90+ API Testing Interview Questions & Answers

APIs are a critical part of the modern web, as they allow developers to share data across different platforms.

As a software tester, you may have been asked to test an API. If so, you’ll want to know the best way to approach this task from both a technical and non-technical standpoint. In order to do so, it’s important that you have a strong understanding of what APIs are and how they work.

In this blog post, we’ll be going over some of the most frequently asked Web API testing interview questions and answers. We will discuss what they are and how to answer them as well as provide a list of other related topics that you should know.

Before going ahead, let’s see some unavoidable Interview Questions which every hiring manager asks you in any Software Testing interview.

• What Are The Reasons For Choosing Software Testing As Your Career
• Tell Me About Yourself (Detailed Answer)

Let’s move with the actual post on API Interview Questions And Answers.

Best Web API Testing Interview Questions

Before going ahead, I would like to let you know that we have another post where we covered 30+ Postman Interview Questions separately.

1. What is an API?

API is an acronym and it stands for Application Programming Interface. API is a set of routines, protocols, and tools for building Software Applications. APIs specify how one software program should interact with other software programs.

In simple words, API stands for Application Programming Interface. API acts as an interface between two software applications and allows the two software applications to communicate with each other. API is a collection of software functions that can be executed by another software program.

2. How does an API work?

An API works as an intermediary that allows two applications to communicate with each other. It acts as a bridge that defines the methods and data formats necessary for interaction, ensuring consistency and efficiency. When an API request is made, the client sends specific parameters or data to the server through the API endpoint. The server processes this request, performs the necessary actions, and responds with the requested data or an appropriate status message.

For example, consider a weather application on your smartphone. When you input your location to check the weather forecast, the application sends a request to a weather API with your location data. The API processes this request by querying the backend database or external data sources and then returns structured weather information, such as temperature, humidity, and forecasts, in a specified format like JSON. This seamless process allows the weather application to display the requested data to you without requiring you to interact with the underlying systems directly. APIs, therefore, enable streamlined communication between various software systems, enhancing productivity and integration.

3. What are the types of APIs?

When discussing the types of APIs, it’s essential to understand the various categories that serve different purposes in software development. Here are some of the main types of APIs:

• Web APIs: These are interfaces that allow interaction between web servers and clients. They commonly use HTTP protocols to facilitate communication, enabling applications to access and exchange data over the internet. Examples include RESTful APIs and GraphQL.
• Operating System APIs: These APIs provide functionalities for interacting with the operating system resources. They allow software applications to perform tasks such as managing files, handling memory, and managing processes. Examples include the Windows API and POSIX.
• Library APIs: These consist of a set of routines, protocols, and tools for building software and applications. Library APIs allow developers to use predefined functions and processes without having to reinvent the wheel, thus speeding up the development process. Examples include the C Standard Library and Java’s JavaFX API.
• Hardware APIs: These interfaces allow software to communicate directly with hardware components. They provide the necessary commands and controls to interact with physical devices, like printers or graphics cards. Examples include the JavaScript Web API for accessing device capabilities and the Android Open Accessory Protocol.

Each type of API plays a crucial role in enabling developers to interact with different layers of technology, facilitating a smoother integration and development experience.

4. What are the different ways to authenticate an API?

There are several methods to authenticate an API to ensure secure communication and access control:

1. API Key Authentication – This involves providing a unique key, generated by the API provider, which the client includes in the request header or URL. API keys help identify the client but should be used over secure protocols like HTTPS to prevent interception.
2. Basic Authentication – This is a simple method where a username and password are encoded in base64 format and included in the request header. It is straightforward but less secure unless used alongside HTTPS.
3. OAuth (OAuth 1.0, 2.0) – OAuth is a robust framework that allows third-party authentication without passing sensitive credentials. OAuth 2.0 is particularly popular, offering tokens for secure communication between server and client.
4. Bearer Token Authentication – Commonly used with OAuth 2.0, it involves sending a token in an HTTP Authorization header. The bearer token grants access to specific resources based on the token’s scope and validity.
5. JWT (JSON Web Tokens) – These tokens are compact, JSON-based, and include claims about the user or client. JWTs are signed and optionally encrypted, providing secure, stateless authentication.
6. Digest Authentication – Unlike basic authentication, digest authentication uses a hashing technique to secure credentials, making it more secure over non-encrypted channels.
7. Mutual TLS (mTLS) – This method uses client certificates in addition to server certificates during the TLS handshake to verify both parties before proceeding with communication.

Each method has its own use cases and security considerations, making it essential to choose the one best suited for your application’s needs.

5. What is the role of headers in API testing?

Headers play a crucial role in API testing as they convey critical information between the client and server. They include metadata such as authentication tokens, content type, and caching directives, ensuring proper communication and data handling. Proper validation of headers is essential to ensure API functionality, security, and compliance with standards.

6. Can you discuss the different API protocols?

There are several API protocols that facilitate communication between systems, each with its own use cases and characteristics.

1. REST (Representational State Transfer) – REST is one of the most widely used protocols for building APIs. It leverages standard HTTP methods like GET, POST, PUT, and DELETE and works with a stateless communication model. REST APIs are highly scalable, flexible, and easy to implement, making them a popular choice.
2. SOAP (Simple Object Access Protocol) – SOAP is a protocol that relies on XML-based messaging. It is designed for exchanging structured information in web services, emphasizing security and reliability. SOAP is often used in enterprise applications where transactional reliability is crucial.
3. GraphQL – GraphQL is a query language and runtime for APIs, allowing clients to request exactly the data they need. It offers greater efficiency by reducing over-fetching or under-fetching of data and is favored in applications requiring high flexibility in data fetching.
4. gRPC (gRPC Remote Procedure Call) – gRPC is an open-source protocol developed by Google. It uses HTTP/2 for communication, supports multiple programming languages, and is highly performant. It is particularly suited for microservices architectures.
5. WebSocket APIs – WebSocket is a protocol for two-way communication between a client and server over a single, long-lived connection. WebSocket APIs are commonly used in real-time applications like chat apps, live updates, and multiplayer gaming.

Each protocol has its strengths and ideal scenarios for implementation, giving developers the flexibility to choose the one that best fits their project’s needs.

7. What is API Testing?

API testing is a type of software testing that involves testing APIs directly and also as a part of integration testing to check whether the API meets expectations in terms of functionality, reliability, performance, and security of an application. In API Testing our main focus will be on the Business logic layer of the software architecture. API testing can be performed on any software system which contains multiple APIs.

8. What is the difference between manual API testing and automated API testing?

Manual API testing involves testers executing test cases in an ad-hoc manner without the use of automation tools. This method is exploratory in nature and allows for a hands-on approach where testers can understand the application’s functionality, examine responses in real-time, and quickly adapt test cases based on immediate findings. Although it offers flexibility, manual testing can be time-consuming and error-prone, especially when dealing with complex APIs or large datasets.

In contrast, automated API testing uses scripts and tools to run tests without human intervention. This approach is efficient for repetitive tasks, large-scale testing, and regression testing, as it ensures consistent results and reduces human error. Automated testing can significantly speed up the testing process and is particularly useful for continuous integration/continuous deployment (CI/CD) environments. However, it requires an initial investment in time and resources to develop and maintain the automated tests.

Both methods have their advantages and are often used in conjunction to maximize testing effectiveness.

