30+ API Testing Interview Questions and Answers with Examples

Are you looking for API testing interview questions to prepare for a software engineering or tester position? In this article, we will explore some common API testing interview questions and provide insightful answers to help examples so that you can prepare for your API testing interview. This article is a must-read to help you ace your following interview.

API Testing Interview Questions and Answers

What is an API?

An API (Application Programming Interface) is a set of protocols, tools, and standards used for building software applications. It defines how software components should interact with each other, providing a way for different applications to exchange data and services.

Example: An example of an API is the Google Maps API, which allows developers to integrate it into their applications.

What are the benefits of API testing?

API testing helps to ensure that the API functions as expected, it detects errors and issues early in the development cycle, improves the overall quality of the software, and reduces the cost of testing.

Example: API testing can help ensure that a payment gateway API returns the expected response when processing a payment request, ensuring that payments are processed accurately and efficiently.

What is an API endpoint?

An API endpoint is a URL that represents an API resource. It defines the location where clients can access the API’s functionality.

Example: A Twitter API endpoint could be “https://api.twitter.com/1.1/statuses/home_timeline.json”, which returns the most recent tweets from a user’s timeline.

ServiceNow API’s Integration and Examples

What are the different types of API?

The different types of API include SOAP, REST, XML-RPC, JSON-RPC, and GraphQL.

What is API testing and what are the types of API testing?

API testing is a type of software testing that involves testing the functionality, performance, and security of an API. The types of API testing include functional testing, security testing, load testing, and integration testing.

Example: A functional test for an API can verify that a user is able to create a new account and receive a confirmation email.

What is API automation testing?

API automation testing is the use of software tools to automate the testing of an API. This allows for faster and more reliable testing than manual testing.

Example: An API automation test could be used to verify that a new user is able to successfully log in to an application.

What are the advantages of API automation testing?

The advantages of API automation testing include faster testing, greater test coverage, increased reliability, and reduced costs.

Example: By automating API testing, a company can ensure that all critical API functions are tested thoroughly and consistently, reducing the risk of bugs and errors.

What are the common tools used for API testing?

The common tools used for API testing include Postman, SoapUI, JMeter, REST Assured, and Karate. Postman is a popular tool for API testing that allows developers to send and receive requests and view responses in a user-friendly interface.

What is REST API?

A REST API (Representational State Transfer API) is a type of API that uses HTTP requests to access and manipulate data. RESTful APIs are designed to be scalable, flexible, and easy to use.

Example: The WordPress REST API allows developers to interact with WordPress sites programmatically, allowing them to create, update, and delete content and settings.

What are the different HTTP methods used in REST API?

The different HTTP methods used in REST API include GET, POST, PUT, PATCH, and DELETE.

Example: A GET request to a REST API could be used to retrieve a specific resource, a POST request could be used to create a new resource, a PUT request could be used to update an existing resource, a PATCH request could be used to update specific fields within an existing resource, and a DELETE request could be used to delete a resource.

What is a RESTful API endpoint?

A RESTful API endpoint is a URL that represents a specific resource or collection of resources within a RESTful API. Each endpoint typically corresponds to a specific HTTP method and performs a specific action on the resource.

Example: A RESTful API endpoint for retrieving a specific user’s information could be “https://api.example.com/users/{id}”, where {id} is the unique identifier for the user.

What is API versioning?

API versioning is the process of managing changes to an API over time, typically by creating multiple versions of the API to support different clients or use cases. This helps to ensure that existing clients are not affected by changes to the API and allows new features to be added without breaking existing functionality.

Example: A company can create a new version of their API to support a new set of clients that require different functionality or data formats, while maintaining the existing API version for existing clients.

What is API documentation?

API documentation is a set of instructions and guidelines that describe how to use and interact with an API. This typically includes information about API endpoints, HTTP methods, request and response formats, error handling, and authentication.

What are the characteristics of a good API?

A good API should be easy to use, reliable, secure, and scalable. It should provide clear and concise documentation, follow established standards and best practices, and be well-maintained and supported.

What is API mocking?

API mocking is the process of simulating an API’s behavior for testing or development purposes. This allows developers to test their applications without relying on a live API, which can be time-consuming or difficult to set up.

