slow server responses?

To simulate delayed responses, you can introduce a delay using tools like WireMock or Postman’s “setNextRequest” feature. This helps in testing how your application handles slow API responses.

19. What is the purpose of a mock server in API testing, and how can it be beneficial?

A mock server simulates the behavior of real APIs during testing. It’s beneficial for parallel development, enabling teams to work on different modules independently. 

Mock servers ensure that testing isn’t dependent on the availability of actual APIs.

20. How can you test APIs that require authentication without exposing sensitive credentials in test scripts?

One approach is to use environment variables or configuration files to store sensitive credentials.

During testing, these variables can be accessed to populate the authentication details dynamically.

21. Can you explain the concept of “statelessness” in RESTful APIs and its implications?

“Statelessness” means that each API request from a client must contain all the information needed to understand and process the request. 

The server does not store any client state between requests. This simplifies scalability, as servers can process requests independently.

22. How can you ensure data integrity when testing APIs that involve database operations?

To ensure data integrity, you can perform API tests that involve database operations in a controlled test environment, such as a test database. 

After testing, rollback or clean up the test data to keep the environment consistent.

23. Explain the concept of “content negotiation” in API testing.

Content negotiation allows clients to specify the format in which they want to receive the response (e.g., JSON or XML). 

The server examines the request’s “Accept” header and provides the response in the requested format if available.

24. What is “caching” in API responses, and how can it impact testing?

Caching is the process of storing a copy of frequently used data to reduce the load on the server. 

It can impact testing as cached responses might not reflect real-time data changes. Testing caching involves strategies like cache disabling or expiration validation.

25. How can you perform load testing on APIs? What challenges might you encounter?

Load testing APIs involves sending a large number of concurrent requests to assess performance and scalability. 

Challenges include handling concurrent connections, simulating real-world usage, and monitoring server response times to detect bottlenecks.

These tricky questions are designed to test your deeper understanding of API testing concepts and scenarios. 

Postman API Interview Questions and Answers

Postman API Interview Questions and Answers

Here are 15 common Postman API testing interview questions along with answers

1. What is Postman, and how is it used in API testing?

Postman is a popular collaboration platform for API development that simplifies the process of creating, testing, and documenting APIs. It provides a user-friendly interface to send API requests, view responses, and validate the behavior of APIs.

2. What are Postman collections, and how are they useful?

Postman collections are groups of related API requests organized for efficient testing and collaboration. 

They allow you to save, organize, and execute a sequence of API requests as a single entity. Collections enhance productivity by enabling the creation of test suites and workflows.

3. How do you parameterize requests in Postman?

Parameterization in Postman involves using variables to replace dynamic values in API requests. 

Variables can be defined at the collection, environment, or request level. They allow you to reuse and customize data across multiple requests or scenarios.

4. What are Postman environments, and how do they work?

Postman environments store variables and values that can be used across different requests within a collection. 

They facilitate testing in various environments (such as development, testing, production) and help avoid hardcoding values.

5. How can you extract data from API responses using Postman?

Postman provides various methods for extracting data from API responses, such as using JSONPath or XPath expressions. You can use the pm.response.json() function to access JSON data and apply filters to extract specific values.

6. How do you automate tests in Postman?

Postman allows you to automate tests using scripting. You can write test scripts in JavaScript using the Postman scripting sandbox. 

These scripts can validate responses, check status codes, and perform complex assertions.

7. Explain the purpose of Pre-request Scripts and Tests in Postman.

Pre-request Scripts are executed before sending a request and are used to set up variables or perform calculations. 

Tests are executed after receiving a response and help validate the response data against expected values, headers, and status codes.

8. How can you handle authentication in Postman?

Postman supports various authentication methods, including Basic Authentication, Bearer Token, and OAuth 2.0. 

You can configure authentication settings in the request headers or use Postman’s built-in authorization mechanisms.

9. What is the Postman Runner, and how can you use it for testing?

The Postman Runner is a feature that allows you to execute a collection of requests in a sequence or with iterations. 

It’s useful for running multiple test scenarios, load testing, and verifying the functionality of APIs.

10. How do you share your Postman collections with teammates or colleagues?

You can share Postman collections with others by generating a shareable link or by exporting the collection as a JSON file. 

Additionally, you can collaborate using the “Team” feature in Postman, which allows team members to work on the same collection simultaneously.

11. What are Postman monitors, and how do they benefit API testing?

Postman monitors automate the process of running collections at scheduled intervals. 

They are useful for continuous integration and regression testing. Monitors allow teams to detect issues early in the development cycle and ensure that APIs are functioning as expected over time.

12. How can you handle dynamic values in API responses, such as timestamps or unique IDs?

Dynamic values can be handled using environment variables, scripting, and regular expressions.

Postman’s scripting capabilities enable you to extract dynamic values from responses and update variables for subsequent requests.

13. Can you explain the concept of chaining requests in Postman?

Chaining requests in Postman involves using the response data from one request as input for another request within the same collection. This is achieved using test scripts to extract data and set it as variables, which can then be used in subsequent requests.

14. What is the difference between Postman and Newman?

Postman is the graphical user interface for creating and testing APIs, while Newman is the command-line tool that allows you to run Postman collections in an automated, headless mode. 

Newman is often used for integrating Postman tests into CI/CD pipelines.

15. How do you handle cookies and sessions in Postman?

Postman supports cookies and sessions by automatically managing and sending cookies received in API responses. 

You can access cookies using the pm.cookies object in test scripts. For maintaining sessions, you can extract session tokens from responses and use them in subsequent requests.