9. What are the common API Testing Types?

API testing typically involves the following practices:

• Unit testing: This involves testing individual components or functions of the API to ensure they work as expected. It helps detect errors at an early stage in development.
• Functional testing: This type of testing verifies that the API behaves according to the requirements. It checks that the endpoints are returning the correct data and are functioning as intended.
• Load testing: Load testing evaluates the API’s performance under heavy traffic or stress. It measures how well the API handles multiple requests simultaneously.
• Runtime/ Error Detection: This testing aims to identify any errors that may occur during the execution of the API. It helps find issues that may not be apparent through static testing.
• Security testing: This type assesses the API for security vulnerabilities. It checks for potential threats and ensures that sensitive data is protected from unauthorized access.
• Validation Testing: Validation testing ensures that the API meets the business and technical requirements. It checks if the outputs are valid and comply with the expected formats.
• UI testing: While primarily focused on the user interface, UI testing checks how the API interacts with the front-end application. It ensures that the user experience is seamless and aligns with the API’s functionality.
• Interoperability Testing: This type of testing verifies that the API can successfully interact and exchange data with other services and systems. It ensures that the API adheres to industry standards and protocols, allowing seamless integration across different platforms and technologies.
• WS Compliance Testing: WS Compliance testing focuses on evaluating the API against the Web Services (WS) standards. This process ensures that the API adheres to relevant specifications, such as SOAP, WSDL, and other related protocols, thus guaranteeing reliability and compatibility within web service ecosystems.
• Penetration testing: Using simulated attacks, penetration testing evaluates the API’s security by identifying vulnerabilities that could be exploited by hackers.
• API Hacking: This involves attempting to access the API in unauthorized ways to discover weaknesses. It helps in understanding potential attack vectors.
• Fuzz testing: Fuzz testing sends random or unexpected data to the API to see how it handles unusual input. This is useful for finding bugs and security weaknesses.

Using these different types of API testing helps ensure that the API is reliable, secure, and performs well under various conditions.

Learn more on API Testing Types

10. What are the most important best practices for API testing?

When it comes to API testing, adhering to best practices can significantly enhance the effectiveness and reliability of your testing process. Here are some key principles to consider:

• Comprehensive Test Coverage: Ensure that your tests cover all critical endpoints and functionalities of the API, including positive and negative scenarios. This includes testing for various input parameters, error handling, and response codes.
• Use of Automation: Leverage automated testing tools to run tests repeatedly and efficiently. Automation helps in identifying regressions quickly as your API evolves, ensuring new changes do not break existing functionality.
• Documentation Consistency: Maintain up-to-date API documentation that is clear and detailed. This should include endpoint descriptions, request/response formats, authentication methods, and error codes. Well-documented APIs facilitate better testing and understanding.
• Environment Management: Conduct tests in a controlled environment that mirrors the production environment as closely as possible. This includes simulating network conditions and external dependencies to accurately assess the API’s behavior under various scenarios.
• Performance Testing: Incorporate performance testing to evaluate the API’s scalability and reliability under load. Monitor key metrics such as response time, throughput, and resource utilization to ensure the API can handle expected and peak traffic.
• Security Testing: Prioritize security testing to identify vulnerabilities and ensure data protection. This includes testing for authentication, authorization, encryption, and common vulnerabilities like SQL injection and cross-site scripting (XSS).

By implementing these best practices, you can enhance the robustness of your API testing efforts, leading to higher quality software and a better user experience.

11. What are the best practices for writing effective API Test Cases

Writing effective API test cases is crucial for ensuring the reliability and functionality of your applications. Here are some best practices to consider:

• Understand the API Specification: Before writing test cases, thoroughly review the API documentation to understand the endpoints, parameters, request types, and expected responses.
• Use Clear and Descriptive Names: Name your test cases in a way that clearly describes what functionality is being tested. This makes it easier to identify issues during testing and debugging.
• Test for Edge Cases: Include tests for both valid and invalid inputs to ensure the API behaves correctly under all circumstances. This helps to identify potential failures before they affect users.
• Validate All Responses: Always check the HTTP status codes, response times, headers, and body content to ensure they match the expected outcomes. This helps to verify that the API is functioning as intended.
• Automate Where Possible: Implement automated testing tools that can regularly execute your API test cases. Automation can save time and catch regressions in functionality without manual intervention.
• Keep Tests Isolated: Create tests that are independent of each other, so that a failure in one test does not affect the others. This isolation helps in accurately pinpointing failures.
• Document Your Test Cases: Provide clear documentation for each test case, including the purpose of the test, input values, and expected results. This aids in maintaining the tests over time and helps new team members understand the testing strategy.

By following these best practices, you can create robust and effective API test cases that will enhance your overall testing strategy and contribute to building higher-quality software.

12. How easy or difficult is it to draft API tests?

Drafting API tests can range from straightforward to complex, depending on the specific project requirements and the tester’s experience.

For simpler APIs, creating test cases may involve straightforward steps, such as validating request and response formats or ensuring proper error handling. However, for more intricate APIs, challenges can arise, including managing dependencies between endpoints, simulating real-world scenarios, and dealing with dynamic data.

Additionally, the tester needs a thorough understanding of the API’s functionality and purpose, as well as proficiency with testing tools and scripting languages. While initial setup may take time, leveraging robust testing frameworks and automation tools can significantly reduce complexity and improve efficiency in the long term.

13. What are some best practices for API test automation?

• Understand the API Specification: Familiarize yourself with the API documentation to comprehensively understand the endpoints, request methods, and data formats.
• Use Automation Tools: Select the right tools for API testing such as Postman, SoapUI, or RestAssured, which can streamline the automation process and improve test reliability.
• Write Clear and Maintainable Tests: Ensure that your test scripts are well-structured, easy to read, and maintainable. Use meaningful names for tests and comments where necessary to explain complex logic.
• Test for Different Scenarios: Cover a range of test cases including positive, negative, boundary, and edge cases to ensure the API behaves as expected in all situations.
• Implement Continuous Integration: Integrate API tests into the CI/CD pipeline to ensure they are executed automatically during builds and deployments, which helps catch issues early.
• Validate Response Codes and Payloads: Always check the HTTP response codes as well as the returned data structure and content against expected results to validate the API’s functionality.
• Use Mock Services: When necessary, utilize mock services to simulate API responses, which can help in cases where the actual service is unavailable or still under development.
• Perform Security Testing: Incorporate security testing into your automation suite to identify vulnerabilities in the API, such as authentication issues or data exposure.
• Monitor API Performance: Regularly test the performance of the API, including response times and load testing, to ensure it can handle expected levels of traffic without degradation. 

14. What are the advantages and disadvantages of API test automation?

Advantages of API Test Automation

1. Faster Testing Process: Automated API testing significantly speeds up the testing process by executing tests much faster than manual methods. This efficiency is especially valuable in agile development environments where frequent testing is required.
2. Improved Accuracy: Automation reduces the risk of human error, ensuring that tests are consistent and reliable. This leads to more accurate results and a higher quality product.
3. Reusability of Test Scripts: Test scripts for APIs can be reused across different projects or versions of the application, saving time and resources in the long term.
4. Enhanced Test Coverage: Automation allows for the execution of multiple test scenarios, including edge cases, which improves the overall coverage and robustness of the application.
5. Integration with CI/CD Pipeline: Automated tests can integrate seamlessly into Continuous Integration and Continuous Deployment (CI/CD) pipelines, enabling rapid feedback and efficient development cycles.
6. Cost-Effectiveness Over Time: While the initial setup of automation may require investment, it becomes cost-effective over time by reducing manual efforts and improving efficiency.

