API Testing Interview Questions and Answers Part 1

Hey everyone!

Welcome back to The Testing Academy. My name is Pramod, and in today’s Blog, we’re diving into some crucial API testing interview questions and answers. Let’s get started!

Before we begin, I want to let you know that this Blog is part of our Project Automation Tester series. This series includes multiple parts where we’ll discuss various interview questions related to API testing, Selenium, test automation, and manual testing.

If you’re excited about this series, let me know in the comments! Your feedback motivates me to create more valuable content for you.

API Testing Interview Questions and Answers

Question 1: What is API Testing?

API testing involves testing APIs created by developers. Simply put, it’s about verifying that the APIs function as expected. However, providing such a basic answer in an interview might not be sufficient.

APIs operate primarily on the business layer of a system, where core business logic resides. For example, suppose we have an API that takes two integers and returns their sum. The business logic for this operation is what we’re testing, not the graphical user interface (GUI).

When testing APIs, we’re concerned with the behavior of the API, how it handles data, and its response to various operations like creating, reading, updating, and deleting resources. This type of testing is typically a black-box testing approach, but it can extend to gray-box testing if we know the structure of the API.

In summary, API testing verifies:

  • The core business logic.
  • The functional aspects of the API.
  • The type of output for given inputs.
  • The handling of edge cases and error conditions.

Question 2: What are common test cases in API testing?

Common test cases in API testing revolve around CRUD operations (Create, Read, Update, Delete). We verify:

  • Resource creation.
  • Data modification and update.
  • Key-value pairs.
  • Schema validation.
  • HTTP response codes and headers.

Other important aspects include:

  • Proper messaging for invalid inputs.
  • API reliability and performance.
  • Multi-threading support.
  • Handling of boundary values, equivalence partitions, and null values.

Question 3: Which tools do you use for API testing?

Several tools can be used for API testing, each with its strengths:

  1. Postman: Ideal for manual API testing, but also supports automation.
  2. Rest Assured: A powerful tool for API testing in Java, especially with BDD (Behavior-Driven Development) style.
  3. Karate DSL: A newcomer offering BDD-style syntax, parallel execution, and load testing.
  4. SoapUI: A robust tool for large-scale API testing.
  5. RunScope: Useful but can be slow.
  6. Katalon Studio: Offers an API testing module but is relatively new in the field.

Question 4: What are the differences between API testing and unit testing?

  • Scope: API testing has a broader scope and is mostly black-box testing, while unit testing focuses on individual functions and modules with a limited scope.
  • Who performs it: Testers typically perform API testing, whereas developers perform unit testing.
  • Source Code: Unit tests require source code access, but API tests do not.
  • Execution Level: Unit tests are conducted at the code level, while API tests are performed on the API endpoints.

Question 5: What are the major challenges in API testing?

Major challenges in API testing include:

  1. Proper Flow Testing: Ensuring the correct sequence of requests and responses.
  2. Output Validation: Manually verifying responses can be time-consuming.
  3. Parameter Validation: Handling various input parameters effectively.
  4. Schema Validation: Ensuring the API structure remains consistent.
  5. Performance Issues: Avoiding redundant code that could impact performance.


I hope these questions and answers give you a solid foundation for your API testing interviews. If you found value in this Blog , let me know in the comments. I’m committed to helping you master API testing, and together we can achieve this goal.

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Stay tuned for the next Blog where we’ll tackle more API testing questions. Don’t forget to like, share, and subscribe to support the channel. Share this Blog with others who might benefit from it.

Thanks for watching, and have a great day!

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