Example: Developer can use a mock API to test their application’s ability to handle different types of responses or error conditions without relying on a live API.

What are the different types of mock testing?

There are several types of mock testing, including:

  1. Manual mock testing: Mocking endpoints manually by creating a test server or using a tool such as Postman.
  2. Dynamic mock testing: Generating mock responses dynamically using tools such as WireMock.
  3. Static mock testing: Using predefined mock responses stored in files or databases.
  4. Record and playback mock testing: Recording API requests and responses and using them to create mock responses for testing.

What is API gateway?

An API gateway is a server that acts as a single entry point for multiple APIs. It can handle tasks such as authentication, routing, load balancing, and rate limiting, and can provide a unified interface for clients to access multiple APIs.

Example: Amazon API Gateway is a cloud-based service that allows developers to create, publish, and manage APIs, providing features such as caching, security, and monitoring.

What is API security?

API security refers to the measures taken to protect an API from unauthorized access, manipulation, or exploitation. This can include authentication, encryption, rate limiting, and access control.

Example: OAuth is a popular protocol for API authentication that allows users to grant third-party applications access to their data without sharing their login credentials.

What is API throttling?

API throttling is the process of limiting the rate at which requests can be made to an API. This helps to prevent overload or abuse of the API and ensures that it remains responsive and available.

Example: An API can limit the number of requests that can be made per minute or per hour to prevent excessive traffic from causing performance issues.

What is API caching?

API caching is the process of storing API responses in a cache to reduce the number of requests that need to be made to the API. This can improve performance and reduce server load.

What is API fuzz testing?

API fuzz testing is the process of testing an API by sending invalid or unexpected input to identify potential security vulnerabilities or other issues. This can involve sending malformed requests or injecting unexpected data into requests.

Example: A security researcher can use a fuzz testing tool such as Burp Suite to test an API for vulnerabilities by sending a variety of unexpected input.

What is API virtualization?

API virtualization simulates an API’s behavior for testing or development purposes using virtualization technology. This allows developers to test their applications without relying on a live API, which can be time-consuming or difficult to set up.

What is API key authentication?

API key authentication is a simple form of API authentication in which clients provide an API key with their requests to identify themselves to the API. The API can then use the key to verify that the client is authorized to access the API.

Example: A company can provide each of its clients with a unique API key that they can use to authenticate their requests to the company’s API.

What are the different types of API authentication?

There are several types of API authentication, including:

  • API keys: A unique key provided to a client that identifies them when making API requests.
  • OAuth: A token-based authentication protocol that allows clients to access protected resources on behalf of a user.
  • JWT: A JSON Web Token that contains a verifiable claim that can be used to authenticate a client.
  • Basic authentication: A method of authentication that sends a username and password with each API request.

Example: An API can use OAuth 2.0 for authentication, requiring clients to obtain an access token by making a request to the API’s authorization server. The access token can then be used to make requests to the API on behalf of the user.

What is GraphQL?

GraphQL is a query language and runtime for APIs that allows clients to request specific data from an API by defining the structure of the requested data in a single query. It provides a flexible and efficient way for clients to retrieve exactly the data they need from an API, reducing overfetching and underfetching.

Example: A client can use GraphQL to query an e-commerce API for product information, specifying only the fields they need, such as the product name, price, and availability.

What is CORS?

CORS, or Cross-Origin Resource Sharing, is a security feature of web browsers that restricts scripts from making requests across different domains. It involves specifying which domains are allowed to access a resource, using the Access-Control-Allow-Origin header.

What is pagination in API design?

Pagination is the process of dividing a large set of data into smaller, more manageable chunks that can be retrieved by clients in multiple requests. It involves using query parameters to specify the size of each chunk and the offset of the current chunk.

Example: An API can use pagination to return a list of products, dividing the list into pages of 50 products each and allowing clients to retrieve each page using query parameters such as page=1 and per_page=50.

What is error handling in API design?

Error handling is the process of handling errors and exceptions when clients request an API. It involves using HTTP status codes and error messages to inform clients of the status of their requests.

Example: An API return a 404 Not Found status code and an error message when a client requests a resource that does not exist.

What are the common security issues in API testing?