Disadvantages of API Test Automation

1. High Initial Setup Cost: Creating automated API test scripts requires advanced tools and skilled personnel, which can involve significant initial investments.
2. Complex Maintenance: Changes in the APIs, such as modifications to endpoints or data structures, can necessitate frequent updates to test scripts, resulting in additional maintenance efforts.
3. Limited Usability for Exploratory Testing: Automated tests are predefined and lack the adaptability of manual testing, making them unsuitable for exploratory or invalid case testing.
4. Tool Dependency: Relying on specific testing tools may result in compatibility or scalability challenges, especially as projects grow or technology evolves.
5. Skill Requirements: Effective automation requires skilled testers who are proficient in scripting and understand the technical aspects of the API, which may involve steep learning curves for teams.

By understanding these advantages and disadvantages, teams can better evaluate whether API test automation aligns with their project goals and resources. 

15. What steps can you take to plan and implement an effective API testing strategy?

To plan and implement an effective API testing strategy, consider the following steps: 

1. Define Testing Objectives: Clearly outline what you aim to achieve with your API testing, such as performance validation, functionality verification, or security assurance.
2. Determine Test Types: Identify the various types of tests you need, including unit tests, integration tests, functional tests, performance tests, and security tests, to comprehensively evaluate the API.
3. Select Appropriate Tools: Choose the right tools and frameworks that align with your testing objectives. Tools like Postman, Swagger, and cURL can facilitate manual and automated testing processes.
4. Develop Test Cases: Create detailed test cases that cover a wide range of scenarios, including edge cases, to ensure thorough evaluation of the API’s functionality and performance under various conditions.
5. Set Up a Test Environment: Establish a proper testing environment that mirrors production as closely as possible to accurately simulate API usage and interactions.
6. Automate Where Possible: Automate repetitive test cases to save time and increase efficiency. Continuous integration (CI) processes can help integrate automated tests into the development workflow.
7. Monitor and Analyze Results: After executing tests, monitor outcomes carefully. Analyse results to identify trends, defects, or performance issues, which can guide future improvements.
8. Iterate and Update: Regularly review and update your API testing strategy based on new findings, incoming feature changes, or shifts in application architecture to ensure it remains effective and relevant.

16. What is dynamic input data, and why is it essential for API testing?

Dynamic input data refers to data that is generated on-the-fly during the testing process rather than being pre-defined or static. This approach is vital for API testing as it enables testers to simulate a diverse range of real-world scenarios, making the testing more robust and comprehensive. By using dynamic data, testers can uncover edge cases that static data may miss, ensuring that the API behaves correctly under various circumstances. Additionally, dynamic input helps to reduce biases introduced by predefined data sets, leading to more accurate and reliable testing outcomes. As APIs often interact with unpredictable data inputs, incorporating dynamic data can significantly enhance the overall effectiveness of the testing process.

17. How do you handle dynamic values in API testing, such as timestamps or random data?

Handling dynamic values in API testing, such as timestamps or random data, requires a strategic approach to ensure accuracy and consistency in test scenarios. One effective method is to use libraries or frameworks that can generate dynamic values programmatically. For instance, timestamps can be derived from the system clock, while random data can be produced using functions provided by programming languages or testing frameworks. Additionally, it is essential to document the generated values during test execution to maintain reproducibility for subsequent test runs. By managing dynamic data effectively, testers can ensure that their API tests are reflective of real-world conditions, thereby improving the reliability of the testing outcomes.

18. Name some of the common protocols used in API Testing?

Some of the protocols using in API Testing are as follows:

• HTTP
• REST
• SOAP
• JMS
• UDDI

19. What are some of the architectural styles for creating a Web API?

Some of the architectural styles for creating web api are as follows.

• Simple URI as the address for the services
• Stateless communication
• HTTP for client-server communication
• XML/JSON as formatting language

20. What is API test environment?

An API test environment refers to a dedicated setup where API testing can be conducted safely and effectively. It contains no Graphical User Interface (GUI). This environment mimics the production environment to provide realistic testing conditions while keeping the production data and systems secure. It typically includes a suitable combination of test servers, databases, and various software tools specifically designed for API testing.

By isolating the testing process, developers and testers can evaluate the API’s functionality, performance, and security without risking disruptiveness to live applications. A well-configured API test environment allows for systematic testing, reproducibility of results, and the identification of potential issues before the API is deployed into production.

21. Is a Test Environment Necessary for API Testing?

Yes, implementing a test environment for API testing is highly recommended. A dedicated test environment ensures that APIs are evaluated in conditions that closely simulate the production setup, allowing testers to identify and address potential issues before deployment. This environment provides a controlled space to validate API functionality, security, performance, and reliability without risking disruptions to live systems.

Additionally, it facilitates better collaboration between development and QA teams by offering a stable and consistent setup for testing. By investing in a proper test environment, businesses can significantly improve the quality of their APIs and reduce the likelihood of costly errors post-deployment. 

22. What is an API framework?

An API framework is a set of tools, libraries, and best practices that simplify the process of building and testing APIs. It provides a structured environment that aids developers in creating, managing, and deploying APIs with efficiency and consistency. An effective API framework usually includes functionalities for defining endpoints, handling requests and responses, performing authentication, and facilitating documentation. Additionally, it often integrates testing capabilities, enabling automated testing of APIs to ensure they function correctly and meet specified requirements. By employing an API framework, teams can accelerate development cycles, maintain quality standards, and reduce the risks associated with API integrations.

23. What is an API testing framework?

An API testing framework is a set of guidelines, tools, and practices designed to streamline the process of testing APIs. It provides developers and testers with a structured environment to create, manage, and execute automated test cases that validate the functionality, performance, and security of APIs. These frameworks often support various programming languages and offer features such as test case organization, data-driven testing, and integration with CI/CD pipelines. Examples of popular API testing frameworks include Postman, SoapUI, and Rest-Assured, each catering to different testing needs while enhancing the efficiency and effectiveness of the API testing process.

24. What is an API endpoint?

An API endpoint is essentially a specific URL or URI (Uniform Resource Identifier) that corresponds to a resource or service offered by an API. Each endpoint is designed to handle a particular function or a set of functionalities associated with the API, enabling clients to access, modify, or interact with data. For example, in a weather API, an endpoint might provide current weather data for a specified location. Clients make requests to these endpoints using standard HTTP methods, and the API returns responses, typically formatted in JSON or XML, containing the requested information or the results of an operation. Understanding API endpoints is crucial for effective API integration and usage. 

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

When performing API testing, various error responses can arise, each providing insights into issues that need to be addressed during development and testing. These error types include validation errors, HTTP error status codes, and custom error messages:

Validation Errors: Validation errors occur when the input parameters provided in the API request do not meet the expected criteria or formats. These errors can include missing required fields, incorrect data types, or values outside the acceptable range. For example, if an API expects a numeric value but receives a string, a validation error would be triggered.