REST Assured API testing Interview Questions and Answers

Here are some of the frequently asked API interview questions and answers for rest assured: 

1. What is Rest Assured, and how does it facilitate API testing?

Rest Assured is a Java library that provides a domain-specific language (DSL) for writing robust and maintainable tests for RESTful APIs. It simplifies the process of sending HTTP requests, receiving responses, and validating API behavior.

2. What is the difference between Rest Assured and other API testing tools like Postman?

Both api testing tools, Rest Assured allows for programmatic API testing within Java projects, while Postman is a graphical tool for manually testing APIs. Rest Assured is often preferred for automated testing and integration into larger test frameworks.

3. How can you perform authentication in Rest Assured tests?

Rest Assured supports various authentication methods such as Basic, Digest, OAuth, and more. You can use the .auth() method to specify the authentication credentials or tokens required to access protected resources.

4. How do you validate API responses using Rest Assured?

Rest Assured provides a fluent API for response validation. You can use methods like .statusCode(), .body(), .header(), and .jsonPath() to check the expected status codes, response content, headers, and specific JSON values.

5. What is the method chaining in Rest Assured?

Method chaining is a technique used in Rest Assured where multiple method calls are chained together in a single line. Each method returns an object that allows you to call subsequent methods on it, making the code concise and readable.

6. Explain the difference between given(), when(), and then() in Rest Assured syntax.

In Rest Assured, given() is used to set up the request specification, when() is used to specify the HTTP method and the API endpoint, and then() is used to define the assertions on the response.

7. How can you handle request and response headers in Rest Assured?

You can use the .header() method to add headers to the request, and the .header() method in conjunction with .extract().headers() to extract and validate response headers.

8. What is the purpose of the extract() method in Rest Assured?

The extract() method in Rest Assured is used to extract different parts of the response, such as the response body, headers, cookies, and more. It allows you to validate and manipulate these extracted values.

9. How do you parameterize API requests in Rest Assured?

You can use the .pathParam(), .queryParam(), and .formParam() methods to parameterize API requests. These methods allow you to replace placeholders in the request URL or body with actual values.

10. How can you handle dynamic values in API responses using Rest Assured?

Rest Assured provides powerful features like JsonPath and XMLPath to extract and validate dynamic values from API responses. 

These tools allow you to navigate and manipulate the JSON or XML structure effectively.

11. What is the purpose of the given().spec() method in Rest Assured?

The .given().spec() method allows you to reuse a predefined request specification in multiple API requests. It helps in maintaining consistency and reducing redundancy in request setup.

12. How do you perform assertion on response time using Rest Assured?

Rest Assured provides the .time() method that allows you to assert the response time of an API call. You can specify the maximum acceptable response time and time unit to validate the API’s performance.

13. What is the difference between assertThat() and assertThat().body() in Rest Assured?

assertThat() is used for general assertions on the response, while assertThat().body() is used specifically to validate the response body content, such as JSON or XML attributes and values.

14. How do you handle error responses or exceptions in Rest Assured tests?

You can use the .assertThrows() method to validate that a specific exception is thrown during an API call. This is useful for checking error responses and ensuring proper error handling.

15. How can you perform API testing for file uploads using Rest Assured?

Rest Assured supports file uploads through the .multiPart() method, which allows you to attach files to a request. This is particularly useful when testing APIs that require file uploads, such as image or document uploads.

Tips for API Testing Interview Questions

For freshers, API testing interviews generally focus on evaluating your foundational knowledge, problem-solving skills, and your ability to grasp essential concepts. 

The interviewers understand that you may not have extensive experience, so they’re more interested in gauging your enthusiasm, willingness to learn, and potential to grow within the role

Experienced candidates face a more in-depth evaluation of their API testing expertise, along with a focus on their practical experience, qualities and understanding of QA lead roles and responsibilities, if you’re applying for a managerial position and contributions to previous projects.

Here are few general tips to know before your interview: 

Fundamentals Assessment: 

Expect questions that test your understanding of API basics, such as HTTP methods, status codes, request and response structures, and the purpose of APIs in software development.

 Scenario-Based Questions: 

You might be presented with hypothetical scenarios to assess how you approach testing challenges. Focus on your thought process, how you identify test cases, and your approach to validating API responses.

 Testing Approach: 

Interviewers often inquire about your testing approach. Be prepared to explain how you’d design test cases, what factors you consider, and how you ensure thorough coverage of API functionalities.

Automation Proficiency

If you have automation experience, anticipate questions about the tools and frameworks you’ve used, your approach to building automated tests, and how you manage test data.

Project Examples

Be ready to discuss past projects where you’ve applied API testing. Highlight challenges you faced, how you overcame them, and the impact of your testing on the overall project’s success.


Mastering fundamental API testing interview questions and answers empowers you to confidently navigate the interview process and leave a lasting impression on potential employers. These tools play a crucial role in ensuring the functionality, reliability, and security of applications relying on API interactions.

As you step into your API testing interview, remember that preparation is your strongest ally. Dedicate yourself to understanding the intricacies of API testing and commit to continuous learning; this dedication will undoubtedly shine through.

Embrace the opportunity with confidence, showcasing not only your technical prowess but also your problem-solving skills and adaptability. Approach each question thoughtfully, drawing on your knowledge and experiences.

Best of luck! May your interview be a stepping stone to a successful and fulfilling career in API testing, where you’ll contribute significantly to the development of robust and reliable software systems

Rahnuma Tasnim

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