Common security issues in API testing include:

  • Injection attacks, such as SQL injection and XSS.
  • Authentication and authorization issues, such as weak passwords and improper access control.
  • Information leakage, such as exposing sensitive data in error messages.
  • Denial of service attacks, such as sending a large number of requests to overload the API.

Example: An API can be vulnerable to a SQL injection attack if it does not properly validate input data from clients. An attacker could send a malicious SQL query as part of an API request, potentially gaining access to sensitive data in the API’s database.

What is OWASP and how is it related to API testing?

OWASP (Open Web Application Security Project) is a non-profit organization that focuses on improving the security of software. OWASP provides resources and tools for testing the security of web applications and APIs, including a list of the top 10 security risks for web applications.

Example: An API tester can use OWASP’s list of the top 10 security risks to identify potential vulnerabilities in an API they are testing. They can then use OWASP’s testing guide to conduct more thorough security testing on the API, including testing for injection attacks, authentication issues, and information leakage.

What are the best practices for API testing?

Some best practices for API testing include:

  1. Testing both positive and negative scenarios ensures that the API handles valid and invalid requests.
  2. Automating testing wherever possible increases efficiency and reduces the risk of human error.
  3. Testing for scalability by conducting load testing and monitoring the API’s performance under heavy load.
  4. Testing for security vulnerabilities, such as injection attacks and authentication issues.
  5. Collaborating with developers and other stakeholders to ensure that the API meets all requirements and is ready for production.

What are the common challenges faced in API testing?

Common challenges faced in API testing include:

  1. Limited documentation or outdated documentation.
  2. Lack of understanding of the API’s functionality or requirements.
  3. Complexity of the API, including multiple endpoints, parameters, and authentication requirements.
  4. Integration with other systems, such as databases or external APIs.
  5. Ensuring that the API is compatible with a wide range of clients, including mobile devices and web applications.

How do you approach testing of an API that has no documentation?

When testing an API that has no documentation, an API tester use the following approach:

  • Explore the API’s endpoints and parameters by sending sample requests and observing the responses.
  • Identify any patterns or rules in the API’s behavior, such as expected input formats or error codes.
  • Collaborate with developers or other stakeholders to better understand the API’s functionality and requirements.
  • Develop a comprehensive testing strategy that covers all aspects of the API’s functionality and potential use cases.
  • Use automated testing tools wherever possible to increase efficiency and reduce the risk of human error.

Tips for API Testing Interview

  1. Understand the basics of APIs: Before diving into the technical details, make sure you have a clear understanding of what an API is, how it works, and what its purpose is. Be familiar with different types of APIs, such as REST, SOAP, and GraphQL.
  2. Know the HTTP protocol: APIs use the HTTP protocol to send and receive data. Be familiar with the different HTTP methods (GET, POST, PUT, DELETE) and their purposes.
  3. Learn about request and response formats: APIs use different formats to send and receive data, such as JSON, XML, and YAML. Know how to read and write data in these formats.
  4. Familiarize yourself with API testing tools: There are various tools available for testing APIs, such as Postman, SOAPUI, and RestAssured. Know how to use these tools and understand their features.
  5. Know the common API testing techniques: There are different techniques used for testing APIs, such as functional testing, performance testing, security testing, and load testing. Be familiar with these techniques and their purposes.
  6. Practice writing test cases: Try writing test cases for different scenarios, such as positive and negative cases, boundary cases, and edge cases. This will help you think through different scenarios and be better prepared for the interview.
  7. Brush up on your programming skills: APIs are often tested using programming languages such as Python, Java, or Ruby. Make sure your programming skills are up to par and be prepared to write some code during the interview.
  8. Be ready to discuss testing methodologies and best practices: Be prepared to talk about different testing methodologies, such as Agile or Waterfall, and best practices for API testing, such as API versioning and documentation.
  9. Prepare for behavioral questions: In addition to technical questions, you may also be asked behavioral questions to assess your communication skills, problem-solving abilities, and teamwork skills. Practice answering common behavioral questions beforehand.
  10. Stay up-to-date with industry trends and news: The world of APIs and API testing is constantly evolving, so stay up-to-date with the latest industry news and trends. Read blogs, attend webinars, and follow industry experts on social media to stay informed.

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