HTTP Error Status Codes: These errors are standardized responses defined by the HTTP protocol that inform users or developers about the nature of an issue. Common examples include:

• 400 Bad Request: The server cannot process the request due to client-side errors.
• 401 Unauthorized: Authentication is required but not provided or invalid.
• 404 Not Found: The requested resource does not exist on the server.
• 500 Internal Server Error: An unexpected issue occurred on the server.

Custom Error Messages: Custom error messages are specific to an application or API and provide detailed information tailored to the issue at hand. These error messages are designed to be more user-friendly and informative, helping developers and users better understand and resolve the problems. For instance, a custom message might explain “Invalid product ID – please provide a valid numeric identifier.”

Effectively handling and documenting these error responses is essential for creating reliable and user-friendly APIs. 

26. How do you handle error responses and exceptions during API Testing?

When testing APIs, it is crucial to effectively handle error responses and exceptions to ensure robust functionality and reliability. First, testers should identify the types of errors that can occur, such as client errors (4xx status codes) and server errors (5xx status codes). During testing, it is important to create test cases that deliberately trigger these errors to verify that the API responds correctly.

For example, when an invalid request is made, the API should return an appropriate error response, which includes a status code and a descriptive message in the response body. This helps the client understand what went wrong. Additionally, testers should check that any exceptions encountered are logged appropriately and that sensitive information is not exposed in error responses. Implementing comprehensive error handling in API testing not only helps to diagnose issues but also enhances the user experience by providing clear feedback on failures.

27. How can you effectively test APIs for performance and scalability?

To effectively test APIs for performance and scalability, several key strategies can be employed.

First, load testing is essential to assess how well the API performs under expected user load, simulating multiple requests to identify potential bottlenecks. Tools like JMeter or LoadRunner can help generate traffic and measure response times.

Second, stress testing goes a step further by pushing the API beyond its limits to determine how it behaves under excessive loads and to pinpoint breaking points.

Additionally, using monitoring tools can provide insights into resource usage, helping to track performance metrics such as latency, throughput, and error rates.

Lastly, it is crucial to conduct scalability testing to evaluate the API’s ability to handle increased loads as user demand grows, ensuring that it can effectively scale up without compromising performance.

28. What is Latency in API Testing?

Latency in API testing refers to the time it takes for an API to respond to a request after it has been submitted. It encompasses various delays, including network transmission time, server processing time, and any queuing time that might occur before the API can fulfill the request. Measuring latency is crucial because it directly affects user experience; a high latency can lead to slow application performance and potential user dissatisfaction. Effective API testing should include latency measurements to ensure that the API meets performance requirements and can handle expected load levels efficiently.

29. Difference between API and Web services?

All web services are APIs but not all APIs are web services.

30. What is SOAP?

SOAP, or Simple Object Access Protocol, is a protocol used for exchanging structured information in web services. It relies on XML as its message format and typically operates over HTTP or SMTP. SOAP provides a way for programs running on different operating systems to communicate with each other by sending messages. It is known for its ability to support complex operations and ensure message integrity and security through WS-Security standards.

31. What is REST API?

REST (Representational State Transfer) API is an architectural style that leverages HTTP requests to access and manipulate data. In a RESTful system, resources are identified by URIs, and standard HTTP methods such as GET, POST, PUT, and DELETE are used to perform operations on them. REST APIs are known for their simplicity and scalability, allowing for stateless interactions between clients and servers, which enhances performance and optimizes resource usage. This approach makes REST APIs widely used for building web services that are accessible from different platforms and devices.

32. What is RESTful API?

A RESTful API, or Representational State Transfer API, is a web service that conforms to the architecture principles of REST. It uses HTTP methods such as GET, POST, PUT, and DELETE for communication between the client and server. RESTful APIs are stateless, meaning each request from a client contains all the information necessary for the server to process that request. These APIs typically return data in formats like JSON or XML, making them lightweight and easy to integrate with various applications. The design of RESTful APIs emphasizes scalability, simplicity, and consistency, making them a popular choice for modern web and mobile development.

33. What is the difference between REST API and RESTful API?

The terms “REST API” and “RESTful API” are often used interchangeably, but there is a subtle difference between them.

A REST API refers to an API that adheres to the principles of Representational State Transfer (REST) architecture. It is a specific implementation of the REST paradigm that allows clients to interact with server-side data in a stateless manner and typically uses standard HTTP methods (GET, POST, PUT, DELETE).

A RESTful API, on the other hand, is an adjective used to describe an API that is designed to be in line with REST principles. It emphasizes how closely the API conforms to the RESTful architectural constraints, such as stateless communication, resource-based URIs, and the proper use of HTTP methods.

In essence, all RESTful APIs are REST APIs, but not all REST APIs are necessarily RESTful if they do not strictly adhere to REST principles.

34. What is the difference between REST and API?

To understand the difference between REST and API, it is essential to recognize that REST (Representational State Transfer) is an architectural style or set of principles for designing networked applications, while an API (Application Programming Interface) is a specific interface that allows different software applications to communicate with one another. An API can be designed in various styles, including REST, SOAP, GraphQL, and more.

REST, as a style, defines a set of guidelines that an API can follow, such as stateless communication, resource identification through URLs, and standard HTTP methods like GET, POST, PUT, and DELETE. On the other hand, an API is the actual implementation that enables interactions between systems. Simply put, REST is a methodology, and an API is the mechanism that implements it—or other styles. While many APIs today are RESTful, not all APIs conform to REST principles, and some APIs use entirely different paradigms. This distinction highlights that REST and API are interconnected but not synonymous. 

35. Difference between SOAP and REST?

SOAP:
1. SOAP is a protocol through which two computers communicate by sharing XML document
2. SOAP supports only XML format
3. SOAP does not support caching
4. SOAP is slower than REST
5. SOAP is like a custom desktop application, closely connected to the server
6. SOAP runs on HTTP but envelopes the message

REST:
1. REST is a service architecture and design for network-based software architecture
2. REST supports different data formats
3. REST supports caching
4. REST is faster than SOAP
5. REST client is just like a browser and uses standard methods An application has to fit inside it
6. REST uses the HTTP headers to hold meta information

36. What are the common tests conducted on APIs?

Some of the common tests we perform on APIs are as follows.

• Verify whether the return value is based on the input condition. The response of the APIs should be verified based on the request.
• Verify whether the system is authenticating the outcome when the API is updating any data structure
• Verify whether the API triggers some other event or request another API
• Verify the behavior of the API when there is no return value

37. What are the advantages of API Testing?

• Time effective: API Testing is time effective when compared to GUI Testing. API test automation requires less code so it can provide faster and better test coverage.
• Reduce cost: API Testing helps us to reduce the testing cost. With API Testing we can find minor bugs before the GUI Testing. These minor bugs will become bigger during GUI Testing. So finding those bugs in the API Testing will be cost-effective to the Company.
• Language independent: API testing is language independent, allowing developers to utilize any programming language to write automated tests by using standard data formats like XML or JSON for communication.
• Core functionality testing: API Testing is quite helpful in testing Core Functionality. We can test the APIs without a user interface. In GUI Testing, we need to wait until the application is available to test the core functionalities.
• Reduce risk: API Testing helps us to reduce the risks.

