11 API Testing Interview Questions (and Answers) to Help You Prepare For Your Next Interview

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API testing is an essential part of software development that involves testing an API’s functionality, reliability, performance, and security. And since so many web applications that are in use today depend on at least one API, API testers are in high demand.

If you have an API testing interview coming up, one of the best ways you can prepare is to review questions that you might be asked during your interview. You can practice answering these questions on your own or consider doing a mock interview with a friend. If you can set up a mock interview, try to recreate a similar environment to the one you’ll be in during your real interview. For example, if you’ll be interviewing over Zoom, do the mock interview over Zoom so that your practice is as close to the real thing as possible.

To help you prepare for API testing interview questions, here are some of the most common questions you’re likely to face and tips on how to answer them.

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1. What does API mean?

During your technical interview, the interviewer may start things off with questions that seem easy. An ice-breaker question can be an opportunity for you to shake off some nerves while also answering the question with details that may catch the interviewer’s attention. This might be a recent milestone you hit or a fun project you’re working on.

For this question, you should answer by first defining the acronym API, which is Application Programming Interface, and then you can outline what this means. Specifically, you should mention that an API is a set of functions and procedures that allows a program to access features or data from another piece of software or service. As a result, it enables multiple applications to interact with each other.

2. What is API testing?

This is another ice-breaker question, and it gives you a chance to show that you know some of the “why” behind API testing. You should discuss how an API test checks to see if the function being called is behaving as expected. During an API test, a function is tested against a wide range of inputs to see if it returns the expected value from each test. Edge cases and corner cases are included in the test to ensure that the function can handle extreme cases. API testing is generally done at the end of development to check and see if the software is performing as expected.

3. What are some of the most common protocols used during API testing?

This is a straightforward question, and getting it right shows you understand the API testing environment on a higher level. In your answer, you should mention REST, SOAP, HTTP, UDDI, and JMS.

4. What are the most common kinds of API testing?

While there are many different ways of using API testing, the typical methods are:

  • Function testing, a test used to test the API’s functionality against functional requirements.
  • Load testing, a test to emulate expected load, such as traffic, in a steady stream that can determine issues that may arise from running an API for a prolonged period of time.
  • Unit testing, which verifies whether individual parts of the source code behave and work as expected.
  • User interface testing, which tests the aspects of an API that a user will interact with.
  • Security testing, a series of tests that test the security of the API. Entry points, flow of data, and shadow APIs are all areas that should be tested during security testing.
  • Penetration testing (or pen test or ethical hacking), a type of security testing that simulates a cyber attack against your API to uncover vulnerabilities.
  • Fuzz testing, a test that sends random data to all the endpoints of the APIs. During fuzz testing, servers shouldn’t crash or display any odd behavior.
  • Runtime and error detection is used during all of these tests and enables APIs to report any issues that occur while it’s on.

When answering this question, you could focus on the tests that are used by the company to show your specific knowledge in that area.

5. Describe a typical API testing environment

This is your chance to show you know the difference between API and other kinds of software testing. When testing an API, you first have to configure the database and server to ensure the API can be installed. After installing it, you can then start verifying its correct function. As the test continues, you evaluate the environment using API calls and analyze the results to see if it’s working as it should.

Here’s an example of a testing environment that you can give when answering this question: You can use Postman to test APIs. Postman allows you to make HTTP requests to an API and view the responses you get formatted in JSON.

6. Which architectural styles are used to create web APIs?

You may be asked this question because the type of architectural style used to create an API can inform the API testing protocol. The more common architectural styles are:

  • REST API Style
  • GraphQL API Style
  • RPC API Style
  • SOAP API Style
  • gRPC API Style
  • Falcor API Style

7. What does SOAP mean?

This is almost guaranteed to come up during your interview. SOAP is an acronym for Simple Object Access Protocol. This is a messaging protocol based on XML, and it makes it easier for computers to communicate with each other.

8. What is a REST API?

This is another question that’s likely to be asked. In fact, it’s hard to imagine an API testing interview without it.

A REST API (also known as RESTful API) is an API that meets the constraints of REST architectural style, which is a set of architectural constraints for providing standards between computer systems on the web. These constraints make it easier for systems to communicate with each other. REST is an acronym for REpresentational State Transfer.

9. What are some differences between REST and SOAP?

Because SOAP and REST can accomplish the same objectives, there’s a high probability that this question will pop up. Here’s a basic breakdown of the differences between REST and SOAP:

  • SOAP is a protocol computers use to share XML documents, while REST is a design and service architecture used to set up software environments on a network.
  • SOAP strictly supports XML, while REST supports several data formats.
  • SOAP doesn’t support caching, while REST does.
  • SOAP is slower.
  • SOAP is like a normal computer app, while a REST client is more like a browser that allows apps to run inside it.
  • SOAP envelops a message while running on HTTP, while REST makes use of HTTP headers to hold its metadata.

10. What are some of the most common API tests performed?

This question has several good answers, and your answer will likely depend on the tests you have the most experience with.

For example, you can discuss how an API is tested to see how it handles an HTTP (GET, POST, or other) request. With this test, you’re evaluating if the variables sent with the HTTP request were processed properly. This test also looks to see if there is a request error (40X error), and if so, what is it and why is it happening? Then, if the request is successful, did the API respond with the expected values properly formatted? An API test will also see if it’s communicating with the proper endpoint.

11. What are some of the benefits of API testing?

This is another chance to dig into the “why” of API testing. In your answer, you can highlight how API testing can save time because it may require less code than graphical user interface (GUI) testing. You can test APIs without a user interface, meaning you don’t have to wait for an application to be available. Another benefit is that API testing isn’t limited to a specific coding language. And API testing is a good way to reduce risk cost-effectively, especially if you’re searching for minor bugs.

Practice makes perfect

If you need a refresher or you’re looking for more exposure to APIs, we offer several skill paths and courses that focus on APIs and the architectures that use them.

You can brush up on your foundational knowledge of the API development lifecycle in our API Development with Swagger and OpenAPI course, or you can learn how to build a web API with the Spring framework in the Create REST APIs with Spring and Java skill path. You could also take your skills to the next level with our ​​Learn Testing for Web Development course, where you’ll dive into how to test applications at the model and server levels, including tests for dynamic HTML content and other API responses.

If you’re looking for more advice and support for your upcoming interview, read over our complete guide to the technical interview and our advice on answering behavioral interview questions. We also have tips for the whiteboard interview that you can review before your interview.

If you’re looking to learn a new skill or expand on your existing knowledge, take a look through our full course catalog.

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