38. What are the disadvantages of API Testing?

• Limited User Interface Testing: API testing does not cover the user interface, which means potential issues related to usability and visual elements may go unnoticed.
• Complexity: Developing and maintaining API tests can be more complex than UI tests, especially if APIs have extensive configurations or require intricate setup.
• Requires Technical Skills: API testing typically necessitates a deeper understanding of APIs and programming, which can be a barrier for non-technical team members.
• Mocking Dependencies: When testing APIs that depend on other services, creating mock services can add an extra layer of complexity and may not always accurately reflect real-world scenarios.
• Lack of Visual Feedback: API testing can be less intuitive than UI testing, as it does not provide the immediate visual feedback of how an application behaves or looks, making it harder to spot front-end issues.

39. What exactly needs to be verified in API Testing?

Basically, on API Testing, we send a request to the API with the known data and we analyze the response.
1. Data accuracy
2. HTTP status codes
3. Response time
4. Error codes in case API return any errors
5. Authorization checks
6. Non-functional testing such as performance testing, security testing

40. Name some tools used for API Testing?

Some of the tools used for API Testing are as follows:

• Postman: Widely used for manual and automated testing, Postman offers a user-friendly interface to create, send, and test API requests.
• SoapUI: Ideal for testing SOAP and REST APIs, SoapUI provides comprehensive testing features including functional testing, load testing, and security testing.
• RestAssured: A Java-based library that simplifies the testing of REST services, RestAssured allows for writing readable and maintainable tests using a fluent API.
• JMeter: Primarily a performance testing tool, JMeter can also be utilized for API testing, enabling the simulation of various load scenarios and testing the API’s performance under stress.
• Swagger: With tools like Swagger UI and Swagger Codegen, developers can not only document APIs but also test and generate client code for different programming languages.
• Karate: A test automation framework that combines API testing, UI testing, and performance testing in a single solution, simplifying the testing process with its DSL (Domain Specific Language).
• Katalon Studio: An all-in-one automation tool that supports API, Web, and Mobile testing, providing features for easy API test creation and execution.

 Some other tools are Assertible, Tricentis Tosca, Apigee, JMeter, API Fortress, Parasoft, HP QTP(UFT), vREST, Airborne, API Science, APIary Inspector, Citrus Framework, HttpMaster Express, Mockbin, Ping API, Pyresttest, Rest Console, RoboHydra Server, SOAP Sonar, Unirest, WebInject

Learn more on API Testing Tools

41. What is API Documentation in API testing?

API documentation is a user manual for a software interface that allows different programs to communicate with each other. It explains how to use the API, detailing its features and functionalities. This documentation typically includes details about API endpoints, request and response formats, authentication and authorization methods, error handling, and other relevant information. It serves as a guide for developers, helping them understand how to connect their applications with the API effectively. Good API documentation is clear, easy to follow, and provides examples to illustrate how the API works.

42. What are the important factors should be taken into account while writing API document?

When creating API documentation, clarity and comprehensiveness are paramount. First, ensure that the language used is clear and concise, avoiding technical jargon that may confuse users. Including comprehensive reference documentation is essential, as it provides context and details that users need to understand the API’s capabilities fully. Additionally, it’s vital to incorporate documentation into the overall development process; this practice helps keep the documentation up-to-date with any changes or improvements made to the API. Quickstart guides should also be provided to help users get up and running quickly, offering practical examples and simplified instructions. Lastly, consider the target audience’s experience level, tailoring the documentation to meet both novice and advanced user needs.

43. List some commonly used API documentation templates?

Some of the API documentation templates are as follows.

• Swagger
• FlatDoc
• RestDoc
• API blueprint
• Slate
• Miredot
• Web service API Specification.

44. Name some of the API examples which are quite popular.

Some of the popular API examples are

• Google Maps API
• YouTube
• Twitter
• Amazon Advertising API

45. Difference between API testing and Unit Testing?

46. What are the main challenges faced in API testing?

Some of the challenges we face while doing API testing are as follows

• Selecting proper parameters and its combinations
• Categorizing the parameters properly
• Proper call sequencing is required as this may lead to inadequate coverage in testing
• Verifying and validating the output
• Due to the absence of GUI, it is quite difficult to provide input values
• Lack of proper documentation

47. What are the types of bugs we face when performing API testing?

Issues observed when performing API testing are

• Failure to handle negative test cases
• Duplicate or missing API functionality
• Incompatible error handling mechanism
• Stress, performance, and security issues
• Reliability issues
• Improper status codes
• Improper error responses
• Multi-threaded issues
• Improper errors
• Unimplemented errors
• Unused flags

48. What is error handling in APIs and how do you address it?

Error handling in APIs refers to the process of anticipating, detecting, and resolving issues or errors that may arise during the interaction between an API and its clients. Effective error handling ensures that users receive clear, informative feedback when something goes wrong, enabling them to troubleshoot and resolve issues efficiently.

To address error handling, APIs should generate meaningful error messages accompanied by appropriate status codes (e.g., 400 for bad requests, 401 for unauthorized access, 500 for server errors). These messages should clearly outline the nature of the error and suggest possible solutions. Additionally, APIs should be designed with resilience, implementing mechanisms such as rate limiting, retries with exponential backoff, and input validation to prevent or mitigate errors proactively. Providing detailed documentation on error codes and responses, coupled with robust logging and monitoring systems, further helps developers diagnose and fix problems while enhancing the overall reliability of the API. 

49. How is UI testing not similar to API testing?

UI (User Interface) testing is to test the graphical interface part of the application. Its main focus is to test the look and feel of an application. On the other hand, API testing enables the communication between two different software systems. Its main focus is in the business layer of the application.

50. Name some most commonly used HTTP methods?

Some of the HTTP methods are

GET: It enables you to retrieve data from a server
POST: It enables you to add data to an existing file or resource in a server
PUT: It lets you replace an existing file or resource in a server
DELETE: It lets you delete data from a server
PATCH: It is used to apply partial modifications to a resource
OPTIONS: It is used to describe the communication options for the target resource
HEAD: It asks for a response identical to that of a GET request, but without the response body

51. Can you use GET request instead of PUT to create a resource?

No, GET request only allows read only rights. It enables you to retrieve data from a server but not create a resource. PUT or POST methods should be used to create a resource.

52. What is a “Resource” in REST?

A “Resource” in REST refers to any entity or object that can be accessed and manipulated within the REST architecture. Each resource is uniquely identified by a URI (Uniform Resource Identifier). Resources can represent data or services and are often presented in various formats such as JSON, XML, or HTML.

53. What is the difference between PUT and POST methods?

PUT and POST methods are sometimes confused in regards to when each should be used. Using POST request, our intent is to create a new object on the server whereas with PUT request, our intent is to replace an object by another object.

POST should be used when the client sends the page to the server and then the server lets the client know where it put it. PUT should be used when the client specifies the location of the page

54. Is it possible to use a GET request instead of a PUT request to create a resource?

No, it is not appropriate to use a GET request to create a resource. According to the principles of RESTful architecture, a GET request is designed to retrieve data from a server without causing any side effects or changes to the resource state. In contrast, a PUT request is specifically intended for creating or updating resources on the server.

55. What is API versioning, and why is it crucial for effective API testing?

API versioning is all about including a version number in the API endpoint or headers. This helps keep things compatible as the API evolves. It’s super important in API testing too—you want to make sure you’re testing the right version and that any updates won’t mess up existing client applications. 

56. What are HTTP verbs?

HTTP verbs, also known as HTTP methods, are a set of request methods used to perform various actions when interacting with resources on a server over the HTTP protocol. They define the type of operation that the client wants to execute on a resource. Common HTTP verbs include:

• GET: Retrieves data from a specified resource; it is used to fetch information without modifying it.
• POST: Sends data to the server to create a new resource.
• PUT: Updates or replaces an existing resource with the data provided.
• DELETE: Removes a specified resource from the server.
• PATCH: Partially updates a resource rather than replacing it entirely.
• HEAD: Similar to GET but only retrieves the headers of a resource, not the body.
• OPTIONS: Describes the communication options available for a specific resource or server.

These verbs enable clients to effectively communicate their intentions to servers, forming the foundation of RESTful APIs and other web interactions.

57. What is an HTTP Request?

An HTTP request is a message sent by a client to a server as part of the Hypertext Transfer Protocol (HTTP). It is the foundation of data exchange on the web, allowing clients (such as web browsers or APIs) to request specific resources or perform actions on a web server.

An HTTP request consists of several components, including the request method (e.g., GET, POST, PUT, DELETE), the URL of the resource being requested, headers (which provide additional context or parameters for the request), and an optional body or payload (used for sending data, typically with methods like POST or PUT).

The server processes the HTTP request and sends back an HTTP response, containing the requested data or the result of an action, along with status codes to indicate success or failure. 

58. What is an HTTP Response?

An HTTP response is the server’s reply to a client’s HTTP request. It contains a status line, headers, and optionally a body, depending on the context of the request.

The status line includes a status code that indicates the outcome of the request, such as `200 OK` for success, `404 Not Found` for a missing resource, or `500 Internal Server Error` for a server-side issue. The headers convey metadata, such as content type or caching instructions, while the body may carry the requested data, such as HTML, JSON, or another format.

HTTP responses are fundamental for communication between clients and servers, as they provide the necessary feedback and data exchange required for web interactions. 

59. What is a URL?

A URL, or Uniform Resource Locator, is the address used to access resources on the internet. It provides a specific path to a file, webpage, or other resources hosted on a web server. A URL typically consists of several components, including the protocol (e.g., HTTP or HTTPS), the domain name (e.g., www.example.com), and sometimes additional elements such as a port number, path, query parameters, or fragments. URLs play a crucial role in navigating and retrieving content on the web, ensuring accurate and efficient communication between users and servers.

60. What is the difference between URI and URL?

61. What are the differences between REST, SOAP, and GraphQL API?

62. What are HTTP Status Codes? Name some of the important Status Codes?

HTTP Status Codes are standardized codes returned by a server in response to a client’s request, indicating the outcome of the request. They are grouped into categories such as informational responses, successful responses, redirection messages, client errors, and server errors.

Here are the primary categories and some common codes:

• 1xx: Informational
  • 100 Continue: The initial part of a request has been received and has not yet been rejected by the server.
  • 101 Switching Protocols: The server is switching protocols as requested by the client.
• 2xx: Success
  • 200 OK: The request has succeeded, and the server has returned the requested data (or acknowledgement for methods like POST).
  • 201 Created: The request has been fulfilled, resulting in the creation of a new resource.
  • 204 No Content: The server successfully processed the request, but is not returning any content.
• 3xx: Redirection
  • 301 Moved Permanently: The requested resource has been assigned a new permanent URI.
  • 302 Found: The resource is temporarily located at a different URI, indicated in the response.
  • 304 Not Modified: The resource has not been modified since the last request, allowing the cached version to be used.
• 4xx: Client Error
  • 400 Bad Request: The server cannot process the request due to a client error (e.g., malformed request syntax).
  • 401 Unauthorized: Authentication is required and has failed or has not yet been provided.
  • 404 Not Found: The server cannot find the requested resource, indicating that it may not exist.
• 5xx: Server Error
  • 500 Internal Server Error: The server encountered an unexpected condition that prevented it from fulfilling the request.
  • 502 Bad Gateway: The server, while acting as a gateway or proxy, received an invalid response from the upstream server.
  • 503 Service Unavailable: The server is currently unable to handle the request due to temporary overload or maintenance of the server.

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

The request body in API testing serves to send data to the server, allowing for the execution of operations such as creating or updating resources. Conversely, the response body contains the data returned by the server, which provides insights into the outcome of the request and includes any relevant information or error messages related to the operation performed.

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

The request headers in API testing provide essential metadata that informs the server about the nature of the request, including content type and authentication credentials. In contrast, the response headers convey crucial information about the server’s response, such as the status code and any caching policies. Together, these headers facilitate effective communication between the client and server, ensuring that the API behaves as expected.

65. What is the procedure to perform API testing?

1. Understand the API Requirements: Begin by thoroughly reviewing the API documentation to understand its functionalities, endpoints, inputs, and outputs. Identify the scope and purpose of the API to ensure the testing aligns with the intended use cases.
2. Set Up the Testing Environment: Prepare the testing environment, ensuring all dependencies, such as servers, databases, or third-party services, are appropriately configured. Use tools like Postman, Swagger, or other dedicated API testing frameworks to aid in the process.
3. Define Test Scenarios: Create a list of test scenarios covering all possible use cases, including functional, performance, security, and edge cases. This should include both valid and invalid inputs to test error handling and response robustness.
4. Execute the Tests: Perform the tests by sending requests to the API endpoints and analyzing the responses. Validate the API’s behavior against expected results, ensuring the correct status codes, data formats, and response times.
5. Analyze Results: Verify that the API handles all requests as expected. Check for issues such as incorrect data, latency, and security vulnerabilities. Any discrepancies should be reported for further action.
6. Regression and Continuous Testing: Perform regression testing after every update or bug fix to confirm that the changes have not negatively affected existing functionality. Incorporate continuous testing into the CI/CD pipeline to ensure consistent quality over time.
7. Generate Reports: Document the test results and findings clearly for stakeholders. Highlight any discovered defects, performance bottlenecks, or areas requiring improvement.

By systematically following this procedure, teams can ensure that APIs are reliable, secure, and perform well under varying conditions.

66. What is API Mocking and Its Purpose in API Testing?

API mocking refers to the practice of creating a simulated version of an API that mimics the behavior of a real API. This technique is commonly employed in API testing to enable developers and testers to evaluate the functionality of applications without relying on the actual API. By using mock APIs, teams can conduct tests in a controlled environment, ensuring that the application performs as expected, even in scenarios where the real API may be unavailable or unpredictable. This approach not only accelerates the development process but also enhances the reliability of testing outcomes.

67. What are the advantages of using API mocking in API Testing?

• Early Testing: Allows testing to begin even before the actual API is available.
• Independent Development: Developers and testers can work separately, reducing dependencies on backend services.
• Cost-Effective: Saves time and resources by eliminating the need for a fully developed API during testing.
• Improved Reliability: Testing can be conducted without relying on the availability of external services, leading to more consistent results.
• Faster Feedback: Quickly identifies issues, enabling faster iterations and improvements in the development cycle.
• Simulated Error Handling: Testers can easily simulate different responses (including errors) from the API, allowing for robust error handling tests.
• Documentation and Training Aid: Serves as a useful resource for team members to understand API functionality and for onboarding new developers.

68. What is the difference between authentication and authorization?

Authentication and authorization are two fundamental concepts in security. Authentication is the process of verifying the identity of a user or system, ensuring that the person or entity is who they claim to be. In contrast, authorization determines what an authenticated user is allowed to do, defining their access levels and permissions within the system. 

69. How do you perform load testing on APIs?

Load testing on APIs involves simulating a large number of concurrent users or requests to evaluate how the API performs under stress. This is typically accomplished using load testing tools that can generate and send a high volume of requests to the API, allowing testers to measure response times, error rates, and overall stability. The results help identify bottlenecks, ensuring that the API can handle anticipated traffic demands efficiently.

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

API security testing is the process of evaluating an API to identify vulnerabilities and ensure that data is protected from unauthorized access or manipulation. It is crucial because APIs often serve as gateways to sensitive data and functionalities, making them prime targets for cyberattacks. Ensuring robust security measures in API design and testing helps maintain user trust and safeguard critical systems.

71. What are some common security vulnerabilities in APIs?

APIs are susceptible to several common security vulnerabilities, which can lead to significant risks if not properly addressed.

One major threat is injection attacks, where an attacker can insert malicious code into an API request, potentially leading to data breaches or unauthorized command execution.

Additionally, vulnerabilities related to authentication and authorisation can arise when APIs do not implement proper access controls, allowing attackers to gain access to sensitive data or functionalities without proper credentials.

Another one, cross-site scripting (XSS) attacks can occur when APIs do not properly sanitize user inputs, enabling attackers to execute scripts in the context of users’ browsers, which can compromise user sessions or steal sensitive information.

Addressing these vulnerabilities is essential to ensure the security and integrity of API interactions.

72. What is Cross-Site Scripting (XSS), and How Can It Be Prevented in API Testing?

Cross-Site Scripting (XSS) is a vulnerability that allows attackers to inject malicious scripts into web applications, which are then executed by unsuspecting users’ browsers. This can lead to various issues, such as session hijacking, data theft, and defacing of web pages. In the context of APIs, XSS attacks can occur when user input is not properly sanitized, allowing harmful scripts to be processed and returned in API responses.

To prevent XSS in API testing, it is crucial to implement several key practices:

1. Input Sanitization: All user inputs should be thoroughly validated and sanitized, stripping away any potentially harmful scripts or elements before processing them in the API.
2. Output Encoding: Ensure that any data returned to the client is properly encoded, so that any potentially executable code is treated as plain text rather than as a script.
3. Content Security Policy (CSP): Implement CSP headers to limit the sources from which scripts can be executed, thereby reducing the risk of XSS attacks.
4. Regular Security Testing: Conduct regular security assessments and utilize automated testing tools to identify potential XSS vulnerabilities within the API.

By following these preventive measures, developers can significantly mitigate the risks associated with XSS in API interactions.

73. What is Cross-Site Request Forgery (CSRF), and How Can It Be Prevented in API Testing?

Cross-Site Request Forgery (CSRF) is a type of attack that tricks a user’s browser into making unwanted requests to a different site where the user is authenticated. This can lead to unauthorized actions being performed on behalf of the user, such as changing account settings or submitting data without their consent. In the context of APIs, CSRF attacks are particularly concerning because they can exploit authenticated sessions to execute unauthorized commands.

To prevent CSRF in API testing, developers should adopt several important strategies:

1. CSRF Tokens: Implement anti-CSRF tokens that are unique per session and are required for every state-changing request. This ensures that the request is intentional and originates from a valid user action.
2. SameSite Cookie Attribute: Use the SameSite attribute for cookies to restrict how cookies are sent with cross-site requests, providing an additional layer of security against CSRF attacks.
3. Check HTTP Referer Header: Validate the HTTP Referer header to ensure that requests are coming from the expected origin, rejecting any that originate from untrusted sites.
4. User Confirmation for Sensitive Actions: Require additional user confirmations for sensitive actions, such as submitting a form or changing account settings, to safeguard against unintended submissions.

By implementing these protective measures, developers can significantly reduce the risk of CSRF attacks in their API systems.

74. What is JSON, and why is it commonly used in API testing?

JSON, or JavaScript Object Notation, is a lightweight data-interchange format that is easy for humans to read and write, and simple for machines to parse and generate. It is widely used in API testing due to its simplicity, flexibility, and compatibility with most programming languages. APIs often utilize JSON for transmitting structured data between a client and a server efficiently.

75. What is XML, and when is it used in API testing?

XML, or eXtensible Markup Language, is a markup language designed for storing and transporting data in a structured format. It is used in API testing when precise data formatting and validation are required, as its tag-based structure enables clear representation of hierarchical data. XML is particularly useful for complex systems that require extensive metadata or strict compliance with data schemas.

76. What is API performance testing, and How do you measure the performance of APIs in your tests?

API performance testing is the process of evaluating the speed, scalability, and stability of an API under various loads and conditions. It ensures that the API can handle a specific number of calls without degrading user experience or causing failures. To measure the performance of APIs during tests, developers often use metrics such as response time, throughput, and error rates, along with tools like JMeter or Postman to simulate different levels of traffic and analyze the results.

77. What parameters are used in API performance testing?

Several key parameters are used to evaluate API performance during testing:

1. Response Time – This measures the time taken by the API to process a request and provide a response. Faster response times indicate better performance.
2. Throughput – This metric evaluates the number of API requests handled within a specific time frame, reflecting the system’s ability to manage high traffic.
3. Error Rate – The percentage of API requests that result in failure or errors is tracked to assess reliability.
4. Latency – The time delay experienced from the moment a client sends a request to the server until the response begins, which impacts user experience.
5. Scalability – This parameter evaluates the API’s ability to maintain performance levels under increasing load or simultaneous user requests.
6. Resource Utilization – Monitoring CPU, memory, and network usage gives insight into the efficiency of the API under varying loads.

These parameters together ensure comprehensive assessment, helping pinpoint issues and optimize the API for a seamless user experience.

78. What is API Virtualization and What are the Benefits of Using API Virtualization in API Testing?

API virtualization is the technique of simulating the behavior of APIs that are not yet developed or are unavailable for testing purposes. By creating a virtual model of an API, developers and testers can conduct testing on applications that rely on those APIs without having to wait for the actual service to be ready. This approach allows for more efficient testing cycles and helps teams to identify issues earlier in the development process.

The benefits of using API virtualization in API testing include:

1. Accelerated Testing: Testers can work in parallel with development teams without waiting for the actual APIs, speeding up the overall development process.
2. Cost Efficiency: Virtualized APIs reduce the need for costly infrastructure and external services that may be required for testing, leading to decreased operational costs.
3. Isolation of Systems: Virtualization allows teams to test API interactions in a controlled environment without affecting the production systems or relying on external systems that may be unstable.
4. Improved Test Coverage: With the ability to simulate various scenarios, including edge cases, teams can ensure that their applications are robust and can handle unexpected inputs gracefully.
5. Enhanced Collaboration: Teams can work more effectively together by using shared virtual APIs, leading to better communication and workflows among development, testing, and operations teams.

By leveraging API virtualization, teams can create a more agile and responsive testing environment, ultimately leading to higher-quality software products. 

79. What is API monitoring?

API monitoring is the process of tracking and evaluating the performance, functionality, and availability of an API to ensure it is operating as expected. It helps in detecting issues, measuring response times, and verifying uptime, which is essential for maintaining a seamless user experience and meeting reliability standards.

80. Why API monitoring important?

API monitoring is important because it ensures that APIs function reliably and efficiently, providing consistent user experiences. It helps identify performance issues, detect downtime, and prevent potential disruptions in real-time. By monitoring APIs, businesses can maintain trust, optimize performance, and meet service level agreements (SLAs) effectively.

81. Is it possible to hack API while testing?

Yes, it is possible to hack an API while testing. During testing, vulnerabilities such as weak authentication, improper data validation, or insufficient encryption may be exploited by attackers. API penetration testing can help identify and mitigate these security flaws to ensure robust protection against potential breaches.

82. What do you understand by Input injection? 

Input injection refers to a technique where untrusted inputs are deliberately provided to an application to test its behavior and identify vulnerabilities. This can involve injecting data into APIs, forms, or other input fields to assess how the system processes and validates the inputs. It is commonly used in security testing to detect issues like SQL injection, cross-site scripting (XSS), or command injection. Proper input validation and sanitization are crucial to mitigate risks associated with input injection.

83. What is input validation and why it is important?

Input validation is the process of ensuring that the data provided by users or external systems meets the expected format, type, and range before it is processed by an application. It is crucial because it helps prevent security vulnerabilities like injection attacks, ensures data integrity, and improves the reliability and functionality of the system. Validating inputs reduces the risk of malicious exploitation and ensures smooth operation.

84. What is API contract testing and why it is important?

API contract testing is a type of testing that validates the defined contract between the API provider and its consumers. It ensures that the API meets the agreed-upon specifications, including inputs, outputs, and behavior. This is important to maintain consistency, prevent integration issues, and build trust between different systems relying on the API.

85. How do you determine which API test cases to prioritize for regression testing?

When prioritizing API test cases for regression testing, focus on high-risk areas such as critical functionalities, frequently used endpoints, and areas affected by recent code changes. Additionally, prioritize test cases that cover integration points and have a history of defects, as these are key to ensuring system stability. 

86. What is the purpose of query parameters in API testing?

Query parameters in API testing are used to filter or specify the data being requested from an API. They allow testers to send additional information to the server, such as search criteria, pagination details, or sorting preferences, ensuring the API responds with relevant and targeted results for the test cases.

87. What is the difference between the path parameter and query parameter?

Path parameters are part of the URL and are used to specify a specific resource or entity, such as `/users/{id}`, where `{id}` identifies a particular user. On the other hand, query parameters are appended to the URL after a `?` and are used to filter or sort data, such as `/users?page=2&sort=asc`. While path parameters are essential for defining the endpoint, query parameters provide additional context or options for the request. 

88. What is the way to represent the resource in REST?

In REST, resources are typically represented using standard formats such as JSON, XML, or YAML. JSON is the most commonly used format due to its simplicity and ease of use, allowing data to be exchanged efficiently between clients and servers. Resource representations provide all necessary information, including data and links, to interact with the resource.

89. What protocol is used by the RESTFUL Web Services?

RESTful web services typically use the HTTP protocol for communication. HTTP methods like GET, POST, PUT, and DELETE are employed to perform operations on resources. The simplicity and ubiquity of HTTP make it an ideal choice for RESTful architecture.

90. What are the characteristics of REST?

REST has several key characteristics, including statelessness, meaning each request from a client must contain all the information the server needs to fulfill it. It uses a uniform interface for resource interaction, enabling simplicity and consistency. REST is also cacheable, which improves performance by allowing responses to be stored and reused. Additionally, it is built on a client-server architecture, ensuring clear separation of concerns.

91. What is messaging in RESTFUL Web Services?

Messaging in RESTful web services refers to the communication process between clients and servers through HTTP requests and responses. These messages consist of a method (e.g., GET, POST), a URI, headers, and an optional body containing data. The standardized format ensures seamless data exchange across different systems. 

92. Explain payment APIs?

Payment APIs are tools provided by payment gateways or processors that allow businesses to integrate secure payment processing functionality directly into their applications or websites. These APIs enable seamless communication between the business, the customer, and the payment processor to complete transactions efficiently. They support a variety of payment methods, such as credit cards, bank transfers, and digital wallets, ensuring flexibility for users. Additionally, payment APIs are designed with robust security measures, including encryption and tokenization, to safeguard sensitive payment data. They often include features like fraud detection, recurring billing, and multi-currency support, making them a comprehensive solution for modern e-commerce and subscription-based businesses.

93. How do you perform load testing on APIs?

Load testing on APIs can be performed by simulating a high number of requests over a period of time using tools like JMeter, Postman, or Locust. Define realistic scenarios that mimic expected user behavior, set performance benchmarks, and monitor metrics such as response time, throughput, and error rates. Analyze the results to identify bottlenecks and areas for optimization.

94. What are some techniques for handling API timeouts and retries in tests?

To handle API timeouts and retries in tests, consider setting reasonable timeout values based on expected response times and network conditions. Implement retry mechanisms with exponential backoff to avoid overloading the server. Additionally, ensure proper error logging and response handling to identify and address issues effectively.

95. How do you handle versioning and backward compatibility in your API tests?

To handle versioning and backward compatibility in API tests, it is essential to maintain tests for all supported API versions and verify that changes do not break existing functionality. Use version-specific test suites, validate deprecated features still function as expected, and ensure responses remain consistent across versions for critical use cases.

96. How do you handle API changes and updates in your tests?

To handle API changes and updates in tests, it is crucial to implement automated testing workflows that detect and flag changes. Update test cases promptly to reflect new API behaviors while maintaining coverage for existing features. Use mock servers or contract testing tools to validate API updates without disrupting dependent systems or workflows.

97. What is the purpose of authentication in API testing? 

Authentication in API testing ensures that only authorized users or systems can access the API, safeguarding sensitive data and functionality. It verifies the identity of the requester and prevents unauthorized access, ensuring secure interactions between clients and the API. This is a critical step in maintaining the integrity and confidentiality of the system.

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

To handle API authentication in tests, use secure methods like API keys, OAuth tokens, or session-based authentication. Store sensitive credentials securely, such as in environment variables, to prevent exposure. Simulate authentication flows where possible and validate tokens or credentials to ensure proper access control during the testing process.

99. When should you use an API automation testing framework?

You should use an API automation testing framework when your application relies heavily on APIs for communication between its components or with external services.

If your project involves repetitive testing tasks, complex data flows, or demands consistent regression testing, an automation framework can significantly reduce manual effort and increase test coverage.

It is especially beneficial for large-scale projects with frequent updates, as automated tests can be quickly executed to detect issues early.

Additionally, using an automation testing framework is ideal when you want to ensure the reliability of APIs under different conditions, improve the accuracy of test results, and streamline integration with CI/CD pipelines for faster delivery. 

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Conclusion

I would like to conclude this post “API Testing Interview Questions” here. Final words, Bookmark this post “API Interview Questions And Answers” for future reference.

Here I have hand-picked a few posts which will help you to learn more interview related stuff:

• Postman Tutorial (Beginner to Advanced Level)
• SOAP Interview Questions
• Manual Testing Interview Questions
• Agile Interview Questions
• Selenium Interview Questions
• Java Interview Questions
• TestNG Interview Questions
• SQL Interview Questions
• General Interview Questions

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